Assignment

AssignmentSoil Stabilization Methods

Submitted to: Engr. Mehboob Rasool

Prepared By:

Mirza Farquleet Baig

Roll #: l114667

SOIL

From Civil Engineering point of view, soil is an unconsolidated (loose) agglomerates of minerals with or without organic matter found at or near the surface of earth crust, with which or upon which civil engineers build their structures compared to rocks , soil are easy to excavate and generally disintegrate when agitated in water. Soil mass is a particular material consisting of solid particles with voids (pores) filled with air or water or both.

Soil Stabilization

Soil stabilization refers to the process of changing soil properties to improve strength and durability. There are many techniques for soil stabilization, including compaction, dewatering and by adding material to the soil. This summary will focus on mechanical and chemical stabilization

TYPES OF SOIL STABLIZATION

1) Mechanical Mechanical stabilization improves soil properties by mixing other soil materials with the target soil to change the gradation and therefore change the engineering properties.

Dynamic Compaction Soil Reinforcement Addition of Graded Aggregates Materials Mechanical Remediation

2) Chemical

Chemical stabilization used the addition of cementations or pozzolanic materials to improve the soil properties. Chemical stabilization has traditionally relied on Portland cement and lime for chemical stabilization.

Stabilization with Lime Stabilization with Cement Stabilization with Bitumen Stabilization with Fly Ash

3) Physical stabilization4) Electrical stabilization5) Thermal stabilization6) Physic-stabilization

Soil stabilizer at work

Soil Stabilization Process

In soil stabilization we artificially change soil properties for construction purposes at natural site. As result of soil stabilization, the bearing capacity of the foundation of the structure is increased.

The currently-employed technologies for soil stabilization include multiple alternatives. One choice involves the pulverization and homogenization of existing materials in-place, without the addition of an additive to change or improve the characteristics of the material. This technique is typically performed when the in-situ material is suitable.

Stabilization of soil is treatment of soil which renders it more stable in engineering construction. Stabilization means addition and mixing an admixture with soil before compaction is carried out. Stabilization may be applied in place to a soil in its natural position. Stabilization may be applied in a plant and then transported to the site for placement and compaction.

Mechanical Stabilization:

Mechanical stabilization refers to either compaction or the introduction of fibrous and other non- biodegradable reinforcements to the soil. This practice does not require chemical change of the soil. There are several methods used to achieve mechanical stabilization.

(i) Compaction:

Compaction typically employs a heavy weight to increase the soil density by applying pressure from above. Machines such as large soil compactors with vibrating steel drums are often used for this purpose. Here over compaction of the soil should be avoided and given great consideration because in the case of over compaction, the aggregates get crushed and the soil loses its engineering properties.

(ii) Soil Reinforcement:

Soil problems are sometimes remedied by engineered or non engineered mechanical solutions. Geo-textiles and engineered plastic mesh are designed to trap soils and help control erosion, moisture conditions and soil permeability. Larger aggregates such as gravel, stones and boulders are often employed where additional mass and rigidity can prevent soil migration or improve load-bearing properties.

(iii) Addition of graded aggregate materials:

A common method of improving the engineered characteristics of a soil is to add certain aggregates that lend desirable attributes to the soil such as increased strength or decreased plasticity. This method provides material economy, improves support capabilities of the sub-grade and furnishes a working platform for the remaining structure.

(iv) Mechanical Remediation:

Traditionally this has been the accepted practice to deal with soil contamination. This is a technique where contaminated soil is physically removed and relocated to a designated hazardous waste facility far from centers of human population. In recent times however, chemical and bioremediation have proven to be a better solution both economically and environmentally.

Chemical Stabilization

1. Stabilization of soil with Lime:

The use of lime to dry, modify or stabilize soils has been documented in studies as much as fifty years old. When lime is intimately mixed with the soil. The transformation start within a hour of mixing and significant changes are realized within few days depending upon type of lime used. Hydrated lime (calcium hydroxide) is mainly used.

There are two basic types of lime: High Calcium & High Magnesium.

Their soil-stabilizing ability is roughly equal. Quicklime is occasionally used to stabilize heavy clays. Several techniques have been developed for lime stabilization.

Conventional large-area stabilization calls for these steps:

I. Grade areaII. Scarify and pulverize

III. Spread limeIV. Add water during pre laminar mixingV. Rough grade with light compaction

VI. Preliminary cureVII. Final rotary mix and pulverize

VIII. CompactIX. Final cure

Lime should not be spread dry during windy weather because it will create dusting problems. A sprinkling with water will reduce dusting. Lime applied as slurry will eliminate the dusting problem entirely.

The cost of lime stabilization is primarily governed by:

a. The procedure chosen, which depends on the nature of the site, the performance characteristics desired, and the time available for treatment.

b. The type of soil. Heavier clays require longer and more extensive treatment. Low plasticity soils may need a pozzolan.

c. The cost of spreading.d. The quantity of water to be added.

