Design and construction of directional drilling crossing project for large-diameter pipeline in complex stratums

As one of the construction items of the 2nd West-to-East Gas Pipeline, Jushui crossing project with directional drilling way was carried out, with the specified design pressure 10 MPa and pipe diameter 1219 mm. The one-crossing method designed in original crossing scheme was failed when the pipe was towed back at the interface of soil layer and rock layer. A modified scheme was presented by re-drilling at a parallel location 10 m right away from previous point along air flow direction, applying opposite-direction drilling. Also, by excavating at the other end, using tampering casing and injecting grouting to consolidate the loose soil layer, the drilling succeeded finally. Analyzing the failure reasons, the unsuccessful backtow was from the step-shaped curve at the interface of soil layer and rock layer, which resulted from nonconsolidated soil layer, too large drilling diameter and the heavy bore-expander. For large diameter drilling crossing the soft-hard alternating layer, the soil layer had to be consolidated, the bore expansion, repair, clean and towback should proceed continuously. In special cases, the shut-down time for towback should not more than 4 hr.