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THE COVER From the (Under)ground Up: A New Vision for the Notre Dame Cathedral - Story on page 10 CHANNELS ENVIRONMENTAL + SUSTAINABILITY 12 Innovations and Benefits in the Trenchless Technology Industry STRUCTURES + BUILDINGS 14 Global Stability Analysis Methods, Common Pitfalls, and Strategies for Successful Performance TRANSPORTATION + INFRASTRUCTURE 17 Applying Effective Traffic Control Planning to Civil Engineering Construction Projects 20 Addressing Pakistan’s Needs: the PEC and Hill International WATER + STORMWATER 21 No Funding Issues for Water Infrastructure Projects – Options are more Abundant than ever 22 The Past and Future of Water Infrastructure Software BUSINESS NEWS 23 Perspectives: The Value of Field Work in Engineering 24 Forecasting 2023 with Hill International’s Raouf Ghali 26 Leading from the Front: WSP’s Women Leaders are Paving the Way to a More Equitable Future 27 Fueling Change through Community: A Look Inside ElevateHER 2023 29 2023 Forecast: Optimization, Agility, and Project Management SOFTWARE + TECH 30 Automation by Design: A Case Study 31 Data, Data, Everywhere: Using Data-Driven Insights from Location Intelligence to Develop a Holistic View of Capital Projects 33 8 Technologies Impacting Architecture & Engineering Firms SURVEYING 35 Going Underground: The UK’s Busiest Highway meets its Fastest Railway Network
departments 8 Events 46 Reader Index
Columns LOOKING BACK, MOVING FORWARD 6 The Ground Beneath Our Feet Luke Carothers
VOLUME 9 ISSUE 3 csengineermag.com
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2023 SEMINAR CALENDAR We provide training for every aspect of your fir m, targeting nearly every level of the organization from project managers to C-Suites. What sets our learning programs apart is that they are taught by our top advisors who work inside and alongside AE C fir ms daily. They bring real life data and stories of what really drive performance and purpose in today’s AE C fir ms. We also o ff er customized in-house training programs that are custom-tailored to address your fi rm’s unique needs.
SEPTEMBER 13 M&A NEXT
ElevateHER Symposium Dallas, TX | The Pittman Hotel
Frisco, TX | Omni PGA Frisco Resort Reserve your seat at the table as Zweig Group’s M&A thought leaders share insights and provide deep learning through an interactive experience focused on current and “next” practices in the world of M&A.
ElevateHER connects grassroots e ff orts from around the country, and makes the outcome available to all. At the symposium, we will share what Zweig Group's latest market research data shows about the recruitment and retention outlook, and what the past ElevateHER cohorts have developed so far to mitigate this industry-wide challenge. MARCH 30 & 31 Leadership Skills: Strategies & Tactics Austin, TX This course equips leaders with practical skills to identify opportunities, develop and execute strategy, and build support for initiatives within their organization.
ElevateAEC Conference & Awards Gala Frisco, TX | Omni PGA Frisco Resort The 2023 winners of the Hot Firm list, Best Firms To Work For, Marketing Excellence, Excellence in Client Experience, Rising Stars, Top New Ventures, and the Jerry Allen Courage In Leadership Awards will be celebrated at the iconic black-tie awards gala.
OCTOBER 11 & 12 CSO Roundtable Bentonville, AR
JUNE 22 & 23 CEO Roundtable Napa Valley, CA
Crystal Bridges Museum of American Art The modern day C-suite organizational architecture is rapidly changing, and as a result, the role of the Chief Strategy Offi cer is becoming more pivotal than ever. Join other AEC CSOs to explore the depth of the role, and facilitate a discussion on strategic focus. NOVEMBER 2 & 3 The Principals Academy Nashville, TN The Principals Academy is Zweig Group’s fl agship training program encompassing all aspects of managing a professional AEC servic e firm. Learning and networking at this premiere event challenges traditional seminar formats and integrates participatory idea exchange. DECEMBER 7 & 8 Leadership Skills for AEC Professionals Tampa, FL This course equips leaders with practical skills to identify opportunities, develop and execute strategy, and build support for initiatives within their organization.
Come prepared to discuss your biggest challenges and successes during this highly interactive session. With you in control of the subject matter, roundtable discussions strike at the heart of what you need to e ff ect change in your organization. JULY 12 Project Management for AEC Professionals Boise, ID By addressing the most important aspects of any project – the people – this
course will provide practical techniques that can be immediately implemented for a positive impact on any AEC team or business.
Boise, ID JULY 13 & 14
The Principals Academy
The Principals Academy is Zweig Group’s fl agship training program encompassing all aspects of managing a professional AEC servic e firm. Learning and networking at this premiere event challenges traditional seminar formats and integrates participatory idea exchange.
