Performance of Preloading Applied on a Peaty Clay Deposit

A considerable part of Bangladesh, especially the southern part near Shunderban, the world's largest mangrove forest, is covered by deep-seated soft to very soft soils. A major road is being constructed through this soft deposit in Mollahat-Noapara at Bagerhat connecting the capital city with the southern part of the country. Several boreholes were drilled at the project site along the road section for soil characterization. SPT-N values were measured for at least 30 m at the interval of 1.5 m down each borehole. Both disturbed and undisturbed samples were collected from various depths. Various laboratory testing were conducted on these samples. Based on test results, a settlement of 336 mm was predicted at the project site under the future traffic load in 180 days. In order to develop a proper methodology regarding the improvement of underlying soil at the project site, two trial sections were constructed along the road section and was subjected to preloading to bring about the predicted settlement as quickly as possible. It was observed that the average settlement due to preloading after 180 days was 220 mm. SPT-N values and compressive strength measured after preloading were increased considerably.