Site-Structural Engineering for the Urban Environment

Having projects in the urban environment representing a large proportion of my career experience, I am always a little surprised when I encounter design professionals and contractors who do not fully appreciate the challenges and constraints associated with building on urban sites. While I find that a lot of design professionals, contractors and other stakeholders have urban project horror stories, they do not necessarily associate those adversities with choices that were made or not made during the project. It is almost as if they believe that nothing can be done.

Perhaps I should not be surprised. The fact is that most of the Architecture, Engineering and Construction (A/E/C) industry is focused outside of the urban cores. In a lot of major metropolitan areas, development has focused on low-density sprawl with large parking lots and generous setbacks. For these projects, consideration of the outside world may be limited to curb cuts and utility connections. Is it any wonder then that designers and constructors underestimate what it takes to build on a constrained urban lot. Continue reading

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Will the Sun Rise Tomorrow? Leveraging What You Know When Investigating Existing Conditions.

Existing conditions of a site are a common and stubborn constraint and source of challenges for construction projects. Unlike new construction, existing conditions cannot be specified. However, existing conditions are often difficult to observe and variable, creating a significant source of uncertainty and risk. Exploration and testing are the standard means of mitigating the uncertainty associated with existing conditions. This may include visual observation, probing, material sampling and in-situ and laboratory testing. However, investigations are expensive and never fully eliminates uncertainty. As a result, a lot of design professionals have trouble managing the risk associated with existing conditions and resort to excessively conservative design, increasing construction costs and often creating added risks. A more rational approach to the uncertainties of existing conditions can result in more cost-effective investigation programs and reduce construction costs and risk. Continue reading

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The Most Expensive Subway or Why Construction Costs so Much in New York

It is not exactly news that construction costs in New York City are exceptionally high, especially for underground infrastructure. However, given New York’s importance to the American economy and the state of its infrastructure, construction costs are a real constraint on future growth. In addition, there are lessons that other cities can learn from New York’s experience.

Last month, the New York Times published a long-form piece on the East Side Access (ESA) project, which they labeled the “Most Expensive Mile of Subway Track on Earth” and other major capital projects Metropolitan Transportation Authority (MTA). MTA is the semi-independent state agency that owns and manages various transportation infrastructure, including the commuter rail lines and the subways in New York City. Continue reading

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What’s Wrong with Commodity Geotechnical Reports

FHWA NHI-01-031 NHI Course No. 132031
Subsurface Investigations— Geotechnical Site Characterization, May 2002

A couple of weeks ago, I was using a geotechnical report to develop a critical parameter for design of a particular foundation system. Like so many geotechnical reports I see, this report had many of the signs of being the product of commodity geotechnical services, as is often practiced when materials testing agencies offer geotechnical engineering. When geotechnical services are provided at the lowest possible cost, the effort to perform a subsurface exploration and provide a report must be reduced to the minimum, using the lowest-cost staff available. There is no budget for detailed analysis of data or development of site-specific recommendations by senior staff. The report is similar as to form as those provided a higher cost, but the substance and the level of service that produced it are not the same.

Interestingly, the services and reports provided by commodity geotechnical firms have a lot of the same short-comings. Perhaps this should not come as a surprise. To be competitive, these firms will have to use a lot of the same means to reduce the price of their services as similarly situated firms. This price competition on increasingly similar products and services is the essence of commoditization. Reaching the end of the process is to be a true commodity and be indistinguishable, except on price. While commodity geotechnical services are less expensive, they often increase cost overall by incentivizing excessive conservatism in design, leading to higher cost of construction and also by increasing uncertainty during construction, leading to higher risk of claims and delays.

Having had a lot of experience reading and using geotechnical reports, as well as experience producing them, the signs of commodity geotechnical services are quickly recognizable to me. They reflect a lack of thought and attention to detail in scoping the subsurface exploration, collection and presentation of data and development of recommendations. Here are a few common problems: Continue reading

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Delaware Earthquake or Earthquakes Can Happen Anywhere

As reported by the United States Geological Survey and various news organizations, a magnitude 4.1 earthquake occurred outside Dover Delaware on November 30, subjecting much of the mid-Atlantic region to weak to light shaking. Assuming the magnitude is not revised down, it would be tied for the largest magnitude earthquake in Delaware history. No damage or injuries have been reported as of this writing.

