Expansive Soil Presentaion Msc.pdf

Foundation Construction On Expansive Soils Problematic Soils

Contents • • • • • • • •

Introduction Composition Identification

Properties Associated Problems Mitigation

Case Studies Conclusion

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EXPANSIVE SOILS •

Soils which expand when they gain water and shrink when they loose water

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Also called shrink-swell soils Found in arid & semi arid areas

In Pakistan this soil is found in D.G Khan, Gujranwalla, Sialkot and Khairpur (Sindh).

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EXPANSIVE SOILS

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EXPANSIVE SOILS • They are also commonly known as expansive, or montmorillinitic soils. • Soil volume may expand 10 percent or more as the clay becomes wet. • The powerful force of expansion is capable of exerting pressures of 20,000 psf or greater on foundations, slabs or other confining structures. • Generally their color is reddish brown to brown, but may vary from blackish brown to grey.

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Composition The soils rich in montmorillonite minerals are generally expansive

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Swelling Process

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Identification Direct Observation

Cracks & Popcorn Texture

Soil Survey Maps

Survey Maps Developed By Different Agencies

Identification Mineralogical Identification

Laboratory Testing

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Single Index Method (Indirect Method)

Consolidometer Test (Direct Method)

Properties of Expansive Soils COLOUR

BROWN & RED

LIQUID LIMIT

45-70%

PLASTIC LIMIT

30-50%

SHRINKAGE LIMIT

8-28%

SPECIFIC GRAVITY

2.67-2.8

CLAY CONTENT

35-100% 9

Associated Problems • Misaligned doors and windows • Sticking of Doors and windows • Sloping of the floor • Cracks in the floor or tile • Gaps around the doors and windows • Cracks in the foundation • Differential movement under the same construction • Change of soil level in the same place from up to down according to seasonal changes of moisture content and water table levels

• Doming Of Soil and Cupping Of Soil • Ruptured pipelines • Heaving and cracking of side walks, roads, floor slabs and walls. 10

Associated Problems

Cracking due to differential settlement

Damages due to swelling soil

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Associated Problems

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Associated Problems

Cracks in exterior walls, as a result of upward clay expansion

House built on swelling soil

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Associated Problems

Mitigation Measures • Avoidance • Alter the soil. • All forms of drainage control • Limit the foundation depth if swelling soil is at some depth • Extend building foundations beneath the zone of water content fluctuation • Load the soil to sufficient pressure intensity to balance swell pressures • Chemical treatments • Limit surface infiltration during the rainy winter months • Pre-wetting • Enclosure of Foundation • Deep Foundations • Proper Drainage System 15