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By Dominik Gächter, Wojciech Szczepinski, Jakub Bieszczad

Increased requirements for rail transport north of Oslo have forced Norwegian Authorities to invest in the development of double-track rail to decrease traveling time and increase the frequency of the rail service. Part of this development is Tangenvika Bridge which is built on the largest lake and drinking water reservoir in Norway (Mjøsa). Once completed, it will be the longest railway bridge in Norway. The foundation design consists of drilled and driven composite piles. All the works are performed on water and because of its depth, all piles are installed from floating container pontoons instead of jack-up barges. In order to meet the strict steel quality requirements of composite piles, all piles are welded on land in a controlled environment and then transferred onto the transfer pontoons on water. Close to shores, due to the local presence of sensitive soils and the risk of underwater landslides, a total of 78 drilled piles (1016mm) are executed using the reverse circulation method (RC). All piles are drilled 2m into bedrock using a fully integrated ring bit system. In the deepest parts of the lake, a total of 60 driven piles (1430mm) are installed using 350kJ hydrohammer. The bottom of the piles are finished with a closed-ended pile tip, which is the most popular driven pile tip in Norway. All drilled and driven piles are installed in single lengths of up to 85m and net weight of 102t at 1:5 inclination. The lifting process of the piles on the water provides significant challenges for which a combination of 400t crane, 2 transfer pontoons, and a tugboat is used to provide a safe execution method.

Oct 7, 2024

By Ramin Motamed, Reza Mohammadi

Finite element methods play a crucial role in analyzing dynamic responses within soil-foundation-structural systems during earthquakes. The validation of these models using seismic recordings is paramount for their application in the seismic design of foundations. This paper focuses on the refinement and validation of finite element models developed to study the response of drilled shafts at the Hayward-I580/238 bridge in California. The research methodology employs a two-step finite element modeling approach. In the initial phase, a free-field soil model of the site was developed in a two-dimensional model with OpenSees. Subsequently, a drilled shaft with an elastic section was modeled to investigate the response of the deep foundation to earthquake motions. However, acknowledging that these assumptions may not fully represent actual conditions, a three-dimensional free-field model of the bridge site was developed using OpenSees software in this study. Additionally, an inelastic section model for one of the bridge's drilled shaft was introduced to better capture the shaft's response under seismic forces. Given the relatively weak ground motions recorded by the accelerometers at the Hayward-I580/238 bridge, hypothetical earthquake scenarios were generated to depict the nonlinear response of the model. The available recorded motions were used to fit the target design spectrum at the Hayward-I580/238 bridge following AASHTO-2009. Subsequently, the shaft's reaction was analyzed under seismic forces, examining various parameters such as displacements and reaction forces. The results highlight the impact of the introduced modifications on the accuracy of the finite element models under both weak and strong earthquakes. In conclusion, the enhanced models not only contribute to monitoring drilled shaft behavior during seismic events but also establish a robust framework for future seismic designs of drilled shafts, showcasing the benefits of OpenSees in seismic design of deep foundations. Keywords: deep foundation, drilled shaft, OpenSees, soil-foundation interaction, seismic design

Oct 7, 2024

By Mark Wade

This presents an overview of the successful construction of a large diameter using trenchless technologies for renewal in Casper, a region with few large-scale projects. This project preserved and enhanced the City's aging wastewater infrastructure for an additional 100+ years. The pipeline, known as the North Platte Sanitary Sewer Interceptor (NPSSI) represents a nine-mile conveyance system that was initially constructed in four phases between 1980 and 1983 as part of a wastewater regionalization effort in the Casper metropolitan service area. The pipe material for the interceptor was unlined reinforced concrete pipe (RCP). Due to elevated levels of H2S within the pipeline, associated sulfuric acid formation became problematic along the entire interceptor alignment, causing serious deterioration of the NPSSI. The project team of CEPI, BlueWater, and Jacobs utilized a series of internal inspections and investigations of the entire interceptor over a three-year period to assess its condition and requirements for rehabilitation. This led to the first phase of strategic rehabilitation utilizing cured-in-place pipeline (CIPP) by Aegion/Insituform. Construction of the most critical portions of the NPSSI began in mid-2022 and was completed in early 2023. The project scope consisted of 7,600’ of 48-54” pipe rehabilitation along with numerous deep-bury point repairs, junction structures, river siphons, and inlet/outlet structures. Despite record cold winter weather and numerous site challenges encountered, Insituform Technologies delivered the project to the City of Casper with only a single time extension. The total cost of the project was below the original contracted amount, or $8.1M. The Casper NPSSI demonstrates who the successful renewal of a deteriorating wastewater interceptor within a stream-sensitive aquafer can be done using trenchless renewal in the best way possible. Added value was provided from the collaboration by all stakeholders, careful planning, and executing innovative technologies, to achieve an outcome beyond expectation.

