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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 Glynn Price

Myrtle Creek has been impacted by the subsidence associated with longwall mining at Tahmoor Coking Coal Mine in Picton, NSW.  Specific impacts are fracturing of the rock bed resulting in a reduction in surface flow and pool holding capacity behind the rock bars that are a characteristic of waterways in the southern coalfields. A specific pool, Pool 23, within the impacted Myrtle Creek, was selected for remediation using permeation grouting. First, an investigation was undertaken at Pool 23 to characterise the fracture network and advise on remediation grouting design. The investigation identified the fracture and hydraulic conductivity profiles as well as local hydraulic gradients. Second, a permeation grouting program was implemented which included drilling and permeation grouting completed by Pointe Engineering as per a grout plan and design, using a single part polyurethane grout.  The layout took the form of a grout curtain, perpendicular to the creek and in longitudinal alignment with the rock bar. Permeation grouting as a strategy for remediation of the subsidence impacted water course was demonstrated to have a positive correlation with creek surface flow and pool holding capacity to date.

Oct 7, 2024

By Md Kausar Anik, Ramin Motamed

The phenomenon of liquefaction-induced ground settlements has been frequently observed in several significant earthquakes, such as the 2010–2011 Canterbury Earthquake Sequence (CES) in New Zealand, the 2011 Tohoku earthquake in Japan, and the more recent 2023 Kahramanmaras Earthquake in Turkey. Various ground improvement methods have been used in engineering practice to lessen the effects of soil liquefaction at shallow depths. Those ground improvement methods signify the outflow of ozone-depleting substances and the release of greenhouse gases, resulting in global warming and consequential environmental changes. Amongst all greenhouse gases, carbon dioxide (CO2) stands as the predominant compound. In our study, we adopted the installation of sheet piles as a measure to mitigate the liquefaction-induced foundation movements. However, the carbon footprint and cost associated with the installation of full-length sheet piles can be reduced by adopting partial floating sheet piles (PFS). Nevertheless, the behavior and characteristics of PFS have not been thoroughly investigated in the existing literature, indicating a research gap in this area. To accomplish these objectives, a 1/5 scaled model, representative of a large-scale shake table test conducted by the University of Nevada, Reno (UNR), is utilized. The scaled model comprises three distinct soil layers with different relative densities: a 50% relative density top crust layer, a 30% relative density middle liquefiable layer, and an 85% relative density bottom dense layer. A shallow foundation is placed atop the crust layer, followed by the insertion of sheet piles (both full-length and PFS) at 0.625 times the foundation width (B) from the center, utilizing the press-in technique. Finally, the scaled models are subjected to harmonic input motions with amplitude and dominant frequency properly scaled based on the large-scale shake table test. The effectiveness of PFS is assessed by comparing reductions in carbon footprint, foundation movements (settlement and tilt), and generated excess pore water pressures with those achieved by full-length sheet piles. In addition, this research also contributes to raising awareness regarding the environmental impact of carbon emissions when selecting mitigation measures.

Oct 7, 2024

By Michael Arnold, Matteo Bertoni

This paper presents a project which received a DFI Special Recognition Award as a runner-up in the 2023 DFI Outstanding Project Award competition. The East St. Louis levee system is located in St. Clair and Madison Counties, IL, along the left descending bank of the Mississippi River and provides flood protection to approximately 250,000 residents and over $4.5 billion in economic value. The system is aged and requires rehabilitation. The United States Army Corps of Engineers (USACE) devised and designed a cutoff wall to be installed in the Metro East Sanitary District, one of the levees that form the system. The design provided for the installation of an approximately 4,440-foot-long wall, with a minimum 24-inch thickness and a maximum design depth of over 142 feet, through alluvial and outwash soils, and embedded in bedrock. The prescribed “panel method” consisted of overlapping primary and secondary panels, each no longer than 30 feet. The maximum allowed vertical deviation of each panel was 0.5 percent of its full depth. Two sections of single-phase cutoff wall and two sections of seepage barrier using jet grouting were subsequently added to the project, to provide partial closure at two locations where the installation of panels from ground surface to bedrock was not feasible due to the presence of utilities vital for the area. The jet grout columns that comprised the seepage barrier were to be installed at angles varying from 0 to 30 degrees and to depths up to 146 feet. The project included the installation of a minimum 75-foot-long test section and a thorough QC/QA program that provided for the collection and testing of wet grab samples, and the coring of the installed cutoff wall. The paper introduces the project, the geotechnical site conditions and the requirements specified by USACE.  It describes the pursued installation approaches along with the equipment used and focuses on the specific adaption of the methods to site conditions and project requirements.  Selected quality control and verification results obtained from an extensive testing program are presented. The paper also discusses challenges encountered and related lessons learned.

