Washington Avenue Tunnel Project: Fortifying Aging Underground Infrastructure

"The Washington Avenue tunnel in Kingston, NY was completed in 1912 to convey combined storm water and sanitary sewage. Over a mile in length, the tunnel was driven almost entirely in bedrock, with the exception of an approximately 170 foot long brick arch segment constructed in soil. About 90 years after the tunnel was put into service, persistent subsidence problems and sinkholes were observed in Washington Avenue above the shield-driven soil tunnel segment, eventually causing the important traffic thoroughfare to be closed. Subsequent tunnel inspections revealed a breach in the brick arch and a significant volume of fine soil within the tunnel. A two-phase remediation program was implemented to control seepage, reduce soil migration, and remedy sinkhole problems. The first phase included in-situ soil densification by vibratory pile probe driving to improve density in shallow sandy soil loosened by ground loss. The second phase included installation of a continuous soilcrete arch structure over and alongside the tunnel, extending to rock or compact glacial till and spanning the length of the soil tunnel segment. Overlapping vertical soilcrete columns were installed through interlayered sandy and clayey silt by jet grouting to form a continuous arch structure, using grout parameters verified by full scale field testing.PROJECT BACKGROUNDThe Washington Avenue tunnel in Kingston, NY (Figure 1) was completed in 1912 to convey combined storm water and sanitary sewage to Rondout Creek by the Board of Water Supply of the City of New York. The tunnel is over a mile in length and constructed primarily in rock. Contract documents indicate the tunnel was designed with a horseshoe shape at least 3 ft wide and 5.5 ft high."