Evaluation of in-service subgrade resilient modulus with consideration of seasonal effects

Woojin Lee, Purdue University

Abstract

The resilient modulus (M$\sb{\rm R}$) is a definite material property to characterize roadbed soil. The incorporation of M$\sb{\rm R}$ in pavement design practice requires the establishment of testing capabilities and the development of data base. In this study, efforts were concentrated on the development of correlations between M$\sb{\rm R}$ and parameters from simple, routine tests. Five cohesive soils and a dune sand sampled from in-service subgrades in Indiana were tested. The procedures were developed to establish M$\sb{\rm R}$ by use of the MTS 810 test system and TESTLINK software. Changes in subgrade condition, such as freezing, thawing, and changes in moisture condition after construction, were simulated in the laboratory. An unique relationship between M$\sb{\rm R}$ and the stress at 1 percent strain in the unconfined compression test (S$\sb{\rm u1.0\%}$) was found. This relationship is applicable to all the cohesive soil types considered in the present study, and to both in-service and as-compacted subgrades. A significant reduction in M$\sb{\rm R}$ due to freeze-thaw of cohesive soils was observed, and an unified relationship between thaw-weakened M$\sb{\rm R}$ and S$\sb{\rm u1.0\%}$ was developed. The reduction in M$\sb{\rm R}$ due to increased water content after construction depends on the soil type, and it can be estimated from the developed relationship between $\Delta$M$\sb{\rm R}$ and $\Delta$w/c. The M$\sb{\rm R}$ of frozen cohesive soils appears to be independent of the deviator stress for all cohesive soils tested. Vibratory compacted dune sand shows better resilient response than impact compacted sand. Resilient characteristics of dune sand are not affected by water content, while permanent deformation under repeated loads increases as water content increases. Procedures to estimate M$\sb{\rm R}$ were developed for new and reconstructed pavements. They can be incorporated into the 1986 AASHTO Guide for the Design of Pavement Structures. The proposed correlation will help control the resilient properties of constructed fill, and restrict the resilient deflection of pavement.

Degree

Ph.D.

Advisors

Altschaeffl, Purdue University.

Subject Area

Civil engineering

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