Oct 7, 2024

By Tajebe Bezabih, Tonya Sanders Thach, David Sinkhonde, Samia Kirchner, Hunter James, Derrick Mirindi

With the increasing demand for wood driven by population growth and urbanization, this study explores the potential of three-layer particleboards reinforced with waste fibers as a sustainable and eco-friendly alternative in building material technology. It focuses on various waste fibers such as sisal, bagasse, leather shavings, and waste papers, assessing their impact on the structural properties of particleboards. The research thoroughly evaluates key mechanical properties such as the modulus of rupture (MOR) and modulus of elasticity (MOE), as well as essential physical properties like water absorption (WA) and thickness swelling (TS). This investigation delves into the innovative use of organic and natural bio-waste particulates as reinforcing agents in polymer composites, specifically examining their role in enhancing particleboard characteristics. A significant finding of this study is that the enhanced particleboards not only meet, but sometimes exceed, the minimum standards set by various international guidelines for general purposes. This indicates that it is feasible to replace traditional wood fibers with certain organic waste materials while maintaining or even improving the performance of conventional particleboards. This advancement is particularly relevant to the construction industry, as it suggests that these improved particleboards can be effectively used as sustainable structural materials. By utilizing waste fibers, it not only aligns with global sustainability goals but also provides a practical solution for waste management across multiple industries. Consequently, this research represents a significant step forward in the development of building materials that support eco-friendly construction practices and contribute to the circular economy.

Oct 7, 2024

By Francisco Humire

Contemporary design criteria for ground improvement supporting structures frequently specify a maximum post-liquefaction reconsolidation settlement value. Typically, those settlement values are evaluated using methods developed to represent free field conditions in the absence of ground improvement. Centrifuge and full-scale field tests have shown that arrays of dense gravel columns reinforce the ground leading to a reduction of post-liquefaction settlements relative to free field values. Therefore, free field settlement estimations that do not account for the vertical reinforcement effects provided by columnar ground improvements lead to conservative estimates of post-liquefaction settlements. Gingery (2019) proposed a constitutive model able to capture the development of post-liquefaction volumetric deformations and presented its implementation in a finite difference numerical model. The model proposed by Gingery (2019) has the advantage over more simplified approaches in that it more rigorously captures many of the physical processes including porewater pressure dissipation, gradual regain of soil stiffness and strength, downdrag, and stress redistribution. The objective of this work is to further validate the constitutive model proposed by Gingery (2019) and investigate the post-liquefaction settlement reduction due to vertical reinforcement effects for different subsurface profiles. This is done by (1) validating the constitutive model against more recent centrifuge and full-scale field tests, and (2) quantifying the post-liquefaction settlement reduction that is attributable to vertical reinforcement effects for different site conditions. Our simulations show a reduction of 15 to 20% of post-liquefaction settlements relative to free field values when considering vertical reinforcement effects.

