Typical drilling production rate, continuous sampling

[tpk72]

I'm trying to negotiate a contract for a drilling job that has continuous sampling for a depth of 20'. Just curious if anyone out there has a rule of thumb for continuous sampling. I typically use 5' spacing, and I don't have a great feel for how much continuous will slow down the process.

The borings will be drilled through med to stiff clay soils.

Thank you much!

 

[BigH]

We, as a typical standard, sample at 2.5 ft intervals to 15 ft, then at 5 foot intervals thereafter so it was "nearly continuous". If you actually need to sample fully throughout, try using a 2 ft spoon instead of a 1.5 ft spoon. In NJ, we used to drive three continuous spoons from the surface before putting down any augers. (Yes, I realize there is "some" additional friction involved - but then again, if I am not mistaken, ASTM requires one to have at least a foot below the previous sample to the next sample - in most cases the concerns are "lost" in practice.

Using solid stem augers, our drillers would do a hole like this in about 1 to 1.5 hours in the Toronto area till plains. Set-up and moving time extra. If you are using thin-walled tubes instead of split spoons, you probably should add on an hour or so for handling and waxing - and you would have a hard time pushing into a stiff clay.

 

[mudman54]

i wish more engineers would specify the top 20 feet continuous. costs should be reasonable because the driller can stand the rods and rapidly clean out between samples. you should find out if the objective is environmental or stratigraphic and make sure the samples do not have any gaps. if the investigation is geotechnical, the blow counts are more important so be careful with the overlapping disturbances between samples.

 

[emmgjld]

When you say Continuous Sampling' I would have a couple of comments, in addition to the above.
I will assume you are not using the CME Continuous Sampling system with hollow stem augers. The quality and anticipated use of the samples will open and close your options.

For good quality samples, assuming the soil conditions allow, I have sampled with:
1) 1st a Shelby Tube (12"+ as possible) followed with a SPT (24"), cleaned with auger to near bottom of SPT, followed by the Shelby Tube & SPT combination, to total depth. The SPT will fit in the Shelby Hole with minimal sample disturbance. The Shelby which follows the SPT will include the soil disturbance in front of the SPT and should continue into relatively undisturbed soils.

For good to atrocious quality samples, assuming the soil conditions allow, I have sampled with:
1) 1st a Dames & Moore Spoon(24") followed with a California Spoon (24"), followed with a SPT (24"), cleaned with auger to near bottom of SPT, and repeat until the driller's arm falls off.

 

[Ron]

100 to 125 feet per day.

 

[BigH]

emm... this is what I have done to in India to sample of fairly thin soft clay layer - increases the number of samples to better define the stratum.

Ron - with good drillers and a per foot rate! Let's see - 1-1/2h per hole for 20 at 8hr/day = 5.3 holes/day x 20ft/hole, say 5 holes = 100 ft/day!

 

[coneboy]

Another approach would be to do CPT testing in conjunction with solid stem auger sampling.
This approach would give you complete soil profile, a complete SPT profile and a pretty good estimate of the soil shear strengths.

The CPT/auger sampling approach will cost more on a daily basis but you should be able to get 180 feet of production in single working day. After you have looked at the CPT data you could go back and get a piston tube or vane test at any critical zones.

Using the CPT approach will negate any hammer/energy and borehole correction factors.

Of course, the availabilty of CPT contractor might be a cost issue. I guess it also depends on if you prefer analyzing CPT data or lab testing data.

 

[molerat2210]

I say about 1.5 hour to drill 0-20' with 2' spoons assuming normal conditions (no rubble, auger drilling, no running sand, etc). This is average of 9 minutes per spoon. I usually assume 6 hour workday of acutal drilling production.

 

[eldeibi]

Are this geotechnical or environmental borings? Because one type or the other affects what equipment you'll use. From samplers to rigs...

For Geotech borings, you can take undisturbed samples alternated with spt samples for few borings and if you feel comfortable that you determined your parameters with the undisturbed sample testing and once you have your engineering properties you could correlate with SPT (if clay is consistent through site and you know where G.W. is through site)

For Environmental the most important thing would be avoiding cross contamination... The contractor must have couple of spoons for SPT and decontaminate them in between testing. Or you could use a macro core for testing also.