The Blacks Run Interceptor – Division 1B – Replacement project scope included 3,700-lf. of 48-in. sanitary sewer installed by open-cut and trenchless methods. A 200-lf. section that crossed under Stone Spring Road requiring a tunnel boring machine to maintain traffic on a busy arterial roadway.
• 72-in. steel casing to house a 48-in. sanitary sewer interceptor
• Critical line and 1.02% downhill grade • Limited geotechnical information available
• The test bore showed the presence of lean clay, soft weathered rock, limestone, dolomite at launch and exit shafts
• Strict timeline was in place for the tunnel to keep pace with the open-cut operations going on elsewhere on the project site
• Groundwater encountered at the half-way mark during the downhill run
Akkerman supplied a powerful TBM with a mixed-face disc cutter head mixed-face disc cutter head capable of 24,000 UCS psi to tackle the varied ground conditions.
• Full-face of rock was encountered at various sections of the tunnel, but the mixed-ground cutter head and TBM system tackled it without issue
• The tunnel was completed on line & grade and on time for crews to go home for Christmas.
