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By Alexandra Weidle, Seffen Leppla, Rolf Katzenbach, Matthias Seip

"A lot of different deep mixing systems have been developed in the last decades for a wide spectrum of applications, e.g. retaining and foundations systems, soil improvement, sealing of toxic substances or dyke strengthening. The paper will deal with special aspects of constructions with deep mixing systems for infrastructures like soil improvement for cyclic loadings and underpinnings in difficult soil conditions by presenting cases from engineering practice.1. DEEP DRY SOIL MIXING FOR SOIL IMPROVEMENT OF RAILWAY TRACKS IN VERY SOFT SOILS1.1 IntroductionRailway tracks are set into vibrations by train passing. In very soft soil this leads to long-term deformations which lead to speed limits, temporary closings and big maintenance efforts. The energy of the dynamic loading is transmitted into the soil by compression and shear waves and at the surface by rayleigh waves (Wood 1968). The expansion of the waves are influenced by•,thickness of the soft soil layer•,density of the soft soil layer•,stiffness of the soft soil layer•,saturation of the soft soil layer•,frequency of the dynamic loadingThe frequency of the dynamic loading depends on the train velocity and the distance of the wheels and wheel sets. If the frequency of the dynamic loading is in the range of the natural frequency of the soft soil layer the vibrations increase extremely (Lieberenz et al. 2003). As a result the long-term deformations will increase as well.To avoid these long-term deformations and the resulting operation restrictions and maintenance efforts an adequate soil improvement is necessary. For the optimization of the soil improvement field tests have been carried out.1.2 Experimental field testsThe field tests have been carried out at a 300 m long test track with five different setups, each 30 m long:•,test track TS 0: no soil improvement•,test track TS 1: soil improvement with single lime-cement-columns 5.9 m deep (Figure 1a)•,test track TS 2: soil improvement with single lime-cement-columns 5.9 m and 10.4 m deep (Figure 1b)"

Jan 1, 2015

By Fei-chiu Huang

A 17-acre landslide occurred in February 2001, on a slope below Via Bellota in the City of San Clemente, California. Three homes were destroyed and many others placed in jeopardy. The landslide, involving portions of five separate developments, continued to move significantly in the years following. Litigation ensued among the affected parties, and investigations continued through 2007. A mediated repair resolution was ultimately reached among the parties. The agreed upon repair consists of a multi-million dollar stabilization program that included grading, drainage, and structural systems. Part of the construction cost was offset by creating 4 new ocean view custom lots and 20 new mobile home lots. The landslide repair and slope stabilization design involved removal and replacement of portions of the landslide debris and construction of buttress and stabilization fills as well as installation of 74 shear pins in two rows. The shear pins were designed as 4-foot diameter by 50 feet in length and incorporated continuous W30x211 wide flange steel. The shear pins were designed to be installed 25 feet above the slide plane and 25 feet below the slide plane at each location. Construction of the 74 shear pins was initiated in 2008 and completed in 2009. Four-foot diameter holes were drilled by utilizing a truck-mounted, flight-auger-style drilling rig with a 4-foot diameter solid-flight auger. Prior to the installation of the shear pins, an engineering geologist downhole logged strategically selected holes to further evaluate the actual slide plane elevations. The wide flange steel shear pins were then lowered to the desired elevations and encased within 4,500 psi, Type V, 0.45 maximum water/cement ratio concrete. Inclinometers installed within four pin shafts and behind the pin rows indicated performance in accordance with the design. Slight to non-perceivable shear displacement was measured which mobilized the intended capacity at the monitored shear pins. No excessive slope movement was detected at any of the inclinometer locations during or after the construction period. Actual shear displacement of the steel wide flange elements was less than the movement anticipated before shear pin installation.

Jan 1, 2010

By Arturo Ressi di Cervia

"The Construction of the Thrust Pits for Jacking of the I-90 Tunnel for the Central Artery/Tunnel Project (Part of Contract No. C09A4) in Boston MA was nominated for DFI’s 2002 Outstanding Project Award. In the judging, the project and the specialty subcontractor, Treviicos Corporation, was chosen for a Special Recognition Award. INTRODUCTIONBoston’s Big Dig, as the construction of the underground artery became known, is undoubtedly the largest urban construction project of this century.The Central Artery/Tunnel Project, or CA/T, to call it by its proper name, runs approximately eight miles through the heart of Boston, five miles of which are built underground while maintaining traffic on the elevated existing structure, while at its southern end I-90 is extended to Logan airport under active rail lines, Fort Point Channel and Boston Inner Harbor.Since the alignment of the road closely parallels the shoreline as it existed in colonial times, the cut and cover construction had to contend with substantial portions of filled ground, not to mention existing subway lines, live utilities, building foundations and, last but not least, the irritable Boston drivers and litigious adjacent property and business owners.Consequently, while it is impossible to single out the most difficult or challenging contract, the jacking of the tunnels of I-90 under the live rails of Amtrak certainly will rank high on the list.Never before, anywhere in the world, was an attempt made to jack tunnels of this size: the South Bay Interchange consists of three 78 feet (24 m) wide by 38 feet (11.6 m) high tunnels, the shortest of which is 167 feet (51 m) long. TECHNOLOGYIn order to achieve this engineering feat it was necessary to consolidate the soil under the track to prevent it from moving or settling during the jacking process. After a detailed analysis of the geological profile to be traversed it was decided that freezing was the most suitable method, since it could be applied to the full range of soils present on the proposed alignment."

