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By William (Bill) H. Walton

"I arrived in Chicago in 1993 with Dr. Ralph Peck’s University of Illinois bulletin titled Engineering Properties of Chicago Subsoils (Bulletin 429), which he published in 1954 with William Reed. Being an outsider, I wanted to learn from Chicago geotechnical practice leaders that included Clyde Baker, Jr., John Gnaedinger, Charles Pfingsten, Dr. Safdar Gill, Robert Lukas and Dr. Jorj Osterberg, who have influenced foundation designs for the structures that make up the contemporary Chicago skyline. One of my immediate goals was to get the Illinois Structural Engineering license to be on par with the likes of Eli Cohen, Mike Tylk, Stan Korista, Bob Halverson, Joe Burns, Ron Johnson, Bill Baker, Bob Sinn, Chuck Anderson and Dave Eckmann, who have led their structural firms in the design of the skeletal core and frames of many of Chicago’s iconic buildings (and for many other buildings around the world). From my time with GEI Consultants (GEI), then on with STS Consultants (STS, and now AECOM), and now back with GEI, I have had the opportunity to analyze and design foundations and, with the help of many skilled foundations and building constructors, to verify that predicted foundation performance matches actual movement data. The theme of Chicago’s foundation design practice is to assume and verify. In 1948, Peck published the History of Building Foundations in Chicago (Bulletin 373) that was updated in 1998 by Baker, Pfingsten and Gnaedinger, who meticulously documented hundreds of Chicago’s foundations, and have shown the value of advanced analyses and testing to advance the deep foundation design practice that includes a variety of high-capacity driven and drilled deep foundations. Mehmet Uyanik, Peck and Baker have made Chicago’s subsurface into a full-scale foundation test laboratory. They confirmed soil mechanics principles like Terzaghi’s 1-D consolidation theory when early foundations bearing on sand-clay crust over soft to medium silty clays (e.g., Auditorium, Masonic Temple, Monadnock Block and Old Board of Trade buildings) took 40 to 60 years to consolidate clay 1 to 2 ft (0.3 to 0.6 m). They also confirmed proven increases in bearing pressures based on measured performance of deep foundations bearing on the glacially derived hardpan clay till and in solid dolomite that underlies Chicago."

Jan 1, 2017

By Djk Arentsen

A new technique to drive tubular piles by impact hammer inside the pile has confirmed a dramatic reduction of noise and the opportunity to save steel. Also a reduction in driving time and a higher bearing capacity has been observed during a test program of this technique. As part of the so-called "Down-the-hole" driving technique, a wave equation analysis has been developed to calculate driveability and pile stress. The main feature of the new "Down-the-hole" technique is the development of a patented device allowing uncoupled penetration of pile tip and pile shaft, which makes it possible to drive both closed or open end piles and reduce the stress level induced in the pile wall. During a test program, a number of instrumented piles were driven and compared with traditional driving of the same pile with the same hammer on top (also instrumented). Also the stresses and performances were compared with precalculations. This paper, explains the technique and presents the test and noise results, in comparison with traditional top-pile-driving. The "Down-the-hole" driving technique is an interesting alternative for special applications where traditional pile driving requires a large wall thickness or in areas where noise is a hot item.

Jan 1, 1996

By Siavash Mahvelati, Alireza Kordjazi, Joseph Thomas Coe

Deep foundations are often constructed as end bearing members with a significant amount of their capacity derived from bedrock. Sites with highly variable bedrock conditions therefore present a unique challenge when attempting to estimate the design elevation of deep foundations. Typical subsurface characterization techniques such as drilling, standard penetration testing (SPT), and cone-penetration testing (CPT) may fail to adequately establish top-of-rock elevation in geologic settings prone to karst and/or significant amounts of residuum, saprolite, and deformed bedrock. Seismic surface wave geophysical methods have been increasingly used to map bedrock topography in such settings. However, the current standard of practice for these methods introduces resolution limitations in spatially variable subsurface conditions due to averaging effects from the analytical framework used to process the acquired data. This study explores the use of a tomographic approach with full waveform inversion (FWI) to map top-of-rock elevations at a numerically simulated site representative of highly variable bedrock topography. Comparisons are made with seismic refraction (SR) and a dispersion-based multichannel analysis of surface waves (MASW) approach as more commonly used in geophysical subsurface investigations. The results highlight that FWI provides a superior estimate of top-of-rock topography than SR and MASW at a cost of a significant increase in the required computational resources and time.