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looking back, moving forward
It wasn’t until recently that humans gained a tenable grasp on traversing the skies. For far longer, the great builders of so- ciety were much more interested in what lay beneath the ground. History is filled with examples of different peoples using the tools and techniques available to gain access to the ground. The reasons were not uniform; some sought shelter from weather and enemies in excavated caves; other groups knew underground storage would make their food last longer. Not least among the reasons for our obsession with the underground, however, is the bounty in materials it holds. The extraction of underground material is almost synonymous with the development of human culture and technol - ogy. The oldest example of mining activity by humans–the Ngwenya Mines in Swaziland–are at least 42,000 years old. During the Middle Stone Age, the people in the area began extracting red haematite and specularite from the ground, which was then used to create red paint. Although rudimentary in its composition, this early form of paint still exists in many places–dotting cave walls throughout Swaziland even in the modern age. Similar examples exist all over the world–of minerals being extracted and used for paint–and are a testament to the development of human communication and expression over history. By using tools to excavate minerals in under - ground spaces, humans became capable of new forms of lasting expression. Paintings on rock walls contained key information for early humans–communicating the presence of food, water, shelter, and danger. This access to paint allowed humans to express their thoughts and feelings in a new and lasting way. It’s also no surprise that many of these early humans chose the walls of caves as their canvas. As humans were learn - ing to construct external shelters capable of withstanding the elements, caves served an important purpose for many migratory groups. As our tools and materials became more advanced, humans began to cluster into groups based around constructed buildings. Many of these early settlements formed around resources that could be extracted from underground. Access to these resources shaped the way cities were built and added to their wealth and influence. Advances in technology have changed what resources and their methods of extraction, but this pattern for shaping the built environment still exists for cities built in the modern era. For example Kansas City, Missouri was founded on the site of a trading port on the Missouri River in 1850. Following the American Civil War, the once-rural trading port began to grow rapidly as a result of the Hannibal & St. Joseph Railroad bridge being constructed. To accommodate the resulting population boom, massive amounts of concrete needed to be sourced. The answer lay beneath the Missouri soil as the area’s hills were laden with the ideal limestone for cement production. During the latter half of the 19th century through the early 1900s, engineers and miners carved out millions of square feet of limestone in and around the Kansas City metropolitan area. In a period where technological capacities directly align with material need, Kansas City became a very large met - ropolitan city in a relatively short period of time. This time of growth coincided with the City Beautiful movement, of which Kansas City became a leading example. Neighborhoods, parks, and buildings were constructed under the belief that their beauty would intrinsically improve the lives of the population. Fueled by the limestone being quarried and the ideals of the City Beautiful movement, iconic buildings such as Union Station and neighborhoods like Southmoreland elevated Kansas City from a small “cowtown” to a large, cosmopolitan city. There are countless examples mirroring Kansas City both in America and throughout the length of history. Indeed, access to underground material and the understanding of its properties is also at the heart of the modern AEC indus - try. Starting during the industrial revolution, the need arose for specialized professionals who could develop tools and machinery to extract and process resources. Shortly after, further specializations were needed for things like moving materials over long distances. Many of the modern engineering disciplines can find their roots in either the extraction and processing or logistical movement of these key resources. As the AEC industry navigates the challenges of the next decade and beyond, our historical relationship with the ground and resources beneath can provide important context that can help in these struggles. Humans have an in - extricable link to these resources, and we have relied upon them to develop socially and physically. When viewed in comparison to our historical relationship, our modern understanding is still in its infancy. As we continue to grow our understanding of the underground, it is important to recognize and respect this need to continue learning because, as history would suggest, many solutions to these problems can be found underground.
The Ground Beneath Our Feet
LUKE CAROTHERS is the Editor for Civil + Structural Engineer Media. If you want us to cover your project or want to feature your own article, he can be reached at email@example.com.
