中文摘要：

蒋家沟流域内大量泥石流由滑坡引发,在滑坡转化为泥石流的3个过程中,首先是在斜坡体内大范围剪切破坏。在其物源区与沉积区内分布大量砾石土,其强度特征对于蒋家沟泥石流的起动机理以及流域内土壤侵蚀具有重要意义。由于降雨过程中,坡体内砾石土含水率逐渐增大,影响其力学性质特征,加之砾石土颗粒粗大,粗细粒配比和试验尺寸对强度特征有一定的影响。为此,在室内和现场两用大型直剪仪下进行蒋家沟砾石土不同含水率下的直剪强度试验,结果表明,试样在ρd=1.9 g/cm3不同含水率下,剪应力-水平位移关系没有明显峰值,应力-应变曲线为应力硬化型;同一含水率试样在γ=0.02时的剪切模量G0.02随垂直压力增加而增大;含水率7.07%试样各级压力下G0.02最大;φ值与含水率w符合二次函数关系式：φ=-0.471w^2＋6.7462w＋3.9262;试样C值与含水率w符合二次函数关系式：C=-0.7307w^2＋8.4784w＋1.462。

英文摘要：

Most of debris-flows are triggered by landslide in Jiangjia Ravine, widespread shear failure of slope is the first step in the three processes of debris-flows triggered by landslide. There is widely distributed gravelly soil in the triggering and sedimentary area. The strength behaviour of the gravelly soil is important for mechanism of debris-flows triggering and soil erosion in Jiangjia Ravine. Because the large grain size, coarsegrained content and specimen size have much effect on the gravelly soil strength behaviour, the large scale direct shear apparatus is used to test direct shear strength behaviour of the gravelly soil with different water contents. As a result ,it is found that there is no peak in the curve of relationship between shear stress and horizontal displacement at dried density equal 1.9 g/cm~ ,belong to the type of stress-harden. The shear modulus when horizontal shear strain is 0.02 G0.02 increase with increment of upright stress at the same water contents. And G0.02 increase with increment of water contents at the same upright stress, which is larger at lower upright stress than higher stress. The G0.02 under each upright stress with W=7. 07% is larger than others. The relationship between friction angle and water contentss w is qg= -0. 471w2 ＋6. 7462w＋3. 9262, and the relationship between cohesion C and water contents w is C= --0. 7307W^2 ＋8. 4784w＋1.462.