2017 International Conference on Transportation Infrastructure and Materials (ICTIM 2017) ISBN: 978-1-60595-442-4 Safety Control and Mechanical Response of Existing Tunnels Induced by Excavation of New Shallow Tunnel in Beijing Jianchen Wang1,2,3, Yunliang Liu3, Dingli Zhang1, Sulei Zhang4, Nanxin Du3, Fanwei Meng4 1Key Laboratory for Urban Underground Engineering of Ministry of Education, Beijing Jiaotong University, Beijing 100044, China *Corresponding Author, Email: [email protected] 2Beijing Urban Construction Group Co., Ltd., Beijing 100088; 3Beijing Urban Engineering Design and Research Institute Co., Ltd., Beijing 100037， China 4 CCCC-SHEC Second Engineering Co., Ltd., Xi'an, 710119, China ABSTRACT: In crossing engineering, new tunnels’ section and construction methods are numerous, geological conditions are complex, and existing tunnels’ structure forms are various. New tunnels, geological conditions, and existing tunnels have a complex composition relationship which is no corresponding research. 18 sets of measured data from 13 projects in Beijing were found to summarize the construction methods of the new tunnels, analyses the existing tunnel’s deformation law and study the existing tunnels’ mechanical response by the two stage method. Research shows: (1) the new tunnels have three types of municipal pipelines, subway stations and metro tunnel. The new tunnel construction method have guiding hole method, bench method, cavern-pile method and center drift method. The corresponding relationship between the construction method and excavation area is clear. (2) The probability distribution of the existing tunnels’ maximum settlement accorded with normal distribution. The mathematical expectation is 4.89, and the variance is 16.4. The existing tunnels’ average maximum settlements are 2.56mm, 3.82mm and 11.07mm, which caused by excavation of municipal Pipeline, metro tunnel and subway stations. The research results can provide reference for similar engineering of new subway tunnels excavated beneath adjacent existing underground structures in urban areas. KEYWORDS: Crossing engineering; existing tunnel; mechanical response; safety control INTRODUCTION Existing underground structures gradually increased with rapid developments of underground engineering in Beijing, which making it’s inevitable for new tunnels to cross below the existing structures.[1] Undercrossing construction reduce the intensity of underground structures foundation that further change the settlement and internal force and eventually effect the normal application and structural safety. Thus, selecting suitable schemes of crossing construction to reduce the disturbance on existing underground structures has becoming an urgent issue in the construction of urban underground engineering. Numerous researches on deformation laws of underground structures and safety controlling technologies in crossing engineering have been carried out by domestic and foreign scholars. Ma[2] analyzed four examples of measured deformation of existing underground structures which was conformed to the normal distribution in undercrossing projects. Han[3] counted undercrossing projects of London (10 cases) and Beijing (2 cases), considering that Peck formula could analyze and predict the deformation of existing underground structures. Zhang, Yao et al.[4-6] proposed a grouting uplift method after investigating the deformation controlling technologies and measured displacements of crossing engineering in Chongwenmen Station of Beijing subway line 5. Simultaneously, they also collected ten cases of closely undercrossing projects in Beijing confirming the flexibility of existing underground structures in global deformation and rigidity in single segment between two deformation joints.[7] Chen et al.[8] investigated controlling technology and standard of deformation in closely undercrossing engineering based on the Dongzhimen Subway Station of Line Airport above and beneath Line 13 in Beijing. Zhang[9] analyzed deformation and stress of existing tunnels under the effect of adjacent construction in accordance with two-phase method. Among the current researches, safety controlling technologies and measured deformation analysis in single engineering were targeted lacking universality while there are so many types of crossing projects. Deformation of underground structures can be predicted by modified Peck formula which seems incapable of analyzing its mechanical characteristics. Both of deformation and stress characteristics can be solved by two-phase method and finite element analysis method but only for specific projects. With numerous kinds of new tunnel forms and construction methods as well as varieties of existing underground