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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Earth Sci.</journal-id>
<journal-title>Frontiers in Earth Science</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Earth Sci.</abbrev-journal-title>
<issn pub-type="epub">2296-6463</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="publisher-id">1346536</article-id>
<article-id pub-id-type="doi">10.3389/feart.2024.1346536</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Earth Science</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>The application of the game theory combination weighting-normal cloud model to the quality evaluation of surrounding rocks</article-title>
<alt-title alt-title-type="left-running-head">Zhao et al.</alt-title>
<alt-title alt-title-type="right-running-head">
<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.3389/feart.2024.1346536">10.3389/feart.2024.1346536</ext-link>
</alt-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Zhao</surname>
<given-names>Bing</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/writing-original-draft/"/>
<role content-type="https://credit.niso.org/contributor-roles/investigation/"/>
<role content-type="https://credit.niso.org/contributor-roles/data-curation/"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Shao</surname>
<given-names>Yang-Bing</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
<uri xlink:href="https://loop.frontiersin.org/people/2591197/overview"/>
<role content-type="https://credit.niso.org/contributor-roles/writing-original-draft/"/>
<role content-type="https://credit.niso.org/contributor-roles/methodology/"/>
<role content-type="https://credit.niso.org/contributor-roles/funding-acquisition/"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Yang</surname>
<given-names>Chao</given-names>
</name>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/Writing - review &#x26; editing/"/>
<role content-type="https://credit.niso.org/contributor-roles/validation/"/>
<role content-type="https://credit.niso.org/contributor-roles/supervision/"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Zhao</surname>
<given-names>Chao</given-names>
</name>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
<role content-type="https://credit.niso.org/contributor-roles/Writing - review &#x26; editing/"/>
<role content-type="https://credit.niso.org/contributor-roles/resources/"/>
<role content-type="https://credit.niso.org/contributor-roles/conceptualization/"/>
</contrib>
</contrib-group>
<aff id="aff1">
<sup>1</sup>
<institution>School of Civil Engineering</institution>, <institution>Nanyang Institute of Technology</institution>, <addr-line>Nanyang</addr-line>, <addr-line>Henan</addr-line>, <country>China</country>
</aff>
<aff id="aff2">
<sup>2</sup>
<institution>Henan Kaiyang Architectural Design Co, Ltd</institution>, <addr-line>Nanyang</addr-line>, <addr-line>Henan</addr-line>, <country>China</country>
</aff>
<aff id="aff3">
<sup>3</sup>
<institution>School of Civil Engineering</institution>, <institution>Sichuan University of Science &#x26; Engineering</institution>, <addr-line>Zigong</addr-line>, <addr-line>Sichuan</addr-line>, <country>China</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>
<bold>Edited by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/87809/overview">Manoj Khandelwal</ext-link>, Federation University Australia, Australia</p>
</fn>
<fn fn-type="edited-by">
<p>
<bold>Reviewed by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/2623897/overview">Fei Ding</ext-link>, Beijing University of Technology, China</p>
<p>
<ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/2623904/overview">Haiqiang Jiang</ext-link>, Northeast Agricultural University, China</p>
</fn>
<corresp id="c001">&#x2a;Correspondence: Yang -Bing Shao, <email>guxinbao11@163.com</email>
</corresp>
</author-notes>
<pub-date pub-type="epub">
<day>08</day>
<month>04</month>
<year>2024</year>
</pub-date>
<pub-date pub-type="collection">
<year>2024</year>
</pub-date>
<volume>12</volume>
<elocation-id>1346536</elocation-id>
<history>
<date date-type="received">
<day>29</day>
<month>11</month>
<year>2023</year>
</date>
<date date-type="accepted">
<day>06</day>
<month>03</month>
<year>2024</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2024 Zhao, Shao, Yang and Zhao.</copyright-statement>
<copyright-year>2024</copyright-year>
<copyright-holder>Zhao, Shao, Yang and Zhao</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<p>The status of surrounding rocks dramatically influences the safety of construction workers, so the quality assessment of surrounding rocks has great significance. The uniaxial saturated compressive strength of rock (X<sub>1</sub>), the quality index of surrounding rock (X<sub>2</sub>), the frictional coefficient of the structural surface (X<sub>3</sub>), the joint spacing (X<sub>4</sub>), the state of groundwater(X<sub>5</sub>), and the integrity coefficient (X<sub>6</sub>) are selected as the initial evaluation index. Then, the game theory combination weighting-normal cloud model is introduced. Second, the certainty degree matrix of each index is established, and the weight coefficients of assessment indexes are determined based on the game theory combination weighting method. Finally, the quality level of surrounding rocks is judged. Compared with the traditional methods, the proposed model solves the fuzziness and randomness of different indexes, improves the reliability of the assessment process, and enhances the predictive accuracy of assessment results. In addition, it can provide a solution scheme for the evaluation indicators, which are difficult to quantify, and reduce the influence of human factors. The results obtained from the suggested model are consistent with the current specification. Its accuracy approaches 100%, and the method is feasible for the quality level assessment of surrounding rocks, providing a new technique and approach to assessing the risk level of surrounding rocks.</p>
</abstract>
<kwd-group>
<kwd>quality evaluation</kwd>
<kwd>surrounding rocks</kwd>
<kwd>the game theory combination weighting method</kwd>
<kwd>normal cloud model</kwd>
<kwd>application</kwd>
</kwd-group>
<custom-meta-wrap>
<custom-meta>
<meta-name>section-at-acceptance</meta-name>
<meta-value>Geohazards and Georisks</meta-value>
</custom-meta>
</custom-meta-wrap>
</article-meta>
</front>
<body>
<sec id="s1">
<title>1 Introduction</title>
<p>With the development of the economy in China, more extensive infrastructure is being constructed more quickly (<xref ref-type="bibr" rid="B2">Chen et al., 2022</xref>). Many large-scale underground projects are used in water conservancy, hydropower, transportation, mining, and other projects (<xref ref-type="bibr" rid="B26">Zhou et al., 2012</xref>). At the same time, the stability of underground engineering due to the excavation of a large amount of rock and soil has become a critical problem faced by engineers (<xref ref-type="bibr" rid="B4">Chen and Zhou, 2019</xref>). An underground tunnel is often in a complex geological environment. Where the geological conditions and stability of surrounding rock vary, the evaluation of surrounding rock quality is essential to understanding the engineering characteristics (<xref ref-type="bibr" rid="B23">Zhou et al., 2015a</xref>). An accurate assessment of the surrounding rock is significant in ensuring a reasonable survey design and smooth construction on site.</p>
<p>Researchers and scholars have performed many investigations on methods of assessing surrounding rocks in recent years (<xref ref-type="bibr" rid="B9">Gu et al., 2021</xref>). <xref ref-type="bibr" rid="B18">TAN et al. (2022)</xref> established the fuzzy assessment model based on the hierarchy analytic method to predict four indexes of rock mass in each section of the tunnel. <xref ref-type="bibr" rid="B19">WANG and CAO (2013)</xref> used a matter-element extension evaluation model and concluded that uniaxial compressive strength and groundwater seepage volume have the most significant effect on the stability of surrounding rocks by <xref ref-type="bibr" rid="B19">WANG and CAO (2013)</xref> using the matter-element extension evaluation model. <xref ref-type="bibr" rid="B21">WEI et al. (2016)</xref> introduced a cloud model that transforms qualitative concepts and quantitative data to determine the quality method of the rock mass. <xref ref-type="bibr" rid="B5">Qiu (2008)</xref> established a quality assessment model of surrounding rocks in the tunnel by using the result of reduction as the input samples of an artificial neural network. In addition, <xref ref-type="bibr" rid="B16">QIN et al. (2016)</xref> classified the various factors that affected the stability of the surrounding rock of a deep mine roadway and established the three types of hazard impact factor model using the fuzzy comprehensive evaluation method in combination with the three types of hazard classification method. The ideal point method is applied to calculate the proximity of the surrounding rock by <xref ref-type="bibr" rid="B14">HUANG et al. (2014)</xref>, and the weight of the corresponding index in the evaluation system is determined using the entropy weight theory.</p>