Jan 3, 2003

By Morris J. D, Baldwin Z., Wiltcher P. M

21 Moorfields is an oversite development in central London spanning Moorgate tube station. It required the installation of both the highest loaded bearing piles and the highest top loaded static pile test ever undertaken in the UK, at 50.5MN (5,680 tons). The 17-storey building is founded on only 15 large diameter bored piles installed through the roof of the live station. The piles are located in two parallel rows 50 m (164 ft) apart, bridging the underlying train lines and the Crossrail tunnel below. This unique project required a diverse cross-section of skills and experience from the Project Team as we not only pushed the boundaries of design but also those of construction practices. Our team therefore needed to be made up of members from multiple businesses and disciplines. The team worked together, in a highly collaborative environment, for around two years before any work started on site. A key challenge for this project was that there was only one opportunity to construct each pile. If a position had to be abandoned there were no alternative locations and the impact on the project would have been catastrophic. It was therefore vital that all events that may have led to the abandonment of a pile were investigated ahead of commencement on site. Risk elimination and mitigation strategies were developed for all eventualities whether they be associated with the design or construction processes. The successful pile load test, coupled with all contract piles being fully instrumented with state-of-theart fiber optic (CemOptic) cable along their full length, has improved our understanding of the performance of such large and heavily loaded piles. The works piles will all be monitored during the construction of the new building, providing new insight into their real-world performance. Such groundbreaking work has never been undertaken before in the UK and has the potential to significantly influence the industry’s understanding of pile behavior, and design, in the future. This paper will discuss the challenges the team encountered during the design and construction of this highly complex urban project, particularly when adopting, by necessity, a pioneering approach.

By Ronald E. Walkington

The U.S. Department of Energy (DOE) is building the world's newest accelerator-based, pulsed-neutron system, called Spallation Neutron Source (SNS). The facility, located in Oak Ridge, Tennessee, is a partnership of six DOE national laboratories - Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge. Oak Ridge has the responsibility for managing the partnership and ultimately operating SNS. SNS will provide opportunities for up to 2,000 researchers each year from universities, national laboratories and industry from around the world for basic and applied research and technology development in the fields of materials science, magnetic materials, polymers and complex fluids, chemistry and biology. When completed, this state-of-the-art research facility will provide neutron beams that are 12 times more intense than any other such source in the world. Most of the world's neutron sources were built decades ago. Therefore, it is easy to understand how SNS will provide new research opportunities unavailable elsewhere, and at the same time restore United States leadership in neutron sciences. Neutron scattering research provides valuable information about materials that cannot be obtained through microscopy, X-rays, spectroscopes, or other techniques. The information gained from neutron scattering research leads to improved materials that are used in high-temperature superconductors, powerful lightweight magnets, aluminum bridge decks, jet aircraft, compact and computer discs, magnetic recording tapes, shatter-proof windshields, and many other applications. SNS is like a flashing strobe light providing high-speed illumination of an object and will record the structure of physical and biological materials from plastics to proteins. Because neutrons have no charge, they can penetrate more deeply into materials than do X-rays, light, or electrons and thus reveal bulk structure and properties of materials. SNS will help to understand and "engineer" better materials and the manufacture of better products at the atomic level. Our high-technology society demands new materials that are stronger, lighter, and cheaper yet perform well under severe conditions. SNS, which is designed with the future in mind, will be the leading neutron research facility for many years to come.

