Disturbance Caused by Test Procedure

To reduce disturbance during open water operations, it is normally recommended that both the vertical movement of the drill string be restricted and the test procedures are speeded up. An example of this philosophy is that CPTs are typically conducted, at a 

Loads on soil below a drill bit. (After Richards, A.F., and Zuidberg, H.M., In-situ determination of the strength of marine soils. In Strength Testing of Marine Sediments, STP 883, Chaney, R.C., and Demars, K.R., eds., American Society for Testing and Materials, Philadelphia, PA, 11-40,1985. Reprinted with permission. Copyright ASTM.) 

Schematic illustration of the pressure calculations and potential bearing capacity failure at the bottom of an offshore borehole. Note y = where is theunit weight of seawater. (From Sangrey, D.W., Marine Geotecli., 

Reprinted with permission of Taylor Francis Group.) 

To help minimize the variation in vertical load and movement during sampling or testing, a sea clamp is used on the seabed. The seabed clamp is just a large weight that is clamped onto the drill string to resist the vertical cyclic motion. 

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