Grouting 2017: Jet Grouting, Diaphragm Walls, and Deep Mixing

The multifan jet grouting method of ground improvement was developed to reduce the amount of redundantly improved soil. In this study, we geometrically examined the effectiveness of multifan-shaped columns for lattice- or wall-form ground improvements. Consequently, ground improvement work could be performed more effectively with multifan columns than with oval or round columns. Furthermore, we developed new equipment to construct multifan columns, and conducted field tests to confirm its workability. Consequently, we confirmed our assumption that it is possible to construct multifan-shaped columns for ground improvement.

As part of the Southeast Louisiana (SELA) drainage program, designed to reduce flood damages in the City of New Orleans and surrounding parishes, several individual projects required ground improvement work to replace the soil between parallel lines of sheet piles with a soil-cement mass, having the purposes of both eliminating under-seepage, thus creating a so-called bottom plug, and providing structural support for the underground concrete box culverts, as well as providing a stable and dry work platform for the subsequent operations of excavation, forming, casting, etc. The U.S. Army Corps of Engineers (USACE), New Orleans District, selected the jet grouting technology for the construction of the bottom plugs. For the contracts it was awarded, the specialty geotechnical contractor proposed to accomplish the task utilizing their proprietary and innovative elliptical bi-fluid jet grout technology. This technology, introduced for the first time in an actual production work in the U.S., offers great benefits in terms of productivity and flexibility, while always maintaining the necessary quality of the work. It may also provide important environmental benefits in terms of reduced binder and transport needs. This paper will present in detail the main features and advantages of the elliptical jet grouting technology, and will provide supporting evidences from the successfully completed SELA-22 and the ongoing SELA-26 projects in New Orleans.

After a big earthquake hit east Japan, there is an increasing number of projects to reinforce aseismatic structure of buildings. Jet grouting is one of the effective methods to cater to the increasing needs. However, there are few cases applying jet grouting to the foundations of buildings because jet grouting is more expensive and more difficult to control the quality than mechanically mixing methods. To reduce the cost of jet grouting, we invented a new technique to construct rectangular-like columns instead of circular columns and set them in a row. This technique reduces the total number of columns, the production time and the production cost. Some field tests were conducted to construct the new columns. We succeeded in constructing the new columns and confirmed that the qualities and the construction efficiencies of the rectangular-like columns are not less than existing columns.

This paper addresses an unconventional application of jet grouting, where improved soil columns acted as the bonding section of ground anchors installed in loose alluvial soil with an unusually high capacity. A retaining wall, 25-m high, which had been constructed to support refuse and waste material, began to suffer displacements that became so large as to reach very critical conditions in terms of stability safety. To improve its stability 120 ground anchors were installed, each capable of withstanding a 4900 kN working load. The bonding section was achieved by a 1.5-m diameter jet-grouting column. Suitability tests were performed to confirm the adequacy of the design and acceptance tests were carried out on all the ground anchors, both at a loading force of 5900 kN. All the anchors performed very well, showing good elastic behavior at each loading level and no symptoms of incipient failure.

This paper presents the implementation of an electrical resistivity push probe to estimate the diameter of jet grout columns. The probe is pushed into the jet grout column immediately after mixing and removed such that no damage is done to the column. The probe allows direct coupling of electrodes to the soilcrete, providing a demonstrated improvement over existing techniques. Field testing was conducted on columns with diameters ranging from 0.9 m to 2.5 m at two sites, in Berlin, Germany, and Miami, Florida. The results show that the technique routinely estimates the diameter to be within 5% of the as-built diameter.

The various technological solutions of jet grouting, normally grouped into single, double and triple fluid, aim principally at increasing the efficiency of treatments obtaining larger diameter of columns and reduce construction time and cost. Rarely attention is put on the influences of the technology on the mechanical properties of the material, considering this as a secondary issue. The present paper focuses on this aspect summarizing the observation of a comprehensive field trial where sixteen columns have been created with single and double fluid jet grouting varying the injection parameters. The large number of laboratory tests performed on samples cored from the columns show a predominant role of the technology, being the material created with single fluid systematically stronger than the one formed with double fluid. This aspect has been herein explored on samples of original soil compared with materials cored from single and double fluid jet columns: the morphology of the samples has been investigated by scanning electron microscopy (SEM), while the mineralogical composition has been inferred with X-ray diffraction (XRD), differential thermal (DTA), and thermo-gravimetric analysis (TGA). The analysis shows that, if on one side the wrapping of the jet with an annulus of compressed air enhances the cutting capacity of the double fluid jet and is this able to create larger diameters, on the other side it leads to a lower proportion of cement in the columns, that is responsible for worse mechanical properties of the material.

The current techniques to reinforce bridge approaching embankments reducing settlement are still ineffective and less sustainable. Jet Grouting has high potential application to mitigate settlement but has limit applications. This paper investigated mechanical behaviors of soilcrete created from the in-situ soils in the Mekong Delta. Cement PCB40 (A), cement mixed with 10% slag (B), and cement mixed with 50% slag (C) were used. Water:cement (w:c) ratios were 1:1 and 1:0.7 with a designed replacement ratio of cement slurry to the in-situ soils of 50%. About 200 specimens were made in the laboratory and cured at various curing times to determine soilcrete characteristics. The results show that (1) q_u at a curing time of 3 days higher 10 times than those of the in-situ soils; (2) E₅₀ varying from 43 to 147 times to q_u; (3) Strain at failure varying 1-3%; (4) q_u increasing in percentage of slag; (5) a w/c of 1/0.7 providing suitable strength and viscosity.

Jet grouting technique is special in that the ground becomes highly heterogeneous after installing the improvement columns. The surface wave method was recently shown to hold good promise to assess the average property of the improved ground and evaluate the area replacement ratio. Even though the improved ground was highly heterogeneous along the seismic survey line, the surface wave method worked well and yielded a homogenized shear wave velocity profile. The increase of shear wave velocity after ground improvement was found to be correlated with the area replacement ratio. This study further examined the quantitative relation between the percentage increase of shear wave velocity and the area replacement ratio. The effect of offline sampling (perpendicular to survey direction) was also investigated. 3D spectral element method was utilized for the numerical investigation. Numerical results show that the offline sampling range is about 75%-85% of the wavelength. Hence, it should be noted when planning survey lines. Furthermore, a positive correlation between replacement ratio and velocity increase exist and the difference caused by the velocity contrast between soils and improved columns could be neglected as the velocity contrast becomes greater than about 5. An empirical predictive model between the velocity increase percentage and area replacement ratio was established based on the numerical simulations.

Jet grouted horizontal plug was used to seal the bottom of 20.5-m deep TBM launching shaft constructed for a new underwater road tunnel in Gdańsk. The plug was positioned right below the excavation level, and anchored with hollow bar steel micropiles 76 mm in diameter and 15-m long, installed centrally in 1-m diameter and 10-m long jet grout (soilcrete) columns. The columns were arranged in a triangular grid with side length of 2.1 m, and constructed as part of a single production cycle together with the plug columns that were 3.1 m in diameter and 3.5 m in length. The pull-out capacity of micropiles was determined by the frictional resistance mobilized at the tendon/soilcrete interface, and the measured average bond to soilcrete strength ratio was 0.25. A novel aspect was a combined use of the soilcrete plug as structural and watertight element. The adopted design solution contributed to reduction of bending moments and horizontal deformations of diaphragm walls, to more safer and controllable execution of works, and to cost and construction time savings.

To provide additional protection to a 70 year-old dam in case of a seismic event, the local utility company, BC Hydro, required the construction of a backup seepage cut-off wall in the right abutment of the John Hart North Earthfill Dam, using jet-grouting, a well-known technique that uses a high-velocity jet of grout mix at high pressure (300 to 500 bars) to erode and simultaneously mix cementitious grout with the soil in situ. The main challenge was the use of these high pressures during construction of the seepage cut-off wall in the dam fills and foundation soil while avoiding reservoir drawdown, to minimize the risk of hydro-fracturing or hydro-jacking in the embankment. The contractor carried out a field trial in a safe area with similar soil conditions and, with the utility, developed a jet-grouting procedure that minimized the risks. The paper describes the jet-grouting procedures, grout mix used, results of the field trial, and safety and environmental precautions implemented on site to reach successful completion.

Jet grouting and cementitious permeation grouting was carried out as part of the construction of a series of dikes within Second and Third Portage Lakes at Agnico Eagle’s Meadowbank Mine in Nunavut, Canada. The dikes consist of broad rockfill shells, granular filters, and a central low permeability element. The dikes were constructed to permit dewatering of the isolated portions of the lakes to expose areas for development and extraction of ore from open pits. The low permeability elements are comprised of a combination of soil-bentonite and/or cement soil-bentonite cut-off walls that were excavated using slurry trench technology through the granular filters to bedrock or into a dense foundation soil. In deeper portions, where the cut-off wall did not reach bedrock, jet grouting was carried out between the base of the cut-off wall and the bedrock surface. Grouting of the shallow bedrock and the interface between the bedrock and the base of the cut-off wall and/or jet grout columns was then carried out. This paper describes the techniques used for dike construction with emphasis on the treatment of materials left in place beneath the constructed cut-off wall through jet grouting, along with techniques used for permeation grouting of the shallow bedrock and the interface between bedrock and the base of the cut-off wall and/or jet grout wall (i.e., the contact zone). As the earthworks component of the construction was carried out during the short, open water season of each summer, the grouting works were carried out through the winter and shoulder seasons. For this, a significant level of winterization for all equipment had to be employed. The constraints imposed by the necessity of carrying out permeation grouting operations through the Canadian Arctic winter also led to the development of a novel approach to sealing the contact zone. Steel casings were installed through the cut-off wall and jet grout columns to bedrock, and the underlying bedrock drilled and grouted through the bottom of the casings. The casings were then perforated with a casing perforator tool and the contact zone sealed. Based on the successful dewatering and on-going performance of the dikes, the construction and grouting techniques employed are now considered as viable methods in the Canadian Arctic environment. The successful completion of these works would not have been possible without collaboration between the owner, the contractor and the designer.

Jet-grouting is often used in British Columbia, Canada, as an earth retention system for excavation support and, contemporarily, as water cut-off. This paper mention briefly few case histories, with particular emphasis on the application of jet-grouting technology, as a soil improvement technique, for the excavation support and the underpinning of the Georgia Viaduct foundations, for the construction of a 32 story above grade tower with over five levels of below grade parking. Some iconic Vancouver Buildings, such as Olympic Village, built for the 2010 winter games, have been constructed with the use of jet-grouting, but, probably the most challenging is the Rogers Arena South Tower. The tower is located in False Creek, Vancouver, in proximity of Rogers Arena, home of the local NHL hockey team, the Vancouver Canucks, immediately North of Griffiths Way at Pacific Boulevard and South of the Georgia Street Viaduct. The presence of the existing viaduct results in extreme structural challenges that were overcome with the use of jet-grouting and micropiles. The paper will describe the jet-grouting soil improvement design and construction used for the underpinning of the viaduct piers and the temporary shoring, as well the instrumentation used for the monitoring of the viaduct piers and shoring.

Jet grouting is an extremely versatile ground treatment method for water cutoff and excavation support applications. The jet grouting process features unique characteristics that enable it to be used where other ground treatment methods cannot. Jet grouting uses relatively small diameter tooling compared to soil mixing, yet it can create soil-cement columns with diameters many times larger than the tooling. This allows jet grout columns to be installed beneath utilities or structures that must be left undisturbed. In addition, jet grouting creates soil-cement columns through the erosive action of high velocity fluid(s) exiting the nozzles. The erosive action scours the surface of underground structures and enables jet grout columns to conform to and seal against these surfaces. The erosive action also enables jet grouting to successfully treat a wide variety of soils. Jet grouting can be used as a stand-alone method to create water cutoff and excavation support structures. It can also be used to complement other technologies. This paper presents three case histories of jet grouting used in very different applications. The first project used jet grouting to build a partially unreinforced circular shaft and tunnel structure that was tied into an existing brick sewer. The jet grouting successfully stabilized contaminated soils and prevented the contaminants from entering the excavation. The second project used jet grouting to seal full-depth gaps in a cement deep soil mix wall for a cut and cover subway tunnel. The gaps resulted from numerous utility crossings along the project alignment. The third project used jet grouting to form a seal slab at the bottom of a braced sheetpile excavation in sand beneath the water table. The jet grout seal slab was installed prior to any excavation. The seal slab enabled excavation to proceed in the dry and provided permanent resistance to seismic-induced liquefaction of the soil beneath the new structure.

The site of the Barangaroo Project forms part of an old Sydney Gas Works and is heavily contaminated with hazardous materials. A perimeter retention wall is to be created with minimum UCS strengths of 5 MPa. Construction of this wall involves overlapping jet-grouting columns, performed within negative pressurised tents with all personnel subjected to fully enclosed hazardous PPE and controlled decontamination procedures. Two fluid jet grouting was considered to be of high risk to personnel due to creating a high level of airborne contaminates within the tent. Single fluid jet grouting utilising a patented optimized monitor enabled the construction of columns up to 1.8 m in diameter in typical sandy clays and coal tars. This paper describes the jet grouting works with focus on hydration of slag base cements within coal tar environments, environmental protection procedures, contamination controls and there overall effectiveness, as well as specific spoil management.

The Eglinton Crosstown Light Rail Transit (ECLRT) Project involved the construction of 11 km of 6.3-m excavated diameter twin tunnels beneath Eglinton Avenue in Toronto, in advance of shored excavations for future cut-and-cover station construction. Over 37,000 cubic meters of dense glacial and interglacial soils were improved by the jet grouting methods to depths of up to 43 meters below ground surface (mbgs). Jet grouting was performed at station headwalls and tunnel cross-passages to manage groundwater and improve soil stability. The paper discusses the implementation of the jet grouting work in a congested urban environment, the quality control methodology and the effectiveness of the jet grout blocks during tunneling.

This paper presents the wall-stabilization design and implementation for a 165-linear-meter masonry and concrete gravity-type retaining wall flanking the west perimeter of a 29,825-square-meter parcel in the Bronx, New York. This paper will discuss the results of static and dynamic stability analyses performed for the pre- and post-excavation phases for the proposed 91-meter-wide excavation extending up to 4.3 meters below the toe of the retaining wall. The wall stabilization consisted of over 74 inclined drilled and grouted anchor dowels, and 55 tiebacks drilled and grouted to the underlying mica-schist bedrock. Three overlapping rows of jet grout columns were used as the foundation stabilization for the existing retaining wall. The jet grout wall served three purposes: (1) as underpinning and excavation support for the removal of contaminated site soils, (2) as a permanent hydraulic barrier, and (3) as resistance against a deep-seated failure within the thick clay layer at the site. The originally designed jet grout wall had unexpected negative effects on the existing retaining wall. The jet grouting program was modified while the observational method was employed to minimize wall movements during installation. This paper discusses the diagnostic methods used to determine the cause of retaining-wall movement; implementation of a remedial ground-improvement program; modification to the jet grout installation procedure; and ultimate performance of the jet grout wall.

The Anacostia River Tunnel is one of a series of new CSO tunnels designed to capture sewage overflows that currently feed into Washington, D.C.’s, rivers and divert them to the blue plains advanced wastewater treatment plant. The TBM assembly and main work shaft for the tunnel consists of twin 21.3-m (70-ft) diameter shafts connected by a 30.5-m (100-ft) long tunnel mined by the sequential excavation method (SEM). During the hand mining of the inter-shaft connector tunnel, a ground loss event occurred which resulted in approximately 1900 m³ (2,500 yd³) of material flowing into the tunnel and formation of a sinkhole which encompassed the area between the two shafts. The immediate response included flooding the shaft and tunnel, backfilling of the sinkhole, and an array of exploratory holes to map the limits of disturbance. Jet grouting was selected as the ground improvement method to restore ground conditions in the crown of the SEM tunnel so that mining could resume. Several other ground improvement methods were required to support the jet grouting work, including non-cementitious grout for void filling, compaction grouting to create an interim bulkhead, and jet grouting to create a contiguous improved ground structure and provide a stable face for the subsequent recommencement of tunneling. After six months of remedial work, the connector tunnel was completed and the TBM was launched. This paper describes the design steps and implementation of this complex, challenging and time-sensitive remediation effort.

Jet grouting has progressed to be one of the most versatile ground improvement techniques available. In its 30 years of being used in the U.S., jet grouting has made the journey from an unknown and misunderstood process, to an indispensable ground improvement tool. Commonly specified throughout North America, jet grouting is used in different sectors of the construction industry. Now a mature product, this paper explores how the market has steered the technology by examining its modern day applications.

In April 2013, a deadly collapse of a ready-made garment (RMG) building occurred in Bangladesh which caused instant death of 1,134 and injury to more than 2500 people. RMG in Bangladesh faces challenges to ensure workplace safety for the millions of garment workers. The recent structural assessment of the existing 3,500 RMG factory buildings identified that approximately 700 factories needed to be urgently retrofitted. In this paper, the methodology to retrofit a 4-storied RMG building in Chittagong was described in detail. The existing foundation of the building was inadequate, jet grouting together with bored piles were used to improve the foundation condition. The paper also describes the design, construction and performance of the jet grouting process. Soil modeling, settlement of the mat foundation under super structural loads and static pile load test for JGC (jet grouted column) is discussed. The choice of jet grouting as a soil and foundation improvement solution and its advantages are pointed out. In application of jet grouting, type of treatment, application procedure and operational parameters are also discussed.

The adoption of the United States Environmental Protection Agency’s coal combustion residuals (CCR) regulations has stirred renewed interest in the stabilization/solidification (S/S) of fly ash residuals stored in landfills and surface impoundments. Soil mixing methods can be used to S/S a variety of materials to improve static slope stability, resistance to dynamic and static liquefaction, geotechnical properties for handling and movement, and to provide a stable surface upon which to construct a final cover for closure in place or to repurpose the site for other uses. While many geotechnical studies of fly ash reuse as a construction material have been conducted, studies of in situ S/S (ISS) of fly ash are limited. Further, most of the work to date has involved mixing lime or Portland cement with fly ash. While these conventional approaches can be successful, limited research has shown the potential for improved performance through the addition of sodium sulfate salt during mixing of fly ash with cement. The need for additional study of fly ash ISS is a direct result of the recently passed CCR regulations. In order to assess the feasibility of ISS, a study was designed and conducted to examine the use of ISS with lime and Portland cement to improve the ash properties in addition to assessing the potential benefits in ash improvement associated with using sodium sulfate salt in conjunction with Portland cement. Performance measures included unconfined compressive strength (UCS) and hydraulic conductivity. The results indicate that improved geotechnical performance can be achieved when sodium sulfate salt is a component of a cement based mix design for the ISS of fly ash using soil mixing methods.

The quality assurance (QA) practice of deep mixing treatments usually involves unconfined compression tests on cored samples, retrieved from the stabilized columns after a given curing period. Another approach to QA could be the cased-pipe sampling that allows to retrieve “undisturbed” in situ cured core samples at any given curing time. The aim of the study is to investigate the influence of soil sampling on representativeness of the actual mechanical properties of cement stabilized soil. A series of tests were carried out on three kinds of samples obtained from laboratory mixing, cored columns and in situ cured cased-pipe. The analysis of the results clearly show that the cased-pipe samples better represent the actual mechanical characteristic of the soil mixed material as compared to the cored ones.

TVA recently capped a coal ash landfill at the Kingston Power Plant. Cement-bentonite slurry walls were built around the two-mile (three-kilometer) circumference of the facility. The landfill contains roughly 18 million cubic yards (14 million cubic meters) of coal fly ash, including material recovered after the 2008 dike failure at the site. Constructed on the footprint of the failed facility, the new landfill must survive a 2,500-year seismic event. The subsurface, perimeter retaining wall system was designed to stabilize the landfill slopes and contain the stored ash in an earthquake that triggers soil liquefaction. The wall layout consists of evenly spaced shear walls, oriented perpendicular to the landfill perimeter, plus circumferential walls in critical segments. Stantec designed the walls using complex, 2D dynamic computer simulations and 3D structural stress analyses. Deep mixing methods were assumed in the bid package, but prospective contractors were encouraged to propose alternate construction technologies. The winning contractor (Geo-Con, now Geo-Solutions) successfully built the walls using cement-bentonite, slurry trench methods. Over 11 miles (18 kilometers) of wall were constructed, requiring over 520,000 cubic yards (400,000 cubic meters) of slurry. Challenges during construction included characterization of achieved wall strength, mitigation of soil inclusions in the slurry walls, treatment of cold construction joints, soft working conditions on top of the old ash deposits, and collapse of trenches in areas with high groundwater levels.

Column type deep mixing of improved ground has frequently been used to increase stability of embankments constructed on a soft ground. Model tests and numerical analyses have been carried out to study the behavior and failure pattern of improved ground subjected to embankment load, where the sliding, overturning and bearing capacity failures of the improved ground were studied in the external stability, the shear and bending failures of the deep mixing columns were studied in the internal stability. Almost all studies investigated the stability of the improved ground sitting on a horizontal foundation. However the stability of the improved ground sitting on an inclined foundation has not been well studied. In this study, the external stability of DMM columns on an inclined foundation was investigated by centrifuge model tests. The model test results were compared with the finite element analyses. As a result, the experiment and finite element analyses revealed that the columns showed a rotational failure pattern and the stability of improved ground was almost constant irrespective of the inclination of foundation layer.

A 2 km section of the Evergreen Line Rapid Transit Project is supported on improved ground consisting of cement deep soil mix (CDSM) panels because of highly variable and challenging soil conditions, especially the potential for seismic liquefaction-induced lateral spreading. This paper discusses the selection of soil-cement parameters for use in the performance-based design, the preconstruction testing undertaken, and some construction challenges including the proximity to mainline railway tracks, highly variable soil types including sticky clays, the presence of obstructions (buried tree trunks, boulders, and glacial erratics) and artesian pressures. Wet grab samples were collected daily from select columns and field monitoring was conducted to demonstrate that the installation of CDSM panels would not adversely impact the safety of the adjacent tracks or other sensitive infrastructure. Significant challenges were experienced with verification testing because of the variable nature of the soils, difficult workability of sticky clay, core barrel size, and the abundance of gravel which effected the recovery of intact core samples.

The confluence of the Wood River and the Mississippi River, in East Alton, Illinois, has been plagued with seepage under Lower Wood River Levee to the point that remediation was needed. The Southwestern Illinois Flood Prevention District Council enlisted experts to evaluate, design and construct under-seepage controls. The selected design required the construction of a cement-bentonite cutoff wall, 140 feet deep, excavated through alluvial and outwash soils and embedded in bedrock. The unique aspect of this project was that the cutoff wall was installed using a hydromill cutter under self hardening slurry (SHS), to a depth that had not been reached using this method in past cutoff walls constructed in the United States. The quality control/quality assurance (QC/QA) testing was comprehensive throughout the entire process. This paper will give an overview of the project and a summary of the test results.

This study presents the results of cyclic unconfined compression tests of cement-treated soil specimens prepared in a laboratory. Unconfined compression tests, in which a monotonic loading is applied to a specimen, are also conducted to evaluate the mean and variation of the unconfined compressive strength q_u of the prepared specimens. The cyclic loading tests provide the cyclic strength q_cyc versus the number of cycles to failure n_f plots, which is known as S-N curve. The ratio of q_cyc to q_u at prescribed cycles is evaluated on the basis of the S-N curve obtained as the sample regression line. Moreover the variance of linear regression is analyzed because there is a large scatter in the data on the S-N plots. The comparison of the variance of linear regression with that of q_u indicates that the variability of specimen strength results mainly in the variability in the data on the S-N plots.

Deep soil mixing (DSM) was used to form an 8.5-m (28-ft) diameter retrieval shaft for a 3-m (10-ft) diameter tunnel boring machine constructed up to 26.5-m (87-ft) deep in porous limestone in Miami, Florida. Three-dimensional finite element modeling was used to simulate the construction sequencing and final break-in of the tunnel boring machine. The initial design parameters for the soil-cement material was based on reported test results from a nearby site in similar ground conditions. An independent check on the stresses around the tunnel opening was performed using analytical solutions. The final design incorporated seventy-five, 2.1-m (7-ft) diameter soil cement columns forming a shaft with an effective wall thickness of 2 m (6.5 ft) and a 4.6-m (15-ft) thick base plug. A full-scale trial program on site indicated that the in situ DSM strength parameters were lower than expected and the drilling rates were significantly reduced at the lower elevations. Based on the strength results of the trial, the shaft design was re-evaluated and the construction sequence was revised to accommodate the drilling and mixing challenges found in the trial. A comprehensive quality assurance program undertaken during construction indicated the compressive and tensile stresses of the DSM obtained from wet grab and cored samples were greater than the revised design values. Inclinometers and settlement points indicated that shaft wall deformation was negligible and ground settlements were less than 2 mm (1/16 in.).

This paper presents the design and construction of an embankment supported on a reinforced concrete load transfer slab founded on deep-soil-mixing columns completed as part of the seismic upgrade of the Airport Way South Viaduct project in Seattle, Washington. The project included replacement of the timber trestle approach structures constructed in 1928 with mechanically stabilized earth (MSE) approach embankments. Ground improvement was incorporated in the design to mitigate compressible/liquefiable soil conditions within the new MSE approaches. Both the limit equilibrium methods and 3D numerical modeling were used to evaluate the performance of the new embankments and to ensure strain compatibility between the soils and the DSM columns. By including the reinforced concrete load transfer slab in the analysis, the amount of DSM columns and ground improvement in the original design were significantly reduced. Settlement monitoring was completed throughout the construction and confirmed that the specified performance criterion was met.

Deep soil mixing was proposed as a means to improve the poor subsurface conditions at the site of a proposed new electrical substation situated in Burnaby, British Columbia, Canada. Tender documents specified minimum compressive and tensile strengths, as well as a minimum compression modulus, with no acknowledgement of the inter-related nature of these attributes, and no bench scale testing to inform prospective bidders. This paper discusses the contractual risks introduced by use of the set of inconsistent criteria adopted in the project specification, and provides details and results of the trial program utilized by the contractor to establish a mix design criteria that would achieve the specification. Further, the paper discusses two testing options employed for the determination of the tensile capacity of soil-cement, the variation in results obtained for each method, the variation in the relationship of each method to the unconfined compressive strength (UCS), and compares these to previously published relationships.

Antero Dam is an earthen embankment about 45 feet high and about 4,200 feet long located on the South Platte River in Park County, Colorado, at an elevation of about 9,000 feet. The dam and reservoir are owned and operated by Denver Water. Embankment construction was completed between 1908 and 1909 with a hydraulic fill core in a wide, shallow valley with variable alluvial soils over highly variable sedimentary and volcanic geology. Concerns related to seepage stability began shortly after construction of the dam and prevented complete filling of the reservoir. Reservoir storage has been restricted to less than 1/4 of the total storage. The area downstream of the dam generally along the entire length of the toe has always been wet and marshy, with areas of standing water. No evidence of movement of fines at the current restricted storage level have been previously documented. Antero Dam has undergone a significant rehabilitation that occurred over several phases and construction seasons. Rehabilitation has included a downstream filter trench installed using the bio-polymer method, a toe and chimney drain, flattening the upstream and downstream slopes, additional upstream slope protection, installation of a soil-bentonite barrier wall through the center of the embankment, hardening of the spillway, and raising the outlet works tower. This paper will focus on the evaluation, design, and construction of the soil-bentonite barrier wall installed through the center of the dam. Extensive evaluations occurred during design to select the installation method and backfill material type appropriate for this 107-year-old embankment. Significant consideration was given to the risk for damage to the embankment during construction related to hydraulic fracturing or trench instability that could lead to additional dam safety concerns. Regular quality control and quality assurance testing occurred during construction to verify the slurry properties, backfill properties, trench stability, and that the total excavation depth met the requirements and intent of the design. Additionally, daily dam safety inspections occurred in the vicinity of the open trench to confirm dam safety incidents were not developing. Construction was successfully completed in fall 2015 without incident, under budget, and on schedule.

The Tuen Mun-Chek Lap Kok Link Project involves the design and construction of a dual two lane subsea tunnel of approximately 5-km long (3.1-mile) between Tuen Mun Area and the future Hong Kong Boundary Crossing Facilities (HKBCF) on Lantau Island. Two tunnel boring machines (TBM) of 14-m (46-ft) and 17.6-m (57.8-ft) diameter started operation in March 2015 from northern side of the reclaimed land at Tuen Mun. In order to improve the ground conditions for the world’s largest 17.6-m diameter TBM to break in, mass treatment with a combination of CSM panels and jet-grouting columns was employed to carry out the ground treatment works at the location ahead of the launching shaft. Break-in plug properties, as designed by the main contractor, were an unconfined compressive strength of 3 MPa (435 psi) minimum in reclaimed sand, 1.5 MPa (220 psi) in marine deposit and alluvium layer with a minimum 1x10^-6 m/s global permeability of the treated ground. A mass treatment by overlapping cutter soil mixing (CSM) panels was proposed, associated to a layer of deeper jet-grouting columns made to anchor the break-in treatment into decomposed granite underneath. A row of overlapping jet-grouting columns were also used to guarantee a good continuity between the launching shaft D-Wall and ground treatment. This paper presents the design considerations and the application of the CSM technique at the project site Tuen Mun–Chek Lap Kok Link Northern Connection Subsea Tunnel Section. Additional technical points and results based on experience will also be discussed.

Ground-improvement techniques can increase the strength of the ground. They can be used with the existing soils; therefore, the impact upon the environment is very small. If the compressive strengths of the ground improvements are increased, the amount of the ground improvements being used can be reduced, thus proving effective in reducing the impact on the environment. Therefore, these techniques have been increasingly utilized in recent years. In this study, to increase the compressive strength, ground improvements using a slurry with low water–cement ratio (approximately 40%) has been developed. The laboratory test results for developing a dispersing agent suitable for low water–cement ratio slurry are presented and the properties of this slurry and the slurry mixed soil are described. Furthermore, in-situ construction experiment using a low water–cement ratio slurry are carried out, and the quality survey results of constructed ground improvements are also presented.

The deep mixing method of ground improvement blends additives to soil in-situ to increase strength, increase stiffness, and/or decrease hydraulic conductivity. The deep mixing method can be used to support embankments, structures, and excavations; mitigate liquefaction; and create seepage barriers. Contractors continually develop new equipment and procedures to improve the quality and decrease the cost of deep mixing. Equipment types include vertical-axis mixing rigs with one to six shafts, horizontal axis mixing machines with two rotating cutting wheels or one rotating drum, and chain-saw type mixing machines with a vertical post. Cutting and mixing teeth and blades vary in number, type, and orientation. The binder can be injected as dry powder or wet slurry, and air-slurry emulsions have been used. Slurry can be injected on the down-stroke or the up-stroke under low, moderate, or high pressure, and the injection nozzles can be located at the bottom of mixing shafts, along mixing blades, or from the shaft just above the mixing blades. Not all equipment and procedures are suitable for all soil conditions or project types, but more than one approach is feasible in most situations. Collaboration among owner, engineer, and contractor enable the benefits of innovations, and different contracting mechanisms enable different degrees of collaboration. Even in a design-bid-build contract, the engineer can develop the design and prepare the plans and specifications to allow for contractor innovation while protecting the owner’s interests. Strategies include: expressing the geometric requirements in normalized terms, with appropriate limits; using statistically based acceptance criteria; making full use of construction quality control records; and involving the design engineer during construction.

Mass stabilization by dry soil mixing (DSM) is a ground modification technique that involves pneumatically injecting and mechanically mixing dry binder powder (Portland cement or a blend) with in situ soils. This produces a soilcrete mass that has higher strength and lower compressibility than the original soil. DSM by Mass Stabilization is ideally suited for loose or soft soils having high natural moisture content, including organic soils, located within 7 m or less of working grade. During the design process, the required unconfined compressive strength and elastic modulus of the soilcrete are determined based on the magnitude of the loads that are being supported and the amount of settlement that is acceptable. DSM was completed on several soft soil sites at Port Everglades, Florida. A total of fifteen new petroleum storage tanks at three new tank farms, for three different owners, were constructed on standard ring wall foundations after the highly organic in situ soils were improved by mass DSM. The above ground storage tank sizes ranged from 12.19 m to 18.29 m tall, and from 12.19 m to 42.7 m in diameter. Soilcrete material quality was verified during construction by coring and by penetration testing. After the tanks were constructed, full-scale hydrostatic load tests were performed to verify that the tank settlements were within acceptable limits. The load-settlement responses of the tanks were better than anticipated, and easily satisfied the stringent performance criteria. The DSM design procedure and the data from the load testing are presented and discussed.

This experimental study investigates the long-term material behavior under endogenous curing and show the influence of soil clay and cement content on elastic and failure mechanical properties. Several empirical correlation equations based on fast and easy measurements allow estimating both costly and time-consuming properties of soilcretes. The final part focuses on mechanical damage assessment under mechanical loading. The results show a stronger impact of soil clay content on the elastic properties than on compressive strength and underline the importance of density in prediction models. This work shows that mechanical damage under loading mainly depends on cement content.

The blade rotation number is the typical parameter used to evaluate the degree of mixing during the installation of deep mixing (DM) elements. Several limitations in the use of such quality index occur when a tool geometry different from the standard vertical shafts equipped with a series of blades is utilized in the field. Cutter soil mixing (CSM) represents one of such cases. CSM differs significantly from conventional DM methods, since it makes use of two sets of cutting wheels rotating around horizontal axis to produce rectangular panels of improved soil rather than one or more vertical rotating shafts creating circular stabilized columns. For this reason, an alternative mixing quality index related to energetic principles has been defined in this paper based on the comparison between strength and permeability results obtained from in-situ and laboratory specimens. The first outcomes seem to confirm the capability of the new index to describe the differences in quality in both types of samples.

The design and execution of a non-conventional support system for an excavation pit in a slope will be presented in this paper. Because permission of placing ground anchors in neighboring property was not given, panels made by the Deep Mixing method, extending below the level of the planned building, have been constructed. Based on the specifications of the sub soil and groundwater condition the design concept as well as analytical and numerical calculations will be discussed. The main focus is put on the construction procedure and problems during the execution of the panels. Results from deformation measurements during the construction of the panels and the excavation of the pit will be presented and discussed. In a short summary the main lessons learnt from this difficult case history will be presented.

Rehabilitation of Buckeye Lake Dam in central Ohio presented significant logistical and technical challenges given the history of the site, limited access and the proximity of private residences to the work. Covering almost 200 years, Buckeye Lake has a rich and varied history of industry and recreation. Presently a State Park administered under the Ohio Department of Natural Resources, the seepage, stability and hydraulic performance of the existing embankment dam was deemed unacceptable necessitating rehabilitation of the structure. Flanked by private residential and commercial properties at the downstream dam crest, construction of the new seepage barrier and new dam necessitated selection of appropriate construction methods and close coordination with the public. After presenting a brief history of the site, this paper focuses primarily on the different deep soil mixing methods utilized to construct the seepage barrier as well as the use of additional deep soil mixing downstream of the seepage barrier to construct a composite gravity dam structure.

The single column mixing–double rotary head (SCM-DRH) method of deep mixing has been in operation now for a couple of years. The use of two counter-rotating mixing tool components achieves exceptionally intensive levels of mixing between soil and slurry. Therefore, the newly developed SCM-DRH tool represents a significant improvement of the single column mixing tool, as it enables to move the borderline of suitable soils for soil mixing applications. As it acts like a compulsory mixer, the grade of achievable homogeneity allows intensive levels of mixing between soil and slurry and the construction of soil mix columns not only in granular soils but also in cohesive soils where soil mixing usually gets to its limits. The paper will focus on initial field trial studies on the system and the different applications of the system, for instance soil improvement for settlement control, and also experiences made in various countries.

This paper summarizes the Japanese guidelines for design and quality control (QC) process for soil cement columns (SCC) in order to support foundations for building structures. A case history which used the SCC method to support shallow foundations and a floor slab for a building structure in Japan will be presented.

The seismic hazard on new and existing structures due to its significant effects on life safety and economy have become a primary issue for civil engineers and technical regulators. Several studies and research programs are still oriented to find solutions that could restrict the effects of the seismic events on heritage buildings. Inspired by the functioning principles of structural seismic isolators, this paper presents a research study on a new earthquake resistant ground improvement technique. The aim of the study is to evaluate the effects of the interposition of a specially treated thin layer of soil at a certain depth in a natural deposit, on the seismic motion at surface. A series of bench scale tests, numerical analyses and shaking table tests were carried out for a general evaluation of the effectiveness of the technique. The analysis of the results leads to promising outcomes, with sensible reduction of surface seismic effects.

SR 83/US 331 is a primary North/South roadway in Walton County that is a crucial link for tourism and commerce between the Walton County beaches and the heavily traveled I-10 corridor in the panhandle of Florida. The facility also serves as the primary hurricane evacuation route from southern Walton County. This 3.4 mile project involves expanding the current two-lane crossing of Choctawhatchee Bay to a four-lane facility to increase capacity and dramatically improve mobility within the corridor. One of the major goals of the project is to perform ground stabilization using deep and shallow soil mixing (DMM & SMM) along existing causeways. Ground stabilization was required due to the existence of moderately deep very loose soils that have settled considerably over the years. As a result, the Florida Department of Transportation (FDOT) incurred significant maintenance expenses and was unable to maintain an acceptable ride quality. The FDOT considered soil mixing as one option to control this settlement. A design was developed using a combination of SMM and DMM to transfer the loads to the more competent underlying strata. A complete field test program was performed to determine the appropriate mixes to utilize for the soil mixing given the high variability of the existing soils. Once the field test program was complete, a full scale load test along with a Plate Load Test was performed on a completed section of the South Causeway to ensure the FDOT required settlement criterion was met. The results of this test program confirmed the design assumptions and this paper will give an overview of the project with emphasis on the test program.

The Clean Rivers Project is DC Water’s ongoing program to reduce combined sewer overflows into the District of Columbia’s waterways; being the Anacostia and Potomac Rivers and Rock Creek. The Project is a massive infrastructure improvement designed to capture and clean water during heavy rainfalls before it ever reaches the public waterways. To create the massive underground structures that form the solution to combined sewer overflows (CSOs), tunnel boring machines are being used to excavate tunnels more than 100 feet underground. Known as the Blue Plains Tunnel, this first section of tunnel is a 4-mile reach of the 13-mile Anacostia River Tunnel, stretching from the blue plains waste water treatment plant, to the Main Pumping Station in downtown, Washington, D.C. Along the route of the Blue Plains Tunnel is the largest advanced wastewater treatment plant in the world, the TBM launch shaft, retrieval shaft, several drop shafts (around which pumping stations are to be constructed), and numerous diversion sewers and ancillary structures to complete the massive CSO infrastructure system. At each of these locations, various forms of ground modification/ground improvement were performed, including independent SOE systems, support for micro-tunneling operations, ground-water control, utility protection, and settlement protection. This paper discusses the challenges and solutions for this specialty work.

The cutter soil mixing (CSM) technique was used to construct an extensive deep mixing scheme for foundation support of mechanically stabilized earth (MSE) walls at the Kitimat Liquefied Natural Gas (LNG) facility in Bish Cove, British Columbia, Canada. Using real-time monitoring from the Bauer B-tronic system, the performance of CSM in highly variable subsurface conditions that consisted of thick deposits of fine-grained soils overlying granular soils was assessed, and the data used to develop a set of termination criteria for deep mixing using the CSM technique that would achieve the ground improvement design requirements. Real-time monitoring data was also used for interpretation of highly variable subsurface conditions, identifying areas where modifications to the deep mixing design was required, allowing fine-tuning of the termination criteria used for problematic areas that included dense granular till, thick organic layers, and obstructions, and identifying areas where increased in-situ wet grab and/or post-installation core sampling and testing would be most appropriate for quality control (QC) and quality assurance (QA). The merits of using real-time monitoring data as part of the engineering decision-making process including the development of “inferred torque” based on pressures at the cutter wheels to develop a simplified termination criteria in highly variable soil conditions is presented.

When the deep mixing columns were used to support embankment slope, the columns may fail under either the internal or the external failure pattern, dependent on the strength of columns, soil condition, and loading condition. A shallow layer, produced by shallow mixing method, was proposed to fix and reinforce these isolated columns. In this study, the centrifuge model tests were carried out to simulate the embankment construction on the soft ground, improved by the columns and the shallow layer. The effect of the shallow layer and column strength on increasing the embankment stability can be addressed from the model tests. The failure of isolated columns was compared to that of columns with the reinforcement of shallow layer in terms of internal stability. In addition, by using the test data simple calculations based on limit equilibrium were also carried out to access the failure patterns of column in both internal and external stabilities.

From 2012 to 2015 BAUER Foundation Corp. (BFC) performed deep foundation cut off/barrier wall works in the framework of the Center Hill Dam Foundation Remediation Project. This paper introduces the project, the requirements specified by the United States Army Corps of Engineers (USACE), and the approach taken by BFC. It describes the excavation equipment and excavation methods used. It discusses the steering capabilities of the hydrocutter and the real-time, as-built information provided to the operator via the B-Tronic system that is used to determine when and where to steer the cutter in the excavation. The achieved performance for verticality parameters including deviation and rotation are presented and compared to the requirements. Implications of the use of steerable hydrocutter technology on verticality specifications in complex geologic conditions are discussed.

For the conventional suspension bridge under construction in Maputo, MZ, the 2 main cables are tied into a massive counterweight of over 100,000 ton on each side of the Bay. This structure is placed in a circular shaft constructed by diaphragm walls of 1.20 m in thickness. With an outer diameter of 50 m, panel depth of 56 m and an inner excavation depth of 17.50 m and 37.50 m these shafts are among the largest presently being constructed worldwide. The depth was defined by the soil conditions, groundwater and the counterweight solution. Insight to the design, construction and excavation, additional foundation works, measurements and soil improvement inside of the shaft are given. The shafts have recently been closed after inside-filling of concrete and homogenous sand in chambers and the erection of the steel construction for the main cables are on their way.

A major goal of each U.S. Army Corps of Engineers (USACE) project is to capture lessons learned and communicate them forward from project to project. This permits sharing of knowledge and experiences nationwide and helps improve the USACE contractual methodologies, reducing overall costs, and improving designs. An example of this is the evolution of seepage barrier wall contracts. From the first Wolf Creek Dam cutoff wall in the 1970s to the more recent Bolivar and East Branch Dam cutoff walls, documentation and sharing of lessons learned have increased the efficiency and effectiveness of cutoff wall designs and contract specifications. The evolution process includes updates in contract philosophy, methods for verifying that construction meets design requirements, and inclusion of effective data management solutions for use both during construction and long-term documentation of the project.

The use of numerical modelling in solving geotechnical problems has significantly increased in the past two decades due to its widespread acceptance by geotechnical engineers and the rapid growth in computing power. In this work the failure of a slurry wall system which was the subject of a dispute between two contractors is investigated. The failed slurry wall was part of an excavation shoring system for a power plant intake structure in Australia. The construction sequence provided by the wall designer/contractor was not followed by the main contractor. The slurry wall failed and resulted in flooding of the excavation and significant ground deformations. This was followed by extensive and costly remediation works. The main contractor believed that the adopted construction procedure was not responsible for the failure, but its inadequate design was. This paper presents the methodology and results of modelling undertaken of the slurry wall installation to determine the magnitudes of induced stresses and displacements in the wall as a result of the adjacent excavation for two scenarios, “as designed” and “as constructed”. The analysis was carried out utilizing the FLAC 2D program (Itasca group) for a plane strain case, and its built-in elastic-plastic Mohr-Coulomb stress-strain model.

This paper sets out the site procedures to be adopted when using polymer fluids as alternatives to bentonite slurries for excavation support. These fluids are now accepted as alternatives to bentonite slurries for the excavation of drilled shafts and diaphragm walls. Field trials have shown that they can give better shaft friction and lower concrete overbreak than traditional bentonite slurries and yet they have fluid properties that utterly contradict the norms established for bentonite slurries. For example, the rheology of polymer fluids is quite distinct from that of bentonite slurries–they have effectively no gel strength and the appropriate operating range of Marsh funnel times for a polymer fluid may be from 60 to over 100 seconds, markedly higher than for bentonite slurries and yet clean displacement of the excavation fluid by concrete is achieved. In contrast, specific gravities are markedly lower with that for fresh polymer fluid at 1.0, that is, the SG of water and typically a maximum prior to concreting of <1.02. It will be shown that site-operating practice with polymer fluids is also very different from that with bentonite slurries. For example, no soil-fluid separation plant is required (that is, no screens, hydrocyclones, centrifuges etc.). Also fluid disposal is necessary only at the end of a job and after minor treatment can be to municipal sewer.

Since 1975, there has been a rich history of embankment dam remediation in the U.S., mostly to prevent seepage and erosion through and under these structures. The history of these works has been described by many authors, the compendium of Bruce (2012) being the most recent, addressing projects completed up to 2010. Since then, a number of extremely large remediations have been completed, including cutoffs at Clearwater, Wolf Creek, Center Hill, Pine Creek, Bolivar Dams, and Herbert Hoover Dike. Together these more recent projects greatly exceed the combined cost of similar works conducted in the prior 35 years. This paper provides an updated compendium of these projects, and provides detailed references for future researchers to develop.

The construction of a plastic concrete cut-off through the core of a newly completed embankment dam is a comparatively rare practice. This paper discusses the design, procurement, construction and performance of the cut off wall and the role of real-time monitoring in securing success of the works. Site conditions required an embankment type dam and ground investigation identified extensive granular alluvial deposits in the valley floor overlying bedrock of mudstone and sandstone. To overcome anticipated shortfall in suitable core fill and to cut through the alluvial soils it was proposed to install a plastic concrete cut off from the dam crest down in to the bedrock. Construction had to overcome variable ground conditions including high pore pressures in the core fill, obstructions in the alluvial soils, coarse granular bands and a relic slip in the bedrock. During construction panel alignment was checked using real-time readout in X and Y planes from logger in the hydraulic grab. Real-time monitoring of pore pressures in the fill, alluvial soils and bedrock was obtained from data loggers connected to vibrating wire piezometers. Upon completion the performance of the wall was monitored as the reservoir impounded by comparing pore pressure readings upstream and downstream of the cut-off.

The Red Rock Hydroelectric Project is currently under construction at the existing U.S. Army Corps of Engineers Red Rock Dam on the Des Moines River near Pella, Iowa. A reinforced concrete diaphragm wall constructed of large T-shaped panels was required to form the intake approach channel for the project. In the permanent condition, the wall will be a 69-foot-high cantilever with total depth of 130 feet, including the soil and rock socket, to retain the upstream slope of the existing embankment dam. The diaphragm wall will also be utilized for excavation support during construction of the intake structure and upstream penstocks. An additional diaphragm wall was constructed along the crest of the dam to form a cutoff wall. Both diaphragm walls are critical elements for maintaining dam safety during construction and throughout the life of the project. Therefore, quality control during excavation and construction was paramount.

Unfavorable lands consisting of problematic subsurface conditions stands as a major challenge against the use of earth berms in the passive side of embedded retaining wall for stabilization and performance improvement. Additional challenges are encountered when discontinuous berms are needed. This paper discusses the use of jet-grout columns in enhancing the ability of discontinuous berms to control the inward movement of diaphragm walls embedded in soft soils during the critical stage of berm removal. 3D finite element analyses were used to model the wall, berm, and grout-column configurations. The effect of the jet-grout column configuration was varied in a parametric study by changing the depth and width of improved area, area improvement ratio of the jet-grout columns, and the opening width of the discontinuous berm. The effect of improvement configuration was depicted in terms of deflections, settlements and bending moments. Utilizing jet-grout columns allowed for the ability of introducing bigger openings through the berm’s removal process, and enhancing performance by decreasing maximum wall deflections, settlements behind the wall and maximum bending moments.