A Study on Suction-rainfall Response of a Cut Slope in Unsaturated Residual Soil Using a Field Rain Simulator

Mariappan S,Faisal Hj Ali,Bujang B.K Huat

doi:10.3844/ajessp.2005.11.15

Abstract

This research describes the design and construction of an artificial rain simulator system and the results obtained with regards to suction-rainfall response of a cut slope in unsaturated residual soil of weathered sandstone of various weathering grades. From the field measurements, the shallow tensiometers are found to record an immediate initial increase in matric suction within the first 20 min of the simulated rain before a gradual drop in suction takes place. However no such initial spikes in suction readings were recorded by the deeper tensiometers. With constant rainfall for the next 130 min, a clear drop in soil suction was observed in all cases illustrating the effect of net infiltration process. Positive pore water pressure was even recorded by some of the deeper tensiometers. The suction recorded by the shallow tensiometers was always higher than those of the deeper tensiometers, indicating a reduction in suction with depth below the ground surface. In term of weathering grades, residual soil of weathered sandstone of weathering grade III has the highest infiltration rate indicating the more porous nature of this soil material. Like wise there is a steeper drop in suction during the rain at the said location.

Highlights

Rainfall has been considered the cause of majority of slope failures and landslides that happened in regions experiencing high seasonal rainfalls [1, 2]
The shallow tensiometers appear to record an immediate initial increase in matric suction within the first 20 min of the rain before a gradual drop in suction take place. No such initial spikes in suction readings were recorded by the deeper tensiometers
With constant rainfall for the 130 min, a clear drop in soil suction was observed in all cases illustrating the effect of net infiltration process

Summary

Introduction

Rainfall has been considered the cause of majority of slope failures and landslides that happened in regions experiencing high seasonal rainfalls [1, 2]. Correlation between rainfall and infiltration, slope stability involves large number of factors Some of these factors such as rainfall duration and intensity, slope surface cover, degree of saturation, slope angle, permeability ratios and perched water table are extremely difficult to evaluate. When the rainwater infiltrates into the slopes, it is known that it will start to saturate the soil, i.e., reduce the matric suction. A deep ground water table condition is normal in hilly area of the tropical countries In this case, the negative pore water pressure or matric suction plays an important role in controlling the soil shear strength and the stability of many steep slopes. When water starts to infiltrate into the soil, the matric suction especially near the ground surface will slowly reduce and become zero as the soil approaches saturated condition. In order to have a better control of the timing as well as intensity of the rain, an artificial rain

Objectives

Conclusion