Innovations in Grouting and Soil Improvement

The wet method of deep mixing is an important technology used to construct excavation support systems and improve ground beneath embankments and structures. However, a wide variety of terminology and varying definitions for the same terms create confusion and cause miscommunication among designers, contractors, and testing laboratories. Furthermore, different testing laboratories produce quite different strength test results because there is not a standardized and widely-accepted laboratory procedure in the United States for preparing, curing, and testing soil-cement specimens applicable to the wet method of deep mixing. This paper proposes use of a set of well-defined terms, including volume ratio, cement factor, cement factor in-place, cement content, water-to-cement ratio of the slurry, and total-water-to-cement ratio of the mixture. Relationships among these terms are provided in forms that can be used to control construction operations and determine mixture component quantities for laboratory testing. In addition, a laboratory procedure is described that controls the principal factors producing variability in test results. The laboratory procedure is applied to five easily-mixed soils, and the unconfined compressive strengths of the mixtures correlate more strongly with total-water-to-cement ratio than with cement factor, cement factor in-place, or cement content.

The process of grouting is fraught with uncertainties and is affected by a large number of variables. This paper presents an approach to categorizing uncertainties to mitigate potential risks in the design and performance of limited mobility grouting. Issues addressed will include appropriate site characterization as well as measures to validate conditions expected through the grouting process. Also to be addressed, are necessary grout monitoring measures to verify the design and provide a measure of grouting performance.

Five horizontal concrete plugs were designed and constructed in a deep gold mine near Randfontein, South Africa. Intended to resist water heads of up to 1500m, they were up to 30m long and measured 4 by 4.5m in cross-section. Each plug was constructed in four separate, contiguous segments using the mortar intruded preplaced aggregate ("colcrete") process. They have been designed conservatively to provide a service life of at least 100 years. This paper focuses on the construction aspects, and in particular the very intense levels of QA/QC and performance verification which were considered appropriate to the project, given the potentially horrific consequences of failure to the mine labor.

This paper reviews "best of current practice" concepts under four broad categories. The concept of a Quantitatively Engineered Grout Curtain (QECG) is held to be the most responsive level for design purposes and its basic components are described. In rock drilling the principles of Measurement While Drilling (MWD) are reviewed to illustrate how maximum geotechnical benefit can be achieved from every production drill hole. An introduction is provided of contemporary standards for field testing of grouts. Fourthly, the advantages of using Advanced Integrated Analytical (AIA) systems to collect data, monitor progress, keep records and reports, and generate technical analyses are described.

This paper describes innovative applications of jet grouting to solve complex design problems for a large-scale basement construction in soft clay. Because the site was located adjacent to an existing mass rapid transit station and viaduct, very stringent criteria were imposed on the permissible displacements caused by site construction activities. A system of jet grout slab and block configuration, in conjunction with diaphragm walls and temporary steel struts, was adopted to provide lateral bracing for the main basement excavation. Ground treatment for a narrow excavation at a long vehicular ramp included a combination of jet grout slabs and vertical jet grout walls. The excavation of three large stair core openings was supported using vertical jet grout walls. A self-stabilized jet grout retaining structure, with terraced slopes on the front and back, was formed across the width of the basement to retain a temporary excavation 12m deep. This allowed simultaneous excavation for the basement to proceed, while foundation works were still in progress at the ground surface on the retained side of the jet grout structure. The triple fluid jetting technique was adopted to minimize disturbance to the existing ground during jet grouting operations. Excavation for the basement was successfully executed with inward wall deflections limited to 11.2mm where a jet grout block was used and 38.4mm generally.