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events + virtual Events
is a place, where the global AI in AEC community meets and pushes together the industry to take the next step in AI deployment. It is time to move from building the foundation towards creating the value from
Conexpo March14-18 – Las Vegas, NV
data and AI. See you in future! #AIAEC2023 https://www.ril.fi/en/events/ai-in-aec-2023.html
The largest construction show in North America. More equipment. More people. More possibilities to bring your business to the next level. https://www.conexpoconagg.com/
Digital Twins 2023 March 23
A digital bridge over three continents: designing and building scalable, interoperable and reusable digital twins for sustainable cities and resilient infrastructure. https://www.digitaltwins2023.com/
The UK Concrete Show March15-16 – Birmingham, England
Over 200 exhibitors from across the industry will be displaying some of the latest & greatest innovations and products on offer. With everything under one roof at the UK’s only show dedicated to all things Concrete, this is the event you will not want to miss. https://concreteshow.co.uk/
Leadership Skills for AEC Professionals Spring March 30-31 – Austin, TX
Zweig Group’s strategy approach, previously reserved for advisory clients, is brought to the training environment for the first time ever. This course equips leaders with practical skills to identify opportunities, develop and execute strategy, and build support for initiatives within their organization. This training provides a high impact learning experience that is designed to help emerging and current leaders master the one area that is so often neglected in modern leadership training: developing and executing strategy to solve complex problems. https://zweiggroup.com/products/leadership-skills-for-aec- professionals-spring-2024 April 2023 ACI is pleased to be hosting its ACI Concrete Convention in-person, in San Francisco, CA, USA, on April 2-6, 2023. The convention will have a robust schedule that includes traditional in-person activities. Select programming will also be available on-demand to attendees who choose to participate remotely. All committee meetings and all social events will be limited to in-person attendees. https://www.concrete.org/events/conventions/currentconvention.aspx AUVSI PRESENTS: DATA PRIVACY April 2-6 – San Francisco, CA With the increased use and deployment of uncrewed and autonomous systems, concerns about privacy often come up. Whether it is personal privacy, civil rights, or civil liberties, collecting and using data safely and appropriately is of utmost importance for legal concerns and public acceptance. Join this webinar to hear from leaders in the privacy space on overcoming concerns and ensuring appropriate and legal collection and use of data. https://www.auvsi.org/events/webinars/auvsi-presents-data-privacy AUVSI PRESENTS: DATA PRIVACY April 12
Adobe Summit March 21-23 – Las Vegas, NV
Summit 2023 is an in-person and virtual event with innovative keynotes, 200+ sessions, hand-on labs, preconference trainings, and networking activities. It’s a unique opportunity to join a community of Experience Makers from around the world to learn, be inspired, and make connections – and ultimately, to empower you to make the digital economy personal. https://summit.adobe.com While the U.S. has a military advantage over its adversaries, competition is growing. As the government funnels more resources into strategic competition, uncrewed systems will be at the forefront of U.S. competitiveness. Join AUVSI to learn how uncrewed air, maritime, and ground vehicles help set the stage for future combat, and gives the U.S. a competitive, strategic edge. https://www.auvsi.org/events/webinars/auvsi-presents-uncrewed- systems-strategic-competition AUVSI PRESENTS: UNCREWED SYSTEMS & STRATEGIC COMPETITION March 22 Artificial Intelligence in Architecture, Engineering and Construction March 22-23 We are facing the new era in AEC industry. AI has arrived in the arena, and it is now present from design to construction and usage phases. Building information modelling, smart buildings and creation of smart cities have exponentially added to the amount of the existing data. Whereas visual programming has made data-driven design more reachable, and the immersive technologies have enhanced the visual management of the data. To succeed in the digital landscape, we should further develop our AI capabilities and match them with the customer values and business opportunities. To make a breakthrough with AI in AEC, we need open-minded and future-orientated business leaders beside the AI-orientated engineers and researchers, as well as companies and universities working together in an international context. This conference will offer in-depth review of current status and future impact of AI in AEC industry. It is about sharing, sparring and networking. It
BAU 2023 April 17-22 – Munich, Germany
Messe München will once again be the industry meeting place for the construction industry: with 250,000 visitors and over 2,000 exhibitors
from almost 50 countries, BAU is one of the leading events for the construction industry worldwide. The Nemetschek Group uses this large stage to present its solutions for more efficiency and sustainability along the entire construction life cycle together with the ten brands ALLPLAN, Bluebeam, CREM Solutions, dRofus, FRILO, Graphisoft, Nevaris, SCIA, Solibri and Vectorworks. https://bau-muenchen.com/en/ This course is designed for individuals who never had the opportunity to study design of structures in a university-level course, but are involved in the design, construction, and inspection of wood buildings. The primary focus and objective of this course are a knowledge of wood design basics and understanding of the many factors routinely used and required by the 2018 National Design Specification® (NDS®) for Wood Construction. https://www.cpe.vt.edu/sdwnds/index.html Design of Wood Structures introductory course April 26-27 – Blacksburg, VA The WES Annual Conference brings together women and allies from across all disciplines for a two day conference. The event will showcase the inspiring role models and demonstrate how organizations are striving to improve diversity and empower women in engineering. This year the theme will focus around safety and security. https://www.wes.org.uk/events/wes-annual-conference-2023 May 2023 XPONENTIAL is a yearly gathering of global leaders and end users in the uncrewed systems and robotics industry. Founded on the belief that cross-pollination drives innovation, it features opportunities to connect and problem-solve with experts across markets and domains. At XPONENTIAL, more than 8,500 of the world’s top experts in autonomous technology come together to change the course of human progress. We’re proud to welcome technologists, users, policymakers, and strategists from over 20 industries and 60 countries. No matter where you fly in from, XPONENTIAL will help you stay competitive and take advantage of immediate opportunities. https://www.xponential.org/xponential2023/Public/Enter.aspx WES Annual Conference April 27-28 – Birmingham, England Xponential May 8-11 – Denver, CO Equip yourself today to meet tomorrow's threats. At AUVSI Defense, military officials from across all branches, federal security personnel, and industry leaders discussed the most critical issues surrounding the integration of uncrewed technologies — including acquisition, global competition, and industry/government collaboration. https://www.auvsi.org/auvsi-defense-2022 AUVSI DEFENSE 2022 May 8-11 – Denver, CO
