Experimental Research on Ground Deformation of Double Close-spaced Tunnel Construction

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1 Research Journal of Applied Sciences, Engineering and Technology 4(22): , 212 ISSN: Maxwell Scientific Organization, 212 Submitted: May 8, 212 Accepted: June 8, 212 Published: November 15, 212 Experimental Research on Ground Deformation of Double Close-spaced Tunnel Construction Zhongchang Wang and Huijun Wu School of Civil and Safety Engineering, Dalian Jiaotong University, Dalian 11628, China Abstract: In this study, we obtain the optimal ratio of similar materials of soil layers by similarity principle and uni-axial compression tests. The two-dimensional similar material model is established for Dalian double-tube parallel tunnels line No.1. The laws of ground deformation for successively construction are obtained by measuring the internal displacement of model. It is shown that the subsidence rate of early period of construction is larger than that of lately period of construction. The vertical settlement rate of shallow stratum is greater than that of deep stratum. The surface subsidence of two tunnels is superimposed. The settlement is larger in the side of early excavating tunnel. The characteristic of non symmetrical two peak of the vertical deformation of stratum is obvious. The horizontal displacement of axis of two tunnels approximately decreases linearly with the increase of the depth. The horizontal displacement in the location of center line and axis of two tunnels is not. The obvious shear layer appears in the inner of the soil layers. The pile and shear wall within this range is easy to appear the crack owing to tunneling. Keywords: Double-tube parallel tunnels, ground settlement, model experiment, shear layer, the optimal ratio INTRODUCTION The condition of the rock layers in Dalian area is complex and changeful. The mining method becomes the preferred construction method in interval and subway station construction. The deformation and disturbance of soil is complex owing to excavation of two close-spaced tunnels. The studies of the double line tunnel construction such as Gauss curve based on the superposition theory (Suwansawat, 27), normal curve of double-round tunnel settlement (Addenbrooke and Potts, 21), settlement calculation formula caused by soil loss (Wei et al., 211), equivalent circle model (Qinghuo, 26), revised Peck method (Liu et al., 26), the random prediction method (Liu et al., 28), similar material model test of multi-arch tunnel of highway (Li, 28, Liu et al., 21), centrifugal model test of close spaced tunnel (Qinghuo, 26) and numerical analysis of double-line tunnel (Li et al., 21; Lin et al., 29; Song et al., 28) focused mainly on settlement analysis of ground surface and much research focused on shield tunnel. There are few researches on deformation mechanism of different rock layers by mining method. The similar material model test which is used to study soil movement of tunnel excavation is intuitive and effective method that can avoid the mathematics and mechanics modeling difficulties. Taking interval of double-line tunnel with mining construction between Dalian xueyuan square and maritime university as a model, the optimal ratio of similar materials of soil layers is obtained by similarity principle and uni-axial compression tests. The twodimensional similar material model of double tunnel is established. The laws of deformation and disturbance caused by construction are obtained by monitoring internal displacement of the model. The scientific reference is provided for tunnel construction (Ling et al., 21). In this study, the optimal ratio of similar materials of soil layers is obtained by similarity principle and uniaxial compression tests. The two-dimensional similar material model is established for Dalian double-tube parallel tunnels line no. 1. The measurement of inner displacement of tunnel is conducted. The main results are that the change of vertical displacement of different strata with time can be seen as negative exponential function of time; moreover, the settlement of double tunnels is similar to superposition of single tunnel and the horizontal displacement between two tunnels is very small. THE DESIGN OF SIMILAR MATERIAL MODEL TEST The range of interval of Dalian Metro Line no.1 project is located at AK AK The Corresponding Author: Zhongchang Wang, School of Civil and Safety Engineering, Dalian Jiaotong University, Dalian 11628, China 484