Oct 7, 2024

By George Onorato, Giovanni Bonita

Deep soil mixing (DSM) has become a widely used ground improvement technique globally, producing soil-cementitious materials for various complex civil and environmental applications. In the field, the soil-cement materials form under confining stress conditions, which are often overlooked, as most wet grab specimens are cured and tested under ambient atmospheric conditions. This oversight has led to an underestimation of the engineering and mechanical properties of the soil-cement mixed material. With support from the DFI Technical Committee Project Fund, the authors initiated a multi-phased comprehensive research study in collaboration with industry experts to gain a fundamental understanding of these effects. This study investigates the curing conditions to which in-situ materials are exposed and how these conditions influence the strength of deep mixed materials. The findings reveal that the curing conditions for in-situ materials, including applied stresses and temperatures, significantly differ from those under which typical quality control specimens are cured. Neglecting these conditions can lead to a substantial underestimation of in-situ material strength. The data compiled for this study encompass strength and temperature data obtained from specially designed laboratory bench tests, field-conducted modified oedometer tests, in-situ instrumentation tests within deep mixed columns, and a review of independent coring data from deep mixed projects across North America. Analysis of these collective studies reveals a correlation between curing stress and unconfined compressive strength (UCS). The rate of strength gains follows a linear pattern and is influenced by the soil type being treated. Fine-grain soils, in particular, exhibit a higher rate of strength gain when subjected to in-situ curing stress (with depth) compared to granular soils. The paper delves into fundamental processes such as drainage, consolidation, and interparticle behaviors of deep mixed materials from their fresh state until the treated column has cured. It also presents empirical and analytical methods to correct in-situ strength measurements to account for the effects of curing stresses.

Oct 7, 2024

By Andreas Stimpfle-Ziegeler, Harald Heinzelmann, Karsten Beckhaus, Rabea Barhum, Askin Onur

In October 2023 Bauer has completed the execution of deep foundations for the Saint-Brieuc offshore wind farm 16 km off coast north of France. Once operational, the 496MW wind farm will generate enough clean energy for 835,000 inhabitants. Ailes Marines, owned by Iberdrola, contracted Van Oord who deployed Bauer. In total, 190 shafts have been drilled and the same number of pin piles were grouted to support 62 wind turbines, based on triple jackets, and an offshore substation, based on a four-pile jacket. Bauer did the works from Van Oord’s offshore installation vessel called “Aeolus”. The Atlantic environmental conditions in combination with the extremely hard and rocky seabed and high requirements to geometrical tolerances and other key quality indicators challenged the contractor’s expertise and equipment in several ways. The paper shall illustrate the planning, execution and particular solutions to meet the client’s demands to their full satisfaction. First of all, an innovative drilling method was used to install the foundations for which project-specific “dive drills” were engineered and constructed by Bauer. Secondly, the underwater survey tasks needed smart solutions and skilled personnel to prove the accurate final position of the pin piles. The survey must ensure the precise position of the newly designed drilling template, which functioned as a positioning and casing drilling tool, but also the subsequent placement of the pin piles.   Last but not least, the pin piles inserted into the shafts needed a fixed and force-locked connection with the ground. Great efforts were done to get to the necessary fresh and hardened properties of the cementitious grout itself, and to control the complete filling and necessary integrity of the structural sleeve grouting. All above three aspects, the dive-drill method, the underwater survey and the sleeve grouting will be explained in detail and challenges experienced offshore will be showcased. Eventually, a full set of individual expert features for drilling, monitoring and grouting techniques have been developed towards an optimized installation system of which parts have been already introduced into other fields of geotechnical works. Accepting challenges based on passion for progress for this outstanding project has brought innovative techniques and features into the deep foundations industry with great potential for adaptions in other fields of geotechnical works.

