Effect the Shape of Gravel on Improving CBR and Compaction Behaviour of Clayey Soil

Abstract

Investigating the effect of adding various types and shapes of materials on the behaviour of engineering properties of clayey soil is very important. In this study, various shapes of gravels have been used with different ratios (from 0 to 50% with 10% intervals) to show their effect on improving the mechanical properties of clayey soil. Many tests have been conducted on clayey and clayey-gravel soil mixtures. Modified compaction tests showed that by increasing percentages of gravel, amount of maximum unit weight (MUW) increased and optimum moisture content (OMC) decreased especially when rounded gravel was added. The increasing in amount of MUW of the clayey soil was about 10.32% after adding 50% of rounded gravel and it was about 8.98% after increasing same amount of crushed one. Values of California Bearing Ratio (CBR) increased after adding more amounts of gravel with more extent during adding crushed gravel. The addition of 50% gravel by weight to clayey soil resulted in 101.47% increase in the maximum CBR value for rounded gravel and 198.53% for crushed gravel. The swelling ratio decreased from 4.5% for the clayey soil to 0.2% after adding 40% of rounded gravel while it decreased to 0.56% after adding same ratio of crushed one. After adding 50% of both shapes gravel, a slight change in swelling ratio was appeared by increasing from 0.2% to 0.45% for rounded gravel and from 0.56% to 0.87% for crushed one.