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By Alice Arana, David M. Cacoilo, Joel L. Volterra

"To make space for the new South Ferry Station in lower Manhattan, engineers and contractors carved out a new tunnel beneath three operating subway tunnels and tangentially to yet another tunnel. Creating the space required the design and construction of complex temporary excavation support and underpinning systems and the design and installation of real-time monitoring systems. Construction for the new station and tunnel was mainly cut-and cover in a mixed-face area of soil and rock approximately 2,000 linear ft long, 60 ft wide and up to 70 ft deep. Close coordination between the design/build team and the project owner, the Metropolitan Transportation Authority (MTA), was critical.With the construction of this $400 million project, the MTA and New York City Transit (NYCT) are correcting the numerous physical and operational deficiencies of the existing station and improving the lives of millions of commuters. Built in 1905, the original South Ferry Station is on the IRT Broadway–Seventh Avenue Line of the New York City Subway and is the southern terminal of the #1 subway service, which forms a loop to return uptown. The station has a sharply curved single platform on the outside of the outer track of a two track loop. This platform is short and does not allow the rear five cars of a normal 10-car subway train to load or unload. In addition, once the train stops at the station, commuters wait while retractable floor grates bridge the gap created between the platform and the subway car doors, and then they have only one exit from the station. Spray nozzles keep the tracks lubricated to reduce the train wheels’ friction caused by the tight curve. The sharp curvature of the loop and the inability to use half of the subway car doors slow train operation. With the new ADA-accessible station, 10-car trains will be able to open all doors, and additional entrances, escalators and elevators will greatly reduce travel times."

Jan 1, 2008

By Deep Foundation

Whenever an organization launches an initiative, the question arises whether that initiative has staying power. Or is the initiative, as is quite often the case, merely a fad; that is, just an activity that suddenly becomes popular, but which does not stay popular for very long. When the Federal Highway Adminis- tration (FWHA) started its Advanced Geotechnical Methods in Exploration (A-GAME) initiative, that question was addressed, especially considering the fact that up to 50% of major infrastruc- ture projects suffer impacts to schedule or cost due to geotechnical issues. Many of these issues relate to risks identified directly or indirectly to the scope and quality of site character- ization work. Effective site charac- terization is critical for recognizing. potential problems that may affect design and construction and for ensuring safe, well-performing and cost-effective projects. Grounded on that, knowledge of all available site investigation methods should continue to be shared widely and the application of those methods should be encouraged on an ongoing basis throughout the project lifecycle. The A-GAME initiative covers five technologies: Cone penetration testing (CPT), monitoring while drilling (MWD), electrical geophysical methods, seismic geophysical methods, and optical and acoustic televiewers. Of these, three soil and rock investigation methods were highlighted that are underutilized not only here in the U.S., but also in many places around the world: CPT: a well proven and established method for soil characterization that turned 90 last year, in which continuous in-situ data are col- lected quickly and consistently. Geophysics: the science that assesses the physical properties of the soils and rock using seismic and electrical techniques, which con- tinues to advance in leaps and bounds as the application of well- understood technologies become more powerful.

May 1, 2023

By Nagarajan. D, Raja Rajan. K, Vijayakumar. T

Major bridges crossing mighty rivers must be constructed in flowing water. Constructing the sub-structure in water has been a challenging job for contractor. Special construction techniques with marine fleets to be adopted for waterfront construction. Enabling works like temporary piling platform and cofferdam used for pile and pile cap construction. Apart from this, enabling works like load out jetty to transport the materials from land to water; temporary walkway for access of workman to work location; temporary access bridge for construction vehicles movement; temporary liners for tower crane foundation; Concrete block to act as dead man anchor for barge movements were all required by the contractor for smooth functioning of site as per construction schedule. Investment in enabling works by contractor plays a significant role on profit margin of the project and of course with utmost safety. Design of enabling works for waterfront structures involves hydrological data like afflux, bathymetry survey, current force, scour depth and wave force to be taken cautiously for safe and economic design. Type of foundation and pile/well cap top level corresponding to water levels shall influence the construction scheme. Usage of geotechnical software like Wallap and Plaxis required for enabling work design to enhance the safety of the structure. Bathymetry and soil condition play a critical role in design and construction of enabling works. Water Discharge quantity in river along with water levels like low water level, high flood level, seasonal fluctuation of water levels has a great impact on design of enabling works. Establishing enabling works for waterfront construction near to an existing bridge is an additional challenge for the contractor. Along with design, constructing the enabling works in water requires special construction methodology and sequence of work. This paper shall provide insights on overview of design and construction of enabling works for waterfront construction.