Jan 1, 2001

By Abhijit R. Sheth, Craig M. Benedict, John Brun, Ara G. Mouradian

"Amtrak recently replaced the 1907-era bascule two-track bridge over the Niantic River between East Lyme and Waterford, Connecticut. The project included new approach embankments, with approximately 2,500 lineal feet of retaining wall along the west approach and 780 lineal feet of retaining wall along the east approach. The paper focuses on the design and construction of the east approach retaining wall, whose alignment is directly adjacent to an existing wetland area which required protection. An anchored prestressed concrete sheet pile retaining wall was selected for the east approach. A combination of concrete anchor piles and ground anchors were used to support the wall. The design of the wall took into account two simultaneous train live loads, support of electric traction catenary structure foundations, and construction live load, while at the same time preventing permanent impacts to the adjacent wetlands. The design considered challenging subsurface conditions, shallow groundwater, the close proximity of the existing operating tracks, construction staging, and storm surge events in Long Island Sound.INTRODUCTION AND PROJECT HISTORYThe National Railroad Passenger Corporation (Amtrak) recently replaced the 1907-era bascule two-track bridge (No. 116.74) over the Niantic River, between East Lyme and Waterford, Connecticut, along the heavily-traveled Northeast Corridor (NEC). The two NEC tracks, which carry over 50 trains per day, run east-west over a narrow spit of land known as “The Bar”, which separates the Niantic River’s marine estuary to the north from the Niantic Bay to the south, before crossing the river. The bay is an arm of Long Island Sound and is occasionally subject to storm surge from hurricanes.The 1907 bridge was built as a replacement for the previous 1891-era swing-span bridge, and was constructed parallel to, and 49 feet north of, the swing-span structure. The two-track 1907 bridge consisted of a single-leaf bascule span and four approach spans supported on stone masonry piers and abutments. The new bridge increases horizontal navigational clearance for marine traffic in the river from 45 feet to 100 feet, and vertical clearance from 11.5 feet to 16 feet above mean high water with the bridge in closed position. The new bridge, constructed 58 feet south of the 1907 structure, features a single-leaf bascule span of 141.5 feet, with an approach span on either side."

Jan 1, 2017

By Sebastian Fischer, Rolf Katzenbach, Steffen Leppla

"The risk management in the case of liquefaction is one of the most serious and also difficult issues in geotechnical engineering because failure caused by liquefaction is always a sudden failure without ahead indication. For that reason ground improvement technologies for the prevention of liquefaction are necessary. The paper explains the responsible and effective risk management. Methods for the risk management and stabilizing the soil sustainably are described in detail.1. INTRODUCTIONDue to population growing more and more settlement area is needed, which is often including improper regions (e.g. mountain and coast regions) with raised risk of various kinds of disasters. But also in densely populated areas the risk of disasters like landslides can occur. One reason for the raising of risk in densely populated regions can be the opencast mining for raw material production. An essential element of the opencast mining is the loose deposition of the removed overburden, the so-called “overburden dump”. When an opencast mining is running out of the raw material, an opencast hollow remains in landscape. The slope areas of these hollows mostly consist of loose bedded material of the overburden dump. Due to the end of groundwater conservation these loose bedded slope areas are flooded. In consequence the slopes are in extreme danger of becoming liquefied. The result of a liquefaction in these slopes will unavoidably be a slope slide. Such a slope slide can extend up to several hundred meters into the landscape and can move several million cubic meters of material. An upsetting example for such a landslide is the slope failure in the German city of Nachterstedt on July, 18th 2009, which made necessitate remedial measures and also prevention works for the further utilisation of the region. The phenomena of liquefaction is not limited of slopes in series of opencast mining. Especially in regions with a highly appearance of earthquakes the phenomena of liquefaction is well known.2. RISK MANAGEMENTAn essential part for the stability assessment of slope systems is the investigation of sensitivity against liquefaction. In the case of given sensitivity against liquefaction there is no calculation method according to soil mechanics to determine the factor of safety against slope failure. Just for the case that sensitivity against liquefaction is not met, a comparison of the load (effect) E and the resistance R which is the traditional verification of stability against slope failure, can be calculated (Figure 1)."

Jan 1, 2015

By Jean Wehbe, Daniel C. Brahana

"This paper presents a case history of drilled pier construction for a new stadium in Atlanta, Georgia. The stadium structure is supported on several different foundation types, with the heaviest ""mega columns"" typically bearing on drilled pier supported mats. The project includes 141 drilled piers with design diameters of 5.5, 6 and 6.5 feet. The piers bear on bedrock at depths of 20 to 110 feet below the ground surface. Many of the piers included rock sockets with design lengths of 5 to 18 feet. A pre-production drilled pier load test program was completed including one Statnamic load test, two Osterberg Cell tests and two lateral load tests. Non-destructive testing (crosshole sonic logging and sonic integrity testing) were also performed during construction. Production pier installation with over 3800 linear feet of earth excavation and over 1350 linear feet of rock excavation was completed in a little over four months. The piers were installed using both the cased hole method and the slurry method. All cased holed required downhole inspection and slurry holes were initially inspected with a mini-SID device and subsequently by sounding. Advanced drilling equipment and tooling were used to meet the production requirements for the project. This paper reviews the highly variable soil and rock conditions encountered at the site, briefly presents the results of the load tests, and discusses pier installation procedures and the equipment used for installation. The paper also presents conclusions related to the installation and lessons learned.INTRODUCTIONWith the opening of AT&T Stadium in Dallas, a new era of stadium construction began in the U.S. The new age stadiums are larger and have more amenities than their predecessors. The new Atlanta Falcons stadium is no exception. Many of the new features, including Atlanta’s innovative retractable roof, result in extraordinary structural loads. The roof structure is supported by a series of mega columns that bear on eight large caps, six of which are drilled pier supported. Each of the pier caps contains between 8 and 16 drilled piers that bear in the underlying bedrock. The design pier diameters are 6 and 6.5 feet. Augercast piles were used to support two of the mega column caps. Drilled piers, augercast piles, aggregate piers and spread footings are used to support the more lightly loaded portions of the structure."

