Clarifying the effectiveness of drainage tunnels in landslide controls based on high-frequency in-site monitoring

An increase in groundwater table is a critical trigger for a deep-seated landslide. An effective way of improving the stability of the deep-seated landslide is to reduce the groundwater table through drainage works. This study aims to clarify the effectiveness of drainage tunnel systems in preventing and controlling deep-seated landslides based on high-frequency field-monitoring data. In the study, we measured depth of groundwater table data and the deformation process of a deep-seated landslide before and after construction of a drainage tunnel. Our study shows the drainage tunnel improved the stability of the landslide significantly. Furthermore, the depth of groundwater table increased rapidly, and there was a significant reduction of surface displacement and crack width of the slope after construction of the tunnel. The results of numerical modeling also showed that the safety factor increased from 0.92 to 1.063 after the tunnel’s construction. The variation of the safety factor before and after the construction of drainage tunnel induced by different return period storms was also estimated.