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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 Clint Judisch, Ty Jahn

Nestled at the apex of Big Sky Resort's Lone Mountain, in Big Sky Montana, (3,400 m), making it the highest scenic overlook in the state. Boasting breathtaking views that span over 20 different mountain ranges, this engineering marvel replaces the original tram after a 28-year run that exceeded the original design life. The new tram consists of a top and bottom terminal, as well as a singular support tower that sits about three quarters of the way up the span. The project team consisted of Condon-Johnson & Associates as the general contractor who self-performed the construction of the foundations for the top terminal and tower, involving intricate processes such as blasting, excavation, drilling, installation of micropiles and tiebacks, and concrete. Doppelmayr manufactured and supplied the tram car plus components. Garaventa designed and erected the metal tram structure, built the ropeway and tram stations.

Apr 1, 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 Johann Kraxenberger, Matthew Gregory, Bauer Maschinen, Deon Lauw, Franz-Wener Gerressen, Robert West

High Speed Two (HS2) is a major high-speed railway project in the U.K. connecting London to the West Midlands. The 21 km (13 mi) of twin-bore tunnels in London include numerous geotechnical structures and extensive foundation works, such as embedded retaining walls and cut-and-cover box structures. There are approximately 1,800 rotary bored contiguous retaining wall and bearing piles in the Euston Station Approaches alone. Piles are constructed mainly in the London clay formation and Lambeth group. Some, however, were advanced to the Thanet sand formation at approximately 49 m (160 ft) from ground level. The diameters of these piles range from 750-1,800 mm (29-71 in) and most are constructed using a polymer support fluid to stabilise the soils during boring. Pile cut off level was located within the cohesive soils of the London clay with each pile reinforced with a full-length cage. Striving to achieve low carbon solutions for typical opera­tions on the site, several innovations were conceived.

Nov 1, 2024

By Brendan Stepek, Michael Senior, Gary Brill

Freight railroads are classified as critical infrastructure and are an important piece of the U.S. economy. Railroad tracks cover the entire nation, allowing freight trains to transport goods and materials between ports and other transportation hubs. We have shaped the landscape to construct America's vast network of railroads; we have flattened mountains, carved into hillsides, filled valleys and spanned gorges. As natural geotechnical hazards occur at railroad sites, it is critical to remediate the hazard in a timely and minimally disruptive manner to main­tain operations. Norfolk Southern Railway has mainline rail passing through the foothills of the Blue Ridge Mountains of Central Virginia that services about 15 to 20 trains per day. Along this rail is a 70 ft (21 m) high cross valley embankment fill that has experienced a long history of instability and numerous attempted repairs. In 2020, after a noticeable increase in rail movement, Norfolk Southern elected to have a compre­hensive geotechnical study of the embankment performed, install instru­mentation and ultimately stabilize the soil slope. The instrumentation and design of the slope stabilization system was performed by Schnabel in 2021 and was constructed by Goettle in 2022.

May 1, 2024

By Barry Sheppard, Abid Adekunte, Alec Hinder

The main competencies of a chartered/professional engineer include demonstrated abilities to implement knowledge, skills and attitudes towards the restriction of the amount of natural resources consumed on projects, limitation of the quantities of wastes produced during construction, whilst ultimately minimising the overall carbon footprint associated with every scheme. These are important obligations to the environment and society that must be dutifully fulfilled by every practising engineer, by continually striving to maintain reasonably good balance between safety and economy on every project. In support of the above professional obligations, this paper details independent literature review of shaft adhesion factors that are appropriate for the economical designs of CFA-bored piles in clay in the UK and Ireland. The geotechnical appraisals had originally been carried out by Deep Foundations Specialists (DFS) as independent 3rd party-checks to resolve disputes between a number of piling contractors and structural warranty companies in respect of the design aspects of the piling works for large scale residential developments in Hampshire and Cambridgeshire, England. The geotechnical appraisals are supported with case histories of 15 No. historical piling projects completed, static load-tested and backanalysed in different geographical regions of the United Kingdom & Ireland. Essentially, the literature review confirms the shaft adhesion factor,  = 0.6 adopted by the piling contractors in designs for the initially disputed schemes to be appropriate, safe and economical, albeit higher than the generic value,  = 0.5 recommended by guide documents including the BS8004 (2015) and the London District Surveyors Association’s Guidance Note No. 1 for the Design of Straight Shafted Bored Piles in London Clay (2018). The conclusions of the literature review ultimately resulted in the acceptance of the piling contractors’ designs by the structural warranty providers. The paper recommends that whenever it is possible, design engineers should place greater reliance on site-specific pile test data or pile test data from other sites with similar ground conditions, pile geometries and pile installation methods, in order to produce the most economical and sufficiently optimised pile design for every site.