This paper presents an innovative seismic retrofit of the historic Posey Tube in the San Francisco Bay area of California. The tube, which forms an underwater link between the cities of Oakland and Alameda, is located between two major active faults, the Hayward Fault and the San Andreas Fault. The Posey Tube, completed in 1928, was then the first pre-cast underwater tunnel to be built in the world. Approximately 40 years later, another tube, the Webster Street Tube, was built parallel to and 152 meters (500 feet) west of the Posey Tube. Construction of the two tubes required excavation of a trench along an approximately 976-meter (3,200-foot) stretch of alignment over land and water, and backfilling of the trench with dumped fill. During a major earthquake, the tube sandy backfill materials and the sand bedding immediately below the tubes would be susceptible to liquefaction, resulting in the loss of soil strength. Consequently, the tubes could become buoyant in the heavily liquefied material, causing substantial displacements and damage. The seismic retrofit in the Posey Tube consisted of installing jet grout columns along both sides of the Posey Tube, and while that in the Webster Street Tube was composed of pipe pile stone columns which is discussed in a separate paper. The objective of the seismic retrofit in the Posey Tube was to prevent flotation of the tube due to liquefaction of the sandy soils underneath the tube. This was achieved by constructing a row of 1.83-m (6-ft) diameter overlapping jet grout columns on both sides of the tube, each to a depth of about 13.7 meters (45 feet) from approximately 1.5 meters (5 feet) below the crown of the tube. These two rows of columns serve as barriers to contain the liquefied, loose, saturated sand in place during a major earthquake. This innovative design concept is considered to be the first of its kind to be applied to an immersed tube of this magnitude in the world. This paper discusses: (1) challenges confronted by the unique site and soil conditions with the use of triple fluid system of jet grouting, (2) the use of jetting specific energies to determine the overall structural integrity of grout cores, and (3) results of field and laboratory testing that included pre- and post-construction borings, permeability testing, and unit weight/unconfined compressive strength testing. These are followed by a discussion of lessons learnt from the jet grouting operation along the Posey Tube.

The owner of a parking garage in Baltimore, Maryland, wanted to increase parking capacity by adding two additional supported levels. Adding two new levels of parking increased the loading on the existing belled caisson foundation by 42 to 102%. There was only limited data available regarding original foundation construction, specifically describing only depth, diameter and capacity of the caissons. The task at hand was to assess the available capacity and, if needed, provide a method for increasing the capacities of these foundations. A load-testing program was developed where the existing caisson was loaded to the maximum increased load values plus a safety factor. Due to unacceptable performance under this testing, a Limited Mobility Grouting (LMG) program was implemented at this location to enhance the pile bearing materials. The shaft was retested with significantly improved performance. Based on this performance, the remainder of the columns where increased loading was an issue was treated with similar LMG injection around and under shafts. This paper discusses the site investigation, load testing method, LMG program, and pre- and post-load test results.

Design of Compaction Grouting for improvement of soil properties is often based on previous experience and relies on pre- and post-construction evaluation of soil properties. However, this design practice is not always suitable. An aerator tank at a food-processing facility, in Georgetown, Delaware, provided a good opportunity to evaluate design procedures in Compaction Grouting. The perimeter walls of the tank had been undergoing significant vertical displacement and rotation, presumably due to insufficient bearing capacity of the underlying loose sands. A Compaction Grouting program was designed to improve the bearing capacity of the soils through the combination of the effects of soil densification and soil reinforcement induced by the grout inclusions. Standard Penetration, Cone Penetration, and Dilatometer testing were used with limited success to evaluate the effectiveness of grouting. Post-construction monitoring of the structure revealed that the treatment was successful. This paper describes the process followed for design and installation of the compaction grouting elements, as well as the results of the monitoring collected to date. The paper also discusses the difficulties encountered during interpretation of the in-situ testing. Some recommendations for design and evaluation of compaction grouting in loose, granular soils are presented.

Two drilled shaft supported columns for a pedestrian bridge exhibited excessive settlement. Jet grouting techniques were used to extend the support for the drilled shafts to a deeper dense sand stratum. Upon completion of the jet grouting, the bridge deck was raised to its original position using temporary shoring with heavy steel transfer beams and hydraulic jacks.

