Effect of groundwater level on slopes to construct the SWCC curve for unsaturated soil

The occurrence of landslides and rockfalls has been on the rise, leading to unfortunate consequences and instilling anxiety and fear within the population as the rainy season approaches. During this time, the soil experiences a significant influx of water, causing the water level to rise and the transition from unsaturated to saturated soil. As a result, the shear strength of the soil decreases, leading to gradual slope instability. While the parameters of unsaturated soil resemble those of saturated soil, the inclusion of a SWCC curve is necessary. This study aims to examine the impact of groundwater levels on slope stability by considering the SWCC curve of the soil using the finite element method. The findings reveal that with an increasing groundwater level, the safety factor remains constant when the slope is assumed to be fully saturated. However, when the slope is evaluated with both fully saturated and unsaturated components using the SWCC, the safety factor declines significantly from 1.82 to 0.393. Similarly, according to the Fredlund-Xing method, the safety factor decreases from 1.754 to 0.393. Regardless of the method used, the safety factor consistently decreases as the groundwater level rises, eventually converging to the same value when the groundwater level reaches the ground surface.