Underwater Rock Removal in Support of Berth Deepening

Abstract: The Massachusetts Port Authority’s (Massport) Paul W. Conley Container Terminal is in South Boston, Massachusetts. Conley Terminal is the largest container terminal in New England with an average of 4 to 5 vessels calling every week. The Terminal has three primary berths (Berth 10, Berth 11 and Berth 12) but larger ships already using the terminal often extend beyond the limits of a single berth. The access channel (Reserved Channel) is of limited width and has berthing on both the north and south sides. Massport operates Conley Container Terminal on the south side of the Reserved Channel and also operates Flynn Cruiseport Boston on the north side of the channel. Often vessels need to leapfrog one another when arriving or departing, so work within the channel, including deepening, requires significant coordination.
In 2014, Massport began the Conley Terminal Intermodal Improvements and Modernization Initiative (Initiative), an $800-million investment into the infrastructure of the Port of Boston. The Initiative included rehabilitation Berths 11 & 12 and construction of a new deep-water berth (Berth 10) that expands Conley Terminal onto the adjacent Former Coastal Oil Site, a former fuel storage facility. Massport, in agreement with the United States Army Corps of Engineers (USACE), sponsored a program to deepen the main ship channel into Boston Harbor. As part of this partnership, Massport committed to providing two Berths with a minimum berthing depth of 50’. One of the berths was to be new construction (Berth 10) and the other was a rehabilitation and strengthening project to upgrade the existing Berth 11.
Berth 11 has been in use since World War II and was originally of completely timber construction. The original design draft for the facility was -40’ Mean Low Water (MLW). In the early 1980’s, the berth was retrofitted with a concrete deck. As part of this retrofit, high-capacity concrete crane beams supported by steel piles were added to support low-profile ship-to-shore container cranes. In 2001, bracing was installed on the outshore crane beam piles to allow dredging down to 45’ MLW. In 2018 the berth was improved again, as part of the Initiative, allow further deepening to -50 Mean Lower Low Water (MLLW).
During initial site investigations, shallow rock was encountered. This shallow rock quickly turned a dredging project into an underwater rock removal project. Underwater rock removal requires a much higher level of scrutiny from environmental regulators, due to risks of impacts to marine life. Extensive studies and mitigation strategies were required to be implemented to minimize the overall impact of the project to the marine environment. Additionally, due to the rock’s close proximity to existing structures, constraints were required to limit the vibrations generated from underwater blasting and prohibitions on the use of explosives to fracture rock nearby existing structures were required. As such, a combination of blasting and mechanical rock removal was required to advance the various projects of the Initiative in this location. This paper will discuss regulatory permitting as well as design, construction and final certification of berth depth.

How does this project / topic contribute to the advancement of the industry and profession?: As vessels get larger the need for deeper ports is required. Rock which historically has not been an issue is now becoming an issue as ports seek to provide deep draft berths for the vessels. The regulatory and planning requirements are much more significant than just improvement dredging. This project steps through the regulatory requirements as well as the planning.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: Underwater rock removal is much more involved and the requirement to minimize impacts to aquatic life is something that is still being evaluated and required multiple various measures to be implemented prior to blasting (mammal observers, fish startle systems, scare charges/ blasts).

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: The regulatory and planning requirements are much more significant than just improvement dredge projects. This topic helps steps through the regulatory requirements and regulatory approvals required prior to allowing rock removal, how to limit blast sizes while monitoring adjacent structures to ensure no damage, and the planning from drilling initial holes through the transfer of charges onto the water, then into the hole, and finally blasting and confirmation survey.

Who is the target audience for this paper?: Engineers, Designers, Planners, Regulatory Permitting, Port Directors, Port Terminals