ABSTRACT Full scale pipe-soil interaction tests to determine soil resistance to lateral motions of untrenched pipelines have been carried out with a specially built laboratory test facility. Four typical offshore soil types were tested: loose silty fine sand, medium/ coarse sand, soft clay and stiff clay. The test facility allowed for a force/displacement controlled regular/irregular time history. High priority was given to soil preparation and control. Sufficient uniformity and repeatability were successfully achieved for each soil. The main results were: small oscillatory motion generally increases the resistance in loose medium/ coarse sand and soft clay, large-amplitude oscillications may degrade resistance in loose silty fine sand, resistance in dense medium/coarse sand and stiff clay is less sensitive to prior cycling, consolidation on clays increases the resistance to monotonic loading but the increase is quickly broken down by cycling. INTRODUCTION Hydrodynamic forces generated by waves and current are often the design loading for the weight coating specification for untrenched pipelines. The resulting conditions may be such thatLoads are totally balanced by the lateral soil resistance.Loads are balanced partly by the lateral soil resistance and partly by pipe inertial force. (Some pipe movement occurs.) The present state of the art in pipeline design is to idealize resistance as Coulomb friction with friction coefficients selected by whether the soil is cohesionless (sand) or cohesive (clay). To improve the pipe-soil interaction experimental data base and the understanding of pipe-soil interaction this project was initiated in late 1983 as one part of a comprehensive pipeline on-bottom stability study. The total project was performed at the Norwegian Hydrotechnical Laboratory, NHL, (Affiliated with SINTEF) for Esso Norge and Statoil with technical assistance from Exxon Production Research Company. The tests described herein- were carried out from August 1984 to June 1985. TEST SETUP Test Pipes Four 1.6 m long half cylinders, made up of a 4 mm thick metal plate were used for the pipe sections. The outer diameter of the pipes were 0.5 m and 1.0 m. The end walls had screened openings, so that the water level inside the pipe section adjusted quickly to the outside water level, to ensure that constant buoyancy of the test pipe was maintained during its vertical and horizontal motions. The surfaces of the test pipes were prepared to simulate concrete coating roughness. Test Rig Figure 1 shows the test set-up, including the pipe, the test rig, and the soil flume. Figure 2 shows in more detail sketches of the test rig, including the placement of the force and position transducers. The Test rig facilitated the transfer of horizontal and vertical forces to the pipe. It provided a reference for the horizontal and vertical force measurements and the horizontal and vertical movements of the pipe. The test rig consisted of a steel carriage (length x width x height = 3.3 × 3.3 × 2.0 m) made up of square.