Alternative HDD Construction Method for Ocean Outfall


Alternative HDD Construction Method for Ocean Outfall

Authors:

Craig Camp, GHD, San Diego, CA US
Sharron Lynn, City of Rehoboth Beach< br> Kelvin George, GHD
Nick Strater, Brierley Associates

Abstract: On August 14, 2017, the Rehoboth Beach Commissioners unanimously approved awarding four bid packages to various contractors to begin construction on an ocean outfall project. The four bid packages were treatment plant improvements, effluent pump station, on-shore pipeline, and offshore pipeline including a diffuser. The pipeline shore landing design required a horizontal directional drilling (HDD) installation to reduce surface impacts to Rehoboth Beach.

This paper will briefly introduce the purpose and design of the project including the imposed construction season and environmental concerns. The project design included pipeline routing, construction alternatives, and regulatory requirements. One of the biggest impacts to the project was construction season, which required winter marine work and the system operational by June 30, 2018. The winter of 2017-2018 was most notable for four nor’easters in March, which directly affected marine construction.

The paper summarizes the offshore construction and the lessons learned by Manson Construction and sub-contractor the HDD Company. Construction included installation of 6,000 feet of outfall and diffuser. HDD installed 3,800 feet of the offshore ocean outfall pipeline, consisting of 24-inch HDPE. Construction of the marine outfall commenced in November 2017 following review of the submittals. The Contractor elected to construct the project in a manner not specifically included in the bid documents, using a forward push casing installation intended to reduce the need for offshore equipment support. The combination of these events and decisions lead to several significant challenges for the contractor, which required offsetting the alignment, and re-drilling 1,200 feet of the borehole.

Publication Date: 2019

Presented at:
NASTT’s 2019 No-Dig Show Chicago, Illinois
March 17-21, 2019 | Paper Number: MM-T2-03


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