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By Karen Dawson

This paper presents a case study of the deformation-based design, construction, and performance of stone column ground improvement (GI) beneath a mechanically stabilized earth (MSE) wall and bridge abutment with heights up to 50 feet. As part of the widening of Interstate 5 (I-5) to allow High Occupancy Vehicle (HOV) lanes in Tacoma, Washington, a new approach and span over the Puyallup River will be constructed. During the soils investigation and design phase of the project, low plasticity silts (ML) inter- bedded with silty sand layers and organic silt where identified as being potentially liquefiable. Stone column ground improvement was designed using a deformation-based approach to address static settlement and seismic stability of the proposed MSE embankments. The deformation-based design of the stone columns resulted in significant savings over a limit equilibrium-based approach. This paper presents the results of sonic coring taken from the initial stone columns installed and compares these results to the real-time data acquisition reports from the stone column installations. Vibration monitoring results during stone column installation are included. Settlement monitoring at the face of the MSE wall and buried vibrating wire settlement monitoring elements are presented and compared to the original settlement predictions.

By Mikael Calando, Thomas Joussellin

"San Francisco's rapid growth has caused the city to plan for the Transbay Transit Center Project, a visionary transportation and housing project, that will transform downtown San Francisco and the San Francisco Bay Area’s regional transportation system by creating a “Grand Central Station of the West” in the heart of a new transit-friendly neighborhood that will be home to more than 20 new towers rising a high a 1,070 ft. This paper describes the specificities of using advanced diaphragm wall technology, tooling, equipment and installation practices for deep foundation and permanent underground structures. In particular, this paper will emphasize on the urban constraints, geotechnical conditions, and the novel approaches adopted for the construction challenges of the Transbay Transit Center’s Load Bearing Elements, or Barrette PilesPaperThe Transbay Transit Center Project consists of the construction of a new multimodal, five-story Transit Center located in the South of Market neighborhood near the Financial District in San Francisco. The future Transit Center will incorporate nearly 83,000 square feet of retail, a 5.4-acre rooftop park, an extensive public arts program and bus ramps that will connect the Transit Center to a new off-site bus storage facility and the San Francisco–Oakland Bay Bridge. The new facility will accommodate more than 100,000 passengers each weekday and up to 45 million per year. Additionally, the new Transbay Transit Center will replace the since-demolished San Francisco Transbay Terminal, and nearly 20 towers, such as Salesforce Tower, will take advantage of the height increases allowed through the Transit Center District Plan.The approximately $4.5 billion project features a new five-story structure (including two underground stories) and new bus ramps which include a cable-stay bridge. The deep foundations for the pylon of the bridge (Pylon 9) consist of two each 21 ft x 5 ft barrettes (also called Load Bearing Elements in the US) extending more than 180 feet below grade and 10 feet into the bedrock. The barrettes were chosen because of the combination of high loads, significant depth and small footprint. The barrettes are installed using the Diaphragm Wall technology. Nicholson Construction was contracted by Shimmick Construction to install the cable-stay bridge’s foundation elements."

Jan 1, 2016

By Ehab S. Shatnawi

It is common in practice to design laterally loaded rock-socketed drilled shafts using the p-y curve methods. However, the existing p-y curve criteria for rock were derived either semi-empirically or based on the assumption that the rock is an elastic isotropic continuum. The assumption of isotropy may be invalid for rocks with intrinsic anisotropy or for rocks with joints and bedding planes. Therefore, there is a need to develop a new p-y curve criterion to take into account the effects of rock anisotropy on the response of laterally loaded shafts. This paper presents a method for estimating the initial tangent Ki to the p-y curve for rock that can be characterized as transversely isotropic elastic continuum. Examples of transversely isotropic rock formation can be seen in most sedimentary rock where dominant bedding planes exist. The knowledge of the initial tangent to p-y curve is important, because it controls to a large extent the predicted deflection of laterally loaded drilled shaft in rock. The 3-D finite element parametric study results of a laterally loaded drilled shafts socketed in transversely isotropic continuum are employed to develop a series of design charts for estimating Ki as a function of transversely isotropic elastic constants.

