An extensive full scale experimental program for investigating pipe performance in soil was carried out at C-CORE, as part of a large international research project on soil-pipe interaction. Various soil materials, soil-pipe relative flexibility and loading mechanisms were considered. The experimental testing program comprised 24 tests of axial and lateral pipeline soil interaction. The tests were conducted in C-CORE's full-scale pipeline/soil interaction test facility, which includes a well-serviced laboratory containing a plywood-lined testing tank, with reaction wall, actuators and mobile gantry crane.
A series of lateral loading tests were conducted, using sand and clay soils. The sand was well-graded with a maximum grain size of 4-5mm, a uniformity coefficient of 4, and a coefficient of curvature of 0.8. A series of tests were performed for a rigid pipe buried in both loose (approximately 0% relative density) and dense (approximately 100% relative density) sand. The clay was a Grade D kaolin with a liquid limit of 56%, a plastic limit of 31% and a specific gravity of 2.66. This clay was reconstituted from powder at either a 33% or 37% water content depending on whether soft or stiff soil conditions were desired.
To displace the pipelines, actuator rods (2" diameter) were each connected via an in-line load cell to an actuator system comprising a high-torque, low power electric gear motor and a 35 tone Duff-Norton screw actuator. The speed control utilized two frequency inverters connected in a master/slave configuration. A shaft mounted encoder on each motor provided closed loop speed regulation. Each actuator incorporated a set of limit switches. Electronic as well as passive instrumentation were used during each test. The force-displacement response of the pipelines was monitored using 2 load cells and 2 displacement transducers. Pore pressure and contact pressure transducers were placed in the soil bed, on the tank walls and on the pipe surface. An ultrasonic surface profiler surveyed the testbed surface throughout each test. Movements were measured within the testbed using anchors embedded at discrete locations, connected to external linear string potentiometers through flexible soft plastic tubing. Vertical deformation tubes were driven into the testbed to measure deformation profiles. The deformation tubes consisted of flexible plastic tubing connected to a metal tip. Following the test, the tubes were injected with a fiberglass resin which was allowed to set overnight. A staged excavation permitted the profiles of the tubes to be recorded. The pre and post test positions and inclinations of all the displacement tubes were surveyed.
The experimental program included also tests of axial loading of a rigid pipe in clays and sands, and moment loading of a flexible pipe in dry and saturated sand. The experimental program is on-going.