Nov 1, 2022

By Stephen Buttling, Zhong Rui

"A single unit gas fired power station was being built on the edge of the Gulf of Thailand in 2001. The soil conditions consisted of very soft to soft Holocene Marine Clay, and the site was part of a coast line which had been subsiding below high water mark for some time. In order to provide access around the power station a road system in a figure-of-eight formation was required, and this also needed to be above the design flood level, allowing for future settlement. A ground improvement scheme was proposed and constructed, which consisted of two spacings of prefabricated vertical drains (PVD) over two depth ranges, vacuum consolidation and pre-loading, and rigid inclusions.During the construction phase, the vacuum consolidation was applied for 202 to 221 days in different zones, and monitoring allowed a prediction that the future settlement, including secondary consolidation over a period of 25 years, would be within the range of 175 to 355 mm, which met the contract requirement of less than 400 mm.The power plant was completed and became operational in 2003. Monitoring of the road levels continued, as did the settlement, and in early 2010 the total settlement since the end of vacuum consolidation had reached about 800 mm. The monitoring data both during the ground treatment and for the following 7 years is presented and analysed. This is supported by numerical analysis using 3D finite element methods which shows good agreement with the measured data, and allows a preliminary explanation as to why the predictions were so far out.BACKGROUNDAfter a period of bidding and negotiation, the Eastern Power and Electric Co Ltd (EPEC), an Independent Power Producer, entered into an agreement with the Electricity Generating Authority of Thailand (EGAT) in November 1997 to sell them power. In 1999 an Engineering, Procurement and Construction (EPC) contract and an Operation and Maintenance contract were signed with a supplier to provide a gas-fired (with oil as a back-up fuel) 350 MW combined cycle power plant in Bang Bo, Samut Prakarn Province, east of Bangkok. The site of the plant at Bang Bo is located immediately to the east of the Samut Prakarn Wastewater Treatment Plant, adjacent to the Gulf of Thailand (see Figure 1) in an area of very soft to soft marine clay (Bangkok clay) having low shear strength and potential for excessive settlement. The site layout comprises the main Power Plant components of generating block, cooling towers, fuel unloading area and storage tanks, switchyard and administration block, separated by access roads."

Jan 1, 1900

By Garland Likins

The Texas Department of Transportation, now considering using Augered Cast-In-Place (ACIP) Piles (also known as Continuous-Flight-Auger or CFA Piles) in their foundations, awarded a research project to Professor Mike O'Neill at the University of Houston (UH) to study the advantages and potential difficulties with ACIP/CFA piles. ACIP/CFA piles were installed on three sites for UH; they had extra instrumentation and additional measurements by UH staff during installation which are beyond the scope of this paper. Independent visual logging of the pile was done by an experienced inspection firm. The main advantages of ACIP/CFA piles are their speed of installation and their economy. Potential savings are substantial. Disadvantages include an unknown structural condition of the shaft. Inspection is critical, but many simultaneous observations make accurate inspection difficult. Because of resulting uncertainty, many engineers have avoided ACIP/CFA piles in the past.

Jan 1, 1998

By Martin D. Larisch, Ronald Damen

The design and construction of temporary working platforms for cranes and piling rigs is a high-risk activity. It requires the careful selection of the appropriate input parameters to obtain the correct load cases, as well as the application of robust and reliable design methods to assess the required thickness and stiffness of the working platform. The document introduces some of the most common and most relevant guidelines for working platform design which are currently used in Australia and New Zealand. The authors will also discuss the basic assumptions and considerations about load transfer from construction plant, debate ground risk, compare the applicability of different design methods for various ground conditions and suggest some common verification methods for working platform certification.

May 1, 2022

By Michael D. Justason

This paper describes the technology behind the development of an automated energy control system for a diesel pile hammer. Some background is given on experience using an energy monitoring system on the Route 1/I-95 interchange in Alexandria, Virginia. An adjustable hammer throttle and feedback from an energy monitoring system was then used to create a fully automated hammer energy control system. The performance of this system is described in reference to a piling project in Canada where the automated energy control system was used to obtain an unprecedented level of quality control and assurance ? data and graphs from the project are presented. The hammer energy control system (ECS) was used to successfully control and maintain a prescribed impact energy for the diesel hammer. This paper presents the first ever results from a truly automated diesel pile hammer and points to a new direction in quality control and assurance in pile driving.

