Geotechnical Investigation of a Proposed Dam Project, Iyah Gbede, Kogi State, Nigeria

International Journal of Research and Innovation in Applied Science (IJRIAS) | Volume VI, Issue VII, July 2021|ISSN 2454-6194

Geotechnical Investigation of a Proposed Dam Project, Iyah Gbede, Kogi State, Nigeria

Oyanameh O.E¹, Olabode O.O², Korode A.I³, Osisanya W.O⁴, Fatoye O.V^5
1,⁵Department of Earth Sciences, Anchor University, Ayobo, Lagos, Nigeria
²Department of Geology, University of Ibadan, Ibadan, Nigeria
³Department of Petroleum Engineering and Geosciences, Petroleum Training Institute, Effurun, Nigeria
⁴Department of Physics, University of Benin, Benin City, Nigeria.

Abstract
Geotechnical study was conducted at the proposed Dam project of Iyah Gbede, Ijimu Local Government Area of Kogi State with the aim of evaluating the subsoil layers that constitute the foundation soils and their competence as foundation soils for the civil engineering structures. The study involved drilling of three (3) boreholes and eleven (11) trial pits as well as Standard Penetration Test (SPT) to obtain the in situ strength parameters of the sandy layers. The lithological formations that constitute the study area layers are lateritic top soil, grey brown sandy clay, yellowish brown coarse sand, gravel and weathered rock. All the soils have average natural moisture content because it agrees with the average range of (5 – 15%) specified by Federal Ministry of Works and Housing FMWH, (1997) for civil engineering construction which is an indication of low water absorption capacities of the soil materials. The results of the geotechnical parameters of the soils obtained indicate good characteristics as construction materials with good bearing strength, good baseline information and foundation design for the establishment of the proposed dam site.

Keywords: Soil Tests, Borehole drilling, Geotechnical Study, Dam Site.

1.INTRODUCTION

With increasing cases of collapse of engineering structures reported in Kogi state (Adama 2021) and other parts of the country (Olayinka et al., 2017), this has necessitated a detailed investigation of a proposed dam site through the adoption of geotechnical study despite the geophysical investigation survey (Olabode et al., 2021) that was earlier carried out at the same site. More so, geotechnical survey gives true subsurface information and a more reliable result of any investigated site than geophysical investigation which gives apparent subsurface results. The aim of this study is to ascertain the subsoil layer condition of the soil properties that make up the foundation soils in order to establish the dam site project on a competent layer of the subsurface.
A dam is a structure constructed across a river or flowing water body to increase the water level or impede the water from flowing thereby creating a reservoir. An established dam can be used to generate hydroelectricity, flood control, irrigation, recreational activities, fish farming, tourism, regularisation of water flow, navigation etc. Water plays a very important role in life as well as global economy. The livelihood and sustainability of humanity depend largely on availability of water supply (Tanchev 2014, Pedro and Cesar 2017).
The geotechnical test method adopted at the dam site is known as Atterberg Limits which include the liquid limit, plastic limit and plasticity index. The liquid limit of a soil is the moisture content, expressed as a percentage of the weight of the oven-dried soil, at the boundary between the liquid and plastic states of consistency. The moisture content at this boundary is arbitrarily defined as the water content at which two halves of a soil cake will flow together, for a distance of ½ in. (12.7 mm) along the bottom of a groove of standard dimensions separating the two halves, when the cup of a standard

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