Oct 7, 2024

By Joseph Seibold, Kavin Khatri, Siobhan O'Reilly-Shah, Neel Neelakantan

San Francisco’s New Headworks Facility Project consists of the design and construction of a state-of-the-art Headworks Facility designed to treat up to 250 million gallons of wastewater a day. The site is located in the Bayview District of San Francisco, California and is subject to various geohazards, including liquefiable artificial fill, compressible Bay Mud, multiple aquifers (including a pressurized aquifer), and high seismicity. To mitigate these hazards, and to accommodate the anticipated structural load demands, the New Headworks Facility structures were designed to be supported on large diameter drilled shafts. Bi-directional load tests (BDLTs) were designed and carried out to calibrate the analysis and confirm the design. During pre-production construction, two 36-inch-diameter drilled shafts approximately 125 feet long were installed at the project site. Each drilled shaft was instrumented with a bi-directional load cell, Linear Vibrating Wire Displacement Transducers, and eight strain gauges at select locations. The BDLTs were carried out after shaft installation. With careful consideration of the geotechnical conditions, the upward and downward displacement of the shaft segments above and below the bi-directional load cell mobilized at about the same time, allowing for significant data acquisition that resulted optimization for the foundation design. Through the successful implementation of a BDLT program, the drilled shaft lengths were able to be reduced significantly, resulting in substantial cost savings to the San Francisco Public Utilities Commission (SFPUC). This paper presents a discussion of the BLDT program performed for the New Headworks Facility Project, and how BDLT can be implemented as an effective method for estimating capacities on large-scale public infrastructure projects. Keywords: Bi-directional load testing, load cell, drilled shafts

Oct 7, 2024

By Scott Lakes

In recent years, Southeast Florida water agencies have been collaborating to develop a regional water supply that is sustainable and affordable. The C-51 drainage canal was selected as a leading candidate for the construction of a water reservoir – named the C-51 Reservoir – to store raw water for future use. The reservoir will capture storm water that is currently lost to the Lake Worth Lagoon estuary for storage. Phase One, recently completed, is estimated to store 14,000 acre-feet and supply 35 million gallons per day (MGD) of raw water to participating utilities. In addition to sustainable water storage and supply, the C-51 Reservoir Project will reduce excess freshwater discharges to the brackish Lake Worth Lagoon and improve water quality. The reservoir would also serve to assist with flood control and Everglades restoration efforts The reservoir design includes a cutoff wall that runs the entire length of the embankment’s axis. The cutoff wall largely consists of a minimum 2.5-foot-wide soil-bentonite (SB) wall with a small section of a soil-cement-bentonite (SCB) wall where twin 96-inch diameter conveyance pipes for the gated control structure cross the cutoff wall alignment. The total length of the cutoff wall is about 20,400 feet and extends through a limestone stratum into underlying sands with a total depth of about 50 feet. The cutoff wall ties into an RCC embankment. This paper provides the approach to construction, quality, and lessons learned from the cutoff wall construction. Details and issues with the cutoff wall tie in are described. Keywords: cutoff wall, soil-bentonite

Oct 7, 2024

By Daniel Escobar, Tom Szynakiewicz

The City of Park City recently undertook a renovation of the initial 400 ft of the historic Spiro Tunnel.  The Spiro Tunnel is a historic mining tunnel along active ski lifts and ski slopes and speaks to the local mining history of the region.  The tunnel is at least 14,000 ft deep and once it was decommissioned for mining purposes, served as a novelty chair lift in the ’60s, bringing guests up the mountain on what came to be known as the Skier Subway, a 45-minute ride through the tunnel ending at what is today’s Thaynes Vertical Shaft.  The tunnel produces between 4,000 and 10,000 gallons of water per minute which is collected within the first 400 ft of the tunnel and flows under gravity to the Park City water treatment plant.  It is estimated that the city gets approximately 30% of its municipal water supply from this source.  The stabilization of the initial part of the tunnel included the deconstruction and removing of existing steel and timber sets in very fractured, blocky and angled rock-plane conditions followed by intensive bolting and shotcreting.  The project was completed by replacing the two under-foot 24” water pipelines that ran at the base of the tunnel followed by the replacement of the rail ties and reestablishment of rail that runs inside the tunnel and provides a means of locomotion for maintenance and inspection.  The project also involved extensive slope cut-back and stabilization at the portal and the installation of an architectural facade.  The authors will discuss the overall project implementation including design and construction.