Oct 1, 2021

By Siavash Mahvelati, Alireza Kordjazi, Joseph Thomas Coe

Deep foundations are often constructed as end bearing members with a significant amount of their capacity derived from bedrock. Sites with highly variable bedrock conditions therefore present a unique challenge when attempting to estimate the design elevation of deep foundations. Typical subsurface characterization techniques such as drilling, standard penetration testing (SPT), and cone-penetration testing (CPT) may fail to adequately establish top-of-rock elevation in geologic settings prone to karst and/or significant amounts of residuum, saprolite, and deformed bedrock. Seismic surface wave geophysical methods have been increasingly used to map bedrock topography in such settings. However, the current standard of practice for these methods introduces resolution limitations in spatially variable subsurface conditions due to averaging effects from the analytical framework used to process the acquired data. This study explores the use of a tomographic approach with full waveform inversion (FWI) to map top-of-rock elevations at a numerically simulated site representative of highly variable bedrock topography. Comparisons are made with seismic refraction (SR) and a dispersion-based multichannel analysis of surface waves (MASW) approach as more commonly used in geophysical subsurface investigations. The results highlight that FWI provides a superior estimate of top-of-rock topography than SR and MASW at a cost of a significant increase in the required computational resources and time.

Sep 8, 2021

By Nick Hytiris, Mohammed Al Maadheedi, Slobodan B. Mickovski

This paper explores the capacity effects of a square steel plate welded at the ground surface on a driven open-ended steel pile (i.e. the plate would touch the ground surface after the pile achieves the required penetration). A series of strain-controlled, 1-g laboratory tests were undertaken on piles with and without a square steel plate attached. The piles were driven in dry, loosely packed, uniform sand. Two plates were used, one with a breadth equal to two times the diameter of the pile (2D) and the other with a breadth equal to three times the diameter of the piles (3D). A 20% increase in capacity was recorded for the 2D plate, and a 110% increase in capacity was recorded for the 3D plate when compared to the pile without an attached steel plate. The back-analysis of the results allowed the derivation of a new expression to calculate the capacity of bearing plates, which accounted for the effects of sands compaction and dilation. By extrapolating the findings of these tests to a hypothetical scenario, a model design problem was described where the length of a pile can be reduced by 20% to 60% (depending on the load) by using a plate attached to the pile. The results of this study can help designers to minimise penetration depth; thus, achieving a more economical and sustainable design.

By Mohammed Al Maadheedi

This paper explores the capacity effects of a square steel plate welded at the ground surface on a driven open-ended steel pile (i.e. the plate would touch the ground surface after the pile achieves the required penetration). A series of strain-controlled, 1-g laboratory tests were undertaken on piles with and without a square steel plate attached. The piles were driven in dry, loosely packed, uniform sand. Two plates were used, one with a breadth equal to two times the diameter of the pile (2D) and the other with a breadth equal to three times the diameter of the piles (3D). A 20% increase in capacity was recorded for the 2D plate, and a 110% increase in capacity was recorded for the 3D plate when compared to the pile without an attached steel plate. The back-analysis of the results allowed the derivation of a new expression to calculate the capacity of bearing plates, which accounted for the effects of sands compaction and dilation. By extrapolating the findings of these tests to a hypothetical scenario, a model design problem was described where the length of a pile can be reduced by 20% to 60% (depending on the load) by using a plate attached to the pile. The results of this study can help designers to minimise penetration depth; thus, achieving a more economical and sustainable design.