Jan 1, 2006

By Arvindh Gupta

BC Hydro proposed to improve the stability of the existing Seven Mile Dam with 54 corrosion protected, re-stressable anchors comprising 92/0.6? strands each, in phase 2 of the program. Being globally the largest capacity anchors ever build, coupled with extra ordinary specifications, the project was a challenge for the entire post tensioning industry. The paper discusses the challenges associated with the anchor material supply as per specifications, extensive research and development carried out by Con-Tech Systems ltd. to overcome the challenges and contribute in making the project a success. The substance of this article is published in the Aug/Sep issue of ADSC magazine.

Jan 1, 2004

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 Seth H. Hamblin, John E. Regan, Dimitrios Palantzas

"Through reliability-based calibration of larger pile load test databases, recent developments of the Load Resistance Factor Design (LRFD) methods, which include geotechnical load and resistance factors for deep foundations design, have advanced the state of practice for geotechnical engineering. These load test databases upon which the current geotechnical load and resistance factors have been developed are limited, however, and do not provide sufficient data to support the development of resistance factors for uplift (tension) pile capacity. As such, some recommended resistance factors for uplift capacity estimation methods are simply derived by reducing the recommended resistance factors for piles in compression by a factor of 0.10.The results of three (3) tension loading tests performed to failure on 508 mm (20- in) square precast, prestressed concrete piles, driven though granular soil in southeastern Massachusetts, are presented and compared to static pile capacity calculations and dynamic analyses performed using the Pile Driving Analyzer (PDA) during installation. These results are presented along with current recommended LRFD resistance factors for driven piles under uplift (tension) loading conditions. These comparisons offer an assessment of the applicability and limitations of current resistance factors methods for piles under uplift loading and may be useful additions to the existing database for future calibrations of LRFD resistance factors for driven prestressed concrete piles in sand.IntroductionIn 2010, two (2) natural draft cooling towers were constructed by Kiewit (Kiewit) Construction Company of Woodcliff Lake, New Jersey at the Brayton Point Power Station in Somerset, Massachusetts. These massive 500 foot tall, 400 foot diameter cooling towers were designed to convert the existing “open loop” system into a “closed loop system” thereby dramatically reducing the thermal impact to Mt. Hope Bay.Based on design guidance from the German VBG Design Code and the Massachusetts State Building Code (MSBC), tension (i.e. uplift) and lateral loads due to wind loads and design seismic events represented the critical loading conditions.Weighing approximately 190,000 kips upon completion, the cooling tower loads are transferred to 44 foundation nodes (i.e. pile caps) evenly spaced along ring beams which run the circular perimeter of each tower base. Each pile cap node was designed to resist a 2,000 ton compression load, 200 tons in tension (i.e. uplift), and 600 tons in the lateral direction."

Jan 1, 2015

By Gokhan Inci

Stability problems with dam spillways on existing landslides and appropriate mitigation measures to remedy them are ongoing concerns for geotechnical engineers. The first successful application of drilled piers as stabilizing structures under the spillway was at the Trinity Dam in Sicily, Italy. ?Underpinning? was considered as an alternative to spillway relocation during the Alpaslan 2 embankment dam design in eastern Turkey. Based on the available literature the first application of drilled piers to stabilize a spillway chute in the U.S. was at the Ralston Dam in Colorado. Ralston Dam, which is a 175-foot-high zoned fill dam located 15 miles northwest of downtown Denver, was built in the late 1930s. The concrete spillway for the dam was built on the Pierre Shale Formation in the left abutment. Since reservoir operations began, mass movements have occurred downstream of the chute area. These movements have required periodic spillway maintenance. After the occurrence of recent movements and because of high piezometeric levels, URS was contracted by Denver Water to develop a more permanent solution by the installation and monitoring of additional instrumentation, analysis of slope stabilizing measures, design, repair, and reconstruction of the distressed section of the spillway chute. With state of the art modifications that include: 1) a stabilizing berm with a toe trench that improves the global stability; 2) seepage prevention and control measures that prevent the infiltration of water; and 3) the structural support of the replaced chute section with drilled piers and reinforced concrete the probability of future displacements or other problems have been reduced for the Ralston Dam Spillway.

