Evaluation of dynamic cone penetration test for determination of degree of compaction for compacted soil layers.

Abstract

Quality control during soil compaction relies on the determination of the insitu dry density, which is then compared with the maximum dry density obtained from Proctor test from which degree of compaction is got. This degree of compaction has to be equal or greater than a given value stated within the specification for any compacted layer to pass. In order to determine the insitu dry density, sand replacement method has been the commonest used method. However, due to challenges associated with above method, several alternative tests such as dynamic cone penetrometer (DCP) have been introduced as testing tools for soil compaction quality control. However, no reliable correlations are available in the literature to employ these tests for soil compaction quality control. The main objective of this research was to evaluate DCP test for determination of the degree of compaction for compacted soil layers with specific emphasis on determining the effect of moisture on Dynamic cone penetration index (DCPI) and developing a relationship between degree of compaction and DCPI. Two different materials that is to say G7 and G3 were used in model development and validation respectively. The results indicated that there was an exponential increase of DCPI as moisture content increased from -1% of OMC for any given degree of compaction. There was evidenced scatter of DCPI values for points below - 1% OMC. This implies reproducibility of DCPI values at dry side of OMC is hard. It has further been shown that post compaction moisture content changes from OMC affect DCPI and the rate of change depending on the magnitude of the water content change relative to the optimum moisture content. Equations have been developed which can correct DCPI for change in moisture content. Furthermore, it was revealed how the equation without water content component had lower r2 of 25.1% which improved to 80.05% with introduction of moisture component. The estimated degrees of compaction using the prediction equation were compared with measured values of the degree of compaction obtained from validation data. The results show that there is good agreement between the actual DC and predicted DC