By Song-yu Liu, Chao Yan, Yong-feng Deng

"In order to investigate the stability of embankment on soft subgrade improved by T-shaped deep mixed column composite foundation, the internal forces and failure modes of columns were analyzed on the shape of critical slip surface and the displacement fields of composite foundation through strength reduction method of three dimensional numerical simulation. Then comparison between T-shaped and conventional deep mixed column composite foundation were conducted. The simulation results indicate that the stability analysis was overestimated by limit equilibrium methods. Piles within the slope shoulder provide great resistance slide effect through the vertical bearing capacity, while the piles nearby slope shoulder and outside slope shoulder providing great moment to resistant slip. The embankment stability of T-shaped deep mixed column composite foundation is higher than that of conventional deep mixed column composite foundation while cost less cement and construction time.INTRODUCTIONThe soft soil has many unfavorable project properties such as high compressibility, low strength, and high water component. Embankment built on the soft soil will face subsidence, horizontal displacement and stability problems. Cement-soil deep mixed column composite foundation is more commonly used as a method for construction of embankment on soft ground [1-2]. For the existing problems of China's current cement-soil pile (wet jet mixing pile), including strength uneven, effective treatment with shallow depth and high cost, a new technique, T-shaped bidirectional deep mixed column, is introduced [3]. An automatic expanding mixing blade was developed by Liu et al. shown in Figure. 1, to install TDM columns [4].T-shaped deep mixed (TDM) column combines bi-directional deep mixing technique and T-shaped deep mixing technique: ?Using concentric biaxial drill pipe, opposite rotational direction of the blade on the inner drill pipe and the outer drill pipe. By squeezing action of the blade on the outer drill pipe, forward and reverse rotation of the blades bidirectional mixing at the same time, blocking the way to take the grout, the uniformity of cement mixing is improved. ?Scalable stirring blades, which can be stretched for two different radius at any depth below ground, expand cross-section of the upper pile (enlarged head), forming expanding cross-section within the upper part of a certain depth which is similar to the shape of nail. As a new composite foundation, T-shaped mixing pile composite foundation is widely applied. However, studies on the stability of T-shaped column treated soft subgrade are rare in the research. So the stability study on T-shaped column composite foundation under embankment for guiding the design and construction has important significance."

Jan 1, 2015

By Ross T. McGillivray, David S. Graham, Dan A. Brown, Steven D. Dapp

"The Selmon Expressway includes an elevated structure extending across several miles of weathered karstic limestone geology, and represents a challenge for design because of the high variability of the material and the difficulty in characterizing the strength. The nature of the epikarst in this region of Tampa is such that variability can be extreme within distances of only a few feet. The weathered rock includes extremely soft soil infill within solution features on and within the formation. The limestone is so weathered that coring typically does not yield useful samples for strength testing, and in-situ Standard Penetration Testing (SPT) tests often encounter refusal blow counts. Thus the challenge for foundation design includes two components of reliability risks: the uncertainty associated with the ground conditions at a given foundation location plus the uncertainty associated with the foundation performance at a given location even when the stratigraphy is determined.This paper describes the design approach that has been implemented successfully for two projects at the Lee Roy Selmon Crosstown Expressway (LRS) in Tampa, Florida: the assessment and remediation of the reversible elevated lane (REL) foundations constructed in 2004, and the elevated expressways widening project constructed in 2012. Included in this design approach is a method developed for computing axial resistance in this local geology. Design for axial loading relies primarily on the development of side resistance, which was considered less subject to performance risks than base resistance. The calculation method incorporates a statistical analysis of SPT data, tempered by engineering judgment, to characterize stratigraphy at a given location into either soil, intermediate geomaterial (IGM) or rock.IntroductionThe subsurface stratigraphy of sites underlain by weathered limestone formations can be highly variable with respect to material layer thicknesses and strengths, even over short horizontal distances. This is the case for much of Florida, and particularly the Tampa area. These conditions present a challenging environment for the design of drilled foundations because of the need for a reliable determination of subsurface conditions at each foundation location, as they relate to the expected axial performance. Contributing factors include:"