The existing Effluent Pump Station (EFPU) at the Columbia Boulevard Wastewater Treatment Plant (CBWTF) was retrofitted to upgrade the pumping capacity and seismic stability of the structure. The structure is located on a slope above the Columbia Slough. The geotechnical exploration and analysis for the project showed that the slope between the structure and the Slough had liquefiable soil under the design seismic event. Furthermore, the slope was likely to fail and move into the Slough during the design earthquake. Cement deep soil mixing (CDSM) was chosen to reinforce the slope and maintain the integrity of the structure during a seismic event. The design called for soil improvement of a bench of soil between the EFPU and the slough, approximately 13.7 meters (m) (45 feet) deep. The treated area was designed as a gravity buttress, or retaining wall. Treating the soil in the bench area also improved the resistance to slope movement of the untreated soil on the slope during the design earthquake. During construction, the specified test section was replaced with additional quality control during final testing. Test results showed excellent mixing characteristics as well as higher than specified strength for the material. The site itself was constrained in terms of space and obstructions were encountered in several of the columns, but these factors did not affect the final product.

This paper presents a case study of the application of the Deep Mixing Method (DMM) to a state DOT construction project. The project was developed in-house and was contracted with special provision for the work to be performed under a performance-based specification. The paper presents a general overview of the project, including the scope of work, how deep mixing was selected as a design element, plan and specification development issues, installation methods, construction issues, and project costs. Results of a lab testing program for the stress/strain behavior of deep mixing cores from the site are presented in addition to an in-situ field monitoring program investigating load and deflection response in the improved columns and surrounding soils.

The results of unconfined compression and oedometer compression tests confirmed the existence of optimum mixing clay water content for economical and efficient mixing of cement and clay for the deep mixing method (DMM) application. The optimum mixing clay water content (C_w,opt) is defined as the total clay water content of the clay-water-cement mixture that would yield the highest possible improvement in strength of cured cement-admixed clay. A concept supporting the existence of optimum mixing clay water content is discussed together with a conceptual diagram of the clay-water-air-cement interactions. Based on the test results presented, the C_w,opt would fall near the liquid limit of the base clay. Significantly, at this optimum mixing water content, only 10% cement content by weight is needed instead of the corresponding 17% in the conventional method of mixing, with a consequent 40% reduction of cost of cement.

This paper discusses strength and modulus changes of the surrounding marine clays during and after deep mixing using three different installation methods: high-pressure jet mixing (HJM) method, powder jet mixing (PJM) method, and slurry mixing (SLM) method. Field and laboratory investigations were conducted on Ariake marine clay to evaluate these changes around columns installed by each deep mixed method (DMM). The Ariake clay is a structured clay and sensitive to disturbance. Field and laboratory test results indicate that the degrees of disturbance (DOD) to the clays around the DMM columns depend on the method of deep mixing. Among these three installation methods, HJM, PJM, and SLM had the average DOD to the surrounding sensitive clay of 41%, 21%, and 15%, respectively. The rate of strength recover during curing also depends on the method of deep mixing. The strength ratios in 30 days after deep mixing using HJM, PJM, and SLM methods ranged from 0.79 to 0.98 with an average of 0.86, 0.84 to 1.0 with an average of 0.92, and 0.9 to 1.17 with an average of 1.1, respectively. The recovery of the surrounding soil modulus was slower than that of the strength.

In the study, field and laboratory tests were conducted to investigate the degree of strength variance within cement treated soils. The cement treated soils were the dredged soils mixed with a small amount of cement. They were produced by Pneumatic Flow Mixing Method, which had been recently developed in Japan. In the paper at first the outline of Pneumatic Flow Mixing Method system is presented. Then several backgrounds causing the strength variance within the cement treated soils are described. It is found that the cement-water ratio of treated soils was stable, which was monitored and controlled during their production. The effect of mixing adequacy of the soil-cement mixture and that of non-homogeneity of dredged soils on the strength variance is also discussed. Finally the effective measure to reduce the strength variance is described.

