Advances in Grouting and Ground Modification

Compensation grouting, or the use of grouting techniques to control ground settlement during soft ground tunnelling, has become a well-established technique. While compensation grouting can be applied using compaction grouting (Baker et al., 1983) or soil fracture grouting techniques, the majority of applications to date have used the soil fracture technique. This paper contrasts the concept and theory of the two techniques and describes the application of soil fracture grouting, along with a review of several case histories.

Design of an efficient and economical compaction grout program requires a firm understanding of the primary controlling parameters and mechanisms. These include the soil conditions and overburden pressure, the grout composition, injection rate, and injection pressure. This paper describes a series of small-scale model compaction grouting tests performed in a geotechnical centrifuge to examine the effects of grout composition and injection rate on grout take and grout bulb development. The response to a one-stage grout bulb injection in dry cohesionless soil is examined at various full-scale equivalent prototype depths and injection rates using two grout mixes, and preliminary trends regarding grout bulb development and shape are evaluated. Preliminary results indicate that the grout bulb development is a function of the overburden pressure, injection rate, and grout composition. When similar volumes of grout are injected, grouts with smaller clay content developed into smaller grout bulbs than greater clay content grouts. The shape of the grout bulb does not appear to be measurably affected by injection rate, but is influenced by injection depth and clay content. Given a known volume of injection, the final grout bulb volume is a function of the depth of the injection and, to a lesser extent, the injection rate.

This paper describes an alternate compaction grouting system. It also provides the theory and a mathematical model to assess and quantify the degree of soil improvement caused by compaction grouting. It further discusses a field application where this system has been successfully used. The most common objective of compaction grouting is the densification of the soil whereby the grout does not permeate or fracture the soil matrix. This is typically accomplished by using low mobility grouts. Predictable results can also be obtained for some applications by utilizing the further described alternate method. The alternate method involves the following: Regular sleeve pipes (similar to those used in permeation grouting) are installed to the required depth, through the soil strata that need to be treated. Geotextile bags are strapped ("concertinad" on the sleeve pipe) straddling all or some of the sleeves. The geotextile bags are inflated via a double packer with a balanced, stable, low viscosity cement based suspension grout with high resistance against pressure filtration. Several bags (on different pipes) are inflated at the same time. The inflation process is done in stages to allow the water to slowly (pressure) filtrate through the geotextile bags. During each grouting stage the pressure is systematically increased. Because the compaction process is time related (with reference to Terzaghi's time settlement equations) the compressibility of these layers is gradually and systematically reduced. The spacing between the grout pipes has to be such that the soils are subjected to vertical stresses in excess of those they will eventually be subjected to. The volume reduction of the surrounding soils under the grouting pressure, as well as the influence radius of the compaction grouting can be mathematically estimated with the method described in this paper. This in turn dictates the spacing between the grout pipes. By not attaching a geotextile bag on every sleeve, hydrofracturing or permeation grouting in conjunction with hydrofracturing can be conducted via these sleeves, after the compaction grouting has been completed. A mid-rise condominium structure in Toronto suffered differential settlement as a result of the construction of an adjacent underground parkade. An array of sleeve pipes was installed in the loosened soils and the above mentioned process was implemented. All further settlement was arrested.

The repair of sinkholes in the core of WAC Bennett Dam required an unusually controlled implementation of compaction grouting. Control was obtained by developing a detailed prognosis of what could be achieved under what circumstances, and then using this prognosis to understand the measured grouting response. Ongoing detailed analysis of grout pressure-take relationships allowed the improvement in this soil density to be monitored. The prognosis and analysis were based on a large strain critical state elastic-plastic finite element program developed for compaction grouting. Procedures to predict and analyze the effect of compaction grouting are presented, and their use shown for controlled grouting. The numerical procedures developed and validated show that compaction grouting can substantially densify soils, in contrast to the more widely held perception that the primary effect of compaction grouting is to increase horizontal stress. In the case of WAC Bennett Dam, compaction grouting substantially densified the loose soils beneath the two sinkholes, reinstating the core to a density approaching the pre-sinkhole condition. The dam is now back in service.