For anyone who thinks that it is “common sense” that earthquakes cannot happen in their area, this should serve as a reminder: earthquakes can happen anywhere.  In the Central and Eastern United States (CEUS), earthquakes are not directly caused by plate tectonic activity, and are, consequently, more infrequent and harder to predict.  However, much of the CEUS is subject the moderate earthquake hazards and a few locations are subject to high hazards. Take a look at the hazard map below produced by USGS.  Continue reading

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Should Temporary Structures be Designed with Higher Allowable Stresses?

Traditionally, designers of temporary structures for use in construction had little guidance binding on their designs. Some owners, particularly infrastructure operators, provided standards and guidelines that permitted increased allowable stresses for certain temporary conditions. Sometimes the increased allowable stresses were limited to new materials or were subject to other stipulations. However, this practice came from a time when codes were much simpler and, in some respects, more conservative than they are now. Should increased allowable stresses still be used in the design of temporary structures, or is this practice anachronistic?

The answer is not simple and depends on who you ask. Different professional approach temporary works in very different ways. Structural Engineers are typically squeamish about construction means and methods and are often very conservative about soils and other loads commonly supported by temporary structures. Some structural engineers will, incorrectly, claim that a structure has “failed” if the computed factor of safety is below design code values. Geotechnical engineers typically view factors of safety to be a matter of judgment and some deprecate codes and standards and structural design generally. Thus geotechnical engineers will take a more aggressive approach to temporary structures, but may take risks unwittingly, especially when considering elements and systems that are not in contact with soil. Construction engineers are often highly risk-tolerant, but use simple and typically conservative methods for their temporary structures designs. It is hard to find consensus as to design approach, much less a standard of care among such disparate perspectives. Continue reading

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The Lost Art of Foundation Engineering

When I began my career, my first job title was “foundation engineer”. The title was an anachronism, even at the time, but the scope of my work was consistent with the domain of foundation engineer going back to the early 20th century, at least. I was involved in geotechnical subsurface investigation and classification, development of design parameters, structural design of foundation elements, earth-retaining systems and underground structures and construction consideration for these systems. Foundation problems have always been subject to uncertainty due to the inability to specify and fully observe the subsurface conditions. Therefore, foundation engineering has always relied on empiricism and judgment to provide reliable predictions about foundation performance.

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Profile and Practice Overview

Richard J. Driscoll, Consulting Engineer (RJDCE) provides consulting structural and foundation engineering services to owners, design professionals, contractors and other construction project stakeholders in the northeast and mid-Atlantic regions. The practice specializes in managing the technical challenges and risks associated with foundation systems, below-ground structures, existing structures and construction in the urban environment. RJDCE utilizes a broad base of experience and knowledge to assist stakeholders balance performance, cost and risk on projects subject to uncertainty.

For more information, see RJDCE’s new Profile and updated  Practice_Overview.

Richard J. Driscoll, Consulting Engineer - Profile
Profile
Richard J. Driscoll, Consulting Engineer - Practice Overview
Practice Overview

 

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Why Does the Construction Industry Love Silos?

Have you ever noticed how much the construction industry seems to love silos? Not the kind of silos that hold grain and other bulk materials, but metaphorical silos within organizations in which subgroups have different asymmetric information and interests and limited points of communication with each other. The resulting “silo mentality” is a result of poor information sharing and hierarchical communication, specialization and conflicting incentives. This may lead to subgroups working at cross-purposes and counter to the goals of the organization as a whole.

In the construction industry, the organizations are typically ad hoc, assembled for a particular project. The subgroups include the owner, the architect, engineers, the contractor and subcontractors. On simple projects, the hierarchy might be rather flat. An architect and contractor report to the owner, each of who has one tier of subs. However, larger and more complex project may have a few more tiers. For example, the excavation contractor might have a specialty foundation contractor, who might, in turn, have an engineer. A project organization of this complexity is bound to develop a few silos.

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Another Deck Failure…No Injuries, This Time

I often find a lot of owners want to cut corners when constructing or repairing deck structures (decks, porches, balconies, etc.) by neglecting code requirement or working without permits, among other things. They assume that these structures require less care because they are accessory to and thus less important to the building. The reality is that decks are among the most dangerous types of structures in terms of injuries and deaths associated with them.

Photo Credit: DC Fire & EMS (Twitter @dcfireems)

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