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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

By Eric Brichler

Shaft Construction Using Diaphragm and Cement Bentonite Walls at Shoreline Storage Tunnel Eric Brichler, Senior Estimator, Major Projects eric.brichler@nicholsonconstruction.com Nicholson Construction Company, Denver, Colorado The Shoreline Storage Tunnel (SST) Project in Cleveland, Ohio is part of EPA-mandated Project Clean Lake, Northeast Ohio Regional Sewer District’s program designed to reduce pollution in Lake Erie by 4 billion gallons per year over the next 25 years.  The $3-billion program includes construction of large ‑diameter storage/conveyance tunnels, shafts at key combined sewer overflow (CSO) pick-up points, underground pump stations, improvements to wastewater treatment plant capacity and treatment, and expansion of green infrastructure.  When completed, SST will comprise over 2.5 miles of 23-ft-diameter tunnel installed 87 to 135 ft below ground.  The storage tunnel will manage higher flow volumes and keep stormwater out of the combined sewer system to reduce overflow occurrences.  As part of the project, three deep shafts (SST-1, SST-2, and SST-3) were constructed to provide access to the tunnel, launch and retrieve the tunnel boring machine, and provide ventilation.  Several additional structures will serve as diversion structures, drop manholes, gate structures or gate control structures.  A short connection tunnel will connect the SST to the Dugway Storage Tunnel, which was completed earlier in the Project Clean Lake program. The shaft support of excavation system was designed using diaphragm wall methods.  This innovative solution provided watertight, continuous shafts keyed into rock that significantly reduces risks as compared to traditional secant piles combined with a rib and liner plate system.  Unreinforced concrete diaphragm walls were constructed using mechanical clamshells for shafts SST-2 and SST-3, and clamshell equipment and a hydromill were used for SST-1.  All the SST shafts were lined with reinforced cast-in-place concrete and include baffle drop structures. Outside of the SST-1 and SST-3 shafts, several ground improvement blocks were installed using overlapping cement bentonite panels. These ground improvement zones were created to provide increased strength and water cutoff in the soil at locations where the TBM broke into and out of the shafts. A gate structure attached to both the SST-2 and SST-3 diaphragm wall shafts was supported by a soldier pile reinforced cement bentonite wall.  The design of the gate structure SOE was handled collaboratively with the owner and their engineer, McMillen Jacobs Associates.  The team worked together to resolve challenges surrounding tying in the originally designed bracing scheme to the new SOE method and methods for exposing and supporting a 100-year-old existing brick sewer, as well as excavating through an abandoned brick sewer. This case study will present the design for the shafts and gate structures, the diaphragm wall construction methods, the unique challenges overcome for each shaft, and the benefits of the final solution to the overall project.

Oct 7, 2024

By Eric Lindquist, Scott Chambers, Rob Jameson

The Salt Lake Temple is undergoing its most significant renovation since its dedication in 1893. The renovation includes a seismic retrofit of the historic stone structure’s foundations using base isolation. This paper focuses on the temporary underpinning of the 16 to 35 feet thick unreinforced masonry perimeter walls of this massive structure. Conventional needle beam or direct structural underpinning approaches to support the Temple in place during base isolator installation were precluded by its immense weight and extremely thick walls. The design-build team instead developed a unique temporary support of excavation (SOE) program to allow the 19-foot-deep excavations for the new base isolator foundations. The SOE scheme allowed the massive structure to be supported on confined soil “columns” located directly below the masonry wall footings while excavation to construct the new foundations was advanced concurrently along the Temple’s outer perimeter and inside the building. Shoring system stiffness was critical to mitigate settlement risk for this historic building and construction methods were selected to minimize detrimental installation effects.    The structural engineer’s permanent design required sequentially jacked steel pipes immediately below the walls, which were filled with post-tensioned reinforced concrete to create transfer beams. After completion of the foundation excavation, two new grade beams separated vertically by base isolators were constructed along both the interior and exterior sides of the perimeter walls. The concrete filled steel pipe transfer beams were structurally connected into the upper grade beams above the isolators. After load transfer is completed, the soil directly below the walls will be excavated to allow free movement of the structure and grade beams above the base isolators in the event of a future earthquake. The historic temple SOE and underpinning system employed multiple construction methods, including micropiles, secant piles, tieback anchors, tensioned tie-rods, temporary attachments to the jacked permanent steel pipes, hand-dug underpinning piers, permeation grouting and steel structural headers supporting interior walls. Design and construction of the historic retrofit SOE system is detailed in this paper.