Compaction grouting techniques as a means of densifying loose soil or lifting settled structures have grown in popularity since its introduction in the early 1960's. The success of compaction grouting for lifting structures has been well documented in numerous case histories. The success of densifying loose, liquifiable soils is less well known because the limited case history data on such projects. This paper presents one case history where compaction grouting was used to lift settled structures and two case histories where compaction grouting was used to densify loose soil. Confirming data on the effectiveness of the densification is presented in each case history.

Along the San Lorenzo River, the Laurel Street Bridge in Santa Cruz, California was constructed in 1967. As was typical in design and construction of that time, seismic issues were not fully understood, analyzed or implemented. This became very apparent when the performance of the downtown area of Santa Cruz following the Loma Prieta Earthquake of 17 October 1989 (Magnitude 7.1) was investigated and documented by Kropp and Thomas. The study indicates substantial ground failure effects on the west side of the Laurel Street Bridge and both sand boils and ground cracking in the areas north and south of the eastern abutment. With the results of this study it was determined that a definite potential for liquefaction during a design level earthquake (Magnitude 8.0) existed. This could result in lateral spreading, differential settlement, and axial and lateral support failure of the existing pile foundation. In 1996 plans were in place to further research the potential for liquefaction and develop the necessary solutions. The original geotechnical explorations were analyzed, and additional studies were performed. The combination of these investigations along with California Department of Transportation (CalTrans) seismic design criteria led to the development of a geotechnical and structural retrofit program to overcome the now apparent seismic issues. A large portion of this seismic upgrade of the bridge was to treat the liquefiable soils underlying and surrounding the bridge piers. Insitu densification of the liquefiable soils by a ground modification program of compaction grouting was accomplished. This increased the density and cyclic shear strength of the soil, thus resisting liquefaction. In turn, the soil would continue to provide the lateral support and frictional resistance to the piles so that the bridge will maintain stability.

Limited Mobility Displacement (LMD) Grouting is the injection of stiff grout that displaces material during injection but does not travel far from the point of injection, forms a compact mass and may fill voids. Applications of LMD grouts include compaction grouting, construction of grout columns, structural lifting, rock grouting and slab jacking. LMD grouts are typically soil-cements. This paper presents some design considerations that are important to the successful application of this method of grouting. The paper presents a brief introduction to LMD grouting followed by a discussion of geotechnical parameters that are important in the design of LMD grout applications. Several methodologies are also presented for design.

SuperJet Grouting was performed for the first time in North America to create an in situ wale and strut system at the base of a cut-and-cover tunnel, part of the Atlantic City Expressway Extension. The application of any new technology creates an enhanced need for verification and control. The fast track nature of this design-construct opportunity meant that there was little room for error, particularly so since the use of SuperJet grouting was predicated on cost and schedule savings. SuperJet grouting is a form of jet grouting that permits the construction of exceptionally large soilcrete columns, up to 5 m (16 ft) in diameter. Compared to standard jet grouting, this represents a 400 percent increase in column size. Furthermore, this increase is achieved without any decrease in product quality. The SuperJet system does this by mechanically and hydraulically focusing the injection of the cementitious grout for pinpoint cutting and erosion of very large volumes of soil in situ. The excess soil-grout mixture is simultaneously expelled at the surface, preventing pressurization and hydrofracture and leaving a high-cement-content, soil-grout mixture in situ to solidify. SuperJet grouting, as applied on the Brigantine-Atlantic City Connector project, realized a substantial decrease in time and cost while providing a product of exceptional quality. This paper describes the system and its utilization on the project, with focus on the quality aspects of the product in situ. All methods of sampling and testing are described and the results of testing are summarized.