Jan 1, 2015

By Dino Kartofilis, Rick Deschamps, Giovanni (John) Bonita

"Anew condominium complex in Arlington, Va., presented some formidable constraints. One was the requirement for a permanent retaining wall to support a 48.5-ft (15-m) cut and an existing 16- story building on top of the slope. Another was the adjacent property owners’ refusal to allow tieback anchors to encroach on their property. The General Contractor (GC) proposed an innovative design incorporating vertical concrete load-bearing elements (LBEs) supported by post-tensioned tiedowns. The owner accepted and the project was successfully completed in 2007.The original designer had proposed a system that included a temporary, raked soldier pile and lagging wall and a permanent cantilever retaining wall with a large piled footing. The system was potentially costly and its constructability questionable.The GC then asked for a design-build alternative to reduce costs and enhance the schedule. The first idea was a diaphragm wall with vertically anchored T-sections. However, configuring a crane to excavate perpendicular sections using grab equipment seemed impossible. There were also utilities approximately 25 ft (9 m) from the existing building, two tiered retaining walls down the slope and a large swimming pool at the base. However, the GC was committed to providing a stable bench 20 ft (6 m) wide along the wall alignment to support the crane.The design evolved to single bite panels using diaphragm wall technology, commonly called LBEs, or barrettes, when they carry vertical loads. For this project, 44 LBEs were horizontally spaced at 9 ft (2.75 m) on center, oriented perpendicular to the wall, extending into bedrock and anchored vertically on the upslope side to resist overturning moments. They were essentially large soldier piles that provided both temporary and permanent support of excavation.An unusual formal agreement was established with the GC to complete the work based on pricing, and prior to completion of final design. This arrangement allowed for an exchange of ideas that increased project efficiencies and lowered costs — without the fear that design concepts would be “shopped” to competitors."

Jan 1, 2009

By Roderic A. Ellman

The new Woodrow Wilson Bridge (WWB) will replace the existing bridge over the Potomac River to connect Alexandria, Virginia to Prince Georges County, Maryland. The new WWB will extend approximately 1.1 miles across the river, with a 367-ft long bascule span in the main river channel where the water depth is about 36 ft. The bridge is primarily comprised of fixed spans in relatively shallow water and a bascule span over the navigation channel. The subsurface soil profile was quite variable along the bridge alignment. In Virginia, there was fill over soft Alluvial deposits underlain by dense Terrace deposits, as well as remnant foundations from a former ship yard. At the bascule span, there was up to 50 ft of a soft organic silty clay layer underlain by a deep deposit of stiff Cretaceous clay. Along the Maryland approach, there were Alluvial deposits over dense Terrace deposits over stiff Cretaceous clays and dense Cretaceous sands. The variation in subsurface conditions led to the selection of alternative deep foundations that suited the specific conditions and were based on the design phase testing program, from which ultimate design capacities were determined. During construction, there were instances of unexpected pile performance, notably different than that experienced during the design phase testing, requiring changes to the contract installation criteria and re-design. This paper will present the types of deep foundations used for the project, the performance criteria assumed during the design, the measured performance and difficulties encountered during construction, and the resulting remedial actions, i.e., changes to contract installation criteria and/or re-design due to the unanticipated field conditions.

Jan 1, 2009

By Nick O’Riordan, Kaitlyn L. Fleming, Michael Riemer, Youssef M. A. Hashash, Stephen McLandrich, Mohamad Jammoul, Pierre Gouvin, Andrew Yeskoo

"To accommodate urbanization, cities are developing more underground space as a means to house public transportation systems and other entities. Underground developments often require construction of deep excavations in an environment dense with infrastructure. The success of such a project is related to the amount of impact imposed on adjacent structures and economic activity; impact should be limited to insignificant amounts in order to mitigate damage and disruption. Thus, large-scale urban construction projects require extensive monitoring of ground movements and installed support performance to facilitate informed decisions for adjustment of construction activities and support design when necessary.In downtown San Francisco, a unique large-scale excavation in saturated soft soils was constructed for the Transbay Transit Center (TTC). Construction of the excavation began in April 2012 and was completed almost two years later in February 2014. To monitor ground and structure response to construction, the project team used an extensive instrumentation network that included automatic inclinometers, piezometers, strain gages and total stations paired with survey markers. Innovative imaging techniques developed a record of construction in order to relate measured deformations to construction activity.Transbay Transit CenterThe Transbay Transit Center (TTC) is being constructed as a modern day transportation hub in downtown San Francisco to replace the former Transbay Terminal. The project is located in the South of Market area, less than half a mile from the San Francisco Bay. The final center will connect eight counties in the Bay Area through 11 different transportation systems, some of which will be housed in the TTC including Caltrain, Golden Gate Transit and California High Speed Rail. The aboveground structure will consist of two levels for retail and a third level with a bus terminal beneath a rooftop garden. There will be two subgrade levels to serve as a lower concourse and the train platforms. This structure required construction of a deep excavation closely surrounded by buildings and roads in an area thriving with economic activity."

