Firstly, let me commend geoforum on this website. Exactly what I have been looking for!
Anyway, my question(s):
I am looking at the following two aspects of (offshore) pipeline-soil interaction:
1. SOIL RESPONSE DURING PIPELINE EXPANSION – a slow failure process involving up to a couple of meters of longitudinal displacement at either end of the pipeline, occurring over a period of days. The soil conditions in the areas of interest consist primarily of soft clays. 2. SOIL RESPONSE FOLLOWING PIPE-LAY ON A SLOPE – a fast failure process whereby the pipeline tries to slide down the slope immediately following ‘touch-down’ or ‘pipe-lay’. The soil conditions in the areas of interest consist primarily of stiff clays.
I am currently trying to come up with a means of mimicking these failure mechanisms in a laboratory, but have a few areas of concern. I am considering either a DSS (Direct Simple Shear) or a DS (Direct Shear) test. The main reason I have opted for these tests in place of any others is that they will allow me to fail the soil against the actual FBE (Fusion Bonded Epoxy) coated steel, or a sample of.
My first question is, which test lends itself best to each of the above failure mechanisms (1 and 2)?
My thoughts: 1.The failure process is slow, suggesting a drained test. The pipeline will have been in place on the seabed for many weeks, if not months, so it is safe to assume that a bond will have been achieved between the soil and pipeline. Perhaps a consolidated-drained test? 2.The failure process is fast, suggesting an undrained test. The pipeline will not have the chance to bond to the seabed soils - rather it will try to ‘fail’ immediately upon contact. Probably more like an unconsolidated-undrained test?
Anyone out there have any thoughts on any of the above?