Under contract with MSD in FY 2012 to provide General Engineering Services (Geotechnical), Geotechnology, Inc. performed drilling, laboratory testing and engineering services and submitted geotechnical data and interpretive reports to the MSD Engineering staff preparing the preliminary design of approximately 7,340 linear feet of sanitary sewer pipe in tunnel with four drop shafts and appurtenances. The purpose of this tunnel is to eliminate the combined sewer overflow (CSO) that discharges into Gingras Creek. The tunnel alignment extends generally from the Hillcrest Apartments south of Interstate I-70, northward under I-70, the Lutheran North High School Athletic fields, the Lucas & Hunt Village Apartments, the Lucas & Hunt Road Right of Way, the Memorial Park Cemetery, The Village of Country Club Hills (Municipal Park), and the McLaran Avenue right-of-way in north St. Louis County, Missouri. The tunnel flowline will be approximately 24 to 116 feet below the existing ground surface. It is anticipated that the tunnel will be excavated using a Tunnel Boring Machine (TBM).
TBM launching and termination shafts are planned at both ends of the tunnel. In addition, two drop shafts are planned one near the Lucas & Hunt Village Apartments and one near the intersection of McLaren and Esterbrook Drive along the proposed tunnel alignment.
The field exploration consisted of drilling seven borings along the tunnel alignment to auger refusal, performing Standard Penetration Tests (SPT’s), obtaining split spoon and Shelby tube samples of soil overburden and coring rock using double tube NX wireline methods. Temporary monitoring wells were installed in to obtain groundwater level measurements at intervals following completion of drilling. Packer tests were performed select borings to measure the hydraulic conductivity of rock.
Laboratory tests included visual classification of soil sample (ASTM D 2488), natural moisture content (ASTM D 2216), unit weight of relatively undisturbed soil samples, liquid and plastic limits (ASTM D 4318), unconfined compression tests (ASTM D 2166), consolidated-undrained triaxial tests (ASTM D 4767), uniaxial compressive strength of rock (ASTM D 2938), and liquid and plastic limits of shale (USACOE EM 1110-2-1906).