TABLE OF CONTENT
TITLE PAGE i
TABLE OF CONTENT vi-viii
LIST OF FIGURES ix
LIST OF TABLES x
- GENERAL STATEMENT 1
- GEOLOGICAL SETTING 9
- FIELD INVESTIGATION 14
- TYPICAL LATERITIC SOIL 18
- GENERAL ENGINEERING PROPERTIES OF LATERITIC SOILS 18
- STRUCTURE OF ROAD PAVEMENT 19
- GENERAL STATEMENT 31
- CONCLUSION 43
- RECOMMENDATION 43
LIST OF FIGURES
FIG. 1: MAP SHOWING THE VEGETATION OF NIGERIA 5
FIG. 2: MAP SHOWING THE LOCATION OF THE STUDY AREA 6
FIG. 3: A MAP SHOWING THE STRATIGRAPHY OF THE EASTERN DAHOMEY BASIN 13
LIST OF TABLES
- SPECIFIC GRAVITY OF THE SOIL SAMPLES 32
- SHOWING THE SIEVE ANALYSIS OF CA 33
4.12 SHOWING THE SIEVE ANALYSIS OF CB 34
4.14 SHOWING THE SIEVE ANALYSIS OF CC 35
4.31 SUMMARY OF THE RESULT OF CONSISTENCY LIMITS OF THE SOILS STUDIED 37
4.41 RESULT OF MOISTURE DENSITY RELATIONS 39
- GENERAL REQUIREMENT FOR SUB BASE MATERIALS 41
- RESULT OF CALIFORNIA BEARING RATIO 42
The construction of Foundations of most engineering structure requires that adequate information about the engineering properties of the soil and sub-soil condition of the area are known. This is necessary for the engineering planning, design and construction of such foundations to be based on sound geotechnical parameters.
This is more important especially in the design and construction of highways, where there is need for a good and sound knowledge of the geotechnical and engineering properties of the subgrade and more importantly, the construction materials properties for sound engineering decisions to be taken. Such geotechnical parameters include the strength, the maximum dry density (MDD), the amount of fines (Clays and Silts) as well as the compaction performance of the proposed highway construction materials.
In Nigeria, the non-availability of generalized relevant data in this region, particularly for initial preliminary engineering planning and design, has been the bane and cause of failure of most of our highway construction projects, such that, failure occurs almost immediately after the project is commissioned. The construction material which is used for engineering highway projects is therefore as important as other engineering design factors. Thus, in road pavement design, the soil (sub-base and base course) materials used in the pavement is a function of the ease and rigidity of the pavement soil to transmit the stress induced in it to the sub-soil such that necessary deformation is avoided.
In this tropical part of the world, laterite soils are used as a road making material and they form the sub-grade of most tropical road. They are used as sub-base and bases for low cost roads and these cause low to medium traffic.
Since its discovery by Buchanan, 1807 in Malabar, India, Laterite has been defined and described by a number of researchers in several different ways. Ola (1978), used local terminology in defining laterite soils as a product of tropical weathering with reddish brown color with or without nodules or concretion but not exclusively found below hardened ferruginous crust of hardpan. Osula (1984) defined laterite as a highly weathered tropical soil; rich in secondary oxides of iron, aluminium and manganese. Laterite also known as “red soils” is used to cover tropically weathered soil that has been involved in the accumulation of oxides of iron and aluminium. According to Alexander and Candy (1962), it is nearly devoid of bases and primary silicate, but it may contain large amount of quartz
and kaolinite. It is either hard or capable of hardening on exposure to wetting and drying. (Agbede, 1992).
A literature review has revealed that the geotechnical characteristics and engineering behavior of red soil depend mainly on the genesis and degree of weathering (i.e. Decomposition, Laterization, desiccation and Hardening). Morphological characteristics as well as the type and content of secondary minerals are other genetic characteristics. (Agbede, 1992).
Good Understanding of the basement soil on which highways and other transportation facilities are constructed are very important. Salter (1988) said the performance of a highway pavement is influenced to a very considerable extent by the subgrade material.
GEOTECHNICAL SUITABILITY OF LATERITE FROM ONIHALE/ISOROSI ROAD, IJAKO-IFO BURROW PIT AS A SUBGRADE MATERIAL