Oct 7, 2024

By Samar Saad, Mazen Adib, Farid Motamed, Medji Sama

Abstract Deep foundations were necessary to support bridges, retaining walls, and other structures at the I405 Improvement Project in Orange County, California. The ground properties and stratigraphy were primarily investigated using cone penetration tests (CPTs), with confirmatory boreholes and laboratory tests. A CPT-based design calculation method, the LCPC-CPT by Bustamante and Gianeselli, was followed to predict the axial geotechnical resistance. To justify a resistance factor of 0.7, extensive Pile Driving Analyzer (PDA) measurements were performed to allow calculation of the driving resistance using Case Pile Wave Analysis Program (CAPWAP). The piles included open ended 24-inch diameter steel pipe piles, 14, 16, and 18 inch H Piles, and 14-inch square Precast Prestressed Concrete Piles. The paper presents the subsurface conditions and ground properties from the CPTs and the predicted versus CAPWAP axial capacities for the various types of piles. The paper will also present challenges encountered and opportunities from lessons learned. It was observed that, in general, the CAPWAP axial capacities were in acceptable agreement with the LCPC-CPT predictions, although capacity incorporating full setup was not measured on all piles. Also, the correlations between LPCP-CPT predictions versus CAPWAP axial capacities depended on the type of pile.

Oct 7, 2024

By Soon-Hoe Chew

Deep Cement Mixing (DCM) is a well-established ground improvement technique renowned for its efficacy. It has been widely adopted due to its robustness and effectiveness in stabilizing weak or soft soils, thereby enhancing its applicability across various engineering applications. Traditionally, the quality assessment of Deep Cement Mixing (DCM) columns is reliant on post-curing coring test. Thus, it will not be able to give any indication on strength and permeability until later stage of curing, when coring tests are conducted. This delayed QA/QC hinders quick remediation when unsatisfactory strength or permeability values are obtained. This study advocates a proactive quality assessment methodology of the DCM columns, right from the initiation of the DCM process. On one hand, this approach provides an early warning which prompts for early intervention. On the other, this approach also allows for an early confirmation of the acceptance of the completed works. In addition, this approach can also reduce the number of coring tests needed. The proposed assessment methodology leverages real-time data of various operational parameters during the construction of each and every individual DCM column. By scrutinizing critical operational parameters, such as drilling rate, injection method and pattern (i.e. penetration or withdrawal injection), slurry flow rate, mixing duration, and termination criteria, extracted from real-time operational process, this study endeavours to establish correlations indicative of columns’ quality. Hence, the goal is to develop predictive models capable of pre-emptively gauging the quality of strength and permeability improvements, without the need of prolonged curing and coring test (or reduce the number). The meticulous analysis of these parameters serves as a benchmark to gauge the quality of the DCM columns constructed against predetermined design specifications.

Oct 7, 2024

By Sathya Subramanian, Jun Yuan Ryan Lee, Angelina Yi Tian Theng, Kai En Low, Soon-Hoe Chew, Yeow Chong Tan, Kai Yang Toh, Pei Ling Goh

