Geotechnical engineering services to support replacement of the existing seawall along Manet Avenue in Quincy, Massachusetts.
The project consists of the design and construction of a new seawall in rough alignment with the existing seawall along the northwest slope of Houghs Neck. The proposed replacement seawall will be supported by a concrete pile cap bearing on micropiles. An impervious steel sheet pile will be constructed within the approximate middle of the concrete pile cap.
Designs currently anticipate the proposed wall to have a top of pile cap at El. 9 feet, which will support three phases of construction of precast concrete blocks. Phase 1 will consist of a precast concrete seawall built to El. 13, Phase 2 built to El. 15, and the final Phase 3 built to El. 18.
challenges
- Sections of the wall are directly adjacent to existing homes, limiting construction activity, support of excavations, and foundation options.
- Retaining walls had to be designed for lateral shears and moments in two directions, one to support retained soil, and two to resist the high lateral loads of waves in the extreme conditions.
- Due to proximity to the ocean and groundwater, seepage and scour under the seawall had to be considered.
solutions
- In order to limit vibrations and potential damage to the existing homes, drilled solutions were recommended for both the foundation options and any potential support of excavations needed during construction.
- Due to the high lateral loading, two (2) rows of micropiles were recommended at various sections along the seawall. Installation of the micropiles would also cause minimal vibrations.
- A finite-element seepage evaluation was performed along the proposed seawall. Based on our evaluations, a minimum sheet pile length of 25 feet below bottom of pile cap was recommended to provide seepage cutoff.
results
The design team was able to communicate to understand the project requirements and constraints, then worked together to provide a safe and cost-effective solution for the client.