Jan 1, 2007

By Don C. Warrington

This paper describes a new wave equation analysis program called ZWAVE, which is a program specifically for external combustion hammers. The program is de-scribed in detail, the discussion dealing with topics concerning the program such as 1) the numerical method the program uses to integrate the wave equation, which is different from most other wave equation programs; 2) the modelling process of both cushioned and cushionless hammers; 3) the automated generation of mass and spring values for both hammer and pile; 4) the method of dealing with plastic cushions; 5) the use of a recently developed model for computing shaft resistance during driving; 6) the computation and generation of values based on basic soil properties such as shear modulus, Poisson's Ratio and soil density; 7) the completely interactive method of feeding data to the program; 8) the method used to compute the anticipated rebound and the energy used to plastically deform the soil; and 9) the format of the inter-active input of the program and the program's output. Sample problems for the program, along with comparison of the program results with data gathered in the field, are presented.

Jan 1, 1988

By Ali Azizian, Brian Hall

"Driven piles were selected to support the Fraser Heights Bridge bents. Piles were a key component of the top-down construction approach, which was adopted for minimizing potential impacts on an environmentally sensitive wetland. Project requirements mandated verification of pile capacities using dynamic methods. More than 40 Pile Driving Analyzer (PDA) tests were performed. The subsurface conditions were highly variable. On the east side, piles extended through loose sands, soft silts/clays, and two peat layers and were founded in glacial till-like soils at about 45 m depth. However, on the west side, till-like materials were so shallow that it was difficult to drive the piles sufficiently deep to obtain the necessary lateral support. This paper provides an overview of the geotechnical considerations of the bridge design and top-down construction approach, and expands on the presentation of PDA results and how they compared to pile capacity estimation methods and parameters recommended in the applicable design codes.INTRODUCTIONThe Fraser Heights Bridge (FHB) was a component of the Fraser Heights Connector (FHC), a 2 km section of the South Fraser Perimeter Road (SFPR), constructed as part of the Port Mann/Highway 1 (PMH1) Improvement Project. The FHC is located in northeast Surrey BC (Fig. 1).Two major design and construction determinants were: 1) a mandated tight schedule to provide a non-tolled alternative to a new toll bridge; and, 2) an obligation that construction had to occur with minimal impact on the environmentally sensitive wetland the FHB crossed, including limiting the footprint of the permanent and temporary works to less than 45 m2, and prohibiting construction access onto the wetland. Construction equipment was only allowed on the wetland on temporary trestles or on the finished structure. This latter requirement resulted in the bridge being constructed span by span, using a top-down approach."

Jan 1, 2016

By Martin B. Hudson, Andrew K. Cho, Rolff B. Knobel, Les R. Chernauskas, Jonathan L. Ernst

ABSTRACT The Bruce Museum, located in Greenwich, Connecticut, is home to an extensive display of art and natural history exhibitions. A large addition was designed to be constructed adjacent to the museum requiring new spread footings to be installed up to 16.5 feet below the existing foundations. The soil conditions at the site consist of highly variable sand and gravel overlying weathered rock and sound bedrock. The Contract Documents called for traditional foundation underpinning. Traditional underpinning techniques, however, presented two major challenges on this Project; (1) deep underpinning pits would be required involving multiple levels and staging with tieback support and (2) the highly variable soil and bedrock composition and elevations presented uncertainty in the design and construction of the pits. In lieu of traditional underpinning, Geosciences Testing and Research, Inc. (GTR) proposed an “active” soil nail underpinning system. A major reason that the soil nail underpinning option was feasible, related to the fact that the soil nails and facing could be installed slightly in front of the existing footings rather than directly underneath the existing footings. The soil nail wall design involved one to four rows of soil nails with nail positions and wall depth able to be adjusted “on the fly” as excavation progressed depending on the field conditions encountered. To create the “active system,” the soil nails were pre-loaded to mitigate wall deformations that would be associated with a standard passive soil nail wall design. To evaluate the performance of the active soil nail wall and confirm design assumptions, an extensive automated monitoring, on-site testing and inspection program was proposed and executed by GTR to monitor deformations of the wall and the museum in real-time, evaluate and confirm bedrock and soil bond stresses and ensure that each soil nail was pre-loaded and locked off. Careful analysis, planning, and use of the observational method illustrates the importance of collaboration between design and construction personnel and applying engineering judgement throughout construction. The use of the observational method includes the potential for modifying design based on conditions observed. This paper presents a unique case study of the “active” soil nail underpinning system to support and protect sensitive structures, close collaboration between design and construction facilitated by real-time deformation monitoring, and its successful application as a safe and cost-effective alternative to traditional underpinning.

