Laboratory Testing of Soil-Structure Interaction on Rock Dump Carpets-Paper

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The study investigates the sliding resistance of steel plates on rock-dump carpets, which is important for predicting the movement of offshore pipeline end structures on improved seabeds. Laboratory tests used a 400 mm-deep bed of loose, dry red granite. Five plate types—plain, rusted, and three perforated designs—were tested under downward pressures of 2.5–20 kPa and pulled horizontally at a constant rate.<br /><br />Measurements included pulling force, plate settlement, rock heave, and surface damage. Pulling force fluctuated considerably as rock-plate contact points changed and particles rolled beneath the plate; sudden settlement often coincided with drops in resistance. Despite these fluctuations, the calculated friction coefficient was largely independent of applied pressure.<br /><br />Average friction coefficients were 0.47 for plain steel, 0.58 for rusted steel, 0.58 for the plate with one large perforation, 0.50 for the five-hole plate, and 0.51 for the nine-hole plate. The large perforation allowed rock to protrude through the plate, producing the greatest resistance alongside rusted steel. Peak resistance was generally mobilised after only 0–12 mm of horizontal displacement.<br /><br />Profilometer measurements identified scratches but showed that rock-induced plate damage was limited, typically less than about 0.15 mm deep. The results demonstrate that plate surface condition and perforation geometry can influence sliding behaviour, while also highlighting the complex, variable interactions between plates and loose rock.

Keywords

sliding resistance

steel plates

rock-dump carpets

friction coefficient

offshore pipeline

granite bed

perforated plates

plate settlement

surface damage

rusted steel