ABSTRACT
The intrinsic suitability of some lateritic soils as materials for construction of layers for flexible pavements is evaluated herein. The pavement layers assessed were the base course, sub-base and sub-grade. Laboratory results of samples from these layers show that the CBR values of the sub-grade materials met the requirement while about 40% and 70% of the locations for sub-base and base materials respectively, presented CBR values less than those specified by the local code of Nigeria. Also, the fine proportions as required were significantly absent. This resulted into failure of the road along its profile at many sections, such as the roadway and shoulders. It was noted that the fine proportions would have been leached away due to inadequate drainage facilities at the failed road sections or rather poor quality control during construction. A total reconstruction with adequate drainage facilities is suggested for this road due to its importance in Nigeria, and with the adequate materials.
CHAPTER ONE
INTRODUCTION
1.1 Background to the Study
A road pavement is a structure of superimposed layers of selected and processed materials that is placed on the basement soil or sub-grade. The main structural function of a pavement is to support the wheel loads applied to the carriageway and distribute them to the underlying sub-grade. The term sub-grade is normally applied to both the in-situ soil exposed by excavation and to added soil that is placed to form the upper reaches of an embankment. Modern pavement design is concerned with developing the most economical combination of pavement layers that will ensure that the stresses and strains transmitted from the carriageway do not exceed the supportive capacity of each layer, or of the sub-grade, during the design life of the road. Major variables affecting the design of a given pavement are therefore the volume and composition of traffic, the sub-grade environment and strength, the materials
economically available for use within the pavement layers, and the thickness of each layer.
Pavements deteriorate with age and use, and the engineer needs to identify the type of deterioration and if possible, its cause in order to establish a priority in the highway maintenance programme.
For any road pavement to perform its function of carrying vehicles and passengers in safe, comfortable, and efficient manner from one place to another it must have been well constructed following proper Highway Engineering methods, be adequately maintained and rehabilitated from time to time in order to improve on its service life (Uruaka, 2012).
According to Oguara (2006), the term ‘pavement’ refers to the hard materials constituting the structure of a road that are constructed on top of the natural soil. Pavement here differs from the British definition of pavement which is defined as a paved way at the side of a street for people on foot. While earth roads can be considered as special pavements, modern highway, airfield or parking lot pavements are usually made up of layers of materials of differing quality with the highest quality material at or near the surface. The Civil Engineer is responsible for the planning, design, construction, maintenance and rehabilitation of these pavements.
The design is concerned with the determination of the total thickness of the pavement structure as well as the thickness of the individual material layers, having regard to the quality of the materials in each layer under all climatic conditions and the expected traffic loads over a design period.
With various pavement construction and maintenance equipment, and procedures that have been developed over the years, the Engineer should be able to construct and maintain pavements that are able to carry traffic safely, conveniently and economically with materials that are capable of protecting the natural soil from the effects of traffic loads and climatic environment.
1.2 Problem Statement
Pavements deteriorate with age and use, and the engineer needs to identify the type of deterioration and if possible, its cause in order to establish a priority in the highway maintenance programme.
The cause of the incessant and sporadic incidence of road failure in Nigeria today could be attributed to defective design, lack of soil tests, poor soil properties investigation, poor supervision and construction strategies e.t.c. These failures are in form of wavy surface, corrugations, rutting, pot holes, consequent cracking to mention a few.
1.3 Aim and objectives of the Study
The aim of this work is to determine the effects of the in-situ properties of granular pavement layers to the stability of Minna-Bida road. The length of the road is 85km. The objectives are as follows:-
i. to determine the index properties of lateritic soils that make them suitable for use as layer materials.
ii. to determine the strength of lateritic soils used as subgrade, sub-base and base course for Minna-Bida road in terms of California Bearing Ratio (CBR) considering soaked and unsoaked soil samples.
1.4 Scope of Study
The road has a total length of about 85km of asphalt concrete surfacing. The prevalent
distress mode on this road are wide cracks (longitudinally and transversely), potholes, corrugations at close intervals and failures along the shoulders due to erosion. This was done through a site reconnaissance survey.
The work is limited to the in-situ properties and strength of the pavement layers in terms of California Bearing Ratio (CBR) of the lateritic soils used as sub-grade, sub- base and base course for the construction of Minna-Bida Road. To achieve the objectives of this work, most of the laboratory tests conducted were aimed at determining the index properties and stability in terms of CBR of the sub-grade, sub- base and base course of the road in question.
This material content is developed to serve as a GUIDE for students to conduct academic research
EVALUATION OF INSITU GEOTECHNICAL PROPERTIES OF ROAD PAVEMENT LAYERS MATERIAL: A CASE STUDY OF MINNA–BIDA ROAD
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