Abstract

ABSTRACT Liquefaction occurs in shallow, loose, saturated deposits of cohesionless soils subjected to strong shearing stresses. This leads to the transfer of stress from the soil skeleton to the pore water precipitating a decrease in effective stress and shear resistance of the soil. The study gives the results of the liquefaction potential assessment in some part of Lagos wetland areas of Lagos. The aim of this study was to assess the liquefaction potential through the evaluation of its severity in response to Earth tremors. In order to achieve this purpose, Multi-channel Analysis of Surface waves (MASW) and Cone penetration testing (CPT) were carried out. For an optimal coverage of the study area, twenty-four channels 4.5Hz geophones connected to the ABEM Mark 6 Seismograph through two cable reels were used to detect the generated seismic wave produced by the weight drop of about 19.1 kg. The CPT soundings for assessing subsurface stratigraphy with respect to liquefiable soils were carried out with a 10-Ton Dutch Cone Penetrometer. The softwares used were SeisImager, for processing the MASW data and CLiq for the CPT measurements. The shear wave velocity models were generated for the MASW measurements. The models show that sand sediments with velocity ranging from 118 - 279 m/s dominated most of the study area. Also, the results show that for the potential liquefiable sands identified, the shear wave velocity ranges between 118.0 – 180 m/s delineated at depths between 10.0 – 20.0 m within study profile an is typical of liquefiable sands. Simplified procedure of assessment of Liquefaction potential from CPT showed a model curve whereby some CPT points were within the liquefiable zones.

Keywords: Liquefaction, Coastal sands, CPT, MASW, SPT, and Lagos