Jan 1, 2017

By Alexandre Alex) J. Bredikhin

"DISCLAIMER: the statements presented herein are those of the author and do not necessarily represent the views of US DoD or its Components.ABSTRACTProgress on the $750M lock project on the Monongahela River was derailed by discovery of large anomalies in the 6.5-7-ft dia. drilled shafts of the new river wall foundation. The anomalies were located 45 to 50’ below the top of the wall at the critical shaft-to-wall interface, and ranged in thickness from several inches to 2-plus feet. A Specialty team, comprised of representatives from the contractor, the Government, and structural design consultants, was formed to evaluate the extent of the problem and the impact on the new lock wall. With no standard method in place, the Government took the lead to develop acceptance criteria for the repairs while the contractor took the lead to identify the repair means and methods. The Government developed a detailed Quality Control plan to capture and document all of the repair data and to approve each shaft repair in a timely manner. This paper provides an overview of the anomalies encountered and the need for repairs; discusses the details of the repair plan; and provides details on the unique quality control measures employed to verify the repairs. By developing and adhering to a detailed quality control plan, the structural integrity of all of the shafts was successfully restored.INTRODUCTIONThe new Charleroi Locks Project is currently under construction by the U.S. Army Corps of Engineers (USACE) in Pittsburgh, Pennsylvania. In the region, the Corps of Engineers is modernizing the series of locks and dams on the Monongahela River. One facet of this modernization is replacement of the existing Locks #4 (aka Charleroi Locks) located upstream of Pittsburgh, Pennsylvania with new and larger capacity locks. The relative location of the project is shown on Fig. 1. The original construction of twin locks (56’x720’ & 56’x360’) and the fixed-crest dam was completed in 1932, with lock walls supported on timber pile foundations. The fixed crest dam was replaced with a gated dam in the 1960’s. The existing lock is undersized and in poor condition and thus needs to be replaced. The project requires the construction of the new river chamber adjacent to the existing land chamber which must remain operational to navigation throughout the construction. In order to accomplish this, the lock walls need to be constructed in the wet. The river wall was constructed using two construction methods referred to on the project as “cofferbox” and “non-cofferbox” construction."

Jan 1, 2017

By Mark A. Rohrbach, Timothy R. Kovacs, PhD Saidin

"Crosshole Sonic Logging (CSL) testing is commonly used to verify the integrity, quality and ultimately the acceptability of the concrete in structural elements such as drilled shaft foundations, secant pile cutoff walls, and secant/tangent pile earth retention structures. Besides concrete quality, many factors can impact CSL test results (e.g. laitance, air temperature, access tube spacing, access tube debonding, etc.). Effective use of CSL testing requires fully informed qualified practitioners capable of distinguishing between abnormal readings unrelated to deficiencies in the drilled shaft concrete and similar readings indicating the presence or possible presence of drilled shaft defects. Based on data and experience gathered from CSL testing of thousands of drilled shafts across North America, this paper discusses such factors and other information useful when evaluating CSL test results, and provides practical recommendations intended to reduce the potential for incorrect test data interpretation. The CSL testing industry is lacking in a clear, universally accepted guideline for the interpretation of CSL data and acceptance criteria of these concrete elements. This paper proposes terminology and a streamlined process for use when atypical results are obtained. The proposed terminology and method are intended to simplify and expedite the submittal review and approval process. Because construction activities for these elements are often on the project’s critical path, the benefits obtained in terms of project savings and reducing costly delays areundoubtedly valuable.1. INTRODUCTIONCSL testing is used extensively throughout the world on many projects to verify the quality of concrete used for drilled shaft foundations, secant pile walls, diaphragm walls, etc. In this paper, these structural elements will be referred to as “drilled shafts,” as they are the most common subject of this test method. In the United States, CSL testing is frequently specified by state and regional transportation agencies, ports, design builders, and others. Although other methods are currently available such as Gamma-Gamma Logging and low-strain Impulse-Echo or Sonic-Echo testing, and new methods are under development such as the Thermal Integrity testing, CSL testing is likely to remain one of the most useful tools for evaluating the acceptability of constructed drilled shafts for quite some time. The popularity of CSL as a testing method can be attributed to two main factors: 1) there is no depth limitation to the method and 2) the apparent ease of interpreting the results. A third advantage of CSL testing is that, when correctly interpreted and with adequate test coverage, it is unlikely to misrepresent a defective profile resulting in acceptance of a defective or inadequate drilled shaft. In other words, CSL testing is very likely to underestimate concrete quality/drilled shaft acceptability within its area of coverage."

