CHAPTER I
INTRODUCTION
1.1
Introduction and Background
Compacted soil is an essential element in the construction of highways,
airports, buildings, sewers, and bridges. Even though soil density is not the most
desired engineering property, it is used almost exclusively by the transportation
industry to specify, estimate, measure, and control soil compaction. This practice
was adopted many years ago because soil density can be easily determined via
weight and volume measurements. Soil compaction on construction sites occurs
when foundation and sub-grades are prepared for construction. Soil compaction
decreases porosity, which results in reduced flow of air and water through the
soil. To determine whether the soil is compacted or not the degree of compaction
needs to be quantified. However, measuring soil compaction on construction sites
poses many difficulties. The high degree of variability within an urban soil, and
characterizing soil compaction in deeper soil layers showed that clay soils were
compacted to depths of 0.8m (Randrup, 1997). This study describes alternative
method of determining soil compaction on construction sites. The theory and use
of Nuclear Densometer is presented in detail. The Nuclear Densometer has
become increasingly common on construction site as it was developed for quality
control of sub-grade and base material compaction during road construction.
1.2
Problem Statement
The present methods for measuring density are slow, labor-intensive,
dangerous, and/or of uncertain accuracy. Numerous accidents and fatality has
been reported where technicians were preoccupied with performing Sand
Replacement tests and did not see or hear heavy construction vehicle before it ran
over them. Hence, construction sites are often under sampled, causing inadequate
compaction to go undetected or feedback to be provided too late for the costeffective correction of problems. Sometimes, the opposite is true. Designers are
encouraged to over specify to allow for the significant variability of the finished
product, and contractors are encouraged to over compact to ensure acceptance and
avoid rework. All of which means added cost to the owner.
1.3
Objective
The objectives of this study are to:i)
Determine the result of field density test using Sand Replacement
Method.
ii)
Determine the result of field density test using Nuclear
Densometer Method.
iii)
Correlate the results obtained from Sand Replacement Method
with Nuclear Densometer in determining the soil field density.
1.4
Scope of Study
The location of study selected is the “Electrified Double Track Railway
Project” between Rawang and Ipoh. The project was selected for various reasons
such as the availability of comprehensive and exclusive soil laboratory with the
test equipment required for this study, the vicinity of the project and more
importantly the embankment design and construction which requires a “zero”
settlement rate. Compaction is of an important factor in this project to achieve the
“zero” settlement rate.
1.5
Importance of Study
The importance of this study is to establish the accuracy of the Nuclear
Densometer against the conventional method of Sand Replacement checking the
compacted density of various types of soil. Since this project involves a stretch of
180 km and approximately 20 million cubic meters of earth fill volume it is
arguably the best choice to sample different type of soils. With this study it is
aimed to considerably reduce the time to carry out field density test and results
made available much faster so that time can be saved which means reducing
idling time of earthworks equipment hence the cost of earthworks and overall
project considerably cut. Even though the initial cost of the Nuclear Densometer
equipment is much higher than conventional equipment, but with large number of
test to be carried out (3 numbers of test for 2000m2 of fill) its cost is negligible
compared to the quantity of earth fill.