Improvement of engineering characteristics of expansive clays by sand mixing

Expansive Soils are a worldwide problem that poses several challenges for civil engineers. They are considered potential natural hazard, which can cause extensive damage to structures if not adequately treated. The expansive soils have caused severe distresses to various civil engineering structures, especially to lightly loaded structures such as houses, floors, highway pavements, canal linings etc. One of the mitigation techniques of such soils is to mix them with soils which are not swelling in nature. In this paper, the results of three series of tests are presented in which a swelling clay has been mixed with sand in varying amount ranging from zero to 35%. Through these tests, the effects of sand mixing on deformation and strength characteristics of swelling clay have been investigated. For performing such tests, the swelling clay samples have been procured from an expansive soil area in Pakistan. The clay-sand samples were remolded at Modified AASHTO density and optimum moisture content with proportion of sand ranging between 0-35 percent. Three series of tests performed included, Modified AASHTO compaction, California Bearing Ratio, One-dimensional consolidation tests in addition to basic property tests. The results of the study showed that mixing of sand in swelling clay remarkably reduces swelling potential of expansive clay and improves its strength characteristics. The sample with out mixing sand content showed a swell potential of the order of 3.5 % and this reduced to about 0.5% when the clay was mixed with 35% of sand. The swell pressure for sample without mixing sand was found to be 90 kPa and reduced to about 10 kPa for sample mixed with 35% sand. The CBR values increased from a value of 4% in case of pure clay sample to a value of 8% when the clay was mixed with 30-35% sand. The Modified AASHTO density was increased from 18.2 kN/m3to 19.4 kN/m3in case of pure clay and clay mixed with 30-35% sand, respectively. These results are very promising and have application when such clays are being used as highway subgarde soil, where there is requirement of mitigating their expansive nature along with improving their strength characteristics like CBR etc.