2 Res. J. Appl. Sci. Eng. Technol., 4(22): , 212 3m axis of tunnel 4m 1m 3m 4m Fig. 1: Structural section of twin tunnel Table 1: Mechanical parameters for soils of metro tunnel Elastic modulus /MPa Types of soil Thicknenss /m Density /kn/m 3 Possion s ratio Cohension /kpa Frictional angle/ Plain fill Clay Pebble Strong weathering slate Medium weathering slate Table 2: Similar materials test table of Sand, lime, gypsum, mica and water Soil Ratio of material Compressive strength /kpa Plain fill 8.:.7:.2:.1: Clay 8.:.5:.2:.1: Pebble 8.:.5:.3:.2: Strong weathering slate 8.:.4:.4:.2: Medium weathering slate 8.:.4:.6:.1: Equivalent reinforcing layer 6.: 1.5:.3:.: Uniaxial compressive strength/mpa Fig. 2: Compression test of different mixture ratio of sample sand. The retarder is borax. To obtain similar physical and mechanical properties of materials, the compression test is conducted by 162 samples with different ratio. The dimension of samples is cm. the number of samples with each ratio is 3. The days of natural conservation are 7 days. The test machine of WE-2 is used to load. The loading rate is 2 mm/s. The uni-axial compressive strength of sample is determined. The compression test of samples with different material proportioning is shown in Fig. 2. The complete stress- length is m. The bottom elevation of structure is m. The mining construction and composite lining is used. The thickness of C25 concrete of initial support is 3 mm. The diameter of mortar anchor at side wall is 22 mm. the length is 3.5 m. The space of mortar anchor is 8 12 mm. The diameter of the advanced small pipe is 42 mm which is set within the 15 of arch. The space of steel mesh is mm. The space of steel grid frame is 8 mm. The waterproof reinforced concrete of C35 and P8 is used in the two lining. The thickness is 4 mm. the space of two tunnels is 1 m. The mean buried depth is 15 m. The section diagram of tunnel is shown in Fig. 1. The mechanical parameters are shown in Table 1. The stratified medium is moca. The cementing material is gypsum and lime. The aggregate is fine strain Stress (Mpa) Ratio of pebble Ratio of equivalent reinforcing layer Ratio of weathered slate Strain (1-2) Fig. 3: Different compression test of different mixture ratio of sample

3 Res. J. Appl. Sci. Eng. Technol., 4(22): , 212 Table 3: Similarity ratio of material parameter Name of similar ratio Value Name Value Length 5 Frictional angle 1 Density 1.6 Displacement 5 Stress 8 Possion s ratio 1 Elastic modulus 8 Strength 8 Cohension 8 Time 7.7 Stress 1 External load A B C D E F G H I 7 pressure sensor 8mm 8mm R6 R6 Fig. 4: Plane model and sensor placement 115mm 78mm The pre-buried micro pressure sensors are used to obtain internal stress of soil. The type of sensor is BW11-2. The sensitivity is.1 kpa. The sensors are connected with YE2539 high speed static data acquisition system. The arrangement of sensors is nonequal interval. The arrangement of sensors is dense when it is close to the tunnel. The surface displacement of model is measured by the drawing grid lines. DJ6 the odolite is used to measure the angle change of intersection of grid lines on the fixed position. It is shown in Fig. 4. The continuous monitoring of the soil stress is conducted by stress sensor after the model is completed. The displacement monitoring is conducted when the stress field is stable after a day. Then the tunnel is excavated. The successively tunneling is used. The interval is 24 h. It is equivalent to the actual 7 days. The supporting ring is installed when the tunnel is excavated through. The continuous measurement is conducted after excavation and support is completed. The interval of displacement measurement is 4 h. The interval of stress measurement is 3 min. The arrangement of measuring points of stress and displacement is shown in Fig. 4 and 5. THE ANALYSIS OF EXPERIMENTAL RESULTS Fig. 5: Displacement measurement curve of samples with different ratio is shown in Fig. 3. The reasonable ratio and mechanical parameters are shown in Table. 