中文摘要：

崩岗是我国南方特殊的一种土壤侵蚀现象,其形成主要是由于岩土稳定性降低所致;土壤抗剪强度是表征崩岗岩土稳定性的重要指标,而土壤含水量是影响抗剪强度的关键因子。以通城县2处崩岗为研究对象,采集淋溶层（A）、淀积层（B）、过渡层（BC）和母质层（C）原状土样,通过室内直剪试验,研究崩岗岩土不同层次抗剪强度与含水量的关系及变化规律。结果表明：A层抗剪强度随含水量增加呈现先增大后下降趋势,其余各土层抗剪强度整体上随含水量增加呈现而下降,B层抗剪强度较大,C层抗剪强度最小,且B层抗剪强度受含水量影响最大;土壤黏聚力变化幅度较大,A层随含水量增加先增大后减小,其余各层均随含水量增加而减小,B层黏聚力在4个层次中最大,同时其衰减幅度也较大,C层因黏粒质量分数低、缺少胶结物质而黏聚力极低;土壤内摩擦角4个土壤层次均随含水量增加而减小。研究结果可为崩岗侵蚀机理研究以及进一步防治崩岗侵蚀提供理论依据。

英文摘要：

[Background] Collapsing hill is a serious soil erosion phenomenon in granite areas of south China,it causes severe damages to ecological condition,agriculture and economy. The decrease of soil stability usually contributes to the collapsing hills. Soil shear strength is an important indicator to investigate the stability of collapsing hills,soil moisture is also the key factor of shear strength and the critical basis for conducting the soil erosion. [Methods] This study used a direct shear test to analyze the relationship and regularity of shear strength variation with soil moisture in different soil layers.According to the variation of soil characteristics such as color and texture,soil profiles can be divided into4 layers,including the eluvial horizon（ A）,illuvial horizon（ B）,transitional horizon（ BC）,and parent horizon（ C）. The undisturbed soil samples were collected from two collapsing hills in Tongcheng County,southeast of Hubei Province,where is one of typical granite collapsing hill regions in China. To each horizon,there were 5 soil moistures from dry to saturation by controlling the length of air-drying duration.After pre-treatment,the samples were tested for different normal pressure（ 50,100,150,and 200 k Pa）and various soil moisture. All of the tests were repeated once. Excel 2010 and SPSS 22. 0 were used to analyze the relationship and Pearson correlation of shear strength and soil moisture. [Results] With the increase of soil moisture,the shear strength of layer A increased first and then decreased,others showed a trend of descent in soil shear strength,the shear strength reached the maximum in layer B and minimum in layer C. Besides,soil moisture affected the shear strength of layer B most,the shear strength of layer BC was among all the layers. Soil cohesive force presented wide variations,layer A showed a trend of decrease after first increase,the cohesive force of remaining soil layers declined with the increase of soil moisture; the cohesive force of layer B was the largest a