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

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

Oct 7, 2024

By Takefumi Takuma, Masashi Nagano, Yuichi Matsuoka

Pressed-in sheet pile bulkheads were built as part of an environmental cleanup known as the Gowanus Canal Environmental Remediation Project in Brooklyn, New York. These pressed-in piles minimized the potential settlement and displacement along the existing canal frontage and nearby buildings. The sheet piles were fully interlocked to be impervious, which was verified with non-declutching sensors. The soil conditions consisted of a top layer of contaminated soft sediment with debris and underlying sand and gravel layers with equivalent N-values ranging from 20 to 100. Coated Z-shaped sheet piles in lengths of up to 70 feet were installed.

Oct 31, 2023

By Scott Lakes

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

Oct 7, 2024

By Alan Walka, Paul Deterling

Nestled among the lovely 19th century Greek revival, Queen Anne and Italianate architecture, Somerville High School sits atop the Spring Hill in Somerville, Massachusetts. Originally constructed in 1872, the high school has experienced several major renovations and This is the first in a additions throughout it 147-year history. Citing inefficient heating and cooling systems, inadequate access, structural repairs to its exterior, and that all major building systems were at the end of their useful life, the Massa­chusetts School Building Authority approved a feas­ibility study for construction and renovation and city residents voted overwhelmingly to fund the estimated $256 million project, making it the most expensive high school construction project in Massa­chusetts' history.

Jul 1, 2024

By Andrew Moran

In 2021, the University of Pittsburgh began construction of a new recreation and wellness center for students and faculty in the heart of its main campus in Pittsburgh. The design and plans for the center promote the university's goals to create a unique place for members to stay active and to sustainably develop the area within its urban campus. The new 270,000 sq ft (25,000 sq m) center is being constructed within the footprint of two former campus buildings that were demolished, the O'Hara Parking Plaza and the Learning Research and Development Center (LRDC). The recreation center borders O'Hara Street on its south side, the ramp to receiving for the Western Psychiatric Hospital (WPIC) on the west side, an internal campus service road called University Drive A on the north side and a long thin area that will become a new terraced pathway on the east side. The existing site grade ranges from elevation 965-1,058 ft (294-323 m) within the area of the proposed recre­ation center. The ground surface at the site slopes between O'Hara Street in the south upward to the service road in the north with a grade difference of approx­imately 100 ft (30.5 m). The bottom of the excavation for the new center will be near the lowest elevation of O'Hara Street, requiring support of excavation (SOE) on the north (LRDC and O'Hara walls) and west (WPIC wall) sides. Mascaro Construction Company, the general contractor, engaged Nicholson Construction Company for the first stage of the construction, which included existing building demolition, earthwork and SOE systems. Nicholson designed and constructed the SOE systems along the site's north and west sides as described.

Jun 1, 2024

By Daniel Escobar, Tom Szynakiewicz

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

Oct 7, 2024

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

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

Oct 7, 2024

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

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

Oct 7, 2024

By Thomas Fiala, Derrick Speakman

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

Oct 7, 2024

By Daniel Renosto, Crysthian Azevedo

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

Oct 7, 2024

By Junho Lee, Lin Huang, Alejandro Martinez, Charles Aubeny

Offshore wind farms are one of the principal sources of renewable energy worldwide due to their large potential for energy generation and remote locations. In the U.S., a number of offshore wind farms have been operating for several years on the East Coast, while two potential locations have been approved on the West Coast. While the shallower waters in the Atlantic Ocean allow for building wind turbines with fixed foundations like monopiles, the substantial water depths of the Pacific Ocean, which can exceed 1,000 m (3,280 ft), require the use of floating turbines with mooring systems. In fact, 65% of the U.S. offshore wind resources are located in deep water regions where water depth is greater than 60 m (197 ft). Since foundation systems typically account for 15-20% of the total construction cost of floating offshore wind turbines, optimizing the design can have a large impact on their cost competitiveness with respect to other sources like onshore wind and solar. A strategy that has received signifi­cant attention recently is to share anchors between floating wind turbines. This differs from the conventional configuration consisting of three nonshared anchors per turbine. The benefits of the shared anchor configur­ation are significant. For example, if every anchor in a wind farm is shared by three turbines, this reduces the number of required anchors by a factor of three. The capacity of offshore anchors depends on a number of factors including the loading inclination angle, embedment depth, soil properties and loading history. Of these, the former depends on the water depth, distance between turbines and mooring line configuration (i.e., taut versus catenary). This article focuses on assessing the effect of the loading angle on the monotonic capacity of ring anchors in sand.

