| With the rapid development of China’s urbanization process and the formation of urban rail transit network,the number of deep excavation is increasing,and the geological environment conditions are becoming more complex.Cities are increasingly short of ground resources,the development of underground space is deeper,which would cause that encountering rock formations in foundation pit construction is more and more common.At present,the worldwide research on the deformation law of soil-rock composite foundation pit is little,and it has a certain regional characteristics.The design and construction of this particular foundation pit still follow the method of foundation pit in soft soil area,the lack of theory and experience affects its stability,construction safety and economy in some degree.Therefore,it is of great significance to pursue research on the stress and deformation law of the retaining structure in soil-rock composite stratum,which ensures the smooth completion of the project and guide the design and construction of similar projects in the future.Based on the foundation pit project of Nanjing Metro Line 5 Yancangqiao station,this paper analyzes the deformation characteristics and influencing factors of the retaining structure in soil-rock composite by means of experience reference,field monitoring,numerical analysis and theoretical derivation.The main contents are as follows:（1）The monitoring data of yancangqiao station are collected,and the typical section is selected to analyze and study the measured data of surrounding ground surface and building settlement,lateral displacement of retaining structure,support axial force and groundwater level,so as to summarize the stress and deformation law of foundation pit excavation in soil-rock composite stratum.The results show that the data of settlement,lateral displacement and axial force at the shallow measurement points of the section are basically smaller than those at the deeper measurement points of the adjacent rock layer,and the deformation and force law of each measurement point at each stage of the foundation excavation is also slightly different.（2）Based on the engineering data of yancangqiao station,a three-dimensional model is established and corrected to predict and analyze the deformation law of the surrounding surface and retaining structure after the excavation of the second stage foundation pit,which is also used for studying the influence of different excavation procedures and the horizontal position of the soil-rock interface on the deformation of the retaining structure and the surrounding environment.The results show that the influence of different excavation processes on the foundation pit and the surrounding environment after the end of construction is small,and there is a significant influence on the lateral movement of the blocking wall in the pit;in the case that there is a height difference between the rock and soil in the soil-rock horizontal junction section,the advancement of the soil-rock horizontal joint surface along the long side of the foundation pit produces an effect similar to squeezing toothpaste on the lateral movement of the enclosure structure,and there is a settlement peak on the side of the shallow burial depth of the rock layer in the soil-rock horizontal joint surface.（3）Based on the stratum conditions of yancangqiao station,a soil-rock composite foundation pit section in Nanjing area is established.The deformation and mechanical characteristics of retaining structure under the change of soil-rock interface depth,insertion ratio,weathering degree of fixed end rock strata,the modulus ratio of rock and soil are analyzed by using finite difference software Flac3D.The results show that when the rock layer at the embedded end is of good quality,the depth of the soil-rock joint surface changes to below the bottom of the enclosure structure,and there is a sudden increase in its bottom lateral displacement;the variation range ofδhm/H is（0.074,0.176）and Hm/H is（0.385,0.805）when the embedded rock enclosure structure of the soil-rock foundation pit in Nanjing area changes between R=0.2-0.55.（4）Referring to the previous studies,this paper,the monitoring data and the soil-rock composite strata characteristics,retaining structure rock-socketed segment is assumed to be the fixed end,ignore lateral force of rock formation,so as to put forward a simplified method of retaining structure deformation and stress calculation,and set up the case of foundation pit comparison and analysis of traditional method,the calculation result of numerical simulation method.The results show that the simplified calculation results are between the numerical simulation results of moderately weathered and fully weathered rock strata,and the calculation method has certain applicability and reference value. |
