Hultman Aqueduct

The Hultman Aqueduct is the principal transmission pipeline servicing the Metropolitan Boston area. GEI was the geotechnical and environmental consultant on an engineering team selected to evaluate the condition of the 15.3-mile, 13.3-foot diameter near-surface portion of the aqueduct, assess the risk of its catastrophic failure, and design repair measures.

GEI’s work included review of construction data, geologic reconnaissance, observation of boring and test pit explorations, laboratory testing of soils, and static and seismic analyses.

Twenty-two borings were performed to obtain information on the character of soils supporting the Aqueduct. Cone penetration tests were also performed at the most severe leak site to obtain information on the extent of loose soils adjacent to the pipe.

Approximately 12 deep test pits were excavated to expose the pipe for evaluation of the condition of the pipe and the supporting foundation soils. Many of the test pits were excavated at locations of leaks in the aqueduct. GEI prepared geotechnical specifications for the test pit excavations and designed construction dewatering systems for four of the test pits. The dewatering systems were sized to control the groundwater as well as the leak water from the aqueduct.

GEI provided field observation services during excavation of the test pits. GEI performed testing in the test pits to measure the percent compaction of soils supporting the pipe. Repair clamps were successfully installed over leaking joints in the aqueduct.

GEI also performed seismic analyses to estimate deformations of the pipe for various earthquake levels, estimate permanent differential settlements of the pipe due to seismic straining of supporting soils, and evaluate the potential for liquefaction of soils supporting the pipe. Slope stability analyses were also performed to estimate the potential for lateral movement of the pipe during an earthquake. GEI’s analyses were used to support a probabilistic risk assessment of damage to the aqueduct.