LITERATURE REVIEW

INTRODUCTION

Grouting which has several application in the field of civil engineering was once considered as a mysterious operation. The effectiveness of grouting requires a lot of understanding, skill, meticulous attention and an intuitive perception. Even though grouting was started 200 years ago, it was treated for a long time, as an art which included scientific investigation and improvement (Nonveiller, 1989). Its performance was for some time, more or less or privilege and a well protected secret of a few specialist companies. The curious image of grouting is changing slowly, as research and development broaden our knowledge in this area.

Grouting is a procedure by means of which grout is injected into folds, fissures, crevices or cavities in soil or rock formation in order to improve their properties specifically to reduce permeability, to improve strength or to reduce the deformability of formations. Grouting has a wide application under the water retaining structures, control the erosion of soil, increase the strength of material below foundation of heavy structure and a reduced deformability of the material in the foundation, fill the voids between rock and tunnel linings, form cut off walls, fill voids for reabilitation e.t.c.

Grouting is injected under pressure into the material to be grouted until fills the desired volume of material around the hole or until the maximum specified pressure is attained and a specific minimum grout flow is reached from injected watery suspension, injected water is squeezed out in the pores and the compacted mass of the injected compound fills the fissures and voids.

STRENGTH IMPROVEMENT ON DENSIFICATION

Numerous instances arise of soils at a site being of inadequate strength to support a proposal structure and for which the needed improvement cannot be obtained using such method as vibration rolling or preloading either because of economics consideration (Shroff and Shah, 1992).

Soil compaction can offer effective solution for many foundation problems and is especially useful for reducing total settlements in sands. However, efficient use of soil compaction methods requires that the geotechnical engineer understands all factors that influence in compaction process carefully. The poor quality soils especially their low bearing capacity; make it necessary to improve their properties by stabilization. Soil compaction requires geotechnical competence and carefully planning on the part of the design engineer. The selection of the most suitable method depends on a variety of factors, such as soil condition, required degree of compaction, as well as site specific considerations, available time for completion of the project, competence of the contractor, access to equipment and materials e.t.c. (Massarch and Fellenius, 2002).

Bement and Selby (1997) investigated the compaction settlement of granular soils when exposed to vibrations typical of these generated in the ground by vibrodiving piles that the compaction of soil is strongly dependent upon vertical effective stress, the type and grading of the soils. Broadly, a well graded soil compact more than a uniform soil, the moisture content is also a significant parameter and saturated soils compact the most with much smaller settlement from dry soil.

For cohesionless soils with dominant particle size increase, the angle of shearing resistance increases with increase of particle size at both resistant density and constant relative density. However, the increase for constant density is insignificant compared to that in the case of constant relative density for increase in relative density for any particle size of cohensionless soils. There is a definite increase in angle shearing resistances. But the rate of increase of angle of shearing resistance with respect to relative density is much higher at bigger size particles compared to that of lower sizes (Chattopadhya and Saha, 1981).

GROUTING TECHNIQUE

Soil stabilization with content grouts injected under pressure has come into wide spread use in construction. At present, the method of grouting is highly prevalent in a number of branches of structural engineering, in hydraulic engineering for the building of anti seepage curtains for imparting mono-lithicity and impenetrability to the concrete masonry of structures; in mining for the opening of shafts, side drifts, and other workings; and in foundation engineering for the reinforcement of existing foundations beneath buildings and structures as well strengthening the soils in their beds. The primary merits of the method of grouting lie in its technical simplicity, convenience of use, and high reliability of the results achieved. Moreover, the method is sufficiently economic and does not require complex equipment and is also ecologically safe for the environment (Ibragimov, 2005).

Permeation grouting is commonly used in geotechnical engineering either to reduce the permeability or improve the mechanical properties of soil and rock. Success in a given grouting operation requires that the desired improvements in the properties of the formation are attained. Grouts are generally categorized as suspension or particulate grouts, which are prepared with ordinary Portland or other cements, clays, or cement-clay mixtures, and fine sand in some cases, and solution, or chemical grouts, which include sodium silicate acrylamide, acrylates, lignosulfonates, phenoplast and aminoplast as well as other material that have no particles in suspension (Zebovitz et al, 1987).