<p>The above methods have prompted the substantial development of the assessment theory of surrounding rock quality. However, it still has some shortcomings (<xref ref-type="bibr" rid="B11">Gu and Wu, 2016</xref>). For example, the evaluation of surrounding rock quality is a nonlinear and complex problem (<xref ref-type="bibr" rid="B10">Gu et al., 2022a</xref>). In addition, the fuzziness and randomness of surrounding rock quality evaluation are neglected, and the relative importance of the evaluation index and the calculation of weight distribution must be optimized (<xref ref-type="bibr" rid="B12">Gu et al., 2022b</xref>).</p>
<p>The game theory combination weighting-normal cloud model is introduced to overcome the shortcomings of the above methods and to assess the quality level of the surrounding rock in the Pingzitou Tunnel. First, the game theory combination weighting method is introduced to determine the weights of the assessment index. Relative to traditional subjective or objective weighting methods, combination weighting theory not only considers the subjective factors of expert assessments but also involves some objective assessments. This has improved the accuracy of assessment prediction. When the game theory is combined with the combination weighting theory, the contradiction between subjective and objective weights can be dealt with effectively, the advantages of subjective and objective weights are integrated, the agreement and compromise in the conflict of both are searched, and the difference between subjective and objective weights is reduced. Finally, the deviation between the basic weight and the ideal weight is minimized. Therefore, the uncertainty of the evaluation results is lowered (<xref ref-type="bibr" rid="B3">Chen and Zhou, 2024</xref>). Third, a new assessment model is formed when the normal cloud model is introduced. It has many virtues, such as the preciseness of algorithms and operability in practice. Compared to traditional cloud theory (<xref ref-type="bibr" rid="B1">Alison et al., 2022</xref>), the suggested method needs no significant amount of data, and its operation is easy. In addition, it can provide a solution scheme for the evaluation indicators, which are difficult to quantify, and reduces the influence of human factors (<xref ref-type="bibr" rid="B15">Li and Wu, 2023</xref>; <xref ref-type="bibr" rid="B24">Zhou et al., 2015b</xref>). The method dramatically improves the traditional cloud model (<xref ref-type="bibr" rid="B27">Zhou et al., 2016</xref>).</p>
<p>The paper is organized as follows: in <xref ref-type="sec" rid="s2">Section 2</xref>, the engineering overview is introduced. In <xref ref-type="sec" rid="s3">Section 3</xref>, theory and methodology based on the game theory combination weighting-normal cloud model are presented. In <xref ref-type="sec" rid="s4">Section 4</xref>, the assessment model of the surrounding rock quality is established, and the assessment results of the proposed model are compared. Conclusions are drawn in <xref ref-type="sec" rid="s5">Section 5</xref>.</p>
</sec>
<sec id="s2">
<title>2 Engineering overview</title>
<p>The Pingzitou Tunnel is located in the Daping village, Pingzi town, Guizhou province, and plotted in <xref ref-type="fig" rid="F1">Figure 1</xref>. The railway tunnel goes under the tunnel&#x2019;s entrance; the export end is parallel to the railway. In all, the pile number of the left tunnel entrance is Zk2 &#x2b; 880, the pile number of the tunnel exit is Zk4 &#x2b; 972; the elevation of the tunnel bottom is 1,473.36&#x2013;1,686.11 m, the total length is 2092 m, the vertical slope gradient is &#x2212;2.8%, the plane is located on the curve and straight line section of R &#x3d; 735 m, and the maximum superelevation of the tunnel pavement is 4%. The karst in the entrance section of the tunnel is well-developed, and the karst is strong along the karst fissure. Most of the surface forms are karst gullies and sinkholes, which are mostly developed vertically. The covering layer in the tunnel section is mainly gravel soil, and lightly weathered dolomite limestone is located at the lower part. The surface strata at the exploration area are mainly Quaternary Holocene (Q<sub>h</sub>) strata, mostly composed of macadam soil with small thicknesses and uneven distribution. The underlying bedrock is a Carboniferous dolomite limestone formation. The surface water system in the tunnel area has not been developed. There are three kinds of groundwater in the site: bedrock fissure water, karst groundwater, and structure fissure water. A specific picture of the tunnel is shown in <xref ref-type="fig" rid="F2">Figure 2</xref>.</p>
<fig id="F1" position="float">
<label>FIGURE 1</label>
<caption>
<p>Geographical location of the survey area.</p>
</caption>
<graphic xlink:href="feart-12-1346536-g001.tif"/>
</fig>
<fig id="F2" position="float">
<label>FIGURE 2</label>
<caption>
<p>Picture of the tunnel.</p>
</caption>
<graphic xlink:href="feart-12-1346536-g002.tif"/>
</fig>
</sec>
<sec id="s3">
<title>3 Assessment process</title>
<sec id="s3-1">
<title>3.1 The combination weighting method</title>
<p>The common weight calculation methods are divided into subjective, objective, and combination weights. Combination weighting is a common method; two or three kinds of subjective and objective weights are combined to obtain the comprehensive weight, which can reduce the error caused by a single method to a certain extent (<xref ref-type="bibr" rid="B8">Ding et al., 2022a</xref>; <xref ref-type="bibr" rid="B6">Ding et al., 2022b</xref>; <xref ref-type="bibr" rid="B7">Ding et al., 2023</xref>). Based on the discussion in the introduction, the entropy weight and criteria importance through inter-criteria correlation (CRITIC) methods are applied to represent the subjective and objective factors, and the combination weights are obtained using game theory (<xref ref-type="bibr" rid="B29">Zhou and Yang, 2007</xref>).<list list-type="simple">
<list-item>
<p>(1) The entropy method</p>
</list-item>
</list>
</p>
<p>The entropy weight method is an objective weighting method to determine the weight coefficient according to the degree of information utility value of each evaluation index. The entropy weight method can reflect the degree of discreteness among the index data (<xref ref-type="bibr" rid="B22">Zhao et al., 2021</xref>).</p>
<p>Its calculative process is listed as follows:<list list-type="simple">
<list-item>
<p>&#x2460; Constructing the original matrix of assessment index <inline-formula id="inf1">
<mml:math id="m1">
<mml:mrow>
<mml:mi>X</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</p>
</list-item>
</list>
</p>
<p>Assuming that there are <inline-formula id="inf2">
<mml:math id="m2">
<mml:mrow>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> evaluation indexes and <inline-formula id="inf3">
<mml:math id="m3">
<mml:mrow>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> evaluation objects, <inline-formula id="inf4">
<mml:math id="m4">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is the corresponding value of the <inline-formula id="inf5">
<mml:math id="m5">
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> assessment index at the <inline-formula id="inf6">
<mml:math id="m6">
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> assessment object; then, its origin assessment matrix can be expressed as follows:<disp-formula id="e1">
<mml:math id="m7">
<mml:mrow>
<mml:mi>X</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mi>m</mml:mi>
<mml:mo>&#xd7;</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>m</mml:mi>
<mml:mo>;</mml:mo>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
<label>(1)</label>
</disp-formula>
<list list-type="simple">
<list-item>
<p>&#x2461; Normalization and forward processing</p>
</list-item>
</list>
</p>
<p>To eliminate the impact of the different types of indicators and dimensional differences, dimensionless processing needs to be performed for each index; the indexes are expressed as follows:<disp-formula id="e2">
<mml:math id="m8">
<mml:mrow>
<mml:mrow>
<mml:mfenced open="" close=")" separators="|">
<mml:mrow>
<mml:mrow>
<mml:mi>Y</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi mathvariant="normal">y</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>m</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(2)</label>
</disp-formula>
</p>
<p>The positive indicator is expressed as follows:<disp-formula id="e3">
<mml:math id="m9">
<mml:mrow>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mi>n</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>min</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
<mml:mrow>
<mml:mi>max</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>min</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:mfrac>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(3)</label>
</disp-formula>
</p>
<p>The negative indicator is expressed as follows:<disp-formula id="e4">
<mml:math id="m10">
<mml:mrow>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mi>n</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mi>max</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
<mml:mrow>
<mml:mi>max</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>min</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>x</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:mfrac>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(4)</label>
</disp-formula>
</p>
<p>where <inline-formula id="inf7">
<mml:math id="m11">
<mml:mrow>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is the standard value of <inline-formula id="inf8">
<mml:math id="m12">
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> assessment index at the <inline-formula id="inf9">
