DEVELOPMENT OF A MODEL FOR STRUCTURE FOUNDATION INSTABILITY IN NIGER DELTA SOILS: A CASE STUDY OF THE PORT HARCOURT AREA, RIVERS STATE, NIGERIA

This research focused on the “development of a model for foundation stability” in the Rivers State of Port Harcourt. Port Harcourt has a low-lying topography, and the subsurface soil is typically poorly drained. Hence, the area falls within the heavy annual rainfall. Therefore, the cost of making a structural foundation in the area is too high due to the amount of work involved in terms of testing owing to changes in the moisture content of the clay soil in the area leading to structural foundation failure. Four sites were randomly selected and visited in different parts of the study area. These sites include Eneka East West Road, Odilli Road, Ameachi Drive, and Woji Avenue. The shell and auger method was used to collect clay samples from the subsurface strata. A sampling tube was attached to the auger and then pushed into the soil up to a depth of 6m and retrieved gradually to collect the undisturbed sample. The samples were subjected to unconsolidated un-drained triaxial and consolidation tests were conducted using the samples. The generated data were correlated to determine their variation and relationship. The variation and relationship of these sites were analyzed using regression analysis. The results obtained for the allowable bearing pressure and the ultimate settlement were as follows: Qa= 23D + 133 St = 0.0044loge P 0.0014 Where Qa= allowable bearing pressure, D = the depth of the foundation, St = the ultimate settlement and P = the imposed load on the foundation. The model equation is related to the original soil shear strength and the ultimate settlement equation. However, the model reduced the amount of testing work required; hence, the allowable bearing pressure and ultimate settlement can be obtained by directly substituting the sample depth and imposed load on the foundation in the model equation. The above expressions are recommended for predicting foundation stability in the Port Harcourt city area; hence, other types of foundations can be explored for further comparison with the strip foundation model