Analysis of the suction evolution during direct shear test in a silty sand soil

Omar Al-Emami,Gabriela M Medero,Melis Sutman,Fernando A M Marinho,R Cardoso,E Romero,C Jommi

doi:10.1051/e3sconf/202019503031

Abstract

Shear strength of soils is one of the essential parameters for analysing and solving divers geotechnical problems (e.g. the bearing capacity of shallow footings pile foundations, slope stability and earth embankments). In this study, a series of conventional large-scale (300 X 300 mm) direct shear tests were carried out on saturated and constant water content silty sand specimens at ei = 0.6 and 1.0 tested under applied vertical stresses of 100, 200, or 400 kPa to investigate the influence of matric suction on the shear strength characteristics of the tested material. A loading steel cap was modified to allow the direct measurements of the matric suction using two commercial available Equitensiometer suction probes (EQ3). The experimental program indicated that, for both studied void ratios, the obtained shear strength of specimens under constant water content is found to be distinctly greater than those obtained from saturated samples. The results showed that the samples compacted at ei = 1.0 exhibited collapse behaviour during saturation stage, whereas same samples did not show any volume change during stabilisation stage when tested under constant water content condition. The study results also showed that the matric suction reduction during consolidation stage depends on initial void ratio of the tested samples as well as the level of applied vertical stress. Moreover, the matric suction evolution during shearing process of both studied void ratios specimens decreased with increasing the level of applied vertical stress.

Highlights

In nature, the soil located in the zone between the deepest water table and the earth's surface is usually defined as the unsaturated soil
Soil compaction is the mechanical process producing unsaturated soils which generally contain a combination of water and air in their voids between the soil particles and have a degree of saturation ranging from 75-90% [3]
Conventional large-scale direct shear apparatus integrated with Equitensiometer suction probes (EQ3) was used to measure the evolution of matric suction in the compacted silty sand soil samples

Summary

Introduction

The soil located in the zone between the deepest water table and the earth's surface is usually defined as the unsaturated soil. Unsaturated soil is generally defined as a three-phase system composed of soil solids, water, and air. The relative distribution of these three components is important to understand the properties of the soil, primarily because the nature of the air – water interface is controlled by the distribution of these three components. Soil compaction is the mechanical process producing unsaturated soils which generally contain a combination of water and air in their voids between the soil particles and have a degree of saturation ranging from 75-90% [3]. Several man-made geotechnical infrastructures such as earth dams, roads, embankments and retaining walls are actual examples involved in their construction on the use of the compacted soils. The performance of the geotechnical infrastructures is highly influenced by the matric suction changes along with volumetric strains emerging under

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