Conventional Quality Assurance and Quality Control (QA/QC) methods for Cement Bentonite (CB) walls rely on destructive coring, which is carried out at specific curing times like 28 days or 91 days. The key parameters determined are strength and permeability. Hence, the conventional methods will not be able to give any indication on strength and permeability until later stage of curing. This delayed QA/QC hinders quick remediation when unsatisfactory strength or permeability values are obtained. To address this limitation, this study utilizes non-destructive resistivity monitoring system to provide indications of the parameters at early days of curing. By continuously assessing resistivity of CB at various depths, this method aims to provide predictive indicators of long-term strength and permeability, enabling proactive interventions before the conventional 91-day coring, if needed. A comprehensive case study is presented, which includes scaled model in a laboratory, as well as a actual measurement in the field. The large-scale laboratory setup models the actual thickness of the CB wall in the field (0.8 m). Specially designed and fabricated resistivity devices are installed in the laboratory setup, and two sections in the field CB wall. Findings show that in terms of resistivity development with curing time, the field resistivity continuous monitoring data displays a similar trend to those resistivity measurements conducted in the laboratory-scaled model. Cored samples were also taken in the laboratory and field at specific curing time of 91 day. The resistivity correlated well with the cored samples’ strength and permeability values. 

Oct 7, 2024

By David Eley

Coastal communities continue to be at risk with sea levels rising. Along these coastal shorelines, vegetated marshes and ridges provide habitat for wildlife and resiliency against storm surge and erosion in low-lying areas. Often, spoils from maintenance dredging of harbors and rivers are placed in confined disposal sites (impoundments), providing little benefit to the environment. Reusing these spoils to restore low-lying marsh areas that are disappearing because of sea level rise, storm damage, sediment deficits, and other natural and manmade processes is growing trend. Design and construction using dredged sediments in a coastal environment can be challenging. It is critical to design and place fill in sensitive habitats in a controlled, thoughtful manner that enhances the environment. Low dikes are often used to contain fill, which is typically excavated and placed using a hydraulic dredge. These dikes are long linear features, often in a marsh environment, and can be difficult to construct. During construction, the project team (contractors and designers) must understand that these are controlled fill projects, with elevation targets and containment requirements. Distribution of sediments to meet project goals typically requires regular movement of the dredge outfall and monitoring during construction to prevent over-topping of containment dikes, and ensure sufficient fill has been placed to meet project objectives. Dredged sediments can be a renewable resource to restore coastal areas when used in projects that are designed and constructed correctly. In this paper, we will discuss design considerations, construction challenges and construction monitoring, including innovative instrumentation, that can help enhance the sustainability and resiliency of low-lying coastal communities.

Oct 7, 2024

By Jason Huang, Thamer Yacoub, Steve Chai

RS-GPT (Rock and Soil Generative Pre-Trained Transformers): Large Language Model solution for geotechnical engineering applications.  Seok Hyeon Chai[1], Jason Huang [2], Sina Javankhoshdel [3], and Thamer Yacoub[4] 1,2,3,4 Rocscience, Toronto, Canada steve.chai@rocscience.com The use of Natural Language Processing (NLP) in the field of engineering seems complex with many applications which require calculations and engineering judgements. Large Language Models (LLM) have been successfully presented to be one of the most effective solutions in many specific fields such as arts and literature, to finance, to even software development. However, the use of LLM in the field of Civil Engineering and specifically in Geotechnical Engineering has not been discussed often compared to the other fields of expertise that utilize the functionalities of Application Programming Interfaces (API) of OpenAI. This paper aims to cover the details of the framework and breakdown of how LLMs can be used to train a domain-specific dataset, specifically related to settlement analysis, ground improvement, to slope stability analysis and provide results that are generated from a fine-tuned model with the dataset of research papers and technical documents provided by geotechnical engineers. The paper presents three folds: introduction for LLM models with pre-trained models, and choice of the models used. Then, the paper discusses the fine-tuning process of the LLM model with a domain-specific database. The paper provides benchmarks and metrics for performance of the model using the technique called Recall-Oriented Understudy for Gisting Evaluation (ROGUE) for validation of the outputs by comparing the result with prompt-completion pairs.  With sufficient data for the prompt-completion pairs from the experts in the field and also from the scientific literature and localized technical documents, the LLM model trained with data related to the geotechnical engineering domain provides reasonable responses that otherwise would not have been achieved with the original ChatGPT LLM model. This paper introduces innovative way to manage current database of geotechnical documents and literature that can be optimized to be used with LLMs.  The paper provides discussion of the comparative results and the future potential capabilities of its fine-tuned model.  Key words: Large Language Models (LLM), ChatGPT, Civil Engineering, settlement analysis, slope stability analysis, fine tuned models, APIs with OpenAI.

