Date of Award

Spring 1976

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering - (M.S.)

Department

Civil and Environmental Engineering

First Advisor

Edward J. Monahan

Abstract

Several physical methods are described for the practical measurement and rating of angularity (shape) of cohesionless soil particles. Angularity is determined by utilizing the fundamental property of a sphere: a sphere has the smallest contact surface area of any shape for a given volume. Therefore, any other shape will exhibit a greater contact surface area and consequently will have a greater frictional resistance which is a function of its degree of angularity.

The effects of angularity on the physical behavior (e.g. strength) of cohesionless soils was investigated at various relative compaction densities. For this purpose a combined compaction and direct shear test device constructed from a modified standard Proctor compaction mold was devised.

The samples used to determine the effect of particle shape on the physical behavior of cohesionless materials were produced in the lab from pure quartz. This was done in order to avoid the problem of variations due to mineral composition and grain size distributions. It was hoped that this would insure a greater uniformity of test results. In addition, the shear test results derived from lab-produced quartz samples were compared to those of natural field samples in order to determine whether the behavior observed during lab tests was representative of natural field soils.

These experiments demonstrated that the strength of a cohesionless material increases with degree of angularity and relative density to an optimum point. Surpassing the optimum value implies substantial particle crushing which reduces the particle interlocking effect and can result in a reduction of soil strength. Crushing is greatest when cohesionless particles are poorly graded, highly angular, and large in size.

Generally, the degree of particle crushing influences strength, and particle shape determines the degree of crushing. Shape (angularity),therefore, significantly controls the overall strength of a cohesionless soil.

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