GEOSTRATA Magazine

As a young geotechnical consulting engineer working in New York City, I was always curious as to why the city's building code prescribed a maximum allowable rock-socket skin-friction value of 200 psi for caisson design (rock-socketed drilled shaft with permanent casing) and left little evaluation of the rock to the geotechnical engineer. Generally, the caisson design process in NYC involves drilling boreholes and coring rock, establishing where the “good” rock begins, and then designing using 200 psi. Often, not much more evaluation of the rock goes into the design. The entire industry uses 200 psi — and that's just the way it is.

In 1791, President Washington appointed French engineer Pierre Charles L'Enfant to plan Federal City — today's District of Columbia. L'Enfant's methodical design called for the center of the city to be the U.S. Capitol located on Jenkin's Hill (Capitol Hill today), with numerical and alphabetical streets radiating outward across four quadrants (e.g., northwest, southeast). For more than 150 years, the city's layout adhered to L'Enfant's plan.

Satellite-based interferometric synthetic aperture radar, or InSAR, has gained unequivocal importance as a routine and precise monitoring method for large and small areas alike. Historical datasets allow us to “go back in time” to build large stacks of radar images that can be used to detect and measure deformations of buildings, infrastructure, and the ground surface near tunnelling, construction, or dewatering activities. Time-series analyses enable measurement of vertical or horizontal movement over time at thousands of points with millimetric precision. With increasing availability of data that cover all parts of the world, InSAR is proving to be a critical tool for assessing long-term stability of structures in many types of projects.

Experienced project owners realize that utility conflicts can be risky and pose unexpected impacts on the cost and delivery of projects, especially in urban settings. To help overcome these impacts, Subsurface Utility Engineering, or SUE, an engineering practice that has evolved considerably over the past few decades, combines aspects of civil engineering, surveying, and geophysics. SUE is often included as part of the design process on large, complex megaprojects. Ontario has been a leader in the inclusion of SUE into the planning phase of most large projects. While SUE started on municipal projects, it's now used on larger government and public-private funded transit and highway megaprojects.

The International Society for Trenchless Technology defines trenchless technology as “Underground construction methods of utility installation, rehabilitation, inspection, location and leak detection, with minimum excavation from the surface.” Today, trenchless contractor innovations and technology improvements are responding to the demand for cheaper and faster trenchless construction at a rapid pace. Innovation is expanding the range of subsurface conditions where existing equipment can achieve owner-prescribed design criteria. Business sectors with linear underground infrastructure are realizing benefits related to reduced cost, schedule, permitting conditions, and avoidance of right-of-way acquisition as a result of these technology advances and innovations in a maturing trenchless technology market. To understand the values of these advancements, some historical background on the technology offers perspective and context regarding their value.