Jet grouting done to stabilize underlying marine clay using double fluid system, a thick layer of jet grouting pile provided from 5m thick using ultra high pressure cement grout under controlled insertion, rotation and withdrawal. The formed jet grouting pile, increase in shear strength acts as a barrier forming impermeable strate, structs the sheet pile as structural support excavation (Vadivel, 2006)

Compaction grouting could be effectively used to mitigate liquefaction of the susceptible soils. The greatest improvement from grouting was achieved in sands. Silts were also improved but the grouting was less effective (Miller and Royerof, 2004).

Microfine cement suspensions with a water: Cement ration of 4 or higher can be successfully injected into fine sand (D10 as low as 0.15mm with a hydraulic radius as small as 0.002mm) under a pressure of about 10psi and will have a depth of penetration of at least one half meter. Cement particles are captured around the contact points between and grains and are deposited on the grain surface to form a thick cake, which upon hardening, provides the grouted mass with improved mechanical properties. Microfine cement grouts are being proposed increasingly as an alternative to chemical grouts (which often contain one or more toxic components) for grouting fine sands, but their successful use is influenced strongly by the relationship between the suspended solids (individuals particles pr particle aggregations) in the grout the pores in the porous medium. Although advocated by some practitioners, the use of concentrated (low water: cement ratio) suspensions and high injection pressures can lead to non-homogenity in the grouting of a soil formation due to the development of preferential paths during injection or hydraulic fracturing of the soil mass (Arenzana et al, 1989)

The concept of a limiting effect or a boundry effect of grouting is of great value in both theoretical research and the practical application of grouted sand. The selection of grouting for a specific job is mainly affected by the amount of improvement, in strength and/or stiffness, that can be achieved, and the limitations for this improvement, in strength with increased depth or confinement (Ata and Vipulonandan, 1999). Particle size distributions are used in characterizing the soil and to determine the grouting ability of soil (Vipulanandan and Orgunel, 2009).

The procedure adoption for preparation of a grouted bed in the laboratory was given by Dane et al; (2004). The sand was placed with zero fall height in a transparent and rigid cylindrical column made of PVC of diameter of 80mm and a height of 900mm. A few simultaneous hammer strokes on the PVC tube compacted the soil. A fixed volume of grout equal to 1.2 times the initial volume of the granular skeleton was the injected from the base to the top of the column at a flow rate of 3cm3/s column was kept in a humid condition for a period of 28 days.

LittleJohn (1982), Lowe and Standford (1982) Clarke et al (1992) and Schwarz and Krizek (1992) made significant contribution on the study of grout materials, properties, equipment and procedure for grouting.

The safe construction and operation of many structures frequently require improvement of the mechanical properties and behaviour of soils by permeation grouting using either suspensions or chemical solutions. The former have lower lost and are harmless to the environment but cannot be infected into soils with gradations finer than coarse sands. The latter can be injected fine sand or coarse silts but are more expensive and some of them pose a health and environmental hazard (Karot, 1982, 1985). Grouting has a minimal effect on the angle of internal friction of sands or yields an increase of up to 4.5o. There are strong indication that pulverized cementitious, fly ash with appropriate additives can be effectively utilized for permeation grouting of coarse sands (Markow and Atmatzidis, 2002).

Bouglanger and Hayden (1995) reported that in many situations, the bottom up method can be used as effectively as the top down method if appropriate modificatiosn are adopted at shallow depths. Even this the extra cost of much modifications, it is likely that the bottom up method will be the most economical choice.

Berry and Buhrow (1992) studies the settlement, structural failure and in-place repair of above ground storage tanks with many sizes placed on foundation of varying nature. The causes of tank stress on foundation of varying nature. The causes of tank stress and failure are reviewed including some environmental control concern and causes and related to tank foundation problems the uneven movement and settlement of foundation soil can be stopped by grouting.

The permeability and strength of grouted sand is strongly influenced by the method of grouting because different mechanism govern the deposition and packing of cement particles within the pure structure. During the injection process, perforential flow paths allow the migration of cement particles into the soil, and micro structural packing undoubtedly varies within the pores of the grouted sand, this is in contrast to the more uniform distribution of cement particles in hand mixed specimens (Schwarz and Krizek, 1994).