Jan 1, 2015

By Renato P. Cunha

The paper presents the results of a comparative and parametric analysis in which a numerical program developed exclusively for groups of deep foundations under general loading (vertical, horizontal and moment loads) was used. This program, developed in the doctoral thesis work of Zhang (2000), extends the finite layer method to accommodate a simultaneous general loading on top of piled raft foundations, allowing the establishment of a coupled relationship between displacements (in all three directions), rotations (in two directions), and external loads. Zhang (2000) has extensively tested and validated this program against well known case histories, but has not applied it to piled rafts overlying unsaturated tropical soil materials. Hence, this paper further explores the applicability of this program by using it to simulate the behavior of experimental field loading tests carried out at the University of Brasilia (UnB) experimental site. At this site, Cunha and Sales (1998) and Sales (2000) carried out several loading tests on small scale isolated rafts (1 x 1m) and piles (L=5m, dia=0.15m), group of piles (4 piles, raft clear off the ground) and piled rafts (1 and 4 piles underneath a raft in contact with the soil). The authors adopt Zhang's program to backcalculate, hence simulate, this series of experimental field loading tests under vertical loading. They also use this set of results to "calibrate" the program for further parametric analyses. The parametric analyses were carried out with different piled raft configurations in this same soil type, trying to evaluate their field behavior under the effect of distinct (geometric) configurations of pile distribution.

Jan 1, 2002

By Cem Altuntas

This paper is the second in a series of two describing the design and construction of a foundation for a major high-rise real estate development on the west side of Manhattan, N.Y. The foundation members consist of large-diameter rock-socketed caissons, driven closed-end steel pipe piles bearing on rock, and a secant-pile retaining wall surrounding the entire site. This paper focuses on the Osterberg cell (O-Cell) load test completed for determining the allowable side-shear resistance between the concrete and the sides of the rock socket. Different qualities of mica schist bedrock, demonstrated by the penetration of rock with the soil auger or drill casing, were encountered. Accordingly, an additional subsurface investigation consisting of test borings at each caisson location was completed. Unconfined compressive strength tests were performed on representative rock samples. The ?soft? mica schist was observed to have vertical foliations and high mica content. For the first time in Manhattan, an O-Cell load test was performed to determine the allowable side shear resistance for both the soft and hard mica schist bedrock. The side shear resistance obtained from the O-Cell load test is compared with the side shear resistance allowed by the New York City Building Code and empirical correlations using unconfined compressive strength values for rock. The rock socket design for the caissons was refined based on the O-Cell load test results.

Jan 1, 2008

By Karsten Beckhaus

Barrier walls in levees and dams are designed and constructed for new structures and for rehabilitation or upgrade of existing structures to control seepage. Construction methods applied are often deep soil mixing with a cementitious slurry or excavating a trench and refilling it with a plastic concrete. This paper explains the technical background of jointless cementitious barrier walls inevitably developing thermal tensile stresses and how these stresses can be controlled. The theoretical background of thermal stresses is explained based on experimental and numerical studies of essential factors. Although a low cracking risk is generally inherent, risk mitigation measures should be taken to thermal cracking and to ensure the permanent function of such walls as a low-permeability and high-deformability barriers.

Sep 8, 2021

By John L. Walkinshaw

It is obviously not possible in the time given me today to review in great detail all the research of the past 20 years that the (FHWA) has sponsored or participated in. In this presentation I will highlight some of the principal programs that I am familiar with. This handout lists practically all the reports prepared for the FHWA involving deep foundations and some related work involving the same structural elements (piles, shafts, ground anchors).

