Properties of Monterey Sand.

Soil liquefaction is a devastating effect of earthquakes. It occurs when saturated granular soils lose their shear strength because of a sudden increase in pore water pressure under dynamic loads. Over the last six decades, considerable focus has been placed on understanding the mechanisms and phenomena associated with liquefaction, making it a critical area of research. Evaluating soil liquefaction accurately is crucial for maintaining the seismic safety of construction. To investigate how fines content affects soil liquefaction resistance under cyclic simple shear loads and gradual principal stress rotation, a series of cyclic hollow cylinder tests (CHCT) were carried out under isotropic consolidation and undrained conditions. The experiments were conducted using medium Monterey No. 0/30 Sand (MS), where five varying percentages of fine content were analyzed under two confining pressures (σ3’ = 103 kPa and 206 kPa) and at two relative densities (Dr = 30%, 45% and 60%). The results of CHCT tests contributed to the development of liquefaction-potential evaluation curves. The findings demonstrated that increasing the acceptable fines content up to 15% reduces liquefaction resistance. However, when fines content exceeds 15%, further increases lead to enhanced liquefaction resistance. Based on all laboratory test results, back propagation neural network (BPNN) was applied to predict cyclic stress ratios leading to initial liquefaction after cyclic loading cycles. The BPNN model can give superior precision with mean absolute percentage error (MAPE) values of 1.05%, and also can help engineering better understand liquefaction potential of soil samples with different fines content.土壤液化（soil liquefaction）是地震所引发的极具破坏性的灾害效应。当饱和粒状土体在动荷载作用下孔隙水压力骤增，进而丧失抗剪强度时，便会发生该现象。近六十年来，学界围绕土壤液化相关机制与现象展开了大量研究，使其成为地震工程领域的核心研究方向之一。精准评估土壤液化风险，对保障建筑工程的抗震安全至关重要。为探究循环单剪荷载与主应力逐步旋转条件下，细粒含量（fines content）对土壤液化抗性的影响规律，研究团队在各向同性固结与不排水条件下开展了一系列循环空心圆柱试验（cyclic hollow cylinder tests, CHCT）。本次试验采用中等粒径蒙特雷0/30号标准砂（Monterey No. 0/30 Sand, MS），设置5组不同细粒含量，分别在2种围压（σ3’=103 kPa与206 kPa）以及3种相对密度（Dr=30%、45%与60%）条件下开展测试。循环空心圆柱试验的结果为液化潜力评估曲线的构建提供了数据支撑。研究结果表明，当细粒含量提升至15%时，土体的液化抗性会随之降低；但当细粒含量超过15%后，进一步提升细粒占比则会增强土体的液化抗性。基于全部室内试验数据，研究团队采用反向传播神经网络（back propagation neural network, BPNN）对循环加载后引发初始液化的循环应力比进行预测。该模型预测精度优异，平均绝对百分比误差（mean absolute percentage error, MAPE）仅为1.05%，同时可帮助工程人员更好地理解不同细粒含量土样的液化潜力。