Horizontal Directional Drilling offers several advantages over repetitive patterns of horizontal tunnel face drilling and grouting or surface based drilling methods for the installation of Tube-a-Manchette (TAM) pipes for soil stabilization by permeation grouting. However, this technique has practical limitations as well as technical and cost ramifications not typical of conventional drilling and grouting programs. This paper provides a comparison of the advantages and disadvantages of using horizontal directional drilling techniques for TAM pipe installation and provides experience-based guidance in the practical implementation of a Horizontal Directional Drilled Grouting Program (HDDGP), including considerations necessary for the successful injection of solution grouts to provide increased stand-up time and groundwater control as an aid in subsurface excavations.

In this study, a field sand deposit was grouted with a sodium silicate grout, allowed to cure in situ, excavated, and cut with a water jet into handleable blocks. These blocks were then transported to the laboratory and hand-trimmed or machine-cored to obtain test specimens. The measured permeability, modulus, and strength values for these specimens were used to determine the spatial and directional dependence of these engineering properties in the in situ grouted mass. Then sodium hydroxide was used to dissolve the grout and recover the weight of sand in a given volume, thereby providing an assessment of the grout content and original dry density at particular points in the deposits. Notwithstanding considerable scatter in the data, there were modest indications of anisotropy but no clearly identifiable changes in the engineering properties with distance (up to about 1.6 meters) from the grout injection point. Cored specimens showed little, if any, variations in strength or modulus relative to hand-trimmed specimens, but the strength and modulus of the field-grouted specimens were significantly higher than those of laboratory-prepared specimens using the same grout mix and sands.

Contemporary grouting equipment must be capable of accommodating a wide variety of applications, materials and performance parameters. The paper provides an overview of the major features of mixing, storage, pumping, and monitoring equipment. Typical details of modern equipment are provided to illustrate the range available.

The quite different "rules of thumb" used by American and European grouting practitioners for selection of grout injection pressures have for many years been a subject of great controversy between the two groups. Practitioners who are not "married" to either rule have long suspected that each may be an artifact of the respective systems of measurement used. Although use of the "American rule" commonly is rationalized on the basis of protection against possible uplift of horizontal strata, application of the pressures that this rule seems to dictate may not be sufficient to cause grout to adequately penetrate and fill small openings in potentially permeable fractured rock. Conversely, these same pressures may be excessive for use in very weak rock. "European rule" pressures would, of course, be potentially damaging to weak rock, but they have been widely and successfully used in "average" bedrock foundation conditions. Nonetheless, even higher pressures than would be allowed by that rule also have been widely and successfully used. Therefore, it should seem evident that — rather than mindlessly following either "rule" — grouting practitioners should base their selection of grout injection pressures on site-specific factors, including — to the maximum extent feasible based upon grout hole logging and water test data — the conditions at each specific hole into which grout is to be injected.

In addition to particle size, the ability and ease with which cement-based grouts permeate cohesionless soil and fractured rock in grouting applications is governed largely by the viscosity and yield stress of the grout. These rheological characteristics, in turn, are strongly influenced by the evolving early age morphology of the cement grouts due to hydration and the chemical reactions that occur when cement particles come in contact with water. Reported here are the results of a laboratory study undertaken (a) to document by means of environmental scanning electron microscopy the evolution of these early age (first hour after mixing) microstructural formations in microfine cement grout and (b) to correlate the observed morphology changes with measured values of the rheological properties during this period. Changes in both the rheological characteristics and the morphology of microfine cement grouts are dependent on the cement type, the particle concentration, and additives.

