Between a Track and a Hard Place—Thrust Restraint Alternatives in a Constrained Location

To make way for the redevelopment of Denver Water’s 35 acre Operations Complex, a 54-inch reinforced concrete cylinder pipe (RCCP) water transmission conduit required relocation, including the addition of an isolation valve and two new 90-degree bends to realign around planned buildings. The joints in the 1930s-era pipe were not restrained so the design required extensive analysis of thrust forces and evaluation of thrust restraint alternatives to prevent movement in the existing joints of the 80 year old Conduit No. 18 pipeline operating at 200 psi. The upstream end of the relocation connected to a section of pipeline that passed below multiple active railroad tracks. Relocation to replace the existing pipe under the railroad was not feasible. Traditional thrust blocks were not feasible due to site constraints and subsurface conditions. To address the thrust restraint, the segment beneath the railroad was sliplined with steel pipe designed to carry the full thrust of internal pressure and external loads from the rail traffic. This paper discusses the thrust force analysis, thrust restraint alternatives that were considered, and site constraints that had to be accommodated to develop a successful solution for the necessary relocation.