The groutability ratio is not a universally applicable criterion, and values large or smaller than the limiting value of 25 do not necessarily indicated success of failures respectively, as a specific grouting operation using a particulate grout, experimental evidence suggests that the grain size distribution and relative density of the fine sands may control the grouting operation (Zebovitz et al; 1989).

The grouting technique is the MRRB project at kaohsing city in the southern part of Taiwan, shows a significant increase of horizontal stress within the improved soil mass. Preloading effect was more significant in reducing wall displacement than anticipated. Jet grouting also increase the overall strength of improved soil mass. Other improvement method, such as compaction grout column and displacement pile driving may be even more effective than jet grouting (Hsien et al; 2003).

GROUTING MATERIALS

The selection of the appropriate grout compound to be injected depends on the effect to be achieved and on the properties of the injected materials to be permeated. Two classes of grouting material are generally recognized; suspension types grouts and solution types grouts. The suspension type grout include soil, cement, lime, asphalt, emulsion e.t.c. While the solution type grouts include a wide variety of chemicals such as sodium silicates acrylamide lignosulphonates, aminoplast, phenoplast e.t.c. (Shroff, 2009).

Cement based grout mixture can be investigated in soil laboratories in order to study their flow characteristics, bleeding, consistency, gelation, time of set, density, compressive strength and PH. Simple testing procedure such as flow cone, bleeding and compressive strength tests are usually sufficient for the development of thin grout mixtures which are not injected under flowing water condition and therefore is not a fundamental requirement (Counmoulus and Koryalots, 1983).

In order to take into account the effect of cement grout in the pores of the granular material, adhesive forces were added at each contact point to the mechanical forces determined from the external stress applied on the granular assembly. The magnitude of those adhesive forces depends on the nature of the grout and on the concentration of the grout in cement particles. The expression of this adhesive force as a function of cement content is based on extensive experimental work performed by Dano (2004) on grouted sand.

The groutability of sand with acrylamide grout was influenced by the fine content. The grout pressure fines content relationship was nonlinear. Unconfined compressive strength of grouted was influenced by the particle size and gradation, density and fines content of sands (Ozgurel and Vipulanandan, 2005).

Soil grout mix called soilcrete was used for ground improvement to prevent liquefaction in Jackson lake Dam and Wickup Dam in United States. While soilcrete was produced by deep soil mixing in Jackson lake Dam, it was created by jet grouting in Wickup dam. Field tests showed that jet grouting was very successful and the strength attained were sufficient to make an appropriate design alternative as far as time and cost were concerned (Yilmaz et al; 2008).

Suspended particles with an equivalent diameter less than about one third the hydraulic radius of porous medium will pass through the medium and be present in the effluent (Arenzana et al; 1989).

Improving ground strength, consideration should include the ease which include the cement may be introduced and the robustness of the strength. Portland cement gives a more ductile and strain hardening response compared with the other cements studied (Ismail et al; 2002)

Some recommendations can be advanced regarding the development of a standard method for laboratory preparation and testing of grouted specimens. Sand specimen should be grouted by injection to more closely simulate the field process. Longitudinally split moulds should be used to avoid jacking to minimize sample disturbance. Adequate curing time should be provided to assure full development of the mechanical properties of the grouted mass (Christopher et al; 1989).

Cement and clay mixtures have found widespread use on Tennessee valley authority foundation composed largely of extremely porous limestone and dolomite cement-clay grout is more chemical and is satisfactory from the porosity point of view for filling solution channels and cavierms in rock subjected to erosion or leaching from hydrostatic pressures (Elston, 1958). There are two basic factors which govern the penetrability of grout, the first one is the viscosity of the grout and the second is gramulometry of the grout material vis-à-vis the permeability and dimensions of pore space in the formation to be grouted depends much on the viscosity of the grout. The viscosity of an ideal grout mix should be sufficiently be low so that it can be pumped easily and can penetrate through the fine interspaces, but not as low as to travel long distance without appreciable pressure drop (Datye, 1961). Among various properties of grout suspensions, fluidity and stability are of prme importance (Nonveiller, 1989).

