Modify Shelby Tube?

[rsteiner]

My question is what are the advantages and disadvantages for using a modify shelby tube (Lug Barrel - a shelby tube with drilling bits welded to the outside of the shelby tube) compared to a standard shelby tube?

The reason I was told drillers use this is save time from trips in and out of the boring hole. This modify tube allows them to drill during a rotary wash setup and then push the tube on the same trip.

Any suggestions or opinions on this would be appreciated.

 

[Ron]

It seems that the procedure you are describing would produce a highly disturbed sample.

 

[rsteiner]

I would agree. He is a little more info i found out on the the modified barrel and procedure.

The modify tube has six inch lugs/teeth welded about 120 degrees apart from one another around the bottom of the barrel. The lugs/teeth stick passed the bottom of the tube approxiamately 1 to 2 inches.

I was told the process goes as follows. The driller would attach the modify tube and begin drilling to the desired depth, lets say the desired sample interval is 48' to 50'. The driller would rotary wash down to 48' using the lugs/teeth to drill away the soil. Then the driller would wait til the soil cuttings were washed up the boring hole and then the driller would cut the pump off to stop the water flow. The driller would then push the tube down to 50' and gain the desired sample. I was told, by drillers, that you can not tell the difference in the sample.

 

[Ron]

You were told that by the DRILLERS, but what does the guy running the geotechnical lab say? I still think the lugs interfere with a good sample.

 

[oldestguy]

Let's see what a geotech on the job at one of these jobs has to say before we say it is something to explore. It sort of reminds me of fish tail bits with a jet coming straight off the bottom jetting everything in its path, chewing up what ever is then to be sampled.

 

[GeoPaveTraffic]

I don't see anyway that a Shelby tube modified in that manor could provide a relatively undistrubed sample. Use a tri-cone bit for mud rotary drilling and a Shelby tube for sampling. Unless you are continuously sampling at great depths the time to trip in and out of a hole is very small.