ABSTRACT
Nigeria, a country in the tropical region is characterized with heavy rainfall and high temperature. It is therefore appropriate to say that climatic factors affect its roads. Many of the roads are flooded with water after heavy rains due to inadequate drainage system. The design of the pavement layers to be laid over sub grade soil starts off with the estimation of sub grade strength and the volume of traffic to be carried. Design of the various pavement layers are very much dependent on the strength of the sub grade soil over which they are going to be laid. Sub grade strength is mostly expressed in terms of CBR (California Bearing Ratio). Weaker sub grade essentially requires thicker layers whereas stronger sub grade goes well with thinner pavement layers. The sub grade is always subjected to change in saturation level due to precipitation, capillary action, flood or abrupt rise or subsidal of water table. Change in moisture level in sub grade causes change in the sub grade strength. And it becomes quite essential for an engineer to understand the exact nature of dependence of sub grade strength on moisture variation. An understanding of the dependence of the CBR strength of local soils on water content will contribute towards better design and maintenance practices. Normally CBR test is an easy and well adopted method conducted on soil samples to measure the strength of sub grade.
However, many other tests are also considered for assessing the sub grade strength. The strength of soil, used for sub grade may vary largely on the amount of saturation in it, i.e. amount of water exposed to the soil. Hence, in this study an attempt has been made to vary the degree of soaking and hence the saturation level in various types of soils in AWGU LGA and study the engineering properties of soils including CBR at different saturation levels.
It is observed that as the soaking period increases from day 1 to 5 for all the samples, there was remarkable decrease in the CBR of soil samples from 100% to 5% in all the samples.
TABLE OF CONTENTS
Declaration – – – – – – – – – – i
Certification – – – – – – – – – – ii
Approval page – – – – – – – – – – iii
Dedication – – – – – – – – – – iv
Acknowledgement – – – – – – – – – v
Abstract – – – – – – – – – – – vi
Table of Contents – – – – – – – – – vii
List of Table – – – – – – – – – x
List of figure – – – – – – – – – xi
CHAPTER ONE
INTRODUCTION – – – – – – – – – –
1.1 General – – – – – – – – – – 1
1.2 Objectives – – – – – – – – – 2
1.3 Scope of work – – – – – – – – – 2
CHAPTER TWO
REVIEW OF LITERATURE – – – – – – – – 4
2.1 Sub-grade soil – – – – – – – – – 13
2.1.1. Significance of sub-grade soil – – – – – – – 13
2.1.2. Sub-grade strength – – – – – – – – 14
2.1.3. Sub-grade performance – – – – – – – – 14
2.1.3.1. Load bearing capacity – – – – – – – – 14
2.1.2. Sub-grade strength – – – – – – – – 14
2.1.3. Sub-grade performance – – – – – – – – 15
2.1.3.1. Load bearing capacity. – – – – – – – 15
2.3. Soil types-(reff.5) – – – – – – – – – 15
2.4 Index properties of soil – – – – – – – – 16
2.4.1 Liquid limit test- – – – – – – – – – 16
2.4.2 Plastic limit test- – – – – – – – – – 17
2.4.3 Plasticity index- – – – – – – – – – 17
2.5 California Bearing Ratio (CBR) – – – – – – – 17
CHAPTER THREE
EXPERIMENTAL INVESTIGATIONS – – – – – – 19
3.1 Investigation- – – – – – – – – – – 19
3.2 Grain size distribution- – – – – – – – 19
3.2.1 Wet sieve analysis – – – – – – – – – 19
3.2.2 Specific Gravity Test – – – – – – – – 20
3.3 Liquid limit test – – – – – – – – – 20
3.4 Plastic limit test – – – – – – – – – 20
3.5 Compaction test – – – – – – – – – 20
3.6 Modified Proctor Test – – – – – – – – 21
3.7 CBR Test – – – – – – – – – – 21
CHAPTER FOUR
ANALYSIS OF RESULTS AND DISCUSSIONS – – – – 22
4.1 Soil Sample 1 – – – – – – – – – 22
4.2 Soil Sample 2 – – – – – – – – – – 25
Soil Sample 3 – – – – – – – – – – 28
Soil Sample 4 – – – – – – – – – 30
Soil Sample 5 – – – – – – – – – 33
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIN
5.1 Conclusion – – – – – – – – 73
5.2 Recommendation – – – – – – – – 74
REFERNCES – – – – – – – – – 75
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Nigeria, a country in the tropical region is characterized with heavy rainfall and high temperature. It is therefore appropriate to say that climatic factors affect its roads. Many of the roads are flooded with water after heavy rains due to inadequate drainage system. The design of the pavement layers to be laid over sub grade soil starts off with the estimation of sub grade stren gth and the volume of traffic to be carried. Design of the various pavement layers are very much dependent on the strength of the sub grade soil over which they are going to be laid. Sub grade strength is mostly expressed in terms of CBR (California Bearing Ratio). Weaker sub grade essentially requires thicker layers whereas stronger sub grade goes well with thinner pavement layers. The sub grade is always subjected to change in saturation level due to precipitation, capillary action, flood or abrupt rise or subsidal of water table. Change in moisture level in sub grade causes change in the sub grade strength. And it becomes quite essential for an engineer to understand the exact nature of dependence of sub grade strength on moisture variation. An understanding of the dependence of the CBR strength of local soils on water content will contribute towards better design and maintenance practices.
