7/31/2019 soil stab

1/3

Modification of black cotton soils by chemical admixtures is a common method for stabilizing

the swell-shrink tendency of expansive soils. Advantages of chemical stabilization are that

they reduce the swell-shrink tendency of the expansive soils and also render the soils less

plastic. Among the chemical stabilization methods for expansive soils, lime stabilization is

most widely adopted method for improving the swell-shrink characteristics of expansive

soils. Lime stabilization of clays in field is achieved by shallow mixing of lime and soil or bydeep stabilization technique. Shallow stabilization involves scarifying the soil to the required

depth and lime in powder or slurry form is spread and mixed with the soil using a rotovator.

The use of lime as deep stabilizer has been mainly restricted to improve the engineering

behaviour of soft clays Deep stabilization using lime can be divided in three main groups:

lime columns, lime piles and lime slurry injection. Lime columns refer to creation of deep

vertical columns of lime stabilized material. Lime piles are usually holes in the ground filled

with lime. Lime slurry pressure injection, as the name suggests, involves the introduction of

a lime slurry into the ground under pressure. Literature review brings out that lime

stabilization of expansive clays in field is mainly performed by mixing of lime and soil up to

shallow depths. The use of lime as deep stabilizer has been mainly restricted to improve the

engineering behaviour of soft clays. Use of lime in deep stabilization of expansive soilshowever has not been given due attention. There exists a definite need to examine methods

for deep stabilization of expansive soils to prevent the deeper soil layers from causing

distress to the structures in response to the seasonal climatic variations. In addition, there

exists a need for in-situ soil stabilization using lime in case of distressed structures founded

on expansive soil deposits. The physical mixing of lime and soil in shallow stabilization

method ensures efficient contact between lime and clay particles of the soil. It however has

limitation in terms of application as it is only suited for stabilization of expansive soils to

relatively shallow depths. Studies available have not compared the relative efficiency of the

lime pile technique and lime-soil mixing method in altering the physico-chemical, index and

engineering properties of expansive black cotton soils. To achieve the above objectives

laboratory experiments are performed that study: 1. the efficacy of lime piles in stabilizingcompacted black cotton soil specimens from Chitradurga District in Karnataka. The

efficiency of lime piles in chemically stabilizing the compacted black cotton soil mass was

investigated as a function of: a)amount of lime contained in the lime pile b)radial migration

of lime from the central lime pile c)migration of lime as a function of soil depth 2. the

relative impact of the lime pile technique and lime-soil mixing method in altering the

physico-chemical, index and engineering properties of expansive black cotton soil. The

organization of this thesis is as follows After the first introductory chapter, a detailed review

of literature performed towards highlighting the need to examine stabilization of expansive

soils using lime pile technique is brought out in Chapter 2. Chapter 3 presents a detailed

experimental programme of the study. 25 mm and 75 mm diameter lime piles were

installed in the compacted soil mass to study the influence of amount of lime contained inthe lime pile on the soil properties. The amount of quick lime contained in the 25 mm and

75 mm lime piles corresponded to 1 % and 3 % by dry weight of the soil mass respectively.

Radial and vertical migration of lime from the central lime pile was examined by sampling

soil specimens at different radial distances from the central lime pile and at different depths

of soil sample. At a given depth and radial distance, migration of lime was estimated by

comparing the exchangeable cation composition, pH and pore salinity of the treated soil

with that of the natural (untreated) black cotton soil specimen. Alterations in the soil

