An Investigation of Soil Volume Changes at Four Dimensional Points of Peat Soil Sample in Parit Nipah and Pontian

Peat soils occur in many countries and formed naturally through the decomposition of plant and animal matter. These soils are known as a very problematic soft soil due to its low bearing capacity and high compressibility. These two main factors may be based on the characteristics of the soil itself. This study is focused on its physical properties and shrinkage measurement. It is also to investigate the shrinkage measurement that was obtained from the diameter of the samples at four dimensional points and bar linear shrinkage method for both location peat samples. There are various method that can be used in order to obtain a full description of the shrinkage behaviour of peat. The sample was taken from two different locations which are Parit Nipah and Pontian. The linear shrinkage method is used to determine the soil shrinkage from linear measurements on a bar mould with disturbed soil that passing 0.425mm sieve. However, this method was modified by using undisturbed samples to compare the result with bar linear shrinkage method and the measurement was obtained by the reduction of its diameter at four points of the sample. Linear shrinkage values obtained from Parit Nipah and Pontian by following British Standard method are 34.77% and 33.09% respectively while modified linear method gives the value of 35.25% for Parit Nipah and 32.85% for Pontian. Modified method shows that peat soil from both locations shrinks in irregular shape due to Point C of Parit Nipah and Pontian peat sample has the smallest diameter compared to other points within 24 hours oven-dried. It also shows that Parit Nipah peat soil has a higher percentage of linear shrinkage for both methods instead of Pontian peat soil. The linear shrinkage values that obtained from bar linear shrinkage and modified linear shrinkage gives smaller different values which are nearly same for both methods.


Introduction
In civil engineering, there are many construction problems related to the development on soft soil areas especially peat soil area.According to soil taxonomy, peat consists of three organic matter decomposition stages that are fibric, hemic and sapric.This type of soil is also considered as most problematic soil due to its low bearing capacity and very high compressibility.There are two main factors poses as a challenge to constructions when they deal with this type of soil [1].
Peat soil areas can be found in South East Asia about two thirds of 30 million hectares [1].[2] stated that there are more than three million hectares of peat and organic soil areas in Malaysia which consists of 8% of the total areas.Before beginning with any construction works, the study of shrinkage behaviour of peat soil has to be conducted in order to avoid any failure in future development.There are several tests can be determined the shrinkage measurement of soil.Linear shrinkage and shrinkage limit is one of testing that can be conducted.This study was focused on the shrinkage tests on peat samples from two different locations in the state of Johore.
Due to the rapid development of infrastructure in Malaysia, the construction on peat soil areas have to be stabilized and implemented.The construction of roadways and structures on peat soil will always be exposed to enormous deposition and unstable condition.The shrinkage characteristics of peat soil may lead to the failure of a structure.

Purpose and Scope of Study
The purposes of this study are to investigate its physical properties and shrinkage measurement that obtained from the diameter at four dimensional points and bar linear shrinkage method.It is also to compare the shrinkage behaviour of peat soil in two different locations.
The study towards the shrinkage behaviour of peat soil was conducted on undisturbed samples from Parit Nipah and Pontian.All the samples were collected at 0.5m depth from the top surface of soil.The tests that involved in this study are linear shrinkage method that according to BS1377: Part 1:1990 that had been modified which compatible with real phenomenon.All these tests were conducted at the Research Centre for Soft Soils (RECESS), Universiti Tun Hussein Onn Malaysia.

Literature Review on Peat Soil and Linear Shrinkage
Peat soil definition.The definition of peat varies between soil science and engineering as well as different countries.According to the soil scientists, peat soil has an organic content more than 35%, whilst geotechnical engineers stated that all the soils with organic content larger than 20% is known as organic soil.Peat soil is an organic soil which has organic content more than 75% [3].
The organic contents classified as peat is basically remains of plant whose rate of accumulation is faster than the rate of decay.The content of peat soils differs from locations due to the factors such as temperature and degree of humification.Decomposition or humidification involves the loss of organic matter either in gas or solution, the disappearance of the physical structure and change in chemical state [3].
Based on the fibre content classification, peat is divided into three groups that are fibric, hemic and sapric.Fibrous peat has a high organic and fibre content with a low degree of humification.It consists of undecomposed fibrous organic materials, easily identifiable and extremely acidic meanwhile sapric peat contains highly decomposed materials.Peat may be classified on the basis of their degree of decomposition.The scale used is known as 'Von Post Classification' which conventionally divides peats into ten classes, named H1 to H10 [2].