SHEAR STRENGTH OF GROUTED SOILS

Cement grouting can be profitably used for strengthening foundation beds. The shear strength parameters, C and D show phenomenal increase when grouted with cement. The cement water ratio of the grout act as a key parameter in the control of strength gain of sandy soils. The investigation ion improvement of bearing capacity of sandy soils by grouting shows that there is considerable promise and scope of developing their bearing capacity, especially in case of cohensionless soils (Glory et al; 2001).

Introduction of a cementing agent into sand produces a material with two components of strength. That due to the cement itself and that due to friction. The friction angle of cemented sand is similar to that of uncemented. Weakly cemented sand shows a brittle failure mode at low confirming pressures with a transition to ductile failure at higher confirming pressures. For brittle type cementing agents, the cementation bonds are broken at very low stream while the friction component is mobilized at large strains. Density, grain size distribution, grain shapes and grain arrangements all have a significant effect on the behaviour of cemented sand (Clough et al; 1981).

Generally, the strength of the soil is estimated by Mohr-colilenil’s failure criteria. It is generally accepted that grouting effectively increase the compressive strength of the sand by filling the voids and by imparting a chesion or adhesion factors, yet the grouting contribution cannot simply be added to the sand strength. The introduction of silicate grout into sand particles and modifies to the type of failure of grouted sand (brittle failure at strains less than 0.3%) (Ata and Vipulanandan, 1999).

COMPRESSIVE STRENGTH

The gradation and type of sand influenced the compressive properties of grout sand. The compressive strength increase with the increase of uniformity coefficient of the sand (better gradation) and with the increase of the particle’s angularity. For curing periods beyond 28 days and up to 2 years. The variation in the unconfined compressive strength modules, and strain at peak were very small compared with the properties at 28 days (Ata and Vipulanandan, 1999).

The compressive strength of the grouted soil specimens was decreased and the permeability of grouted samples was increased due to an increase in water cement ratio. The Dr of the soil affected the injection and an increase in the Dr decreased the groutability of the soil. The compressive strength of grouted samples slightly decreased with an increase in the Dr, an increase in the finer content in soil increased the grouting pressure while decreasing the groutability of soil medium. The grouting with 3% superplasticizer were easily injected into soil samples and the strength increased as compared with the cement grouted samples only (Atbulut and Saglamer, 2002).

PERMEABILITY STUDIES ON GROUTED SANDY SOILS.

Hydraulic conductivity defines the capacity of a porous medium to conduct a particular fluid, and is a function of both the medium and the fluid (Uppot and Stephenson, 1989).

The permeability and strength of grouted sand is strongly influenced by the method of grouting because different mechanisms governs the deposition and packing of cement particles within the pore structure (Schwarz and Krizek, 1994).

Grouting of granular materials is usually done to arrest or reduce water movement to strengthen the material for the purpose of increasing bearing capacity or reducing settlement under existing loads, or both of these functions. Grouting is also done to increase shearing resistance for stability against lateral movement (King and Bush, 1961).

The permeability of stabilized sand may increase remarkably due to flow channels caused by the shear stress increment and that the relationship between the permeability of stabilized sand and shear stress increment depends upon density, grain size and type if chemical grout. In sand stabilized by silicate grout, the permeability of stabilized sand with large grain size and type of chemical grout. In sands stabilized by silicate grout, the permeability of stabilized sand with large gain size increase the other hand, if the grain size of stabilized sand is small, the permeability does not increase excessively as long a dilatency doe not occur (Mori and Tamuria, 1986).

Is: 4999-1991 gives the recommendation for grouting of pervious soils for control of seepage. These are applicable whenever the primary purpose of grouting is to reduce the permeability of the soil.

For grout injected specimens, decreasing the water to cement ratio of the grout and increasing the curing time significantly lowered the permeability and increasing the strength, whereas increasing the distance from the injection point had little effect on the permeability and produced meaningful reductions in strength. These trends are consistent with the sand acting as filter for the grout suspension (Schwarz and Krizok; 1994)