Oct 31, 2023

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 Jesse Rauser, Gavin Gautreau, Xin Peng

The field of deep foundation engineering is undergoing significant changes. Long reliant on established methods and expert judgment, the industry is now integrating data-driven techniques that are transforming how infrastructure is designed and built. This shift is not about abandoning proven practices, but about enhancing them with advanced analytics and data tools to improve accuracy, efficiency and adaptability in construction projects. Picture a worksite where decisions are made not just from experience, but also informed by data from previous projects and real-time analysis. This isn't a vision of the distant future but the reality of today's deep foundation projects. Data-driven techniques are being combined with engineering expertise, creating smarter and more reliable solutions that can handle the increasing demands for sustainable, resilient infrastructure. While traditional methods based on empirical data and experienced judg­ment have served the industry well, they are sometimes limited in ad­dressing modern challenges, such as evolving environmental regulations While traditional methods based on empirical data and experienced judg­ment have served the industry well, they are sometimes limited in ad­dressing modern challenges, such as evolving environmental regulations foundational engineering processes. These new techniques allow profes­sionals to analyze larger volumes of data to optimize designs, enhance decision-making and achieve better project outcomes.

Nov 1, 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 Katie Kontos

The changing landscape of the deep foundations industry is being propelled by many things-most prominently, digitalization, automation and increased emphasis for sustainability. But this is only the tip of the iceberg when it comes to innovation. With all this change ahead, DFI turns to several of its forward thinkers to ask what the future looks like. What challenges will arise? How can the industry prepare to head into the new world of artificial intelligence (Al)? And what can be done NOW to support and empower the future generation of geoprofessionals?

Nov 1, 2024

By Alex Sherman, Gretchen Connelly

The Soo Locks, which date back to the 1800s, are the major cargo connection point between Lakes Superior and Huron. The locks allow the movement of approximately 86 million tons of freight annually through the Great Lakes, the St. Lawrence Seaway and the international markets. Considered a feat of engineering, the locks raise and lower boats to allow passage between the two Great Lakes using a series of gates and chambers that are powered solely by gravity, without the use of any pumps. The Soo Locks are currently made up of the Poe, MacArthur, Davis and Sabin locks. The Poe Lock, the most utilized of the four, was rebuilt in the 1960s to accommodate larger ships. Currently, approximately 90% of the commodities transported through the Soo Locks are restricted to the size of the Poe Lock. The MacArthur Lock, the southernmost lock, is also currently operational. Neither the Davis nor the Sabin Lock are currently in operation.

Jan 1, 2024

By Ryan Nagle, Eric Lindquist, Rob Jameson, Kelli Mccurdy, Serena T. Jang, John Gouchon

This paper discusses the challenges associated with the design and construction of a deep basement in downtown San Jose, California for the 200 Park Avenue project. The aim is to present the critical design issues, how the challenges were addressed, details of the selected shoring design, and the performance of the shoring system during construction. The critical design issues that will be discussed related to retaining the deep excavation and constructing the basement include shallow groundwater, artesian pressures, settlement outside of the excavation, shoring earth pressures, and shoring wall movement. Subsequently, the paper will describe why a tied-back cutter soil mix (CSM) cutoff wall was selected as the shoring system and how it addressed the critical design issues. The design of the tied-back cutoff wall will also be discussed. Lastly, the performance of the tied-back cutoff wall during dewatering and excavation and how it compared to the design will be included. The performance was measured through a monitoring program, including survey data points and piezometers.

Oct 31, 2023

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 Lauren Speakman, Mark Reinders, Thomas Fiala

In the heart of downtown Toronto, a full city block at 481 University Avenue and 210 Dundas Street West has become the site of one of the most complex heritage preservation efforts ever attempted in North America. The development of the United Bldg., a 50-storey mixed-use tower, required the complete in-place retention of two culturally designated façades: a 9-storey Beaux-Arts structure built in 1928, and a 10-storey Modern Classical building completed in 1961. The City of Toronto By-law 1393- 2017 designated the façades of both 210 Dundas Street West (Maclean Pub- lishing Company Building, 1928) and 481 University Avenue (Maclean- Hunter Building, 1961) as heritage sites due to their architectural, historical and contextual significance. Regulations imposed by this bylaw prohibited dismantling or relocating any part of the heritage façades. All original finishes brick, stone, concrete and steel - had to remain undisturbed and fully supported throughout construction. At 10 storeys tall, the façade retention system (FRS) designed for this project was a monu- mental engineering and construction marvel that was unprecedented in the industry. The complexity of this project was only amplified by the spatial lim- itations imposed. Dense urban infra- structure - including streetcars, sub- way tunnels and congested utilities not only restricted the available options for the FRS design but also imposed stringent monitoring criteria. The solution selected needed to restrict ground settlement to fewer than 3 mm (0.1 in) and façade movement of 15 mm (0.6 in). This led to the development of a highly integrated hybrid support system, merging elements of the existing structure with the FRS and the support of excavation (SOE) design to allow four levels of underground construction beneath the retained façades and structure. On the United Bldg. project, Canadian specialty contractor Green Infrastructure Partners was responsible for delivering the demolition, shoring scopes and façade retention. This included the full demolition of two brick buildings and the partial demolition of 210 Dundas Street West and 481 University Avenue. The shoring scopes executed the full deep foundation system including secant piles, micropiles, caissons, tiebacks, walers and shotcrete. The façade retention entailed the fabrication, supply and installation of all FRS steel and connections, as well as the jacking of the retained structures onto the new foundations.

Sep 1, 2025