Digital Construction Week May 17-18 – London
Join thousands of the brightest minds in digital construction to learn, innovate and connect in-person. On 17-18 May 2023 at ExCeL London, DCW will put the spotlight on the tech and tools solving the built environment’s most pressing challenges. See hundreds of expert speakers and inspiring brands all in one place. Register your interest today and be the first to hear about next year’s show. https://www.digitalconstructionweek.com/ As we unlock the potential of geospatial information, it’s more important than ever to connect and collaborate to drive the profession forward. GEO Business 2022 hosted 120 global brands and cutting-edge start- ups showcasing the newest tech, tools and solutions for geospatial. Plus, a CPD accredited education programme with 200 sessions offered everything you need to get up to date with the latest developments. GEO Business is back at ExCeL London on 17-18 May 2023. Register your interest to be the first to know when free registration opens. https://www.geobusinessshow.com/ GEO Business May 17-28 – London The workshop provides an opportunity for members to meet, present and exchange data, and share experiences and developments. The program includes technical presentations covering states of practice; advancements of micropile construction, materials, research and development; and educational/promotional activities. The workshop also features the 11th Lizzi Lecture, the 9th Lizzi Scholarship and the 4th World Cup of Micropiles. The technical program chair is Ty Jahn, P.E., Condon-Johnson Associates. https://www.ismicropiles.org/workshops.asp September 2023 Reserve your seat at the table as Zweig Group’s M&A thought leaders share insights and provide deep learning through an interactive experience focused on current and “next” practices in the world of M&A. This highly interactive event is designed to provide M&A education and practical application through interactive roundtable discussions, thought leadership from expert panelists, and focused networking to connect leaders from across the country. You will end the day better 15th International Workshop on Micropiles May 31-June 2 – Vail, CO M&A next Symposium September 13 – Frisco, TX informed about the opportunities for M&A as a growth strategy. www.zweiggroup.com/products/2023-m-a-next-symposium
During its more than eight centuries, the Notre Dame Cathedral in Paris has seen, hosted, and survived more than its fair share of historical events and disasters. Perhaps most harrowing of these was the fire that engulfed the cathedral’s roof and spire in April of 2019. By the time the blaze was controlled, Notre Dame’s famous spire had collapsed, most of the roof was destroyed, and there was extensive damage to the upper portions of the structure’s walls. Images of this cultural icon burning elicited an outpouring of grief from around the world, which quickly reverberated as shockwaves of support and aid. One of the most prominent examples of this aid came from the AEC industry as rebuilding efforts began immediately fol - lowing the fire. Led by its CEO Andrew Anagnost and Vice President of AEC strategy Nicolas Mangon, Autodesk aided in the rebuilding efforts by using their technology to create a 3D BIM model of Notre Dame Cathedral before the fire. With tools provided by Autodesk, the process of cleaning and scanning the structure began. During this time, Autodesk continued to support the teams working on the structure–offering tools and advisors to anyone working on the project. This period of the restoration process lasted nearly three years, with the modeling sequence and cleanup ef- forts being completed in the Fall of 2022. Using this BIM model, the teams working to restore the structure to its previous state are better equipped to manage construction sequences and logistics as well as calculate fluid dynamics for stability. While the structure is being restored to its former self, its immediate surroundings will be updated to support its continued operations in the modern era. Running parallel with the restoration efforts, the City of Paris launched a design competition in 2021 to reimagine the urban landscape surrounding the cathedral. The project site includes the fore- court of the cathedral and its underground space as well as areas over the bank of the Seine River. The immediate surroundings of Notre Dame constitute one of the most heavily trafficked areas in the world. Largely untouched for centuries, this area now creates problems for its modern usage, resulting in things such as traffic and congestion. With cleanup and scanning taking place and the outbreak of Covid-19 in 2020, the lack of visitor traffic in the area provided a good opportunity to re-envision what the space could be. Four international multidisciplinary teams–led by architects, urban planners, and landscape architects–were invited to submit their design proposals. Autodesk was the technology partner for the competition, providing technological expertise throughout the competition. Au - todesk’s BIM solutions were used to create a 3D model of the exist - From the (Under)ground Up: A New Vision for the Notre Dame Cathedral By Luke Carothers
