Analysis of Geotechnical-Assisted 2-D Electrical Resistivity Tomography Monitoring of Slope Instability in Residual Soil of Weathered Granitic Basement

Oladunjoye P Olabode,Muhd H Ramli,Lim H San

doi:10.3389/feart.2020.580230

Oladunjoye P Olabode, Muhd H Ramli + Show 1 more

Open Access

https://doi.org/10.3389/feart.2020.580230

Copy DOI

Abstract

Prolong heavy rainfall is increasingly inducing slope instabilities on the high-risk hills of weathered granitic basement in Penang. These slope instabilities are spatially controlled with changes in geotechnical properties of the slope soils. A reliable method to include density as part of geotechnical properties to calibrate Electrical Resistivity Tomography (ERT) resistivity distribution in slope instability monitoring is still rare. Hence, we present six ERT data that were acquired with survey length of 60 m and 1.5 m electrode spacing using Wenner-Schlumberger array from 2019-2020. The results were calibrated with the laboratory determined geotechnical properties- Moisture Content (MC), Particle Size Distribution (PSD), density and Hydraulic Conductivity (HC). The result of the analysis of ERT models classified resistivity distribution into saturated zones of 20% silt and clay, weak zones of 600-3000 Ωm and basement rocks of >5000 Ωm. The presence of floaters and boulders of resistivity >4000 Ωm overlie saturated zones coupled with multiple rainfall events that act as triggering factors for slope instability and failure. Geotechnical results show strong correlation of R≈0.94 between density and resistivity values which are crucial for the calibration of the ERT models because low-resistivity <600 Ωm areas have high MC, 30.1% with low density, 1176 kg/m3 and HC, 2.02x10-5 m/s whereas high resistivity <3000 Ωm areas have lower MC, 11.4% with relatively high density 1458 kg/m3 and HC 1.34x10-2 m/s. Therefore, we conclude that low-resistivity areas are composed of earth materials that are less dense low-permeable unstable zones of displacement which constitute subsurface drainage paths that are precursors to slope instability.

Highlights

There are great concerns around the world over the years on the occurrences of damaging landslides (De Vita et al, 2018; Froude and Petley, 2018; Hojat et al, 2019; Whiteley et al, 2019)
It shows the results of moisture content, particle-size distribution, density, and hydraulic conductivity
Two electrical resistivity tomography (ERT) profiles were acquired in November 2019, while the remaining four ERT profiles were acquired in January 2020

Summary

Introduction

There are great concerns around the world over the years on the occurrences of damaging landslides (De Vita et al, 2018; Froude and Petley, 2018; Hojat et al, 2019; Whiteley et al, 2019). The world is experiencing heavy and extreme rainfall events because of global climate change (Kirschbaum et al, 2020), the continuous precipitation during typhoon increases slope instability around mountains which has led to severe mudflows and landslide events (Baum et al, 2010; Pradhan and Lee, 2010; Epada et al, 2012; Jeong et al, 2014; Chien et al, 2015; Hakro and Harahap, 2015; Baharuddin et al, 2016; Sidle and Bogaard, 2016; Jeong et al, 2017; Kumar and Rathee, 2017; Soto et al, 2017; Tomás et al, 2018; Kirschbaum et al, 2020). Understanding the hydrogeology of soil–water dynamics is required for motoring and predicting slope instability to provide early warning to be able to avert impending landslide catastrophic events

Methods

Results

Discussion

Conclusion