Optimizing the Compaction Characteristics and Strength Properties of Gravelly Soils in terms of Fine Contents

Mingzhi Zhao,Yangang Li,Gang Liu,Longxiang Deng,Georgios I Giannopoulos

doi:10.1155/2021/6634237

Abstract

Gravelly soils are widely adopted as civil construction materials in engineering practice. Although the influence mechanism of fine contents (FCs) on the mechanical behavior of gravelly soils has been emphasized in the previous studies, few discuss the compaction and strength properties concurrently. Besides, FCs of gravelly soils were discussed separately in many cases regardless of the variation in water content. In this study, modified Proctor compaction test and medium-sized triaxial test were performed to investigate the mechanical properties of gravelly soils containing different magnitudes of fine contents. It is shown that an optimum FC exists for gravelly soils although the value of the optimum FC varies with grading curves of the coarse-grained portion. By adjusting FC in the gravelly soils, not only could the maximum dry density ρdmax be improved but also the optimum saturation degree Sropt rises significantly, and synchronously, the minimum air void ratio v a min decreases notably. Besides, fine particles are just right to fill with the voids formed by the coarse-grained skeleton for the optimum FC sample. The soil structure corresponding to the optimum FC status can be termed as a densely filled skeleton structure, which is the densest and most stable. As fine contents increase or decrease from the optimum value, soil structure will loosen and deteriorate the mechanical properties. In addition, the increase in water content has quite different effects on strength properties of gravelly soils with different FCs in a triaxial test due to the opposite effects of pore water softening and negative pore pressure strengthening. Such results are expected to provide guidance for the preparation of gravelly soils in engineering practices.

Highlights

Soil is a kind of coarse-grained soil that has relatively excellent physical and mechanical properties
E gravel sample with 5% fine contents (FCs) is denoted as 5% FC in the figure. e denotations of gravel samples with other magnitudes of FCs remain the same. e asymptotic compaction lines under the condition that both specific gravity Gs and saturation degree Sr are given can be deduced from the three-phase relationship of the soil, as shown by the following equation: ρd
As the deviatoric stress reaches its peak value, it will decrease with the increase in axial strain until the deviatoric stress levels off to its residual value. us, graded gravels with different FCs present strain softening characteristics under saturation water content (SWC) and optimum water content (OWC) conditions when σ3 20 kPa

Summary

Introduction

Soil is a kind of coarse-grained soil that has relatively excellent physical and mechanical properties. It is widely adopted as a kind of civil and construction material in railway engineering, highway engineering, hydraulic dam engineering, and so on. Graded gravel, as a kind of gravelly soil, is ordinarily used to fill the surface layer of subgrade bed for high-speed railways in Japan, Germany, France, Spain, and China [1]. Gravelly soils are widely adopted as construction materials in civil engineering, their mechanical properties are uncertain and susceptible to grading properties, void distribution features, origin of the fine particles, fine contents, and so on

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Conclusion