Numerical analysis of crack generation in saturated deformable soil under row-planted vegetation

Desiccation cracks play an important role in the drainage of excess water via the subsurface drainage system in clayey puddled paddy fields. The present study focuses on the linear inter-row cracks induced by water absorption from row-planted rice. The shrinkage behavior of clayey puddled soil, which can be regarded as the consolidation of saturated soil subject to pore water suction, was simulated using a numerical model based on the Biotʹs two-dimensional consolidation theory. The model demonstrates how row-planted cropsʹ absorption of soil water induces the deformation of the soil and the development of tensile effective stress. The model requires parameters to specify the mechanical and hydraulic properties of the soil. These parameters can be determined from the e–log p (void ratio and mean stress) relationship and the e–log k (void ratio and saturated hydraulic conductivity) relationship. The calculations were performed using the finite element method (FEM). The simulation demonstrated a concave distribution of suction between rows and showed the induced deformation of the soil fabric. It showed that the peaks of tensile effective stress are not necessarily located at the center of the rows; the peaks are typically found near the Fronts of a Suction Rise (FSR), where the suction is about to rise. Further numerical experiments demonstrated that the distribution of tensile effective stress is characterized by either single or double peaks, depending on the following conditions. Greater transpiration flux, wider row-spacing, and a thinner soil layer induce the double-peaked distribution of tensile effective stress. This phenomenon corresponds to the field observation that the linear inter-row cracks running parallel to the rows are single in narrower row-spacing, and double in wider row-spacing.