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By Joel Moskowitz, George J. Tamaro

"A new office complex is being constructed within 25m of the Hudson River in New Jersey. The project, about 140m by 100m, will include 4 basements under the entire footprint. The perimeter was to be secured by a 0.8m thick diaphragm wall, laterally supported by high capacity tieback anchors to rock. Columns were to be supported on footings or piers to rock at a nominal bearing pressure of 3.8MPa at depths up to 17m. Although some variation in rock quality was observed in borings, a substantial vertical seam of weathered and/or decomposed rock, 1 to 2 meters wide by as much as 8 meters deep, was encountered during construction necessitating field redesign. In some locations, the seam dipped below rock that is more competent. Footings were redesigned for support on drilled caissons, or soft rock was excavated and replaced with concrete necessitating a reduction in bearing pressure of the footings by one half. The tower covering the south half of the site was topped out in 2002 and the garage levels in the north half of the site were completed in 2003.PROJECT DESCRIPTIONIn September 1999, a major investment company began the due diligence process to evaluate a property on the shore of the Hudson River in Jersey City, New Jersey for a new multi-use complex. The site offers a spectacular view of lower Manhattan directly across the river from the site of the former World Trade Center. The site, covering two city blocks, was previously occupied by manufacturing and office facilities of Colgate-Palmolive.The building footprint is approximately 140m by 100m, the southern half of which is occupied by a 260m tall office tower, shown in Fig. 1. As of this writing, design of the structure for the northern half of the site has not been finalized, but it is expected to comprise an 11-story office building. A glass-covered atrium will occupy the street that formerly separated the two blocks. As part of the due diligence process and preliminary design evaluation, alternatives were considered to accommodate various numbers of parking places, both above and below existing grade. A major consideration for below grade parking is the proximity of the Hudson River some 25m east of the east building line."

Jan 1, 2004

By Greg Canivan, Bernie Hertlein, Les Chernauskas, Joram Amir, Garland Likins, E. Anna Sellountou, Tim Kovacs, Peter Kandaris

Nondestructive testing of drilled shaft foundations via Crosshole Sonic Logging (CSL) is often performed as part of the quality assurance process to assess the soundness of concrete. The intent of CSL testing is to identify irregularities such as soil intrusion, necking, soft bottom, segregation, voids and other defects that could result in poor structural performance of the foundation. Over time, CSL rating criteria based on first arrival time and relative energy have incorrectly evolved to often be the sole means of determining the acceptability of a shaft. Some of these criteria have found their way into regulatory agency specifications, with acceptance values often differing from agency to agency.The purpose of this document is to review the state of the practice (including experience gained over the past 20 years), propose improved CSL rating criteria and make recommendations for additional assessment, as well as educate the industry on the proper interpretation of CSL test. CSL test results alone should not be the sole means of rejecting or accepting a shaft. A task force of industry exerts was formed to review the existing CSL rating criteria and propose improvements where appropriate. The recommendations presented herein are the consensus of the task force, which believes that they should be incorporated into future criteria, codes and specifications. This paper was produced as a joint effort between the Codes and Standards Committee, the Drilled Shafts Committee and Testing and Evaluation Committee. A task force was authorized under Testing and Evaluation Committee. The task force contributed their expertise in web-based discussions often every two weeks over a period of three years. Interested participants were invited to participate at any time. The document had two rounds of broad industry review, two rounds of DFI Technical Advisory Committee reviews, and a Public Comments process. All comments were considered in producing the final document.

