中文摘要：

蒋家沟流域内大量泥石流由滑坡引发,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制具有重要意义。由于砾石土颗粒粗大,粗细粒配比和试验尺寸对强度特征有一定的影响。为此在室内现场两用大型直剪仪下进行蒋家沟砾石土不同粗粒含量下的直剪强度试验,结果表明：在干密度为2.0g/cm3、含水率为7%时,砾石土除在粗粒含量为74.31%的低垂直压力（50,100 kPa）时剪应力-水平位移关系有峰值外,其余土样没有明显峰值;同一粗粒含量试样在水平剪切应变值为0.02时的剪切模量G0.02随垂直压力增加而增大;在相同垂直压力下,G0.02随粗粒含量增加而增大,且在较低垂直压力下的G0.02随粗粒含量增长更为显著。内摩擦角值随粗粒含量增加而增大;黏聚力在粗粒含量为48.7%时最小。粗粒含量小于48.7%时,试样黏聚力值随粗粒含量增大而减小;当粗粒含量大于48.7%时,黏聚力随粗粒含量增加而显著增大。

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 in Jiangjia Ravine. Because the large grain size, coarse-grained 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 coarse-grained 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 2.0 g/cm3 and water content equal 7 %, except for the specimen of coarse-grained contents equal 74.31% under lower upright stress（50 kPa, 100 kPa）. The shear modulus when horizontal shear strain is 0.02 G0.02 increase with increment of upright stress at the same coarse-grained contents. And G0.02 increase with increment of coarse-grained contents at the same upright stress, which is larger at lower upright stress than higher stress. Friction angle increase with increment of coarse-grained contents. Cohesion drop to the minimum at coarse-grained contents equal 48.7 %, and decreases with increment of coarse-grained contents as coarse-grained contents litter than 48.7 %, however cohesion increases obviously with increment of coarse-grained contents when coarse-grained contents larger than 48.7 %.