ENGINEERING GEOLOGICAL INVESTIGATION OF SOME SOILS OVER METAMORPHIC COMPLEX ALONG AKUNGBA-IKARE AKOKO ROAD ONDO STATE, NIGERIA

CHAPTER ONE

1.0     INTRODUCTION

Engineering geology is the application of geologic science to engineering practice for the purpose of assuring that the geologic factors affecting location, design, construction operation such as road construction building construction, dam and bridge construction and it maintenance are recognized and are adequately provided for (Ige, 2011).      
Soil can be defined as the upper layer of the ground made up of unconsolidated material produced due to weathering agencies which acted on the rocks. It can also be referred to as ‘’TERRAFIRMA’’ meaning solid ground; a good base for road, building and all kind of structures project (Gidigasu, 1972).         
The engineering approach to this research project will focus on the characteristics of soils as construction materials and their suitability to withstand loads applied by structures of various types. A good understanding of the engineering geological properties of the soil around Akungba-IKare Akoko area of Ondo State, Southwestern part of Nigeria will aid quality construction project.        Soil samples responded differently to various geotechnical tests or engineering tests they are subjected to and this will give an insight to the suitability of the soil. Lack of information would affect the suitability and performances of any engineering structure. This Research project work will deals with the geological investigation on some soil around Akungba- Ikare Akoko area in order to determine their usefulness for construction material.     

1.1            Location and the extend of the study area

The area of study, Akungba-Ikare Akoko road is located in the northern part of Ondo State. The area lies between latitudes 070.27’N and 070.31’N   and longitudes 0050.43’E and 0050.47’E Greenwich Meridian (figure 1.1 and figure 1.2). Akungba-ikare Akoko area is moderately populated and it is surrounded by settlement such as Ogbagi, Iwaro Oka, Ugbe Akoko.

1.2 Aim and Objectives of the Research project work.

The aim of this geologic study is to determine the engineering geological properties of some soil developed over the metamorphic rock in the study area, thereby accessing its strength, stability and suitability for the purpose engineering constructions.

Objectives

(1) To determine the nature, and the strength of the geological material based on the component of construction materials 
(2) It will provide some relevant information about the engineering properties of soil in the study area. 
(3) To determine the suitability of the soil for construction purposes.  

1.3            Previous work/ Literature Review

Many research works had been carried out in the past on the engineering properties of subgrade soils in some parts of Ondo state and other parts of the country by different researchers, but the engineering geological investigation of some soils over metamorphic complex along Akungba-Ikare Akoko is the first of its kind in this area. Notable among these works are the works of Adeyemi 2000, Jegede 1998 and Gidigasu 1997. Most of these workers attributed pavement failure to poor subgrade material /fill soils.        
The reports of selected works are presented below: Adeyemi, (2000) worked on geotechnical basis for failure of some sections along the Lagos- Ibadan expressway of southwestern Nigeria. They made comparison between the stable and unstable portions of the road and concluded that significant differences need not to have existed between the geotechnical properties of soil below the stable and the unstable sections of the road before such parameters can serve as basis for predicting the stability of flexible expressway pavements in the tropics. Jegede (1994) worked on the pavement failure at a section along Ikere-Igbara-Odo road in Ekiti state of Nigeria. He found out that the California Bearing Ratio of the soil ranges around 50% which showed poor soil physical properties lack of drainage facilities combines with the excess fine soil grade ranging between 20-40% was responsible for the failure along the area.           
Jegede (1998) investigated failure over Talc-Tremolite-schist terrain of Ife-Ilesha expressway in Osun state and concluded that since the subgrade and the burrowed materials are schist derived, they contain talc and hydromica, which make it impossible for field compaction. The engineering geological properties of sub-grade soil of the proposed Ilawe-Ekiti high way Southwestern Nigeria was carried out by Jegede (1998), the result obtained showed that the natural  moisture content range from 2.0% to 2.8%. The liquid limit range from 36.0 to 43.0% linear shrinkage range from 2.1% to 2.60% specific gravity range from 2.66 to 2.74. The compaction of the soil indicate dry densities from 1910kg/m^3 to 2,050kg/m^3 at optimum moisture content of 15% to 18.2%. These data obtained shows that the soil is good for road construction work as sub grade and sub base material.          
The engineering geological assessment of soil from southwestern Nigeria as seal in sanitary land fill carried out by 0.01GE. the result showed that the specific gravity ranges from 2.50 to 2.77 while the percentage of the fines ranges from 23 to 75% liquid limit values range from 27.7 to 62.5% while plasticity indices values ranges from 20.8 to 41.2%. The highest permeability value of 1.4 x 10^-8m/s is also obtained all soil investigated. The soil tested can be considered suitable for sanitary landfills.