Soil Tests Analysis for Raft and Pile Foundations of a 5 Storey Building in Yenagoa, Bayelsa State, Nigeria

Umeonyiagu. I. E., Agboga. M. A., Okeleke. J. N.

Abstract


This work involved the designs and analyses of the foundation of a 5-storey building in Yenagoa, a water-logged area of Bayelsa State, (Nigeria), using both raft and pile foundations. Preliminary soil tests were carried out in order to determine the physical properties and the bearing capacity of the soil. These tests were Dutch cone penetrometer tests, Borehole characteristics test involving standard penetration test, particle size distribution tests, direct shear test, triaxial tests and consolidation tests. The Dutch cone penetrometer tests recorded resistance to cone penetration of 345-355kg/cm2. The Borehole characteristic tests showed that the top soil was dry grayish mottled clay, followed by soft silty/sandy clay up to about 6m depth. Below 6-7m depth was sand. The clay end bearing minimum pressure was 54kN/m2 and maximum pressure was 68kN/m2. Sand end bearing minimum pressure was 416kN/m2 and maximum was 697kN/m2. The clay skin friction ranged from 10kN/m2 to 13kN/m2. The sand minimum skin friction was 77kN/m2 and the maximum skin friction was 129kN/m2.The allowable bearing capacity of the soil ranging from 64kN/m2to 71kN/m2 for a shallow depth of 1m – 2m and 177kN/m2 to 517 kN/m2 for a deep depth of 10m to 20m. The pile sizes ranged from 305mm to 500mm. Design of the structural elements (superstructure) as well as the design of the foundations (Raft and Pile)  were executed with  ultimate column axial load of 4138 kN and serviceability  column axial load of 2164 kN. The cost analysis was also performed. From the  cost analysis, the cost of the raft foundation was  N78,884,505.00 (Seventy Eight Million, eight Hundred and eighty four Thousand, five Hundred and five Naira only) while the cost of the pile foundation was N117,551,700.00 (One Hundred and seventeen Million, five Hundred and Fifty one Thousand, Seven Hundred Naira only).

This showed that the cost of the pile foundation was greater than that of the raft foundation by 39%. It is recommended that raft foundation be used on the area in order to minimize cost.


Keywords


Raft; Pile; Foundations; Shear; Designs.

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References


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