The active lateral earth pressure and displacement ignore the influence of the pile side frictional resistance. It is considered that the active side vertical direction Rli is constant and the horizontal direction R3ai is reduced (unloading). For each step excavation, the following formula is calculated: Rli=Czi+q, ( 1) where: q is overload, zi is the thickness of the soil at node i, does not change with excavation, C is the soil gravity, and Rli is the vertical stress of the soil at node i. R3ai=R0i-qai, (2) where: R3ai is the horizontal stress of the soil at the node i; the initial value of R0i is k0Czi, k0=1-sinU, U is the effective internal friction angle of the soil, and R0i-qai is assigned every time one step is calculated. Give R0i as the initial value for the next excavation. Qai=Fai/bid, where d is the diameter of the slope protection pile, bi is the length of the pile section, and Fai is the active earth pressure increment of the soil at the junction of the i, that is, the active side soil spring is stretched by the tensile force. The resulting increase in pull force. The consolidation ratio of soil before excavation of foundation pit is k0=R3/R1, (5)R2=R3=k0R1, (6)Rm=(R1+R2+R3)/3, where Rm is before excavation of soil Initial consolidation pressure. Considering the unloading modulus calculation formula of the stress path, the stress-strain relationship of the soft soil is found by the unloading stress path test, which can be described by the following hyperbola <3>. (R1-R3)-3(1-k0)1+2k0Rm=Eaa+bEa. (7) where (R1-R3) is a deviatoric stress; Ea is an axial strain. a=1/Eui (Eui is the initial unloading modulus) b=1(R1-R3)ult-3(1-k0 ) 1+2k0Rm. (8) The denominator term in equation (8) is the asymptote value of the hyperbola represented by equation (7). The destruction ratio is defined as Rf=(R1-R3)f-3(1-k0)1+2k0Rm(R1-R3)ult-3(1-k0)1+2k0Rm. (9) When (R1-R3)f is the principal stress difference at the time of sample failure, b=Rf(R1-R3)f-3(1-k0)1+2k0Rm. Therefore, equation (9) can be rewritten as R1-R3=Ea1Eui+EaRf(R1-R3)f-3(1-k0)1+2k0Rm+3(1-k0)/(1+2k0)Rm. (10) The stress-strain relationship shown in equation (10) can be easily used for stress increment analysis. For equation (10), the stress-strain curve (R1-R3) to E1 tangent slope at any point on the curve is expressed as :tan=5(R1-R3)5Ea. Derivation of horizontal resistance coefficient In the finite element analysis of the bar system, the horizontal resistance coefficient ks is a very important and particularly sensitive coefficient. At present, the commonly used methods for evaluating ks are Zhang Youling, c, m and JEBowles. Jin Yabing made a reasonable amendment to the JEBowles law. The Zhang Youling method, the c method and the m method do not consider the size effect of the pressed area. JEBowles is also an empirical method. In essence, ks is not only related to soil quality, but also to the pressure area (the effect of size effect) and the soft soil unloading mode. The amount is related to the stress path.
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