The U. S. Naval Civil Engineering Laboratory has conducted field and laboratory tests to investigate the effort required to remove partially embedded objects from cohesive seafloor soils. This work is intended to aid in proper selection of elements for salvage and rescue operations. This report of presents the results of the tests and an analysis of the results. Procedures are given for use by field engineers in predicting forces required to remove objects immediately and in estimating times required when lesser forces are applied. The accuracy of the force prediction procedure is about plus or minus 50 percent; the accuracy of the time prediction procedure is about plus or minus 100 percent. These accuracies are comparable to those usually attainable with other time-dependent soil mechanics problems and should be acceptable for typical object retrieval operations.
Objects either partially or completely embedded in soil often require forces greater than their own weight to dislodge them. This additional force -requirement, termed the breakout problem, enters into the planning and execution of many underseas operations. Among these are the salvage of sunken vessels and ordnance, the retrieval of bottom-sitting devices or structures, and the use of embedment anchors. In each of these cases, it would be desirable to be able to predict in advance the magnitudes of these breakout forces so that the elements of the operation would be selected and used appropriately.
The over-all problem of breakout is very extensive. However, it is possible to divide it into several subproblems that are less broad and, therefore, simpler to study. Division can be made along lines of object embedment depth, soil type, and nature of breakout operation.
A convenient division point for the object embedment depth is the smallest lateral dimension of the object (width). If the object is embedded by an amount greater than its width, breakout usually occurs through failure of the soil above the base of the object. This is the principle of embedment anchor utilization. If the embedment depth is less than the object width, the breakout force problem is mainly concerned with factors below the object base. This latter case will be referred to in this report as the breakout of partially embedded objects.
Soil can be roughly divided into two general types: cohesive and cohesionless. Cohesive soils (clays) are very fine grained and relatively impervious to water flow; cohesionless soils (sands) are coarse grained and very permeable. Shallow breakout from cohesionless soils generally requires very little force in addition to the object weight. The breakout force required with cohesive soils, however, may be substantial.
The nature of the breakout operation can be separated into aided and unaided breakout.