2. The first Digital of ratio number indicates ratio of sand binder, the second, third or fourth digital in one cement indicates the ratio of lime, gypsum, mica powder. The ratio of 3:4: 4:2 denotes 3:1 of the sand binder ratio. In one cement, the ratio of lime, plaster, mica is.4,.4,.2. The ratio of water is 1/9 of the mixture. The specimen is dried to 8% of moisture content. The physical and mechanical parameters, initial conditions and boundary conditions should be all similar on the basis of similarity ratio of bulk density and geometric in elastic range. The geometric similarity ratio is which is determined according to practical tunnel buried depth and size of two tunnels and the size of test table. The length high width of similarity model is equal to m. The radius of tunnel model is.12 m. It is equivalent to 6 m. The space of tunnel is.2 m. It is equivalent to1 m. The similarity relations of model test are shown in Table 3. A large number of test data are received after the excavation of tunnel and 2 h of continuous monitoring. The measuring points C2, D2, E2 and C5, D5, E5 is selected to analyze vertical settlement rules of stratum with time. The vertical deformation curves of 2 and 5# ground with time after tunnel excavation are given in Fig. 6 and 7. It can be seen that the settlement rate is larger within the interval of -4 h. The settlement rate decreases to be slow within the interval of 4-6 h. The settlement rate increases after 6 h and be stable until about 1 h. The maximum value of vertical displacement is located nearby the axis of the tunnel, rather than the center of two tunnel connection. The soil between two tunnels has a pillar effect. The space of two d tunnels can C2 D2 E Fig. 6: Time-settlement curve of 2# stratum 4842

4 Res. J. Appl. Sci. Eng. Technol., 4(22): , C5 D5 E #line -4. 4#line #line Fig. 7: Time-settlement curve of 5# stratum Fig. 8: Settlement trough of 2# horizontal line First day Second day Third day First day Second day Third day Fifth day Eighth day Fifth day Eighth day Fig. 9: Settlement trough of 5# horizontal line effectively reduce the mutual disturbance. The vertical displacement of upper stratum is slightly lower than that of lower stratum. The vertical settlement of 2 and 5# stratum is shown Fig. 8 and 9. The characteristic of non symmetrical two peak of vertical deformation of stratum is obvious with the increase of depth. The settlement of upper stratum is larger than that of lower stratum. The ground subsidence of 2# stratum is bigger within the first three days. The value is about 7-8% of total settlement. Fig. 1: Settlement trough of different strata at the third day #line 4#line 5#line Fig. 11: Horizontal curves of strata at the third day The laws of settlement of 5 and 2# lines have similar features. The proportion of settlement of 5# horizontal line is bigger than that of 2# horizontal line with 5 days. The subsidence trough curve of different stratum is shown in Fig. 1 at the third day. The value of settlement increases with the increase of depth. The width of settlement trough decreases with the increase of depth. The width of settlement trough is about 3 cm. The settlement of double tunnels is similar to superposition of single tunnel. The curve of settlement trough of first tunnel is shaped of typical normal distribution. The depth and width of settlement trough is smaller. The settlement trough of double tunnels is obvious asymmetry. The settlement is larger in the side of early excavating tunnel. The curve of lateral displacement of different stratum at the third days is given in Fig. 11. The lateral displacement of soil after tunnel excavation completed has closer trend to the center. The variation range of lateral displacement is about mm. The extreme point of horizontal displacement of 2 and 4# stratum is located in about 2 cm position of the distance of center line of double tunnels. The trend is symmetrical. And the lateral displacement is larger in the side of early excavating tunnel. The horizontal displacement of 5# stratum is different from that of 2 and 4# stratum. The point of the maximum horizontal displacement is located in 15 cm of left side of center line of double tunnels. The point of 4843

