A great number of gravels exist in the sliding zone soil of ancient landslides in the eastern margin of Tibet Plateau, which play an important role in the strength of the sliding zone soil. Determination of the mobilized strength of the gravelly sliding zone soil is the key to stability evaluation and disaster prevention for reactivated ancient landslides. Taking the Jiangdingya (JDY) ancient landslide reactivated in 2018 as a typical case, the mobilized strength of gravelly sliding zone soil is studied through laboratory tests and back analysis in this paper. The results indicate that: (1) After long-distance shearing, the cementation between soil particles is gradually lost, and the residual strength is mainly controlled by the sliding friction resistance between soil particles. The higher the gravel content, the greater the residual strength. A positive linear correlation can be established between the friction coefficient and the shear surface roughness. Due to the existence of gravels, the shear surface friction resistance increases, leading to the increase of residual strength. (2) The statistical analysis shows that the residual internal friction angle φ_r of gravelly sliding zone soil is controlled by both the clay and gravel content, which is significantly different from the clayey sliding zone soil dominated by the clay content. It is suggested that the ratio of gravel to clay content can be used as an index to evaluate the residual internal friction angel of gravelly sliding zone soil. (3) The mobilized strength of ancient landslides is generally greater than the residual strength, but slightly less than the recovery strength. The sliding zone soil strength has gradually attenuated from the recovery strength to the residual strength before reactivation. The ancient landslide is in a creeping state as a whole. Under the action of external forces, the strength of sliding zone soil is likely to decrease rapidly, which triggers accelerated sliding of ancient landslides.

青藏高原东缘古滑坡滑带土中存在大量砾石，对滑带土的强度起着重要作用。碎石滑带土的动员强度的确定是古滑坡活化后稳定性评价和防灾的关键。本文以2018年重新激活的江顶崖(JDY)古滑坡为典型案例，通过室内试验和反分析，研究了砾石滑带土的动员强度。结果表明：（1）长距离剪切后，土粒间胶结作用逐渐丧失，残余强度主要受土粒间滑动摩擦阻力控制。砾石含量越高，残余强度越大。可以在摩擦系数和剪切表面粗糙度之间建立正线性相关性。由于砾石的存在，剪切面摩擦阻力增加，导致残余强度增加。(2) 统计分析表明残余内摩擦角φ _[R砾石滑带土的黏性和砾石含量共同控制，这与以黏土含量为主的黏性滑带土有显着差异。建议用砾石与黏土的比值作为评价砾石滑带土残余内摩擦角的指标。(3)古滑坡的动员强度一般大于残余强度，略小于恢复强度。滑带土强度从恢复强度逐渐衰减到再活化前的残余强度。古滑坡整体呈匍匐状态。在外力作用下，滑带土的强度很可能迅速下降，从而引发古滑坡加速滑动。