<mml:math id="m13">
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> assessment object.<list list-type="simple">
<list-item>
<p>&#x2462; Calculation of the information entropy of the <inline-formula id="inf10">
<mml:math id="m14">
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> assessment index</p>
</list-item>
</list>
<disp-formula id="e5">
<mml:math id="m15">
<mml:mrow>
<mml:msub>
<mml:mi>h</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mn>1</mml:mn>
<mml:mrow>
<mml:mi>ln</mml:mi>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>n</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:msub>
<mml:mi>e</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>ln</mml:mi>
<mml:mo>&#x2061;</mml:mo>
<mml:msub>
<mml:mi>e</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(5)</label>
</disp-formula>
<disp-formula id="e6">
<mml:math id="m16">
<mml:mrow>
<mml:msub>
<mml:mi>e</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>n</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfrac>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(6)</label>
</disp-formula>
<list list-type="simple">
<list-item>
<p>&#x2463; Calculation of weights <inline-formula id="inf11">
<mml:math id="m17">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mi mathvariant="normal">i</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>:</p>
</list-item>
</list>
<disp-formula id="e7">
<mml:math id="m18">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mi mathvariant="normal">i</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2212;</mml:mo>
<mml:msub>
<mml:mi>h</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
<mml:mrow>
<mml:mi>m</mml:mi>
<mml:mo>&#x2212;</mml:mo>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>m</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:msub>
<mml:mi>h</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfrac>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(7)</label>
</disp-formula>
</p>
<p>where <inline-formula id="inf12">
<mml:math id="m19">
<mml:mrow>
<mml:mn>0</mml:mn>
<mml:mo>&#x3c;</mml:mo>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mn>1</mml:mn>
<mml:mi>i</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2264;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>m</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mi>i</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>m</mml:mi>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
</inline-formula>
<list list-type="simple">
<list-item>
<p>(2) The CRITIC method</p>
</list-item>
</list>
</p>
<p>Criteria importance through inter-criteria correlation (CRITIC) is an objective weighting method proposed by Diakoulaki that synthetically measures the index weight by calculating the variability and conflict of the index. Its calculative procedure follows (<xref ref-type="bibr" rid="B25">Zhou et al., 2014</xref>):<list list-type="simple">
<list-item>
<p>&#x2460; Assuming that there are <inline-formula id="inf13">
<mml:math id="m20">
<mml:mrow>
<mml:mi mathvariant="normal">m</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> estimated objects and <inline-formula id="inf14">
<mml:math id="m21">
<mml:mrow>
<mml:mi mathvariant="normal">n</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> assessment indexes, construct a matrix <inline-formula id="inf15">
<mml:math id="m22">
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mi>m</mml:mi>
<mml:mo>&#xd7;</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>,where <inline-formula id="inf16">
<mml:math id="m23">
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>m</mml:mi>
<mml:mo>;</mml:mo>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
</list-item>
</list>
</p>
<p>
<list list-type="simple">
<list-item>
<p>&#x2461; Matrix <inline-formula id="inf17">
<mml:math id="m24">
<mml:mrow>
<mml:mi>A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>is standardized based on the Z-score method. Its expression is shown as follows:</p>  </list-item>  </list>
<disp-formula id="e8">
<mml:math id="m25">
<mml:mrow>
<mml:msubsup>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
</mml:mrow>
<mml:msub>
<mml:mi>s</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mfrac>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>m</mml:mi>
<mml:mo>;</mml:mo>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>b</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(8)</label>
</disp-formula>
</p>
<p>where <inline-formula id="inf18">
<mml:math id="m26">
<mml:mrow>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:mi>a</mml:mi>
</mml:mrow>
</mml:mfrac>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>m</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>; <inline-formula id="inf19">
<mml:math id="m27">
<mml:mrow>
<mml:msub>
<mml:mi>s</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msqrt>
<mml:mfrac bevelled="true">
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>m</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
<mml:mrow>
<mml:mi>a</mml:mi>
<mml:mo>&#x2212;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:mfrac>
</mml:msqrt>
</mml:mrow>
</mml:math>
</inline-formula>; and <inline-formula id="inf20">
<mml:math id="m28">
<mml:mrow>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf21">
<mml:math id="m29">
<mml:mrow>
<mml:msub>
<mml:mi>s</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> are, respectively, the mean value and standard deviation of the <inline-formula id="inf22">
<mml:math id="m30">
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> assessment index.<list list-type="simple">
<list-item>
<p>&#x2462; Calculate the coefficient of variation of different indexes as follows:</p>
</list-item>
</list>
<disp-formula id="e9">
<mml:math id="m31">
<mml:mrow>
<mml:mi>B</mml:mi>
<mml:msub>
<mml:mi>Y</mml:mi>
<mml:mi mathvariant="normal">j</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac bevelled="true">
<mml:mrow>
<mml:msub>
<mml:mi>s</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
<mml:mrow>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
</mml:mrow>
</mml:mfrac>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(9)</label>
</disp-formula>
</p>
<p>where <inline-formula id="inf23">
<mml:math id="m32">
<mml:mrow>
<mml:mi>B</mml:mi>
<mml:msub>
<mml:mi>Y</mml:mi>
<mml:mi mathvariant="normal">j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is the variation coefficient of the <inline-formula id="inf24">
<mml:math id="m33">
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> index.<list list-type="simple">
<list-item>
<p>&#x2463; The coefficients of correlation are calculated based on the standardization matrix <inline-formula id="inf25">
<mml:math id="m34">
<mml:mrow>
<mml:msup>
<mml:mi>A</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msup>
</mml:mrow>
</mml:math>
</inline-formula>. Its expression is listed as follows: <inline-formula id="inf26">
<mml:math id="m35">
<mml:mrow>
<mml:mi>X</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>r</mml:mi>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mi>l</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mi>n</mml:mi>
<mml:mo>&#xd7;</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>n</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>l</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>b</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf27">
<mml:math id="m36">
<mml:mrow>
<mml:msub>
<mml:mi>r</mml:mi>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mi>l</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is the coefficient of correlation between the <inline-formula id="inf28">
<mml:math id="m37">
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf29">
<mml:math id="m38">
<mml:mrow>
<mml:mi>l</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> index, and</p>
</list-item>
</list>
<disp-formula id="e10">
<mml:math id="m39">
<mml:mrow>
<mml:msub>
<mml:mi>r</mml:mi>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mi>l</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>m</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:mrow>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>k</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>l</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>l</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:mrow>
<mml:mrow>
<mml:msqrt>
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>m</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:msup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>k</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mn>2</mml:mn>
</mml:msup>
</mml:mrow>
</mml:msqrt>
<mml:msqrt>
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>l</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>m</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:msup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>l</mml:mi>
</mml:msub>
<mml:mo>&#x2212;</mml:mo>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>l</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mn>2</mml:mn>
</mml:msup>
</mml:mrow>
</mml:msqrt>
</mml:mrow>
</mml:mfrac>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>r</mml:mi>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mi>l</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>r</mml:mi>
<mml:mmultiscripts>
<mml:mo>;</mml:mo>
<mml:mprescripts/>
<mml:mrow>
<mml:mi>l</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
<mml:none/>
</mml:mmultiscripts>
