Geotechnical assessment of near-surface sediments and their hazardous impact: Case study of Jizan city, southwestern Saudi Arabia

Abstract

The geotechnical parameters of near-surface sediments in Jizan city have been assessed through shear wave velocity (Vs) from twenty-two profiles of multi-channel analysis of surface waves (MASW) through Jizan city. The Vs varies between 106 and 560 m/s indicating wide range of soil stiffness properties. While the allowable bearing capacity, qa varies from less than 1 kg/cm2 at sites till depth 21 m indicating very soft/loose materials; these are considered by building codes as special cases and increased into 2.5 kg/cm2 suggesting stiff or medium dense materials Moreover, qa reaches 6.5 kg/cm2 indicating dense materials, while reaches 8.5 kg/cm2 suggesting the presence of very dense materials. Accordingly, the allowable bearing capacity at a depth of 13 m is less than the recommended values for foundation materials by building codes. Jizan city differentiated into two zones; Jizan salt dome to the west and sabkha deposits to the east. Several weakness zones in the Jizan salt dome zone have been detected with significant variations in the topography of salt rock. While sabkha deposits have low shear strength which requires engineering treatment before construction. Furthermore, shear modulus varies both vertically and laterally through Jizan city where values of shear strength of the near-surface sediments overlying salt rocks are greater than those of sabkha zone. Therefore, deep foundation and ground improvement are highly recommended.