Jan 1, 2007

By John P. Turner, Steven S. Dapp, Dan A. Brown

"The Goethals Bridge Replacement (GBR) spanning the Arthur Kill Waterway between Elizabeth, NJ and Staten Island, NY consists of a dual-span 1,982.5-ft long cable-stayed bridge with approach spans of 2,545 ft on the NJ side and 2,788 ft on the NY side. The bridge is supported on over 200 drilled shaft foundations ranging in diameter from 4.5 ft to 10 ft and socketed into Passaic Formation siltstone. Drilled shaft resistances for design were based on load tests as described in a companion paper (Dapp et al. 2016). This paper presents the main foundation design considerations and challenges. The approach to construction of the rock sockets, with a focus on quality in order to support the use of high nominal values of side and base resistance, is described. Lessons learned from this project and their application to future similar projects are presented.INTRODUCTION AND BACKGROUNDThe Goethals Bridge Replacement (GBR) project is a Public-Private Partnership (P3) that represents a major milestone for the Port Authority of New York and New Jersey (PANYNJ) in its distinguished history of bridge building in the greater New York City metropolitan area. The new bridge will replace the existing Goethals Bridge, named after Major General George W. Goethals, Chief Engineer of the Panama Canal and the first consulting engineer for the Port Authority. The existing Goethals Bridge along with the Outerbridge Crossing and the Bayonne Bridge comprise the three Port Authority bridges connecting Staten Island with New Jersey. The existing Goethals Bridge and the Outerbridge Crossing are cantilever truss structures and both opened on the same day in 1928. They were designed by J.A.L. Waddell under the supervision of the eminent engineer Othmar H. Ammann (1879-1965), who was the designer of many other iconic bridges in the NY City area including the Bayonne Bridge (1931), the George Washington Bridge (1931), and the Verrazano Narrows Bridge (1964). The designer of record for the replacement Goethals Bridge is Parsons Corporation, which is the successor firm of Robinson & Steinman, whose principal David B. Steinman was also a notable NY area bridge designer and a contemporary and rival of O.H. Ammann.The replacement Goethals Bridge is supported on over 200 rock-socketed drilled shaft foundations. Each main pylon tower is supported on a group of six 9-ft diameter drilled shafts and each anchor pier is supported by two 10-ft diameter shafts. Each approach pier consists of a two-column bent with each column supported on a rock-socketed drilled shaft. A rendering of the Main Bridge crossing the Arthur Kill is shown in Fig. 1."

Jan 1, 2016

By Tae Hwan Lee, Jun-Shin Lee, Daejin Kwag, Sangchul Bang, Gerard T. Houlahan, Moo Sung Ryu

"Geotechnical engineers have been installing innovative, permanent underwater foundation systems utilizing suction buckets for the offshore industry since the early 1980s (Senpere and Auvergne, 1982). This foundation system has been successfully used on numerous and various types of offshore structures in a wide range of environments. Suction buckets have numerous advantages compared to conventional underwater foundation systems. The more notable advantages include easy installation, large loading capacity, low noise and retrievability. The application of reduced water pressure inside the bucket facilitates the installation of the suction buckets, where a suction pump attached at the top of the bucket can accomplish the entire driving operation. Because of this efficient operation, very large suction buckets can be driven into the seafloor, which eliminates the use of a large number of small piles.In Korea, one of the most economical and reliable renewable energy sources is wind power; however, onshore wind power generation has encountered many problems, such as the lack of favorable sites and public concerns about noise and environmental damage. Consequently, offshore wind power generation has attracted increasing attention due to its abundant potential, high efficiency of grid connection, and availability of easy expansion.In November 2011, the government of Korea announced a national offshore wind power development roadmap, which targeted its offshore wind power generation with the goal of becoming one of the top three nations in the world for offshore wind power generation. Korea Electric Power Corporation Research Institute (KEPRI) is the main research arm of the Korea Electric Power Corporation (KEPCO) and conducts research and development on electricity, power generation, renewable energy and other energy-related matters. KEPRI ultimately provides forefront knowledge and leadership to KEPCO with respect to energy and related areas for its near- and long-term needs. Financial support for the overall project, of which the suction bucket foundation system installed for the pilot phase wind turbine is described below, was provided from the New and Renewable Energy Program of the Korea Institute of Energy Technology Evaluation and Planning funded by the Korean Government Ministry of Trade, Industry and Energy."

