Study On Macroscopic Deformation Characteristics And Microstructure Evolution Mechanism Of Collapsible Loess Before And After Modification

The area of loess in China is about 630,000 square kilometers,accounting for 6.6% of the total land area of China,and it is widely distributed.About 60% of the loess has different degrees of collapsibility,which seriously restricts the economic development and urban construction in loess areas.The loess in the natural state has the characteristics of high strength and low compression.Once it meets water,the original soil structure will be destroyed and obviously collapsible deformation will occur under the joint action of external force and water.Geological disasters such as foundation settlement and landslide caused by collapsibility deformation of loess not only bring huge economic losses,but also seriously endanger people’s life safety.Therefore,it is of great significance for sponge cities in loess region to make correct judgment on loess collapsibility and how to weaken or even eliminate loess collapsibility.In this paper,on the basis of predecessors had a lot of research,somewhere in xi ’an of shanxi province to a certain depth of subgrade foundation loess as the research object,adopt mixed with different ratio of bentonite to modification of the loess,studies the void ratio of loess3 before and after modification,the compression deformation,collapsibility coefficient and the change of microstructure,get the following conclusion:(1)A series of basic geotechnical tests were carried out on the physical and mechanical indexes of the loess.The results show that the average moisture content of the samples is 10.46%,the control particle size of the loess is 0.0488 mm,the average particle size is 0.0386 mm.The Cu,Cc and specific gravity of the loess samples are 9.037,1.428 and2.71 respectively.The liquid limit of the sample is 28.05%,the plastic limit is 18.04%,and the plastic index is 10.01,which belong to the low liquid limit soil.(2)In order to study the effect of water content on shear strength of loess,direct shear tests of loess with different water content under different axial loads were carried out.The results show that with the increase of water content,both cohesion c and internal friction Angle φ show a decreasing trend.The difference is that the internal friction Angle is basically linear small,and the change of cohesion with water content is roughly a quadratic function.(3)The deformation of loess with different moisture content,dry density and bentonite content was studied by consolidation compression test and subsidence test in laboratory.Analyzed in the different vertical load the above factors on the collapsibility loess void ratio,compression deformation and the influence of the deformation,has proven the moisture content and dry density before modification from low to high collapsibility of loess porosity ratio and the influence of,discussed after mixed with different ratio of bentonite modified loess under the different moisture content and dry density of collapsibility compression deformation and change,The feasibility of bentonite modification of loess was verified,and the optimal dosage was more than 4%considering the influence of actual engineering.(4)In order to study the change of the microstructure in the process of loess collapsibility and bentonite abate the mechanism of the collapsibility of loess,with the help of scanning electron microscopy(sem),under the condition of different dry density and moisture content,different bentonite content of collapsibility loess samples in the microstructure were observed before and after analyses the moisture content,dry density and bentonite content of loess microstructure change,In this paper,the mechanism of loess collapsibility was explained by comparing the microstructure characteristics of samples before and after collapsibility,and the action mechanism of bentonite to weaken or even eliminate loess collapsibility was expounded from the perspective of micromechanics.As the content of bentonite in soil increases,the large pores between particles are filled,and the strength of particle skeleton structure becomes larger,the structure becomes more stable,and it is not easy to be destroyed.