[H-DS08] Landslides and related phenomena

[HDS08-P16] Geotechnical study on the rain-induced shallow landslides in Mt. Diwata, Monkayo, Davao de Oro, Philippines

*Kristine Mae Rodriguez Carnicer¹, Joel Tiu Maquiling¹ (1.Ateneo de Manila University)

Keywords:Rain-induced shallow landslides, Soil shear strength, Cohesion, Friction angle

This study conducted a geotechnical investigation to identify the potential mechanism of the frequent rain-induced shallow landslides in Mt. Diwata, Monkayo, Davao de Oro, Philippines. Slope failures are a perennial problem in the area, especially during the rainy months of November to March, mainly due to its steep slopes, loosened soil, escarpments, and tension cracks. Rampant mining activities also aggravated the situation. Soil samples from the five most recent soil slip events were collected for laboratory testing. The physical and index properties were determined, and the effect of varying the moisture content of the soil to its shear strength parameters was also tested. The study's results showed that the soil composition and grain size significantly influence its shear strength behavior. The contrasting behavior of fine-grained and coarse-grained soils was also noted, particularly in the soil's apparent cohesion. For coarse-grained soils, the apparent cohesion increases with increasing water content. However, for fine-grained soils, cohesion initially increases when the water content increases, but it decreases when a specific moisture content is attained. Since water generally reduces the soil's shear strength, the results imply that fine-grained soils' shear strength is primarily dictated by cohesion. In contrast, the friction angle has a more significant influence on coarse-grained soils. The data gathered in the study can provide valuable insights to identify the most appropriate engineering interventions and mitigating solutions for this recurring problem in Mount Diwata.