LIMIT EQUILIBRIUM ANALYSIS OF SOILS STABILITY AT SHALLOW TUNNEL END UPON SHIELD EXCAVATION
SONG Kezhi1,WANG Mengshu2,SUN Mou3
(1. College of Civil Engineering,Ludong University,Yantai,Shandong 264025,China;2. Tunnel and Underground Engineering Research Center of Ministry of Education,Beijing Jiaotong University,Beijing 100044,China;3. China Railway Group Limited,Zhengzhou,Henan 450053,China)
Abstract:A working shaft enclosed by the continuous wall must be built at two ends of the tunnel to be excavated for shield starting and arriving in shield tunneling. Soil body at two ends of the tunnel may collapse along a sliding surface and pose a high risk in shield tunneling. A combined sliding mode of straight line and logarithmic spiral line was proposed for shallow shield tunnel. A formula to calculate the stability of the soil at the ends of shallow tunnel was deduced by means of limit equilibrium analysis and the factors influencing the soil stability were analyzed with the derived formula. The soil stability at tunnel ends is dependent on the soil strength,the thickness of reinforced soil body,the strength of reinforced soil body and the diameter of tunnel outlet. The greater the internal friction angle and the cohesion of the soils are,the higher the soil stability. The greater the thickness and the strength of the reinforced soils are,the higher the soil stability. The soil stability at tunnel end decreases with the increasing of the diameter of the tunnel outlet. The method was successfully used to calculate the soil stability and the thickness of the reinforcement of soil body of a shield tunnel of metro in Nanjing.