5 Res. J. Appl. Sci. Eng. Technol., 4(22): , 212 the maximum horizontal displacement of right tunnel is same with that of 2 and 4# stratum. The horizontal displacement of axis of two tunnels approximately decreases linearly with the increase of the depth. The horizontal displacement in the location of center line and axis of two tunnels is not. The lateral displacement of 5# stratum change complex. The variation of lateral displacement of soil between double tunnels does not have a consistent. The variation of lateral displacement of measuring point on both sides of tunnel is severe. The orientation of the lateral displacement of 2 and 5# stratum is reversed at the location X = ±5 and X = ±3 cm, as is shown in Fig. 9. The soil layer with shearing motion is called shear layer caused by tunnel excavation. CONCLUSION The optimal ratio of similar materials of soil layers is obtained by similarity principle and uni-axial compression tests. The two-dimensional similar material model is established for Dalian double-tube parallel tunnels line no. 1. The measurement of inner displacement of tunnel is conducted. The main conclusions are as follows: The change of vertical displacement of different strata with time can be seen as negative exponential function of time. The settlement rate of vertical displacements is different in different monitoring time for the different measuring points of same stratum. The initial settlement rate is larger than later settlement rate. The settlement rate of vertical displacements is different in measuring points of different stratum for different monitoring time. The settlement rate of shallow stratum is larger than that of deep stratum. The settlement of double tunnels is similar to superposition of single tunnel. The curve of settlement trough of first tunnel is shaped of typical normal distribution. The depth and width of settlement trough is smaller. The settlement trough of double tunnels is obvious asymmetry. The settlement is larger in the side of early excavating tunnel. The horizontal displacement between two tunnels is very small. The horizontal displacement of axis of two tunnels approximately decreases linearly with the increase of the depth. The horizontal displacement in the location of center line and axis of two tunnels is not. The obvious shear layer appears in the inner of the soil layers. The pile and shear wall within this range is easy to appear the crack owing to tunneling. ACKNOWLEDGMENT The author would like to thank the financial support by the National Natural Science Foundation of China (Grant No ) and Education Foundation of Liaoning (No. L2138). REFERENCES Addebrooke, T. and D.M. Potts, 21. Twin tunnel interaction: Surface and subsurface effects. Int. J. Geomech., 1(2): Li, D., 28. Research on Physical Model Test and Numerical Simulation for Traffic Tunnel with High Geostress. Institute of Rock and Soil Mechanics, Chinese Academy of Sciences Wuhan, China. Li, P., S. Yuan and Z. Lin, 211. Analysis on 3D numerable stimulations for construction of double line tunnel in Wuhan metro with shielding method. Railway Standard Design, 4: Lin, Z., H. Zhu and X. Ca-chu, 29. Numerical modeling study on interaction between twin shields tunneling. Chin. J. Underground Space Eng., 5(1): Ling, H., Q. Wen-Ge and S. Bing, 21. Study of adjacent construction of two tube shield tunnels by centrifugal model test. Rock Soil Mech., 31(9): Liu, B, T. Longguang and D. Chenggang, 26. Prediction for ground subsidence induced by subway double tube tunneling. J. China U. Min. Technol., 35(3): Liu, D., T. Dejing and W. Mingnian, 28. Stochastic method for predicting ground surface settlement and deformation induced by metro double tube tunneling. Rock Soil Mech., 29(12): Liu., X., Z. Guo and J. Wang, 21. Wang Influence on new tunnel mechanics behavior induced by construction about adjacent spacing. J. Chong Qing U., 33(2): Qinghuo, L.Z., 26. Model of surface ground subsidence occurred by double round shields construction of metro system. Mine Constuct. Technol. 27(1): Song, W., R. Chen and J. Du, 28. Numerical analysis of earth pressure balance shield tunneling at guomao-shuangjing interzone of Beijing subway line no. 1. Chin. J. Rock Mech. Eng., 27(supp.2): Suwansawat, S., 27. Einstein describing settlement troughs over twin tunnels using a superposition technique. J. Geotech. Geoenvir. Eng., 133(4): Wei, G., K. Zhu and W. Chen, 211. Ground settlement induced by double-o-tube shield tunneling under different construction conditions. Chin. J. Geotech. Eng., 33(3):