Bearing capacity of embedded cylindrical object

Abstract

The bearing capacity of soft sediment on the seabed is of fundamental importance for the stability of offshore facilities. A particular issue that dictates the design process of on-bottom pipelines is reliable prediction of the embedment depth. However, the prediction is often hindered by the difficulties in assessing the undrained shear strength, su, of the marine sediment. With the advances in site characterization techniques, in particular the use of a T-shaped cylindrical full-flow penetrometer, estimation of the shear strength of soft soil has become more accurate than that measured by conventional methods. Nonetheless, related theoretical solutions for shear strength interpretation are based on idealized soil conditions, and proper use of them requires a more thorough understanding of the resistance factor that links the measured bearing resistance to undrained shear strength of the soil. This paper aims to explore experimentally the change in resistance factor of a cylindrical object mimicking a T-bar penetrometer or a pipe segment during the penetration process through a series of laboratory penetration tests. Pipe segments of different diameters have been considered to identify possible scale effects. Particular attention has been placed on the change in mechanism of the process and the associated resistance factor. Results are compared with theoretical solutions and guidance is given on the use of resistance factor at shallow depths during interpretation of T-bar penetration tests.