Cement Soil Permeability And Its Calculation Model

This study mainly focused on“sponge city”.In order to speed up the permeability of the foundation,a permeable cement soil was proposed.Permeable cement soil,that is,under the premise of ensuring that the cement soil has a certain strength,the cement soil is pored to increase its permeability coefficient.The analysis model of permeability coefficient and pore size distribution was established from a microscopic perspective,so that it can be used to regulate the permeability coefficient of porous media in the future.The specific research content can be concluded as follows:?1?Analyze the hole-making and strength-enhancing technology of cement soil and increase the permeability of cement-soil using foaming technology and sulfate corrosion hole-making technology.Furthermore,explore and discuss the relationship of change of permeability between coefficient and strength.Then select a typical sample for mercury injection test to find the relationship between microscopic pore structure and permeability coefficient and strength.The test results show that the permeability coefficient of foamed cemented soil is negatively related to the cement mixing ratio,density and age in general;the permeability coefficient of cemented soil mixed with Na₂SO₄ is negatively related to the age,and the relationship of soil mixed with the Na₂SO₄ is:When the content of Na₂SO₄ is less than 7%,the permeability coefficient is negatively related to the content of Na₂SO₄.When the content of Na₂SO₄ is greater or equal to 10%,the permeability coefficient of cement-soil becomes larger;At the same time,the permeability coefficient and strength of cement-soil are negative.In the related relationship,the increase of the permeability coefficient will reduce the strength,and vice versa;However,there are many dead holes and blind-end pores in cement soil from the mercury intrusion test which are not helpful to the permeability of cement and soil.The permeability coefficient of cement soil does not depend on the pore volume inside the cement soil,but mainly depends on the number of macropores?>1?m??the probability of the macropores becoming dead or blind pores is lower than that of the pores?.The greater the proportion,the greater the permeability coefficient.?2?In addition,this study correct the analysis model proposed by O.Amiri appropriately for predicting the permeability coefficient of porous media,and the corrected results are compared with the actual permeability coefficient prediction values.The conclusions are obtained as belows:the analysis model has certain reliability and accuracy which can be applied to the pore size distribution of all shapes and be provided reference for the regulation of the permeability coefficient of porous media;When using the analytical model to calculate,it is found that the pore size below 1?m is ignored,and the result is better than taking all the apertures into the calculation result.More accurate and closer to the real situation.It is shown that the seepage flow with the pore diameter less than 1?m is negligible in the seepage process of porous media.?3?Finally,in order to achieve the aim of this study,the finite element software COMSOL Mutilphysics was adopted to analyze the percolation of porous media.Hence,the effects of the pore size of the porous media,the porosity,as well as the structure of the skeletal structure of the solid particles on the permeability coefficient were researched.The results showed that when the average pore diameter obtained by the mercury intrusion test is used as the pore size of the numerical model,the calculation result and the actual permeability coefficient value are kept in the same order of magnitude,indicating that the method is used to calculate the permeability coefficient value with certain accuracy;During the seepage process,the narrower the seepage channel?ie,the smaller the pore size?,the lower the permeability coefficient,but when the pore size is reduced to a certain value,the permeability coefficient will be closer to the measured value of the permeability coefficient;The permeability coefficient of the porous medium varies with the pore the increase in the rate of increase,the main reason is that when the porosity becomes larger,the internal pore size also becomes larger,which causes changes in the permeability coefficient.;Changes in the permeability coefficient with the variation porous particle's solid particle skeleton structure and its main internal reason is the hole is enlarged or reduced when the particle position or size changes,which in turn affects the permeability coefficient value.