SPECIFYING AND VERIFYING CONSTRUCTION PERFORMANCE FOR REMEDIAL CAPPING-A CASE STUDY FROM SAN DIEGO BAY, CALIFORNIA

摘要

A sediment remediation project is currently being completed by the Unified Port District of San Diego at the former Campbell Shipyard site on San Diego Bay. Following site demolition and localized dredging, the project involves the construction of a sediment isolation cap comprised of multiple layers: a filter fabric base, a 0.6-meter (2-foot) layer of sand for chemical isolation, a layer of filter gravel and a protective surface layer of armor rock.This project serves as a case-study example of the key considerations that are involved with designing and preparing bid specifications for construction of a complex sediment remediation cap under challenging conditions. This paper also discusses various methods used by the Port and its design engineer to oversee and verify the Contractor's work, so as to ensure that the remedial cap meets project specifications.Project specifications were generally written to identify minimum performance criteria rather than specifying contractor means and methods. It was the Contractor's responsibility to determine the equipment and methods they would use to effectively achieve the required performance criteria. The specifications also required the initial construction of an initial "Pilot Cap" area, to demonstrate the Contractor's abilities to construct the cap to meet the performance criteria using the Contractor's proposed methods. During the Pilot Cap construction, the Contractor's initial technique of placing sand material resulted in significant amounts of overly-thick cap. Since then the Contractor has continued to refine their placement methods to provide tighter control of cap thicknesses.Several monitoring methods were employed to measure and verify the accuracy of the capping operations. The Contractor provided daily progress bathymetric surveys that depicted the overall thickness of the materials placed and their surface elevations. The Port evaluated these surveys in conjunction with dive inspections and sediment probing of the placed cap thicknesses. Dive inspections were also used to evaluate whether previously-placed layers were being excessively disturbed by the ongoing work.