Effect of collapse-type lateral pressure induced by irrigation

Abstract

Loess collapse-type lateral pressure may have a landslide-promoting effect in loess slope areas. However, research on the magnitude and characteristics of collapse-type lateral pressure and its impact on slope stability remains blank. A study on the variability of loess collapse-type lateral pressure in the Heifangtai area and its sliding mechanism has been analyzed. Collapse tests and numerical simulations by FLAC3D of loess were conducted according to local safety field theory. The results indicate that Heifangtai loess is self-weighted collapsible loess; soil of the irrigated area at depths of 0-15 m are slightly collapsible; soil at depths of 20-25 m are moderately collapsible loess, and the loess in the unirrigated area regardless of depth is highly collapsible. As the depth or moisture content increases, the lateral pressure gradually increases, correspondingly the deformation becomes greater. In saturated state, the maximum lateral pressure reaches 123 kPa when collapsible deformation occurs, the collapse-type lateral pressure coefficient increases of up to 1.4 times, and horizontal deformation is also correspondingly large. As the water content of the slope increases from 4% to 20%, the total slope displacement increases from 12 mm to 140 mm and covers a large part of the slope, the lateral pressure coefficient also gradually increases, and the range of increase gradually expands; the slope safety coefficient also decreases, the area of failure becomes gradually wider until the slope toe is penetrated; the shear fractures move gradually toward the slope toe, and shear failure occurs at the 1/3 of the slope toe in the collapse deformation process. Collapse action leads to tensile stresses in the upper part of the slope, making it prone to collapse-type crack formation, resulting in dominant channels of surface water infiltration and forming landslide scarps. What’s more, collapse action also enables the formation of compressive stresses in the lower part of the slope, resulting in outward extrusion of deep soil, increased sliding force, and landslide formation.