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2006.10.21 The Study on Choosing Construction Methods of Underground Works Based on The Risk Analysis The Study on Choosing Construction Methods of Underground Works Based on The Risk Analysis Speaker: Congpu Yao Affiliation: Tongji University

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Content 1. Introduction 2. The Principle of Analytic Hierarchy Process Theory 3. Establishment of Evaluation model 4. Project Case Study 5. Conclusion

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1. Introduction

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The construction of underground works has some certain characteristics: 1. Introduction the uncertainty of geology the poor construction condition the complex surroundings

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2. The Principle of Analytic Hierarchy Process Theory 2.1 Establishment of hierarchy process structure 2.2 Establishment of judging matrixes 2.3 Calculation of factor’s weight under the single principle 2.4 Calculation of synthesis weights of bottom elements

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2.1 Establishment of hierarchy process structure

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valuemeaning 1 Compared to each other, the two elements have the same importance index. 3 Compared to each other, the former is slightly more important than the latter. 5 Compared to each other, the former is obviously more important than the latter. 7 Compared to each other, the former is strongly more important than the latter. 9 Compared to each other, the former is extremely more important than the latter. 2 4 6 8 median count down The ratio of importance of i element and j elememt is Then the ratio of importance of j element and i element is 2.2 Establishment of judging matrixes

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consistency index C.I. Compare the factors of A 1, A 2,…A n to get the judging matrix, and do the problem of eigenvalue. Here, n represents the Matrix dimension, that is also the number of elements. The values of ωshould be normalized so as to be the weight of A 1, A 2,…A n under the principle of C k Equation 1 Equation 2 2.3 Calculation of factor’s weight under the single principle

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Check the R.I. (random index) Matrix dimension 12345678 R.I.000.520.891.121.261.361.41 Matrix dimension 9101112131415 R.I.1.461.491.521.541.561.581.59 Calculate C.R. (consistency ratio) Equation 3

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Also, we may check the consistency step by step. From up to bottom, calculate the weight index of element on k level under the principle of k-1 level. And then multiply the weight indexes of elements on k-1 level under the principle of target level. We may get the synthesis weights of bottom elements. 2.4 Calculation of synthesis weights of bottom elements

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3. Establishment of Evaluation model 3.1 Establishment of hierarchy process structure 3.2 Calculation of synthesis weights of bottom elements 3.3 Quantification of evaluation model 3.4 Comprehensive evaluation

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3.1 Establishment of hierarchy process structure

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Using the Sample method, combined with my knowledge, we may get the judging matrixes between every two factors, and their weights under single principle. Then calculate the weights of bottom elements under the principle of target level from up to bottom. Calculating flow chart Take D 1 as an example. Basic ideas 3.2 Calculation of synthesis weights of elements

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Calculating flow chart Calculating weight of B 1 under the principle of A Calculating weight of C 1 under the principle of A Calculating weight of C 1 under the principle of B 1 Calculating weight of D 1 under the principle of C 1 Calculating weight of D 1 under the principle of A

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Table 1. Matrix of [AB] AB1B1 B2B2 B3B3 B4B4 B5B5 ω B1B1 11/22230.2444 B2B2 213340.403 B3B3 1/21/31120.1367 B4B4 1/21/31120.1367 B5B5 1/31/41/2 10.0791

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Table 2. Matrix of [B 1 C] B1B1 C1C1 C2C2 C3C3 C4C4 ω C1C1 11/31/21/40.0997 C2C2 31210.3452 C3C3 21/21 0.185 C4C4 41210.3701 C1C1 D1D1 D2D2 D3D3 ω D1D1 111/20.2402 D2D2 111/30.2098 D3D3 2310.5499 Table 3. Matrix of [C 1 D]

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Table 4. The weight of factors C 1 ~C 4 for target level A CB 1 =0.2444ω C1C1 0.09970.0244 C2C2 0.34520.0844 C3C3 0.1850.0452 C4C4 0.37010.0905 D C 1 ＝ 0.0244 ω D1D1 0.24020.0059 D2D2 0.20980.0051 D3D3 0.54990.0134 Table 5. The weight of factors D 1 ~D 3 for target level A

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factor ClayRockSand Self- stability of soil and rock Easy- dealing in danger The limit of excavati on depth Water level Water pressur e Load- bearing water Water- emergi ng D1D1 D2D2D3D3 D4D4 D5D5 D6D6 D7D7 D8D8 D9D9 D 10 weight % 0.590.511.344.642.031.770.572.071.883.17 factor Sand - flowi ng Lique factio n Harm ful gases Time limit for a project Cost of the equipme nt The number of workers The manage ment of construc tion The amount of excavat ion Precipi tation Frozen metho d D 11 D 12 D 13 C5C5 C6C6 C7C7 C8C8 C9C9 D 14 D 15 weight % 3.170.991.719.645.607.424.037.420.811.85 The weights of bottom elements

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factor Grou ting meth od Air- press ure meth od The maintena nce of building in the period of operation Weath er conditi on Removal of pipes and roads Buildi ngs nearb y The space of constr uction The grade of technic al automa tization The reuse of equip ment The whole construc tion group’s quality and ability D 16 D 17 C 11 D 18 D 19 D 20 C 13 C 14 C 15 C 16 weight % 0.890.482.170.710.361.432.504.371.153.16 factor The ability of constr uction worker s The work ing inten sity Ease in heart The social impac t The ground settlem ent/up heaval Surface building s nearby Traff ic jam The defor matio n of pipes Dust pollut ion Noise pollut ion Castof f polluti on C 17 C 18 C 19 C 20 C 21 C 22 C 23 C 24 D 21 D 22 D 23 weight % 1.936.233.591.931.092.791.092.360.230.260.10 The weights of bottom elements

