Responses of Shallowly Buried Flexible Pipes under Static Live Loads

A large number of flexible pipeline structures exist under roadways. When the cover thickness over the pipeline is limited, effects of live loads can be more pronounced on the structure, especially when a relatively heavy vehicle is moving at low speeds or comes to stop over it. There is a need to address the topic of this paper because only a small number of publications made about buried flexible pipes have paid attention to their performances under static live loads. In this paper, first a few published field tests are examined to find out how shallowly buried flexible pipes respond differently to live loads than to the dead loads. In the second part of the paper, new equations are derived so that the deflection responses of a shallowly installed flexible pipe can be estimated under a static live load. The new equations fill a gap that currently exists in the AASHTO LRFD Bridge Design Specifications. The new deflection equations produced mixed results when their estimates were compared to the field test pipe deflection measurements reported in the literature. This may be partially because of the way the loading tests were carried out in the field. The new equations point out the importance of having a stiff layer above the pipe when the cover thickness is very limited.