Effect Of Freeze-thaw Cycles On The Mechanical Behavior Of Microbial Treated Sand

Microbially Induced Calcite Precipitation(MICP)is a new soil improvement technology.This technology uses calcium carbonate precipitation generated by microbial metabolic processes to bind soil particles together and to improve the strength and stiffness of the soil.The MICP method is more environmentally friendly and sustainable than conventional soil treatment methods.one of the most emerging and promising biological soil improvement techniques.This technology has been widely explored and promising with potential in various technical applications.In this paper,a series of triaxial compression tests were conducted on the treated sand which experienced the freeze-thaw process.The mechanical properties of the treated sand with different freeze-thaw conditions were compared to explore the effect of freeze-thaw cycles.The main research work and results of this paper are as follows:1.Standard sand was treated by the MICP method to prepare the treated sand samples.The prepared treated sand samples were experienced different number of freeze-thaw cycles,observed the microstructure changes by scanning electron microscopy.The triaxial tests were conducted on the treated sand after the freezethaw process.The results show that the freeze-thaw has few effects on the mechanical properties of the treated sand,indicating that the treated sand is not sensitive to freezethaw cycles.2.According to the mechanical properties of microbial treated sand,established a new elastoplastic constitutive model of the treated sand by introducing the cohesive strength and damage variables and their evolution laws.This model is based on the Super-subloading surface model which can better describe the over-consolidation and structure soil.The effects of different damage variables and their evolution parameters are analyzed by numerical simulation.The results show that the new proposed elastoplastic damage model can well describe the influence of damage on the mechanical properties of soil.By using the model,the one-dimensional compression behaviors of soils with different initial parameters are obtained.The compression curve of the soil is calculated with different parameters such as overconsolidation parameters,structural parameters,cementation strength,and damage variables.The results show that the model can simulate the compression curve of the soil with structure and can reasonably describe the influence of damage variables on the compression behavior of the soil.3.By numerically calculating the established constitutive model under one-dimensional compression stress conditions,the compression curves of soils with different initial parameters are obtained.The compression curve of the soil is calculated by selecting different parameters such as overconsolidation parameters,structural parameters,cohesive strength,and damage variables.The results show that the model can simulate the compression curve of the soil with structure and can reasonably describe the influence of damage variables on the compression behavior of the soil.3.The constitutive model of the MICP sand was used to predict the triaxial test results of the samples after several freeze-thaw cycles,and the numerical simulation results were in good agreement with the test results.The results show that the proposed model can reasonably describe the effect of freeze-thaw cycles on the mechanical properties of the treated sand.With the increase of the freeze-thaw cycles,the cementation strength decreases and damage variable increase due to the degradation of the bonded structure in MICP sand.