Oct 7, 2024

By Joshua Zimmermann

For years, a subdivision in Glenrock, Wyoming, suffered from various odd damages, including the sudden appearance of artificial springs, flooded basements/crawlspaces, and shifting foundations. The source of this damage was the underlying Glenrock No. 1 and No. 2 Mines, where years of collected groundwater had resulted in high-pressure artesian conditions within the mined interval. The high groundwater pressures within the mine eventually hydraulically fractured the overlying rock, resulting in the communication of the shallow groundwater table with the deep aquifer within the mine interval, damaging the homes in the overlying community. Additional damages, such as subsidence, also impacted various homes in the area. To address these conditions, there was a question as to whether or not void fill grouting would be feasible for mitigation in an area known to exhibit high artesian head pressures. A pilot program was initiated to determine the feasibility of this method and create the methodology/design approach to alleviate any potential risks from the mitigation program to the surrounding densely populated overlying sub-division. These potential risks associated with the injection and pressurizing high mobility grout included displacement of groundwater into building foundations, inducing the structural collapse of the mine, infrastructure sub-grade failure through over-saturation, environmental considerations, and ground surface movement. After extensive analysis of this pilot study, a specially designed mitigation program was established for mitigating the mine subjacent to a sub-development and took place during the Summer of 2021 using an extensive groundwater monitoring network, specially designed discharge wells, and remote sensing technologies to mitigate the area with no damage reported to the overlying community.

Oct 7, 2024

By April Fontaine

Climate change is occurring, and owners/agencies are seeing the impact of warming temperatures and extreme weather on landslides and other geohazards across the globe. Asset management is becoming more important and more challenging with the rapidly changing environment.  State and Federal agencies need to collaborate and partner on new ways to address these challenges; design of one-size-fits-all engineering solutions won’t work effectively anymore.  Alaska is an obvious nexus of these issues as the state is experiencing observable and measurable impacts from climate change in real time.  Landslides and climate (as well as resilience) are significant administration priorities, and there is benefit in understanding how other agencies are approaching today’s challenges.  These topics were explored at a peer exchange meeting in Alaska in 2023.  Key takeaway from that exchange include: the need to understand the inventory of hazards; the context of each agency, which provides key differences in strategy, policies, and priorities; the constraints that will drive risk reduction versus risk mitigation; the need to evaluate the entire system and not look at each individual hazard; and the criticality of relationships across organizational boundaries – no one agency can solve these challenges on their own.  Strategies used by various agencies in Alaska can inform practices in other regional settings with their own distinct climate and extreme event challenges and project characteristics.

Oct 7, 2024

By Muhammad Naeem, Allison Digregorio, Sam Yao, Joshua Core

Located at the Eastern shoreline of the San Francisco Peninsula, the Potrero Power Station Project is transforming a 29-acre industrial site into a mixed-use redevelopment with 7 acres of new waterfront public spaces. The primary goals of the infrastructure renovations are to protect the new waterfront developments against sea level rise (SLR) and to mitigate the risk of seismic instability of the shoreline. As a result, the site was generally raised by approximately 8 ft. Various design solutions were developed and implemented to address differing field conditions throughout the site. Deep soil mixing (DSM) buttresses were used to combat seismically induced slope instability throughout the entire shoreline. New pile-supported wharves were designed using an innovative engineering solution to resist kinematic seismic loading in the offshore slope. Several types of retaining walls and a grouted tieback system were selected along the shoreline to facilitate numerous waterfront recreational experiences for the public. Collectively, these structures and ground improvements have minimized adverse impacts of SLR and ensured seismic stability of the shoreline. This paper presents a successful project that demonstrates the benefits of tailoring design solutions to unique field conditions to enhance the resilience of the San Francisco waterfront development.