ing area surrounding the cathedral. This model allowed the teams to understand the unique constraints of the site. The teams again utilized Autodesk’s BIM technology and advisors to create photorealistic visu - alizations of their design proposals. Furthermore, the digital documents produced during the competition were available to the four teams, the City of Paris, and Autodesk, which allowed them to collaborate in real time on the Autodesk Construction Cloud platform. In June of 2022, the City of Paris announced that the team led by Bu - reau Bas Smets was selected as the winner of the design competition. Led by landscape architect Bas Smets, urban planners GRAU, and heritage collaborators Neufville-Gayet, the winning design is exten - sive–reimagining the square and underground parking spaces beneath it. This reimagining also includes the archeological crypt, the Jean XXIII square located behind Notre Dame, the riverbanks, and some adjacent streets. A major part of this redesign focuses on the areas below the cathe - dral’s forecourt. Under the forecourt is a large parking structure that was built in the 1970s, which has fallen out of use. The winning design by Bureau Bas Smets seeks to breathe life into this space by turning it into a reception area for visitors to the cathedral. This new design creates a passageway with an area of 3,170 meters for such a purpose. To create this passageway, alterations will be made to the parking structure such as the removal of the immediate ceiling, which will create a four meter high and 60 meter long entrance hall for the cathedral. Furthermore, the parking structure’s concrete pillars– which will flank this new entrance hallway– will be sandblasted to
create a more aesthetic surface finish. Along with creating a welcome center better adapted to host visitors in the modern age, this new plan for the areas underneath Notre Dame’s forecourt also connects these visitors with two other important areas: the Crypt of Notre Dame and the river Seine. Opened to the public in the 1980s, the crypts beneath Notre Dame Ca - thedral house several important archeological discoveries that pre-date the building of the cathedral and even the city of Paris itself. Over the years, researchers have found the remains of a Gallo-Roman dock - ing port and public bath, stretch of fourth-century ramparts, and parts of a medieval road and church. Despite this wealth of archeological history, the crypts beneath Notre Dame are vastly under-visited when compared to the structure above. A large part of this is due to the entrance to the space being offsite since its opening. The new plan for the space under Notre Dame cathedral is set to change this and elevate this historical site to the forefront. The new entrance space envisioned by the Bureau Bas Smets team will feature a new entrance to the crypts, adjacent to the entrance to the cathedral. This new onsite entrance to the crypts below Notre Dame is one of the key ways this new vision for the area will create stronger links between the future and the past. Another major way this project will connect the future and the past is by including the river Seine. The history of Notre Dame and the Seine are inextricably linked, and this new design pays tribute to this connection. Along with providing entrances to the cathedral and crypts, the new underground space will also open onto the Seine via a new opening in the quay wall. Using tools provided by
Autodesk, the winning design team was able to test and model design options for their concept. Work on the winning project is expected to begin in 2024 and complete in 2028. When the project is complete and restorations are finished, the Notre Dame Cathedral will be entering into a new era of its his - tory. When images of Notre Dame burning filled television screens around the world in 2019, the world held its breath and braced for loss. However, with an outpouring of support from around the world–and the tools and expertise of the AEC industry–this iconic structure is not only going to be restored. Rather, the Notre Dame Cathedral will be renovated in such a way that builds on its unparalleled past. In doing so, this new vision for the world icon is able to strike a fine balance between the past and modernity.
LUKE CAROTHERS is the Editor for Civil + Structural Engineer Media. If you want us to cover your project or want to feature your own article, he can be reached at firstname.lastname@example.org.
March 2023 csengineermag.com
I firmly believe that we should all be good stewards of the environment. Additionally, it’s important to also recognize that infrastructure and their continual improvement is critical to society and our way of life. That’s precisely what excites me about the trenchless technology indus - try: it allows us to construct necessary infrastructure while minimally impacting our communities and the environment. These technologies allow us to cross sensitive areas with minimal to no impact on the environment, and when done properly, are both extremely meaningful and beneficial for our society. Future Ready with Less Disruption Trenchless technology is a series of construction techniques used to install or rehabilitate underground infrastructure – primarily pipelines and underground utilities – with minimal disruption to surface traffic, businesses, residents, and the environment. This technology offers numerous benefits for both clients and com - munities. It minimizes disturbances to the existing environment, as well as traffic impacts and contributes to less disruption in congested urban areas. It also reduces the need for new space underground and problems associated with pipeline routing; requires less overall space underground, which minimizes the chances of interfering with existing utilities or abandoned pipes; requires less exposed work area and is therefore safer for workers, communities, and the environment; sig- nificantly reduces the need for excess spoil removal; and minimizes damage to pavement and disturbances to other utilities. Trenchless Technology inherently supports WSP’s Future Ready® principles, as the methods of installation are resilient and environ- mentally sensitive, and often help to reduce the carbon footprint of the construction project by minimizing impact and reducing spoil removal, while also being capable of dealing with a wide range of constraints and challenges. Digging Achievements WSP recently used trenchless technology to help Indiana and North Carolina construct their first curved microtunnel projects. Microtun - neling includes the use of remotely controlled microtunnel boring machines, which are commonly used to install pipelines less than 96 Innovations and Benefits in the Trenchless Technology Industry Everett Litton, Vice President and National Practice Lead for Trenchless Technology at WSP USA, discusses the upsides of using trenchless technology construction By Everett Litton, PE
Photo: Michael Flanagan, WSP
inches in diameter, and usually too small for manned tunneling opera- tion. While using trenchless technology for these projects is not uncom - mon, curved microtunneling is relatively new within North America and poses greater difficulties that we are now able to overcome. The first curved microtunnel in Indiana — was the State Road 37 (SR37) Improvements Project — included years of collaboration be - tween the cities of Fishers and Noblesville, Hamilton County and the Indiana Department of Transportation. This led to a concentrated effort to address traffic congestion and public safety challenges along SR37 in Hamilton County.
