Research On Creep Behavior And Nonlinear Rheology Constitutive Model Of Giant Slow-moving Landslides' Slip Zone

The mechanical behavior of rock and soil is one of the key factors controlling slopes' stability and activity character,especially the slow activity of giant slow-moving landslides is closely related to slip soil's creep behavior.However,the long-term slow activity history shows that the slip soil's creep behavior is typical residual state creep character,not traditional peak state.This phenomenon has raised interest of a few foreign scholars,while no civil research was involved at present.Based on the two famous domestic giant slow-moving landslidesSuoertou landslide and Xieliupo landslide in Gansu Zhouqu and their slip soils containing various amounts of gravel-size particles,using medium-sized direct shear creep test combined with numerical simulation,this thesis systemically studied the creep behavior of clay soils with gravel-size particles under residual state and its internal mechanism.Based on the results of tests,a nonlinear rheology constitutive model of the clay soils with gravel-size particles was established.Using the object-oriented C++ the nonlinear constitutive was programmed in FLAC₃D,and it was used to analyse the main factor controlling Suoertou lanslide's activity and predict its activity trends.The systemetically tests of slip soils under residual state indicates that all slip soils in this study with various amounts of gravel-size particles showed creep behavior obviously.An attenuating creep was observed when the applied shear stress was less than their residual strength,while a non-attenuating creep with no evident secondary creep occurred when the applied shear stress is slightly greater than their residual strength.Thus,long-term strength of slip soil under residual state is greater than its residual strength.It may be related with the crushing of gravel-size particles and the strength recovery due to great reduction in shear rate pre-residual and at the residual state during creep.For all soils tested in the study the long-term strength and the residual strength tended to markedly and nonlinearly increase with gravel content.The displacement until their tertiary creep was increased with more gravels,and so do RCSR value.This is because the more gravel-size particles crushed,the greater the resistance to creep shear,thus the longer shear displacement.While the elapsed time until their tertiary creep showed no identifiable correlation with gravel content,which may be related to the difference in the weathering degree of the gravel-size slate fragments within the soils.Based on the creep behavior of slip soils under residual state,with the method of inversion fitting,a new nonlinear rheological constitutive model-modified Nishihara model was established by replacing the linear Bingham element with a nonlinear one.With the method of the object-oriented C++,the nonlinear constitutive was programmed in FLAC₃D and verified.Based on the programmed modified Nishihara model,the contribution factors to the activity of Suoertou landslide was to analyzed with the use of FLAC₃D.The numerical simulation results showed that under different controlling factors,Suoertou landslide's dynamical mode was similar,but with different displacement velocities.By comparing the various factors contribution to the velocity of landslide,it was found that other than the creep behavior of Suoertou landslide's slip soil,groundwater table fluctuation and fault activity were the main factors causing the slide's long-term slow-moving.And the effect of water table raising was greater than fault activityin controlling the dynamical of the slide.However,the incision of Bailongjiang river only had an influence on the velocity of the front part of the slide.Furthermore,it was predicted that by addding increased groundwater level or seismic intensity VIII earthquake on active fault,the slide would experience large displacement.