Mitigation of liquefaction potential in granular soil can theoretically be achieved through permeation of colloidal silica. However, practical application of this technique requires an efficient and adequate delivery of the silica. The purpose of this research is to evaluate colloidal silica transport mechanisms. The work consisted of short (0.9 m) column tests to identify the variables that influence stabilizer transport through soil formations. It was found that the primary variable influencing transport is the viscosity of the stabilizer solution. The results show that colloidal silica stabilizer can be delivered to the soil column in an adequate concentration to stabilize the soil. Unconfined compression tests on the treated specimens indicate that treatment with 5 weight percent colloidal silica provides adequate strength for mitigation of liquefaction risk.

Fracture grouting of fissured Ankara Clay with low viscosity cement grouts was investigated through laboratory injections. It was aimed to observe the effects of water/solid ratio of the grout and applied vertical stress on fracturing pressure, volume of grout taken up by the specimen and amount of heaving occurred at the top surface of the specimen due to grouting. For this purpose, undisturbed samples of fissured Ankara Clay of 14 cm diameter and 20 cm height were grouted through a cylindrical injection pipe placed horizontally at the mid height of the specimens. Water/solid ratios of 0.8, 1.0 and 1.2 were used with vertical stresses of 100 kPa and 40 kPa applied on the specimens. It is observed that both the fracturing pressure and the grout volume taken up by the specimen until fracturing occurs decreases as the water/solid ratio of the grout increases. The amount of heaving observed at the top surface of the specimen is almost zero until the soil is fractured. However, once the fracturing occurs and the grout starts to flow continuously through the planes of weakness formed within the specimen a certain amount of heaving, which shows an increasing tendency as the water/solid ratios of the grouts are increased, is captured at the time of fracturing. At a lower vertical stress (40 kPa) applied on the specimen, the fracturing pressures and the amount of grout taken up by the specimen until the soil is fractured decreases and a higher amount of heaving is observed.

In April of 2003, approximately 1,791 cubic yards (cy) of material was dredged from the municipal marina in Nyack, New York. Accumulation of Hudson River sediments had reduced depths in the marina, impeding use by recreational boats. Sediment was removed using a horizontal auger cutterhead dredge and pumped into geotextile tubes in an adjacent parking lot to dewater. Since a priority of this project was the quick and efficient dewatering and removal of dredge material from the site, an open air, settling basin was not feasible. Additionally, there are safety concerns with having a dewatering area in a highly populated area. Polymeric conditioners were added to the slurry during pumping to facilitate dewatering and settling. Material in the geotextile tubes was periodically sampled to monitor the dewatering process. Sediments dredged from Nyack Marina were a mixture of fine-grained silts and clay commonly found on bay and estuary bottoms worldwide. The material was classified as "MH" elastic silt. Small amounts of sand were present near marina edges and storm drains. Paint filter tests were performed on July 15, 2003 for the material in each geotextile tube to determine whether a landfill would consider the material liquid or solid. All six samples passed the test, i.e., no free liquids were observed draining from the sediments and therefore the material was considered a solid. Initial dredge material entering the tubes had approximately 10–15 percent solids by weight. By June 30, 2003, the dredged material had dewatered to a percent solids ranging from 49–56%. At the completion of dredging operations, the geotextile tubes had a top elevation of 5.5 feet. By July 15, dewatering and consolidation had left the tubes ranging in height from 2.2 to 3.1 feet. Dewatering was allowed to continue and by September 22, the geotextile tubes had heights ranging from 1.9 to 2.6 feet. The possibility of using the dewatered dredge material for beneficial use was an important consideration for disposal options. The Village of Nyack intends to re-grade and improve an existing parking lot by using the dredged material from the Nyack Marina as the subbase for the parking lot. California Bearing Ratio (CBR) testing was performed on the dewatered dredge material to determine the suitability for use as a parking lot subbase. The material was found to have an average CBR of 3.43. Due to the relatively high moisture content of the dredged material, lime was chosen as the best additive. At an addition rate of 10% by weight of dry soil, bench-scale testing with hydrated lime showed a 67% increase in shear strength after a curing time of 2 hours. The final design for the parking lot will include geotextile separation/reinforcement and hydrated lime, mixed on site to increase stability.

