Investigation of the Water Retention Characteristics and Mechanisms of Organic Clay

With the acceleration of urbanization, clay with significant variations in organic matter content is commonly encountered in infrastructure construction. Its unique water retention capacity is crucial for engineering safety and stability. This study uses red clay as the matrix and incorporates peat to prepare soil samples with varying organic matter content. Soil–water characteristic tests were conducted using the pressure plate method, filter paper method, and vapor equilibrium method to obtain the soil–water characteristic curves across the entire suction range. Subsequently, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were performed to analyze the mechanisms underlying the water retention characteristics. The experimental results indicate that the three different suction tests accurately reflect the soil–water characteristic curves of organic clay across the entire suction range. As the organic matter content in the soil increases, the air entry value and residual value of the soil samples exhibit a linear relationship with the organic matter content, enhancing the soil’s water retention capacity. The increase in organic matter content alters the microstructure of the clay, transforming the mineral–organic aggregates from ellipsoidal to plate-like shapes. While organic matter can influence the water retention of clay, within a certain suction range, the water retention capacity of organic clay is also related to the pore structure and the state of water within the pores. This is crucial for ensuring engineering safety and optimizing design solutions.