Oct 7, 2024

By Grace Keller, Jay Jackson, Patrick Allen, Scott Lakes

Dam construction and remediation projects generate vast quantities of data. All information must be meticulously tracked, analyzed, catalogued, and submitted to the proper stakeholders to ensure safe construction, compliance with design intent, and efficient execution of the work. Traditional data collection involves hundreds or even thousands of hand-written records and checklists, which must be deciphered and manually digitized to verify work outcomes. This process is time-consuming and leaves much room for error. To maximize quality and efficiency while minimizing errors, we deployed a robust Data Management Program. By utilizing digital tools and cloud-based automation, we optimized the Quality Assurance program on the Gross Reservoir Expansion (GRE) Project. The GRE project is a large-scale dam raise located near Denver, Colorado, designed to increase the capacity of Gross Reservoir by raising the existing dam 131 ft using Roller Compacted Concrete (RCC). Given the complex nature of the project, extensive data management and post-processing were required to ensure quality construction. We eliminated the need for paper records by implementing source-to-source data collection. Contractor data was exported in raw form and automatically collected via cloud-based automation. We also built customized mobile applications for inspections, which sends checklist results directly to a cloud database. Data visualization occurs in real-time, and interactive dashboards track status and automatically reflect the updated database, allowing stakeholders to interact with the data to gain insights. Document generation and distribution were also automated, streamlining reporting and filing processes and directly impacting regulatory site audits. This paper will expand on these tools and solutions to provide greater insight on their purpose, use, and execution and illustrate the benefits of an efficient data management program on large-scale dam projects.

Oct 7, 2024

By Katerina Ziotopoulou, Martin Yossifov, Jim Gingery, Katherine Cheng

Soil mixing is an in-situ soil treatment method that consists of mixing cementitious binders with in-situ soil to create soilcrete. The success of this treatment often relies on the value of the Unconfined Compressive Strength (UCS) of the soilcrete after a given curing time. Estimating the UCS can be challenging because numerous factors influence the results, including soil type, soil moisture content, binder content, soil chemistry, soil heterogeneity, and mixing means and methods. In current North American design-build practice, pre-construction design UCS values are typically estimated qualitatively based on a contractor’s experience. Existing correlations may not be suitable for current applications because of recent advances in deep mixing equipment and methodologies. There is a need for more rational and quantitative estimates of UCS for use in pre-construction design analyses.  This paper will explore the intersection of Machine Learning (ML) with geotechnical engineering and soilcrete applications. A database of soilcrete UCS and site/soil/means/methods metadata is compiled from recent Keller projects and leveraged to explore UCS prediction with advanced ML regression techniques. From this ML exploration, a blueprint of how to scaffold, feature engineer, and prepare soilcrete data for various ML techniques will be created. However, many ML models sacrifice explainability for higher accuracies. To achieve insights from ML models, Explainable ML will be applied to the ML models to explain variable importances. Explainable ML can reveal complex patterns and interactions in the model variables, along with the relative importance of each variable’s contributions to the final UCS value. The insights received from the Explainable ML model can then be further pursued in traditional geotechnical research approaches to expand soil mixing knowledge.

Oct 7, 2024

By Thomas Fiala, Derrick Speakman

Green Infrastructure Partners (GIP) is an experienced specialty contractor who installs deep foundation and excavation shoring.  The last 50 plus years has given us a unique perspective by witnessing firsthand the evolution of deep foundation and shoring works across Canada, but specifically in the province of Ontario and the city of Toronto. Toronto is Canada’s largest city, with the population doubling over the past forty years. The volume and complexity of construction projects has kept pace with this rapid urban growth. In this paper, we explore the massive increases in construction complexity by delving into the past half-century of archives of a Toronto deep foundations contractor. Fifty years ago, two to three levels of underground parking with driven pile foundations was considered a complex project. Today, Toronto sees the construction of basements eight parking levels deep, secant pile headwalls upwards of 60 m (200 feet) deep, and drilled shafts to even greater depths. Projects sites in Toronto have also increased in complexity over the years, with more projects of greater depth being built on less desirable sites such as in the infilled Lake Ontario waterfront neighbourhood. As construction complexity has increased, equipment and monitoring technology has also improved over the years as tighter movement limitations on construction have become the norm, especially in infrastructure projects. We will explore the local philosophy of shoring construction, including how it has evolved over the years to suit the continuously more complex projects. An emphasis will be placed on deep secant walls which have served as cutoff walls up to 60m deep and excavation support over 30m (100 feet) deep. We will use several historical and modern case study examples to illustrate this chronicle as Toronto contractors evolved over the years to be leaders in installing these deep foundations and excavation shoring for these unceasingly more complicated and risky projects. 

