CHARACTERISATION OF THE ELASTIC PROPERTIES OF SOILS IN SOME PARTS OF LAGOS WETLANDS FOR ENGINEERING PURPOSES
The results obtained from the evaluation of elastic properties of some part of Lagos Wetlands were presented for the determination of the competent soil for engineering structures. The study area falls within the reclaimed part of the Lagos wetlands signifying the presence of unstable geological materials. The study area is characterized with alluvium sediments which comprises of materials of low shear strength. Five (5) seismic profile lines were established via the ground rolling technique of Multi-Channel Analysis of Surface Waves (MASW). The data acquisition was carried out with twenty-four (24) channels 4.5Hz vertical geophones connected to the ABEM Mark 6 Terraloc Seismograph. The acquired MASW data were processed using SeisImager to obtain the two-dimensional (2-D) shear wave velocity (Vs) profiles which gives the contrast in the distribution of the velocity along each profile. In addition, dynamic parameters such as rigidity modulus, poisson ratio were estimated for further classification of the geo-earth materials in the study area. In the study area, the shear wave velocity (Vs) values obtained ranged between 94 – 1320 m/s representing different sediments such as saturated loose sand (163 – 204 m/s), loose silty sand (165- 225 m/s), medium – dense sand (220 – 350 m/s), medium dense sand (400 – 700 m/s) and dense-coarse sand (900 - 1380 m/s). However, based on these classification, it is found that saturated loose sand and loose silty sand are not competent for founding layer of engineering structures. Therefore, deep foundation inform of piling system is recommended for engineering structure that will devoid unexpected collapse and partial and differential settlement. The study has revealed that the area is generally comprise of problematic soil(s) that are inimical to construction of engineering structures.