Erosion properties of mud beds deposited in laboratory settling columns

Work has been conducted at Oxford University using H.R. Wallingford's Instrument for measuring Shear stress In Situ (ISIS). The first several experiments show that the equipment is working well in a column setup. Each bed tested is initially eroded by a distinct critical shear stress, or erosion threshold, which may depend on the properties of the mud and the length of consolidation time. The beds seem to erode in a laminar fashion, until at a very high shear rate a large (2 to 3 cm) liquified section of the surface gives way. Contrary to what might be expected, the beds become less resistant to erosion as they mature. It is proposed that the development of a biochemical surface layer, often containing gas, and the feeding and soil reworking by marine worms contribute to this weakening over time.