Evaluation of pavement subgrade support characteristics by dilatometer test : Borden, R H; Aziz, C N; Lowder, W M; Khosla, N P Trans Res RecN1022, 1985, P120–127

Abstract

The problem of evaluating the as-compacted or existing properties of subgrade soils is an important aspect of the design and rehabilitation of flexible pavements. The dilatometer has been shown to have significant potential for obtaining this information both reliably and economically. The relationship between the dilatometer modulus and the as-compacted California bearing ratio (CBR) for different natural soils has been investigated. In general, the test program may be characterized as having evaluated: (a) a range of sample sizes including cylindrical molds of 6.0 in. (152 mm) and 11 in. (280 mm) diameter, a 3 ft x 4 ft (approximately 1 m x 1.25 m) chamber, and several field tests; (b) compactive efforts equivalent to AASHTO T-180, T-99, 50 percent of T-99, and a lower effort that produced a density equivalent to 90 percent of T-99 maximum dry density; and (c) a moisture content range for each soil sufficient to establish maximum dry densities at each compactive effort. The results of the laboratory and field test program lead to the following conclusions: (a) Unique relationships between dilatometer modulus and CBR were found to exist for the as-compacted A-5 and A-6 soils regardless of density and moisture content conditions. (b) A laboratory technique was developed whereby dilatometer penetration could be performed in CBR molds 6 in. (152mm) in diameter such that both pieces of data could be obtained on the same specimen. Although the boundary conditions appear unfavorable in the small mold, the results were consistant with those obtained in an 11-in. (280-mm) mold and a chamber 3 ft x 4 ft (approximately 1 m x 1.25 m). This small mold test did not work well for the A-2-4 soil and would probably not work for any soil that was dominated by granular material with little fine-grained component. (c) Limited field tests on a compacted embankment from which one of the soils (A-6) used in the study was obtained revealed excellent correlation with the laboratory test program.