Shear strength behaviour for older alluvium under different moisture content

Abstract

Moisture content is one of the most crucial factors influencing soil and rock strength. This paper deals with the effect of moisture content on the strength of older alluvium under dry, wet and saturated conditions. Older alluvium is semi cemented sediment, which was eroded, deposited and reshaped by water to become a non-marine setting. The wide distribution of older alluvium in Malaysia creates problems in many field of construction such as excavation, slope stability and foundation in understanding their engineering characteristics especially the behavioral changes in dry and wet condition. In this study, samples were collected from a slope construction site in Desa Tebrau, Johor, Malaysia. The material shows equilibrium between distribution of the clay/silt and gravel with percent finer approximately 38% and 38.5% respectively, while sand content of 23.4%. The natural moisture content tested on the samples is within the range of 17.98% to 19.65%. The results revealed that moisture content have great influence in the reduction of the shear strength t, friction angle Ø and cohesion c. Specimens were tested for shear strength and hardness. Normally in the design of engineering projects, the shear strength, friction angle and cohesion parameters of the older alluvium are assessed at dry condition. However, the test results revealed that the strength was extremely reduced with the increased of moisture content especially at saturated condition. When the moisture content of older alluvium increased, the shear strength reduced to 22.3% and 75.3% at wet and saturated condition respectively (the shear strength equal to 57.4kPa and 18.3kPa for wet and saturated condition respectively) in comparison to the magnitude of shear strength at dry condition (shear strength at dry condition equal to 74.1kPa). Similarly, the friction angle reduced to 18.6% and 66.9% at wet condition and saturated condition respectively (friction angle equal to 55.19o and 22.45o for wet and saturated condition respectively) in comparison to the magnitude at dry condition (at dry condition friction angle equal to 67.83o). In addition, the results show that the magnitude of cohesion at dry condition was equal to 21.044 kPa. At wet condition the cohesion increased to 12.7% (cohesion equal to 23.71kPa) in comparison to the magnitude at dry condition. At saturated condition the cohesion value decreased to 54.6% (cohesion equal to 9.54 kPa) in comparison to the magnitude at dry condition.