Experimental Study On Shear Strength Of Loose Accumulation Soil Along Reservoir Bank

After “5.12” Wen-chuan earthquake, a large number of loose accumulation soil isdistributed on both sides of Minjiang river. It has been four years for these looseaccumulation soil to form, and its stability, physical properties, mechanical propertiesshould be paid special attention in the engineering construction along the reservoir bank.This paper has studied the loose accumulation soil along the Minjiang river inYingxiu-Wenchuan section （original National Road213）. Based on the fieldinvestigation, the rest angle test and large direct shear test are used to establish therelationship between the rest angle and the shear strength indexes, putting forward amethod of determining the strength index of loose accumulation soil. The main workand achievements are obtained as follows:（1） To study the relationship among the rest angle, density and gradation, the restangle test is used to the typical loose accumulated soil which collected in the field. Theresults indicate that the rest angle increases with the density increases. But the rest angledecreases when the d₁₀、d₃₀、d₅₀、d₆₀、d₉₀increases.（2） Through the large direct shear test, the shear strength characteristics and therelationship between the shear strength indexes and moisture content of looseaccumulation slopes under natural drying and moist condition are studied, respectively.And the size effect of the samples is also studied. The results indicate that under naturaldrying condition, the shear strength indexes increase as the density increases. With thed₁₀、d₃₀、d₅₀、d₆₀、d₉₀increases, the cohesion increases and internal friction angledecreases gradually. Under the moist condition, the cohesion is more sensitive to waterthan the internal friction angle. The cohesion and comprehensive internal friction angleincrease at first and then decrease, while the internal friction angle decreases graduallywith the increasing of moisture content. At the same time, through studying the sizeeffect, it shows the larger the geometric dimensioning is, the smaller the shear strengthfrom the experiment, which shows that the size effect is obvious. The sensitivity ofcohesion is relative higher, its value decreases a half when the length, width and heightof the sample increases one time, respectively. And the sensitivity of internal frictionangle is lower, whose value declines about0.9°.（3） Through comparing the static triaxial test with direct shear tests, it shows thatthe result of triaxial test is larger; and the relationship between strength indexes of thestatic triaxial test and density and particle gradation is not obvious. （4） Combined with the relation between the rest angle and density, particlegradation; with between strength index and density, particle gradation, and combinedwith the field investigation, the relation betwwen strength index and the rest angle isestablished, a method of loose accumulation soil shear strength determination isbrought.