Expansive soils with sulfate levels typically greater than 2,000 ppm are prone to sulfate heaving. Heaving in such soils cannot be effectively reduced using conventional stabilization techniques (i.e., calcium or lime based stabilizers). This paper presents research findings from stabilization studies conducted on an expansive soil from south Arlington, Texas with sulfates levels around 5,000 ppm. Four different stabilizers, namely; class F fly ash with type V cement, type V sulfate resistant cement, ground granulated blast furnace slag (GGBFS), and combined lime-fiber treatments were used to reduce the expansive nature associated with sulfate heaving and to enhance strength properties. Experiments were designed to study the effects of stabilization methods on compaction moisture content - dry unit weight relationships, Atterberg limits, linear shrinkage, free swell strain, resilient moduli and unconfined compressive strength properties. The study shows type V sulfate resistant cement provided the most effective treatment, followed by class F fly ash with type V cement treatment, GGBFS and finally the lime-fiber treatment. A simple linear ranking analysis was used to rank the stabilizers in this study based on the soil property enhancements by different stabilizer treatments.

The swelling, swelling pressure and moisture dependent shear strength of expansive soils pose serious problems to civil engineers. Disposal of large quantities of fly ash, which is industrial waste, poses a major ecological problem. This experimental study explores the possibility of utilizing the fly ash with or without lime for stabilizing the expansive soils to improve strength and volume change behavior. The free swell index, swell, swelling pressure and unconfined compressive strength tests have been conducted on four expansive soils (prepared by mixing bentonite with kaoline clay in different proportions) treated with fly ash (0 to 20%) and fly ash-lime (0 to 3%) admixtures. The results clearly indicate effectiveness of fly ash in reducing the expansive characteristics of such soils. These soils when treated with fly ash alone do not exhibit marked change in immediate strength. However, 7 days curing brings a remarkable increase in their strengths.

Foundation systems with geotextile encased columns (GEC) are used for soil improvement and primarily for road embankment foundations in Germany, Sweden and the Netherlands since almost 10 years, but latterly they are also used in dike construction. In this paper the essential main features of the calculation of the bearing and deformation behaviour are described. Further the know-how gained by using the different installation methods and measurement results of the foundation system ‘geotextile encased columns' are discussed: Also a comparison of the gained settlement reduction between encased and non-encased columns (i.e. granualar piles) will be shown.

At a gas-fired power station site, previously placed fill and loose/soft soils to depths of about 4 m required the use of piles or soil improvement for foundation support. Soil improvement by stone columns was selected because removing and replacing the upper soils was not feasible due to shallow groundwater. Also, cost and schedule considerations indicated that stone columns would be more cost effective than piles. Calculations were performed to optimize stone column grids to improve the subsurface conditions and reduce the anticipated foundation settlements to within tolerable limits. A pre-production, large-scale field load testing program provided additional data to support the grid optimization. Stone columns were then installed using the dry/bottom-feed method at configurations determined from the optimization study. Production installation of stone columns, foundation construction, and detailed settlement monitoring for a period of about 1½ years have indicated excellent foundation settlement performance. The results have also validated the design assumptions and confirmed the adequacy of the selected, cost-effective foundation system.

The subsurface conditions for a proposed six-story $94M medical facility in Knoxville, Tennessee, consisted of a thick clay layer overlying an irregular weathered limestone bedrock surface. Because the design loads were significant and because of the sinkhole risk associated with the underlying limestone bedrock, the initial design considered the use of drilled shafts bearing on rock. While drilled shafts represented a robust technical solution, construction of drilled shafts in karst can be expensive and time-consuming. In an effort to save both time and money, the authors and other members of the project design team developed a combination ground improvement program to allow support of the medical facility on conventional shallow foundations. The combination ground improvement program consisted of (1) cap grouting the rock surface to significantly reduce the sinkhole risk, and (2) construction of Geopier® elements to reinforce and stiffen the soils immediately below the planned shallow foundations. For development and refinement of the combination ground improvement program, extensive subsurface characterization was performed using cone penetration testing (CPT) at every column location. The CPT results were used to develop three dimensional models of the subsurface conditions including pertinent karst features. The cost savings provided by the combination ground improvement program is estimated to be in excess of $1M.

