Study On Mechanical Properties Experiment And Engineering Application Of Unsaturated Loess Based On Freeze-thaw And Dry-wet

There are many factors affecting the stability and deformation of the slope.Freeze-thaw cycles,alternation of dry-wet and rainfall infiltration are the major factors that cause the slope instability,and change the microstructure and physical properties of shallow rock and soil.As a result,the strength parameters and shear strength are reduced.Most of soils exist in unsaturated form,and the soil-water characteristic curve(SWCC)is the foundation and focus of the study on the strength of unsaturated soil,which is one of the constitutive relations to explain the engineering phenomenon.Therefore,how to use the SWCC to correctly analyze slope stability is of great guiding significance to engineering practice.Anti-slide piles are one of the important means to reinforce slope,By using the soil arching effect of the interaction between pile and soil,resisting the sliding force of soil so as to significantly enhance stability of the slope.Aiming at the unsaturated loess in Lanzhou area,The determination of SWCC under different dry density and water content was carried out,the quantitative effect of freeze-thaw cycles and freeze-thaw and wet-dry on matric suction and SWCC.Taking advantage of the strength reduction function in ABAQUS,considering freeze-thaw cycles,alternation of dry-wet,pile-soil contact,a numerical model was established to analyze the overall stability of slopes reinforced by anti-slide piles.The main research contents and conclusions are presented as follows:1.The matric suction was measured by filter paper method.The influence of water content and dry density on absorption and desorption curve and hysteretic loop of unsaturated loess,freeze-thaw cycles and freeze-thaw and wet-dry on matric suction were analyzed.It is showed that absorption and desorption curves under different water content and dry density have obvious hysteretic loop,with the increase of water content increases,with the increase of dry density decreases,The smaller dry density,the faster the dehumidification rate,the weaker the water holding capacity,The greater dry density,the law is opposite;With the increase of freeze-thaw cycles and freeze-thaw and dry-wet,matric suction logarithmic decrease;The effect of freeze-thaw/dry-wet on SWCC is more intense and stabilize with increase of times.2.Origin was used to fit the experimental data of unsaturated loess under different working conditions by Gardner model,Fredlund & Xing model and Van Genuchten model,the results show that the gardner formula is simple,the fitting curve is closest to the experimental data.The relationship between permeability coefficient and matric suction or water content of unsaturated loess is built by Childs & Collis-Geroge model.3.The direct shear test of unsaturated loess was carried out with direct shear.The influence of freeze-thaw cycles,freeze-thaw and dry-wet,dry-wet path and water content on strength and strength parameters was studied.The results show that with increase of freeze-thaw,the cohesion exponentially decreased,and the internal friction angle exponentially increased and strength increased;With increase of freeze-thaw and dry-wet,the cohesion and the internal friction angle exponentially decreased,and strength decreased;Dry-wet path has effect on strength and strength parameters,The strength and strength parameters of the soils samples under experimental condition of humidification first and dehumidification then are higher than those of the specimens under the condition of dehumidification first and humidification then;Based on the experimental data,The quantitative expression of strength parameters of unsaturated loess with the change of water content,freeze-thaw cycles,freeze-thaw and wet-dry are established and its reliability is proved,which laid the foundation for future research on strength model.4.Study on effects of freeze-thaw and rainfall-evaporation on the stability of three-dimensional slope reinforced by piles.It is showed that freeze-thaw cycle,the rainfall duration,rainfall intensity,and pile spacing have significantly effect on the stability factor.the range of maximum saturation and saturation of unsaturated zone increases,and the saturation on both sides of pile is obviously stepped distribution;Freeze-thaw and dry-wet change the mechanical properties of unsaturated soil,and change in stability of slope.Freeze-thaw and dry-wet make water in soil migrate and evaporated,resulting in the breaking of soil particle skeleton and destruction of internal microstructure of soil.As a result,change shear strength and strength parameters of soil,eventually cause slope instability.