GEOSTRATA Magazine

When a complicated project is completed, and you ask the engineers, “What was the most challenging part of this project?” a couple of difficulties usually come to mind. We've all heard war stories from engineers who've encountered challenges like endangered species in a project area, extended project duration and scope changes, funding difficulties, tough environmental regulations and conditions, contentious real estate negotiations, utility relocations, coordination difficulties with many stakeholders, railroad crossings in the project footprint, or even Acts of Congress. The South San Francisco Bay Shoreline Project has faced all these challenges, plus the complicated predictions of sea level rise and ecosystem restorations, working in a wet environment, and millions of cubic yards of earthwork on soft Young Bay Mud marine clay.

The Port of Alaska in Anchorage (Port) has embarked on a multiphase modernization program that includes the development of a new petroleum and cement terminal (PCT) berth. The berth consists of a pile-supported trestle that connects to a platform located offshore in the Knik Arm waterway (Figure 1). The terminal is located in a dynamic marine environment with numerous design challenges, including tidal fluctuations of as much as 40 ft, design ground motions associated with a magnitude ${\mathrm{M}}_{\mathrm{w}}$ 9.3 subduction zone earthquake, weak foundation soils, and shoreline conditions that are vulnerable to large-scale seismic displacements. Geotechnical input to the seismic design of the pile-supported terminal required synthesis of extensive in-situ and cyclic laboratory testing data, nonlinear deformation analysis (NDA), and layout of a deep soil mixing (DSM) ground improvement zone for mitigation of seismically induced slope displacements.

Over the past decade, there's been an increased realization of the need to better protect our shorelines, particularly in urban environments along coastlines that have already been impacted by storm surge flooding (e.g., Tropical Storms Katarina (2005), Harvey (2011), Sandy (2012), and Michael [2018]). With an aging waterfront infrastructure, a poor flood resiliency track record, and an increasing concern from climate change, our urban shorelines need significant improvement.

North American Aggregates (NAA), a leading supplier of aggregates in the New York area, recently constructed a new processing facility in Perth Amboy, NJ. One of the final components of the new facility was to replace an aging bulkhead along the perimeter of the plant. The existing bulkheads on-site were constructed in the 1950s to create additional upland property for the Hess Oil & Chemical Corporation that had previously developed the site. These structures, now around 70 years old, were starting to show signs of structural degradation, so NAA looked to its parent company, Weeks Marine, Inc., to construct a new bulkhead.

Gaining insight into the subsurface and developing an understanding of what's hidden below ground is a key to the design and construction process. Geotechnical engineers and geologists often develop their first connection to a site by “strolling its limits” and trying to grasp what's below the visible parts. As a project progresses and construction starts, designers find themselves pushing their heels into the ground, poking the ground with probes and gauges, and observing excavations to develop further understanding of the subsurface stratigraphy. As their connection to the site deepens, the designers' confidence grows or they adjust their recommendations based on unexpected conditions that came to light during construction. They truly are connected to the ground and what lies beneath. However, there are sites that they cannot walk on or physically push their heels into. Such sites are where shallow or deep water stands between the designers and the ground that will eventually bear the structures.