Oct 7, 2024

By Brent Robinson, Matthew Baudo

Matthew Baudo and Brent Robinson PIle Dynamics, Inc. Circular and rectangular deep foundation elements are commonly tested by thermal integrity methods. A multiphysics model was adapted using COMSOL to evaluate the effect on thermal measurements of the size and extent of soil and weak concrete inclusions. The temperature change as measured by nearby wires for small intrusions into the reinforcement cage at and between thermal measurement locations, exposed reinforcement and full cross section contamination are modeled. The modeled temperature versus depth results are analyzed directly as well as using the interpretation recommendations combining placed concrete volume and measured temperature by Piscsalko et al. (2016). A comparison to field measurements is also included. 

Oct 7, 2024

By Mark Brooks, Brian Freeland, Eric Eisinger

Colorado Parks and Wildlife (CPW) operates more dam and reservoir facilities in the State of Colorado than any other single entity and is in the process of completing rehabilitation upgrades to improve operational safety and modernization as required by the Office of the State Engineer. Many of these dam facilities have been operating 50 to 100 years in remote locations presenting challenges related to routine operations, maintenance, and completion of dam safety related repairs. Historically CPW has utilized design-bid-build procurement of construction services to complete these projects which presented additional challenges related to local contracting capabilities and undesirable contract disputes and claims. CPW recently pivoted to a CM/GC procurement process to contract for construction services for dam rehabilitation improvements where the remoteness, seasonal high-altitude limitations, complex topography, availability of local construction resources, stakeholder involvement, and other factors having an increased potential to negatively impact construction success and completion timeliness. The CM/GC delivery method has proven to be beneficial to the success of these projects by early construction contractor involvement as part of a collaborative Integrated Project Team to promote enhanced constructability solutions, innovations to improve quality and cost efficiency, risk identification and mitigation, and schedule and budget adherence. CPW has completed three projects using the CM/GC project delivery approach and select case histories (particularly the most recently completed Alberta Park Dam Rehabilitation in partnership with SEMA Construction) will be presented to demonstrate how this project delivery method overcame project site challenges and constraints to complete complex safety critical rehabilitation projects. The project scope on these projects included improving the capacity and function of service spillways, outletworks, and embankment stability and seepage features, and other dam safety infrastructure.

Oct 7, 2024

By Jason Hertz, Tony Amis

Low to zero carbon ground sourced heating and cooling solutions face limitations in densely populated urban areas, especially when building footprints span entire sites. Despite these challenges, alternative approaches exist. This paper explores one such alternative—embedding geothermal loops into a building's foundations, connected to a ground-sourced heat pump. This innovative method efficiently caters for a significant portion of the base heating and cooling load, with an air-sourced heat pump incorporated for any remaining heating and cooling requirements. The focus of this paper is on the successful deployment of energy foundations in a 250,000 ft² commercial building in lower Manhattan, New York. The building, now fully operational as an all-electric structure, serves as a case study. Insights gained from this project provide valuable lessons for future endeavors. The paper not only discusses the technical aspects of the installation but also offers operational performance data gathered over the past six months. By presenting real-world applications and lessons learned, this paper aims to contribute to the knowledge base for similar projects in urban environments. The insights shared here can guide future initiatives seeking sustainable and efficient heating and cooling solutions, particularly in densely populated areas.