Oct 1, 2022

By Paul Pedini

The challenge of Contract C19E1 of Boston's Central Artery Project called for the construction of two roadways under the commuter rail yard at North Station. Two options were offered for the method of their construction: Slurry Wall Roof-First or Soft Ground Tunneling. The instability of the indigenous soils seemed to rule out the use of tunneling, so the slurry wall method was chosen. However, these soils were incapable of holding up during slurry trench excavation. After many episodes of ground loss on early panel excavations, Modem Continental Construction suggested a method of trench wall stabilization. The Contractor (MCC) both suggested wall stabilization method and requested that the owner participate in the funding for the effort. The Project and the Contractor were able to agree on a solution which resulted in collapse-free excavation...and found an innovative way to fund the solution.

Jan 1, 2002

By Ramin Motamed, Fahim M. Bhuiyan, Raj V. Siddharthan, Joseph Toth

The difficulty in material characterization and the erratic response of cemented soil layers, such as caliche in the Las Vegas valley, creates challenges for practicing engineers to reliably predict the response of deep foundations. The focus of this paper is the numerical prediction of axial response in drilled shaft foundations, which are commonly used in infrastructure projects (i.e., bridges and tall buildings) in Las Vegas, NV. The prevalence of hard caliche layers with variation in the degree of cementation add to the complication in numerical modeling. In this study, the applicability of two existing t-z models, developed for Florida limestone and soft rock, was evaluated based on numerical simulations of three bi-directional load tests conducted at caliche-dominant sites. The corresponding top-down load tests were also simulated for further assessment. A MATLAB-based finite-difference program, NVShaft, has been used to implement the mentioned t-z models in axial load analysis. Complexity originating from drilled shaft construction and the interaction with caliche during one axial load test resulted in a stiffer predicted response compared to measure data. For the other two load tests, both t-z models produced comparable load-displacement responses. It was observed that the t-z model for Florida limestone predicted relatively stiffer responses and higher drilled shaft capacity.

Sep 8, 2021

By Karen Talbot, Noah Maier, Rob Jameson, Giuseppe Gaspari

A storage and drainage tunnel advancing below I-75 in Detroit, Michigan experienced sudden subsidence. The Tunnel Boring Machine (TBM) was damaged to the extent that its shield, cutting head and extensive interior components needed to be extracted and replaced along with several completed tunnel segments. The tunnel was 16 feet (4.9m) in diameter with crown over 79 feet (24m) deep at the time. The tunneling contractor immediately engaged their designers and specialty subcontractors to develop a scheme to access the machine and repair the tunnel. They required a shaft 99 feet (30m) deep, with unobstructed plan dimension of 50 feet (15m) to accommodate the large components that needed to be removed and replaced. This precluded the application of an internally braced excavation and instead earth support solutions focused on use of a compression ring. Since the completed tunnel section behind the TBM obstructed closure of the compression ring below its invert, this paper describes the innovative access shaft solution employed. A conventional compression ring was constructed using 5 feet (1.5m) diameter drilled shafts down to the tunnel crown. In front of, and to the sides of the tunnel heading, the secant shafts were extended to over 150 feet (46m) depth, creating a horseshoe of support extending 50 feet (15m) below the planned excavation invert. Larger diameter "King Pile" shafts were drilled immediately to either side of the tunnel, overlapped into each end of the secant "horseshoe". The king pile shafts, together with a heavily reinforced ring beam above the crown elevation, acted as a door frame to transfer hoop loads from the incomplete secant arc into reaction supports above and below the tunnel. These oversize king pile shafts were extended and socketed into rock over 70 feet (21m) below tunnel invert. Very tight installation tolerances were necessary to maintain secant shaft alignment to depths exceeding 150 feet (46m). The project operational, geotechnical, and quality data was managed and visualized using a custom GIS interface. This paper will present the design approach employed and review the construction and quality program selected to repair the tunnel.

