Safe Bearing Capacity Evaluation For The Construction Of Proposed National Testing Services Building H-8/1 Islamabad

Abstract

Islamabad the capital of Pakistan is a planned city constructed since in 1960 at the foot of the Margalla Hills just north of the old city of Rawalpindi. Rapid growth of both Islamabad and Rawalpindi to a combined population near 1.5 million has made ever-increasing demands of shelter for residence and other purposes a major business involving expert engineering. The present research focuses on the geotechnical investigations outcome carried out by GEOENGINEERS, Islamabad assigned by Designer Consulting Engineers (Pvt.) Ltd. for the construction of the National Testing Services Building Sector H 8/1 Islamabad having two basements and ten stories. The fieldwork started on 28th July 2009 and was completed on dated 16th August 2009. During field operation eight bore holes of varying depth (10 to 18 meters deep) were drilled to evaluate the foundation’s bearing capacity of soil, over which the entire purposed building will rest. The soil samples were collected at regular interval or any change in lithology strata was observed. Selected samples were sent to the geotechnical laboratory to evaluate their index and engineering properties and their results have been compiled. Subsurface soil consists of light brown colored lean clay (CL) followed occasionally by sandy silty gravels (SM). Eastern part of project area consists of few meters of dumped ruble material from surrounding construction sites. The standard penetration test data reveals that N-values vary to minimum of 6 at shallow depths to a maximum of 18 at depth. Geotechnical laboratory analyses for the representative soil samples collected during the drilling of boreholes have also been discussed. Grain size analysis data8 exhibit that gravel ranges from 0% to 5 %, sand ranges from 5.9% to 29%, silt 63 – 94.1% and clay 14.7 to 33.1%. The natural moisture content varies from 11.12% to 24.5%. The soil consistency data reveals that liquid limit for studied samples varies 30.7 to 39.1%, plastic limit is 22.2 to 29.9 % and the plasticity index is from 7.1% to 12.0%. The specific gravity for soil samples are 2.65 g/cc. The unconfined compressive strength varies from 0.91 – 1.15 Kg/cms3. The evaluated dry density is 1.485 to 2.171 g/cc whereas angle of repose is less than 26o indicating gentle fraction. Chemical constitutes reveals that sulfate and chloride are well below the hazardous range.