In the late 1990s, the Washington Department of Transportation undertook a series of new culvert installations and replacement projects in Renton.
The objective of the work was to support the migration of salmon fish upstream of local tributaries for conservation purposes.
The projects were conducted along Service Road, which is a four lane highway road parallel to the Pacific coastline. This project called for the installation of a 1.8 meter diameter, 65 meter long culvert using a trenchless technology method.
The crossing was to take place where the elevated highway traversed a flood plain. A similar project was conducted a year earlier near Everett, utilizing a microtunneling method.
However, the microtunneling boring machine (TBM) used on that project encountered various obstacles immediately below the road surface such as tree trunks, boulders, concrete blocks, and old rail cars, which the contractor used with locally available materials as fill materials when the highway was originally built.
This resulted in significant construction delays, cost overruns, and claims. The TBM got jammed and required the initiation of a costly recovery operation using a pipe jacking technique.
In an attempt to avoid the repeating of such difficulties, an innovative subsurface utility engineering investigation was developed and executed. The investigation consisted of three bores directionally drilled across the highway.
One of these bores was located along the proposed centerline of the new culvert, while the other two were placed 6 foot north and south of it. A 4 inch polyethylene conduit was installed in each of the bores.
A suite of geophysical tools, including borehole ground penetrating radar, induction, gamma, and seismic were used to conduct cross-bore studies.
The results from the different studies were correlated with each other, as well as with observations made during the HDD drilling (i.e. locations along the bores where obstacles were encountered).
Twenty one possible targets were identified along the proposed centerline.
However, the alignment 6 foot south of the proposed centerline had only six obstacles identified. Thus, the culvert alignment was moved 6 foot south, and the project was completed successfully using pipe ramming.
Keywords: Highways/roads/intersections; Electric lines; Design/redesign; EM (Electromagnetic) induction; Gamma rays; GPR (Ground Penetrating Radar); Seismic waves; Crossbores, drilled (QL-B)