Oct 7, 2024

By Fatemeh Pariafsai, Ali Doostvandi

To assess the stability of a soil slope considering uncertainty in soil characteristics (C, Φ), it is necessary to conduct repeated calculations to determine both the Factor of Safety (FS) and the Probability of Failure (PF). The absence of analytical solutions leads researchers to use surrogate approaches of probabilistic modeling. This study aims to assess the PF and FS of a saturated soil slope using one of the Machine Learning (ML) method subsets, the regression Least Squares Support Vector Machine (LS-SVM). The results are compared to those obtained from the Limit Equilibrium Method (LEM) to compare the accuracy of LS-SVM. According to the FS-PF plot, it is concluded that LS-SVM is a reliable tool for determining the stability of a multi-layered saturated soil slope, which significantly improves computational efficiency. Furthermore, since predicting FS and PF from field data requires fewer data points, it will result in significant time and cost savings. However, to avoid false predictions, limitations must be removed, for instance, each layer should be included in the analysis within its probabilistic distribution, so using this method is more efficacious in clay soils where there are values for cohesion, unlike sands (c=0). This helps training data to be prepared well and to prevent misprediction in local failures. In addition, training data are debated in terms of the percentage employed. Furthermore, showing the importance of dataset scattering is concluded that adopting data with uniform distributions plays a crucial role in preparing training data sets and consequently, in having a better prediction of the possible slope failures.

Oct 7, 2024

By Jarod McBride, Mike Johnston

Over the last decade the construction industry, particularly ground enhancement services such as Jet Grouting, have seen a dramatic rise in the cost of waste transportation and disposal services; increasingly representing a significant percentage of total job cost. As these costs increase and our industry continues making strides to become better stewards of the environment, one of the best ways we can contribute is by placing a priority on sustainability. Stage 3 Separation’s unique solutions contributed to sustainability while creating new economic value. This was achieved by reducing waste, reusing materials, and accelerating production when compared to the traditional spoils pit management practice. Stage 3 Separation believes in bringing sustainable solutions to industry and was successful in teaming with HRBT South Island to meet the following project metrics: (1) reduce the overall disposal costs and associated liability, (2) recycle/reuse base materials where fit, (3) meet specified water quality for discharge, (4) do all of this in way that contributes to accelerating the production schedule in a critical job path. The HRBT South Island project overview consisted of over 650 columns, producing north of 150,000 yds3 of slurry.  Our goal was to take the jet grout slurry waste stream and separate the liquids and solids; creating a water phase that met all environmental standards to be treated and disposed of directly into the environment and creating a dry stackable solid that could be sent directly to a landfill. Prior to Stage 3 Separation’s deployment the Jet Grout contactor was being hampered by poor spoils management, long spoil cure times, and at the mercy of costly vac-trucks or less than partial solid loads.  Within weeks of new process and the removal of these impediments production doubled, waste was cut in half, and numerous other efficiencies were gained. Keywords: Jet Grouting, Spoils Management, Sustainability, Waste Reduction, Production Performance

Oct 7, 2024

By Omar Conte, Roger Archabal

In recent years, numerous developers have invested in former deep quarry lake sites, particularly to develop massive new logistics and residential projects in South Florida. Due to the flat geology encountered, necessary construction materials (structural fill, sand, concrete aggregate, etc.) have been quarried from the upper limestone and sand layers encountered in the region. Considering the shallow groundwater, these quarry excavations have created numerous large bodies of water (“lakes”) over the decades. Restoration of these massive lake areas which are now dispersed throughout prime real estate is ideal for development. There is a strong incentive to restore these large lake areas due to the lack of available large tracts of land near Miami or Ft. Lauderdale. The redevelopment of these large and deep-water bodies has important geotechnical challenges that need to be addressed before finalizing the infrastructure and foundation design/construction. This paper will go over the investigation techniques utilized, the geotechnical evaluation, analysis, and soil improvement recommendations to allow for safe bearing support and to overcome the uncertainties associated with settlement potential.  Several geotechnical aspects need to be considered to effectively perform mass lake backfill. These include: 1) the pre-backfill site investigation, 2) understanding the lake bottom conditions and soil layering below the bottom, 3) backfill material selection and backfill methodology, 4) quality control/quality assurance during lake backfilling, 5) post-fill ground improvement (preloading, dynamic compaction, vibro-compaction) and foundation construction are some of the key aspects for these types of projects. The geotechnical findings and lessons learned from several massive lake backfill projects will be discussed in the paper. This includes sites with measured lake bottom sediment layers of up to 15 to 20 feet thick, resulting in consolidation settlement of nearly 3 feet during ground improvement/preload settlement monitoring. The paper will present some innovative exploration and laboratory techniques to obtain important geotechnical data to cost-effectively develop these massive areas.

