Improvement of Coastal Silty Sand of Saudi Arabia Using Preloading Technique: Fid-Bau Portal

Improvement of Coastal Silty Sand of Saudi Arabia Using Preloading Technique

Dafalla, M. A.

The subsurface formation at sites along the western Red Sea coast of Saudi Arabia often have loose to medium dense silty sand at several parts. This type of material was encountered at levels immediately below the foundation depth commonly used in practice. These soils undergo excessive settlement when supporting concrete structures, slab on grade systems and pavement structures. This work was aimed at studying the improvement provided by preloading technique to these coastal deposits. Technical College Building Complex site located at Al Qunfoda was selected for this study. The site was preloaded using 4.5 to 6m height of sand over six month period. The settlement was monitored every week throughout the period of preloading. The density and compressibility of the formation was noted to improve in different stages; an initial fast stage occurring within the first four weeks, intermediate stage which continued for 12 weeks and a slow stage which is noted to continue for more than 26 weeks. A final stable stage is considered when no variation in settlement can be reported over a satisfactory period. The process improved the site and established a close to uniform density across the area studied. Plate load tests carried out on improved areas confirmed that the settlement after preloading was reduced to tolerable limits for a particular foundation stress range. This paper provides a guide for monitoring, verification and decision making tool for practicing geotechnical engineers.