Study On Soft Soil Mechanical Properties Under Wave And Shield Construction

Shield method is usually used to construct multiple circulating water transmission tunnels when constructing power plants in coastal areas.On the one hand,the shield construction will cause disturbances in the surrounding coastal soft soil layer,change the mechanical properties of the soft soil,and then cause the ground settlement;on the other hand,the long-term cyclic effect of wave action exacerbates the softening of the soft soil under the power plant breakwater.Under the interplay of shield construction and wave action,the coastal soft soil strength and stiffness characteristics will further weaken,and even induce the engineering accidents such as breakwater instability.Based on the engineering background with the coastal power plant shield method of circulating water tunnel through the breakwater,this thesis is mainly carried out research in the following aspects:(1)To study on the changes of s soft clay strength-deformation characteristic under the interaction of wave action and shield construction,a series of experiments were carried out using a hollow cylinder apparatus,which simulating the wave loads by continuously rotating the soft soil element principal stress axis and the stress relief due to shield construction under a reducing confining stress.The test results show that the soft clay strain-stress relation all obviously follow the hyperbola curves under various disturbance action.(2)To analyze the influence law of traditional Duncan-Chang model parameters affected by wave action and shield construction,the soft clay modified Duncan-Chang model was constructed on the basis of the functional relation among Duncan-Chang model parameters(K,c,φ),shield construction disturbance degree(δ)and cyclic wave action shearing number(N),which considering the influence of the joint disturbance of wave and shield construction.Calculations show that the mechanical properties of coastal soft soil could be properly predicted by this model,whatever wave cycles and ground loss ratio.(3)Based on ABAQUS platform,the UMAT subprogram was written to make secondary development of soft clay m odified Duncan-Chang model under the combined disturbance of wave and shield construction.Then the correctness of this subroutine was verified by calculations.(4)On the basics of the the numerical simulation under wave action during tunnel driving through the breakwater and by analyzing the variation laws of coastal soft soil stress,displacement and pore water pressure under different wave parameters(such as period,wave height,water depth),summarize the influence law of shield excavation on ground movement under different ground loss rates.Then propose appropriate control measures according to the change rule of soft soil mechanical properties under wave and shield construction.