The effect of soil fabric on shrinkage behaviour and microstructure evolution of soft soils upon drying

Soft soils often contain important fractions of fines and organic matter which are characterized by high shrinkage potential. Investigating the shrinkage behaviour of soft soils is of primary importance to assess the durability of infrastructures exposed to climatic stresses. This paper investigates the influence of soil fabric on the shrinkage properties and the change in the microporosity structures over drying. Soil shrinkage tests were performed on Shenzhen soft clay (SZ soft clay) and fibrous peat. The effect of the initial fabric was investigated by comparing the samples at natural and reconstituted states, and the reconstituted peat samples with different fibre contents. To assist in the interpretation of the results, microstructural changes in the soil fabric were investigated by mercury intrusion porosimetry, scanning electron microscopy, and micro-CT scan. As the water gradually drains from the multilevel pores, different drying stages were identified. Pore refinements occurred during the drying process, accompanied by a progressive reduction in the peak pore entrance. Contrary to SZ soft clay, intensive shrinkage occurred in the last stage of fibrous peats, due to the collapse of interpores and cracks created during drying. The results showed that the magnitude of the intensive shrinkage increased with the fibre content. It suggests that fibres act as an unstable element in peat upon drying.