Particle gradation and water content are important factors affecting shear strength of soil. However, due to chemical cementation and molecular attraction, loess particles commonly stick together forming conglomerations. Till date, the superposition effect of water content and conglomeration gradation on loess shear strength has rarely been studied and undeniably requires further systematic explorations and development. In this study, loess samples were prepared with three conglomeration gradations and five water contents, and the direct shear tests were systematically performed. The shear strength of sample 1 (continuous conglomeration gradation) was found to be the best, followed by sample 2 (large size conglomerations), and sample 3 (small size conglomerations). The difference of samples’ shear strength decreased with increasing water content, and almost closed to zero when water content was 20%. The cohesion of samples first increased and then decreased with increasing water content, the maximum cohesion occurred at 10% water content. The internal friction angles decreased with increasing water content, and reached similar minimum values when the water content was 15%. The increased percentage values of cohesion and internal friction angle caused by conglomeration gradation are in the range of 33.2%–42.1% and 9.8%–32.5%, respectively. Finally, the empirical formulas for water content-cohesion and water content-internal friction angle of different conglomeration gradations samples were established, and the calculated values are in good agreement with test data. The effect of loess conglomeration gradation on shear strength decreased with increasing water content. When the water content was less than 15%, using a good conglomeration graduation could effectively improve loss shear strength.

颗粒级配和含水量是影响土体抗剪强度的重要因素。然而，由于化学胶结和分子吸引力，黄土颗粒通常粘在一起形成团块。迄今为止，含水量和砾石级配对黄土抗剪强度的叠加效应研究还很少，不可否认需要进一步系统的探索和发展。本研究制备了3种砾石级配、5种含水率的黄土样品，并系统地进行了直剪试验。发现样品1（连续团聚体级配）的剪切强度最好，其次是样品2（大尺寸团聚体）和样品3（小尺寸团聚体）。样品的剪切强度差异随着含水量的增加而减小，当含水量为20%时几乎接近于零。随着含水量的增加，样品的内聚力先增大后减小，在含水量10%时达到最大内聚力。内摩擦角随着含水量的增加而减小，当含水量为15%时达到相似的最小值。砾石级配引起的黏聚力和内摩擦角的增加百分比值分别在33.2%~42.1%和9.8%~32.5%之间。最后建立了不同砾石级配样品的含水率-粘聚力和含水率-内摩擦角的经验公式，计算值与试验数据吻合较好。黄土砾石级配对抗剪强度的影响随着含水量的增加而减小。当含水量小于15%时，采用良好的团聚级配可以有效提高损失剪切强度。