Laboratory pull-out tests show that, for anyone object in-situ time prior to pull-out, the relationship between the force ratio R and time t required to break an object free from embedment in a soft Cohesive/sediment may be expressed as t = toe(Ro - R)/m, here Ro and m are empirical parameters. Both Ro and m increase with increasing in-situ time and appearto approach limiting values. For the sphere and vertical cylinder used, m appears to be independent of object shape.
When an object is removed from embedment soft cohesive bottom sediments, the time required to achieve breakout depends on the magnitude of the pull-out force, the sediment properties, and the length of time the object has been embedded prior to pull-out.
This paper presents results of a laboratory study of the effect of object in-situ time on the relationship between breakout force and breakout time. One sediment material was used. Two test objects, a cylinder and a sphere of equal weight to volume ratios, were pulled from the sediment after in-situ times of 2, 4, 8, 16, and 32 hours. For each test object and in-situ time several pull-out forces (at least five) were used to establish the relationship between breakout force and breakout time.
In recent years several writers have discussed the problem of breaking objects free from bottom sediments. While the breakout mechanism is not well understood, most investigators agree that in many cases the primary resisting force is the so-called "mud suction". In a laboratory study DeHart and Ursell1 found that the pull-out force required to achieve essentially immediate breakout depended on object shape, sediment type, and object in-situ in time; hydrostatic pressure (i. e." water depth) had no effect of breakout. Muga2,3 presented results of field tests in San Francisco Bay with six geometrically different test objects and a wide range of in-situ times. He presented an empirical relationship between breakout force and time2 and proposed a numerical analysis based on elastic-plastic sediment properties.) Liu4 combined results of Muga?s San Francisco Bay tests with those from additional field tests in the Gulf of Mexico and from laboratory model studies. He presented an empirical relationship that included object in-situ time, but concluded that breakout time predictions were very difficult.
Vesic5 gave an analytical approach based on earth pressure theory and the expansion of spherical and cylindrical cavities. Time effects were included indirectly through sediment strength and deformation properties. However, his approach is not applicable to soft sediments having water contents greater than the liquid limit.
Liam Finn and Byrne6 discussed the breakout mechanism and presented a simple analytical method for predicting the breakout force required for essentially immediate breakout. Ninomiya et al 7,8 discussed the suction force and the effect of a water jet suction breaker for reduction of breakout force. Roderick9 presented results of a laboratory study on the effect of electro-osmosis for reducing breakout force and time requirements.