Masters Theses

Zhengzhi Li

Date of Award

12-1992

Degree Type

Thesis

Degree Name

Master of Science

Major

Civil Engineering

Major Professor

Eric C. Drumm

Committee Members

R. D. Krieg, A. B. Moore

Abstract

This research developed an alternative test method (ATM) for resilient modulus of fine grained subgrade soils. Through a finite element analysis of typical pavement systems subjected to traffic loading, the stress paths in the subgrades are studied. The stress paths of various laboratory compression tests are compared with those found in pavement subgrades. The study shows that a specially designed flexible confined compression test can achieve a stress path similar to that experienced by the subgrade under a pavement system. The pseudo-dynamic loading process of the pavement system is approximated by a falling weight loading pulse. Based on the stress path and loading process, a single-degree-of-freedom (SDOF) model for a confined compression test with falling weight loading is proposed as an alternative test method. Three variations ( rigid confinement, flexible confinement, and elastic half space ) of the test model are theoretically developed. The rigid confinement model is implemented, and trial tests are conducted on 3 different soils, each at 2 two water contents. The test results show the resilient response obtained by the proposed alternative test method is similar to that obtained by triaxial test. The discrepancies between the results of the two methods are also discussed. The study shows that the rigid confinement model is a very simple method to evaluate resilient modulus for engineering applications, and the flexible confinement model is a promising method to determine both resilient modulus and Poisson's ratio. In the appendices, the test procedure and data processing steps are given for the proposed alternative test method.

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