Barge Drilling-Tests for underwater logging

[Silty]

Hello,
We are going to drill some boreholes for a pipe line under a shallow lake (4 m deep max.). What kind of geotechnical testing would be the best?
Is SPT practical and will give reasonable results? what about shear vane? The proposal did not include any CPT testing and we should do traditional drilling. Any comments on method of drilling?
Thank you

 

[EireChch]

A rotary borehole, with triple tube core barrel should generally be suitable for all soils. STPs vanes, U100, bulk and small samples should be taken.

CPTs should be done also, they are one of the most accurate and practical insitu tests.

 

[GeoEnvGuy]

First off I thought we couldn't drill through water

https://www.cbc.ca/news/canada/sask...ech-investigation-of-riverbed-reeve-1.4829890

second you want to be able to provide the recommendations for pipe burial and excavation requirements on the lake edges and throughout the profile as informed by frost/ice depth and expected settlements.

 

[geotechguy1]

If a barge or specialist amphibious rig is available you can CPT or drill in the water, eg:

https://www.greggdrilling.ca/equipment/.

You need to case the hole for drilling though. Since you're in a lake I'd gamble you're going to get rubbish SPT's so personally I would look at taking shelby tubes in lieu of the SPTs, and then a standard laboratory testing suite (regular grab samples for moisture content testing with atterberg limits). Shear vanes or pocket pens are also a good idea depending on feasibility with the drilling method.

 

[GeoPaveTraffic]

Drilling is done from a barge through water all the time. Set a casing into the soil at the mud line and get to drilling. Drilling method can be hollow stem or mud rotary, just like drilling on land. You do need a driller and a geologist/engineer logger with experience since keeping up with depth/elevation is a little more difficult.

Mike Lambert

 

[geomane]

I would recommend setting casing and using mud rotary drilling techniques over hollow stem auger if you are performing SPT borings. You have to keep the hollow stem auger charged with water or drill mud or a quick/boiling condition will develop at the bottom of the borehole.

I prefer CPTs for insitu tests; however, I like to supplement with SPT borings. You get samples from SPT borings and can also push tubes in soft clays to calibrate your CPT results.

 

[cvg]

if you are just trying to characterize sediment, you might consider vibracore

 

[BigH]

Good one GeoEnvGuy - I guess the Reeve didn't know about offshore drilling platforms and that oil companies wouldn't spend hundreds of millions of dollars without knowing what their oil producing platform was to sit on.

It would be interesting to know more details about the alignment of the pipeline - will it be a long pipeline or relatively short (say 100 m). 4 m deep seems like it would be a very small lake. A barge would be expensive and the OP might not even be able to get a barge to the lake. All the pictures of platforms for offshore are of the "huge" variety. In Indonesia many years ago - we drilled off the coast in the Java Sea - water level about 4 to 6 m. Primitive platforms were made by the drilling contractor by driving poles into the sea bottom - then putting on a wood deck. Using a small diamond rig that could be disassembled, they would manhandle it onto the platform - about 3 m above water level - and then carry out the investigation - as noted, by putting casing to the sea bottom. It worked very well - and given the nature of the project, this might be cheaper than going for a Mercedes. The OP said that they cannot/will not do CPT; yes, it would be nice but the OP has constraints. We do not know the nature of the soil beneath the lake bottom - possible some loon schiesse, maybe not. If it were I, once the platform was in place and given the equipment with which he is to use in the investigation, I would consider driving a Canadian dynamic cone (50 mm cone at 60deg apex on the end of an A-rod driving with the 62.4 kg hammer (140#) dropping 750 mm (30"). This would give the OP a quick understanding of what the OP is dealing with - substantial soft material? Shallow - say 1 m of soft material? etc. This would help him, too, decide what the OP should anticipate using in his "retrieval" methods - SPT, thin-walled tubes, vane testing, etc.

Years ago (1978), I was involved in a CP railroad siding widening up near Estaire Ontario (south of Sudbury). We knew the site was peat underlain by competent material. We had a drill rig with us which moving along the track for probing at, say 50 to 75 m - would involve a lot of moving time and then, too, we had to worry about the existing track being used by trains. We would have to move the drill rig off the hole when a train was coming. I decided to take a split spoon and rods and "hand push" the spoon into the peat until I hit something "hard". This worked very well in that I was able to determine how thick the peat was at many locations (not good for extending the width of the rail embankment and also, with the split spoon at the end I was able to get a sample of the upper few inches of the competent material - to keep in mind that a number of boreholes were to also to be drilled. It seems that ASTM a few years late put out a "standard" on this. I did something similar in north New Jersey from a boat on a local pond that was to be filled in as part of a new building complex.

The OP could also use a small rowboat and probe the lake bottom to determine how much "mud" - or better, loon scheisse was a the lake bottom. Of course, knowing the thickness of incompetent material is very important in the installation of the pipeline.

Sometimes we do not have the money to do a "perfect" job - this is where thinking comes into play 0- to figure out what can be done with what one has.

My view on this post for what it is worth.