Expansive Soils DOCX

Title	Expansive Soils
Author	Muhammad Awan
Pages	5
File Size	64 KB
File Type	DOCX
Total Downloads	232
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EXPANSIVE SOILS Muhammad Arslan Awan Abstract: Expansive soils pose a major threat to the structures and contribute towards huge amount of expenditure by the insurance companies each year. This document highlights the mechanisms involved in formation of expansive soils. It explains as to how clay minerals such as Montmorillonite behave with the introduction or removal of moisture causing expansion or shrinkage. It explains the problems faced by engineers due to this type of soils which includes heaving, differential settlement of the structures as well as damage due to tree roots near the foundation of a structure. It presents remedial measures used in the industry to mitigate these issues. A case study related to the settlement of a breakwater in China which was constructed on soft clay has also been discussed. Keywords: Expansive, swelling, shrinkage, volume change, heaving, foundation, trees, PVD's INTRODUCTION Expansive soils could be defined as soils whose volume changes with introduction of moisture i.e. they either swell or shrink with the increase or decrease in moisture content. To understand the concept of swelling or shrinkage, one needs to have a sound knowledge regarding the formation and constituents of expansive soils. It has been argued [ CITATION Wyo11 \n \l 1033 ] that the expansive nature of any soil is due to the presence of a clay mineral known as Montmorillonite. Igneous rocks are decomposed due to weathering forming sheets of Silicon Tetrahedron and Aluminum Octahedral. In well drained soils, these sheets are combined together to form Kaolinite which is not as prone to expansion by the introduction of water as Montmorillonite which is formed in water deficient areas by isomorphous substitution usually of magnesium or ferrous iron for aluminum. Due to high quantity of oxygen present in well drained soils, Kaolinite forms strong hydrogen bond between its molecules whereas Montmorillonite forms weak van der wall forces. Montmorillonite creates micelles with water and cations to neutralize any electrical charge on it. These micelles are either set compactly in a soil or are arranged in a flocculated manner depending upon the soils. This type of soil behaves normally under load unless moisture content increases or decreases in the soil which consequently causes swelling or shrinkage of the soil. These type of soils are ususally found in arid regions due to the loss of moisture content of the soil from evaporation. This prolonged duration of dryness causes an increase in the area to be affected by the introduction of water. According to Y. Du et al. (1999) dry density, matereial composititon and fabric of the soil also plays an important part in the swelling-shrinkage behavior of the soil. Naturally occuring undisturbed soil develops a certain structure and bond between the soil particles which prevents the occurance of swelling in the soil. In comparison to it a laboratory sample lacks that structural orientation of the soil particles due to the continous moulding and application of compressive force on it. Therefore the fabric of soil does affect the rate of swelling in the soil. ENGINEERING ISSUES There are a number of issues related to the structures constructed on an expansive soil. It has been observed [ CITATION Ins12 \l 1033 ] that the structures prone to damage due to swell- shrink behavior of the soil are usually light weight strucutures which are not as efficient as 1...