Jan 1, 2017

By Ross Cutts

As a public servant geotechnical engineer, I observed how costly and valuable geotechnical field explorations are to the success of every project. Often however, the field exploration is a long and complex process that is made less efficient by the difficulty of retrieving and utilizing nearby internal or external historic geotechnical datasets. As an employee of a public agency, we would often start our investigations for every project from scratch, given the difficulty of locating and utilizing historic geotechnical data. This is an ethical and technical failing of our profession. When we start subsurface explorations from scratch, not only do we often duplicate investigations, we are also likely defaulting to reapplying tradi- tional test methods that yield con- servative geotechnical parameters, resulting in overly conservative and potentially costly construction. To address this issue while working as a public servant, I started a research program with Yunfeng Zhang, Ph.D., of the University of Maryland, to build a tool that could compile internal historic geotechnical data and extract additional value from it, using machine learning. This tool was able to provide, upon request, nearby historic geotechnical data, estimated soil parameters and recommendations for geotechnical test methods best suited for a given project site. This prevented common field ex- ploration problems such as, requesting duplicate data, requesting test methods that were not applicable for the project geology, not realizing presence of karsts, missing permits for wetlands, private property and others. This tool allowed for more efficient field investigations with regards to time and money saved. There was one problem with this tool: it could only be used by internal employees of a single state's depart- ment of transportation (DOT) for which this data was compiled. I realized at that point that it would be of tremendous value to make this concept universally accessible to the geotechnical engi- neering profession. I left public service to devote time to building a platform that would host historic geotechnical data from publicly funded sources throughout the country. The tool I helped build as a public servant was the foundation of Geosetta, a nonprofit company dedicated to serving the geotechnical profession. The nonprofit structure was adopted to prevent acquisition by a for-profit company and to ensure that Geosetta remains an independent steward of our profession's valuable data. Geosetta provides a GIS (geographic information system) platform that enables users to view historic geo- technical data and extract value from it with machine learning-based predictions and visualization tools. This data is provided in an open and interchangeable format called DIGGS, which stands for Data Interchange for Geotechnical and Geoenvironmental Specialists, making it easy for users to integrate it into their workflows. Geosetta is collaborating with the American Society of Civil Engineers' Geo-Institute and other sponsors to extract public data at no cost to the agency and provide the profession with free access to the existing data and access to advanced tools through a subscription to support the nonprofit mission.

Nov 1, 2023

By Tomohide Takeyama, Binh T. T. Nguyen, Masaki Kitazume

"Deep mixing columns are widely used to support embankments constructed on soft ground area. Researches on the stability of deep mixing columns were done by some authors when the columns do not simultaneously fail but individually fail at different time. A layer of shallow mixing is proposed to reinforce these columns as a group to increase the stability as well as loading capacity of columned improved area. Two centrifuge model tests were done to observe the effect of shallow layer on reducing embankment displacement as well as on failure pressure of improved ground. Acrylic piles were used as deep mixing columns in the centrifuge tests to avoid unexpected internal failure of columns. The results of centrifuge tests were also simulated by 2D FEM to back-analyze the centrifuge experiments. A good agreement between the centrifuge experiments and the numerical simulations shows that by using a shallow layer reinforcing individual columns, the horizontal displacement at the embankment toe reduces by 60 % and the tilting failure is clearly indicated in columns without shallow layer. Although, no significant failure was observed under the current centrifuge condition, the failure pressure of improved ground was significantly increased with the columns reinforced by shallow layer.INTRODUCTIONCement or lime and soil mixing technique was firstly used in Japan and Nordic countries since 1970s. The technique is used to improve soft soil by increasing its mechanical properties including strength and consolidation characteristics (Kitazume and Terashi 2013). Various researches were done to investigate the characteristics of mixing material due to various factors including types of binder, condition of soil, mixing condition and curing condition (Terashi 1997). On the other hand, many studies focused on the application of in-situ mixing technique such as supporting embankment and underground structure as well as working as the foundation of building and factory (Kitazume and Terashi 2013). In term of embankment supporting, column-type improvement is taken into account for huge applications. Due to loading from embankment, the deep mixing columns tend to fail either external failure (Kitazume and Maruyama 2006) or internal failure (Kitazume and Maruyama 2007). However, the deep mixing columns do not fail simultaneously but instead one by one at different time (Kitazume and Maruyama 2007). Because the deep mixing columns work and fail individually, the strength and stiffness of all columns cannot be mobilized simultaneously. By using a shallow mixing layer fixing the top of deep mixing columns, individual columns may work simultaneously. A combined technology of shallow stabilization and floating-type cement treated columns is used to reduce settlement of a high embankment on soft ground (Ishikura et al. 2007). A research on effect of surface improvement layer on internal stability of group column type deep mixing improved ground under embankment load was reported in the Port and Airport Research Institute, Japan (Kitazume 2011). However, the failure pattern of shallow and deep mixing combined structure has not well studied. This research focuses on the external failure mechanism of the combined structure by centrifuge model tests and back-analyzed simulation using 2D finite element method. The effect of shallow layer on embankment displacement and the yield point of the improved ground is also discussed in this study."

