Effect Of Particle Size Distribution On The EICP-Treated Earthen Site Soil

The natural weathering has caused huge damage to the soil sites in the northwest region of my country,and also caused a great threat to their safety.The EnzymeInduced Carbonate Precipitation（EICP）is a new type of cultural relic protection technology for soil sites,which can provide a new solution for the anti-weathering reinforcement of soil sites.Generally speaking,soil particle gradation affects the internal pore and skeleton structure of soil,which will affect the permeability of enzyme solution and cementitious liquid in soil,and finally affect the reinforcement effect of EICP.However,in the current study,the effect of soil particle size on enzyme-induced calcium carbonate is often ignored.Therefore,it is necessary to carry out EICP treatment on site soils with different particle gradations to study the changes in their physical and mechanical properties,weather resistance,and microstructure,so as to solve the problem of the applicability of EICP in site soils with different particle gradations.In this paper,silty sand,silt,and silty clay,three kinds of site soil with particle gradation,were used as materials for EICP treatment,and a control group without EICP treatment was set up.Firstly,the effects of the concentration ratio of calcium source,calcium salt and urea as well as the infiltration mode of the solution on the soil of different particle grading sites strengthened by EICP were studied.Afterwards,dry-wet,freeze-thaw cycle tests were carried out to detect the changes in the quality,surface hardness,longitudinal wave velocity and shear strength of the three kinds of site soils with particle gradation after EICP reinforcement.The effect mechanism of particle size on enzyme-induced calcium carbonate precipitation was studied,and the conclusions were as follows:（1）The particle gradation of site soils in northwestern my country is mainly silty sand,silt,and silty clay.In the EICP reinforcement of silty sand,silt,and silty clay type site soils,calcium chloride can be selected as the calcium source to configure the cementitious liquid.Since the concentration of calcium salt and urea in the cementing solution will affect the reinforcement effect of EICP,when the concentrations of calcium chloride and urea are 0.75mol/L and 1.5mol/L,respectively,it is the most suitable for the reinforcement of these three types of site soils.When dripping the solution,the dripping sequence of "enzyme solution-calcium chloride solution-urea solution" is helpful to achieve the best reinforcement effect.（2）After EICP reinforcement: the silty clay surface in the freeze-thaw cycle has a large range of alkaloids,and the top is obviously agglomerated,the silt surface has a small range of alkaloids,and the silty sand has no obvious alkaloids.However,the soils of the three sites after the drying-wetting cycle only had a slight brittle alkali,the appearance was relatively complete,and there was no obvious slag or lump loss;after the drying-wetting,freeze-thaw cycles,the quality,surface hardness,The longitudinal wave velocity all decreased,and the decreasing amplitudes of silty sand,silt,and silty clay increased in turn.Compared with the freeze-thaw cycle,it is found that the damage degree in the dry-wet cycle is smaller,and the reduction of various physical properties is relatively low,indicating that the ability of the site soil reinforced by EICP to resist the dry-wet cycle is better than the freeze-thaw resistance;the direct shear test The results show that the attenuation range of cohesion of silty sand,silt,and silty clay increases in turn,while the internal friction angle has no obvious change,which indicates that the difference of particle gradation mainly affects the cohesion of the samples reinforced after EICP,but The effect on the internal friction angle is small.（3）Through scanning electron microscope test and PCAS software analysis,it was found that after the freeze-thaw cycle,the apparent porosity and average pore diameter of the silty sand,silt,and silty clay reinforced by EICP increased sequentially.The pores gradually develop into larger pores,and the cementation effect between the calcium acid precipitation and the soil particles becomes weaker,which weakens the reinforcement effect of EICP,and this weakening effect gradually weakens in silty clay,silt,and silty sand;During the wet cycle,the pores in the soil develop slowly,and the apparent porosity and average pore diameter of the soil increase slowly.Nevertheless,the development of pores in silty sand,silt,and silty clay is also different.The pores in silty clay will gradually develop into micro-cracks,while silty sand and silt develop slowly,and silty clay structure maintains well.