This paper presents state-of-the art and practice for an innovative seismic retrofit of the historic Webster Street Tube in the San Francisco Bay area of California. The Webster Street Tube, along with the adjoining Posey tube, forms an underwater link between the Cities of Oakland and Alameda. The Webster Street Tube is located between two major faults, the Hayward Fault and the San Andreas Fault. The Posey Tube, completed in 1928, was the first pre-cast underwater tunnel to be built. Approximately 40 years later, the Webster Street Tube was built parallel to and 500 feet west of the Posey Tube. Construction of the both tubes required excavation and backfilling of a trench along an approximately 3,200-foot stretch of alignment over land and water. During a major earthquake, sandy backfill materials and the sand bedding immediately below the tubes would be susceptible to liquefaction, resulting in the loss of soil strength. Consequently, the tubes would become buoyant in the heavily liquefied material, causing substantial displacements and damage. The seismic retrofit consisted of installing stone columns along both sides of the Webster Street Tube. The pipe pile stone column method is the first of its kind to be applied to an immersed tube of this magnitude in the world. The objective of the seismic retrofit was to prevent flotation of the tube due to liquefaction of the sandy soils underneath the tube as well as to densify the surrounding saturated sandy backfill material. This paper discusses (1) the use of pipe pile stone columns to density the loose to very loose saturated sandy backfill surrounding the tube, and confine the loose to very loose sandy soil immediately under the tube — an innovative design to isolate and control the liquefied sand below the tube in place; (2) the overall practicality and constructability of using pipe pile stone columns to density loose saturated sands to silty sands; (3) the impact of the pipe pile stone columns in densifying the in situ soils by means of displacement and vibratory action of the pipe piles; and (4) results of field testing via pre- and post-construction borings and Cone Penetration Tests (CPTs). These are followed by a discussion of lessons learned from conducting the construction of the pipe pile stone columns over water and on land.

Mechanically Stabilized Earth (MSE) walls retain abutment and side-hill fills for the 3-span bridge that takes State Route (SR) 87 over Whiskey Springs in Sunflower located between Phoenix and Payson in Arizona. In May 2001, approximately one year after construction, the 13.7m (45 ft) high MSE wall and the west wing wall at the south abutment started showing distress. Emergency geotechnical investigations were performed by the Arizona Department of Transportation (ADOT) in June 2001. It was determined that the wall was experiencing failure with respect to global stability as well as bearing capacity. Several mitigation measures were evaluated. Two grouting procedures, jet grouting and soil fracture, were put out to bid. The jet grouting technique was used by the selected contractor and the wall was stabilized. The investigation, design and remediation process as well as results of instrumentation monitoring of the wall are presented in this paper.

This paper presents the approach and results achieved through using an innovative idea of integrating the principles of vibro-compaction (stone columns) with geo-grids to improve the soil properties and ensure a uniform geo-technical behavior of the foundation soil of a group of 6 No. 10 MIG steel water reservoirs constructed in the same area in Abu Dhabi in the United Arab Emirates. Tests performed on the soil at site proved that the soil is loosely compacted cohesion-less silty sand (SM) with a bearing capacity less than 100kpa. Depth to firmer strata ranged from 10m to 15m. The 60m diameter reservoir produced a bearing pressure of 200kPa. The solution of piles extending to firm strata was overruled in favor of the more economic solution of vibro-compaction. Vibro-compaction using stone columns provided the optimal solution for improving the upper loosely compacted soil to accommodate the bearing stresses of the reservoirs, while a system of uniaxial and biaxial geogrids ensured a uniform bearing capacity and settlement behavior of the improved soil. The paper presents the case history illustrating the design principles, parameters and the approach adopted to provide the soil improvement solution. The bearing capacity achieved through the adopted solution is 300kPa with a maximum recorded total settlement of 22mm and a maximum recorded differential settlement of 9mm for all 6 fully loaded reservoirs. In addition the economic advantage of using this solution amounted to 20% cost saving and 25% construction time saving.