Experimental Study On The Effect Of Sodium Sulphate Crystallization On The Deformation And Strength Of Fine-grained Soil

Sulphate saline soil is widely distributed in the northwestern part of China,and causes widespread engineering diseases.As the sulphate will crystallize and precipitate when the temperature and water content decrease,the salt start to expand,which will cause the road base to swell and its surface to crack.The road base is often damaged and repaired,which seriously reduces its capacity and life service.Consequenly,the mechanical properties of saline soil will change significantly after salt swelling.Therefore,this paper focused on the deformation and shear strength of sulphate soil,analyzed its internal mechanism,and improved the understanding of the engineering properties of sulphate soil.Through literature research,it has been found that local and foreign scholar have done a lot of researches on the salt expansion deformation and strength of saline soil,but there are still some problems:(1)the salt expansion test does not have a unified test standard;(2)there are some existing swelling models involving too many parameters,hence it is inconvenient to use;(3)the study of the saline soil shear shear strength is often based on a single factor,and the effect of the amount of crystal on the strength of saline soil has not been studied.In this paper,the deformation and strength of different kinds of sulfate soils were studied through laboratory tests;The salt expansion standardization test method was given;The empirical relationship model between the theoretical salt content of the existing salt and the soil salt expansion was verified;The variable method was used to analyze the effects of salt content,water content and temperature on the shear strength of saline soil.The main conclusions of the paper are as follows:(1)Through the one-dimensional salt expansion deformation experiment,the order of factors affecting the salt expansion deformation of sulfate soil from strong to weak are:soil type>water content>cooling rate>compaction/dry density;A one-dimensional salt swelling standardization experimental method is given.Through statistical analysis,the temperature deformation stabilization time of each stage was determined by the 90%deformation completion rate:the salt expansion stability time was 8h at 12?,8? and 5?,and the salt expansion stability time was 1h at 1?.The existing two-parameter linear salt expansion model established by theoretical crystallization volume rate and actual salt expansion rate was verified,and the parameters were calibrated.However,for samples with different water content,the parameters changed greatly.(2)The three-dimensional salt expansion experiment was carried out by self-designed and processed temperature-controlled body strainer,and the three-dimensional salt expansion standardization test method was given.The feasibility and accuracy of the test were demonstrated by three-dimensional salt expansion test.(3)At 25?,the salt in the saline soil is not crystallized,the shear strength of the soil decreases with the increase of the salt content,and the reduction range is:kaolin>silty clay>silt.;the shear strength of saline soil decreases with increasing water content.At 1?,the salt in the saline soil crystallized,At 1?,the salt in the saline soil crystallized,and the shear strength of the sulfate soil increased greatly with the increase of salt content;the soil moisture content was higher than the optimum.When the water content is high,the shear strength of saline soil increases with the increase of water content;when the water content of saline soil is lower than optimum,the capillary cohesion is larger,and the shear strength is larger than that when the water content is high.(4)When the initial salt content,water content and compaction degree are the same,the shear strength of saline soil increases linearly with the decrease of temperature.(5)The law of salt binding strength and salt crystallization is:when the amount of salt crystallization is less than 4g/100g of dry soil,the salt binding strength increases linearly with the increase of the amount of salt crystallization;when the amount of salt crystallization is more than 5g/100g of dry soil,the salt binding strength increase and decrease parabolically with the increase of the amount of the salt crystallization.