IMPACT OF GEOPHONE SPACING ON SOIL STIFFNESS EVALUATION AT KASU, NEW SITE

Abstract

Multichannel Analysis of Surface Waves (MASW) Measurement was conducted at Kaduna State University, New site, Rigachikun Ward, Igabi Local Government Area, Kaduna State, Nigeria, in order to characterize the study area and to study the ability of different geophone configurations. MASW was conducted at five (5) profiles with geophone spacings of 1m, 2m, and 3m for each profile, which covered a maximum of 108m profile length with the aid of ABEM TERRALOCK PRO seismographs, and the field data obtained was analyzed using SeisImager Computer software. The 1m, 2m, and 3m geophones spacing results show a maximum of five (5) layers and both revealed heterogeneous nature of the subsurface geological sequence. The geological sequence beneath the study area for all profiles shows an average shear velocity ranging from 180m/s to 528.50m/s from the velocity profiles and the site is classified as class C (very dense soil and soft rock) and Class D (stiff soil) as the depths of the layers differ from one location to other ranging from 1.5m to 24m. Quantitative interpretation indicates that, the study area is dominated by three major types of soil; clay, sand and gravel as revealed by the 2D model with shear velocity ranging from 215m/s to 610m/s and at depth ranging from 0 to 37m. At 1m geophone spacing about 50% indicates soil class C (Very dense soil and soft rock) and 50% class D (stiff soil) while at 2m geophone spacing about 33% revealed soil class C while 67% revealed soil class D. At 3m geophone spacing, the soil type was 100% at class D.