The at-grade intersections at 126th, 131st, 141st, and 146th Streets were redesigned as underpasses to allow for the free flow of traffic on SR37. For this project, WSP was selected to design two offsite gravity drain - age storm sewers to carry drainage from the depressed underpasses to natural water bodies, and trenchless construction methods were chosen to provide drainage for the newly depressed interchanges. Gravity outfall sewers were selected instead of pump stations, which eliminated long-term operation and maintenance costs. Two drainage outfall storm sewers were designed and successfully constructed, at inverts of 17 to 44 feet below grade, to carry roadway drainage westward to its natural surface water bodies, Shoe - maker Ditch, and the White River. The SR37 project used two trenchless construction methods: two-pass tunneling and microtunneling for installation of the 54-inch diameter storm sewers. The project included the installation of 6,500 feet of storm sewer, which successfully navigated difficult ground and groundwater conditions for the existing 2,650-foot- long south drainage line and the 4,700-foot long north drainage line. Trenchless success was achieved in this project by overcoming boulders and groundwater conditions, and successfully installing a record-breaking 2,304-foot long curved microtunnel. The project won Trenchless Technology magazine’s 2020 Project of the Year, New Installations Honorable Mention, and the American Council of Engineering Companies’ 2021 Indiana En - gineering Excellence Honor Award.
construction, requiring specialty contractors to perform the work. At small diameters the installation cost is actually quite similar to open- cut installation, but only becomes more costly on a per-foot basis at larger diameters. And when the full social costs are considered, such as community and environmental costs, trenchless technologies are often less impactful and competitive — if not more favorable — than open-cut installa- tion methods. There are also significant advantages to both cost and schedule, mostly from permitting efficiencies, when using trenchless technologies for crossing wetlands, roadways, railroad tracks, streams, rivers, and other obstacles or sensitive environmental areas. We are witnessing continual advancement of trenchless technologies based on our experience and innovations developed through previ - ous project successes, which leads to continuous improvements and efficiencies within the industry. Tooling developments are allowing for excavation in a wider variety of geologic conditions, methods are being refined for longer lengths, and longer reaches and more adap - tive tooling continue to reduce the impacts of trenchless technology by reducing the areas disturbed at the surface, along with the carbon expended on each project. Today, when the full spectrum of costs and potential community and economic impacts are considered for the life span of a project, trenchless technology installations are emerging as the most viable and practical option for pipeline projects throughout North America and worldwide. Trenchless Offerings WSP’s capabilities related to trenchless technology include planning, program management, risk management, detailed design and onsite services during construction, resulting in an in-depth understanding of local geology, ground-structure interaction and construction tech- nologies, combined with the systematic application of investigative, scientific, engineering and risk management techniques for multiple trenchless projects. WSP can point to continuous growth and expansion in tunneling technology, from its earliest roots in the US, more than 130 years ago, to its vast international presence today. The firm’s work in the late 1800s includes substantial design and construction of the first New York City Subway. That heritage in tunneling continues to this day and WSP is proud of the advances it is making using modern trenchless technology tech- niques to assist clients and owners.