<mml:mi>k</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>m</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>l</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
<label>(10)</label>
</disp-formula>
</p>
<p>where <inline-formula id="inf30">
<mml:math id="m40">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf31">
<mml:math id="m41">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>l</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> are, respectively, the standard value of measured values at the <inline-formula id="inf32">
<mml:math id="m42">
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf33">
<mml:math id="m43">
<mml:mrow>
<mml:mi>l</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> index for the <inline-formula id="inf34">
<mml:math id="m44">
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> assessment object in the standardization matrix <inline-formula id="inf35">
<mml:math id="m45">
<mml:mrow>
<mml:msup>
<mml:mi>A</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msup>
</mml:mrow>
</mml:math>
</inline-formula>; <inline-formula id="inf36">
<mml:math id="m46">
<mml:mrow>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>k</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf37">
<mml:math id="m47">
<mml:mrow>
<mml:mover accent="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>l</mml:mi>
</mml:msub>
<mml:mo>&#xaf;</mml:mo>
</mml:mover>
</mml:mrow>
</mml:math>
</inline-formula> are, respectively, the mean of standard value of measured values at the <inline-formula id="inf38">
<mml:math id="m48">
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf39">
<mml:math id="m49">
<mml:mrow>
<mml:mi>l</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> index in the standardization matrix <inline-formula id="inf40">
<mml:math id="m50">
<mml:mrow>
<mml:msup>
<mml:mi>A</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msup>
</mml:mrow>
</mml:math>
</inline-formula>.<list list-type="simple">
<list-item>
<p>&#x2464; Calculate the quantitative coefficient about the degree of independence for different assessment indexes.</p>
</list-item>
</list>
</p>
<p>Its expression is shown as follows:<disp-formula id="e11">
<mml:math id="m51">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3b7;</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>n</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2212;</mml:mo>
<mml:mrow>
<mml:mfenced open="|" close="|" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>r</mml:mi>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(11)</label>
</disp-formula>
<list list-type="simple">
<list-item>
<p>&#x2465; The quantitative coefficients of the comprehensive information and the degree of independence of each index are solved as follows:</p>
</list-item>
</list>
<disp-formula id="e12">
<mml:math id="m52">
<mml:mrow>
<mml:msub>
<mml:mi>C</mml:mi>
<mml:mi mathvariant="normal">j</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>B</mml:mi>
<mml:msub>
<mml:mi>Y</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>n</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mn>1</mml:mn>
<mml:mo>&#x2212;</mml:mo>
<mml:msub>
<mml:mi>r</mml:mi>
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mi>j</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(12)</label>
</disp-formula>
<list list-type="simple">
<list-item>
<p>&#x2466; The determination of the weight of each evaluation index can be expressed as follows:</p>
</list-item>
</list>
<disp-formula id="e13">
<mml:math id="m53">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mi mathvariant="normal">j</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:msub>
<mml:mi>C</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi>n</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:msub>
<mml:mi>C</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfrac>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>,</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>.</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(13)</label>
</disp-formula>
<list list-type="simple">
<list-item>
<p>(3) The combination weighting method of the game theory</p>
</list-item>
</list>
</p>
<p>Based on game theory, the combination weight <inline-formula id="inf41">
<mml:math id="m54">
<mml:mrow>
<mml:mi>&#x3c9;</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is obtained by combining the entropy weight method with the CRITIC method. Its procedure is correlated as follows:<list list-type="simple">
<list-item>
<p>&#x2460; The weight sets <inline-formula id="inf42">
<mml:math id="m55">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf43">
<mml:math id="m56">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> were obtained by the entropy weight method and the CRITIC method. It is assumed that <inline-formula id="inf44">
<mml:math id="m57">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf45">
<mml:math id="m58">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> are, respectively, the linear combination coefficient determined by each method, then weight sets <inline-formula id="inf46">
<mml:math id="m59">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf47">
<mml:math id="m60">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> can be linearized as (<xref ref-type="bibr" rid="B28">Zhou et al., 2021</xref>):</p>
</list-item>
</list>
<disp-formula id="e14">
<mml:math id="m61">
<mml:mrow>
<mml:mi>&#x3c9;</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:msubsup>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
<mml:mi>T</mml:mi>
</mml:msubsup>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:msubsup>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
<mml:mi>T</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:math>
<label>(14)</label>
</disp-formula>
<list list-type="simple">
<list-item>
<p>&#x2461; According to game theory, the linear combination coefficients <inline-formula id="inf48">
<mml:math id="m62">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf49">
<mml:math id="m63">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> in Eq. <xref ref-type="disp-formula" rid="e10">(10)</xref> are optimized and are expressed as follows:</p>
</list-item>
</list>
<disp-formula id="e15">
<mml:math id="m64">
<mml:mrow>
<mml:mi>min</mml:mi>
<mml:mo>&#x2061;</mml:mo>
<mml:msup>
<mml:mrow>
<mml:mfenced open="&#x2016;" close="&#x2016;" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mi>k</mml:mi>
</mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mmultiscripts>
<mml:mo>&#x2212;</mml:mo>
<mml:mprescripts/>
<mml:mi>k</mml:mi>
<mml:mi>T</mml:mi>
</mml:mmultiscripts>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mi>k</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mn>2</mml:mn>
</mml:msup>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>k</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(15)</label>
</disp-formula>
</p>
<p>
<list list-type="simple">
<list-item>
<p>&#x2462; According to the differential properties of the matrix, the linear differential equation group for optimizing the first derivative condition of Eq. <xref ref-type="disp-formula" rid="e15">(15)</xref> is determined as follows:</p>
</list-item> </list>
<disp-formula id="e16">
<mml:math id="m65">
<mml:mrow>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:mtable columnalign="center">
<mml:mtr>
<mml:mtd>
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:msubsup>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
<mml:mi>T</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:mtd>
<mml:mtd>
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:msubsup>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
<mml:mi>T</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd>
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:msubsup>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
<mml:mi>T</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:mtd>
<mml:mtd>
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:msubsup>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
<mml:mi>T</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:mtable columnalign="center">
<mml:mtr>
<mml:mtd>
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:msubsup>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
<mml:mi>T</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd>
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:msubsup>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
<mml:mi>T</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(16)</label>
</disp-formula>
<list list-type="simple">
<list-item>
<p>&#x2463; The optimal combination coefficients <inline-formula id="inf50">
<mml:math id="m66">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf51">
<mml:math id="m67">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> were obtained by Eqn. <xref ref-type="disp-formula" rid="e16">(16).</xref> The normalization process is obtained as <inline-formula id="inf52">
<mml:math id="m68">
<mml:mrow>
<mml:msubsup>
<mml:mi>a</mml:mi>
<mml:mn>1</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac bevelled="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf53">
<mml:math id="m69">
<mml:mrow>
<mml:msubsup>
<mml:mi>a</mml:mi>
<mml:mn>2</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac bevelled="true">
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>a</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:math>
</inline-formula>, then based on the game theory, the comprehensive weight <inline-formula id="inf54">
<mml:math id="m70">
<mml:mrow>
