Permeability Anisotropy Of Kaolin-montmorillonite Mixed Clays

Nowadays,during the construction and operation of underground engineering,the consideration of the permeability characteristics of soft clay is mainly isotropic.In fact,the isotropic characteristics cannot reflect the true anisotropic conditions in actual engineering,so the research of permeability coefficient and its anisotropy can provide a better theoretical basis for practical engineering.In this paper,a new mixed clay with the admixture of kaolin and bentonite is used as the research object.The mineral composition,pore characteristics and liquid properties of the mixed clay are researched by a series of tests carried out by the triaxial permeameter.The main conclusions are as follows:Through the study of the influence of mineral composition,pore characteristics and liquid properties on the physical properties of mixed clays,it is found that:(1)The increasing amount of bentonite will reduce the plastic limit of the mixed clay,and the relationship between the amount of bentonite and the plastic limit is linear.For the clay mixed with bentonite,the liquid limit will decrease with the increase of the concentration of the NaCl solution;(2)With the increase of the incorporation of bentonite,the pore content between 200nm and 400nm of the mixed clay will increase,but the pore cotent with the pore diameter greater than 400nm will decrease.With the increase of consolidation stress,the pore greater than 200nm will decrease,and the maximum pore size will decrease.For B20K80,the addition of electrolyte solution makes the pore larger,and larger pores will increase,but the smaller pores have no obvious change.The study on the permeability coefficient and anisotropy of mixed clay found that:(1)After the bentonite is added,the permeability coefficient and the permeability coefficient anisotropy of the mixed clay will significantly decrease.The decreasing trend slows down with the amount of bentonite incorporation increasing,and the final permeability coefficient anisotropy tends to be stable;With the effective consolidation stress increasing,the permeability coefficient anisotropy increases,but the increasing amplitude is decreases;(2)The permeability coefficient of the mixed clay B5K95 decreases with the addition of the NaCl solution,but the permeability coefficient of the mixed clay B20K80 increased.The permeability coefficient anisotropy of the two mixed clays have no obvious change trend with the addition of the NaCl solution;(3)Pore ratio and liquid limit void ratio are not the key parameters determining the permeability coefficient anisotropy,but there is a good linear relationship between the microscopic parameters and the permeability coefficient anisotropy.The pore diameter coefficient D50?D70 is the key parameter affecting the permeability coefficient anisotropy,and a better permeability coefficient anisotropy model is established.In this paper,a inclined glass ring is designed to obtain a sample that penetrates at any angle with the deposition direction,and the study of the sedimentation angle on the permeability characteristics shows:(1)When the angle between the penetration direction and the deposition direction increases from 0°to 90°,the permeability coefficient increases,and this trend does not change with the consolidation stress and the liquid properties;(2)In the two-dimensional plane,the permeability coefficient of the mixed clay is similar to the elliptical distribution,in which the horizontal direction is the main penetration direction,and the horizontal permeability coefficient is the largest,which is the main permeability coefficient;(3)There is a semi-logarithmic correlation between the permeability coefficient and the corresponding microscopic parameters for the samples,and this relationship is actually the expression of the permeability coefficient model.Combined with the uniformity of the permeability coefficient model and the permeability anisotropy model,the aperture parameter 170 is selected as a microscopic parameter,and a permeability coefficient model expressed by the aperture parameter R702 was established.