GROUND IMPROVEMENT TECHNIQUE BY GROUTING NACHIKETHAN VIII CIVIL

CONTENTS INTRODUCTION GENERAL DESCRIPTION ABOUT GROUTING TYPES OF GROUTING MATERIAL METHODS OF GROUTING APPLICATIONS OF GROUT CASE STUDY CONCLUSION REFERENCES

INTRODUCTION

WHAT IS GROUND IMPROVEMENT TECHNIQUE? Ground improvement technique is the process of improving the geo- technical characteristics of soil used in construction. The soil at a construction site is not always totally suitable for supporting structures such as buildings, bridges, highways and dams. For example, In granular soils, in-situ soil may be very loose and indicate large elastic settlement. Under these conditions, soil needs to be densified to increase its unit weight and shear strength. .

Objectives of ground improvement is to: Reduce settlement of structures. Improve shear strength and bearing capacity of shallow foundations. Increase factor of safety against possible slope failure of embankments and dams. Reduce shrinkage and swelling of soils

TYPES OF GROUND IMPROVEMENT TECHNIQUES COMPACTION PILE BLASTING PRE-COMPRESSION STONE COLUMN VIBROFLOATATION GROUTING THERMAL TREATMENT ELECTRO OSMOSIS

GROUTING Grouting is a process where by fluid like material, either in suspension or in solution form are injected into subsurface soil or rock to achieve a decrease in permeability and compressibility, to improve its strength or to decrease seepage flow. The treatment may be applied as a preventive measure before construction or as a rehabilitative treatment for structures suffering post construction distress due to poor soil condition.

AIMS OF GROUTING To decrease the permeability. To decrease the compressibility To increase the shear strength. To increase resistance against deformation To reduce conductivity and interconnected porosity To supply cohesion

GROUT PROVES MORE EFFECTIVE IN THE FOLLOWING CASES When the foundation has to be constructed below ground water table. When there is difficult to the foundation level (ex: city work, tunnel shafts, sewers, subway construction). When the geometric dimensions of the foundations are complicated and involves many boundaries and contact zones. When the adjacent structure require that the soil of the foundation strata should not be excavated In case of structures suffering post construction distress due to poor soil condition

GROUT MATERIALS

CLASSIFICATION OF GROUT MATERIALS A large variety of materials can be used for grouting; the selection depends on requirements of durability, penetration, and strength. Grout materials are classified as follows. SUSPENSION GROUT EMULSION GROUT SOLUTION GROUT

SUSPENSION GROUT This type comprises of mixture of cement plus water and other particulate solids such as clay, fly ash, lime, asphalt emulsion etc. such type of mixtures depending on their compositions, may prove to be stable(i.e., have minimal bleeding) or unstable when left at rest .Stable grouts have both cohesion and plastic viscosity, increasing with time. These suspensions are injected into soil mass to promote permeation. One of the most commonly adopted suspension grout is cement grout

SOLUTION GROUT EMULSION GROUT These are Colloidal solutions, evolutive Newtonian fluids in which viscosity progressively increases with time. Ex: sodium silicate based SOLUTION GROUT Pure solutions, nonevolutive Newtonian solutions in which viscosity is essentially constant until setting, within a controlled period. The liquid homogeneous molecular mixtures of two or more substances is solution grout. Ex: organic resins and a wide variety of chemical grouts

PRINCIPLE TYPES OF GROUT

LIMITATIONS OF CHEMICAL GROUT With chemical grouts, toxicity and permanency have also become an issue. Permanency refers to the resistance against mechanical deterioration due to freeze-thaw or wetting and drying cycles and chemical degradation by reaction with the ground water or soil constituents. Toxicity refers to health hazards in handling the grout and its effects on the quality of the groundwater it is in contact with. Unfortunately, the high-strength, high permanent grouts seem to present the greatest risk with respect to handling, ground water pollution, and corrosion

TYPES OF GROUTING

PENETRATION OR PERMREATION GROUTING DEFINITION: Penetration grouting describes the process of filling joints or fractures in rock or pore spaces in soil with a grout without disturbing the formation. Permeation Grouting is defined as a means of impregnating the voids within a soil or rock mass and thereby displacing water and air from the voids and replacing it with grout, without displacing the soil particles or widening the existing fissures in the rock.