structures in Beijing area, systematic analysis of deformation controlling and mechanical response does not yet exist. Started from the Chongwenmen station of Beijing subway Line 5 beneath the interval of Line 2 in 2005, a large number of crossing engineering have emerged in 10 years which providing possibility for systematically analyzing the safety controlling technologies and the mechanical response regularities of underground structures. This paper collects and fits 18 groups of deformation data in 13 projects of crossing engineering in Beijing area. The results can provide reference for future similar crossing engineering. CASE STATISTICS OF CROSSING ENGINEERING IN BEIJING AREA Case statistics of crossing engineering 18 groups of measured data in 13 cases of undercrossing projects were collected in this paper where Peck formula was applied to fit the measured deformation of existing underground structures. Results are shown in Table 1. The transverse stratum settlement of single-hole tunnel in fitting can be explained as:[7] 2 AVl x sx( ) exp(2 ) （1） i 2 2i As shown in the eq.(1), A is the excavation area, sx()is the settlement of x which means the horizontal distance from the tunnel centerline; i is the distance from the symmetry center of settlement curve to the inflexion point of the curve; Vl is the loss rate of the stratum which indicates the tunneling-induced cavern convergence rate of deformation that not considering the consolidation and it’s related with construction method.[3,7] The transverse stratum settlement of double-hole parallel tunnel is formulated as: DD ()()xx22 AV AV sx( )1ll 1 exp[ 22 ] 2 2 exp[ ] （2） 22ii22ii22 1212 In eq. (2): A1, A2 are the areas of the first and second tunnel; Vl1, Vl2 are the loss rate of the stratum respectively induced by the first and second tunnel construction; i1, i2 are the width of the settlement troughs induced by the first and second tunnel construction too; D is the distance between the two tunnels’ centerline. Table 1. Crossing engineering statistics in Beijing. engin Existing geological Construction eerin New tunnel L H D Z underground h L ×H S V conditions 1 1 method o 2 2 max l g structure The south to Line [10] find sand、 18.3×7.8 0.28 1 North Water 4.2 5.1 8.2 6.22 bench method 1wukesong 4.83 4.83 5 4 Transfer Project pebble Metro station Line 10 Silty clay、 Line 6 pilot tunnel + 19.85×7. 0.14 2[2] gongzhufen 14.1 9.3 63.2 4.66 1gongzhufen 4.51 2.91 find sand、 jack 75 2 Metro station Metro station pebble [11] Line 9 junbo pebble、 16.0 Line 1 Metro 10.4×5.8 0.02 3 9.6 10.5 14.3 6 pilot tunnel 5.3 2.35 Metro station conglomerate 5 tunnel 5 4 silt、Silty Line 2 Metro clay、find tunnel Chongwenmen Chongwenmen 0.29 4[2] sand、 3.6 2.5 - 1.25 bench method 3.87 9.9×5.9 1.74 thermal tunnel Metro 9 medium station~beijing coarse sand、 Metro station pebble silt、Silty Line 2 Metro clay、find tunnel Chongwenmen Chongwenmen 1.18 5[2] sand、 1.9 1.8 - 0.9 bench method 3.87 9.9×5.9 2.6 sewage tunnel Metro 3 medium station~beijing coarse sand、 Metro station pebble Line 1 Metro tunnel Zheng Chang Silty clay、 wukesong 12.05×7. 0.11 6[2] Zhuang thermal 5.8 3.2 - 1.6 bench method Metro 2 1.08 sandy clay、 52 6 tunnel station~wansho pebble ulu Metro station pile 0.72 silt、find 4.62 up line 15.95 airport line foundatio 5 Lin 13 back- 12.05×4. 7[12] dongzhimen sand、 13.3 9.2 - n 8.8 down turning line 18 Metro station medium 4.62 underpinn 11.39 0.64 line coarse sand ing+jack Conside ring the 0.10 final 4.41 2 deforma N tion ort Elimina h te lin jacking e deforma 0.18 8.56 tion 7 before 4 pilot construc Line 4 Line 2 [13] Silty clay、 tunnel tion 19.7×7.9 8 xuanwumen 9.8 9 13.9 6.4 xuanwumen 4.5 +pipe Conside 5 Metro station pebble Metro station roof ring the 0.19 final 5.9 5 deforma So tion ut Elimina h te lin jacking e deforma 0.27 10.27 tion 3 before construc tion Line 5 center Excavation Line 2 Metro 9[6] find sand、 7.2 11.5 - 7.71 5.1 5.9×5.9 31.26 0.89 chongwenmen drift complete of tunnel Metro station pebble、 metho center hole d + cobble、 pipe Displaceme 14.95 0.38 medium roof nt grouting coarse sand Line 10 Metro tunnel guomao [14] find sand、 Line 1 Metro 0.33 10 Metro 6.1 7.8 77 5 6 pilot tunnel 10.6 5.7×6.1 4.69 tunnel 3 station~shuangji cobble ng Metro station Line 6 Metro tunnel dongsi find sand、 Metro medium 4 pilot tunnel + Line 5 dongsi 12.6 0.20 11 6.8 7.8 17 3.9 19×9.9 6.9 station~chaoyan coarse sand、 jack Metro station 8 4 gmen Metro pebble station Line 7 Metro tunnel Silty clay、 Line 10 guangqumenwai 12 find sand、 6.3 6.6 17 3.3 bench method shuangjing 13.8 20×9.6 1.2 0.44 Metro medium Metro station station~shuangji coarse sand ng Metro station Line 6 Metro tunnel chaoyangmen Line 2 Silty clay、 4 pilot tunnel + 22.7×11.