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MCM:115 CONSTRUCTION METHODS & TECHNOLOGYGround Improvement Techniques

Prof. Sanjay Bhoyar

References: Soil Mechanics & Foundation Engineering P. Purushothama Raj Pearson Education

Ground Improvement Techniques P. Purushothama Raj

IS 13094: 1992 Selection of Ground Improvement Techniques for Foundation in Weak Soils Guidelines BIS

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Ground Improvement: Enhancement of the in-place properties of the ground by controlled application of a suitable technique

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Need for Ground Improvement: Soft soil: If the net loading intensity of the foundation exceeds the allowable pressure If, even for relatively low loading intensities, the resultant settlement exceeds the acceptable limits for the structure If the sub-soil is prone to liquefactionNICMAR SANJAY BHOYAR

Remedies for Soft Soils: Designing the structure/ embankment for soft soil Relocating the structure Removing soft soil & replacing it with good one Treating the soil to improve its propertiesNICMAR SANJAY BHOYAR

Methods for GI: Soil compaction Soil stabilization

Soil densification Pre-consolidation

Injection & grouting Soil reinforcementNICMAR SANJAY BHOYAR

Compression of soils: Due to: Elastic distortions

Rearrangement of particles Seepage of water Crushing of particlesNICMAR SANJAY BHOYAR

Compressibility of soils: Initial/ immediate compression: Elastic distortion immediately after load application

Time- dependent compression: Gradual compression due to gradual load transfer from pore water to soil solids ConsolidationNICMAR SANJAY BHOYAR

Primary compression: Completely controlled by resistance to flow of water under the induced hydraulic gradient

Secondary compression: Due to plastic deformation of the soil at zero excess pore water pressureNICMAR SANJAY BHOYAR

Compaction of soils: Increasing the density of a soil using force/ load Packing the particles closer Reduction in air voids Without any significant change in volume of water

Higher compaction Lower the compressibility Higher shear strengthNICMAR SANJAY BHOYAR

State of compaction: Measured by: Dry density, & Associated water content

Maximum dry density & optimum moisture content Standard Proctor Test (IS 2720 part-7) Most applications: highway fills, earth dams

Modified Proctor Test (IS 2720 part-8) Heavier load applications: airport & highway base courseNICMAR SANJAY BHOYAR

Compactive Effort: Application of a given amount of energy per unit volume of compacted soil Static weight (pressure) Kneading action Impact Vibration Dynamic weightNICMAR SANJAY BHOYAR

Compacting Equipment: Smooth wheel roller Pneumatic tired roller Sheeps foot roller Grid/ mesh roller Vibratory rollers Vibratory compactors Plate compactors Earth rammers/ tampersNICMAR SANJAY BHOYAR

Pneumatic tired roller:

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Smooth wheel roller & Sheeps foot roller

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Vibratory Plate compacters

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Field compaction: Process: Transferring soil from borrow areas to the construction site Spreading soil to suitable thickness Adding water Compacting the soil layer

Equipment required: NICMAR

Excavating & hauling Bulldozers & graders Watering equipment Rollers/ special compacting equipmentSANJAY BHOYAR

Compaction Specification: Performance- type specification Physical properties of the compacted layer % of MDD obtained in standard test (95%) Dry density & moisture content Voids ratio Highway & Airfield pavements NICMAR

Work- type specification

Type of equipment Lift thickness The moisture content Amount of work to obtain the necessary density DamsSANJAY BHOYAR

Field control: Checking the density & water content For moisture content: By taking soil samples For every 500-1000 m2, for each layer

For density:

Conventional method slow Proctor needle Lab penetration resistance curve Nuclear moisture gauge

Nuclear density meter - % compactionNICMAR SANJAY BHOYAR

Core- cutter method Sand replacement method

Factors affecting compaction: Moisture content Compactive effort Type of soil Method of compactionNICMAR SANJAY BHOYAR

Degree of compaction contributes to The shear strength The permeability Compressibility Sustainability for repeated loads

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