Simulation Studies On The Mechanical Behaviour And Failure Mechanism Of The Weak Interlayer In Red Bed Slope Under Coupled Thermal-hydrolic-mechanical Conditions

Large-scale catastrophic landslides are serious threats to lives and property of human.The mechanism of slope landslide has been done a lot of research on,but the critical mechanism of slope evolution from unstable state to large-scale landslide is still a difficult problem.So,in order to explore the mechanical behaviour and failure mechanism of the weak interlayer of red bed slope,field measurement,laboratory test,similarity simulation and theoretical analysis are to be used for the research.The relationship between frictional heating produced while a saturated soil mass is sliding down a slope,and thermal expansion pressure induced by frictional heating is to be investigated,and the effects of thermal expansion pressure on permeability coefficient,sheat strength and pore water pressure are to be investigated,and the constitutive model coupling the thermal expansion pressure and pore water pressure is to be established,and the catastrophic collapse mechanism is to be analyzed,and the failure criteria for saturated slope is to be established,and the new evaluating method and monitoring method for saturated slope is to be established.The research results as follows:(1)Seven kinds of interlayer samples with different mix ratios were made by similar materials with bentonite and sand,the mechanical parameters i.e.cohesion,shear strength and internal friction angle of interlayer samples having moisture contents of 10%,13% and 15% at different temperatures were measured by strain direct shear instrument with a heating control system,the change characteristics and failure mechanism of interlayer sample induced by moisture content and temperature were analyzed.The results show that cohesion and shear strength of interlayer sample with higher bentonite contents decrease dramatically and decrease slowly and decrease dramatically with increase of temperature,on the contrary,it is decrease gradually.Cohesion decrease dramatically caused by damaged and destroyed microstructure force of soil particles of interlayer sample at lower temperature,when temperature exceeds 50℃,cohesion decrease dramatically again because of soil particles slip.(2)Slope models having moisture contents of 10%,13% and 15% were established by physical simulation method.The mechanical parameters i.e.pore water pressure,internal friction angle,cohesion and shear stress,and the landslide characteristics have been studied aiming at test slopes with different temperatures.The results show that,cohesion and shear stress decrease with increase of pore water pressure.Pore water pressure slow increase and then dramatic increase with increase of temperature,but initial temperature of increase dramatically of pore water pressure with lower moisture contents is higher,on the contrary,it is lower.When pore water pressure of interlayer with lower moisture contents increases dramatically,the overlying strata of model slope occurs tensile cracks,and then tensile cracks develop gradually and through the whole overlying strata,model slope landslide.But for interlayer with higher moisture contents,when pore water pressure increases dramatically,the first intercalated sliding produces,and then model slope shows pull-type landslide after multiple intercalated sliding.Instantaneous sliding velocity and range of the landslide with higher moisture contents is larger than it with lower moisture contents.(3)The saturated interlayer in a slope was considered as linear elastic body of coupled solid-liquid phase,mechanical model of coupled thermal-hydrolic-mechanical of saturated interlayer in a slope was established and constitutive equations of that was founded.The applicability of mechanical model of coupled thermal-hydrolic-mechanical was verified by comparing theory calculation results and model test results.The research results show that,pore water pressure coefficient and thermal expansion coefficient are the key factors for increase of pore water pressure of saturated interlayer induced by temperature.The discrepancy between the compression characteristics of pore water in drained condition and that of solid phase medium is the main factor causing increase of pore water pressure coefficient,the discrepancy between the thermal expansion of the pore water and that of the pore volume is the key factor causing the thermal pressurization of porous materials.Pore water pressure of saturated interlayer in a slope slow increase and then dramatic increase with increase of temperature,on the contrary,cohesion and shear stress of saturated interlayer in a slope decrease with increase of temperature.Theory calculation results of pore water pressure of saturated interlayer are good agree with model test results.Therefore,mechanical model of coupled thermal-hydrolic-mechanical of saturated interlayer in a slope can reflect the change characteristics of pore water pressure at different temperatures,which can provide some good advises to predict and control the stability of similar saturated slopes containing weak interlayer.(4)The critical point of cohesion reduces dramatically again could be viewed as indicator of interlayer sample failure,and the key point of initial temperature of pore water pressure increases dramatically could be viewed as the important indicator of slope failure.(5)A numerical simulation model is established by FLAC3 D for analyzing the coupling thermal-hydrolic-mechanical state,and the influence of temperature on vertical displacement,vertical stress,shear stress and failure state of the saturated interlayer in a slope.The results of model test and numerical simulation are comprehensively analyzed and show that the temperature is one of the main reasons for inducing landslide while the slope contains weak interlayer.