Jan 1, 2017

By Tony Suckling

"As we head toward the United Nations Climate Change Conference in Copenhagen in December, the environment and sustainability will become headline news for a while. Governments are expected to agree to a set of binding targets to reduce carbon emissions probably before 2020, and certainly before 2050. This will, in effect, initiate a low carbon economy in many parts of the world. Sustainability has mainly been rhetoric so far, the exceptions being projects for those looking to the long-term future and not for short-term financial gains.The probabilities and consequences of negative impacts on the environment and on society over the short term and in the long term can be assessed and mitigated, but mitigation often adds cost. Also, we cannot know what technologies will be available, say 1,000 years into the future, which is about 40 generations of our society. It is easier to have a connection with 100 years into the future, which is only about 4 generations. Individuals may have a different sense of sustainability, and place a different value on mitigation, its cost, its importance and its potential impacts.Sustainability means different things to different parties on a construction project. For example, a land developer is likely to have a different view on the design in terms of sustainability than that of the designer. The developer may also likely to be more interested in sustainabiliy if there are tangible economic benefits that might accrue. Achieving sustainability on any project, leads to conflict between competing interests or demands cooperation between the economic and technical sectors involved. The foundations for a building or bridge, by definition, need to interact with the ground whose behaviour cannot be dictated by man. The aims of sustainability are the same as for the building or bridge, both of which are constructed of manmade materials, but it is less clear how they should be achieved. An example is the driven pile that does not produce spoil waste, but is likely to be too noisy to be acceptable in an urban environment. This then begs the question, should the public accept the nuisance of short-term pile driving to achieve a more sustainable foundation? Additionally, the question has to be asked, can the deep foundations industry develop its techniques and products to help make them more acceptable and appropriate more often than is possible now?"

Jan 1, 2009

By Dennis Wrixon

It was a little bit exceeded. The decision was the uniform settlement is measured at each one corner and the highest one corner is the important one. And in addition there is a differential settlement of 2.1 mm allowed. So we reached about 7.8 or 7.9 mm with the highest corner and in addition 2.1 so it was a little too much. But behind there is a very difficult calculation of the authorities where all of the displacements are combined together and there are of course some more factors of safety in these settlements.

Feb 10, 2003

By Richard Guenther

As available space in urban centers becomes more scarce, builders and developers are increasingly turning to vacant, existing structures to meet cities' growing needs. The developers of City Ridge Roadside Development and North America Sekisui House (NASH) - - found a suitable site for their "urban village" at the former Fannie Mae headquarters complex on Wisconsin Ave. NW in Washington, D.C., which had been vacated in early 2018. The urban village will consist of eight new structures centered around the building that currently sits on the site. All told, the project will include 687 residential units, a 150-room hotel, over 150,000 sq ft (13,935 sq m) of retail space, and 62,000 sq ft (5,760 sq m) of office space. A below-grade parking structure will extend across most of the footprint. The Fannie Mae building, which was designed in the Colonial Revival style to mimic the Governor's Palace in Williamsburg, Virginia, was named a historical landmark following a request from the development team. The central portion of its existing masonry structure was built in 1956 on pile caps with small-diameter cast-in-place piles. Two wings, which were added in 1962, were built on belled caissons. There are three levels above grade and one below.

