MTA Purple Line Tunnel Shaft Project

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The Challenge

Purple Line: $2.2B, 16-mile light rail for Bethesda, Silver Spring, Takoma/Langley Park, College Park, and New Carrollton.
Plymouth Street Tunnel: Starts at Manchester Place, runs under Plymouth Street to proposed station.
Tunnel Location: Poor RQD bedrock complicates recovery and lab testing

The Purple Line is a proposed $2.2 billion, 16-mile light rail transit project that will provide faster, more direct service for the citizens of Bethesda, Silver Spring, Takoma/ Langley Park, College Park, and New Carrollton. The proposed Plymouth Street tunnel would begin at Manchester Place, and then run under Plymouth Street to the proposed station at Manchester Place. The proposed location of the Plymouth tunnel would pass through bedrock with poor RQD which caused issues for recovery and lab testing.

TBD

The Solution

GeoTesting Express (GTX) was delivered multiple rock cores of material by the client. Upon initial sample inspection, it was clear that a large portion of the material was damaged. We were able to implement the necessary precautions to the samples to ensure that there was minimal sample loss during the course of the project. The client was aware of the fragile material and was satisfied with our approach and consideration we were able to give to each sample. Close communication with the client about which samples could and could not be tested had to be established at an early stage of the project. The cores that were provided were one inch diameter, highly weathered Granofels.

The dimension of the core provided problems as most of our equipment and training was based off of the typically tested NX and NQ core. The ability for our technicians and equipment to adapt to the different core sizes proved to be vital in meeting the clients expedited time line. The standard procedure for achieving the end flatness and parallelism for unconfined compression testing had to be altered to achieve the necessary tolerances.