Jan 1, 1993

By Vijaya Bhushan Rao, Jason Redgers

A mixed-use development comprising of multistoried residential towers, retail and associated infrastructure covering an area of 500,000 m2 is under construction in Dubai. The subsoil conditions consist of calcareous sands with high carbonate and shell content with hard and competent strata encountered at varying depths. To achieve the design requirements of soil stiffness, friction angle, limit differential and total settlements and mitigate the liquefaction due to a seismic event then ground improvement were deemed necessary. In order to provide the most time and cost efficient solution numerous techniques were applied to meet the requirements for all depths such as Vibrocompaction, VC (depth >8m), Dynamic Compaction, DC (depth < 8m)] and Rapid Impact Compaction, RIC (depth <4m). The specified ground improvement requirements were translated into a target Cone Penetration Test, CPT line that served as the defacto performance requirements for the project. Suitable correction factors were applied to the CPT results to account for the high carbonate content following the works of Al-Homoud and Wehr 2006, Belotti and Jamiolkowski , 1991 and Vesic, 1965. Furthermore, the alpha factor, α, used to obtain stiffness from CPT results was applied following A.C. Meigh 1987 and Massarsch & Fellenius, 2005 where high over consolidation ratios (OCR) could be demonstrated.

Sep 8, 2021

By Vijaya Bhushan Rao, Jason Redgers

A mixed-use development comprising of multistoried residential towers, retail and associated infrastructure covering an area of 500,000 m2 is under construction in Dubai. The subsoil conditions consist of calcareous sands with high carbonate and shell content with hard and competent strata encountered at varying depths. To achieve the design requirements of soil stiffness, friction angle, limit differential and total settlements and mitigate the liquefaction due to a seismic event then ground improvement were deemed necessary. In order to provide the most time and cost efficient solution numerous techniques were applied to meet the requirements for all depths such as Vibrocompaction, VC (depth >8m), Dynamic Compaction, DC (depth < 8m)] and Rapid Impact Compaction, RIC (depth <4m). The specified ground improvement requirements were translated into a target Cone Penetration Test, CPT line that served as the defacto performance requirements for the project. Suitable correction factors were applied to the CPT results to account for the high carbonate content following the works of Al-Homoud and Wehr 2006, Belotti and Jamiolkowski , 1991 and Vesic, 1965. Furthermore, the alpha factor, α, used to obtain stiffness from CPT results was applied following A.C. Meigh 1987 and Massarsch & Fellenius, 2005 where high over consolidation ratios (OCR) could be demonstrated.

Sep 8, 2021

By Jeff Wilkinson, Brandon Walter

"A&N Electrical Cooperative provides electrical service to the counties of Accomack and Northampton along Virginia’s Eastern Shore and to Smith Island in Somerset County, Md.A&N recently worked to improve the efficiency of power distribution to a small island community and marina on Tangier Island in the Chesapeake Bay. This improvement consisted of upgrading the existing distribution substation with a new 25 kV 2-bay box distribution structure. Earth Contact Products (ECP) collaborated with PowerServices, Inc. (PSI) to design and install a helical foundation support system as part of the substation upgrade. Feasibility EvaluationThroughout the design process, A&Nworked with its partners PSI (design) andT&D Solutions (installation) to identifycost-effective alternatives. Foundationsystems considered included cast-in-placereinforced concrete caissons, precastconcrete foundations, driven steel piles and helical piles. In evaluating all of theoptions, the greatest concern was gettingthe material onto the island, followedclosely by the availability of the equipmentto install the foundations. Clearly, cost,more specifically the installed cost, was asignificant consideration and decisionfactor throughout the process.There were several limiting factors that had to be considered during the design process, the most significant of which was that all of the material had to be barged to the site. With traditional reinforced concrete deep foundations in mind, the cost for installing these piles was projected to be nearly $2,000/cu yd ($262/cu m) of installed concrete. Given that approximately 5 to 6 cu yd (3.8 to 4.6 cu m) of concrete would be required for this structure, the cost was significantly high for this project. What’s more, because the components of the concrete mix would have to be barged and then hand mixed on site, there was concern regarding both the time required to complete the piles and the quality of the installed concrete. For the driven pile alternative, the availability, or lack thereof, of equipment and material cost resulted in a total cost estimate that was more expensive than that of the concrete piling alternative. The high material cost for the piles, which was more than double than the cost of concrete, was due to the number and size of piles needed to resist the overturning moment. Ultimately, the team selected the helical pile alternative. The decision to a use helical pile foundation system was based on many factors, not the least of which was the remote location of the project site and the difficulties associated with getting material, equipment and construction personnel to the project site."