<mml:mi>&#x3c9;</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> can be obtained as follows:</p>
</list-item>
</list>
<disp-formula id="e17">
<mml:math id="m71">
<mml:mrow>
<mml:mi>&#x3c9;</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>a</mml:mi>
<mml:mmultiscripts>
<mml:msubsup>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
<mml:mi>T</mml:mi>
</mml:msubsup>
<mml:mprescripts/>
<mml:mn>1</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:mmultiscripts>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>a</mml:mi>
<mml:mmultiscripts>
<mml:msubsup>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
<mml:mi>T</mml:mi>
</mml:msubsup>
<mml:mprescripts/>
<mml:mn>2</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:mmultiscripts>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(17)</label>
</disp-formula>
</p>
</sec>
<sec id="s3-2">
<title>3.2 The normal cloud model</title>
<p>The normal cloud model is applied to determine the membership degree of different indicators. It is defined as follows: <inline-formula id="inf55">
<mml:math id="m72">
<mml:mrow>
<mml:mi>x</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>E</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>D</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is assumed as a common quantitative set, and <inline-formula id="inf56">
<mml:math id="m73">
<mml:mrow>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is called the domain, where <inline-formula id="inf57">
<mml:math id="m74">
<mml:mrow>
<mml:mi>x</mml:mi>
<mml:mo>&#x2208;</mml:mo>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf58">
<mml:math id="m75">
<mml:mrow>
<mml:mi>D</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is the qualitative conception in domain <inline-formula id="inf59">
<mml:math id="m76">
<mml:mrow>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>. For the random research object <inline-formula id="inf60">
<mml:math id="m77">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> in the domain <inline-formula id="inf61">
<mml:math id="m78">
<mml:mrow>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>, there still exists a random number with the stable tendency <inline-formula id="inf62">
<mml:math id="m79">
<mml:mrow>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2208;</mml:mo>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:mn>0</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>; then, <inline-formula id="inf63">
<mml:math id="m80">
<mml:mrow>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> is called either the membership degree of <inline-formula id="inf64">
<mml:math id="m81">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> corresponding to <inline-formula id="inf65">
<mml:math id="m82">
<mml:mrow>
<mml:mi>D</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> or the definitive degree. The distribution of definitive degrees in the domain <inline-formula id="inf66">
<mml:math id="m83">
<mml:mrow>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is called the membership cloud. If <inline-formula id="inf67">
<mml:math id="m84">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> meets with <inline-formula id="inf68">
<mml:math id="m85">
<mml:mrow>
<mml:mi>x</mml:mi>
<mml:mo>&#x223c;</mml:mo>
<mml:mi>N</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>E</mml:mi>
<mml:msup>
<mml:mi>n</mml:mi>
<mml:mrow>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, and <inline-formula id="inf69">
<mml:math id="m86">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:msup>
<mml:mi>n</mml:mi>
<mml:mo>,</mml:mo>
</mml:msup>
<mml:mo>&#x223c;</mml:mo>
<mml:mi>N</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>n</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>H</mml:mi>
<mml:msup>
<mml:mi>e</mml:mi>
<mml:mn>2</mml:mn>
</mml:msup>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, and then, <inline-formula id="inf70">
<mml:math id="m87">
<mml:mrow>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> can be expressed as follows (<xref ref-type="bibr" rid="B30">Zhou et al., 2008</xref>):<disp-formula id="e18">
<mml:math id="m88">
<mml:mrow>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x3d;</mml:mo>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>exp</mml:mi>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mfrac>
<mml:msup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mn>2</mml:mn>
</mml:msup>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>E</mml:mi>
<mml:msup>
<mml:mi>n</mml:mi>
<mml:mrow>
<mml:mo>,</mml:mo>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(18)</label>
</disp-formula>
</p>
<p>where the distribution definitive degree <inline-formula id="inf71">
<mml:math id="m89">
<mml:mrow>
<mml:mi>u</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> in the domain <inline-formula id="inf72">
<mml:math id="m90">
<mml:mrow>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is also called a normal cloud or Gauss cloud. The expectation <inline-formula id="inf73">
<mml:math id="m91">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>, the entropy <inline-formula id="inf74">
<mml:math id="m92">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>, and the hyperentropy <italic>H<sub>e</sub>
</italic> are, respectively, applied to represent the digital features in the cloud model. <inline-formula id="inf76">
<mml:math id="m94">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> can represent the point of certain conception in the domain; <inline-formula id="inf77">
<mml:math id="m95">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> reflects the accepting range of conception; <italic>H<sub>e</sub>
</italic> demonstrates the uncertainty of entropy, and its magnitude reflects the thickness of the cloud drop. They can, respectively, be expressed as follows:<disp-formula id="e19">
<mml:math id="m97">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:msup>
<mml:mi>c</mml:mi>
<mml:mo>&#x2b;</mml:mo>
</mml:msup>
<mml:mo>&#x2b;</mml:mo>
<mml:msup>
<mml:mi>c</mml:mi>
<mml:mo>&#x2212;</mml:mo>
</mml:msup>
</mml:mrow>
<mml:mn>2</mml:mn>
</mml:mfrac>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(19)</label>
</disp-formula>
<disp-formula id="e20">
<mml:math id="m98">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>n</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:msup>
<mml:mi>c</mml:mi>
<mml:mo>&#x2b;</mml:mo>
</mml:msup>
<mml:mo>&#x2212;</mml:mo>
<mml:msup>
<mml:mi>c</mml:mi>
<mml:mo>&#x2212;</mml:mo>
</mml:msup>
</mml:mrow>
<mml:mn>6</mml:mn>
</mml:mfrac>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(20)</label>
</disp-formula>
<disp-formula id="e21">
<mml:math id="m99">
<mml:mrow>
<mml:msub>
<mml:mi>H</mml:mi>
<mml:mi mathvariant="normal">e</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>k</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
</mml:mrow>
</mml:math>
<label>(21)</label>
</disp-formula>
</p>
<p>where <inline-formula id="inf79">
<mml:math id="m100">
<mml:mrow>
<mml:msup>
<mml:mi>c</mml:mi>
<mml:mo>&#x2b;</mml:mo>
</mml:msup>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf80">
<mml:math id="m101">
<mml:mrow>
<mml:msup>
<mml:mi>c</mml:mi>
<mml:mo>&#x2212;</mml:mo>
</mml:msup>
</mml:mrow>
</mml:math>
</inline-formula> are, respectively, the upper and lower bounds corresponding to the grade standard of the specific index. The hyperentropy <italic>H<sub>e</sub>
</italic> can be selected as a proper constant <inline-formula id="inf82">
<mml:math id="m103">
<mml:mrow>
<mml:mi>k</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>, which is set as 0.01 in the investigation.</p>
</sec>
<sec id="s3-3">
<title>3.3 The determination of the evaluation index</title>
<p>The quality assessment process of surrounding rocks is very complex, and many influencing factors affect the final evaluation results. The evaluation index of a model is often selected based on the actual case in the engineering site. Otherwise, a more significant deviation will occur (<xref ref-type="bibr" rid="B20">WANG et al., 2010</xref>). According to the actual investigation data, six assessment factors are considered the quality assessment index of surrounding rocks. These indexes are the uniaxial saturated compressive strength of rock <inline-formula id="inf83">
<mml:math id="m104">
<mml:mrow>
<mml:mi>R</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> (X<sub>1</sub>), the quality index of surrounding rock <inline-formula id="inf84">
<mml:math id="m105">
<mml:mrow>
<mml:mi>R</mml:mi>
<mml:mi>Q</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> (X<sub>2</sub>), the frictional coefficient of structural surface <inline-formula id="inf85">
<mml:math id="m106">
<mml:mrow>
<mml:msub>
<mml:mi>J</mml:mi>
<mml:mi mathvariant="normal">f</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> (X<sub>3</sub>), the joint spacing <inline-formula id="inf86">
<mml:math id="m107">
<mml:mrow>
<mml:msub>
<mml:mi>J</mml:mi>
<mml:mi mathvariant="normal">d</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> (X<sub>4</sub>), the state of groundwater <inline-formula id="inf87">
<mml:math id="m108">
<mml:mrow>
<mml:mi>W</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> (X<sub>5</sub>), and the integrity coefficient <inline-formula id="inf88">
<mml:math id="m109">
<mml:mrow>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi mathvariant="normal">v</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> (X<sub>6</sub>).</p>