Similarly, in North Carolina, WSP served as engineer- of-record working with Charlotte Water for several one-pass sanitary sewer tunnels. The 3,592-foot-long by 48-inch diameter reinforced concrete utility pipe was installed using a Herrenknecht AVN-1200 mi - crotunnel boring machine, within variable subsurface conditions that consisted of granitic rock with strengths up to 30,000 pounds per square inch, as well as soft alluvial deposits. Construction is ongoing and included an already complete 1,155-foot-long curved microtun - nel, which was the first planned direct jack curved sanitary sewer in North Carolina. Considering Cost Trenchless technology projects are less impactful to the community as compared to open-cut construction projects. Many communities already require trenchless construction as a normal practice, and the technology is being adopted in others, albeit at a slower rate. Contributing to that slower rate in some communities is an impres - sion that trenchless technology is more expensive than open-cut
March 2023 csengineermag.com
Global Stability Analysis Methods, Common Pitfalls, and Strategies for Successful Performance
arc, spiral, noncircular). LEMs utilize the material’s shear strength and do not rely on the soil’s stress-strain behavior. Vertical, horizontal, and moment forces induced along the failure surface (Figure 2) and exter - nal loads acting on the rigid body (e.g., structures), live loads (e.g., vehicles), and temporary loads (e.g., construction loads) are typically considered explicitly in these analyses. In global LEM analyses, the mass of the rigid body is divided into slices. Various global limit equilibrium analysis methods are frequently used throughout the geotechnical engineering industry, including Ordinary Method of Slices, Simplified Bishop (SB), Spencer, Morgenstern and Price (MP), to name a few of the most common. Each global LEM has limitations that the engineer must consider before selecting one or more methods for use. These limitations can include assumptions or simplifications that are only applicable to isotropic soil conditions, circular failure surfaces, etc. Furthermore, some global LEMs, such as Ordinary Method of Slices or SB, are often over-simplified, inaccurate, or both due to various inherent assumptions. GSA Software Considerations, Common Pitfalls, and Strate- gies for Successful Performance Engineers frequently perform GSAs using commercially available, user-friendly limit equilibrium software packages, allowing them to perform multiple analyses quickly and efficiently. Some of these software packages allow engineers to utilize simplified analyses that only partially satisfy force and moment equilibrium (e.g., SB method). Other software packages allow engineers to utilize more robust analy - ses that are considered complete equilibrium procedures (e.g., Spencer, and MP). Further, these software packages can quickly analyze many failure surfaces and loading conditions for multiple LEMs simultane - ously. However, a failure to understand the mechanics of the software combined with a lack of understanding of the inherent assumptions or simplifications of certain LEMs can lead to the use of inappropriate as - sumptions, unconservative analyses, and potentially unsafe conditions. LEM Analysis Methodologies Many LEM analysis methodologies rely on various simplifying as - sumptions or limitations that require careful consideration when performing GSAs. For example, one of the more widely utilized analysis procedures is the SB method. This method uses the forces in the vertical direction and the moments about the center of the circular failure surface to evaluate equilibrium conditions of the failure wedge, whereas the shear forces between individual slices are not considered. While many software packages allow the engineer to analyze slopes for noncircular failure surfaces using the SB method, this method is only appropriate for circular failure surfaces.
By J.E. Hughes, Ph.D., P.E. 1 , Z.K. Boswell, P.E. 2 , B.P. Strohman, P.E., G.E. 3
Introduction Many construction projects incorporate fill or excavated slopes, utilize support of excavation systems, or require retaining walls as part of the necessary site development. These structures create unbalanced loads, requiring a professional engineer to perform global stability analyses (GSA) to evaluate the potential failure surfaces that can develop be - hind and below the structure due to the unbalanced loading condition (Figure 1). Global stability is often described in terms of the factor of safety against failure along a failure surface. The factor of safety is defined as the ratio of the soil shear strength (resistance) to driving shear stress acting along the failure surface. GSAs are a crucial part of the design process for these structures. If per - formed incorrectly, unexpected movement or potential catastrophic failure can result, posing a significant risk to public safety and adjacent property. This paper describes some common global stability limit equilibrium analysis methodologies, software considerations and common pitfalls, and strategies for successful performance. Most of the content herein applies to two-dimensional analyses; however, many of the consid- erations, pitfalls, and strategies are applicable to three-dimensional analyses as well. Common Limit Equilibrium Analysis Methodologies The Limit Equilibrium Method (LEM) is one of the most utilized procedures to perform GSAs. Limit equilibrium is a static analysis technique that evaluates force and moment equilibrium conditions as- suming the soil and/or structure above the failure surface acts as a rigid body above an assumed failure surface of a given shape (i.e., circular/
Unlike the SB method, the MP and Spencer methods satisfy force and moment equilibrium conditions and are appropriate for both circular and noncircular failure surfaces. In the authors’ experience, methods that satisfy force and moment equilibrium conditions provide more reliable results. When performing these analyses, it is imperative that the engineer understand the benefits and limitations of the available methodologies and evaluate their appropriateness for each project. Soil and Groundwater Conditions The soil and groundwater conditions play an important role in deter- mining the global stability of slopes, support of excavation systems, retaining walls, and other structures. Thus, it is essential to utilize and accurately depict the site-specific soil and groundwater conditions for use in the GSAs. The authors recommend the engineer rely on location- specific subsurface investigations and field and laboratory testing, if feasible, to assess the necessary analysis parameters. As part of the evaluation of the soil and groundwater conditions, a detailed understanding of the material’s shear strength is required. Drained and undrained strengths are used to define the behavior of soils during shearing. Drained strength is the strength when the soil is loaded slowly or over a long period of time such that no excess pore - water pressures develop, or when the excess porewater pressure fully dissipates after the soil is loaded. Undrained strength is the strength when the soil is loaded