Cellular grouts are being used in various construction and repair applications because of their light weight, ease of placement and good specific strength properties. Hence, there is increased interest in better characterizing these materials, especially with less cement in the mix. Cellular grouts with fly ash (Class C) as a replacement for cement are characterized in this study based on their setting time, compressive properties, shrinkage and water absorption. Field samples were collected with unit weights in the range of 6.8 kN/m³ (43 pcf) and 8.6 kN/m³ (55 pcf) for this investigation. The effect of using 50% fly ash (Class C) as cement replacement was investigated. The addition of fly ash increased the initial setting time and reduced the compressive strength and modulus of the 8.5 kN/m³ (54 pcf) cellular grout but had a lesser effect on the 6.8 kN/m³ (43 pcf) grout. The addition of fly ash reduced the shrinkage of the grout. The compressive strength and modulus of grouts increased with unit weight of grouts and curing time. Cellular grouts showed varying amounts of water absorption, being dependent on the initial unit weight of the grout.

Ease of placement and performance of the solidified material have made flowable grout as one of the most suitable backfill material for pipes in narrow trenches and retaining structures. Hence there is interest in designing flowable grout mixes with locally available materials. In this study, foundry sand was used with clay and fly ash (Class F) to develop cementitious flowable grout mixes. Effect of cement content on the flowability and mechanical properties of various flowable grouts were investigated. Two methods were used to quantify the flowability of the flowable grouts. The superplasticizer was very effective in optimizing the flowability and mechanical properties of the sand-clay mix. Stress-strain relationships for various mixes have been developed and modeled using a two-parameter model. Compressive strength of the mixes has been related to the cement content. The 28th day compressive strength for the mixes varied from 0.14 to 1.7 MPa. For the flowable mixes, the compressive strength was linearly related to the compressive modulus and pulse velocity.

Polyurethane grouts are used for stabilizing soils, controlling infiltration into water and wastewater systems, treating and containing wastes, slab jacking and structural repairing of concrete facilities. Due to these wide range of applications, there is increased interest in better characterizing the behavior of hydrophilic polyurethane grouts. Polyurethane grout selected for this study had a free volume expansion of over 1500% for water-to-grout mix ratio of 0.5. In this study a hydrophilic polyurethane grout was mixed with varying amounts of water (up to 6 times the net grout volume) and the curing parameters (pressure, temperature, and volume change) and the compressive behavior of cured (solidified) grouts were investigated. Samples were prepared in a specially designed molds by controlling the volume change. Pressure-temperature-time relationships during curing have been developed. Unit weights of cured polyurethane so prepared varied from 3.2 kN/m³ (20 pcf) to 10.4 kN/m³ (65 pcf). The compressive stress-strain relationships of the grouts were influenced by the water-to-grout ratio and the properties were less depended on the unit weight of the cured grouts. Polyurethane grout bonded to the siliceous surface and the bonding strength also varied with water-to-grout ratio.

The behaviour of two 4 m high embankments constructed on soft alluvial strata on the same site are discussed in this paper. One was constructed on undisturbed ground the other on approximately 4 m thickness of contaminated land. Special techniques were required to facilitate safe construction of the contaminated land embankment. Overall behaviour of the two embankments was similar and the main influence of the contaminated fill layer was to provide additional stability and to dictate the construction process required. Predicted and measured primary compression values were similar. However, from the magnet extensometer data, it was seen that the laboratory tests significantly underestimate the normal compression stiffness of both materials by approximately 20%. Therefore the closeness of the predicted and measured primary compression values may have been fortuitous and due to presence of non compressible sand / gravel lenses in the overall alluvium stratum. Insitu consolidation rate was some five times that predicted by laboratory tests. Secondary compression rate recorded insitu was also significantly higher than that predicted by the laboratory testing. Excess pore pressures dissipated rapidly in the contaminated land embankment due to the size and spacing of the vertical drains. Construction control was subsequently achieved using the ratio of maximum lateral movement to maximum vertical settlement. The target value of the ratio was determined from a data base of other Irish soft ground embankments.

