Meyer, V. (ed.), Frontiers in Offshore Geotechnics III: proceedings of the Third International Symposium on Frontiers in Offshore Geotechnics (ISFOG 2015), Oslo, Norway, 10-12 June 2015, CRC Press, Boca Raton, pp. 405-410.
10 Jun 2015
This paper presents a new torsional shear device for interface shear testing of natural and disturbed soils, relevant to the design of hot-oil pipelines. We describe the design of the machine and present test results on samples obtained from North Sea and offshore West Africa locations. This machine is used to obtain pipeline interface strength values of very soft marine samples under axial stress conditions from 2 kPa to 50 kPa with shear speeds ranging from 0.0005 mm/s to 0.5 mm/s. Both monotonic and cyclic tests can be undertaken with cumulative shearing distance only limited by a specified test duration. The tests presented in this paper were undertaken at shear speeds of 0.001 mm/s and 0.1 mm/s using two interfaces of average roughness 0.3μm and 6.1μm. The results show a clear difference in interface friction between the two offshore locations, with the West African sample generating a consistently higher interface friction. All tests undertaken at the faster shear rate exhibited a well-defined peak strength before softening to a residual value. Results of macro imaging analysis and particle imaging velocimetry of sheared samples are also presented, which permit the association of the peak strength, break out behaviour and residual strength with observed micromechanical processes present during each stage of shearing.