Discussion questions for the master drillers out there 4

[Kevin9679]

Hello,

I am not a driller, I am your book-smart white-collar geotechnical engineer. I am located in NY. Drillers are typically limited to your standard, 2" spoon, 3" spoon, retainer baskets on the spoons, NX, NQ, HQ. Let's ignore clay samples for now. I'm asking for master drillers because I'm trying to glean little secrets that us bookworms will never learn from the book.

1. If you have recognized a pattern of success/failure recovering high quality samples (as far as disturbed samples go) in debris fill FROM DRILLING, what are the little things that aren't discussed in your typical text book? What I'm planning is to take a 2" spoon, and when there's low recovery with the 2" go down with a 3". Use a retainer basket for both. But that has limitations as well.

2. How do you keep the borehole from sloughing in when going through intermittent loose soil and cobbles/boulders? Are there advantages/disadvantages to spinning casing instead of driving, besides worse "cut-off?" What causes sloughing in loose Sand even when the borehole is cased or Revert is used? I heard that if the drill bit is pulled out too quickly, it can create suction and pull soil up with it. Is there any truth to that?

3. Coring in fractured rock. Some drillers can recover rock with RQD = 100% even as a vertical fracture runs through it. Others can't recover jack. Us bookworms have this belief that triple barrels will obtain better results. I have a personal belief that H size samplers will provide a higher quality run, although the RQD would have to be determined differently. But does any of that matter when running through a 70 degree sub-vertical fracture or fault? Why do some drillers go right through that as smooth as you can imagine, and others struggle like there's no tomorrow? It's like the samples are falling out of the bit and then being ground up or something. What are the invisible things that the books simply don't cover?

4. Is there a driller's manual that discusses these things in detail? All I ever find online is literature written by engineers.

Thanks,
Kevin

 

[oldestguy]

Nice try. You won't find any of those drillers here.

 

[MTNClimber]

A driller I recently worked with told me that there’s a Facebook group for drillers that like to talk shop. You can always try there.

As for my observations from my time watching them work:

1. If you’re not doing continuous sampling you can ask the driller to overdrive the sampler (instead of 18 or 24 inches, drive it another 6 or 12) to get more recovery. They also make core catchers/baskets for spoons with different stiffness. I usually found the yellow core catchers with less stiffness do better with recovery but you’ll have to re-bend the core catcher after driving it through hard clays or gravel.

2. This is usually a problem when you get below the groundwater table. The driller should keep a positive head of water or drill fluid/mud to prevent this from happening. If you have access to a lot of water (drilling near or on a body of water, close by water spigots, etc.) the driller shouldn’t hesitate to adding water as they’re pulling their rods out of the hole. They may think twice about adding water when you have a well mixed mud in the hole but sometimes it’s better to mix more mud and keep the hole open than letting it collapse.

3. Rock coring is a form of art. Tricky rock will need a good driller with experience coring that rock type. They will know what type of core barrel, rotational speed, and down pressure required to get a good recovery.

4. I haven’t seen or heard of one either.

 

[Kevin9679]

MTNClimber, do you happen to know the name of the facebook group?

Also we've all experienced boreholes collapsing even when the mud tub is up to the top.

 

[MTNClimber]

Sorry, I don’t recall the name of the group and I don’t have Facebook so I can’t even try to dig it up. But it’s all types of drillers, not just test boring drillers, from all over the world.

 

[oldestguy]

In New York State check with these guys, Empire GEO services. I helped them get started way back in 1950's. They can answer all your questions.

 

[geomane]

I would recommend volunteering to go out with your drill crew during your next project. Spend time behind the rig.

 

[oldestguy]

A piece of advice from OG. Two young engineers working for our geotech firm in various positions, including helper-logger on a drill rig were canned by me long ago. Each of these guys were a year or two out of 4 year college, civil engineering. Their positions were with some authority, but generally beginner positions. From time to time out there they were faced with making some sort of decision, such as having some situation not usually there,as well as making approval of some routine facet of work. A beginner usually would check with the higher ups as to what to do. It happened for each that the decision to approve was for a significant part of the job. If it was approved, yet there might be major problems if wrong, then significant job problems might result. In each case I learned about the OK given on the job and thought about the consequences if wrong and they were very significant. Bringing up these possibilities they each rebelled and tried to justify not checking with superiors, rather than recognizing the trouble that may have occurred. To me I didn't need a risk to our position from decisions on the job. since my signatures went on final reports.