Oct 7, 2024

By Kevin Baumgartner, Howard Perko

Common technologies for temporary and permanent support of excavations (SOE) include soldier piles and lagging, secant/tangent piles, slurry walls, and tie-back walls. This paper discusses an innovative technology consisting of helical soil nails with high tensile wire mesh facing.  This novel technology has been used on a number of SOE projects in recent years saving both time and money as well as providing a number of other benefits.  Case histories including Denver Bronco’s training facility, Pulliam Theater, a bridge abutment, and a train platform are presented.  This SOE technology is highly sustainable as both the mesh and soil nails can be removed and re-used, if desired.  The system avoids the need for concrete or grout, so it eliminates curing times and problems associated with field quality assurance and inclement weather placement.  Helical soil nails consist of central pipe or solid steel shafts with small diameter helices spaced over the entire length.  The length of the nails is typically on the order of the height of the excavation.  The nails are spaced relatively close together in rows to reinforce the earth.  The face of the excavation is held back using high tensile strength steel wire mesh over geo-fabric.  The mesh is stretched between the helical soil nails and fastened down using spike plates on the helical nail caps.  Both hand calculation and computer methods for design of this concrete-less alternative to the traditional SOE will be covered. The SNAP 2.0 computer program is used to determine factors of safety with regards to overturning, sliding, and bearing, among other checks.  Through practical applications and real-world calculations, this paper educates the reader on the proper design and application of the helical soil nail and high tensile mesh SOE system.  AutoCAD details and example plans are provided.

Oct 7, 2024

By Kenichi Soga, Andrew Yeskoo

Distributed Fiber Optic Sensing (DFOS) allows the user to measure continuous strain and temperature profiles along an installed fiber optic cable. The technology has successfully been deployed for a range of geotechnical and geostructural applications, including monitoring of deep foundations This paper presents the results of a fiber optic sensing installation for the measurement of strain in a cast-in-drilled-hole (CIDH) foundation element during a top-down load test. DFOS is particularly suited to strain measurements during pile load testing as it can generate continuous strain profiles along the length of the pile, removing the need for interpolation between point-based strain gauges. The hypothesis is that continuous strain profiles allow insight and understanding of the true, non-idealized pile behavior during loading. A field trial was performed north of Sacramento, California, where a series of load tests were performed on sacrificial piles instrumented with fiber optic strain and temperature sensing cables. The fiber optic instrumentation design consisted of 4 vertical strain cables, as opposed to the more common 1 or 2 cables, allowing for the identification and analysis of non-uniform strain distribution across the pile at single depths. This non-uniform distribution has often been ignored through averaging or discarded as erroneous data, missing potentially real behavior within the pile. The fiber optic data was used to evaluate an independently identified outlier strain gauge reading and confirm the reading as valid, as well as identify bending behavior within the pile which contributed to non-uniform strain measurements across the pile. This research demonstrates the value of the use of DFOS for pile strain measurements and the benefit that it offers over point-based measurements and the interpolation that it necessitates between discrete readings.

Oct 7, 2024

By Guoming Lin, Yan Jiang

The Hutchinson Island ferry landing, a vital transportation hub located between the Savannah Convention Center and Westin Hotel, faced a critical infrastructure challenge on June 18, 2022, when the sheet pile bulkhead along the Savannah River experienced movement, resulting in a substantial crack in the brick-paved plaza.  Immediate monitoring efforts commenced within two hours of the bulkhead disturbance, revealing progressive movements over the subsequent two weeks, leading to approximately ten feet of deflection and six feet of settlement behind the bulkhead.  Subsequent repair work involved the extraction of 65-ft-long steel sheet piles. This investigation embarked on a meticulous review of the original design and construction procedures, followed by a comprehensive subsurface exploration program.  The steel sheet piles were originally supported by drilled helical anchors, and the failure mode and pattern were closely scrutinized.  Analysis of the pulled-out sheet piles revealed consistent shape and yield points.  Computer modeling was conducted to replicate the actual deflection profile and yield point as verification of the soil parameters and design models. This paper presents the investigative findings, including an analysis of subsurface conditions and the most probable causes for the bulkhead failure.  The results of the investigation have been instrumental in formulating design recommendations for the repair of the bulkhead system.  By shedding light on the root causes of the failure, this research contributes valuable insights to the soil-structure interaction in the steel sheet pile design. Top of Form

