Soil Fabric and Transitional Behavior in Completely Decomposed Granite: An Example of Well-Graded Soil

Elsayed Elkamhawy,František Vranay,Tarek N Salem,Huabin Wang,Martina Zelenakova

doi:10.3390/jmse9101046

Abstract

Unlike sedimentary soils, limited studies have dealt with completely decomposed granite (CDG) soils, even though they are plentiful and used extensively in several engineering applications. In this paper, a set of triaxial compression tests have been conducted on well-graded intact and disturbed CDG soils to study the impact of the fabric on soil behavior. The soil behavior was robustly affected by the soil fabric and its mineral composition. The intact soil showed multiple parallel compression lines, while a unique isotropic compression line was present in the case of disturbed soil. Both the intact and disturbed soils showed unique critical state lines (CSL) in both the e-log p′ and q-p′ spaces. The intact soil showed behavior unlike other transitional soils that have both distinct isotropic compression lines ICLs and CSLs. The gradient of the unique ICL of the disturbed soil was much more than that of the parallel compression lines of the intact soil. In the intact soil, the slope of the unique CSL (M) in the q-p′ space was higher than that of the disturbed soil. The isotropic response was present for both the intact and disturbed soils after erasing the inherited anisotropy as the stress increased with irrecoverable volumetric change. Soil fabric is considered the dominant factor in the transitional behavior and such a mode of soil behavior is no longer restricted to gap-graded soil as previously thought.

Highlights

A set of isotropic compression and triaxial compression shearing tests have been perperformed on a well-graded completely decomposed granite (CDG) soil originated from monzonitic granite, Guangdong formed on a well-graded CDG soil originated from monzonitic granite, Guangdong provprovince, China
It was found that the isotropic compression lines (ICLs) did not merge in unique line and they were quite parallel
The ICLs of the disturbed soil merged in a unique line, at mean effective stress of 400 kPa, while in the intact samples, the ICLs still exhibit parallelism up to 600 kPa without any tendency of convergence

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Saprolites triggered from different weathering processes on parent rocks are abundant in different regions around the world, in particular the tropical and subtropical regions. Decomposed granitic soil is abundant in southern China and extensively employed in many engineering applications as a construction or filling material. The widespread and extensive use of such soils, limited studies have dealt with it, unlike sedimentary soils. Many engineering problems can be occurred due to our limited knowledge about the fundamental characteristics of such soils; the weathered rocks are in charge of several modes of landslides resulting in loss of lives and property [1,2,3]

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