Experimental Full Scale Tests on Shallow Buried Pipes under Live Load Conditions

Shallowly buried pipes are used as culverts crossing under roads and railways, and for pipelines along main roads. To investigate the load distribution on shallow buried pipes and develop recommendations for their design a research project was funded by the Ministry of the Environment in the state of North-Rhine Westfalia, Germany. The research program consisted of experimental full-scale tests in a large testing facility (6 m×6 m×15 m) at Institute for Underground Infrastructure (IKT), finite element analyses (FEA), and the verification of the loading approaches and calculation schemes used in current German standards. During the experiments various pipe materials were used including concrete, ductile iron, and polyethylene. The main goals were to determine: the vertical and horizontal earth pressure; the stress distribution induced by vehicle loads; the influence of wheel positions and load configuration; the influence of the pavement type; and, the general behavior of the pipe-soil system under impact loads. The main results are as follows: for shallowly buried pipes, the pipe crown is the zone of critical stresses. Soil stresses in tests were similar for the concrete pipe, but lower for flexible pipes when compared with theoretical approaches. Pipe deflections were lower than expected. A time dependent increase of pipe stresses was observed. The pavement type is of significant influence for the pipe stresses. The longitudinal behavior under live loads depends on the pipe type. Soil stresses increase under cyclic loading. The pure Boussinesq approach has been modified in the German code for structural calculation. A load distribution model has been developed instead to consider the supporting behavior of the side fill.