Jan 1, 2019

By Satyajit A. Vaidya

This paper presents a case-study in the design and construction of deep foundation element supported mats for two residential towers on an18,000-square-foot site in Brooklyn, New York. Based on site sub-surface conditions, conventional mat foundations bearing on medium dense sand, having an allowable bearing capacity of 3 tsf, were originally anticipated for the 16 and 25-story towers. However, when the tower shear walls were relocated to the edges of the mat foundations due to architectural revisions, the significantly increased mat edge contact stresses applied to the soil subgrade resulted in calculated settlements of a magnitude that would adversely impact the proposed structures and the neighboring/bordering lot-line building and rail transit subway structures. To address this issue, deep foundation element supported mats were designed for the towers. The design was performed as an iterative process involving structural SAFE and geotechnical Plaxis finite element computer analysis to develop a coordinated geo-structural model of the foundation system. Initial presumptive design values of 45 pci and 445 kips/inch were used for the modulus of subgrade reaction and minimum deep foundation element stiffness, respectively. The designed foundation system consisted of 40 and 60-inch-thick mat foundations for the 16 and 25 story towers, respectively. Initially, the deep foundation elements were designed as 50-foot-long, 14-inch-diameter elements installed to sustain a maximum individual compressive load of 250 tons. The final deep foundation element design was subsequently refined to consist of a 48-foot-long, drilled and grouted IBO Titan 103/51 element designed to sustain a maximum load of 167 tons. Subsequent field load tests on the deep foundation elements confirmed element stiffness ranging from 1,040 to 1,530 kips/inch, with measured mobilized side shear of about 29 psi. The mat foundation reinforcement was adjusted for the pile stiffness values determined in the field load tests, and the deep foundation supported mats were constructed. The two towers were subsequently constructed, and have performed successfully.

Jan 1, 2010

By Jin-Wei Huang, Bradley J. Fleming, Sri Sritharan

"Although soil improvement and its application to deep foundations is gaining popularity in the engineering community, this technique is not widely used in high seismic regions due to lack of fundamental understanding of both the behavior of improved soils under high-strain cyclic loading and the interactions between the pile, improved soil, and unimproved soil. This paper describes part of an ongoing Network for Earthquake Engineering Simulation (NEES) project, where two identical full-scale steel pipe piles were driven at a soft clay site in Oklahoma. The soil surrounding one of these piles was improved using the cement deep soil mixing technique in order to enhance its lateral load behavior. Both piles were tested for seismic resistance using dynamic and quasi-static loading.The pile in unimproved soil provided larger displacements with limited lateral force resistance. This pile was subjected to lateral displacements of up to 400 mm, but experienced minimum inelastic actions. On the other hand, the pile in improved soil reached its lateral capacity at a displacement of 100 mm, at which point the critical region at the base of the pile just above the improved ground experienced buckling and fractured due to low cycle fatigue. Compared to the pile in unimproved soil, the improved ground increased the system strength by 42%. Although the soil was improved over 2900 mm, the effective improvement depth was approximately 1300 mm below the ground surface.In this paper, it is demonstrated that the effects of block type soil improvement of limited horizontal and vertical dimensions can be described using a simplified theoretical approach involving a modification to the well-known p-y representation of soil response. An example using this method is presented and shown to give adequate support to a standard 12-inch diameter steel pipe pile embedded in soft soil,IntroductionPilings are the preferred foundation support for many civil engineering structures including highway bridges, railroad bridges, and port wharves. These structures and their foundations are subjected to forces created by earthquakes, wind, waves, water current, vessel impact, ice, and gravity. All loads applied to the superstructure must be transmitted to the foundation where they are resisted by the surrounding soil. With significant lateral loads, use of pile foundations may be the only solution to transmit large structural loads to competent soils. Piles supported by competent soils are relatively easy to design and costs are often attainable. However, thick layers of weak soils such as soft clays are widespread in high seismic areas (e.g., San Francisco, southern Nevada, Washington, Eastern Missouri, and Arkansas), exacerbating design challenges. Soft clays reduce the lateral resistance of the pile-soil system, making the pile foundation less cost effective. In this case, the current design practice is to use an increased number of larger diameter piles, which is a costly alternative (see SDC, Caltrans 2010). An innovative and more cost-efficient solution to this problem is to improve the soil within a short depth surrounding the foundation, thereby increasing its lateral stiffness. Some well-known methods for improving soil include deep soil mixing, stone columns, and simple soft soil replacement with select granular material."

Jan 1, 2017

By Bradley J. Fleming

Although soil improvement and its application to deep foundations is gaining popularity in the engineering community, this technique is not widely used in high seismic regions due to lack of fundamental understanding of both the behavior of improved soils under high-strain cyclic loading and the interactions between the pile, improved soil, and unimproved soil. This paper describes part of an ongoing Network for Earthquake Engineering Simulation (NEES) project, where two identical full-scale steel pipe piles were driven at a soft clay site in Oklahoma. The soil surrounding one of these piles was improved using the cement deep soil mixing technique in order to enhance its lateral load behavior. Both piles were tested for seismic resistance using dynamic and quasi-static loading. The pile in unimproved soil provided larger displacements with limited lateral force resistance. This pile was subjected to lateral displacements of up to 400 mm, but experienced minimum inelastic actions. On the other hand, the pile in improved soil reached its lateral capacity at a displacement of 100 mm, at which point the critical region at the base of the pile just above the improved ground experienced buckling and fractured due to low cycle fatigue. Compared to the pile in unimproved soil, the improved ground increased the system strength by 42%. Although the soil was improved over 2900 mm, the effective improvement depth was approximately 1300 mm below the ground surface. In this paper, it is demonstrated that the effects of block type soil improvement of limited horizontal and vertical dimensions can be described using a simplified theoretical approach involving a modification to the well-known p-y representation of soil response. An example using this method is presented and shown to give adequate support to a standard 12-inch diameter steel pipe pile embedded in soft soil.

