Data and figures

Stiffness of soil at very small strains G0 is mainly affected by void ratio, effective stress and suction. Empirical equations considering those factors have been proposed to estimate G0. However, for collapsible soil like loess, variations in suction might induce changes in void ratio of soil. The combined effect of these two factors poses challenges in accurately estimating of G0. This paper first presents an experimental study on the G0 of collapsible loess under various conditions, including as-compacted states, wetting/drying and K0 loading. G0 is estimated from shear wave velocity obtained with bender element technique. The changes of G0 with respect to void ratio, suction, effective stress, and wetting under K0 stress conditions are evaluated. Test results reveal that power relationships can be defined between G0 and void ratio, suction and effective stress, respectively. The changes in G0 along wetting/drying shows an “S” shape due to the different dominant effects on soil structure, as well as the induced non-uniform volume changes when suction change at different zones. Under K0 loading, G0 decreases upon wetting at stresses below the compaction stress, while it increases upon wetting at stresses above the compaction stress, due to the combined effects of densification caused by volume collapse during wetting and softening induced by suction decrease. Finally, a G0 model considering net stress and suction as independent stress variable is proposed. This model could effectively capture the change of G0 during wetting, drying and loading, as well as upon wetting under K0 loading for collapsible loess极小应变下土体的剪切刚度G0主要受孔隙比（void ratio）、有效应力（effective stress）与基质吸力（suction）的调控。学界已提出考虑上述因素的经验公式，用于估算G0。然而，对于黄土这类湿陷性土（collapsible soil）而言，基质吸力的变化可能引发土体孔隙比的改变。上述两类因素的耦合作用，给G0的精准估算带来了挑战。本文首先针对不同工况下的湿陷性黄土G0开展试验研究，工况涵盖击实原状状态、干湿循环以及K0加载（K0 loading）。研究通过弯曲元技术（bender element technique）获取剪切波速（shear wave velocity），并据此估算G0。此外，本文还评估了G0随孔隙比、基质吸力、有效应力以及K0应力条件下增湿过程的变化规律。试验结果表明，G0分别与孔隙比、基质吸力及有效应力呈幂函数关系。G0随干湿循环的变化呈现"S"形曲线，这是由于土体结构受到的主导作用存在差异，且不同区域的基质吸力变化会引发不均匀的体积变形。在K0加载条件下，当应力低于压实应力（compaction stress）时，增湿会导致G0降低；而当应力高于压实应力时，增湿则会使G0升高，这是增湿过程中体积坍缩引发的密实效应与基质吸力降低导致的软化效应共同作用的结果。最后，本文提出了以净应力（net stress）与基质吸力作为独立应力变量的G0预测模型。该模型能够有效捕捉湿陷性黄土在增湿、脱湿与加载过程中，以及K0加载条件下增湿过程中的G0变化规律。