# 2-D Cross-Plot Model Analysis Using Integrated Geophysical Methods for Landslides Assessment
## 1 Introduction
### Malaysia Rainfall-Landslides Overview  
Numerous landslide tragedies in Malaysia involve a large number of fatalities and economic loses. The slope failure events are mostly triggered by heavy rainfall due to the tropical rainforest climate with relatively high temperatures and receive rainfall throughout the year. In a tropical region, such as Malaysia, rainfall-induced landslides have become a common geohazard phenomenon, where the soil typically deposits by residual soils [32; 33]. Figure 1a shows a map of the landslide-prone area in Malaysia [34]. The significant thick ness of the unsaturated zone with a deep groundwater table shows the features of residual tropical soil [35]. Malaysia experiences a hot and humid climate all year around with temperature ranges from 22-32 degrees Celsius, with annual rainfall from 2000-2500 mm, and extremities during southwest (occurring during April-October) and northeast (occurring during October-February) monsoons [36]. The formation of residual soil is caused by intense chemical weathering due to the combination of climatic parameters. Under certain geological and topography effects, the rainfall becomes a major factor that triggers the occurrence of landslides, involving both natural and cut slopes. The intense precipitation, such as in highland area, causes the situation to become more hazardous. The hilly area is stable (of a certain range of water saturation); however, under the critical limit, the shear resistance is enhanced due to the effect of suction, which creates an apparent cohesion between particles [37]. Major landslides occur due to water saturation, exceeding a critical limit in certain parts of the slope [24]. The infiltration of rainfall into the soil and its effect on slope failure has been of particular interest for the past few years [38; 39; 40; 41]. The rainfall intensity, soil properties, groundwater table, and slope geometry plays an important role in rain-induced landslide events [42]. The continuous infiltration of rainwater will increase the pore-air pressure and decrease the matrics suction, which leads to instability [43; 44]. According to [PERSON] and [PERSON], two distinct failure mechanisms have been observed for rainfall-induced landslides [45]. For the first mechanism, a significant build-up of positive pressures is observed in a low area on the slope, or along the soil/bedrock interface. Movements along the sliding surface lead to liquefaction along with it, resulting in rapid movements, long run-out distances and, finally, complete liquefaction of the failed mass [46]. In the second mechanism, the soil in the unsaturated state, and slope failure, is due mainly to rainfall infiltration, and a loss in shear strength when soil suctions are decreased or dissipated [47]. Infiltration and near-surface flow create an increase in pore water pressure that causes the stress path to move nearly horizontally to intersect a failure envelope, initiating a failure. In unsaturated loose soils, suction decrease and coupled volumetric collapse may be involved in the failure process [48]. Landslides in weathered granitic rocks for tropical and humid regions have been well documented as the phenomena are strongly affected by types of weathering. In a tropical region, such as Malaysia, an in-depth weathering profile undergoes a thickness of up to 100 m [49]. The nature of weathered material and mass structure is highly controlled the failure mechanism. The soil or rock at the ground surface is highly weathered and tends to slide with a loose condition. The high erodibility with the existence of relict discontinuities, sharp soil-rock boundary, dynamic weathered material under the saturated condition, and the inhomogeneity of weathering structures will lead to frequent slope failure events. The presence of a fracture and structural discontinuity causes cohesion and internal friction decreases or is reduced by severing bonds between particles, creating the discrete failure surfaces [50; 51].