Oct 7, 2024

By Jesus Gomez, Carlos Englert, Amanda Mallon, Mary Nodine

Rigid inclusions are a ground improvement technique that provides soil reinforcement and settlement mitigation using drilled displacement elements. Rigid inclusion installation typically uses a Monitoring While Drilling (MWD) electronic logging system that captures data such as torque, downward thrust, rotary speed and grout take with depth and time. Installation of each rigid inclusion can be considered data from a large-scale in-situ test consisting of penetration of a rotating probe into the ground. Automatically generated graphic logs are typically reviewed visually by members of a project team for quality control during and after installation. This workflow underutilizes the valuable data provided by these MWD systems. This paper discusses the use of MWD installation data integrated with cone penetration test (CPT) data and static load test results to develop a streamlined and robust quality control workflow for rigid inclusions. A compound parameter designated the Penetration Resistance Index (PRI) is computed using soil-tool interface mechanics principles for each production element. The PRI, when plotted with depth, can be correlated with CPT data so that changes in soil profile can be detected as production elements are installed across the site. When the PRI is integrated over element length below the neutral plane, the resulting Integrated Resistance Index (IRI) value can be compared with the IRI of load test elements to rapidly assess element suitability. Use of the PRI and the IRI can help improve quality and efficiency of Rigid Inclusions systems by detecting potential areas where geotechnical conditions are sufficiently different or have improved significantly as production installation progresses. This information allows designers to determine whether optimization of the intended element lengths is possible or where a more intense treatment may be necessary. This quality control workflow can be performed in near-real time.

Oct 7, 2024

By Mangtao (Monty) Du, Brendan Busi, Patrick Bassal, Daniela Zellers

The Living Breakwaters project aims to reduce the impact of climate-intensified events on a coastal community which experienced extremely damaging waves and tragic loss of life during Superstorm Sandy. The project consists of approximately 2400 linear feet (730 linear meters) of near-shore breakwaters that will attenuate waves, reduce erosion, and provide habitat spaces for local marine life along the south shore of Staten Island, New York, USA. The system consists of eight rubble mound breakwater structures with a stone core, a base layer (bedding stone or marine mattresses) and outer layers of armor stones. This paper discusses geotechnical subsurface conditions, design, and construction of the breakwater system. The geotechnical design was predominately governed by global slope stability analyses. These analyses considered dynamic wave loading and wave induced excess pore pressures for the design storm event, as well as pseudo-static seismic loading and liquefaction evaluations. Several construction challenges were encountered with the fabrication and deployment of marine mattresses and underwater geotextile installation.

Oct 7, 2024

By Kurt Breitenbucher, Jeffery Schwarz, Bruce Wagener

Metropolitan Council Environmental Services (MCES) owns and operates nine wastewater treatment plants and 640 miles of interceptor pipeline to serve 111 communities and 2,700,000+ people in the 7-county Minneapolis/St. Paul metro area. Approximately 34 miles of interceptor pipeline, constructed of granite paving block invert, limestone block walls, and an unreinforced cast-in-place concrete arch, are installed within deep tunnels excavated through the soft, friable St. Peter sandstone formation. Some tunnels date back to the 1880’s. To maintain the integrity, reliability, and capacity of the interceptor system, be better prepared for the effects of climate change, and prevent potential damage to the environment due to pipe failure, MCES partnered with Brierley Associates to develop a sandstone tunnel inspection program utilizing historical records and desktop likelihood/consequence risk analyses to prioritize work. This assessment aimed to rank the interceptors by risk priority and provide a framework for MCES to develop projects and improve resiliency. A major challenge in assessing a system of this size is its relationship to adjacent infrastructure. Much of this system was built on vacated right-of-way or through areas not yet heavily developed when the interceptor system was constructed. In other cases, the interceptors had to adjust for natural features such as the Mississippi River's bend or caves. Across the miles of interceptor sewers are multiple encroachments with building foundations, MnDOT tunnels, and bridge foundations, and a cave with columns transferring loads from overlying buildings.  In several segments, it was identified that sandstone slabs had fallen on the interceptor with significant voids above the tunnel crown.  The sandstone(sand) would then enter the interceptor through openings. The voids were filled with grout to reduce deterioration and mitigate sinkhole development. MCES then partnered with CNA Consulting Engineers to devise inspection methods to observe the tunnel liner condition and to locate voids by drilling from above and around the tunnels. Results of the inspections are being used to develop rehabilitation plans, direct capital project expenditures, and enhance system resiliency. 

Oct 7, 2024