Careful Monitoring Keeps Tunnel on Track—Microtunnel Installation in Flowing Sands Beneath Critical Structures

摘要

To meet increasing demand, the City of East Chicago is constructing a new water treatmentrnplant (WTP) designed to treat raw water from Lake Michigan. As part of the overall project a 900-foot gravityrnpipeline was required to convey raw water from an intake structure to the new WTP, which has been successfullyrnconstructed using microtunneling techniques. A 72-inch internal diameter Permalok steel casing was utilizedrnfor installation of the 48-inch internal diameter Hobas carrier pipe. The pipeline was constructed in two separaterntrenchless drives with Drive 2 being the longest and most sensitive. Drive 2 was approximately 760 feet inrnlength and completed through clean, poorly-graded sand below the groundwater table. The drive passed beneathrnseven sets of railroad tracks spanning approximately 140 feet; multiple utility lines that included water, electric,rngas, and telecommunications up to 48 inches in diameter; and approximately 300 feet of Indiana Department ofrnTransportation right-of-way including a highway off-ramp, with associated shallow foundations, and both thernnorth and south bound lanes of Cline Avenue. Due to the propensity for settlement when dealing with runningrnand flowing sands, an extensive geotechnical instrumentation program was conducted during mining. Thisrnpaper will focus on the steps taken by the Owner, Engineer, and Contractor to form effective relationships withrnthe utility and railroad companies to reduce the probability of ground movements, including the use of Drive 1rnto troubleshoot and eliminate issues/problems with means and methods before performing Drive 2.