Jan 1, 2015

By Sebastian Lobo-Guerrero

Welcome to DFI45! our first on-line annual meeting. We cannot deny the severe impacts that the COVID19 pandemic is having in our industry and our lives. We extend our support to all of our members that have been impacted in many different ways. But through the middle of this difficult and challenging times, our beloved annual conference emerges, trying to re-unite our industry and remind us why we love what we do so much. DFI45 was not originally planned to be delivered virtually, but as our world changed, we adapted. Adversity became an opportunity to re-invent our annual conference. Thanks to the vision of our Organizing Committee, we saw the amazing new possibilities and DFI45 is today a reality. Our theme for this year is People + Purpose + Passion. This theme was decided before the COVID 19 pandemic started, but today it is more relevant than ever before. We are a group of very diverse people at DFI. Our organization includes Contractors, Consultants, Suppliers, and Academics just to name a few sub-groups. But we all have a common purpose and try to find common ground. We are all extremely passionate about what we do, and this excitement is really what makes this organization what it is today. This conference celebrates this passion as you can see in our three main Keynote Sessions. On a local scale, we want to go back and remember the contribution of our industry to our beloved National Monuments in Washington D.C. On a national scale, we want to explore and recap the development of Government Guidelines and Specifications that became the world standards. And finally, we want to close the conference with a session celebrating the family legacy and share amazing stories of families with multiple generations working in our industry. Besides our Keynote Lectures, the conference is full of exciting content such as several case histories, experimental research in deep foundations, applications of new technologies, business aspects and risk management considerations for deep foundations, just to list a few. We also have our now traditional events such as the Hal Hunt Lecture, Awards Reception, DFI Educational Trust 5K Fundraiser, etc. For the first time, all this content will be delivered using different virtual formats, including on-demand presentations, plenary sessions, interactive chat rooms, etc. We are excited about these possibilities. To conclude, we need to recognize the people that against all odds made this conference a reality. First our sponsors, they adapted to the most abrupt change never thought before, and they always stayed there with us, providing unconditional support. Without them no conference is possible. Next, our Organizing Committee that re-invented the concept of an annual conference and found new and exciting ways to make this happen! Our Technical Program Committee led by our Technical Program Chairs, Jennifer Nicks and Gregg Piazza, showed us that nothing is impossible. And last, but not least, the amazing DFI staff that make dreams reality. It has been an honor to serve as the Conference Chair for DFI45. It is an experience that will stay with me for the rest of my career. Conference Chair: Sebastian Lobo Guerrero, Ph.D., P.E. American Geotechnical and Environmental Services (A.G.E.S.)

Oct 27, 2020

By Jacob A. Jordan, Rachel M. Garrett, W. Robert Thompson III, James C. Pegues

"Environmental control structures for an existing fossil-fuel power generating plant near Pascagoula, Mississippi faced several design and construction challenges due to space limitations. Conceptual design calculations indicated drilled shaft foundations would likely be needed to accommodate the higher lateral and compressive loads expected under some structures. A maximum drilled shaft diameter of 60-in was preferred due to various space constraints. Smaller diameter drilled shafts were deemed acceptable under structures with more moderate loading conditions. Furthermore, augercast piles were considered where lateral loading was not a governing design criterion.A series of SPT borings and CPT soundings revealed a subsurface profile consisting of soft to firm clays to depths of about 25 feet, underlain by fine to coarse sands. The apparent relative density of the sands was loose just below the clay, with increasing density noted with an increase in depth.Analysis of conventional drilled shafts indicated needed capacities could not be achieved unless shaft lengths exceeded 100 feet. Post-grouted drilled shafts were therefore evaluated to decrease shaft lengths by taking advantage of increased base capacity. Analyses showed the higher predicted capacities needed for some structures could be achieved with this approach. Final design for the project incorporated 90-ft long, 60-in diameter post-grouted drilled shafts; 60-ft long, 48-in diameter post-grouted drilled shafts; and 60-ft long, 48-in diameter conventional shafts. Both post-grouted and conventional trial shafts were installed as part of the detailed design phase of the project. Each trial shaft included CSL integrity testing and Osterberg-cell bi-directional load testing. Load test results revealed that additional base capacity was, in fact, achieved through the post grouting process. The 60-in diameter post-grouted production shafts and the 48-in diameter conventional production shafts have been installed at the site, with the project that would utilize the 48-in diameter post-grouted shafts deferred at this time."