Feb 1, 2022

By Raymond E. Sandiford

"The redevelopment of the World Trade Center (WTC) provided an opportunity for the Port Authority of NY and NJ to complete a long sought underground connection between all of Lower Manhattan’s transit lines, the World Trade Center and the World Financial Center (WFC) (Figure 1). Creating this connection was a challenge because the WFC lies west of the heavily trafficked Route 9A, also known as West Street. The previous connection was a bridge that required pedestrians to make significant level and directional changes to navigate the crossing. The positioning and elevation of the Route 9A pedestrian tunnel was established to provide pedestrians with a clear, single level, climate controlled corridor from the new WTC Transit HUB to escalators leading into the WFC Winter Garden.As the most direct link to the WFC, tens of thousands of people a day will use the pedestrian corridor. To accommodate this large number of pedestrians and provide an obstruction free passage, the tunnel has a clear width of 50 ft (15.2 m). Although only 250 ft (76.2 m) long, that short length presented many technical challenges.Here I describe how the challenges were overcome during the construction. However, some of the truly problematic issues arose from coordinating the phasing of this project with adjacent construction activities at the WTC, the reconstruction of Route 9A, and the WFC’s redevelopment program. The limited access to the excavation areas and confined site logistics were further complicated by having to maintain six lanes of traffic on Route 9A at all times. The efforts were so intertwined that, well into the underpass construction, the Port Authority Construction Department decided to merge a portion of that work into the WFC redevelopment."

Jan 1, 2012

By Gerald Verbeek, Erick Baziw

Stone columns are used in geotechnical site remediation to increase load-bearing capacity and reduce settlement of foundations. Stone columns also improve slope stability and increase the shear strength of a soil. A very challenging problem is to characterize the in-situ shear wave velocities from data acquired from Downhole Seismic Testing (DST) after the insertion of stone columns. DST is an important geotechnical testing tool for site characterization that provides low strain (<10-5) in-situ interval compression and shear wave velocity estimates, but the postanalysis of seismic data acquired from DST in the presence of stone columns is very challenging due to the resulting complicated in-situ soil conditions. To obtain the right results it is necessary to use an algorithm that incorporates source wave raypath refraction. Starting with the Normal Moveout Seismic Cone Tomographic Testing (NMO-SCTT) algorithm developed some years ago, this paper outlines the modifications and additions made to this NMO-SCTT algorithm to facilitate stone column site characterization. To dramatically reduce the optimal solution space for the estimated interval velocities the paper also described a priori conditions that are applied based on the unique nature of the stone column site conditions.

By W. Morgan NeSmith

"The DFI ACIP Pile Committee, in conjunction with the Florida DOT, completed an ACIP Pile installation monitoring and performance test program in late 2016 to advance the inclusion of ACIP piles in future specifications for bridges by state agencies. Piles of different diameters were installed for compression, tension and lateral testing, and one pile was extracted for visual inspection. This paper presents the pile installation, non-destructive testing and load test results of the program.INTRODUCTION The Deep Foundations Institute (DFI) Augered Cast-In-Place (ACIP) Pile Committee performed a ACIP pile installation and test program in the fall of 2016 to demonstrate a fully monitored installation of 18-in and 24-in diameter ACIP piles. The program included automated and manual installation monitoring, Thermal Integrity Profiling, compression, tension and lateral load testing (including monitoring of strain gages embedded along the compression pile shaft), and post-testing extraction of an installed pile for visual inspection.PROJECT DETAILS AND FIELD EXPLORATION A general program location map along with an aerial view of the property in Okahumpka FL is shown in Figure 1. Two Cone Penetration Tests (CPT) were performed at initial reaction pile locations R-6 and R-8 (Figures 2 and 3) The results from CPT R-6 indicated very loose soil conditions at depths below 55-ft, indicating potential relic sinkhole conditions. The test layout was subsequently rotated and moved south of CPT R-8.TEST PILE INSTALLATION DETAILS Seven piles were installed to either 40-ft or 60-ft below grade. Thermal Integrity Profile (TIP) wires were installed in all piles but varied to include one wire each attached to a steel center bar or one wire attached to the steel center bar AND four additional wires (each) attached the steel reinforcing cage installed in these piles. Additionally, the 24-in lateral and compression piles had four steel or PVC casings installed next to the TIP wires for testing by thermal probe and/or wire inserted into the casing."