ADVANTAGES Economical cost. Controlled and accurate placement. Non-vibratory. Formation is undisturbed Limited workspace required

COMPACTION GROUTING The basic concept of compaction grouting is that of injecting a growing bulb of grout that acts as a radial hydraulic jack, displacing surrounding soil particles and thus radially compacting the soil from the point of injection. This grouting uses controlled displacement to increase the density of soft or loose soils. It is typically used for settlement control and structural re- leveling .

Advantages of compaction grouting Effective in a variety of soil conditions Non-hazardous No waste soil disposal Able to reach depths unattainable by other methods

HYDROFRACTURE GROUTING Definition: If the grouting pressure is greater than the tensile strength of the soil or rock being grouted, the soil or rock fails resulting in fractured zone. The grout penetrates this fractured zone forming densified region of soil or rock masses.

The ground is deliberately split by injecting stable but fluid cement-based grouts at high pressures (e.g., up to 4 MPa). the lenses sheets of grout so formed are thought to increase total stress, fill unconnected voids, possibly consolidate the soil locally, and, conceptually, create mainly horizontal, impermeable barriers. However, hydro fracture grouting’s effects are difficult to control, and the potential danger of damaging adjacent structures by the use of high pressure often proves prohibitive. Hydro fracture naturally occurs with conventional cement-based grouts in soil with a permeability of less than 10^-1 cm/sec.

Advantages of Hydro fracture grouting system The control of settlement is carried out from outside the building and hence there is no disruption to the occupants The process can be repeated allowing continued control of settlement (if required)

JET GROUTING The ASCE Geotechnical Engineering Division Committee on grouting defined Jet grouting as a “technique utilizing a special drill bit with horizontal and vertical high speed water jets to excavate alluvial soils and produce hard impervious column by pumping grout through the horizontal nozzles that jets and mixes with foundation material as the drill bit is with drawn”. Can be applied to soils ranging from gravel to clays.

Advantages Nearly all soil types grout able No harmful vibrations Can be performed in limited workspace Maintenance free Safest method of under pinning construction Much faster than alternative method

APPLICATIONS Control of ground water during construction. Void filling to prevent excessive settlement. Soil strengthening to reduce lateral support requirements. Stabilization of loose sands against liquefaction. Foundation underpinning.

CASE STUDY

Dales ford lake development –Berwyn,Pennsylvania. A luxury, four unit town house structure founded on timber piles had exhibited structural distress related to sink hole activity.Surface investigation revealed 5-30ft of miscellaneous fill,including wood chips and building materials, overlaying clay soil. Beneath this,pinnacled karastic lime stone was encountered at depths ranging between 10 and 30ft.Grout pipes were installed to an average depth of 16 to 21ft. Compaction grouting was performed to stabilize the driven pile foundation, re-establish ground contact with the structure, and halt the soil piping that had resulted from sink hole activity.The work was successfully completed while the building remained occupied.  

CONCLUSION Many engineers still consider this grouting technique as a art rather than science. Its successful application requires great deal of experience, thorough knowledge of geological condition and awareness of equipment capabilities and limitations. The overall success of grouting technology is less than 50% of intended goals.

REFERENCES http://www.austressmenard.com.au/permation_grouting.php http://www.judycompany.com/compaction_grouting.htm Ground Improvement by M.P.Moseley Koerner, R. M, (1985) construction and Geotechnical Methods in Foundation Engineering, McGraw Hill Book Company,Newyork. Hausmann, M.R, (1990), Engineering Principles of Ground Modification. McGraw Hill Publishing Company, Newyork. www.hayward baker.com

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