| Consequent slope with low dip angle (dip angle<35°) and clayey interlayer has local failure phenomenon and progressive failure mechanism, however, the theory is lack of in-depth theoretical support. The progressive failure theory for the slope originates from the strain softening effect of geomaterials. In this paper, the strain softening effect for clayey interlayer was first studied. With creation of the contact element of the strain-softening constitutive model and consequent slope model containing strain-softening constitutive contact elements, the failure mechanism and local failure zones for the consequent slope were in-depth studied. Statistics, laboratory test, numerical calculation, theoretical analysis, field monitoring, field research and other research tools were used in the study, and the following are concluded from the study:(1) Through repeating shear tests of different types of multigroup clayey interlayer samples, the shear strength parameters of clayey interlayer in the process of strain softening were systematically studied. On the base of attenuation model of the three-orientation shear strength, the concept "plastic shear displacement"was put forward, and the calculation method of its value was deeply studied, and standard method and procedure of the clayey interlayer strain softening tests were established.(2) Through the shear rheological tests of mudstone clayey interlayer, the time effect for the shear strength of the clayey interlayer was deeply studied. It is found that the composite variation of the long-term strength of the clayey interlayer has a softening/hardening effect over time, and the long-term strength values depend on the dead load shear stress and normal stress characteristics applying to clayey interlayer.(3) The contact element containing the strain-softening constitutive model was studied by the FLAC. Through numerical simulation of direct shear tests with the contact elements, the validity of the contact elements was confirmatory analyzed. It is found that the direct shear test has a process of progressive failure, and evolutions of strength parameters of the contact elements have a linear influence for shear stress-displacement curve. The contact elements model is reasonably effective.(4) The contact elements of strain-softening constitutive model was introduced to mechanical behavior analysis of the consequent slope, the response procedure of the interlaminar stress characteristics of the consequent slope and the chain transfer characteristics of the strain softening effect was in-depth studied. Based on the results of mechanical behavior analysis, the progressive failure process of the consequent slope was in-depth studied, the progressive failure mechanism of the consequent slope was proposed.(5) Using mathematical statistics method, the sensitivity analysis of the parameter factors and regression analysis of the correlation between each major factor and local failure zones were carried out. The toe segment local failure zones of the consequent slope is affected by the parameter factors, such as rock layers dip, layer thickness, slope length, peak friction angle, residual friction angle, peak cohesion, residual cohesion, plastic shear displacement. Basing on the mathematical statistics analysis result, considering the ultimate strain softening characteristics of the clayey interlayer, combing the correction of38data samples in field survey, calculation formula and calculation steps of the toe segment local failure zones of the consequent slope were established, the calculation formula are as follows: Ljjx=5.75a+3.86d-9.06φp-3.81Cp+101.16(6) Through comprehensive analysis of the following three typical projects, the consequent slope of Badong station, Hunan-Chongqing high-speed consequent landslide and Jianyang Leidashi consequent landslide, the calculation formula established in this paper was verified. It shows that the calculation results of the theoretical formula are reasonable and reliable, and it meets the engineering applications. |
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