Jan 1, 2017

By Chris M. Haberfield

The design of side resistance of drilled shafts socketed into rock has traditionally been empirically based on the results of pile loading tests in which the side resistance can be isolated from the side resistance. In practice, this is achieved in one of several ways : loading the pile in tension, using a collapsible base, or by using a device such as an Osterberg cell to load the pile from the base. Although this approach has resulted in generally safe design practice, this has been at the expense of efficient design practice. Safety in design has been achieved through conservatism, which has been necessary because of the large scatter that is evident in the pile socket resistance database (Rowe and Armitage, 1984; Kulhawy and Phoon, 1993). Research at Monash University through the 1980&apos;s has been aimed towards understanding and then modelling the complex mechanisms of shear transfer at the concrete-socket interface of sedimentary rocks. Armed with such an understanding, the important factors which affect the strength of pile sockets can be isolated, and the reasons for the large scatter can be deduced. This paper briefly describes the research approach taken, and the main features of the design method and computer program which have now been developed. Some load-settlement predictions of the program are compared with the results of full-scale pile socket tests. The paper then presents the results of a numerical study which relates predicted socket a factors to unconfined compressive strength of the rock, socket diameter, initial normal stress and socket roughness.

Jan 1, 1996

By Lucian L. Bogdan

"SummaryActive loaded strand anchors are often used for slope stabilization, retaining walls or tiedown anchors. Normally, strands are tensioned against the structure and wedges are locked inside the anchorages at a certain lock-off load. During the life of the structure, anchors can receive additional loading during a surcharge, seismic event or other activity on the structure.In order to have a reliable ground anchor system, the strand must not slip through the anchorage wedges during its service life. Strand slippage has been reported during lock-off, when dirty wedge plates and wedges have been used. Low lock-off loads are believed to contribute to strand slippage too. Since the initial lock-off load for a ground anchor is usually lower than the lock-load for an equivalent capacity tendon in other types of post-tensioning construction, there is a concern that strand slippage may occur if the load on the anchor increases above the initial lock-off load.Corrosion protection grout, placed after the anchor is locked off, fills the pocket and surrounds the strand and wedges. Some anchor installers believe that the grout will prevent the anchorage from developing additional capacity if the load increases above the initial lock-off load.The load-carrying capacity of an anchorage depends on several factors. Most important are: initial applied load, anchorage geometry, friction between wedge-anchorage-strand and condition of the contact surfaces.The ADSC Anchored Earth Retention Committee considers that the industry should know how wedges behave once the permanent strand anchors are stressed and grouted inside the transition pipe, between wedges and inside the grout cap."

Jan 1, 2005

By Kenneth M. Berrry

A unique situation has developed at an abandoned coal mine in St. Clair County, Illinois. Subsidence features have been observed at the ground surface over the mine including settlement of a pair of bridges for Illinois Route 158. The Illinois Department of Transportation (IDOT) is currently replacing the two bridges. Foundation treatment for the two new bridges included backfilling the mine void. The light rail system for St Louis (MetroLink) is also constructing a bridge over the same abandoned coal mine less than 1000 ft from the Route 158 bridges. The new MetroLink bridge is being constructed using piles which extend through the coal mine and overlying bedrock in order to transfer the loads to below the mine floor. The differing foundation types for the IDOT and MetroLink bridges were due to geometry and economic factors involved with the individual structures.

