GEOPHYSICAL INVESTIGATION FOR FOUNDATION STUDIES OF THE PHASE II SITE, AHMADU BELLO UNIVERSITY, ZARIA USING MULTI-CHANNEL ANALYSIS OF SURFACE WAVES
GEOPHYSICAL INVESTIGATION FOR FOUNDATION STUDIES OF THE PHASE II SITE, AHMADU BELLO UNIVERSITY, ZARIA USING MULTI-CHANNEL ANALYSIS OF SURFACE WAVES
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Date
2021-03
Authors
ABUBAKAR, Fahad
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Abstract
The Multi-channel Analysis of Surface Waves (MASW) was employed at the Ahmadu Bello University, Zaria Phase II site to characterize the site for foundation studies. The dispersive nature of the Rayleigh wave was used to estimate the average shear wave velocities (down to 30 m) of the site, using both the 1-dimensional (1D) and 2-dimensional (2D) shear wave velocity models. The average shear wave velocity distribution of the site shows that the soil thickness increases eastwards. Employing the borehole log data and shear wave velocities of soil/rock as control, the 2D models reveal a first layer (topsoil and laterite) with shear wave velocity (𝑉𝑠) in the range of 158 to 290 m/s and corresponding thickness of 0 to 6 m. The second layer (clayey sand) shows a 𝑉𝑠 of 180 to 270 m/s with a corresponding thickness range of 2 to 7 m. The third layer, which is the weathered basement shows a 𝑉𝑠 of 250 to 500 m/s and a thickness range of 4 to 18 m. The fourth layer (fractured basement) has a thickness of 2 to 8 m and 𝑉𝑠 of 400 to 650 m/s. The fifth layer with the highest 𝑉𝑠 (> 650 m/s) is assumed to be the fresh basement (bedrock), which was delineated at 24 m depth in some of the areas. The average Vs30 obtained for the site varies between 273.5 m/s to 446.2 m/s, which reveals the site class of C and D following the National Earthquake Hazard Reduction Program (NEHRP) provision. Following this provision, the site is can be assumed for engineering construction. Nonetheless, we recommend that the clayey material observed should be excavated or densified (perhaps using rock chips) before embarking on construction on the site.
Description
BEING A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF SCIENCE DEGREE IN APPLIED GEOPHYSICS.
DEPARTMENT OF PHYSICS,
FACULTY OF PHYSICAL SCIENCE,
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
Keywords
GEOPHYSICAL INVESTIGATION,, FOUNDATION STUDIES,, PHASE II SITE,, AHMADU BELLO UNIVERSITY,, ZARIA,, MULTI-CHANNEL ANALYSIS,, SURFACE WAVES.