Investigation of Soil-Structure Interaction Effects on Shallow Foundations in Expansive Clay Soils of Benue State

Expansive clay soils present significant geotechnical and structural engineering challenges, particularly in the North Central region of Nigeria where seasonal moisture fluctuations induce heave and settlement cycles. This study investigates soil-structure interaction effects on shallow strip foundations in residential buildings constructed on expansive clay deposits in selected communities in Benue State. Geotechnical site investigations were carried out at twelve locations, including Makurdi, Gboko, and Otukpo, incorporating Atterberg limits testing, free swell index measurement, and undrained shear strength determination. Structural condition surveys of buildings founded on the identified expansive soils documented cracking patterns, differential settlement measurements, and foundation exposure depths. Analysis was conducted using elastic subgrade reaction models incorporating soil stiffness variations corresponding to wet and dry seasonal states. Results indicate that over sixty-five percent of surveyed buildings showed distress symptoms directly attributable to differential heave, with crack widths ranging from 2 mm to 18 mm recorded at wall-foundation junctions. Shallow strip foundations of less than 0.6-metre depth were particularly vulnerable to seasonal volume change. Stabilisation trials using cement-lime admixtures at four percent lime content demonstrated a reduction in free swell index by up to fifty percent. The study recommends a minimum foundation depth of 1.2 metres in expansive soil zones, adoption of raft or pier-and-beam foundations, and mandatory pre-construction soil testing in identified clay-rich areas. Keywords: expansive clay, shallow foundations, soil-structure interaction, Benue State, heave.