<p>According to the relevant specifications, the six evaluation indexes can be classified into five levels in <xref ref-type="table" rid="T1">Table 1</xref>: risk level I (extremely stable), risk level II (stable), risk level III (common), risk level IV (unstable), and risk level V (extremely unstable). The monitoring values of six assessment indexes of the surrounding rocks determined via site inspections and indoor experiments are shown in <xref ref-type="table" rid="T2">Table 2</xref>.</p>
<table-wrap id="T1" position="float">
<label>TABLE 1</label>
<caption>
<p>Risk level classification of the surrounding rocks.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="center">Level</th>
<th align="center">
<inline-formula id="inf89">
<mml:math id="m110">
<mml:mrow>
<mml:msub>
<mml:mi>R</mml:mi>
<mml:mi mathvariant="normal">c</mml:mi>
</mml:msub>
<mml:mo>/</mml:mo>
<mml:mi>M</mml:mi>
<mml:mi>P</mml:mi>
<mml:mi>a</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
<th align="left">
<inline-formula id="inf90">
<mml:math id="m111">
<mml:mrow>
<mml:mi>R</mml:mi>
<mml:mi>Q</mml:mi>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mo>%</mml:mo>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
<th align="left">
<inline-formula id="inf91">
<mml:math id="m112">
<mml:mrow>
<mml:msub>
<mml:mi>J</mml:mi>
<mml:mi mathvariant="normal">f</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
<th align="left">
<inline-formula id="inf92">
<mml:math id="m113">
<mml:mrow>
<mml:msub>
<mml:mi>J</mml:mi>
<mml:mi mathvariant="normal">d</mml:mi>
</mml:msub>
<mml:mo>/</mml:mo>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
<th align="left">
<inline-formula id="inf93">
<mml:math id="m114">
<mml:mrow>
<mml:mi>W</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>L</mml:mi>
<mml:msup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>min</mml:mi>
<mml:mo>&#x2061;</mml:mo>
<mml:mo>.</mml:mo>
<mml:mn>10</mml:mn>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
<th align="left">
<inline-formula id="inf94">
<mml:math id="m115">
<mml:mrow>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi mathvariant="normal">v</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="center">I</td>
<td align="center">250&#x2013;300</td>
<td align="center">90&#x2013;100</td>
<td align="center">0.8&#x2013;1.2</td>
<td align="center">200&#x2013;400</td>
<td align="center">0&#x2013;5</td>
<td align="center">0.75&#x2013;1</td>
</tr>
<tr>
<td align="center">II</td>
<td align="center">100&#x2013;250</td>
<td align="center">70&#x2013;90</td>
<td align="center">0.3&#x2013;0.8</td>
<td align="center">60&#x2013;200</td>
<td align="center">5&#x2013;10</td>
<td align="center">0.55&#x2013;0.75</td>
</tr>
<tr>
<td align="center">III</td>
<td align="center">50&#x2013;100</td>
<td align="center">50&#x2013;70</td>
<td align="center">0.2&#x2013;0.3</td>
<td align="center">20&#x2013;60</td>
<td align="center">10&#x2013;25</td>
<td align="center">0.35&#x2013;0.55</td>
</tr>
<tr>
<td align="center">IV</td>
<td align="center">25&#x2013;50</td>
<td align="center">25&#x2013;50</td>
<td align="center">0.1&#x2013;0.2</td>
<td align="center">6&#x2013;20</td>
<td align="center">25&#x2013;125</td>
<td align="center">0.15&#x2013;0.35</td>
</tr>
<tr>
<td align="center">V</td>
<td align="center">1&#x2013;25</td>
<td align="center">0&#x2013;25</td>
<td align="center">0.01&#x2013;0.1</td>
<td align="center">0&#x2013;6</td>
<td align="center">125&#x2013;250</td>
<td align="center">0&#x2013;0.15</td>
</tr>
</tbody>
</table>
</table-wrap>
<table-wrap id="T2" position="float">
<label>TABLE 2</label>
<caption>
<p>Monitoring value.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="left">Surrounding rocks to evaluate</th>
<th align="left">
<inline-formula id="inf95">
<mml:math id="m116">
<mml:mrow>
<mml:msub>
<mml:mi>R</mml:mi>
<mml:mi mathvariant="normal">c</mml:mi>
</mml:msub>
<mml:mo>/</mml:mo>
<mml:mi>M</mml:mi>
<mml:mi>P</mml:mi>
<mml:mi>a</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
<th align="left">
<inline-formula id="inf96">
<mml:math id="m117">
<mml:mrow>
<mml:mi>R</mml:mi>
<mml:mi>Q</mml:mi>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mo>%</mml:mo>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
<th align="left">
<inline-formula id="inf97">
<mml:math id="m118">
<mml:mrow>
<mml:msub>
<mml:mi>J</mml:mi>
<mml:mi mathvariant="normal">f</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
<th align="left">
<inline-formula id="inf98">
<mml:math id="m119">
<mml:mrow>
<mml:msub>
<mml:mi>J</mml:mi>
<mml:mi mathvariant="normal">d</mml:mi>
</mml:msub>
<mml:mo>/</mml:mo>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
<th align="left">
<inline-formula id="inf99">
<mml:math id="m120">
<mml:mrow>
<mml:mi>W</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>L</mml:mi>
<mml:msup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>min</mml:mi>
<mml:mo>&#x2061;</mml:mo>
<mml:mo>.</mml:mo>
<mml:mn>10</mml:mn>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:msup>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
<th align="left">
<inline-formula id="inf100">
<mml:math id="m121">
<mml:mrow>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi mathvariant="normal">v</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="left">N<sub>1</sub> intermediate weathered dolomite limestone</td>
<td align="center">68</td>
<td align="center">75.4</td>
<td align="center">0.24</td>
<td align="center">35</td>
<td align="center">30</td>
<td align="center">0.55</td>
</tr>
<tr>
<td align="left">N<sub>2</sub> karst development zone</td>
<td align="center">50</td>
<td align="center">55.6</td>
<td align="center">0.15</td>
<td align="center">18</td>
<td align="center">20</td>
<td align="center">0.4</td>
</tr>
<tr>
<td align="left">Structural belt N<sub>3</sub> structural belt</td>
<td align="center">15</td>
<td align="center">16</td>
<td align="center">1</td>
<td align="center">6</td>
<td align="center">125</td>
<td align="center">0.2</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s3-4">
<title>3.4 The construction of the evaluation frame</title>
<p>The quality of surrounding rocks dramatically influences the safety of construction workers. So, assessing the risk level of surrounding rocks has great significance.</p>
<p>A new evaluation method of surrounding rocks based on the game theory combination weighting-normal cloud model is provided in this article. The process is outlined in <xref ref-type="fig" rid="F3">Figure 3</xref>. First, to evaluate the risk level of surrounding rocks, a complete assessment index system is established. Second, the weight of each assessment index is determined according to the game theory combination weighting theory. Third, certain degrees are determined using the normal cloud theory. Then, the magnitudes of synthetic certainty degree <inline-formula id="inf101">
<mml:math id="m122">
<mml:mrow>
<mml:mi>M</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> (shown in Eq. <xref ref-type="disp-formula" rid="e22">22</xref>) are determined; finally, the risk level of surrounding rocks is determined.<disp-formula id="e22">
<mml:math id="m123">
<mml:mrow>
<mml:mi>M</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mstyle displaystyle="true">
<mml:munderover>
<mml:mo>&#x2211;</mml:mo>
<mml:mrow>
<mml:mi mathvariant="normal">i</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mi mathvariant="normal">n</mml:mi>
</mml:munderover>
</mml:mstyle>
<mml:msub>
<mml:mi>u</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
<label>(22)</label>
</disp-formula>
</p>
<fig id="F3" position="float">
<label>FIGURE 3</label>
<caption>
<p>Process of evaluating the risk level of the surrounding rocks.</p>
</caption>
<graphic xlink:href="feart-12-1346536-g003.tif"/>
</fig>
</sec>
</sec>
<sec sec-type="results|discussion" id="s4">
<title>4 Results and discussion</title>
<sec id="s4-1">
<title>4.1 The determination of index weight coefficients</title>
<p>
<list list-type="simple">
<list-item>
<p>(1) Calculation of the weight coefficient <inline-formula id="inf102">
<mml:math id="m124">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> based on the entropy method</p>
</list-item>
</list>
</p>
<p>According to Eqs <xref ref-type="disp-formula" rid="e1">1</xref>&#x2013;<xref ref-type="disp-formula" rid="e7">7</xref>, and in combination with <xref ref-type="table" rid="T1">Table 1</xref>, the corresponding weight coefficient can be calculated as follows:<disp-formula id="equ1">
<mml:math id="m125">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:mtable columnalign="center">
<mml:mtr>
<mml:mtd>
<mml:mn>0.1197</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.1242</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.2688</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.1641</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.2603</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.0628</mml:mn>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
</disp-formula>
<list list-type="simple">
<list-item>
<p>(2) Calculation of the weight coefficient <inline-formula id="inf103">
<mml:math id="m126">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> based on the CRITIC method</p>
</list-item>
</list>
</p>
<p>Based on Eqs <xref ref-type="disp-formula" rid="e8">8</xref>&#x2013;<xref ref-type="disp-formula" rid="e10">10</xref>, and in combination with <xref ref-type="table" rid="T1">Table 1</xref>, the correlation coefficients can be obtained as follows:<disp-formula id="equ2">
<mml:math id="m127">
<mml:mrow>
