土壤容重和含水率对紫色土坡耕地耕层抗剪强度的影响

土壤抗剪强度既可评价土壤侵蚀敏感性,也是反映耕层土壤耕作性能的重要参数。不同剪切方式下土壤抗剪强度指标存在一定差异,以紫色土坡耕地耕层土壤为研究对象,采用室内重塑土三轴及直剪试验方法,研究容重和含水率对紫色土坡耕地耕层土壤抗剪强度的影响,并分析了2种试验方法的差异性。结果表明:(1)紫色土坡耕地耕层土壤黏聚力(c)总体随容重(ρd)增大而增加,随含水率(w)增加而减小,三轴及直剪试验条件下黏聚力最大值均出现在容重1.4 g/cm^3、含水率10%水平下,分别为32.33,21.78 kPa。耕层土壤内摩擦角(φ)随容重增加而增大,随含水率增大而减小,三轴及直剪试验条件下内摩擦角最大值均出现在容重1.4 g/cm^3、含水率10%水平下,分别为22.67°,29.11°。(2)在同一围压下,耕层土壤最大主应力差随容重增加而增大,随含水率增加而减小;在同一容重和含水率水平下,耕层土壤的最大主应力差随着围压升高而增大。(3)耕层土壤容重、含水率的交互作用对黏聚力和内摩擦角影响显著(P<0.05),对坡耕地耕层土壤抗剪强度抵抗侵蚀作用的最优土壤容重-含水率条件为1.4 g/cm^3—10%。(4)不同剪切方式影响了土体抗剪强度指标,耕层土壤黏聚力在三轴试验条件下大于或接近直剪试验结果,而土壤内摩擦角则明显小于直剪试验结果,这主要与两种剪切试验原理差异有关。

Effects of Soil Bulk Density and Water Content on Shear Strength of Cultivated-layer in Purple Soil Sloping Farmland

Soil shearing strength can not only evaluate the sensitivity of soil erosion,but also is an important parameter to reflect the tillage performance of cultivated-layer.There are some differences in soil shearing strength indexes under different shearing modes.In this paper,the soil of purple soil sloping farmland was taken as the research object,the laboratory triaxial and direct shearing test method were used to study the bulk density and water content on remolded purple soil.The effect on shearing strength of the cultivated-layer soil was analyzed,and the differences between the two test methods were analyzed.The results showed that:(1)The soil cohesion(c)of the purple soil sloping farmland increased with the increasing of the bulk densities(ρd)and decreased with the increasing of water contents(w).The maximum cohesive forces of the triaxial and direct shearing tests were 32.33 and 21.78 kPa respectively,both of which occurred under bulk density of 1.4 g/cm^3 and water content of 10%.The internal friction angle(φ)of the cultivated-layer increased with the increasing of the bulk densities and decreased with the increasing of the water contents.The maximum internal friction angles of the triaxial and direct shearing tests were 22.67°and 29.11°respectively,under bulk density of 1.4 g/cm^3 and water content of 10%.(2)Under the same confining pressure,the maximum principal stress difference of the cultivated-layer soil increased with the increasing of the bulk densities,and decreased with the increasing of water contents.Under the same bulk density and water content,the maximum principal stress difference of the cultivated-layer soil increased with the confining pressure.(3)The interaction of soil bulk density and water content in the cultivated-layer had a significant effect on cohesion and internal friction angle(P<0.05).The optimum soil bulk density—water content condition for the shear strength of the soil in sloping farmland was 1.4 g/cm^3—10%.(4)Different shearing modes affected the shearing strength index of the soil.The soil cohesion of the cultivated-layer was greater or closer to the direct shearing test under the triaxial test conditions,while the soil internal friction angle was significantly lower than the direct shearing test result.This was mainly related to the difference between the two shearing test principles.