Influence of soil moisture content on pullout properties of Hippophae rhamnoides Linn. roots

Abstract

Plant root system plays an important role in preventing soil erosion and improving slope stability. However, its performance is significantly affected by soil moisture content, and the role of soil moisture in root reinforcement is not fully understood. In this study, the influence of soil moisture on root pullout properties was studied by experiments. Vertical in-situ pullout tests under four different levels of soil matric suction (12 kPa, 18 kPa, 24 kPa, 30 kPa) were carried out on roots of sea buckthorn plants (Hippophae rhamnoides Linn.) which were artificially cultivated for 7 months. Diameter and length of the root system of sea buckthorn were investigated. The results showed that a very significant correlation was observed between root diameter (D) and root length (L) (P<0.01), and root diameter decreased with soil depth. When soil bulk density was constant, peak pullout force (F) and friction coefficient of root-soil interface (μ) decreased with increasing gravimetric soil moisture content in power functions. Soil moisture content significantly affected root pullout resistance because the increase of soil moisture content decreased the friction coefficient between the roots and soil. Root diameter at breakage point (Db) and length of root segment left in soil (Lb) were increased with soil moisture content. In addition, peak pullout force of the roots increased in a power function with root diameter at the soil surface (Do) and in a linear function with total root length (L). The results provided an experimental basis for quantifying the effects of soil moisture content on soil reinforcement by plant roots.