Subgrade fill strength and bearing characteristics of weathered phyllite blended with red clay

Abstract

ABSTRACT This study presents the results of a systematic investigation on enhancing the shear strength and bearing capacity of subgrade fill by blending the completely weathered phyllite (CWP) with locally won red clay at varying blending ratios. Many CWP soil samples were prepared at varying bended ratios for carrying out a compaction test, micro-penetration test and direct shear test. The effects of the red clay blending ratio, moisture content (w) and compaction coefficient (K) on the shear strength of CWP clay were also been investigated. Micro-penetration test results show that there are three types of micro-penetration strength growth patterns. It is found that, at a given set level of moisture content and compact coefficient, an increase of red clay in the blending ratio result in a higher shear strength and the ultimate bearing capacity. Cubic polynomial function models were developed to predict the ultimate bearing capacity and cohesion of the CWP blended soils with the red clay at varying blending ratios. The observed three stages of strength growth can be predicted, and the mechanism of this phenomenon has been analyzed using the results from soil micro-structure analysis. It has been found that the addition of red clay increases clay content within the soil mass and enhances iron cementation among the soil particles. At a given blending ratio, the ultimate bearing capacity increases linearly with the compaction coefficient and decreases linearly with moisture content. The ultimate bearing capacity calculation model of blended subgrade fill was developed based on the Bzz-100 load standard, and the optimum schemes of blending soils were proposed to meet the requirement of urban road bearing capacity. Field trials and applications show that the optimum scheme proposed in this paper can not only improve the bearing capacity of CWP, but also reduce the cracking potential of red clay.