Modified Experimental Method For Tensile Strength Of Cohesive Soil

With the development of engineering construction,such problems as the hydraulic splitting of earth rock dam and the earth fissures due to uneven land subsidence have been occurred frequently,which causes more attention to be paid on the tensile strength of soils.However,the standard apparatus and test procedure for the tensile properties of soils have not yet been put forward in the world.On the other hand,soil types,moisture content,and dry density vary from region to region,and the loading rate changes in different cases.Consequently,the factors that affect the tensile strength of soils have to be investigated.In the direct tensile tests,stress concentration and resultant failure easily occur at both ends of soil samples,resulting in the invalidation of the test.Therefore,the sampling technique is the key to valid tests.On the basis of previous research work,a new sampling method has been proposed to improve the test efficiency.By using the sampling method and the developed strain-controlled tensile apparatus,a lot of soil samples with various dry density,moisture content,and sizes have been tested.Additionally,the effects of loading rate and matrix suction on the soil tensile strength are studied.The following conclusions can be drawn from the test results.(1)The probability of stress concentration at the end of the soil sample can be greatly reduced by the addition of 0.2%fiber within the 1omm from the ends of the soil sample.Thus,the validity of tensile tests can be improved significantly.(2)For the cohesive soil samples with a certain dry density,the tensile strength approximately decreases with the increasing moisture content linearly,and the slope of stress and strain curve decreases with the increase of moisture content.For the cohesive soil samples with a certain moisture content,the tensile strength approximately increases with the increasing dry density linearly.The peak stress for the samples with low or high dry density differs greatly with that for samples with medium dry density.(3)The tensile strength of cohesive soil samples almost increases with the increasing tensile rate linearly.With the increase in the height and diameter of samples,the tensile strength increases.For the samples with the identical height,the smaller the diameter is,the longer the failure strain is.(4)The relationship between tensile strength and matric suction isσt=Aψm3-+Bψm2+Cψm+D,and the coefficients of A,B,C and D are related to the dry density and moisture content of soil samples.