Field measurements and back calculations of settlements of structures founded on improved soft soils by stone columns

Abstract

The soft soil is extensively located in many areas of Bejaia region, Algeria, which usually have a low bearing capacity, high compressibility, insufficient strength and subject to the risk of liquefaction. Due to the ongoing increase in urban and industrial growth and the need for greater access to the lands, the unfavourable soil conditions require deep foundations or soil improvement. A lot of soil improvement methods have been used to deal with soft soil problems. Since 1999, one of the techniques extensively used in Harbour area of Bejaia is vibro replacement. A shallow raft foundation on stone columns was designed for a battery of 10 steel silos of grain storage. The project was put into operation in March 2006. The structure was instrumented from 2006 to 2012 for monitoring settlements and silo deformations. The measured settlements over seven years are analysed and discussed in this paper. Large settlements are measured. Some problems are observed on the foundation raft starting from a differential settlement of about 7 cm. The settlement evolution indicates that 50% of the total settlements are reached over the first 6 months of the structure exploitation. To compare the load-settlement behaviour prediction with the measurements, calculations are carried out by means of the three-dimensional and the two-dimensional geotechnical finite-element analyses.