CONCRETE PIPE Loads on Jacking Pipe Two types of loads imposed upon concrete pipe installed by the jacking method are the axial load due to the jacking forces applied during installation and external earth and live loads. Did You Know? Based on the pipe size and wall designation, Lafarge can calculate the maximum jacking force permissible for a given project upon request. This is accomplished following ASCE 27-00 “Standard Practice for Direct Design of Precast Concrete Pipe for Jacking in Trenchless Construction”. Here, a concentrically loaded condition is compared against an eccentrically loaded condition, with the more conservative force governing. Axial Loads The axial or thrust loads are transmitted from one concrete pipe section to another through the joint surfaces. To prevent localized stress concentrations, it is necessary to provide relatively uniform distribution of the axial loads around the periphery of the pipe. This is accomplished by assuring that the pipe ends are parallel within the tolerances prescribed by ASTM standards, using a cushion material, plywood, between the pipe sections, and care on the part of the contractor to insure that the jacking force is properly distributed through the jacking frame and parallel with the axis of the pipe. The cross-sectional area of a standard concrete pipe wall is more than adequate to resist stresses encountered in normal jacking operations. For projects where extreme jacking pressures are anticipated due to long jacking distances or excessive unit frictional forces, intermediate jacking stations may be used, and greater care taken to avoid bearing stress concentrations. Earth Loads The major factors influencing the vertical earth load on pipe installed by jacking are: • Weight of the prism of earth directly above the bore • Upward shearing or frictional forces between the prism of earth directly above the bore and the adjacent earth • Cohesion of the soil Live Loads Jacked installations are generally constructed at such depths of cover that effects of live loads are negligible. Highway and aircraft loads are considered insignificant at depths greater than 3 meters (10 feet), however, railroad loads are considered up to 9 meters (30 feet of cover). Additional information on live loading can be found on page 31 of this manual. PAGE 44 LAFARGE PIPE eMANUAL