Assessment of Soil Liquefaction Potential in Defence Housing Authority, Karachi, Pakistan

Abstract

The occurrence of liquefaction phenomenon may be induced in the event of a large magnitude earthquake but sometimes loose, saturated and poorly graded sand may be subjected to liquefaction due to the vibration produced by other sources. Liquefaction could cause damage to building and infrastructure due to sudden increase of pore pressure in the loose layers of saturated sand causing the loss of bearing capacity and shear strength. Defence Housing Authority (DHA) is the well planned residential scheme established by Pakistan Army along the coastal belt of Karachi. The soil occurring in DHA is fine grained, poorly graded and mainly comprises of sandy silt and silty sand of Recent age, where water table is encountered at very shallow depth. Hence, it is important to assess the geotechnical behavior of the soil in DHA area, where most of the high rise buildings and mega civil structures are being constructed. In present study, seismic soil liquefaction was evaluated at 15 sites (30 bore holes) in DHA by using simplified empirical method in terms of Factor of Safety (FS). The Relative Density (RD) was determined with the help of Standard Penetration Test (SPT) data. Grain size analysis was also carried out on each borehole samples. The results revealed that the DHA area is vulnerable to liquefaction during severe seismic event of magnitude between 6.5 and 7.5 in Karachi.