Oct 1, 2022

By Lance Helwirg

New high and low double outfall bridge structures for a juvenile fish bypass system have been constructed on the Washington Shore approximately two miles downstream from the Bonneville Dam on the Columbia River. The high and low outfalls each extend approximately 400 feet into the river from the Washington shore and are designed to release juvenile salmon into the river at above-water discharge elevations for improved survival rates. The two outfall structures include post-tensioned concrete double box flume girders approximately 7 feet high by 13 feet wide, which will be submerged in river flows as high as 15 feet per second. Each of the 6 offshore foundation piers is composed of a single 10-foot diameter reinforced concrete drilled shaft with a permanent steel casing embedded into the river bottom approximately 100 feet. Challenging outfall design conditions included designing the entire structures to be submerged for long periods of time in 15-feet-per-second river water flow with a 60-foot cantilever at the end of each outfall, and with the superstructure 70 to 80 feet above the river bottom. Figures 1-1,1-2, and 1-3 show the high and low outfall structure overhead photos and elevation view.

Jan 1, 2001

By Todd W. Armstrong, Michael D. Reader

"INTRODUCTIONThe Playa Vista Development is the largest urban infill development in the history of the United States. Overall, it encompasses about 1100 acres in the City of Los Angeles and is situated north of Los Angeles International Airport near the Pacific Ocean. The development taking place on the project consists primarily of high-density residential condominiums with 1 to 2 levels of subterranean parking . The geotechnical conditions are typified by high groundwater, soft clays, and liquefaction, in addition to environmental issues such as methane.Due to a combination of the geotechnical factors and noise restrictions, both driven and drilled piles were not feasible once the initial phase of the project was occupied. As a result, the project developer undertook a testing program that consisted of the installation and load testing of 9 piles in order to obtain City of Los Angeles acceptance of a pile installation system that met the site constraints. The testing program was divided between two separate contractors operating on sites set on opposite sides on the street (Figure 1 ). Contractors working in Test Areas A & B employed the ""dry dip"" and ""wet dip"" methods of auger pressure grouted displacement (APGD) pile installation, respectively.This paper summarizes the extraordinary program undertaken to install, document, test, and examine auger pressure grouted displacement piles at this site. The program ultimately resulted in City acceptance of auger pressure grouted displacement piles, a historically difficult challenge given the City's resistance of acceptance of ""new"" technologies.A summary of elements included in the test program are: (1) quality control; (2) load testing; (3) long-term testing; (4) non-destructive testing; and (5) pile exhumation."

Jan 1, 2005

By William G. Ryan, David S. Graham, Dan A. Brown, Rich A. Lamb, Paul J. Axtell

"The St. Croix River Crossing project on the Minnesota-Wisconsin border has been in the process of planning and public debate for two decades, with several changes in alignment. During the course of the earlier planning process in 1995, a drilled shaft load test was performed to obtain preliminary design information. There were some difficulties in maintaining stability within the weak sandstone bearing formation, and the measured axial resistance was relatively low. Subsequent experience by the Minnesota Department of Transportation with similar weak sandstones on the I-35W project suggests that improved construction techniques using modern drilling fluids may offer opportunities for improved performance. During final design in 2012 a second load test program was performed of a full scale test shaft constructed using polymer drilling fluids. The stability of the socket excavation in the weak sandstone appeared to be greatly improved and the measured axial resistance significantly higher.This case history illustrates the excellent performance that drilled shafts can provide in even relatively weak sandstone bedrock as well as the profound influence on axial resistance associated with the construction techniques used. The improved resistance values obtained by the new load test with more recent construction technology allowed the foundation scheme to be substantially optimized with respect to the number and size of required drilled shafts, reducing the size, cost, and risk of the coffercells and footings.IntroductionThe Minnesota Department of Transportation (MnDOT) has awarded the first phase of a bridge construction project that will cross the St. Croix River between Oak Park Heights, MN and St Joseph, WI. The first phase construction contract involves building the river pier substructures including groups of drilled shafts beneath each tower leg. A general location of the bridge project is provided in Figure 1.Prior to award of the construction contract, two separate design-phase axial load tests were performed on non-production drilled shafts with rock sockets. Both tests were static, bottom-up tests using the Osterberg Cell (O-cell). The first test was performed in 1995 when final design and construction was thought to be imminent. After years of public debate and literally, an act of Congress, design of the project was finally restarted and a second load test performed in 2012. The 1995 test was conducted on the Minnesota bank approximately 900 ft southwest of the St. Croix River bank. The 2012 test was conducted in the river about 2,100 ft northeast of the1995 test location. A plan-view of the project indicating the test program locations relative to the bridge alignment is provided in Figure 2."

Jan 1, 2015