Drag forces caused by submarine glide block or out-runner block impact on suspended (free-span) pipelines

The results of a series of physical experiments to quantify the drag force on a submarine pipeline caused by a glide block or an out-runner block impact normal to the pipe axis are presented. The experiments were conducted in a geotechnical centrifuge under submerged conditions at a centrifugal force of 30 times the Earth's gravity (i.e. N=30) and simulated impact situations under steady state conditions and uniform velocities. The soil blocks (approximately 4.5 m high in prototype terms) were made of kaolin clay with undrained shear strengths between 4 and 8 kPa. The model pipes were 6.35 and 9.52 mm in diameter (0.19 and 0.29 m in prototype terms). The impact velocities ranged between 0.04 and 1.3 m/s. The pipe centerline was at mid-height of the block. The shear strain rates, defined as the ratio of impact velocity to pipe diameter. The shear strain rates ranged from about 4 to 137 reciprocal seconds. Hence, the test results are applicable to a wide range of field situations. A method is presented for estimating glide or out-runner block impact drag force on submarine pipelines based on the results of the centrifuge experiments. (C) 2012 Elsevier Ltd. All rights reserved.