<mml:mi>r</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:mtable columnalign="center">
<mml:mtr>
<mml:mtd>
<mml:mn>1</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>1</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.906</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9604</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9103</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9949</mml:mn>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd>
<mml:mn>1</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>1</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.909</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9584</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9131</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9942</mml:mn>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd>
<mml:mn>0.906</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.909</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>1</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.7522</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9999</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.8588</mml:mn>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd>
<mml:mn>0.9604</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9584</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.7522</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>1</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.7589</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9836</mml:mn>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd>
<mml:mn>0.9103</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9131</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9999</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.7589</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>1</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.864</mml:mn>
</mml:mtd>
</mml:mtr>
<mml:mtr>
<mml:mtd>
<mml:mn>0.9949</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9942</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.8588</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.9836</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.864</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>1</mml:mn>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
</disp-formula>
</p>
<p>According to Eq. <xref ref-type="disp-formula" rid="e11">11</xref>, the standard deviation of different columns is obtained as follows:<disp-formula id="equ3">
<mml:math id="m128">
<mml:mrow>
<mml:mi>&#x3b7;</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:mtable columnalign="center">
<mml:mtr>
<mml:mtd>
<mml:mn>0.5085</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.5092</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.5493</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.5025</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.5519</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.5017</mml:mn>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
</disp-formula>
</p>
<p>Similarly, according to Eqs <xref ref-type="disp-formula" rid="e13">12, 13</xref>, the weight of each evaluation index can be calculated as follows:<disp-formula id="equ4">
<mml:math id="m129">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mtable columnalign="center">
<mml:mtr>
<mml:mtd>
<mml:mn>0.0894</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.0883</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.2427</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.2268</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.2352</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.1176</mml:mn>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
</disp-formula>
<list list-type="simple">
<list-item>
<p>(3) The calculation of the combination weight</p>
</list-item>
</list>
</p>
<p>Based on Eqs <xref ref-type="disp-formula" rid="e14">14</xref>&#x2013;<xref ref-type="disp-formula" rid="e17">17</xref>, and in combination with weight sets <inline-formula id="inf104">
<mml:math id="m130">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf105">
<mml:math id="m131">
<mml:mrow>
<mml:msub>
<mml:mi>&#x3c9;</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, the combination weight <inline-formula id="inf106">
<mml:math id="m132">
<mml:mrow>
<mml:mi>&#x3c9;</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> can be obtained as follows:<disp-formula id="equ5">
<mml:math id="m133">
<mml:mrow>
<mml:mi>&#x3c9;</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:mtable columnalign="center">
<mml:mtr>
<mml:mtd>
<mml:mn>0.1125</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.1157</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.2626</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.1789</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.2544</mml:mn>
</mml:mtd>
<mml:mtd>
<mml:mn>0.0755</mml:mn>
</mml:mtd>
</mml:mtr>
</mml:mtable>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>.</mml:mo>
</mml:mrow>
</mml:math>
</disp-formula>
</p>
</sec>
<sec id="s4-2">
<title>4.2 The determination of digital features in the normal cloud model</title>
<p>Based on <xref ref-type="table" rid="T2">Table 2</xref>, and in combination with Eqs <xref ref-type="disp-formula" rid="e19">19</xref>&#x2013;<xref ref-type="disp-formula" rid="e22">22</xref>, the classification standard of normal cloud is depicted in <xref ref-type="table" rid="T3">Table 3</xref>.</p>
<table-wrap id="T3" position="float">
<label>TABLE 3</label>
<caption>
<p>Digital features of the cloud model.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="center">Risk level</th>
<th align="center">Digital feature</th>
<th align="center">X1</th>
<th align="center">X2</th>
<th align="center">X3</th>
<th align="center">X4</th>
<th align="center">X5</th>
<th align="center">X6</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td rowspan="3" align="center">I</td>
<td align="center">
<inline-formula id="inf107">
<mml:math id="m134">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">275</td>
<td align="center">95</td>
<td align="center">1</td>
<td align="center">300</td>
<td align="center">2.5</td>
<td align="center">0.875</td>
</tr>
<tr>
<td align="center">
<inline-formula id="inf108">
<mml:math id="m135">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">8.3333</td>
<td align="center">1.6667</td>
<td align="center">0.0667</td>
<td align="center">33.3333</td>
<td align="center">0.8333</td>
<td align="center">0.0625</td>
</tr>
<tr>
<td align="left">
<inline-formula id="inf109">
<mml:math id="m136">
<mml:mrow>
<mml:msub>
<mml:mi>H</mml:mi>
<mml:mi>e</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
</tr>
<tr>
<td rowspan="3" align="center">II</td>
<td align="center">
<inline-formula id="inf110">
<mml:math id="m137">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">175</td>
<td align="center">80</td>
<td align="center">0.55</td>
<td align="center">130</td>
<td align="center">7.5</td>
<td align="center">0.65</td>
</tr>
<tr>
<td align="center">
<inline-formula id="inf111">
<mml:math id="m138">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">25</td>
<td align="center">3.3333</td>
<td align="center">0.0833</td>
<td align="center">23.3333</td>
<td align="center">0.8333</td>
<td align="center">0.0333</td>
</tr>
<tr>
<td align="left">
<inline-formula id="inf112">
<mml:math id="m139">
<mml:mrow>
<mml:msub>
<mml:mi>H</mml:mi>
<mml:mi>e</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
</tr>
<tr>
<td rowspan="3" align="center">III</td>
<td align="center">
<inline-formula id="inf113">
<mml:math id="m140">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">75</td>
<td align="center">60</td>
<td align="center">0.25</td>
<td align="center">40</td>
<td align="center">17.5</td>
<td align="center">0.45</td>
</tr>
<tr>
<td align="center">
<inline-formula id="inf114">
<mml:math id="m141">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">8.3333</td>
<td align="center">3.3333</td>
<td align="center">0.0167</td>
<td align="center">6.6667</td>
<td align="center">2.5</td>
<td align="center">0.0333</td>
</tr>
<tr>
<td align="left">
<inline-formula id="inf115">
<mml:math id="m142">
<mml:mrow>
<mml:msub>
<mml:mi>H</mml:mi>
<mml:mi>e</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
</tr>
<tr>
<td rowspan="3" align="center">IV</td>
<td align="center">
<inline-formula id="inf116">
<mml:math id="m143">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">37.5</td>
<td align="center">37.5</td>
<td align="center">0.15</td>
<td align="center">13</td>
<td align="center">75</td>
<td align="center">0.25</td>
</tr>
<tr>
<td align="center">
<inline-formula id="inf117">
<mml:math id="m144">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">4.167</td>
<td align="center">4.1667</td>
<td align="center">0.0167</td>
<td align="center">2.3333</td>
<td align="center">16.6667</td>
<td align="center">0.0333</td>
</tr>
<tr>
<td align="left">
<inline-formula id="inf118">
<mml:math id="m145">
<mml:mrow>
<mml:msub>
<mml:mi>H</mml:mi>
<mml:mi>e</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
</tr>
<tr>
<td rowspan="3" align="center">V</td>
<td align="center">
<inline-formula id="inf119">
<mml:math id="m146">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">13</td>
<td align="center">12.5</td>
<td align="center">0.055</td>
<td align="center">3</td>
<td align="left">187.5</td>
<td align="center">0.075</td>
</tr>
<tr>
<td align="center">
<inline-formula id="inf120">