The bearing capacity and settlement behavior of large diameter above-ground petroleum storage tanks are critical in loose and soft soils. On Sand Island in Honolulu, Hawaii, there is a history of large magnitudes of settlement associated with these types of tanks. On a recent tank expansion project, large diameter floating soil-cement columns constructed using in-situ deep mixing were used to improve the bearing capacity and control the settlement of three large diameter storage tanks constructed on sandy lagoonal deposits. Although the settlement of the tanks exceeded predicted values, the deep mixing ground improvement program successfully limited settlement to within the specified and allowable values. Furthermore, deep mixing also provided cost-effective means of treating petroleum-impacted soils at the tank locations.

Vibro replacement is commonly utilized to reduce the settlement and increase the bearing capacity of soft soils subjected to large loads. Several field plate load tests were performed on vibro replaced soils in the Southeastern United States. These sites include a residence hall, a courthouse, and a multi-level office building. The soil profiles range from homogeneous to heterogeneous and consisted of mostly clayey sand and silty sand deposits. The assumptions involved in settlement prediction of vibro-replaced soils from three widely-accepted prediction methods were evaluated. Numerical modeling using the Finite Difference Method was utilized to predict settlement and to analyze the post-construction stress and deformation fields within the soil. The main purpose of the study was to evaluate the accuracy of current analytical prediction methods and to examine the dependency of settlement magnitude on soil type. Based on the findings, guidelines for settlement prediction are outlined and recommendations are made regarding appropriate selection of settlement prediction methods.

The degree of ground improvement is evaluated to determine if the final results in the field meet project design criteria. This evaluation is typically based on values of cone penetrometer tip resistance correlated to an equivalent relative density. It is difficult to consistently apply empirical correlations to soil modified by densification. Therefore, a method to determine the expected degree of improvement, free of correlations, would provide improved design and quality control information for contractors and consultants. The Improvement Index for Densification (I_d) is presented that quantifies the degree of ground improvement by densification methods. I_d is related to the specific energy of penetration and is computed from cone penetrometer tip resistances measured before and after improvement. Results presented for eleven case histories show that I_d is sensitive to variations in soil texture and initial density.

Dynamic compaction method has been proven to be an efficient method to improve both the strength and deformation properties of cohesionless and unsaturated cohesive soil deposits. However, when used alone, this method is not effective on thick saturated soft clays. A modified dynamic compaction method, which combined the dynamic compaction and Prefabricated Vertical Drains (PVD) systems, was applied to improve the 2 to 6 m thick uncompacted colluvial fills over 6 to 9 m of soft marine clay sediment. The design and operation methods are introduced in this paper. Both laboratory and in-situ test results suggest this is an efficient method to treat the highly saturated soft clay soils.

Because of a poor line-of-site for traffic traversing North Getty Street in Muskegon, Michigan, in addition to the potential for flooding of the project site it was desirable to construct two (2) parallel prefabricated BIN-WALL structures on both sides of the existing roadway alignment such that Getty Street could be elevated above Ryerson Bayou. The length of the west BIN-WALL was 152.4 meters (500 feet) in length, the east wall was 173.7 meters (570 feet) in length, and the individual bin heights varied from 1.73 meters (6 feet) to about 5.39 meters (18 feet) along the length of the BIN-WALLs in order to accommodate the topography of the site. Six (6) test borings were performed across the length of the site to ascertain the subsurface conditions beneath the site, which disclosed an extensive deposit of peat, marl, and loose sand that extends to a depth of about 7.7 meters (25 feet) beneath the existing site grade (corrected standard penetration test "N" values were typically revealed to be between 1 and 6 within this deposit). In addition, free ground water was encountered above the proposed bearing elevation over a significant length of each of the proposed BIN-WALLs. Several ground modification techniques such as dynamic deep compaction, vibrocompaction, and stone columns were considered for possible implementation in remediating the site. However, all of the aforementioned techniques proved to be too costly given the funding available for the project. Therefore, an innovative mode-of-operation which included the removal of much of the deleterious soil materials, in conjunction with the subsequent emplacement of a geogrid-reinforced crushed stone structural pad that was placed in the "wet" allowed for the efficient and cost effective solution for this project.