Jan 1, 2001

By Charles G. Crans, Naresh Gurpersaud

"Toronto’s Union Station, a National Historic Site occupying an entire city block, is the busiest commuter rail transportation hub in Canada. An extensive project is being undertaken to revitalize Union Station while maintaining the historical significance of the building and minimizing disruption to commuters. A significant stage of the revitalization involves excavation indoors, to a depth of up to 5.5 m below the existing floor level to create space for a new transit concourse and a new lower-level pedestrian retail concourse. A hybrid excavation support system utilizing micropiles as soldier piles was constructed over an 18 month period between 2010 and 2011.Development and testing of connections between the micropiles, shotcrete facing, lagging, walers, and tiebacks presented significant challenges. The existing viaduct structure was constructed in the 1920’s on land reclaimed from Toronto Harbour, so there was significant (and ongoing) uncertainty with respect to buried obstructions including relic timber wharfs and abandoned steel and timber piles. Collectively all these conditions precluded the use of conventional methodology; new techniques, installed using modified equipment, and for the first time in the Greater Toronto Area, were required.Details of the existing site conditions, installation challenges, design, construction and performance of the hybrid excavation support system inside this historic structure are presented.INTRODUCTIONUnion Station in Toronto, Ontario is the busiest passenger rail facility in Canada, with 65 million passengers annually and an average of 200,000 passengers each day. Construction of the station was completed in 1920. It has been designated a National Historic Site of Canada and inducted into the North America Railway Hall of Fame in the Facility and Structure category.The Union Station Revitalization Project (USRP) was tendered in 2010 and awarded as a 6-year, $450M construction management / trade contract package. Included was a large scale grade reduction, referred to as “The Dig Down”, to create two basement levels and this required extensive excavation support constructed entirely indoors within the active station setting."

Jan 1, 2017

By Nicholas P. Gura

This paper presents the analysis, design, and load test program results for drilled shafts to support a 70-story hotel tower and associated 10 story podium structures located in Las Vegas, Nevada. A mat foundation for the structure, although feasible, would have produced undesirable differential settlements within the high rise tower footprint and at the interface with adjacent lower level podium structures. The resulting foundation system solution for the 70-story, approximately 800-foot long hotel tower was four-foot diameter drilled shafts, extending 100 below shaft cutoff. The design compression capacity for the four foot diameter drilled shaft was 5,000 kips. The load test program proved that the unique Las Vegas valley geology lends itself to efficient installation, precluding the need for engineered slurry or casing. The load testing program included the installation of two four-foot diameter test shafts to 100 feet below theoretical cutoff and the performance of two highly instrumented independent Osterberg load cell tests with maximum sustained test loads of 12,000 kips. Sonic caliper testing was also performed to document actual in-place shaft diameters and verticality. The load test program also provided information necessary for the foundation design of the podium structures. In addition to the tower?s drilled shaft load test program data, continuous flight auger (CFA) pile evaluation and testing was also performed. The CFA testing consisted of traditional ?top down? loading techniques and was performed as an alternative to the recommended shallow drilled shafts for the lower level podium structures. The results of the CFA test program provided supplemental, insightful soil friction data which was used in conjunction with the drilled shaft test program data in evaluating the most appropriate support for the lower level structures.

Jan 1, 2007

By Charles M. Wilk

"Mass stabilization (MS) is a ground improvement technique that can prepare areas of low bearing strength soil for subsequent infrastructure development. The technique involves mixing binding agents such as portland cement, fly ash, slag, or lime into the subject soil while the soil remains in-place (insitu). The binders “cement” the soil grains together to form a cement modified soil or a soil cement. The MS-treated area now has improved bearing capacity to support infrastructure or to prevent movement of the material such as landslides.The same insitu soil mixing technique can be used to address contaminated areas. Binders or reagents are mixed into soil. The treatment protects human health and the environment by immobilizing hazardous constituents within the treated material. When used for the purpose of environmental remediation the technology is called Insitu Solidification/Stabilization (ISS).Both Mass Stabilization and ISS treatments require laboratory studies to develop a mix design of soil and binder(s) that produce the desired physical and/or chemical properties. The mix design is then transferred into the field. Successful MS and ISS treatments rely on reproduction at full-scale of the mix design and the thorough mixing attained at laboratory scale. Fifty to 70% of the cost of a MS or ISS project is in the cost of the binding agent that is to be mixed into the subject soil. Under-dosing, overdosing, non-thorough mixing, and mixing in the wrong areas all create cost over-runs.This paper will discuss recent innovations in mass stabilization systems that improve the cost effectiveness of the treatment technology. Specialized equipment can impart greater mixing shear thus improving the thoroughness of mixing. Dry powder pressure feeders can conserve the “drying capacity” of binder resulting in higher strengths at lower binder dosages. Global Positioning System (GPS)-based systems can guide the mixing operator for complete mixing coverage. An integrated tracking and feeding system can record that proper dosing and mixing was accomplished and generate construction QA/QC reports for the client.INTRODUCTIONNew or expanding infrastructure projects may encounter areas of low bearing capacity soil or areas where marginal materials such as waste, dredged material, or sediment have been placed. Mass stabilization is a geotechnical method that can be used to improve the bearing capacity or stiffness of soil. Mass stabilization involves mixing binding agents into soil subject to treatment while the soil remains in-place or insitu.Mass stabilization technique can also address contaminated soil therefore, the same technique can be used to attain both civil and environmental engineering goals. In this environmental application the technology is known as insitu solidification/stabilization (ISS). ISS protects human health and the environment by immobilizing hazardous constituents within the treated material."

