Experimental Study On The Permeability And Mechanical Properties Of Lime-treated Loess

Loess is a special soil with unique water sensitivity and collapsibility.If construction activities are directly performed on the re-compacted loess without any improvements,it will easily cause collapsible and reduce strength,and even easily induce engineering accidents such as slope instability,pavement roadbed collapse,and uneven settlement of the foundation once the water intrusion occurs.A large number of scientific studies and examples have showed that the improved loess foundation can effectively solve engineering problems such as uneven settlement and deformation of the building foundation,and greatly improve the bearing capacity and stability of the loess foundation.Due to the strong regional characteristics,loess in different regions differs slightly in particle composition and microstructure,resulting in differences in engineering properties.In this paper,Q₃Malan loess and its lime-treated soil in Qingyang area were studied,comprehensive physical property test comprehensive,saturation permeability tests,electron microscope test and conventional triaxial tests on remodeling loess were performed to study its permeability and mechanical properties.The main research work and achievements of this paper are as follows:（1）The comprehensive basic physical properties tests were carried out,including density test,water content test,specific gravity test,liquid-plastic limit test,particle analysis test,compaction test,mineral composition and chemical composition analysis test.From the analysis of the test results,it can be seen that the test loess is a well-graded and continuous Q₃Maran loess,which can be classified as a low liquid limit clay.The main minerals are mainly quartz and feldspar,and the chemical composition is Mainly Si O₂,Ca O,Fe₂O₃.The main effects of lime content on compaction characteristics of loess are showed that the maximum dry density d_rmaxdecreases and the corresponding optimum moisture w_optincreases with the increased lime content.（2）The falling-head permeability tests at various dry densities and lime contents(（0%,3%,6%,9%,15%）were carried on the mixtures.The test results show that saturated hydraulic conductivity of the lime-treated loess has a negative exponential relationship with the dry density and a positive exponential relationship with the void ratio at each lime content,and in a semi-logarithmic scale,the relationship between void ratio and saturated hydraulic conductivity of the lime-treated soils is a cluster of paralleled lines,and establish the formula of the exponential relationship between the two,whose intercept is related to the lime content.（3）To qualitatively and quantitatively study the microstructure characteristics of the lime-treated loess under different lime content and dry density,SEM（Scanning electron microscope）electron microscope test and IPP（Image-Pro Plus 6.0）image analysis and processing software were used.The improved mechanism is explained from the microscopic point of view,and the relation between the microstructure parameters and the macroscopic physical properties is tried to be established.It is found that the size of permeability is directly proportional to the number,area and surface porosity of large and medium-sized pores,which indicated that the permeability of loess is determined by the large and medium pores.In addition,the fractal dimension of the pores is proportional to the complexity of the pore structure and can reflect the macroscopic physical properties to a certain extent.（4）The results of unconfined compression tests on the improved loess with different lime content and void ratio show that both lime content and void ratio can affect the strength,but the strength is not controlled by a single factor,but is caused by their joint coupling.Based on this,the concept of lime-voids ratio V_le/V_vis proposed,that is,the ratio of lime volume to pore volume.Under different lime-voids ratio for soil samples of conventional triaxial drainage experiment was carried out,the results showed that although lime-voids ratio are different,the soil samples with the same lime-voids ratio showed the similar mechanical behavior under the same confining pressure.The deviator stress-axial strain-volumetric and stress-dilatancy variation curves are similar,stability curve approaches and to achieve the strength of the close.The lime-voids ratio is therefore an appropriate parameter to describe the mechanical behavior of the lime-loess mixture.（5）Based on the analysis of the triaxial test results of the remodeling loess,it was found that the stress-strain relationship was in line with the modified Cambridge model theory.Therefore,the modified Cambridge model was used to calculate the constitutive relation of the remodeling loess,and the corresponding program code was written in matlab software.The research results show that the advantages of the modified Cambridge model are that it can accurately simulate the stress-strain relationship during the loading phase in the isotropic isobaric loading and unloading test of remodeling loess,the relationship between the deviator stress of consolidation drainage under low confining pressure,and the critical stress state under high confining pressure.The calculated pore pressure value of the critical state of consolidation undrained are close to the experimental values.However,the disadvantages are that it cannot simulate the hysteresis loops formed during the unloading and reloading stages,and it cannot calculate the plastic deformation generated during the rebound process;it cannot accurately simulate the pore pressure curve of the consolidated undrained shearing process and volume deformation curve of the consolidation drainage.