Geotechnical investigation of soil bearing capacity a case study of Nile university of Nigeria

Abstract

Geotechnical investigation was conducted within Nile University soil with the aid of the master plan showing areas awaiting future developments. This is as a result of the university planning for infrastructural expansion due to such in student’s population. Each time a building construction is to be taken place, the university management spent another set of money on conducting geotechnical investigation. There are no comprehensive geotechnical information of the soil bearing capacity that can represent the whole of Nile university space/area of 1,153,208,008?2. In-situ and laboratory test were carried out. Three boring point were established using map at a regular interval and drilled to a depth where basement was encountered. In each test sample were collected at 1.5m interval. The standard penetration procedure consist of split spoon and u-tube as set forth in ASTM-1990. The test involves counting the number of blows required to drive a spoon sampler by 300mm, using a weight of 64kg hammer with a free fall of 76mm on the anvil of a rod arrangement. An initial penetration of 150mm is allowable on the sampler known as sitting blows before counting the subsequent blow for the required 300mm. another six trial pit were evenly spread at regular interval at different location within the university. It was manually excavated by hand, undisturbed and disturbed sample were extracted by hand auger and shovel. Sample were extracted at 1.5m depth, properly labelled and taken to laboratory. The laboratory test of the extracted soil sample include moisture content, grain size distribution, liquid limit, plastic limit, consolidated drained test and unified soil classification system was adopted. It was observed that the results obtained from Standard Penetration test indicates variance in allowable bearing capacity with depth, between 0.0-0.5m is 56??⁄?2, 0.6- 1.0m is 112??⁄?2, 1.5- 2.0m is 215??⁄?2, 3.0 – 3.5 is 279??⁄?2, 4.5 – 5.0m is 273??⁄?2. The soil type were predominantly medium dense to very dense inorganic silty sand with clay content less than 5%. Point of refusal was encounter at 6m depth, boring was then terminated. The Direct shear box test analyses obtained from site BC and CH gave the allowable bearing capacity values of 250??⁄?2 at pit one, 211.2??⁄?2 at pit two, 798.1??⁄?2 at pit three, at pit four, 798.1??⁄?2, at pit five, 918??⁄?2 , at pit six 960.5??⁄?2, but with the results obtained from oedometer test show that we cannot adopt this allowable bearing capacity value due to it high settlement rate beyond the acceptable settlement rate set by Development Control in Nigeria, which is 100mm. therefore based on the result from oedometer test the allowable bearing capacity of 120??⁄?2 was adopted with a safe consolidated settlement of 52mm at site BC. While an allowable bearing capacity of 100??⁄?2 with safe consolidated settlement of 55mm was adopted for site CH. Site BC is predominantly underlain by Sandy Silt. While site CH the predominant soil type was Clayey Sand. Pad footing at 1.5m depth and 210??⁄?2 allowable bearing capacity should be adopted. It is recommended that for both site BC and CH pad foundation at 1.5m having maximum individual column load less than 600??⁄?2 with a ground beam adopted.