By John P. Turner, Benjamin J. Turner

"Tieback anchors are now used routinely for landslide stabilization in the USA and abroad. It is generally understood by design engineers that friction loss over the unbonded length of a tieback anchor is inherent to the system, and such loss is permitted as long as it does not exceed a certain threshold, typically 20 percent of the post-tensioning load. However, recent experience from projects utilizing tieback anchors with unbonded lengths in excess of 150 feet has demonstrated that this criterion may be difficult to achieve, particularly in certain ground conditions. Furthermore, anchor friction loss, even if below the 20-percent threshold, has important implications for the stability of the slope that are often ignored in practice. This paper presents the results of a study in which friction loss is quantified from load test data for projects in a variety of ground conditions by means of a “wobble coefficient.” Factors that may influence the wobble coefficient are examined, and recommendations for addressing this issue in practice are presented. A recent instrumented load-test program for a landslide stabilization project in Southern California is examined, demonstrating that with appropriate monitoring controls, uncertainty with regard to friction loss can be minimized. IntroductionSteel-strand tieback anchors have been used by the geotechnical community to support shoring systems for many decades, and more recently as a means to stabilize landslides. For strand encased in grease-filled plastic sheathing, which is intended to allow the strand to elongate freely, some load can still be transferred by friction between the strand and the grease and between the grease and sheathing. The sheathing then transfers load to the surrounding grout and, in the case of ground anchors, to the surrounding soil or rock. The resulting decrease in load over the length of the unbonded zone is known as “friction loss.”A widely used criterion for ground anchor acceptance based on load testing is that the measured anchor elongation must achieve a minimum value of 80 percent of the theoretical elastic elongation, or in other words the actual elongation can be up to 20 percent less than the theoretical value. This ensures that the majority of the load applied at the anchor head is reaching the bond zone behind the assumed failure surface, since load shed within the failure mass does not contribute to stability. This criterion acknowledges that friction loss is an inherent feature of the anchor system which cannot be eliminated completely, only minimized."

Jan 1, 2017

By John C. Niedzielski

The PHX Sky Train is a five mile long automated people mover system located at Phoenix Sky Harbor International Airport. Phase I of the PHX Sky Train includes the design and construction of 227 drilled shafts supporting three stations and approximately 9,000 feet of elevated guideway. The guideway includes a 100 foot high, 330 foot long span extending over an active taxiway, which will be the first system of this kind over an active taxiway in the world. The soil conditions in this area generally consist of alluvial Sand, Gravel and Cobbles (locally known as SGC) deposited by the nearby Salt River. The foundation system will support relatively high axial loads, lateral loads and moments due to the height of the guideway above the ground surface, where it needs to pass over existing concourse walkways, bridges, a taxiway and buildings. Drilled shaft design involves designing 4.5-foot to 9-foot diameter drilled shafts within the SGC deposits, most of which extend well below the groundwater table. There is a high potential for collapse of drilled shaft excavation sidewalls within this material. Such extreme design loading conditions, together with difficult ground conditions at the site, result in several challenges for the design and construction of the deep foundation system for the guideway and stations. A load test shaft was designed and constructed as a means to provide site-specific measurement of axial performance under these difficult conditions. Results from the load test were used to reduce the size of the drilled shafts. This paper provides an overall description of the PHX Sky Train project, a summary of the ground conditions, design requirements, load test results and construction methods and equipment used to successfully install the drilled shafts for this project.