Sep 1, 2024

By Basha Qubain, Kamil Nuzha, Jianchao Li

This article pertains to a 52-story residential high-rise building in the Rittenhouse Square section of Philadelphia, a densely developed area with mixed residential and commercial buildings. The tower is surrounded by Moravian Street along the north, Walnut Street to the south, a residential building to the east and a three-story historic building to the west. It measures 40 m (130 ft) long by 22.8 m (75 ft) wide with a finished floor elevation of 12 m (40 ft) and a full basement at elevation 7.5 m (24.5 ft). The historic building has a finished floor elevation of 13.7 m (45 ft) and its basement at elevation 10. 7 m (35.3 ft). It is supported on a 0.5 m (1.5 ft) thick rubble wall with a bottom at elevation 10.6 m (35.0 ft). The tower mat extends 36 ft (11 m) below grade or about 28 ft (8.S) below the existing historic build­ing, thereby requiring underpinning. When fully loaded, the settlement of the mat will cause the abut ting underpinning to also setUe, which would be detrimental to the historic building. Therefore, an innovative solution was necessary to isolate the underpinning from the stresses induced by the adjacent mat to safeguard the historic structure.

Jul 1, 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 Cary E. Ronan, Tyler Toledo, Justin Ray

The Oyster Point development is located near the San Francisco Bay margins in South San Francisco, just north of the San Francisco International Airport. The eastern peninsula of Oyster Point was formerly operated as a municipal landfill from about 1956 until it stopped accepting waste in 1970. The Oyster Point Landfill is currently being redeveloped in phases, in cooperation with the City of South San Francisco, as a combination of public open space, life science campus (laboratory/research facilities, amenities buildings, parking garage), and a hotel. This paper focuses on Phases 1 and 2 of the life science campus development. The site conditions vary drastically across the site with a portion of the site underlain by shallow bedrock and a portion of the site underlain by up to 40 feet of municipal refuse over 50 feet of soft, compressible clay (Bay Mud) and up to 80 feet of alluvial deposits, with bedrock at a depth of about 150 feet. The varying subsurface conditions below the planned buildings led to a foundation system consisting of a combination of shallow and deep foundations. Deep foundations consist of driven steel HP-piles for Phase 1 and augered cast-in-place (ACIP) piles for Phase 2. Because of a steeply sloping site, over 20 feet of fill was placed in some areas to create a level building pad, resulting in over 5 feet of long-term estimated settlement. This paper will discuss the challenges and lessons learned during redevelopment of the Oyster Point Landfill. Specifically, we will discuss the design of piles and utilities to account for longterm settlement and corrosion, pile load test results, and interpretation of load test data. We will also compare and contrast the use of steel HP-piles and ACIP piles installed for building support through the landfill within Phases 1 and 2 of the development.