Physical properties of peat.
There are a few unique physical properties of peat, which should be taken into account when discussing on peat soil.As referred in [2], the physical characteristics such as colour, degree of humification, water content and organic content should be included in a full description of peat.Degree of humification represents the degree of organic content that had decayed.Organic content is a measurement of peat purification from any mineral component and it is important to the classification of peat and related to the morphology of peat deposition.In West Malaysia, the moisture content ranges from 200 to 700% [2].
Meanwhile, specific gravity of peat is greatly affected by its composition and percentage of the inorganic component.Degree of decomposition and mineral content will increase due to increase of specific gravity.Peat is known as high organic content which is 75% and above while the value of specific gravity is in the range 1.3 to 1.8 [2].
Mechanical properties of peat.An important characteristic of organic soils is the shrinkage that accompanies the drainage and the resulting decrease of the base volume.Moreover, in strongly drained fen peat soils, high evaporation rates can lead to reversible shrinkage cracks and clefts [4].
The shrinkage of the soil material, especially the initial shrinkage, leads to strong alterations of the special pore structure [5].Peat will shrink when it gets dry and the shrinkage could reach 50% of the initial volume.However, the dried peat will not swell up upon saturation due to incapability of dried peat to absorb water as much as initial condition; only 33 to 55% of water can be reabsorbed [2].The common value of shrinkage is in the range of 20 -40 in West Malaysia as referred in [6].

Materials and Methods
Some past research had been reviewed to provide rationale data of the study and to give some information on the physical properties of the peat soil.This study was focused on the shrinkage behavior of peat soils.It is determined by two different linear shrinkage method which are bar linear shrinkage that followed by British Standard and modified linear shrinkage which is more compatible with the real phenomenon due to non-homogenous particle in soil.
Bar linear method was used disturbed sample that passing 425µm wet sieving.The shrinkage mould filled by sample with linear measurement of 139mm was first placed open aired until the soil has shrunk away from the walls of the moulds.Then, it is placed in the oven at a temperature not exceeding 65⁰C until shrinkage has largely ceased, and lastly at 105⁰C oven-dried to complete the drying process.
However, the modified linear method was conducted an undisturbed peat sample by placing the mould with samples directly into 105⁰C oven-dried within 24 hours.An undisturbed sample with diameter approximately 75mm and 20mm height was used in this method.The diameter changes were measured by point A, B, C and D as illustrated in Fig. 1.The reading of soil shrinkage for both method was taken at 0.5, 1, 2, 4, 6, 20 and 24 hours.All these laboratory test procedures are followed BS1377-2: 1990 except for the modified shrinkage method.The data obtained was analysed and compared with previous studies to make a conclusion.Organic content.The value of organic content is usually determined from the loss of ignition test as a percentage of oven-dried mass.From the test that have been conducted, the organic content value obtained from Parit Nipah peat soil is 89.87% while the organic content of Pontian peat soil is 75.45%.It can be concluded that the organic content of Parit Nipah was higher than Pontian but it is still in the ranges of organic content values for West Malaysia which is 65-97% [2].Specific gravity.The average value of specific gravity that obtained from Parit Nipah and Pontian were 1.43 and 1.62 respectively which is in the ranges of specific gravity for West Malaysia peat which is 1.38 to 1.70 [2].
Linear Shrinkage.The linear shrinkage of peat soil was determined by using two different methods.The first method is linear Shrinkage Limit test according to BS1377-2 and another method was called as a modified linear method by directly placing the sample into 105⁰C oven-dried.This method was conducted in order to determine the linear shrinkage of the fraction of a soil sample that passing 425µm test sieve from linear measurements on a bar of soil.
Bar Linear Shrinkage.The values of linear shrinkage that obtained from linear method that followed to British Standard are 34.77% and 33.09% for Parit Nipah and Pontian respectively.Modified Linear Shrinkage.A modified linear shrinkage test was conducted in order to show that the linear shrinkage value of peat samples can be determined in various methods.In this study, undisturbed samples are used in this testing in order to make it compatible with real phenomenon.The measurement of the shrinking soil sample was measured by point A, B, C and D and the shrinkage behaviour was determined by 105⁰C of drying temperature.The modified linear shrinkage method gave the value of 35.25% for the Parit Nipah peat sample and 32.85% of the Pontian peat sample.According to the previous study, these values are in the range of shrinkage for West Malaysia peat which is in the range 20-40% [6].  4 shows that Point C of Parit Nipah and Pontian peat sample has the smallest diameter compared to other points.The greatest shrinkage measurement of both samples was shown after 6 hours oven-dried.It shows that the optimum shrinkage of the peat soil occurred when the surrounding temperature was high and reached its shrinkage limit within 20 hours.After the period, there are no any changes to the diameter of the peat soil specimen.
The diameter value of the sample is directly proportional to the volume of sample.The volume will decrease if the diameter value were decreased.The volume of peat sample for both locations were higher when it is wet and started to decrease as the soil sample was dried and shrunk.It is also shown that the shrinkage parameter is variable due to non-homogenous particles.The diameter changes of sample from four points during shrinkage testing were different.Table 2 shows the summary of data for all tests that had been conducted.Modified shrinkage data were obtained from the average of four point measurement.

Conclusions
From this study, it can be concluded as follows: a) The study of peat soil behaviour from two different locations had been obtained from the determination of its physical properties and shrinkage measurements of the soil.b) Parit Nipah peat soil has a higher percentage of linear shrinkage for both methods instead of Pontian peat soil.c) The linear shrinkage values that obtained from bar linear shrinkage and modified linear shrinkage gives agreeing values with minimal difference d) All of the values obtained are satisfied with the previous literature.e) The shrinkage measurement during the drying process influenced the volume of peat soil as the volume decreases when the soil shrunk.It is also shown that there are no volume changes during the drying process within 24 hours.

Table 2 :
Summary of the data