Jan 1, 2010

By Matthias Pulsfort, Jiarui Du, Torsten Wichtmann, Achim v. Blumenthal, Diethard König, Rowena Verst

The influence of the interaction between support fluid and soil, e.g., filter cake formation, on the shear stress transfer in the soil-concrete interface of diaphragm walls and bored piles is still controversially discussed. Actual research on the soil-concrete interface using bentonite suspensions indicates that shear stress transfer is underestimated by existing standards. Investigations on the soil-concrete interface using polymer solutions are rare. Therefore, complementary field investigations and systematic laboratory studies were conducted to analyse the soil-concrete interface using both bentonite suspensions and polymer solutions. Thickness and composition of real-scale filter cakes were investigated on several slurry wall construction sites, where bentonite suspensions were used. Direct shear tests (60 mm x 60 mm) were executed for soilbentonite mixtures with varying amounts of bentonite and different granular fines representing a realistic bandwidth of in-situ filter cake compositions. Larger direct shear tests (300 mm x 300 mm) with preceding horizontal penetration, subsequent vertical tremie concrete placement, and filter cake consolidation were performed using both bentonite suspensions and polymer solutions. The results support the view that shear stress transfer in the soil-concrete interface can be described by a wall friction angle in a range of 25° to 30° for bentonite suspensions and between 35° and 40° for polymer solutions in non-cohesive soils.

May 1, 2022

By Joel Moskowitz, Jan Cermak

"New York City has unique geologic conditions which must be considered when designing pile foundations. Where shallow foundations are not feasible, the City's subsurface conditions require a variety of deep foundation systems, ranging from high capacity rock socketed piles, to piles end-bearing on bedrock, to friction piles bearing in alluvial or glacial deposits. Pile load testing is essential in confirming pile capacities as pile analyses include assumptions on soil and soil-pile response, and pile driving equipment. Load test results must be interpreted to estimate the long-term pile behavior. Except for lightly loaded driven piles, the New York City Building Code (the Code) requires that pile capacities be confirmed by static load testing. The Code provides the number of static load tests required, test procedures, and acceptance criteria. In the last few decades, methods other than static load testing have been developed including dynamic and rapid (pseudo-static) load tests. Recently, those methods have also been employed on several projects in New York City. The traditional approach to pile load testing in New York City is discussed herein including engineering involved in the analyses of test data with examples. In addition, several projects which included non-static load testing are discussed INTRODUCTIONPile load testing complements the subsurface information and pile design by providing further data on pile-soil interaction for the selected pile type and installation method. Traditional approaches to pile load testing in New York City involve static load tests to verify the design capacity of the piles for a given minimum factor of safety.In the late 1950's, Dr. Phillip C. Rutledge summarized his views on the philosophy of pile foundations in an unpublished, in-house document. He viewed pile foundations as good illustrations of pertinent and impertinent aspects of geotechnical engineering. In the analyses of piles he divided engineering into four general types:(a) Theoretical engineering in which decisions are made based on theoretical analyses. This represents ideal engineering, in which all factors affecting the pile design are well established or, at least, few simplifying assumptions with known effects on the analyses are made."

Jan 1, 2005

By Jonathan J. Dewsbury

It is argued that approximate computer based methods are only suited to modelling conventional piled rafts, for pile enhanced rafts where the interactions will be non linear three dimensional finite element analysis is required. However current 3D finite element analysis often relies on symmetry to reduce computational cost and there are concerns over the dependency of the results on the user. Therefore a new strategy within the finite element framework has been proposed. The main advantage of this strategy is that each stage of the model can be checked for consistency. There is also the added benefit that non symmetrical models can easily be constructed by tying the validated components together without dramatic increases in computational time. The proposed strategy compared well to the published results of a hypothetical example of a piled raft previously analysed with numerous methods by Poulos et al. (1997).

