Watson Way Project: Microtunneling Lessons Learned or Revisited?

摘要

Although neither large nor complex, the Watson Way microtunneling project provided some interesting challengesrnduring construction. As usual, some challenges were related to site and geotechnical conditions, while otherrnchallenges were related to the construction contractor’s preference on how to build the project.rnThe project involved the installation of about 3,100-feet of 8 to 24-inch diameter sewer pipeline, mostly using slurryrnmicrotunneling methods, but also reaches of horizontal directional drilling (HDD) and cut-and-cover pipeline. Groundrnconditions were generally favorable, with low groundwater head. As designed, a series of launch and receiving pitsrnwere included to limit the microtunnel drive lengths to about 400 to 600-feet. However, the construction contractorrnproposed a variety of modifications to the design, including reducing the number of launch/receiving pits, extendingrnthe tunnel drives, substituting a pipe ram for the HDD drive, auger boring one planned microtunnel reach, andrnincreasing the amount of cut-and-cover construction.rnAn interesting issue that arose was related to the heat of hydration of the annular grout around the PVC carrier pipe,rnand carrier pipe damage due to grout injection pressure. This paper summarizes the field conditions encountered,rncontractor proposed changes, and construction challenges that were overcome to successfully complete the project.rnThe paper also describes the results of full scale mock up tests to evaluate the heat of hydration within the annularrnspace.