Jan 1, 2015

By Abid Adekunte

"In recent years, developers have had to deal with complexities associated with numerous cases of deep basement construction in built-up areas. Design and construction of deep excavation support systems in urbanised zones come with many technical challenges. Restricted working spaces often render the use of temporary struts as wall restraint systems unpopular, as working space needs to be maximised. Also, tie-back anchors are often inapplicable due to the existence of adjacent structures. Therefore, developing alternative restraint systems for deep basement structures in builtup areas is becoming increasingly important to the present day basement engineer.This paper is centred on the design, construction and monitoring of enabling works for deep basement structures on three sites in the United Kingdom and Republic of Ireland. Traditional tieback anchorage and propping systems were inapplicable on the sites. As alternatives, separate novel wall restraint systems were developed and adopted, to enable excavation on each of the three sites.Performances of the novel wall restraint systems, as well as the responses of adjacent structures were monitored. Numerical modelling and field monitoring results show the three alternative wall restraint systems to be safe and effective. The paper also highlights the advantages of the novel solutions over conventional methods.INTRODUCTIONRecently, deep basement structures have become popular components of urban building developments. As pointed out by Pearlman et al., 2004, this could be attributed to the inadequacy of surface parking spaces in urbanised zones, while underground parking facilities are also believed to improve both aesthetic and commercial qualities of urban structures.However, while the incorporation of basement structure into new urban development appeals to developers and architects, the engineering design and construction aspects of basement works typically come against a whole lot of complexities and challenges. As highlighted by Wong, 2002, engineering problems associated with basement construction in built-up areas are numerous, some of these include; complicated sub-soil conditions, dealing with excessive active pressures, complex temporary works, proximity of sensitive adjacent structures, high level hazards to construction workmen and surrounding community, inadequate working space, etc."

Jan 1, 2015

By Glen Mann, H. G. Vestberg, Robert D. Holtz

"Underpinning of residential and commercial structures is often accomplished using a number of driven-in-place small diameter steel pipe piles. These piles, at least in the Seattle area, are typically described as pin-piles and are driven with an air compressor operated jack hammer to a refusal criterion developed from an empirical basis. Over the past twenty years or so, the materials have improved in quality and strength, and the driving equipment has improved in efficiency and capability. These improvements have resulted in damage to the pin-piles during driving as well as to the driving equipment. The primary objectives of this load testing study were to develop a relationship between the driving penetration resistance of 2-inch diameter pin-piles and the ultimate bearing capacity when piles were driven at different penetration rates and, based on the load test results, to develop an opinion regarding an increase in the allowable axial load capacity [ultimate load capacity divided by a factor of safety] of a 2-inch diameter pin-pile over the currently used permissible load capacity of 4 kips in the Seattle area. Also, if feasible, a reduction in the present driving penetration rate was to be recommended to help reduce the rate and magnitude of pile and equipment damage whilst maintaining the allowable load capacity. The recorded ultimate bearing capacities were also compared with the Tagnent-line and the Davisson analytical methods in an effort to determine if either of these provided a reasonable determination of the pile load capacity.IntroductionThis paper describes the results of a series of load tests performed on small diameter, 2-inch, driven-in-place steel pin (pipe) piles and based on these results, provides the support for a modification to the presently used allowable axial pin-pile capacities.The intent of the load testing program was to determine how much influence the penetration resistance might have on the individual piles' ability to support the allowable axial load without undergoing any significant vertical deformation. For the purposes of this paper the ""allowable load capacity"" is considered to be the ultimate pile load capacity divided by a minimum factor of safety, typically considered to be 2.0 in this area. A pin (pipe) pile comprises an open or closed ended, schedule 80 steel tube which is driven-in-place, usually with an air compressor operated 90 pound pneumatic jack hammer. These jack hammers typically operate at a rate of about 1,200 blows per minute, (Haggard, Holtz and Mann, 2001 )."

Jan 1, 2005

By Abid Adekunte

Traditionally, designers and contractors provide additional external supports to retaining walls through the use of tie-back anchors or braces. Both approaches are known to have their shortcomings; braces limit working space within excavation areas, while tie-backs are seldom used in built-up areas where intrusion into adjacent property of non-cooperative owners has to be avoided or in situations where sensitive structures exist behind the wall. This paper focuses on the design, construction and monitoring of deep excavation support systems on two separate projects located in different ground conditions in the Republic of Ireland. On both projects, conventional ground anchorage and propping were inapplicable. This led to the development and application of two different novel solutions on both projects. Methods of wall performance monitoring on both sites also differ. Wall monitoring results show these innovative methods to be safe and effective. Advantages of the novel solutions over traditional approaches are highlighted.

Jan 1, 2010

By Dan Brown

Improvements in construction equipment and techniques in recent years have made possible the use of drilled shaft foundations in diameters and lengths not previously considered practical or feasible. Many highway bridge and other structures are now routinely founded on drilled shafts which are 2.5 m to 3.0 m (8 to 12 feet) in diameter and extending over 60 m (200 feet) in depth below grade. There are unique challenges associated with constructing such large and deep cast-in-place foundations and engineers should be aware of the special needs associated with site investigation, construction specifications, material requirements, and quality assurance. This paper outlines a number of special considerations for these foundations, along with strategies that may be employed to improve the reliability and quality of large drilled shaft foundations.