A pavement is a durable surface having materials laid down on an area to sustain mainly the vehicular traffic, such as a road or highway. A pavement is typically a structure of various layers resting over soil, either in embankment or in cutting. In the past, cobblestones and granite sets were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. A pavement is generally classified in two categories, i.e. namely a flexible pavement and a rigid pavement. The flexible pavement consists of granular layers of superior quality in upper layers with a preferably bituminous topping, while a concrete pavement consists of a cement concrete slab over occasional granular layers. The design of pavement has seen several modifications over the years. Traditionally the design of either kind of pavement is based on the strength of the compacted soil in the pavement, called sub-grade. The design of the pavement layers laid over the sub-grade soil starts off with the determination of sub-grade strength and the traffic volume which is to be carried. The design of pavement is very much dependent on the sub-grade strength of soil. Design criteria mainly needs thickness of layers. Weaker sub-grade needs thicker layers whereas stronger sub-grade needs thinner pavement layers. The BS 1377 part 9,1990 provides the exact procedures for the pavement layers design which is based upon the sub-grade strength. The strength of a sub-grade soil is normally expressed in terms of the California Bearing Ratio (CBR).
Due to variable nature of soil, the sub-grade strength changes inconsistently. As a result, engineers face so many difficulties or challenges during the design of a pavement. The sub-grade strength is very much dependent on moisture content. As the sub-grade is subject to variation of moisture due to flood, precipitations or all other climatic changes, so it is necessary to examine the behavior of sub-grade under different moisture conditions.
The CBR is one of such tests that can be used to assess the strength of a sub-grade. By this test we can compare the strength of different sub-grade materials .The CBR test is a standard test used to determine or design the strength or thickness of sub-grade layer. CBR value is inversely proportional to thickness of the pavement layer. If the sub-grade is stronger, the higher is the CBR value, so lesser thickness is required and vice-versa.
1.2 Objectives of study
This project investigates the variations of CBR with moisture content of Awgu soil samples at different periods (days) of soaking. It will also assess the influence of test conditions such as plastic limit ,liquid limit, optimum moisture content , maximum dry density etc, on the CBR values. Thus, various soil samples with different densities and moisture content are tested in order to examine strength variation with water contents by soaking the soil samples for variable number of days. A detailed analysis of results has to be carried out to get this inference.
1.3 Scope of the study
- To collect various soil samples along the Enugu-Portharcourt expressway ,AWGU area and determine the basic physical properties such as plastic limit, liquid limit, and grain size distribution.
- To study the soil under heavy compaction test and determine the optimum moisture content (OMC) and maximum dry density (MDD) for the soil sample.
- To conduct CBR test on different soil samples under different moisture contents over varying days of soaking.
- To study the submergence of soil under different days(1 to 5) of soaking.
ORGANIZATION OF THESIS
- The thesis consists of six chapters as described below:
- Chapter 1 gives a brief introduction of the project
- Chapter 2 deals with a review of previous work on laboratory studies.
- Chapter 3 deals with methodology and experimental investigation.
- Analysis of the results and discussion on the experimental investigations is discussed in Chapter 4.
- Conclusions of this research are summarized in Chapter
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