Efficacy of preloading combined with prefabricated vertical band drains in improving a clayey silt stratum in situ.

This paper presents a detailed field study of a soft clayey silt stratum improved in situ with preloading combined with prefabricated vertical band drains (PVDs). The clayey silt stratum was to support a warehouse in a chemical plant. As the bearing capacity of the soil was much lower than the load it was to support, the subsoil condition was improved by installing PVDs in combination with preloading. Thus the rate of consolidation of the clay stratum was increased. The band drains were installed up to a depth of 14·2 m at a spacing of 1·6 m. The intensity of preloading applied was 52 kPa. For preloading, the surcharge fill was placed up to a height of 3·10 m from the natural ground level. The area of both preloading and band drains was 15% greater than that of the floor of the warehouse for more effective improvement of the ground. Preloading was done for 60 days. Settlements were monitored using settlement gauges. The settlements observed across the entire area indicated that the preloading operation was uniform all through. The amount of settlement was large up to the point of filling the surcharge, but thereafter it did not show a significant increase. [ABSTRACT FROM AUTHOR]