Permeable Bedrock Challenges at the Bucklin Point WWTF Expansion Clarifier Support of Excavation-PPT Presentation

PPT Presentation

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The Bucklin Point Wastewater Treatment Facility expansion in Pawtucket, Rhode Island, is part of the Narragansett Bay Commission’s Phase III Combined Sewer Overflow program. Keller provided support of excavation (SOE), dewatering, grouting, and micropile work for the clarifier expansion.<br /><br />The initial design assumed sheet piling driven to bedrock would largely cut off groundwater, with only limited seepage manageable by pumps. Additional investigations and drilling revealed significant water loss into fractured bedrock. Pump tests showed that the rock was far more permeable than the overlying silt and glacial till, with hydraulic connection between the excavation and the Seekonk River. This created a risk of inadequate bottom stability and made deep-well dewatering challenging because of river interaction, permitting, cost, and construction constraints.<br /><br />The team selected a grout curtain to reduce water flow through the upper 30 feet of rock. Keller developed and stamped the grouting procedure, using microfine and Type 3 cement mixes with additives. Grouting took place in two stages from March to June 2024, with primary, secondary, and tertiary holes drilled around the excavation. The expanded scope also included toe pins, dewatering and piezometer wells, tiebacks, and foundation micropiles.<br /><br />In total, the project used 27,425 cubic feet of grout across the grout curtain, micropiles, toe pins, and tiebacks. Keller completed 900 linear feet of sheeting, 79 toe pins, 179 rock-grouting locations, and more than 600 micropiles across the clarifier, pump station, and UV building. Work required careful sequencing and coordination around active plant utilities, existing loaded tiebacks, and other contractors.

Keywords

Bucklin Point

Wastewater Treatment Facility

Pawtucket Rhode Island

Narragansett Bay Commission

Combined Sewer Overflow

Support of Excavation

Grout Curtain

Micropiles

Dewatering

Clarifier Expansion