Experimental Study On The Development And Closure Of Sand-Clay Lining Cracks In Landfill

In order to evaluate the feasibility of sand mixed clay as liner in landfill,a series of experimental studies were carried out on the development of cracks on sand-clay liner.The development law of sand-clay cracks was studied from three aspects of drying time,temperature and sand content,and put forward the best sand content in sand-clay.Through mercury intrusion experiment,the distribution of pores in clay under different sand content was studied.With the relationship between pore size and water form,the mechanism of crack development on sand-clay liner was discussed from the perspective of water form.Based on the development of sand-clay dry cracks,artificially manufactured cracks were used to carry out indoor compression tests to study the closure of specimen cracks under load,and the closure pressure corresponding to the fracture with different width was measured.And analyze the influence of upper pressure on the closure of sand-clay cracks.A mercury intrusion test was carried out on the compressed specimens to study the distribution characteristics of the pores in the sand-clay under pressure and to verify whether the cracks in the sand-clay liner were completely closed.Based on the above experimental research,the following conclusions are mainly drawn:(1)The development process of sand-clay surface cracks with drying time can be roughly divided into three stages:the early term is dominated by the generation of new cracks,the medium term is dominated by the development and expansion of cracks,and the development of cracks tend to stabilize in the later term.The development of clay cracks is more severe under high temperature than low temperature,and there is a certain temperature effect.Sand can be used as a good filler to effectively reduce the development of clay cracks,the optimal content of sand in the compacted clay liner is 30%.(2)The mercury intrusion test shows that the pore size of clay is mainly distributed between 60μm～0.08μm,and the pore size of sand-clay is mainly distributed between 0.1μm～0.01μm and 500μm～90μm.With the increase of the amount of sand mixed,the type of water in the soil is changed to mainly gravity water and bound water.In addition,the content of macropores in soil increases accordingly.These phenomena make the matric suction and capillary water tension in the soil decrease,and further makes the uniform tension on the fracture surface reduce to a certain extent,so as to effectively inhibit the development of the cracks.(3)Under the effect of the upper pressure,the crack closure process can be roughly divided into two stages:the rapid closure of the crack and the slow closure of the crack.The cracks of different widths on the sand-clay surface are affected by the upper pressure,when the upper pressure reaches at 500kPa,cracks with a width of less than 3mm will be completely closed.The closure of the crack is related to the clay mineral composition and the initial width of the crack.(4)After the sand-clay has undergone the compression test,the internal cracks in the sand-clay tend to be closed.After the sand-clay has undergone the compression test,the pore size in the non-crack area is mainly distributed between 60μm～40μm,and the pore size in the crack area is mainly 65μm～50μm.