Modelling the degradation of penetration resistance during cyclic T-bar tests in a Gulf of Mexico clay

Installation and repetitive movement during the operation of a pipeline causes remolding and softening of the surrounding soil. Similar effects can occur around foundations during their operating life. The degradation of the undrained shear strength of soft clays near the seabed is a critical component of the design of subsea facilities, including pipelines and shallow foundations. This paper presents a two-stage strength degradation model based on the framework developed by Hodder et al. (2010) for repeated vertical movement of a cylindrical object (T-bar penetrometer) embedded in a soft Gulf of Mexico (GOM) clay. The model is compared with the behavior observed in four box cores sampled in the Gulf of Mexico, in which 8 cyclic T-bar penetrometer tests were performed. By varying the parameters in the strength degradation model, its applicability for GOM clay is examined, and the effects of the location of cycling within the box core and parameter variability between box cores relative to the average parameters are explored.