Soil Improvement by Grouting

SOIL IMPROVEMENT BY GROUTING AND GEOSYNTHETICS

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Contents:• Introduction to grouting• Purpose of grouting• applications• Methods of grouting

– Intrusion grouting– Permeation grouting– Compaction grouting– Jet grouting– Compensation grouting– Deep mixing method– Chemical grouting

• Geo synthetics• Conclusion• references

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Introduction:• Defined as the injection of a special liquid or slurry material

called grout into the ground for the purpose of improving the soil or rock.

• Grouting generally is used to fill voids in the ground with the aim to increase resistance against deformation, to supply cohesion, shear-strength and uniaxial compressive strength.

DESIGN STEPS:

1.Identify underground construction problem, 2.Establish objectives of grouting program, 3.Perform special geotechnical study, 4.Develop initial grouting program, 5.Develop performance prediction, 6.Compare with other solutions, 7.Refine design and prepare specifications.

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Purpose of grouting:

• The purpose of injecting a grout may be any one or more of the following:

• Void filling to prevent excessive settlement.• Strengthening adjacent foundation soils to protect them

against damage during excavation, Pile driving, etc.• Soil Strengthening to reduce lateral support

requirements.• Stabilization of loose sands against Liquefaction.• Foundation Underpinning.• Reduction of machine foundation vibrations.

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Advantages:

• Can be performed on almost any ground condition. • It doesn't induce vibration and can be controlled to avoid

structural damages.• Improvements to ground formations can be measured.• Very useful for confined spaces and low headroom

applications.• Used for slab jacking to lift or level distorted foundations.• Can be installed adjacent to existing walls.• Can be used to control seepage, groundwater flows and

hazardous waste plumes.

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METHODS OF GROUTING:Intrusion grouting:• Consists of filling joints or fractures with grout.• Primary benefit is reduction in hydraulic conductivity.• Used to prepare foundation and abutments for dams.• Usually done using cementitious grouts.

Permeation grouting:• Injection of thin grouts into the soil.• Once the soil cures, becomes a solid mass.• Done using chemical grouts.• Used for creating groundwater barriers or preparing ground

before tunneling.

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Compaction grouting:• In this method, grout mix is specifically designed so

as not to permeate the soil voids or mix with the soil.• Instead, it displaces the soil into which it is injected.

• In Compaction grouting a very stiff (say 25-mm slump) mortar is injected into loose soils, forming grout bulbs.

• bulbs displace and densify the surrounding ground, without penetrating the soil pores.

• Used to repair structures that have excessive settlement.

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Jet grouti ng:

• Jet Grouting or High Pressure Grouting can be employed in all soils from clays to coarse gravels irrespective of grain size distribution void ratio or pore sizes.

• Jet grouting uses a high pressure jet (approx. 400 bar) to cut the natural soil in order to mix and partially replace it with the grout.

Uses:• Underpinning of existing structures.• Downward extension of foundations in the case of settlements or

increased load.• Soil improvement, even underneath existing structures.• Vertical impervious barriers.

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Jet grouting:

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Grout body produced by jetgrouting (Soilcrete Columns)

Grout body produced by lowpressure conventional grouting(Injection Grouting)

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Jet grouting:

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Compensation Grouting:

• Compensation grouting is the responsive use of compaction, permeation or hydro fracture grouting as an intervention between an existing structure and an engineering operation (particularly tunnel excavations).

• The aim is minimize movement of the ground that would affect the existing structure.

Uses: Structures where subsidence occurs due to tunneling. Slide 19

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Deep mixing method:

• This Method is today accepted world-wide as a soil improvement method

• Which is performed to improve the strength, deformation properties and permeability of the soil.

• It is based on mixing binders, such as cement, lime, fly ash and other additives, with the soil by the use of rotating mixing tools

• This forms columns of a hardening material since pozzolanic reactions between the binder and the soil grains are developed like in the case of jet grouting.

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Chemical grouting: • Chemical grout is defined as any grouting material

characterized by being a pure solution; no particles in suspension.

• The chemicals used are Sodium silicate, Acrylamide, Acrylate and Urethane.

The grout material should be, A powder readily soluble in water. Inexpensive and derived from chemicals in abundant supply. Stable at all anticipated storage conditions. Nontoxic. Noncorrosive.Non explosive.

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Chemical grouting:The grout solution should be: A low-viscosity solution, preferably that of water. Stable under all normal temperatures. Nontoxic, non corrosive, non explosive. Catalyzed with common, inexpensive chemicals. Insensitive to salts normally found in groundwater. Should have stable pH on the positive side Readily controlled for varying gel times. Able to withstand appreciable dilution with groundwater.

The end-product should be:• Permanent gel.• Unaffected by chemicals normally found in groundwater.• Nontoxic, non corrosive, non explosive.• High strength.

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Applicability of grouting as per grain size:

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Goe synthetics:

Soil is stronger in compression than in tension. To improve strength in tension, geo synthetics

placed in soil for soil reinforcement.Types:

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Applications and uses of geo synthetics:• A geotextile is a permeable geosynthetic made

of textile materials. • Geogrids are primarily used for reinforcement;

they are formed by a regular network of tensile elements with apertures of sufficient size to interlock with surrounding fill material.

• Geomembranes are low permeability geosynthetics used as fluid barriers.

Geosynthetics have six primary functions:1. filtration, 2. drainage, 3. separation, 4. reinforcement, 5. fluid barrier, and 6. protection.

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Uses:

• Geotextiles are often used as separators to prevent fine- grained sub grade soils from being pumped into permeable, granular road bases and to prevent road base materials from penetrating into the underlying soft sub grade.

• Geogrid and geotextile reinforcement enables embankments to be constructed over very soft foundations. They are also used to construct stable slopes at much steeper angles than would otherwise be possible.

• Geomembranes, thin-film geotextile composites, geosynthetic-clay liners, and field-coated Geotextiles are used as fluid barriers to impede the flow of a liquid or gas from one location to another.

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Conclusion:

The demand for improving and stabilizing land for different purposes is expected to increase in the future and the best way to fulfill it is by using deep mixing methods.

The technology of grouting is not new; it is constantly developing with innovation of new materials and construction technique.

Geosynthetics is also increasingly and effectively use for soil improvement nowadays.

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References:

• Purushothama Raj.P, “grouting techniques”, Ground improvement techniques.

• “Chemical Grouting and Soil Stabilization”, By Reuben H. Karol.

• “Assessment and Comparison of Grouting and Injection Methods In Geotechnical Engineering” by Sina Kazemian.

• Bowen, R. 1981. “Grouting in Engineering Practice”, 2ndEdition, Applied Science, New York.

• Robert D. Holtz, “Geosynthetics for soil reinforcement”.

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THANK YOU

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Compensation grouting: