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By Raffaella Granata, Daniele Vanni

"This paper presents the drilling and grouting program performed at two abandoned landfills located into former calcarenite rock quarries in Manfredonia, Italy. Tests performed after the abandonment of the landfills detected leachate infiltration into the groundwater, which required the implementation of a remedial program. In order to seal the rock fissures and create an impervious basin at the base of the two landfills, sub-horizontal boreholes were drilled and grouted into the rock under the waste deposits. At the same time, sub-vertical boreholes were drilled and grouted along the perimeter, to laterally confine the landfills. Finally, the landfills were properly capped with an HDPE membrane, geogrid, geotextile and topsoil. The methodology implemented to create a watertight barrier under the two landfills was innovative and cost-effective. Moreover, the drilling and grouting minimized the environmental impact of the remedial work, since the waste remained in their original location and were not affected by the remedial process.IntroductionThe two landfills, “Pariti-1 RSU” and “Conte di Troia”, are located approximately 6 km (4 miles) southwest of Manfredonia, a small town close to Foggia, Italy (Fig. 1). These landfills are located into two rock quarries, formerly used for the extraction of calcarenite (i.e., a weak calcareous sandstone, in tuff facies), and were abandoned in the early 90s. The two landfills cover a total area of about 45,000 m2 (11.2 acres), and mainly include urban solid waste with a depth of up to 25 m (82 ft). The main characteristics of the two waste landfills are listed in Table 1."

Jan 1, 2016

By Piotr Kozlowski, Stanley L. Worst, Matthew J. Niermann

Circular secant pile shafts were installed along the tunnel alignments for both the Ohio Canal Interceptor Tunnel project in Akron, Ohio and the Ohio River Tunnel project in Louisville, Kentucky. The diameters ranged from 34 to 51 feet and the depths ranged from 49 to 107 feet. Verticality and concrete volumes were measured on all piles to verify compliance with the design, which for some shafts consisted of a finite element model with multiple openings using unreinforced concrete secant piles. All secant piles were drilled into rock to seal off the groundwater. This paper will discuss the design, construction and quality control of the secant piles for these projects. INTRODUCTION Many Midwest and Northeast cities have Combined Sewer Overflow (CSO) systems which discharge pollutants into waterways during wet weather events. One way to remedy this issue is to provide a temporary overflow tunnel. A temporary overflow tunnel connects to the combined sewer system and collects the overflow during wet weather events, storing the wastewater until the event has subsided. After the storm event, the stored wastewater can be pumped to the treatment facilities and processed as normal. Project Background – Akron, OH The Ohio Canal Interceptor Tunnel (OCIT) project was performed as a result of the Environmental Protection Agency’s (EPA) Consent Decree with the City of Akron, Ohio. This Consent Decree required modification of the existing Combined Sewer Overflow system. The resulting project consisted of a 27- foot diameter tunnel with multiple points of entry to capture the sewer overflow and prevent it from entering waterways. The tunnel is over 6,000 feet long and is as deep as 150 feet below the ground surface; see Figure 1 below.

Jan 1, 2019

By Gisele R. Passalacqua, Aly Mohammad, Joanna Smith

The $13 billion John F. Kennedy (JFK) airport construction redevelopment program includes new terminals and buildings that are supported on piles to meet the airport expansion demand due to increased travel. This paper presents a case history for JFK airport with main focus on construction activities and lessons learned. Challenges include limited head room, presence of underground utilities, and hard driving. Video inspection of pile proved very beneficial. In general, soil conditions at JFK Airport consists of sandy fill followed by a 5-foot thick organic soft layer. Below the organic layer, glacial sands occasionally mixed with gravel were encountered for great depth with increases in density with depth. The tapertube pile is an ideal choice for foundations with high capacity achieved through skin friction along the taper section. The piles are easy to splice to accommodate low head room. Pile Driving Analyzers (PDA), and Static Compression Load Tests were performed. The results of these tests are presented in this paper to illustrate the high pile capacity achieved. More detailed discussion and analysis of the test results will be presented in another paper related to the same project. Lessons learned from this project are shared to help the engineering community with future design and construction of similar projects.

By Giovanni A. Bonita, Asher H. Peltz, Sean D. Johnson

This paper examines a complex earthwork project in the Washington DC metro area that had project delivery directly impacted by questionable instrumentation monitoring data. The case study summarizes the impacts to the project caused by questionable instrumentation data and reveals how the authors were able to utilize data to extract meaningful insights. The case study also demonstrates how clear data presentation became a key factor in maintaining stakeholder trust and facilitated progress of the project schedule. The case study highlights key points to collecting high quality instrumentation data, approaches to assess and improve value of the data collected, and techniques to reduce and interpret questionable data.

By Phillip E. Glogowski, N. Catherine Bazan-Arias

Steel foundations can be designed to cross-sectional configurations ranging from triangular and square to other multi-side shapes. Adding lateral extensions (hereby called wings) along the length of the steel stem can increase the foundation’s uplift, torsional and lateral load capacities. DiGioia Gray staff developed a methodology for the optimal design for multi-facetted, winged deep steel foundations. A finite element (FE) model is used to represent the steel components and the nonlinear subsurface behavior. The geometry of the foundation can be complex; thus, an optimal design needs to be fine-tuned to the specific site conditions. We created a pre-processor tool to generate the FE model including varying values for the number and size of wings, depths of embedment, reveal/stickup heights, top plate geometries, and subsurface profiles. The analytical model has been partially validated through full-scale testing and the methodology has been applied to two installed projects to date.

Sep 8, 2021

By Thomas W. Scott, Manh N. Tran

Marine environments present a range of challenges for pile construction. This paper contains a discussion on the design and construction of marine piles for a recent Toll Shipping wharf upgrade in Burnie, Tasmania. The project involved several new structures including mooring, berthing and ramp dolphins supported by driven tubular piles with rock sockets, and an onshore mooring dolphin and ramp abutment supported by bored piles. Through the project, a range of construction challenges were experienced, including availability of tubular piles, the different penetration depths of driven piles into rock, the ability to drill out sockets when the piles were raked, the difficulty in verifying the design intent, latent conditions and ship impacts. The paper will present a summary of the different factors that influenced design concepts for the structures involved in the upgrade, and the challenges involved in the design of the structures. Following this, the paper will describe the methodology used to verify the design (including a pullout test), observations made during pile construction and lessons learned on how to limit risk throughout construction.

Nov 1, 2022

By Stefan Larsson, Jan Ekström, Jennie Kock-Larsen, Håkan Garin

"This paper describes the testing procedure (or protocols) for quality control of dry deep mixing columns in a major ground improvement project carried out in Sweden. Quality control was mainly based on column penetration tests performed at different stages in the project and on two occasions after installation. In the paper, the results from the tests are compared with tests on the unimproved clay. As expected, the results show that the correlation between undrained shear strength in the columns and in the unimproved soft soil depends mainly on the in-situ stress. However, the correlation probably depends on when the tests were performed after mixing. When the influence of the in-situ stress was excluded from the analysis, no significant correlation could be identified. This means that the undrained shear strength in the columns and in the unimproved soft can be considered to be uncorrelated when the strengths and the corresponding variability are evaluated with depth from groups of tests.INTRODUCTIONQuality control and quality assessment of deep mixing (QC/QA) constitute a key component in verification of the limit state design. Due to the complex mixing process and varying geological conditions, it is normally not possible to sufficiently assess the strength and deformation properties in advance. In Sweden, the most commonly used QC/QA method for verification of the limit state is the column penetration test (Axelsson and Larsson 2003; Bergman et al. 2013). The method works well but is time-consuming and requires many tests since property variability is normally high. The column penetration test can be used to assess the undrained shear strength Cu,col. However, it is not clear how the strength correlates to the undrained shear strength of the unimproved soil Cu,soil. There are common factors such as the in-situ stress state and the natural water content, which makes a positive correlation probable, i.e. as Cu,soil decreases, Cu,col also decreases and vice versa. The unimproved soil has a natural spatial variability, but it is not known if the improved soil follows the same variation. The mixing process has a substantial influence on the strength variability and may supersede the influence of other factors. However, if a sufficiently good correlation exists between Cu,col and Cu,soil, information from the geotechnical ground investigations can be used in the design and planning of QC/QA of deep mixing in a more stringent manner. Information about the correlation is also essential in reliability based design, where a strong positive correlation may have a negative influence on reliability. However, as discussed by Al-Naqshabandy and Larsson (2013), this correlation may be weak or insignificant for a representative failure domain where the mixing process may have a dominant influence on the strength variability. It is thus of interest to assess the correlation."

Jan 1, 2015

By Yan Lap J. Kan

"A waterfront stabilization system consisting of Deep Soil Mixing (DSM) columns, vinyl sheet pile fascia, and concrete flood walls supported on shallow footings was designed and constructed for a high-density waterfront development in Northern California. The project site is underlain by soft, compressible organic soil locally known as Bay Mud that has been capped with loose sand and imported fill. The waterfront stabilization system constructed at the site mitigates liquefaction, consolidation settlement and seismic potential slope deformation along the waterfront; the system was designed to reduce lateral displacements to tolerable amounts for the proposed structures. This paper presents the general design methodologies, construction challenges and quality control of this waterfront stabilization system.INTRODUCTIONUrban development in Northern California is fueling innovations in geotechnical engineering as more complex sites are developed. ENGEO Incorporated introduced a deep soil mixing technology from Japan to the US and designed a waterfront stabilization system for a high density waterfront development project in Redwood City, California. The approximately 12½-acre project site, as shown on Fig. 1, is surrounded by water on three sides, with an inner marina at the center of the site.The project site is located in the seismically active San Francisco Bay Area in California. The San Andreas Fault, the Monte Vista-Shannon Fault, the Hayward Fault and the San Gregorio Fault are major active faults located within 25 miles of the site. Once a former marshland with a major slough until the late 1950s, the site was reclaimed by placing imported fill over the native compressible clay deposits, locally known as Bay Mud."

Jan 1, 2016

By Filippo Maria Leoni, George Filz, Wesley Schmutzler, Matteo Bertoni

"The US Army Corps of Engineers selected the Deep Mixing Method (DMM) for the required stabilization at the LPV 111 Project (New Orleans, USA). DMM was used for ground improvement/foundation strengthening and consequently to stabilize and support the burden of the new levee. Two different technologies were used: Trevi Turbo Mix (TTM) and Contrivance Innovation Cement Mixing Columns (CI-CMC). LPV 111 is the largest soil mixing project to date in the USA with its more than 18,000 elements installed to a depth of up to 67 feet for a total of 1.7 million cubic yards of treated soil. The preparation and execution of the project presented many challenges from various points of view. The little time available to complete the job led to the simultaneous utilization of eight deep mixing rigs and batch plants which worked 24 hours per day, 5.5 days per week on a stretch of land approximately 5.3 miles long. Given the imposing geographical extent of the project, a four phase laboratory programme and five field validation test programmes, conducted in as many different areas of the project, were completed to design and optimize the grout mixes and the installation parameters. The massive quality control/quality assurance testing programme produced over 500 drilled core holes and over 5,000 tested specimens in order to determine unconfined compressive strength (UCS) and uniformity of the DMM elements. This paper has the purposes of describing the tremendous challenges encountered and providing valuableinformation that may be useful for other future projects, including details not previously published.INTRODUCTIONReach LPV-111 is part of the Lake Pontchartrain and Vicinity Hurricane Protection System designed to protect the city of New Orleans and the surrounding areas from the surge that would accompany a 100 year hurricane event. LPV-111 measures approximately 8.5 km (5.3 miles) long, of which 7.2 (4.5 miles) extend along the north bank of the Gulf Intracoastal Waterway (GIWW) and the remaining 1.3 (0.8 miles) run north and terminates at the CSX Railroad Gate. The Bayou Sauvage National Wildlife Refuge borders the levee on both sides (Fig. 1)."

Jan 1, 2015

By Patrick J. Hannigan, Seth Robertson, Rozbeh B. Moghaddam

The Top-Loaded Bi-Directional Test (―TLBT‖) and the conventional Bi-Directional Load Test (―BDLT‖) are full-scale static load test methods. In both methods, the test loads are applied bi-directionally to the deep foundation. The advantages of the conventional BDLT have been well established for cost efficient static load testing of deep foundations, particularly for large diameter, high-capacity drilled foundations. A conventional BDLT applies the bi-directional test loads using an embedded jack and bearing plates. The TLBT method also applies the bi-directional test load to embedded bearing plates but does so using reusable high-strength threaded bars attached to an above-grade hydraulic jack and load transfer assembly. The new TLBT method is well suited for load testing shafts of a moderate diameter, length, and nominal resistance or ultimate load. TLBT advantages include economic considerations resulting from the method’s reusable load application components and constructability considerations as it readily accommodates a center concrete tremie pipe or pump line location. This paper presents comparison results from full-scale load tests performed using both bi-directional load testing methods. Adjacent 3-foot diameter by 30-foot long BDLT and TLBT shafts were tested. Details regarding subsurface conditions and test shaft construction are included for the comparison of the TLBT and BDLT results. Corresponding test data and analyses for both test shafts are presented and discussed in detail. The BDLT shaft had a maximum uni-directional load of 240 kips at upper and lower bearing plate displacements of 0.5 and -3.8 inches, respectively. The TLBT had a maximum uni-directional load of 300 kips at upper and lower bearing plate displacements of 1.0 and -5.9 inches, respectively. These results as well as the load-transfer behavior and equivalent top loading curve results from the adjacent BDLT and TLBT drilled shafts are discussed. The paper also discusses the strain gage instrumentation on the TLBT load application bars and on the embedded bearing plates.

Oct 1, 2022

By Mohini Patel, Jahnavi Parmar, Pranav R. T Peddinti

Expansive clays pose a variety of geotechnical problems. Although the admixture stabilization is proven to address their problematic swelling and shrinkage characteristics, the influence of unsaturated condition on the engineering performance of these soils needs further research attention. In addition, highly saline soils with high organic content would further alter their performance. A similar soil stratum was encountered at the Gulf of Cambay, Bhavnagar district, India. High salinity in the in-situ expansive soil of basaltic origin and the prevailing unsaturated condition, enforces the engineers to look out for possible soil treatment methods. In this regard, the present work attempts to analyze the unsaturated behaviour of this soil when fly ash is used as an admixture. A comparative study for stabilized and unstabilized mixes is performed in terms of their unconfined compressive strength, electrical conductivity, swell characteristics and California Bearing Ratio.

May 1, 2022

By John Kvinsland

"The Block 43 Project is the future home of the Paul Allen Institute for Brain Science located just off the southern shore of Lake Union in Seattle, Wash. The South Lake Union (SLU) district experienced considerable development over the last 10 years and Vulcan, Inc., which is headquartered in Seattle, is at the forefront of this transition. Once a light industrial/residential location, SLU has transformed into a hub of medical technology comprising new residential units and mixed-use buildings. Malcolm Drilling Company, Inc. constructed four shoring projects for Vulcan in this vicinity over the last year, beginning with Vulcan Block 44, which consisted of 42,000 sq ft (3,902 sq m) of soldier pile and tieback wall to support a below-grade parking facility. Block 44 construction began in February 2013 and ended in mid-April. The feature project, Vulcan Block 43, was in planning stages at the time and began construction in late fall 2013.Awarded by GLY Construction of Bellevue, Wash., in September 2013, Block 43 was the most complex of the block projects performed by Malcolm. Block 43 featured dewatering and ground improvement components along with a water-tight secant pile wall. Following the commencement of Block 43, Malcolm also began work on Vulcan Block 52 in December 2013. Block 52 consisted of 43,000 sq ft (3,995 sq m) of conventional shoring in conjunction with dewatering of 8 ft (2.4 m) of excavation located below the water table. The final Vulcan project was Block 45, which started in January 2014 for Turner Construction of Seattle and consisted of 41,000 sq ft (3,809 sq m) of conventional shoring and required dewatering to complete the final 15 ft (4.6 m) of excavation.Scope and Subsurface ConditionsBlock 43 involved a wide variety of drilling applications for the building to be constructed and properly founded. The primary scope of work involved shoring support for an underground parking structure requiring excavation of approximately 82,000 cu 3 yds (62,694 m ) of soil. The cuts for the excavation were up to 43 ft (13.1 m) in depth, and the excavation was bounded by city streets as well as the South Lake Union Light Rail on its perimeter. In order to excavate beneath the water table, an extensive, deep dewatering system was required to drain the upper fill and reduce the impact of the pressurized aquifer located beneath the excavation. In addition, drilled rigid inclusions, along with compaction grouting, were required for foundation support of the future structure."

Jan 1, 2014

By Ihab Allam PE, Meeok Kim. PE. Ph. D

The wet weather equalization basin (EB) planned for Pacifica, CA is a 45 feet deep rectangular shaped underground water tank containing over 2.1 million gallons of water, and located only 500 feet away from the Pacific Ocean. The location and size of the water tank, and the geotechnical characteristics of the selected site presented many engineering and construction challenges. The engineering had to consider a structural system which can fit into the limited area of the site and yet need to meet the storage volume requirement. In addition, the system construction should meet the city’s tight budget and schedule.

By Francisco A. Flores, Rigoberto Torres

The Complementary Technical Standards of Mexico’s City Building Code do not mention the criteria to compute the bearing capacity of Steel H-piles. It is necessary to increase knowledge in using steel H-piles as foundation elements in very soft soils of Mexico City. Considering their applicability to reinforce structures as well as new foundations in confined spaces, this research is proposed to obtain the axial load capacity of piles at scale in laboratory. This paper describes the construction and testing of scale models in laboratory of steel H-piles to measure their axial compression and tension load capacity in the soft soils of Mexico City. Three types of piles were fabricated at scale. Tests were performed on individual piles and pile groups. Based on the axial load tests, the load-displacement curves are presented both in compression and tension. The analysis of the results is shown, and comments are given regarding the ultimate bearing capacity of piles. Recommendations are presented regarding the determination of the bearing capacity of these piles in the very soft soils of Mexico City.

Sep 8, 2021

By Michael Forrest, John Roadifer, Glen Gorski

"The Calaveras Dam Replacement Project (CDRP) requires large disposal sites to store excess excavated materials that could not be utilized for dam construction. Because of access restrictions during design, the disposal site rockfill toe dike area at the edge of the reservoir could not be explored to evaluate soil conditions. As such, the site had to be explored as part of the construction contract. Exploration revealed very soft clay and loose silty sand up to 40 feet thick that would not be able to support the rockfill dike at the toe of a large disposal site fill. Several alternatives were evaluated to stabilize these soils. Based on constructability, cost and risk considerations, cement deep soil mixing (CDSM) was selected as the preferred method of soil stabilization. The challenge was to design and construct the CDSM stabilization to minimize construction delays. A joint effort by the design engineer, construction manager and contractor achieved CDSM stabilization in about three months, from design through completion of construction. A rigorous quality control program included compression testing of both wet grab and cored soil cement samples to demonstrate that specified strength requirements were being achieved.INTRODUCTIONDisposal Site 3 (Figure 1) is one of the primary CDRP disposal sites having a height of 240 feet and a storage capacity of about 2,500,000 cubic yards. An approximately 40-foot-high rockfill dike at the base of the disposal site provides an erosion resistant toe for the disposal site. The rectangular foundation area shown in red was not able to be investigated during design because of access restrictions."

Jan 1, 2015

By Brandon M. Robinson, Osman F. Besler, Dominik Gaechter

With the increase in population over the last decade, and anticipated population growth over the coming years, Norway is making significant investments in the Country’s infrastructure. Part of this investment in development starts with the Intercity development project in South-East Norway, which is the largest transport project in Norway. The Intercity Development project consists of 270 km (167 mi.) of new doubletrack rail, capable of train speeds reaching 250 km/h (155 mph). The new stations are centrally located in the major cities, in South-East Norway, to provide the benefit to as many citizens as possible. The goal of the project is to reduce the increase in traffic, which is coupled with an increase in population, and reduce the travel times between the cities. The Intercity Development Project has an anticipated completion date of 2034. The Sandbukta-Moss-Såstad (SMS) project, part of the Intercity development, includes 10 km (6.2 mi) of new double-track railway and is situated on the Østfold Line, near the city of Moss, Norway shown in Fig. 1. The 10 km SMS-section covers three open stretches and two tunnels, including 630 m (2,066 ft) substructure for double-track railways on the open line at Sandbukta. The Moss tunnel is a 1720 m (5,643 ft) long tunnel from Sandbukta to Moss center, including a 420 m (1,378 ft) long concrete culvert. The new Moss station includes an 800 m (2,625 ft) long station area. The Carlberg tunnel is a 2350 m (7,710 ft) long tunnel from Kleberget to Carlberg, including a 200 m (656 ft) long concrete culvert.

Sep 8, 2021

By Torsten Wichtmann, Jan Macheck, Frederik Broz, Patrick Staubach, Hauke Zachert

The majority of heavy or strongly loaded structures, for instance high-rise buildings, large span bridges or gas storage tanks are founded on pile groups. However, current design codes and guidelines do not provide a standard procedure for their design under lateral dynamic and high-cyclic loading arising from e.g. wind, temperature or earthquake loads. To establish appropriate design strategies, a better understanding of the pile-soil, pile-pile and pile-cap interaction is required. This paper is focused on finite element backcalculations of centrifuge tests on single piles and pile groups subjected to up to 500 lateral load cycles. For the finite element simulations, a special calculation procedure is applied, combining two kinds of constitutive models, a conventional (Hypoplasticity with Intergranular Strain extension) and a special highcycle accumulation (HCA) model. The parameters of the constitutive models are calibrated based on static and cyclic laboratory tests on the sand used in the centrifuge tests. The performance of the applied numerical procedure is evaluated based on a detailed comparison of the simulation results with the measured data from the centrifuge tests. Overall the applicability of the used numerical strategy for simulating the behavior of pile groups subjected to high-cyclic loading is shown.

May 1, 2022

By Lance Rasband, Richard Hanke

"Seattle Tunnel Partners (STP) started mining on Seattle’s SR99 tunnel on July 30, 2013, working slowly through a 15 ft (4.6 m) thick fiber-reinforced concrete headwall. Once through the headwall, the machine would move through roughly 400 lineal ft (122 m) of jet grout-improved soil at a rate slightly over 6 ft (1.8 m) per day. It was anticipated that once through the improved area, Bertha—the world’s largest tunnel boring machine—would move at a rate of 35 ft (10.7 m) per day. By the end of October 2013, Bertha had mined roughly 430 ft (131 m), averaging 4.73 ft (1.4 m) per day, and had begun mining within native soils. By the start of December 2013, tunneling reached the 800 ft (244 m) mark and Bertha averaged 12 ft (3.7 m) per day, achieving as much as 42 ft (12.8 m) of progress on some days. However, on December 6, 2013, Bertha began to stumble and all progress quickly came to a halt. Preliminary InvestigationInitial reports stated that an obstruction had stopped the machine in its tracks. Malcolm Drilling received an early morning call on Sunday, December 8, 2013, from STP to rapidly mobilize a Bauer BG-50 drill rig with crews to investigate what was hindering Bertha’s progress. Malcolm’s equipment and crews flew into action and were completely mobilized and operational by mid-week. The preliminary investigation involved installation of 10 deep dewatering wells to reduce the hydrostatic head within the ground around the machine and allow STP personnel to inspect the cutter head from within the shaft for presence of obstructions. By the close of December 2013, the wells were installed and the dewatering system was fully commissioned. STP crews were then able to inspect the cutter head and found small fragments of a steel pipe wrapped around the outside of the shield. The steel was apparently from an abandoned 10 in (0.25 m) diameter monitoring well casing previously installed by WSDOT (Washington State Department of Transportation) to monitor groundwater conditions for the design and planning of this very project. After the steel was cut out of the head and cleared from Bertha’s path, she attempted to move forward but was only able to manage a slow crawl"

Jan 1, 2015

By Robert Thurner, Albin Norrman, Sami U. Raja

The West Link is a double track railway project currently under construction in Gothenburg, Sweden. The project includes the construction of 8 kms of track, 6 kms of which will be in tunnels. Beside several large excavations, three new stations will be built: Centralen, Haga and Korsvägen, all within the city of Gothenburg. The first construction phase of the project began in May 2018, and the finalization of the project is expected in 2026. The project is divided into five sections. Keller is involved in four of these contracts since the design & planning phase in 2018 assisting the special foundation works with various geotechnical techniques including Dry deep soil mixing (DDSM), jet grouting, rock grouting, uplift piles, sheet piling and rock dowels. The core idea behind successful collaboration has been to apply the right product for a location specific challenge which can help optimise costs & time for the project with a minimal environmental impact. Due to the extensive nature of the project, a team of experts from various locations around the world is helping design and execute various foundation technologies and providing solutions to the practical challenges in the project like working close to existing structures, rail lines, river etc.

May 1, 2022

By Chris L. Powell, Russell J. Denny.

"The remotely located Cockatoo Island iron ore mine off the Kimberly coast in Western Australia, which has been in operation since 1951, was recently expanded up to 50m below sea-level using staged construction of a rock-filled seawall around the open cut mining operation. The most recent stage of the seawall expansion required a seepage reducing cut-off barrier to be installed through the seawall into underlying seabed sediments. A line of grout holes at 1m centres was proposed to form the seepage barrier, with grouting extending 17m below the top of the seawall. Top hammer drilling techniques were used to penetrate the 12m deep rockfill to seabed level, and permeation grouting carried out within the rockfill to fill voids and stabilise material around grout holes. The local 10m tides meant that tidal washout of fines and grout would be a major risk, and so a combination of cementitious and chemical grout was used to create rapid gel times. Following permeation grouting, holes were re-opened to allow jet grouting to hydraulically mix and grout permeable seabed sediments below the seawall. Using the duplex jet grout system in a single pass to 17m below platform level, the jet grouting was extended upwards into the seawall fill itself to overlap with the earlier permeation grouting. Finally a soil/cement mixed capping trench was installed using slurry trenching techniques with soil/cement/bentonite mixed backfill in order to complete the grout treatment. The approach taken allowed considerable onsite flexibility in technique. An automated slurry batching plant allowed adjustment of mixes to suit the varying subsurface conditions which were encountered during the works.IntroductionLate in 2013 Wagstaff Piling was engaged to install a seepage barrier through a rockfilled seawall built to allow expansion of sub-sea iron ore mining operations on Cockatoo Island off the remote Kimberley coast in the North West of Western Australia. Earlier stages of seawall construction had used a variety of different construction techniques with varied success, and the history of sub-sea mining on the island had been plagued with failures, including failures in the slope of the seawall itself, hanging wall failure underneath and inside the seawall, and footwall failures as the ore was mined leaving the rock face inclined at 55 degrees, parallel to the bedding. The current expansion, known as the Stage 4 expansion, was more tightly constrained by the pit geometry and available materials than previous seawall expansion stages that adopted clay core and sheet pile seepage barrier solutions. In Stage 4, an innovative grout curtain seepage barrier solution was selected to ultimately provide the necessary cut-off to allow access to high grade ore, while protecting the mine from inundation by the sea."

Jan 1, 2016