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HomeMy WebLinkAbout20210755 269 Broadway Site Plan Terracon Secant Pile Wall Comments-Attachment 2 April 7, 2022 1��rr�con Prime Group Holdings, LLC GeoReport 85 Railroad Avenue Saratoga Springs, NY 12866 Attn: Mr. Gerard Moser e: gerard.moser@goprimegroup.com c/o Mr. Michael Roman, RA, AIA C2 Design Group Re: Secant Pile Wall Discussion 269 Broadway Saratoga Springs, NY Terracon Project No. JB205029 Dear Mr. Roman: At your request, Terracon Consultants—NY, Inc. (Terracon)virtually attended a conference call held with City of Saratoga Springs officials and members of the design team on April 1,2022.The purpose of the meeting was to review comments offered during plan review by the City's designated engineer, CHA, and to have a general discussion regarding the design team's approach to the project. As the Geotechnical Engineer of Record for the project, Terracon provided commentary related to the suitability and design of the building's proposed foundation and support of excavation system. In evaluating potential options for the permanent below grade building foundation walls and support of excavation system (SOE), several factors were considered: Subsurface soil, bedrock and groundwater conditions encountered in test borings advanced at the site Proximity of the planned building to adjacent property lines, existing structures and roadways The depth of excavation planned at the site Effects that dewatering operations, both during construction and in the final condition, may have on adjacent properties Review of development approaches in the immediate project vicinity, including at the Park Place Condos and current Rip Van Dam Expansion Availability of suitable contractors to construct the selected foundation and SOE . Performance of similar foundation and SOE designs in the greater Capital District Through review of these factors, the design team selected a secant pile wall system to provide both temporary excavation support and to serve as the permanent below grade building foundation walls for this project. Terracon Consultants-NY, Inc. 30 Corporate Circle, Suite 201 Albany, New York 12203 P (518) 266 0310 F (518) 266 9238 terracon.com � � Secant Pile Wall Discussion 1��rracon West Hempstead CSD Saratoga Springs, NY GeoReport. April 7, 2022 Terracon Project No. JB205029 As discussed during the meeting and subsequently provided by Keller, the secant pile wall option provides significant benefits for this project, including: ■ The secant pile wall can be constructed from existing site grades, which minimizes the amount of excavation required close to neighboring properties ■ The secant pile wall can be constructed with equipment stationed inside of the project site boundaries, without impact to adjacent properties The secant pile wall will act as first the temporary support of excavation during excavation of the below grade parking, and then as the permanent below grade building foundation walls upon which the building will be supported. The secant pile wall will be installed about 5 to 10 ft into the underlying bedrock to create a "bathtub" from within which soils will be excavated to design depths for construction of the below grade levels. Dewatering during excavation will essentially be limited to the volume contained within the "bathtub," thus reducing the impact to neighboring properties from dewatering operations. As discussed during the conference call, the feasibility of the secant pile wall system was vetted by the design team and developer and selected as the recommended approach for this project. We plan to advance additional test borings and install instrumentation to further define the subsurface conditions at the site for use in completing the design. Our design will include recommendations for pre and post condition building/property surveys along with an instrumentation and survey monitoring program to monitor the performance of the secant pile wall and dewatering operations during construction. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us. Sincerely, Terracon Consultants-NY, Inc. � �����'��. Joseph Robichaud, Jr., P.E. John Hutchison, P.E. Principal / Office Manager Sr. Geotechnical Engineer SME Review by: Darrell Wilder, P.E.