Oct 31, 2023

By Erich Steinlechner, Freddy Lopez, Guido Maier

Due to the high damage potential that a possible flood event has for the densely populated areas along the 26 km-long “International Stream” of the alpine Rhine, the discharge capacity needs to be expanded from the current 3100 m³/s (100-year flood) to 4300 m3/s (300-year flood), in line with the requirements of the Swiss-Austrian project RHESI – Flood Control for the Rhine Valley. In this context, the existing 255m-long Rhine Bridge connecting the Austrian towns of Fussach and Hard is no longer able to ensure the primary framework conditions for flood protection and needed to be replaced by a new structure. The new Rhine Bridge Fussach-Hard, a state-of-the-art steel composite bridge with a separated rope construction, was designed to meet the new requirements for flood protection as well as to satisfy the increasing volume of traffic. The extremely unfavorable subsoil conditions, consisting of shallow, very soft to soft plastic lacustrine clay deposits, required a deep foundation solution for the substructure (abutments and piers). Due to the high flood risk, the construction of the substructure could only be carried out during a period of low water discharge (winter), resulting in a very tight construction schedule (winter half-year 2020/2021). For the deep foundation of the substructure, several options were evaluated. Finally, a solution consisting of pile grillages, executed with ductile cast-iron driven piles (320 mm of diameter), was adopted for the project. The fast, safe and simple execution of the piles allowed for the successful erection of the substructure within the limited available time frame. The completion of this construction stage was critical for the further phases. After a construction time of only 28 months, the Rhine Bridge Fussach-Hard was officially opened for traffic on November 18, 2022. The following technical paper presents an overview of the adopted deep foundation solution, focusing mainly on the design and execution of the piled foundation. Furthermore, additional topics such as the sustainability of the adopted solution and possible optimization measures will be discussed.

Oct 31, 2023

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 Chelsea Riddle, Chris Woods, P. Richard Scheller, Kenneth T. Kniss

Throughout the world, there are typical site issues/constraints that could be considered a regional issue, such as soft, silty soils in alluvially defined areas or organic soils found in former marshlands. In areas of variable topography, earthwork, retaining structures, and slope stability are paramount challenges. A case in point is the uncontrolled strip-mine turnover found in the coalfields of northeastern Pennsylvania where the propensity is for available sites to share critical problematic characteristics – massive grading challenges and the presence of uncontrolled mine fills from historic mining operations. At the site of a speculative warehouse distribution center in Olyphant, Pennsylvania, both of these typical issues were present, the latter of which was exacerbated by the higher-than-average fines content of the fill materials, making them more susceptible to changes in moisture content. To further complicate matters, the onset of site construction was set for late fall of 2021, following excessive levels of rainfall in the northeastern United States over the previous two to three months, which led to significant quantities of trapped water within the mine spoil material. This paper will provide a case study on the efforts undertaken to identify and address the issues outlined above, focusing on the several geotechnical construction techniques required in concert to stabilize the site. Specific discussion will focus on the dynamic compaction program implemented for fill stabilization throughout much of the site, the aggregate pier program that became part of the solution in sufficiently loose and saturated areas, and the implementation of a settlement monitoring program conducted following the placement of up to 29 ft (8.8 m) of structural fill to establish the proposed site grades following the ground improvement work.

Oct 31, 2023

By Omar Conte, Feng Lu, Roger A. Archabal

The Sole Mia development is located in an area of North Miami, Florida currently undergoing revitalization that started in 2015. The overall site sits atop 184 acres of a former municipal waste landfill that was closed about 43 years ago. Langan, as the geotechnical engineer of record, has been involved in the design and development of the roadways, an 8-acre “Crystal” Lagoon, two 18-story residential towers, two large mixed-used 6-story complexes and a 7-story hospital with associated parking garage. Currently, Langan is engaged in high-rise development parcels (30+ stories), that are beginning construction. The landfill material is typically about 20 to 25 ft thick and it needs to remain in place during development. Long-term instrumented pilot test programs were created and implemented by Langan to evaluate the effectiveness of deep dynamic compaction (DDC) and preloading in order to minimize/effectively eliminate the short and long-term settlement impacts of landfill on the proposed development. Ground improvement has included DDC and/or preloading for support of roadways, parking lots, major underground utilities and light ground features. Medium to high capacity augered cast-in-place (ACIP) pile foundation systems have been evaluated, tested and ultimately used for support of the buildings/towers, including ground floor slabs. Pile installation through landfill and negative skin friction on the piles had to be considered in design.

Oct 31, 2023

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