Oct 7, 2024

By Daniel Renosto, Crysthian Azevedo

This article presents a case study with field analysis and numerical tests of grillages and helical pile foundations used for tensile and compression loads of transmission line towers in Brazil. Through finite element analysis (FEA), the structural resistance of the pile will be evaluated using pre-established supports with the stiffness indicated in different types of soil along the profile of the transmission line. The variation in this resistance of the grillage-pile assembly depending on these supports will be evaluated. Elements such as couplers, shafts, leads, extensions, helices, welds, and screws are analyzed from the perspective of structural engineering with interaction with geotechnics. Actual structural safety factors are presented in this case study taking into account tensile, compressive, torque, and construction eccentricities loads. Within the scope of quality control of helical piles and grillages of this specific project, it will be possible to verify points of attention and suggestions for improvements for helical piles and grillages in terms of manufacturing, assembly, and execution. This article hopes to present the importance of a structural analysis of soil-structure interaction that is sometimes neglected in foundation projects based on a real case study carried out in Brazil.

Oct 7, 2024

By Takefumi Takuma, Tsunenobu Nozaki

Light rail transit (LRT) systems have been built in cities all over the world in order to cope with increasing population and heavy car traffic in their downtown cores and surrounding areas. Light rail tracks are often sharing the roadways with automobile traffic while some of them are on the dedicated trackage for safer and faster transit. For example, the twin cities of Minneapolis and St. Paul in the state of Minnesota in the U.S. have their Blue and Green LRT lines in operation with the latter line being extended by 23km to a southwestern suburb of Minneapolis. The mostly dedicated extension alignment includes an 875m long cut-and-cover tunnel because the alignment there is just next to a high-rise condominium complex, a cluster of townhouse buildings, and a parallel running railroad track. Sheet pile walls were selected as part of the earth retaining structures needed for this section of the extension project. The distance between the buildings and the sheet pile alignment is a mere 3m at their closest point. In order to minimize negative impacts to these existing structures from sheet pile installation, press-in piling was utilized. The soil conditions were alternating sand and silt layers with the SPT value varying between 23 and above 50, which necessitated the use of auger attachments. It took two press-in piling machines 14 months to install approximately 2,500 pairs of Z-shaped sheet piles with their lengths between 7.6m and 19.8m. After the sheet pile wall installation, excavation between the walls, installation of internal bracing, and construction of a concrete tunnel box followed.   

Oct 7, 2024

By Spencer Ness, Yazen Khasawneh

Onshore wind turbines are complex and dynamic systems, undergoing variable environmental and mechanical loads. These dynamic loads are transferred through the turbine components and tower to the foundation system and, subsequently, the adjacent soil. As the size of onshore wind turbines continues to grow, intermediate-type foundations are being developed and implemented to better leverage the strength of the adjacent soils while avoiding some of the drawbacks of deep foundations. However, these foundations can be relatively sensitive to ground conditions. When considering a wind energy site that may consist of dozens of wind turbines across thousands of acres, it can be difficult to determine a design stratigraphy that is reflective of the entire site and takes conservative approaches to all potential failure modes and design checks. As intermediate foundations are inherently a soil-structure interaction problem, computer-aided numerical methods are often necessary. To highlight this condition a typical intermediate foundation with tower and turbine is assessed under eighteen different soil profiles within a finite element software and performance is compared.