faster than the porewater can flow in and out of the material during shearing. During undrained shearing, excess porewater pressure develops within the soil. Over time, the excess porewater pressures dissipate and the drained strength is achieved. The construction type (temporary vs. permanent), the design life of the structure, and the soil type impact whether an evaluation of the drained condition, undrained condition, or both is necessary. Further, for sites with loose, saturated sands or sensitive clay soils, an evaluation of the potential for post-peak strength loss during shearing is required. The groundwater conditions at a site can also directly influence the shear strength of the soil and the driving forces acting on the failure surface. An understanding of the static groundwater levels is neces - sary and should also consider seasonal groundwater fluctuations and less frequent extreme groundwater events, if necessary. Further, the use of parametric studies to evaluate the sensitivity of the results with respect to the input and analysis parameters is an essential measure to understand the reliability of the analysis results. External Loading Conditions External loading conditions can also significantly impact the response of a structure or slope, both during and after construction. For example, during construction, analyses are typically required at various excava - tion depths, at differing stages of fill placement, or when other unbal - anced loads are placed or removed from the areas near the slope or structure. For analysis of the permanent, long-term condition, loads from adjacent structures and seismic loads should be considered. Of critical importance for GSAs are the magnitude of the load, its location, depth, and extent relative to the structure or slope. Fur - thermore, the authors recommend that engineers exclude temporary loads in GSAs if those loads have a stabilizing effect. These tempo -
rary loads can unconservatively increase shear resistance along the failure surface. Anisotropic Soil Behavior and Shape of the Failure Surface Two key considerations that require detailed attention when evalu- ating the global stability of a structure or slope are soil anisotropy (e.g., soil that has properties that are directionally dependent) and the shape of the critical failure surface. The United States Army Corp. of Engineers (USACE) Engineering and Design Manual for Slope Stability (EM 1110-2-1902), emphasizes the importance of these items, stating, “Stability analyses based on general slip surfaces are now much more common and are useful as a design check of critical slip surfaces of traditional shapes (circular, wedge) and where complicated geometry and material conditions exist. It is especially important to investigate stability with noncircular slip surfaces when soil shear strengths are anisotropic.” To consider the effects of anisotropy of the undrained shear strength, different strength zones are often utilized in GSAs: triaxial compres - sion (TXC) behind the slope or structure, direct simple shear (DSS) below the slope or structure, and triaxial extension (TXE) in front of the slope or structure. While the USACE emphasizes the importance of analyzing non circular slip surfaces for anisotropic soil conditions, it is often necessary to analyze both circular and noncircular failure surfaces using appropriate global LEM methodologies to determine the critical failure surface. The authors recommend that engineers evaluate soil anisotropy and the importance of the different modes of shearing (TXC, DSS, and TXE) when performing GSAs. Evaluation of Failure Surfaces Most global limit equilibrium software packages allow the engineer to either manually define the failure surfaces, or the program automati - cally generates the failure surfaces. If the engineer chooses to define the failure surfaces manually, they should have sufficient experience performing GSAs to assess the suitability of the results. For manu - ally defined failure surfaces, it is typically necessary to define mul - tiple failure surfaces, compare the factors of safety, and evaluate the reasonableness of the results. This process is often both monotonous and time-consuming to identify the critical failure surface and factor of safety. In lieu of manual definition of failure surfaces, it is often more common to have the limit equilibrium software automatically generate the failure surfaces utilizing a user-defined search criterion. This approach often results in the analysis of significantly more failure surfaces. For automatically generated failure surfaces, the engineer should still perform a thorough review to evaluate the suitability of the results and slip surfaces. Engineers performing GSAs either manually or automatically specified failure surfaces should understand how the software defines the failure surface to ensure the critical failure surface and factor of safety are iden- tified. If the program features multiple search algorithms, each algorithm needs to be considered, and the results compared for consistency. Regardless of the failure surface selection approach (manual or auto - matic), the use of narrow model extents typically leads to misleading and often unconservative results. For example, if the model’s edges
March 2023 csengineermag.com
are too close to the structure being analyzed, the program likely will not identify the critical failure surface and factor of safety. To ensure the critical failure surface is not overlooked, the model extents should be at least two times the width of the structure. Refinement of model size and extents can be performed only after the engineer is confident the analysis is capturing the critical failure surfaces and factor of safety (Figure 3). Software Model Verification Model verification is a critical aspect for all engineering analyses, but is particularly important when using commercially available software packages. When performing GSAs, a prudent approach is to verify the reasonableness of the results for a simple case or to use a previously validated problem to assist in validating the results. Typically, the model validation uses the same inputs and analysis methodologies, and if the results are inconsistent, the engineer should evaluate the differ- ences and update the analysis. Closing Remarks Global stability analyses are commonly encountered within the geo- technical engineering industry. Background and knowledge of typical analysis methodologies and commonly utilized commercially available software packages are required to achieve reliable results. Unexpected movements or catastrophic failures can occur if these analyses are performed incorrectly. While recognizing and avoiding common pitfalls aid in achieving successful GSA performance, the authors recommend the following
fundamental strategies, 1) utilize LEMs that are considered complete equilibrium procedures (e.g., Spencer, and Morgenstern and Price), 2) use site-specific information for the subsurface and loading conditions, 3) check the model extents, and 4) verify the analysis software. Follow - ing these approaches provides greater reliability in the analysis results.
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