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3.3 Quantification of evaluation model According to the engineering, strata condition, construction group’s quality and ability, the bottom elements are assigned the value of 0~9. Where the value of 0~1 means bad and not applicable, the value of 2~4 means neither good nor bad, and a little applicable, the value of 5~7 means good and applicable, the value of 8~9 means excellent and very applicable. Use weighted average method to get the applicability value. Equation 4 Where A is the applicability value. p is the value of element. ωis the weight.

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3.4 Comprehensive evaluation For different construction methods the bottom elements have different values of p, which induces different value of A. The value of A represents the relative applicability value of construction methods. So the one that has the biggest value of A is the most applicable method. Equation 5

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4. Project Case Study A subway tunnel lies from Shiqiao road station to Fanyu Square station, which is covered by silty clay and granite in Yanshan period. The fully-weathered granite will be softened when it comes with water, while the compressive strength of little- weathered granite can be up to 120kPa. The line mainly passes the fully-weathered granite. The sides of Fanyu Square station own the little-weathered granite. The project goes through downtown of the city, and the location of pipelines below is very complicated, therefore, it has strict requirements for settlement. The most common methods in the subway tunnel are cut-and-cover method, mining method and shield tunnel method. Due to getting through the downtown of the city, the project is not recommended to use cut-and-cover method. In the following part, we mainly compare the applicability of the mining method and shield tunnel method.

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Construc tion method Constru ction speed Environmental benefits The cost Applicability on strata Construction process Cut and cover Faster Causes traffic jam, produces the dust, and has the noise pollution. Low Is used with the restriction that cover depth is less than 7m. The space is huge while constructing. Simple construction, spaced construction condition, but labor-intensive. Shield tunnel Fast The vibration caused by noise is not so big, but it is hard to totally prevent the settlement of ground, especially in the saturated soft clay. High, but has the tendency of reduction Is used in the soft clay, soft rock and so on. Not influenced by the weather and outside. High automatic, low intensity of labor force. Hard to correct in direction. Hard to continue in shallow soil. Hard to continue in small curvature radius. Mining method Slow Has the damage to rock around, and causes a great impact on the environment. Lower Is used in rock, hand strata and nonsensitive strata on variability. Should have strong control on over-excavation or less- excavation. High risk of construction. Poor working condition. Analysis on three construction methods

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NO.FactorsWeight ω Shield tunnel p Mining method p 1Clay0.59%50 2Rock0.51%27 3Sand1.34%50 4Self-stability of soil and rock4.64%74 5Easy-dealing in danger2.03%55 6The limit of excavation depth1.77%74 7Water level0.57%77 8Water pressure2.07%77 9Load-bearing water1.88%77 10Water-emerging3.17%64 11Sand-flowing3.17%64 12Liquefaction0.99%77 13Harmful gases1.71%74 14Time limit for a project9.64%82 15Cost of the equipment5.60%44 16The number of workers7.42%84 17The management of construction4.03%63 Construction method selection on the project

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NO.FactorsWeight ω Shield tunnel p Mining method p 18The amount of excavation7.42%55 19Precipitation0.81%64 20Frozen method1.85%77 21Grouting method0.89%67 22Air-pressure method0.48%77 23 The maintenance of building in the period of operation 2.17%64 24Weather condition0.71%86 25Removal of pipes and roads0.36%66 26Buildings nearby1.43%54 27The space of construction2.50%55 28 The grade of technical automatization 4.37%85 29The reuse of equipment1.15%77 30 The whole construction group’s quality and ability 3.16%66 31The ability of construction workers1.93%66 32The working intensity6.23%74 33Ease in heart3.59%74

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NO.FactorsWeight ω Shield tunnel p Mining method p 34The social impact1.93%66 35The ground settlement/upheaval1.09%63 36Surface buildings nearby2.79%63 37Traffic jam1.09%66 38The deformation of pipes2.36%64 39Dust pollution0.23%84 40Noise pollution0.26%84 41Castoff pollution0.10%84 It is important to point out mining method is not suitable for clays and sandy soil, so the value of p is 0. From the analysis above, we may see the applicability value of shield tunnel method is 6.44, while the one of mining method is merely 4.31. So as for this project, the shield tunnel method is better, and should be considered first.

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Conclusion Based on the risk analysis theory and Analytic Hierarchy Process theory, the authors promote an evaluation model for the decision of construction methods in the underground works. In the end, a project case is cited to test the model. The merits of this model are quantification of the qualitative results, digitalization of inaccuracy, and rationalization of the evaluation process. The model in the paper can be promoted to other projects, in the case of giving the original value of p based on the specific project. Thus we may get the proper construction method by equation 2. While, because the establishment of judging matrix relies on people’s subjective sense, to some degree the error of the model is enlarged. Besides, the 41elements cannot reflect all risk factors in all projects, because of the complexity of the projects. Both of them call for further research.

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Thank you! Congpu Yao 2006-10-21 E-mail: congpu@163.com

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