Drained Axial Pipe-Soil Resistance at Low Confinement Using Tilt Table and Direct Shear Tests

Establishing a reliable value for the axial pipe-soil interface resistance is critical for the design of offshore pipelines. Over the last few years, several independent research groups have modified existing methodologies or devised new testing setups to further develop our understanding of the behavior of the pipe-soil interface at low contact stresses. The most common laboratory experimental methods adopted have been based on either tilt table tests or interface direct shear tests. However, a direct comparison between the results of these two testing methodologies has not been established. This paper aims at designing and fabricating a tilt table and interface direct shear setup capable of accurately estimating the drained interface resistance at low normal stresses, in addition to comparing their results under identical testing conditions. Both setups tested the drained clay-solid interface response by varying the soil composition (high and low plasticity clay), the interface roughness (smooth and rough), and the normal stress range. Results showed that the drained residual failure envelopes for the clays and clay-solid interfaces were nonlinear and could be modeled by a simple power model. The interface response was clearly dependent on the interface roughness, particularly when the roughness was normalized with the mean grain size. In the case of smooth interfaces, identical friction angles were obtained from the tilt table and the interface direct shear, whereas in the case of rough interfaces, the interface direct shear yielded lower friction angle values.