I have read a number of queries regarding the installation of piles in this forum and would recommend members to contact the above for further information regarding a system of installing piles being developed by Trident Offshore Ltd. Essentially the system has been developed for the Marine Offshore Industry as an alternative to conventional anchors / piles but we are of the opinion that the technology could well be adapted for civil engineering applications with certain modifications. Should anyone be interested I can email some brief details and would be interested in a response to the system.
I have requested and received the information, and have reviewed it quickly.
I believe this system could be modified for land based systems. I have thought of (but never seen) a system which includes an auger that is detached and permanently left in the ground as the pile structure.
In Raleigh North Carolina, subsurface soils at a depth of about 30 feet consist of silty soil to weathered rock with occasional quartz gravel. This material has a very high bearing capacity in-place but when disturbed, or when the confining pressure is removed, it becomes very soft. It is below the water table and when drilled shafts are used, a quick condition is reached and the bearing capacity is lost about 10 minutes after caisson excavation. For an informal load test, we had a 1-foot square plate attached to the end of the Kelley bar of the caisson after excavation. The Kelley bar and plate are lowered to the bottom of the excavation and pushed on the subgrade until the front end of the caisson rig is lifted - this applies a load of about 40 ksf. The subgrade held the load for about 5 minutes and then just gave in - and could be pushed about 2 feet into the subgrade. This and other information verified our belief that a quick condition would be reached.
Driven piles are generally not acceptable in the area due to the noise. As a result, drilled shafts are often designed to go to the bedrock, about 60 feet deep where the casing is "screwed" into the rock. This is very expensive due to boulder removal.
We have avoided the deeper caissons in this area by use of slurry caissons but this requires a lot of room for the tanks, and can be expensive (especially for small projects, time consuming, etc.
I believe a drilled pile consisting of a drilling mechanism that is never removed from the ground and doubles as the pile would be an excellent application in this case. This would avoid the noise problem, the quick condition, and the boulder removal. It would be good if the shaft of the steel tube could be modified to support a little friction.
Liberty Offshore Ltd has been formed by the original team involved in the development of the 'drilled pile system' and we would be delighted to supply further information on our 'Excalibur' deepwater drilled pile anchoring system. Please contact either myself or Mr Duncan Cuthill, Operations Director, for further information. Tel: +44 1224 200168 e-mail: email@example.com Our web site should be live in the next few weeks: www.liberty-offshore.com