Jan 1, 2017

By Christopher J. Ramsey, Don W. Dotson

"An existing four lane section of US 27 was widened to eight lanes. The project lies in the rugged Valley and Ridge Province of the Appalachian mountains starting at the Tennessee River in Chattanooga, Tennessee and extending 2.6 km north to Signal Mountain Boulevard. This terrain presented many challenges to accommodate the road widening in the narrow, rugged topography. Multiple tiered wall systems consisting of large tieback walls, post-tensioned reaction blocks, and gravity MSE walls for a total of approximately 30 retaining walls were required. The retaining walls served to stabilize the thrust faulted geology while also minimizing right-of-way acquisitions. The cut walls consist mainly of a tiered system of tied-back soldier piles walls with cast-in-place concrete facing. Cast-in-place pile shear walls were required along the toe of existing MSE walls to maintain stability during construction. This paper discusses the design methodology, which includes a hybrid (rather than traditional) earth pressure diagram intended to reduce life-cycle maintenance and long-term performance. Further this paper addresses wall construction, slope stability analysis, landslide mitigation alternatives, soldier pile wall design features, site challenges, monitoring and performance (to date) of the wall systems.INTRODUCTIONThis project involves the proposed widening of US Highway 27 (State Route 29) from the north end of the Tennessee River Bridge at Manufacturer’s Road to State Route 8 (Signal Mountain Road), approximately 2.64 km of roadway (Fig. 1). The project site is located adjacent to the Tennessee River on the north side of downtown Chattanooga, Tennessee in Hamilton County. The existing, limited access highway is to be widened from four lanes (two northbound and two southbound) to a minimum of eight lanes. Some portions of the alignment will expand to as much as ten lanes where northbound and southbound ramp acceleration/deceleration lanes coincide.In addition to the number and heights of cuts and fills involved, a major factor in determining an economical design for the alignment is the complicated geologic conditions along the roadway alignment. The existing roadway is situated between several steep cut slopes, some of which are only marginally stable or currently exhibit signs of instability. Due to the proximity of the project to the downtown area, the steep slopes along the alignment, and the relatively dense population near the alignment, widening the pavement and constructing cut and fill slopes to a stable configuration would result in major land acquisition for slope right-of-way."

Jan 1, 2015

By Lucie Spencer, Craig Butterworth

"This paper presents the design of a raft enhanced pile group recently constructed for a hotel development in Perth, WA. At the time of construction in 2016 the hotel was the tallest prefabricated hotel in Australia.The structure covers the entire 12 m by 32 m development footprint, located in an inner city environment, and directly surrounded by existing structures. The small site and lack of space required innovative thinking in terms of the substructure design.The ground conditions comprise a layer of medium dense sand underlain by variable layers of stiff clay, silts and sands. Groundwater was around 1.5 m below ground level.The substructure design was carried out on the basis of a raft enhanced pile group. This allowed the use of much shorter piles than a conventional pile solution, thereby permitting the adoption of CFA piling techniques. This also allowed the raft thickness to be reduced to such that the substructure works were maintained above the groundwater level.The design was carried out in general accordance with the Australian Standard AS 2159 and using conventional piled raft design techniques involving iteration between elastic soil settlement software and structural analysis software until spring reactions were obtained with convergence of the two models. Following this springs were introduced to model piles in the structure.Due to the variable nature of the ground and resulting uncertainty in pile base capacity it was not considered appropriate to design the system as a pile assisted raft with piles loaded beyond their ultimate geotechnical design strength. As a result, all piles were designed based on a maximum load maintained within the elastic response region, with the majority of the load taken by the piles. However, the combined capacity of the raft and the piles allowed for a saving in pile lengths and numbers of around 40%, when compared to a conventional pile group designed in accordance with the Australian Standard AS 2159.The raft slab was monitored during construction in order to check the actual displacements against the design displacements. At the end of construction, the settlements were found to be within 2 mm of the design values.INTRODUCTIONThe Wellington Street area of Perth in the CBD is undergoing recent regeneration which includes the King’s Square development, Perth Arena and the Wellington Street Bus Station. The proposed hotel development is close to the recent developments on a Lot previously occupied by a low rise development. Due to the small size and constrained nature of the site, the substructure design for the tower needed to take into account available space and the impact of the works on adjacent properties. This paper presents reasoning for the choice of substructure design, details of the design methodology adopted, results from limited post construction monitoring and potential improvements that could be considered for similar future developments."

Jan 1, 1900