Oct 7, 2024

By Keith Herman, Lisa Papandrea

While New York City is known for its bedrock and being home to one of the greatest concentrations of tall buildings in the world, its soil conditions are quite variable and can be very challenging in some locations. One such neighborhood is Manhattan’s Upper East Side, particularly near East 96th Street. Historic maps show that the area was once a wetlands network of marshes and creeks. Construction projects in this area have often led to settlement of existing structures, many of which are old, low rise residential buildings supported on shallow foundations bearing on uncontrolled fill.   This case study presents the design, testing, quality control and construction of rotary-driven pipe piles for support of an 8-story medical research facility on the Upper East Side. Three hundred twenty (320) 12.75-inch diameter, rotary driven pipe piles were installed 120 feet deep. The subsurface stratigraphy consists of uncontrolled fill, organic silts, and peat over stiff, saturated, varved silts and clays. Groundwater is approximately 7 feet below grade.  The rotary-driven pipe pile does not fit neatly into any of the pile types prescribed in the NYC Building Code. Challenges were encountered developing installation criteria and a quality control program for code compliance. A “re-torque” program measuring resistance to torque and crowd-force during installation was used to verify production pile capacity and to estimate soil setup, similar to conventional driven pile restrikes.  Design methodology, torque and crowd-force measurements, load test results, and installation observations are presented. The project benefited from coordination and collaboration between the designer, contractor and special inspector during the test program and development of the final installation criteria. The rotary-driven pipe pile provides a novel “no spoils” alternative for installing deep foundations adjacent to sensitive structures. Lessons learned and potential future developments are discussed. 

Oct 7, 2024

By Andrew Lees, Chris Iereidis, Mark Wayne

The design of working platforms typically involves the calculation of a two-layer bearing capacity to ensure that tracked piling plant can operate with an adequate safety margin against rig toppling due to ground failure. A number of guidance documents on the design and management of working platforms have been published in recent years, as summarised in this article. None of these provide definitive guidance regarding design for very soft subgrade soils or on platform edge stability. Among the calculation methods available for working platform punching shear capacity, the T-value method is a practical but accurate method that has been used in working platform design for over four years. A correction to the T value is proposed for very low subgrade shear strengths to take into account the greater sensitivity to subgrade shear strength and the difficulty of constructing and compacting an aggregate over such soft ground. Furthermore, a simple equation was derived by finite element analysis (FEA) parametric study to calculate a safe edge distance for working platform operation taking into account the width and aspect ratio of loaded areas, platform thickness and subgrade soil strength. These findings are being applied in the design of working platforms to include very soft subgrade soils and to help avoid rig toppling near platform edges.

Oct 7, 2024

By Seth Hamblin, Bill Oder, Les Chernauskas

Thermal Integrity Profiling is a non-destructive test method used on cast-in-place concrete deep foundation elements such as drilled shafts.  The method has progress steadily over the last 15 years with improvements to the equipment, data acquisition and analysis of the data. Current analysis of TIP data incorporates temperature vs depth and temperature vs. time. The current acceptance criteria for TIP includes using reductions in effective shaft radius and concrete cover (Piscsalko, et al. 2016).   However, these criteria are heavily based on knowledge of concrete volume and can be significantly affected by the lack of good concrete volume data.  An additional criterion using temperature is proposed for potential use in the industry, which can supplement the existing effective radius/cover criteria and will be less dependent on volume knowledge. However, the relationship between temperature reductions and defect size and position are not well known for various reasons.  The major reasons for this include; not a lot of studies/data available, variations in mix designs, variations in shaft sizes, and variation in defect types. Research was recently performed by the Authors on three drilled shafts with manufactured defects under grants from DFI and ADSC.  The study included running theoretical simulations to predict the sensitivity of temperature reductions to the defect size and location. Data was collected and the temperature with depth was compiled for various defects. The results show a promising relationship between temperature reduction and defect cross sectional area.  When considering local temperatures and average temperature changes, the criteria can consider location and size.   When including data from other recent research studies for similar size shafts and defects, we found the relationship to be consistent with our data.  The findings of this research provided a better understanding of the relationship between temperature reductions and defect size and location and provide the basis of the proposed temperature criteria.  