Jan 1, 2015

By Norm Kirk, Robert Bittner

"The addition of a new powerhouse at the existing Tulloch Hydroelectric site on the Stanislaus River in the western foothills of the Sierras Nevada Mountains of central California required a deep excavation in rock on the downstream face of the dam. A cofferdam (water exclusion device) was necessary to isolate the powerhouse construction site excavation from the existing Goodwin Reservoir and the turbulent discharge from the existing powerhouse. The cofferdam was positioned on a steeply sloping fractured rock surface exceeding 50 degrees.This paper describes the challenges encountered during design and construction of the cofferdam and describes the unique design features used to address these challenges including:•,The use of flat-sheet-piles to form cellular walls on the steeply sloping rock surface.•,The use of 5-ft deep tremie concrete plugs in the bottom of the sheet pocket cells to create the bottom seal of the cellular cofferdam walls against the sloping rock surface.•,The use of vertical post-tensioned rock anchors to provide shear resistance at the contact point between the base of the cellular-wall and the sloping rocksurface.INTRODUCTIONModification or expansion of existing hydroelectric power plants often require downstream cofferdams or water exclusion devices to temporarily separate new construction from turbulent downstream discharge of the existing dam. Most dams are positioned on solid rock in the narrowest and therefore the steepest section of the river. This combination of steeply slopingrock and the need for an exclusion barrier creates a challenge for the design engineer trying to maintain a safe dewatered construction site. Typical cofferdam solutions for hydroelectric dams usually use large granular filled circular sheet pile cells that perform as gravity structures. However, this type of structures is not well suited to steeply-sloping highly irregular rock surfaces in a confined area."

Jan 1, 2017

By Harald P. Ludwig, Matthew J. Niermann

The support of excavation (SOE) for the Capitol Crossing project in Washington, DC consisted of a combination of soldier piles, lagging, tiebacks, braces, underpinning, single auger soil mixed (SASM) walls, micropiles, and a tiedback slurry wall. Over 130,000 square feet of SOE was installed with more than 1,300 tiebacks providing lateral support for excavation depths of up to 72 feet. Several structures including the Holy Rosary Church, the Bell Tower, the Casa Italiana, and a modern office building were supported by a combination of conventional hand dug underpinning pits, bracket piles, and stiff SASM walls. This paper will focus on the design and performance of the SOE adjacent to the Holy Rosary Church and the Bell Tower. Deflection-based design was used to estimate the movements of and limit damage to these structures. An extensive monitoring program was used to provide real time movement data. The results of

By Adrian Mercer, Ashkan Ameri

Due to general degradation, increased traffic levels, and historical ground movement, this road and rail bridge which provides an essential link between the interior of the country and the Port of Abidjan, required significant repair and reinforcement. This included strengthening the pre-stressed concrete box girders and replacement of the existing bored pile foundations. Replacement piles had to be adjacent to, and no longer than, the existing piles, in order to not compromise the stability of the operational bridge during the works. The underlying geology, however, meant that the pile loads had to be predominantly transferred into the ground through end bearing. Rather than installing a greater number of piles or larger diameter piles, innovative thinking changed the usual mind-set of designing the piles to the prevailing ground conditions, to designing the ground conditions to suit the piles. Jet grouted columns were installed beneath the toes of the new piles to increase the bearing capacity of the ground. This significantly contributed to the sustainability of the project and reduced carbon emissions through saving concrete, steel, plus transportation and disposal of spoil.

Sep 8, 2021