A series of 0.5 m diameter oedometer tests and a series of laboratory California Bearing Ratio tests were undertaken on the crushed limestone aggregate used as backfill to a corrugated steel culvert at Newport, Gwent. The method of preparing the specimens was varied to examine the influence of density and moisture content on the compressibility and CBR value of the backfill. The data obtained in this study are compared with previously published data obtained from in situ plate bearing tests and a 1.0 m diameter oedometer test; they are also compared with data derived from a back-analysis of the performance of the culvert. The results show that the compressibility of the aggregate generally decreased with increasing dry density. Saturation of the specimens following preparation had little effect on their compressibility, but compacting specimens at moisture contents above the optimum led to high values of compressibility being obtained. The CBR value generally increased with increasing initial dry density of the test specimens; but the relation between CBR value and stiffness varied with stress level and initial dry density.

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