Jan 1, 2010

By Dinesh Hinduja, Pérez: Miguel

"Large structures are generally exposed to dynamic and structural loading. They require usually either foundation connected to hard rock through sockets or driven foundations, which encounter boulders as well.In this regards drilling hard-rock sockets or boulder offshore or onshore can be a challenging job especially when deep foundations are mandatory. To overcome the challenge, specialized equipment like a Pile Top Drilling rig (PBAs) can be used, which have to be correctly set-up and operated in order to get its maximum drilling performance. High performance drilling with PBAs requires maximizing key elements of its operation. The configuration and management of the drill string components are important. The key elements are constant weight on bit which is done by adjusting ballast and managing thrust force; and selection of cutters and proper flowing discharge.The methodology is based on the experience from over 40 years of building and operating PBAs for different project applications. These applications include drilling offshore and onshore for:?Superstructures and buildings?Drilling platforms, barges and jack-ups?Harbours, jetties, dry docks and dolphins?Bridges, piers and causeways?Marine sewerage diffusers?Offshore wind farms?Dam rehabilitationMHWirth documented methodologies demonstrate that by using PBAs properly it is possible to improves performance of underwater drilling for hard-rock sockets and boulders which ultimately reduces project-cost.Background. There is a significant percentage of total project cost in structural foundations. Equipment capabilities and technics to drill shaft with rock-sockets and embedded boulders onshore and offshore are highly developed due to the dramatic equipment advancement and experience in the last 40 years. Formerly, driven piles accounted for the majority of foundations either onshore or offshore, following the experience of previous practice in the market. Nowadays, deep drilled foundations can be constructed to carry the load through the overburden down to the sound load carrying rock or soil.Scope and objectives. The overall objectives of this study are:?Synthesis information on current practices to drill shaft with rock-socket and/or embedded boulders onshore and offshore with Pile Top Drill Rigs?Identify the principal challenges evolving with practice?Provide suggestions for improvements in the construction of drilled shafts through proper operation of Pile Top Drill Rigs?Convey information through case studies and experiences"

Jan 1, 2015

By Lori A. Simpson

A high-rise building, consisting of two tower structures occupying the entire site, is in construction in San Francisco. The North Tower will consist of 12 and 35 stories above a one-level basement. The South Tower will consist of 9 and 22 stories over one partially below-grade level of common space; a portion of the South Tower will have a three-level basement. The towers will be supported on mat foundations bearing on native very dense sand in the footprint of the three-level basement and on ground improved with soil-cement mixed (SCM) panels that extend through loose sand and marsh deposits into very dense sand. Shoring systems for the basement excavations include cantilevered and tied-back soldier-beam-and-lagging systems and SCM cutoff walls. Subsurface conditions include loose fill and Dune Sand and loose and soft marsh deposits overlying very dense sand of the Colma formation. Groundwater is approximately 15 to 22 feet deep; the three-level basement extends below groundwater. The site is on Market Street in San Francisco, with SF Municipal Railway (MUNI) and Bay Area Rapid Transit (BART) tunnels running below Market Street approximately 45 and 36 feet north of the site, respectively. Both tunnels are 16.5 feet in diameter. The top of MUNI and BART tunnels are 25 feet and 63.5 feet below street grade, respectively. BART has stringent requirements regarding construction adjacent to their facilities, including disallowing adding pressure to their tunnel, lowering groundwater by more than two feet, and vibrations from construction activities. Design of the shoring and the foundations within the BART zone of influence were subject to their design requirements. The project was also subject to a peer review, as required by the San Francisco Department of Building Inspection. We used FLAC to evaluate stresses at the BART and MUNI tunnels and on the SCM panels. This paper will present the mitigations needed to address seismic hazards and BART restrictions and to provide adequate foundation support for a tall building with high seismic loads.

By Lori A. Simpson, Linda H. Liang

A high-rise building, consisting of two tower structures occupying the entire site, is in construction in San Francisco. The North Tower will consist of 12 and 35 stories above a one-level basement. The South Tower will consist of 9 and 22 stories over one partially below-grade level of common space; a portion of the South Tower will have a three-level basement. The towers will be supported on mat foundations bearing on native very dense sand in the footprint of the threelevel basement and on ground improved with soil-cement mixed (SCM) panels that extend through loose sand and marsh deposits into very dense sand. Shoring systems for the basement excavations include cantilevered and tiedback soldier-beam-and-lagging systems and SCM cutoff walls. Subsurface conditions include loose fill and Dune Sand and loose and soft marsh deposits overlying very dense sand of the Colma formation. Groundwater is approximately 15 to 22 feet deep; the three-level basement extends below groundwater. The site is on Market Street in San Francisco, with SF Municipal Railway (MUNI) and Bay Area Rapid Transit (BART) tunnels running below Market Street approximately 45 and 36 feet north of the site, respectively. Both tunnels are 16.5 feet in diameter. The top of MUNI and BART tunnels are 25 feet and 63.5 feet below street grade, respectively. BART has stringent requirements regarding construction adjacent to their facilities, including disallowing adding pressure to their tunnel, lowering groundwater by more than two feet, and vibrations from construction activities. Design of the shoring and the foundations within the BART zone of influence were subject to their design requirements. The project was also subject to a peer review, as required by the San Francisco Department of Building Inspection. We used FLAC to evaluate stresses at the BART and MUNI tunnels and on the SCM panels. This paper will present the mitigations needed to address seismic hazards and BART restrictions and to provide adequate foundation support for a tall building with high seismic loads.