Oct 7, 2024

By Shawna Munn, Katie Castelo, Dave Wiley

The City of Toronto is in the middle of “The Big Move”, a 25 year, $50B plan to address congestion in the Greater Toronto and Hamilton Area (GTHA). This includes 7 new subway or light rail transit lines in various stages of planning or construction, and corresponding major urban densification along major rail corridors in the city. This paper will show how transit infrastructure projects, and projects adjacent to major rail corridors in the GTA, are less economic due to prescriptive based design requirements compared to similar complexity local private projects. Using case histories from several recent projects, the paper will compare adjacent specification driven design and performance-based design examples to show the potential when leveraging performance-based design methodologies safely and effectively rather than a “paint by numbers” approach to design. The paper will describe the risk specification driven design parameters can have on design economy, constructability, and schedule, and outline proposed tendering methodologies for incorporating performance-based designs into contracts to limit risks to both Owners and Contractors.

Oct 7, 2024

By Finlay Leibrick, Muhammad Zaheer, Sourav Agarwal

Limited published information is available on the design guidelines for rock-socket friction of piles in Abu Dhabi, United Arab Emirates. The prevailing industry practice relies on empirical correlations between shaft capacity and the unconfined compressive strength proposed by various authors for the weak rocks. Pile load test results consistently indicate that current design methods underestimate shaft capacities. Despite this, optimization in rock socket lengths is rarely practised in local design and construction. This paper aims to share design experience with the local industry, proposing a suitable empirical correlation for preliminary rock-socket design. The goal is to assist colleagues in avoiding the uneconomical practices currently prevalent in pile foundation engineering in the Emirate of Abu Dhabi. The study analyses the results of eight bi-directional static load tests conducted on instrumented preliminary test piles with diameters of 750mm and 900mm. The test locations represent the typical geological formations found in Abu Dhabi. Maximum test loads ranged from 200% to about 600% of the design compressional loads, attempting to maximize shaft friction mobilization. The study compares the maximum mobilized shaft frictions within various rock units with corresponding characteristic unconfined compressive strength values. The findings suggest that the correlation proposed by Rosenberg and Journeaux (1976) may be suitable for the preliminary design of rock-socket friction of piles in Abu Dhabi, pending verification through preliminary load tests. This approach holds the potential to contribute to value engineering in foundation design and reduce construction costs.

Oct 7, 2024

By James Pegues, Ron Johnson

A solar facility in the western United States was sited within the footprint of a dry lakebed, or playa, with construction completed in 2016. Conventional geotechnical studies were performed prior to design and no unusual conditions or features were noted. The facility has unexpectedly experienced several episodes of ground fissure development after moderate to heavy rainfall events, the first somewhat isolated event occurring shortly after the facility was placed into service. Subsequent fissures developed in 2017 and 2022, with severity of the fissures and their impacts increasing each time, with the final episode resulting in fissure depths on the order of 30 feet. Initial fissure events primarily impacted site access. The 2022 event impacted site access, infrastructure, and solar array pile foundations. Various remedial measures were implemented to address the fissures, including CLSM backfill (2016) and the injection of epoxy-based urethane foam (2017). Prior to developing repairs for the 2022 event, additional studies were performed to evaluate the fissure formation including geophysical exploration, review of historical topography and aerial photographs, hydrologic modeling, and research. Mitigation of the 2022 feature included backfilling with granular backfill and sand-cement slurry and constructing surface water conveyance features to direct surface runoff away from the fissure.

Oct 7, 2024