The effect of inundation on the strength and swell characteristics of some common tropical soils

The purpose of this work is to find out the effect of inundation on strength and swell characteristics of some common tropical soils. Inundation here refers to the state of being covered by water (floods). The main tests carried out in this investigation include California bearing ratio, swell pressure and free swell tests. The materials tested are Lateritic, volcanic and tertiary soils which are considered to be the common tropical soils. Soil classification test was also conducted in order to get the group from which the soils belong according to their engineering behavior. From the results of this test, laterite soil was classified as SC (clayey sand), volcanic soil as ML (silt of low plasticity), and tertiary as SP (Poorly graded Sands). California bearing ratio (C.B.R) test has been conducted on all soil samples (under both soaked and unsoaked conditions). The C.B.R samples were compacted at dry of optimum (W opt-2%), optimum moisture content and at wet of optimum (W opt+2%). Due to soaking, it was found that the C.B.R value for lateritic, volcanic and tertiary soils dropped by 93%, 50% and 11% respectively for samples compacted at dry of optimum moisture content. For samples compacted at wet of optimum moisture content, the drop in C.B.R value was 53% for lateritic and 1% for volcanic soil. From swell pressure test, it was observed that higher swell pressure was developed when the samples were compacted at the dry of optimum moisture content as compared to those compacted at wet of optimum. For laterite soil, the sample compacted at dry of optimum moisture content developed swell pressure of 68% higher than that compacted at wet of optimum. For Volcanic soil, the sample compacted at dry of optimum moisture content developed the swell pressure of 39% higher than that compacted at wet of optimum moisture content. For tertiary soil, the sample compacted at dry of optimum developed the swell pressure of 77% higher than that compacted at wet of optimum moisture content. Free swell for lateritic, volcanic and tertiary soils were found to be 45%, 20% and 40% respectively. From the above observations it is recommended that lateritic, volcanic and tertiary soils should preferably be compacted at the wet of optimum moisture content in order to minimize the strength reduction and higher swell pressures which may develop in case of subgrade submergence.