Jan 1, 2017

By Ryan Sullivan, Lisa Smiley, Jewels Stover

The Westerly Storage Tunnel (WST) Project is part of Project Clean lake, the North East Ohio Regional Sewer Dist years. When completed in 2020, WST will be nearly 2 miles of 25-ft diameter tunnel 200-250 ft below ground. The storage tunnel will manage higher flow volumes, keeping stormwater out of the combined sewer system reducing overflow occurrences. Three deep shafts provide access to the tunnel at the tunnel boring machine (TBM) launch and retrieval sites, as well as a vent shaft. Support of excavation for the access shafts was constructed utilizing unreinforced concrete diaphragm walls. This innovative, value-engineered alternate design significantly reduced risks associated with conventional secant piles combined with a rib and liner plate system. Implementation of the diaphragm wall technology resulted in a water tight, continuous shaft keyed into rock. This case study examines the design, methodology, and installation challenges unique to each shaft, as well as the benefits of the final product to the overall project.

By Peter Cali, Wesley Schmutzler

"The Deep Mixing Method (DMM) was employed to raise and support the LPV (Lake Pontchartrain and Vicinity) -111 Levee in New Orleans. Even using innovative technologies, the tight schedule to achieve the 100 year elevation by June 1, 2011 was a daunting endeavor. The size and scope of DMM proposed for LPV-111 was on a scale never attempted outside of Japan. Over 1.65 million cubic yards of DMM was installed. LPV-111 is adjacent to the Bayou Sauvage Wildlife Refuge, which is the largest urban National Wildlife refuge in the United States. By utilizing DMM to control settlement and improve stability of the taller levee, side slopes were steepened from the conventional 1V:4H to 1V:2.85H, thus avoiding encroachment into the Bayou Sauvage and reducing the amount of clay needed for the completed levee. The COE utilized Early Contractor Involvement (ECI) for this contract. The ECI process allowed for input from the DMM contractor, TREVIICOS South, in order to optimize equipment resources and material requirements. This paper gives an overview of the extensive DMM requirements for LPV-111 and explains the benefits of the ECI process.IntroductionDuring hurricane Katrina the levee that constitutes LPV-111 was overtopped and breached in several locations. The United States Army Corps of Engineers (USACE) was presented with the task of increasing the level of the flood protection around New Orleans after Hurricane Katrina to the 100- Year hydraulic grade - the level of protection that provides risk reduction from a storm surge that has a 1% chance of being equaled or exceeded in any given year - and the firm project completion deadline was June 2011.LPV-111 is located in East New Orleans and a large portion of the levee is adjacent to the Bayou Sauvage National Wildlife Refuge. The levee could not encroach on this area. This provided a limited footprint for the levee and made construction of conventional levee difficult, if not impossible. The total length of the project was 5.3 miles. Included in the project was the rehabilitation of one main pumping station and one smaller pump station for water management within the refuge. Short sections of “T” wall were used at the tie in at the Lake Borgne Surge Barrier, the main pump station and the CSX Railroad crossing"

Jan 1, 2017

By John L. White

The vibro driver/extractor is a machine that grips to a pile and vibrates it up and down. When the vibrating pile is lowered into the ground, all soil around the pile begins to vibrate. A vibrating pile breaks the friction between the pile and the soil, thus allowing it to penetrate the ground. A vibro is usually operated by hoisting it into the air with a crane and then placing it onto the pile. The vibro has hydraulic gripping jaws that are controlled from the ground. Once the operator has successfully lowered the vibro onto the pile, the jaws are closed and locked onto the pile and operations can begin. Please see the drawing below: [ ]

Jan 1, 1990

This paper summarizes seven years of Italian ex­perience with the use of large calibration chambers for the calibration, under closely controlled stress and strain conditions, of some in situ testing devices which are used in sand deposits. At the present time two calibration chambers are operating in Italy, one at E.N.E.L.-C.R.I.S. (Milan) (*) and the other at I.S.M.E.S. (Berga­mo) (**). Both chambers can accomodate cylindrical samples 1.2 m in diameter and 1.5 m in height. A detailed description of these chambers can be found in Bellotti, et. al (1982).