7/31/2019 soil stab

2/3

engineering properties at a given depth and radial distance were evaluated by comparing

the index properties, swell potential and unconfined compressive strength of the lime pile

treated soil specimen with those of the untreated specimen. To compare the relative

efficiency of lime mixing and lime pile technique in altering the swelling behaviour of black

cotton soil, batches of black cotton soil specimens were treated with 1 % and 3 % quick

lime on dry soil weight basis. The compacted soil-lime mixes were cured at moisturecontents of 31-34 % for a period of 10 days. The physico-chemical, index and engineering

properties of the 1 % lime mixed specimens are compared with those of the 25 mm lime

pile treated specimens. The properties of the 3 % lime mixed soil specimens are compared

with those of the 75 mm lime pile treated specimens. Chapter 4 examines the efficacy of

lime piles in stabilizing compacted black cotton soil specimens from Chitradurga District in

Karnataka. Experimental results showed that controlling the swell potential of deep

expansive soil deposits is possible by the lime pile technique. Treatment with lime pile

caused migration of dissociated calcium and hydroxyl ions into the surrounding soil mass. In

case of 25 mm lime pile, the experimental setup allowed measurement of migration of lime

up to three times the lime pile diameter. In case of 75 mm lime pile, the experimental setup

allowed measurement of migration of lime up to 1.6 times pile diameter. In bothexperiments, migration of lime was also uniform through out the soil depth of 280 mm.

Migration of calcium and hydroxyl ions increased the pore salinity and pH of the treated soil

mass. The increase in pH caused clustering of additional exchangeable calcium ions at the

negative clay particle edges. The increased pore salinity and exchangeable calcium ions

reduced the diffuse ion layer thickness that in turn suppressed the plasticity index and the

swell potential of the compacted expansive soil. The laboratory results hence bring out that

lime pile treatment in the field can substantially reduce the swell potential of the soil at least

to a radial extent of 2 to 3 times the lime pile diameter. The 75 mm lime pile contained lime

content in excess of the initial consumption of lime (ICL) value of the black cotton soil -

namely 2.6 %. Laboratory results showed that migration of hydroxyl ions even from the 75

mm pile could not elevate the soil pH to levels required for soil-lime pozzoIonic reactions(pH 12). The very low solubility of lime in water (< 1 g/litre) and the impervious nature of

the black cotton soil are considered to have impeded efficient interactions between lime and

soil in course of treatment of the expansive soil with lime piles. Absence of soil-lime

pozzolonic reactions precluded the formation of cementation compounds in the lime pile

treated soil specimens. Cementation compounds formed by the soil-lime pozzolonic

reactions are responsible for the much higher strengths of lime stabilized soils.

Consequently, treatment with 25 mm pile had no impact on the unconfined compressive

strength of the black cotton soil. Comparatively, treatment with 75 mm lime pile slightly

increased the strength of the treated soil due to increased inter-particle attraction and

particle flocculation. Chapter 5 compares the relative efficiency of the lime pile technique

and lime-soil mixing method in altering the physico-chemical, index and engineeringproperties of expansive black cotton soil. Experimental results showed that mixing of soil

and lime promote stronger chemical interactions between lime released hydroxyl ions and

clay particles than that achieved by diffusion of lime from a central lime pile. The more

alkaline pH of the lime mixed soil specimens rendered the clay particle edges more

negative. Consequently, more calcium ions were adsorbed at the clay particle edges of the

lime mixed soil specimens imparting them higher exchangeable calcium contents than the

lime pile treated soil specimens. Also, at 3 % lime addition, the pH of the lime-mixed soil

7/31/2019 soil stab

3/3

was sufficiently high (in excess of 12) to cause dissolution of silica and alumina from the

clay lattice necessary for the formation of cementation compounds. The stronger lime

modification reactions plus the lime-soil pozzolonic reactions (applicable for soil treated with

lime content greater than ICL value) achieved by the lime mixing technique rendered the

expansive soil much less plastic, much less expansive and much stronger than the lime pile

treated specimens. The results of the laboratory study hence suggest that if a choice existsin the field between conventional method of spreading-mixing-compacting of soil-lime mixes

and treating the ground with lime piles, the former technique should be adopted because of

its greater efficacy in stabilizing the expansive soil. Chapter 6 summarizes the findings of

the study.