Jan 1, 2008

By Charles Roeder, Amy Leland, Dawn E. Lehman

Concrete filled steel tubes (CFSTs) are composite members that are commonly used in many countries today. CFST components are used in the United States, but they are more common in Asia, in part because the connections used in Asia are quite labor intensive and there are not standard connections in the U.S. In addition, US design specifications are prepared by separate groups for structural steel and reinforced concrete structures and so composite systems that use CFST components are not overseen by a single group and as such there are several, conflicting design standards. In the US, steel tubes used for CFST are more slender (i.e., the diameter-to-thickness, D/t, ratio is larger) than some other countries, and labor practices (structural steel labor is different than reinforcing steel labor) also cause potential conflicts in construction. As a result, CFST has had some use in tall building construction in the US, but very limited use in bridge construction. A research program at the University of Washington has been in progress to address many of these issues with an eye towards universal design expressions, simpler, standardized connections and promotion of accelerated bridge construction (ABC). The research has resulted in recent changes to the American Association of State Highway Officials (AASHTO) bridge design specification as well as state departments of transportation (DOTs), which supports the increased use of CFST in bridge pile and drilled-shaft foundations. An experimental research study which investigate the flexural strength, shear strength and connections was conducted. These connections provide good performance under both seismic and gravity loads and address the concerns of US construction. These connections, their design rules and requirements, and their impact on composite behavior and system performance are discussed. These results permit rapid and economical construction of CFST bridge piers, piles and drilled shaft foundations. They encourage the use of more slender and economical tubes, while achieving the benefits of composite construction. INTRODUCTION Concrete filled steel tubes (CFSTs) are widely used for bridge and building construction in Asia, but the use of CFST in bridge construction is limited in the US. The historical use of structural steel and reinforced concrete in US bridge construction have resulted in more developed design expression for those construction methods, which has limited the use of CFST. Bridge construction in the US is inherently different than in Asia because of differences in codes, labor costs and construction practices. As a consequence, design and construction practices that are economical and practical in other countries may not be practical for US bridge construction.

Jan 1, 2019

By Tsuda Wakaki, Naoki Takahashi, Natsuki Okuno, Hidenori Takahashi, Ikuo Towhata, Yoshiyuki Morikawa

"Deep mixing (DM) method has been increasingly employed as a countermeasure against subsoil liquefaction in recent years. Pile-type DM, however, is considered to have little effect as a liquefaction countermeasure, because the shear deformation of unimproved soil around the piles cannot be reduced. However, experimental results, which imply that shear deformation of unimproved soil around DM piles can be reduced, were reported. Furthermore, a new plane-arrangement of DM piles has been proposed to mitigate lateral flow induced by liquefaction. The DM piles in this arrangement confront the lateral flow in any direction, compared with the piles arranged in conventional pattern such as square and triangular arrangements. In this study, a series of dynamic centrifuge model tests was conducted to verify the lateral flow resistance of DM plies in the new arrangement. The results indicate that the DM plies can reduce the lateral flow of liquefied ground when the pile displacement and the pile head rotation are restricted. In addition, lateral load acting on DM pile from liquefied ground, which is required for design strength of the DM pile, was investigated.INTRODUCTIONDeep mixing (DM) method has been increasingly employed as a countermeasure against subsoil liquefaction in recent years. The solidified body formed by the deep mixing method is usually block or lattice shape, composed of solidified columns that overlap each other horizontally. Lattice-type solidification has been shown to be effective as a liquefaction countermeasure despite the presence of unimproved soil inside the lattice wall, because the shear deformation of the interior soil is restrained by the wall (Suzuki et al., 1989). On the other hand, it has been thought that pile-type DM cannot reduce shear deformation of unimproved soil around the piles, because the displacement of the pile is less restricted than that of the lattice wall. DM piles have been reported to have little effect as a liquefaction countermeasure, but to be superior in terms of construction cost and applicability around existing underground structures (Koga et al., 1986). However, there are experimental results implying that DM piles have reduced the shear deformation of unimproved soil and mitigated its liquefaction (Yasuda et al., 2003; Tanaka et al., 2003). Yamamoto et al. (2006) conducted dynamic analyses of ground improved with lattice- and pile-type DM. Their results showed that pile-type DM with an improvement ratio of more than 35% reduces excess pore water pressure generated by earthquakes. Furthermore, the new pile arrangement shown in Fig. 1(a) has been proposed to mitigate lateral flow induced by liquefaction. It was developed and has been verified using dynamic model testing in a 1 g field (Takahashi et al., 2010a; 2010b; 2013; Towhata et al., 2010, Morikawa et al., 2014). The DM piles in this configuration interrupt lateral flow in any direction, unlike those placed in square and triangular arrangements."

Jan 1, 2015