Effect of Strain Softening of Soil on Tunnel Face Stability

With the construction of shield tunnel,the reasonable analysis of stability of excavation face is very important.Finite difference program is used to simulate shear band in the strain-softening sand.The accuracy of numerical method is verified by comparing numerical results with experimental and analytic solutions.Then,3D numerical model of shield tunnel is created.The influence of strain softening on limit supporting pressure of excavation face is analyzed without regard to seepage.When considering seepage,a comparative analysis of the limit supporting pressure,the displacement,plastic zone and ground settlement is conducted on two conditions: taking and not taking account of the strain softening.The results show that the values increase sharply with consideration of strain softening,and more easily cause the instability of excavation face.The effect of face stability with different strain softening behaviors of dilation and friction is also discussed.Finally,considering strain softening of soils the support pressure used in construction of the line 9 of Tianjin metro is predicted.And the forecasts agree well with the monitoring values.