2. Stabilization with Cement :

In cement soil stabilization Portland cement can be used to stabilize and strengthen the Soil. In this method required quantity of Portland cement is spread over the soil uniformly which is to be stabilized. If the moisture content is low it will be necessary to sprinkle the surface with water during process of operation. All soils can be stabilized with Portland cement, provided sufficient quantity is added. Some soils with a high organic content do not react well with cement and hardening may be delayed. As clay content increases, soils become more difficult to pulverize and work, and larger quantities of cement must be added to harden them.

The purpose of the stabilization is to improve the properties of a substandard material.

The method calls for these steps:

a) Grade areab) Scarify, pulverize and pre wet soil as necessaryc) Re graded) Spread Portland cement and mixe) Apply water and mixf) Compactg) Final gradeh) Cure

The central-plant-mixed method calls for this procedure:

i. Grade and compact sub gradeii. Mix soil, cement and water in central plant

iii. Haul mixed material to area and spread

iv. Compactv. Final grade

vi. Cure

Pulverization is necessary with heavier-type soils to break up the soil particles and ensure intimate contact with the cement. Optimum moisture is necessary to both hydrate the cement and facilitate compaction.

The advantages of cement stabilization are several:

Cement stabilization increases base material strength and stiffness, which reduces deflections due to traffic loads. This delays surface distress such as fatigue cracking and extends pavement structure life.

Cement stabilization provides uniform, strong support, which results in reduced stresses to the sub-grade. Testing indicates a thinner cement-stabilized layer can reduce stresses more effectively than a thicker un-stabilized layer of aggregate. This reduces sub-grade failure, pothole formation and rough pavement surfaces.

Cement stabilization reduces the potential for pumping of sub grade fines.

Cement stabilized base spreads loads and reduces sub-grade stress.

3. Soil stabilization with bitumen:

Soil stabilization with bitumen can be done with either of two additives.

Depending upon project conditions, the choice is made between using an asphalt emulsion or using foamed bitumen as the additive. For example, extremely wet soil conditions might dictate the use of foamed bitumen rather than standard asphalt emulsion to compensate for the high field moisture content. Emulsion might be chosen for projects where high-performance emulsions are readily available. Therefore, cost and product availability are practical considerations for stabilization with bitumen, just as with other construction activities.

4. Soil stabilization with Fly Ash:

Fly ash was chosen as the agent to stabilize these highly variable soil types to produce a stable base. Fly ash was spread by distributor truck at an application rate. The fly ash was mixed with the existing sub grade to a depth of (12 inches); water was used to activate the ash‘s

Load distribution

bonding with the in-situ sub grade materials. The stabilized material was then compacted with a pad foot vibratory compactor, and graded to proper profile.

Physical stabilization

In the technique of physical stabilization , the physical properties of the material (soil)are improve by blending two or three soil , together so as to improve the gradation of the mixture to well graded material. This technique is usually used in the construction of roads when more than one type of soil is readily available at or near the site.

Thermal stabilization

Thermal analysis involves a dynamic phenomenological approach to the study of soils by observing its response to a change in temperature. Infrastructure projects such as highways, railways, water reservoirs, reclamation etc. requires earth material in very large quantity. In urban areas, borrow earth is not easily available which has to be hauled from a long distance. Quite often, large areas are covered with highly plastic and expansive soil, which is not suitable for such purpose. Extensive laboratory / field trials have been carried out by various researchers and have shown promising results for application of such expansive soil after

Stabilization with additives such as sand, silt, lime, fly ash, etc. As fly ash is freely available, for projects in the vicinity of a Thermal Power Plants, it can be used for stabilization of expansive soils for various uses.

Electrical stabilization

A plurality of rows of wells are drilled in the soil of the area to be stabilized, and then pairs of electrodes, i.e., an aluminum anode and a copper-graphite cathode connected to a source of a bipolar pulse current, are inserted into each well in such a manner that during operation all anodes of odd wells are connected to a positive terminal (for odd pulses) of the source, while all

cathodes of even wells are connected to a negative terminal (for odd pulses) of the source. After a certain period of treatment the anodes and cathodes are reversed so that all anodes of even wells are connected to the positive terminals (for even pulses) of the source, whereas the cathodes of the odd wells are connected to the negative terminal of the source. Controlled directional structuring of the soil mass is carried out by adjusting the duration of current pulses, intervals between two sequential bipolar pulses of pulse current, and current density in the pulses. Prior to initiation of the soil stabilization process, salts, which correspond to the type of treated soil, are introduced into the wells. Furthermore, water under pressure is fed to the area of the soil being current stabilized as an additional measure for affecting soil temperature control.

Physic-chemical stabilization

Stabilization of soil using both the physical and chemical method such as lime stabilization or cement stabilization etc is known as physic-stabilization of a soil the picture given below is showing the physic-chemical stabilization of soil. Foundry sand used to stabilize poor soilfor working platform.