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黄土沉积区在地震期间经常发生大型滑坡，为减少滑坡危害，研究滑坡机理，选取１９２０年中国海原地震中黄土滑坡的土样为试材，采用密封剪切试验，测定滑坡外摩擦角。由于滑动面处于非排水状态，因此在非排水条件下，进行剪切试验。试验结果表明：在非排水条件下，样品最终达到稳定状态，剪力继续增大，间隙水压保持不变，而位移增大，外摩擦角为６．５°。外摩擦角与过压密比无关，与剪切变形而形成的新土壤结构强度有关。剪切位移很大时，不饱和黄土（自然状态下饱和度为３２．６％）的外摩擦角并不减小．因此，不饱和黄土不易形成强烈的滑坡。
Large loess landslides often occur during the earthquake in the loess sedimentary area. In order to reduce the landslide hazard, the landslide mechanism is studied. The loess landslide samples taken from the 1920 Haikyuan earthquake in China are selected as the test materials and the shear friction test is conducted to determine the external landslide friction angle. Since the sliding surface is in a non-drained condition, the shear test is performed under non-draining conditions. The experimental results show that under the condition of non-drainage, the sample finally reaches a steady state, the shear force continues to increase, the gap pressure remains constant, and the displacement increases, and the external friction angle is 6.5 °. The external friction angle has nothing to do with over-pressure ratio, which is related to the strength of new soil formed by shear deformation. When shear displacement is large, the external friction angle of unsaturated loess (32.6% saturation under natural conditions) does not decrease. Therefore, unsaturated loess is not easy to form a strong landslide.