Jan 1, 1987

By Shawna Munn, Carol Dounitch, Erika Acton

The EQ Bank Tower, a 24-storey office tower with 4 levels of underground parking, is currently under construction at 25 Ontario Street in the downtown core of Toronto, Canada. The tower geometry required an 18 m (60 ft) deep excavation inside an existing 3-storey 100-year-old façade, to be retained in place throughout construction. This presented a variety of design challenges that required several innovations and a customized monitoring program. In this paper, we will discuss two major challenges, and highlight the innovative and adaptable solutions carried out using performance-based design leveraging the observational method. The first was installation of a shoring system in a 500 mm (20 in) gap between the historical façade and a live gas main. The second involved excavating 10 m (33 ft) into expansive shale bedrock adjacent to a sensitive neighbouring building.

Oct 1, 2022

By M. Hesham El Naggar, Mehdi Heidari

"Equivalent fixed-base cantilever model is a common approach for performance base seismic design of bridge structures supported by extended pile-shaft. In this method, global displacement ductility factor is related to local curvature ductility demand by assuming a concentrated plastic hinge at location of maximum bending moment. Equivalent plastic hinge length is one of the key parameters that should be assumed accurately in kinematic expression of the cantilever model. Although, some expressions have proposed to estimate the length of the in-ground plastic hinge; however, these relations yield differing results. In this paper, a general expression is derived based on the concept of distributed plasticity to predict the plastic region of yielded piles in clay and sand. A length modification factor is defined to relate the equivalent length of plastic hinge to the real plastic zone. Then, results from nonlinear pushover analyses are used to propose an equation for the modification factor as a function of displacement ductility factor.IntroductionDuring severe earthquake events, development of the plastic hinge in pile foundation below ground level is inevitable for bridge structures supported on extended pile-shafts. A common approach for seismic design of the yielding pile-shafts is to replace the pile-soil system by an equivalent fixed-base cantilever assuming the equivalent system has the same global response as that of the pile-shaft (Budek et al. 2000; Chai 2002). In this method, plastic curvature is concentrated at the center of the equivalent plastic hinge below ground surface. Prior knowledge of plastic-hinge length is essential for proper assessment of assess plastic displacement at the top of the pile-shaft. Unfortunately, existing recommendations for estimating plastichinge length are largely incomplete and/or inadequate.During the last two decades, several relationships have proposed for evaluating the equivalent plastic hinge length, Lp, based on experimental and numerical studies. Budek et al. (2000) conducted numerical modeling to calculate the plastic-hinge length of piles embedded in cohesionless soil. They found that the plastichinge length varies linearly with both soil stiffness and aboveground height, e. Chai and Hutchinson (2002) conducted full-scale experimental tests on reinforced concrete piles in sand. They reported that Lp depends primarily on the aboveground height of the pile, neither sensitive to the soil stiffness nor to the value of displacement ductility factor. They stated that the equivalent plastic hinge length is relatively independent of the displacement ductility factor and is not very sensitive to the change in soil density. On the contrary, Goel (2014) and Liu et al. (2016) conducted nonlinear numerical analyses which revealed that Lp changes with the displacement ductility factor and even suggested that using different values of Lp for different seismic design levels is essential for a reliable estimation of the ductility capacity."

Jan 1, 2017

By James L. Christensen, Gregory Sanchez, Michael P. Walker

The Fogg Museum expansion project required excavation and construction in a congested urban area in Cambridge, Massachusetts. A soldier pile tremie concrete (SPTC) wall provided the support of excavation and now serves as the permanent basement wall of the new expansion of the museum. The existing Fogg museum had a single basement level. The new expansion has a two-level basement for new exhibit space and an amphitheater. The east side of the site is about 20 feet above the basement level of the existing Fogg structure which resulted in a significant unbalanced load that needed to be resolved without damaging the original Fogg structure. The SPTC wall was supported with a combination of tiebacks and internal bracing. The final depth of the excavation was about 40 feet below street level. Strict movement control was imposed because the existing museum contained an Italian Renaissance-style courtyard. The southeast corner of the SPTC wall had to accommodate underpinning of an historic concrete ramp which was ultimately incorporated into the expansion. Challenges during construction included excavating the SPTC wall panels up to 12 feet into argillite bedrock which had occasional diabase dikes and sills. The following topics are discussed in more detail after a general project.

Jan 1, 2015