<mml:math id="m147">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>n</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">4</td>
<td align="center">4.1667</td>
<td align="center">0.015</td>
<td align="center">1</td>
<td align="center">20.8333</td>
<td align="center">0.025</td>
</tr>
<tr>
<td align="left">
<inline-formula id="inf121">
<mml:math id="m148">
<mml:mrow>
<mml:msub>
<mml:mi>H</mml:mi>
<mml:mi>e</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
<td align="center">0.01</td>
</tr>
</tbody>
</table>
</table-wrap>
<p>According to <xref ref-type="table" rid="T3">Table 3</xref>, the characters of the cloud model corresponding to different indexes are calculated using the forward cloud generator, which is plotted in <xref ref-type="fig" rid="F4">Figure 4</xref>.</p>
<fig id="F4" position="float">
<label>FIGURE 4</label>
<caption>
<p>Cloud of each assessment index.</p>
</caption>
<graphic xlink:href="feart-12-1346536-g004.tif"/>
</fig>
<p>Its horizontal coordinates present the magnitude of different variables; the vertical coordinates present the magnitude of certainty degree. A sub-figure in <xref ref-type="fig" rid="F4">Figure 4</xref> includes five grades: I (very good), II (good), III (common), IV (unstable), and V (extremely unstable). This is the assessment result for the suggested model. When a certain variable is fixed, the certainty degree of the specific point at the state grade can be obtained.</p>
<p>According to <xref ref-type="table" rid="T2">Tables 2</xref> and <xref ref-type="table" rid="T3">3</xref>, and with Eqs (17)&#x2013;(18), a comprehensive membership degree is obtained. Its results are listed in <xref ref-type="table" rid="T4">Table 4</xref>, and the results compared with the actual investigation are plotted in <xref ref-type="fig" rid="F5">Figure 5</xref>.</p>
<table-wrap id="T4" position="float">
<label>TABLE 4</label>
<caption>
<p>Comprehensive membership degree.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th rowspan="2" align="center">Sample no.</th>
<th colspan="5" align="center">Quality level of surrounding rocks</th>
<th rowspan="2" align="center">Comprehensive assessment</th>
</tr>
<tr>
<th align="center">&#x2160;</th>
<th align="center">&#x2161;</th>
<th align="center">&#x2162;</th>
<th align="center">&#x2163;</th>
<th align="center">V</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="center">N<sub>1</sub> intermediate weathered dolomite limestone</td>
<td align="center">0</td>
<td align="center">0.0455</td>
<td align="center">0.4344</td>
<td align="center">0.0066</td>
<td align="center">0</td>
<td align="center">III</td>
</tr>
<tr>
<td align="center">N<sub>2</sub> karst development zone</td>
<td align="center">0</td>
<td align="center">0</td>
<td align="center">0.2285</td>
<td align="center">0.3421</td>
<td align="center">0</td>
<td align="center">IV</td>
</tr>
<tr>
<td align="center">Structural belt N<sub>3</sub>
</td>
<td align="center">0.2626</td>
<td align="center">0</td>
<td align="center">0</td>
<td align="center">0.0293</td>
<td align="center">0.2854</td>
<td align="center">V</td>
</tr>
</tbody>
</table>
</table-wrap>
<fig id="F5" position="float">
<label>FIGURE 5</label>
<caption>
<p>Comparison results of the three methods.</p>
</caption>
<graphic xlink:href="feart-12-1346536-g005.tif"/>
</fig>
<p>The suggested model is applied to assess the surrounding rocks. The complete results are shown in <xref ref-type="table" rid="T4">Table 4</xref>. <xref ref-type="table" rid="T4">Table 4</xref> shows that the quality levels of three different types of surrounding rocks differ. Based on the maximum membership degree criterion, the quality level of N<sub>1</sub> intermediate weathered dolomite limestone is III; one of the N<sub>2</sub> karst development zones is IV; one of the N<sub>3</sub> structural belts is V. It means that the risk level of intermediate weathered dolomite limestone is common; one of the N<sub>2</sub> karst development zones is unstable, and one of the structural belt N<sub>3</sub> is very unstable. The qualified rate of the quality level of surrounding rock quality is 33.3%. Because the quality level of N<sub>1</sub> intermediate weathered dolomite limestone is common, no measures need to be performed. Necessary consolidation measures must be adopted for the N<sub>2</sub> karst development zone and the N<sub>3</sub> structural belt. For example, rock bolts should be fixed in the surrounding rocks (<xref ref-type="bibr" rid="B17">Shao et al., 2022</xref>).</p>
<p>Based on the comparative results of the assessment model in <xref ref-type="fig" rid="F5">Figure 5</xref>, the results assessed by the suggested method are consistent with the actual investigation. Its accuracy rate arrives at 100% in the text method, which is higher than the results from the basic quality indicators (BQ) method (67%) (<xref ref-type="bibr" rid="B13">HUANG et al., 2012</xref>). Compared to the BQ method, the suggested model improves the reliability of the assessment process and enhances the predicative accuracy of assessment results. Therefore, it is feasible to estimate the quality level of surrounding rocks using the suggested model. The method not only provides accurate results but also adds detail. For example, <inline-formula id="inf122">
<mml:math id="m149">
<mml:mrow>
<mml:mi>R</mml:mi>
<mml:mi>Q</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> for the N<sub>1</sub> intermediate weathered dolomite limestone is 75.4, which should belong to level II according to <xref ref-type="table" rid="T1">Table 1</xref>. In addition, according to <xref ref-type="table" rid="T1">Table 1</xref>, the quality level of the other indicators obtained by the suggested model belongs to level III, so the quality level probability at the N1 intermediate weathered dolomite limestone at level III is more significant than that of levels I, IV, V, and II. Therefore, its quality level belongs to level III, and it is very unlikely that it would be assigned to levels I, IV, V, or II. The results obtained using the suggested model can accurately demonstrate the quality level of surrounding rocks.</p>
</sec>
</sec>
<sec sec-type="conclusion" id="s5">
<title>5 Conclusion</title>
<p>A new assessment method is established in this article based on the game theory combination weighting-normal cloud model, and considering the uniaxial saturated compressive strength of rock (X<sub>1</sub>), the quality index of surrounding rock (X<sub>2</sub>), the frictional coefficient of structural surface (X<sub>3</sub>), the joint spacing (X<sub>4</sub>), the state of groundwater(X<sub>5</sub>), and the integrity coefficient (X<sub>6</sub>).</p>
<p>The proposed method is applied to assess the quality level of surrounding rocks. The result is compared with the current specifications and the BQ method; the results obtained based on the suggested method are consistent with the actual investigation. Its accuracy arrives at 100%, which is higher than the results from the BQ method (67%). The results give various quality grades of surrounding rocks from nos N<sub>1</sub>-N<sub>3</sub> samples. The quality level of N<sub>1</sub> intermediate weathered dolomite limestone is III; one of the N<sub>2</sub> karst development zones is IV; one of the N<sub>3</sub> structural belts is V. This means that the risk level of intermediate weathered dolomite limestone is common; one of the karst development zones is unstable, and one of the structural belts is very unstable. The qualified rate of the quality level of the surrounding rock is 33.3%. Necessary consolidation measures must be adopted for the karst development zone and the structural belt. In addition, the quality levels of the other indexes obtained for the N<sub>1</sub> sample by the suggested model belong to level III, so its quality level probability at level III is more significant than that of levels I, IV, V, and II.</p>
<p>In total, the results from the proposed model accurately predict the quality levels of surrounding rocks and further determine the quality grade ranking for different samples at the same level. The suggested method provides a new approach to evaluating the quality grade assessment of surrounding rocks.</p>
</sec>
</body>
<back>
<sec sec-type="data-availability" id="s6">
<title>Data availability statement</title>
<p>The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.</p>
</sec>
<sec id="s7">
<title>Author contributions</title>
<p>BZ: writing&#x2013;original draft, investigation, and data curation. CY-Bing Shao: writing&#x2013;original draft, methodology, and funding acquisition. CY: writing&#x2013;review and editing, validation, and supervision. CZ: writing&#x2013;review and editing, resources, and conceptualization.</p>
</sec>
<sec sec-type="funding-information" id="s8">
<title>Funding</title>
<p>The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. This work is supported by the Opening Project of Sichuan Province University Key Laboratory of Bridge Non-destruction Detecting and Engineering Computing (2022QYJ02, 2023QYJ02, and 2022QYY02) and the key scientific research project of colleges and universities in Henan province (23B560019).</p>
</sec>
<sec sec-type="COI-statement" id="s9">
<title>Conflict of interest</title>
<p>Author Y-BS was employed by Henan Kaiyang Architectural Design Co., Ltd.</p>
<p>The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec sec-type="disclaimer" id="s10">
<title>Publisher&#x2019;s note</title>
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