Oct 7, 2024

By Tony Sangiuliano, Jason Weck, Ryan Regier, Alper Turan

Cast-in-place concrete piles socketed in rock are a commonly used foundation solution in the province of Ontario. Although cast-in-place concrete piles are common, limited pile load testing has been undertaken on these foundations to confirm shaft friction (side shear) and end bearing parameters. Particularly, the large diameter piles bearing on rock makes conventional pile loads tests impractical and costly due to large capacities that need to be mobilized during testing. Performance of piles loads test come with the advantage of confirming the assumed geotechnical design parameters and permitting the use the larger strength reduction factor as per LRFD design. This paper presents the preparation, execution, and result interpretation of a pile load test carried out on two Cast-in-place concrete piles with diameters of 1.5m and 1.8m for Garden City Skyway Project in the City of St Catherines Ontario, Canada. The 1.5m and 1.8m diameter test piles were socketed 4m and 6m into shale bedrock. Osterberg cells were used in both load tests to provide end bearing and shaft friction parameters for the shale bedrock as well as overlying layers of till and soft clay. The results of the load test provided valuable insight into the load settlement performance exhibited by these piles. The results are also compared with the analytical estimates of the pile capacities presented in geotechnical report as well as the results of a number of other analytical socket design approaches.

Oct 7, 2024

By Rajni Saggu

This study presents the cyclic load-displacement response of thermal piles in a pile group consisting of thermal and mechanical piles. To investigate the effect of different (i) layouts of thermal piles and mechanical piles, (ii) pile spacing, and (iii) soil type on the pile displacements and axial stresses, numerical analyses were performed over 50 cycles of thermal loading and unloading of the thermal piles. The analysis outcomes show that the thermal changes in the load-displacement characteristics of the piles become complex during cyclic thermal loading and unloading of the thermal piles. The mechanical piles also exhibit uplift after thermal loading of the thermal piles, and significant differential displacements occur at the pile cap, head and base for all the piles. Higher pile spacing imposes a positive effect in terms of lower thermo-mechanical stresses in the piles compared to the case of closely spaced piles. Axial stresses in each pile are notably non-uniform after the thermal loading cycles applied on the thermal piles. Cyclic alterations in the load-displacement of thermal piles also impose alterations in load-displacement of the mechanical piles. Further, the layout of thermal piles, pile spacing, and soil type control the long-term cyclic thermo-mechanical response of the pile group.

Oct 7, 2024

By Seth Robertson, Alex Ciccone, Lawrence Johnsen, James Davis

The most sustainable foundation is the one that is already in place. That doesn’t mean it is the easiest to RE-use. This was realized when replacing a multi‑story hospital parking garage in Hartford, Connecticut. The previous garage was constructed in the 1980s and was supported on grade beams with 3.0‑ and 4.5‑foot‑diameter drilled shafts that extended through 100+ feet of problematic soft Connecticut Valley varved clay, glacial till, and end‑bearing in or on arkose bedrock. The proposed garage consisted of relatively high loading demands, was susceptible to excessive settlements, and was also located adjacent to an active hospital with sensitivity to vibrations, thereby limiting many foundation design options. An innovative solution was proposed to re-use many of the existing drilled shafts, supplemented with a combination of micropiles and composite piles. Composite piles were comprised of 3.0‑foot‑diameter drilled shafts with a central, 11.75‑inch‑diameter micropile to transfer structural loads to bedrock. Installation information on the existing drilled shafts was heavily limited. Dynamic load tests were therefore performed on 12 existing shafts spread across the garage footprint, confirming geotechnical resistances up to 4,500 kips and significantly improving quality assurance of the existing foundation construction. Additionally, two micropile load tests were performed in tension to 900 kips, confirming design loads could be resisted by the bond strength in rock. The foundation re‑use methodology saved over 3 million dollars in installation costs, weeks of construction schedule, and resulted in a significant carbon reduction compared to conventional, and inherently more substantial, foundation replacement strategies. Critical aspects of the foundation re‑use design strategy and limitations of alternatives will be discussed. Implementation of innovative load testing techniques are addressed, focusing on optimizing quality assurance for utilizing existing deep foundations in modern construction. Lessons learned and recommendations for future practice are presented.

Oct 7, 2024