Soil collapse is a phenomenon triggered by wetting a loaded soil, the structure of which contains large pores. This type of soil response has been studied since the 1970s and models that can predict its occurrence and magnitude were proposed from the 1990s. In particular, the concept of loading collapse (LC) curves has been developed in the framework of unsaturated soil mechanics and it has been validated using low-reactivity soils. Several publications have highlighted that the microstructure of expansive soils evolves significantly during swelling, a phenomenon that may affect the location of the LC curve. With that perspective, some studies mention a need to shift the LC curves for experimental data and model predictions to agree. This paper brings new insight into the significance of microstructure for the collapse of a reactive soil. A series of tests was conducted to characterise the microstructure of soil specimens compacted under different initial conditions. Then, three pairs of wetting tests under constant load and under controlled suction were conducted in order to identify the zone of onset of collapse. It was found that the conventional LC curves cannot adequately predict the occurrence of collapse. In contrast, analysing the swelling response in the light of microstructural characterisation led to the conclusion that, for Maryland clay, occurrence of collapse can be tracked by the evolution of the void ratio associated to the macro porosity during wetting.

中文翻译：

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土崩塌的微观结构视角

土壤崩塌是由于润湿负载的土壤而引发的现象，该土壤的结构包含大孔隙。自1970年代以来就对这种土壤响应进行了研究，并从1990年代提出了可预测其发生和强度的模型。特别是，在非饱和土力学的框架内已经建立了荷载倒塌（LC）曲线的概念，并已使用低反应性土壤进行了验证。一些出版物强调膨胀土的微观结构在膨胀过程中会显着发展，这种现象可能会影响LC曲线的位置。从这个角度出发，一些研究提到需要移动LC曲线以使实验数据和模型预测一致。本文为微观结构对反应性土壤塌陷的重要性提供了新的见解。进行了一系列测试，以表征在不同初始条件下压实的土壤样品的微观结构。然后，在恒定载荷和受控吸力下进行了三对润湿测试，以确定塌陷的开始区域。发现传统的LC曲线不能充分预测塌陷的发生。相反，根据微观结构表征分析溶胀响应得出的结论是，对于马里兰黏土，塌陷的发生可以通过润湿过程中与大孔隙率相关的空隙率的演变来跟踪。为了确定塌陷发生的区域，在恒定负载和受控吸力下进行了三对润湿测试。发现传统的LC曲线不能充分预测塌陷的发生。相反，根据微观结构表征分析溶胀响应得出的结论是，对于马里兰黏土，塌陷的发生可以通过润湿过程中与大孔隙率相关的空隙率的演变来跟踪。为了确定塌陷发生的区域，在恒定负载和受控吸力下进行了三对润湿测试。发现传统的LC曲线不能充分预测塌陷的发生。相反，根据微观结构表征分析溶胀响应得出的结论是，对于马里兰黏土，塌陷的发生可以通过润湿过程中与大孔隙率相关的空隙率的演变来跟踪。