Student: ALIOUNE BADARA SAMB Nagaoka University of Technology
Supervisor: HIROFUMI TOYOTA Geotechnical Laboratory
Date: 2020/03/10
SMALL STRAIN DEFORMATION CHARACTERISTICS IN ANISOTROPICALLY CONSOLIDATED COHESIVE SOIL
ABSTRACT
Lateritic soil, classified as cohesive soil is widely distributed in Africa. Most lateritic soils can be used for multi earthworks: they are used for foundation material to support the load exerted by structures and earth structures such as earthfill dam and highway embankment. In many tropical countries, the heavy, seasonal rainfall makes lateritic soil becoming quickly saturated with rainwater. This unfavorable environmental condition often cause heavy damage during civil engineering constructions even completing the construction because of a lack of understanding of the ground behavior. The ground deformation induced by many structures varies from very small strain (<0.001%) to large strain (>1%). Accurate determination of shear modulus at small strain is very important to evaluate the deformation of underground structures. The soil’s deformation properties are mainly quantified by the initial shear modulus G0. Therefore, comprehensive study has been undertaken to elucidate parameters influencing the initial shear modulus. However, the effects stress history in term of anisotropic stress conditions and overconsolidation ratio (OCR) has paid a little attention.
In this research, deformation characteristics of anisotropically consolidated cohesive soil have been examined at small strain range under drained conditions using advanced triaxial apparatus. The testing apparatus is equipped with bender elements (BEs) and local small strain (LSS) measurement to investigate the initial shear modulus G0 by dynamic and static estimation, respectively. Main factors controlling the initial shear modulus in the well-known Hardin’s empirical equation were investigated: those are OCR, mean effective stress, void ratio, and stress ratio K ('3/'1). Although results have proven K did not affect strongly the initial shear modulus, the initial shear modulus G0 was found to decrease slightly with increased K. Higher degree of anisotropy was observed in G0 obtained from LSS test than from BE test. Finally, parameters in Hardin’s equation were assessed in the case of lateritic soil.