Moral here: Never try to play "big shot" when the decision could easily be checked out first when early in your work position. I look at the introduction by the poster and I sense that "big shot" attitude dismissing the benefit of advice from practicing engineers.. All of us have heard reasons for some problem and the fix, sometimes totally wrong when given by experienced workmen.

 

[geotechguy1]

Sample recovery on a job can be impacted by variables you'd never think of, even with a highly skilled drill crew. For example: Job is after a long weekend, drill crew is still recovering from hangover and other substance use. Logger is an asshole to the drill crew vs logger plays nice, brings coffee, makes sure there's a portta pottie for the job or drives the drill crew to somewhere with a bathroom.

Hire a reputable company, and play nice with the drill crew!

 

[BigH]

geotechguy1 - hangovers after weekend? Have you worked with Quebed diamond drillers before? With them it was every morning!!

First off Kevin9679, what kind of rig are you using? Auger rig (not for sands) but hollow stem auger could be. Diamond drill like a Longer 24, 24 or 44? I almost always used casing through sands and gravels - with wash boring. Very slow and tedious process - drive casing to level, clean out with a chopping bit. As noted earlier, keep water in the cased hole above the guestimated groudwater level. Drilling with mud - yes, collapsed holes happen, not so with cased holes.

Coming with litte recover . . . one could use the "side scraper spoon" as shown in Terzaghi and Peck to get a sample for more recovery (go down in same hole to same depth and scrape the sides) - see figure 11.2 of Terzaghi Peck and Mesri - page 37 - although I think there is a better picture of it in 1967 Terzaghi and Peck (2nd Ed). The little spring catchers - worked sometimes - didn't work other times. Figure 11.2 has a number of "tools" for drilling. 50 mm spoons are not good of course if gravel in the formation. Try 75 mm spoon. May not be that either - hit the gravel at the wrong place, you end up driving the spoon like a cone. In Canada, we used to carry out the pentest (see Canadian Foundation Manual - first edition). It is a 60 degree cone attahed to the end of the A-rod, driven by the 63.5 kg hammer dropping 760 mm (i.e., SPT hammer and drop). It gave good blow counts but no sample, of course. For gravel materials, consider the Becker Hammer.

https://www.foundex.com/equipment-35-AP-1000-Becker-Hammer

(I knew Foundex back in the early 80s out in British Columbia - good outfit).

As MTNClimber stated - drilling rock, especially fractured rock, is an art - not all can do it and not all, even very seasoned and experienced chaps, sometimes just can't do it. Depends on a lot of things. I guess one, if really need "actual in situ" conditions in blocky/fractured rock (say super important dam foundation) - could grout ahead of the drill and then, after allowing setting time, core - could tell what is "nature" and what is grout - but very time consuming and may not work - just a thought. Use of triple tube core barrels might help. Looking at the core for "grinding".

As geomane said - if you haven't already done so - go out and spend time (lots of time) on the drill - when I started at Golder and then the "original" Geocon in Canada, all drilling investigations were overseen by a geotechnical engineer - and this was for up to 4 years (although year 3 and 4 were not continuous). You will learn a lot. Have your own logging and reporting the operations is imperative to a proper job and you should be available to advise them when problems - but how can you if you haven't experienced the same problems yourself? I was on rigs in the arctic, norhtern Canada, east coast of Canada - many different types of soils and rock.

I am very particular about noticing thin seams of differing material in a soil stratum. Was involved in a forensic investigation in Eastern Canada where the Contractor for a large sewer line experienced blowouts while he was carrying out deep open cut excavations in sands. The original investigation showed that the stratum was all "sand" - logged by the drillers with no appreciation as I found out when putting down boreholes that there were layers of finer material i.e., macroscopic layerings of some 50 to 75 mm thick which in fact had microscopic partings of fine sands, silts and clays of 1 to 2 mm in thickness. The reason for the blowouts was as the water level in the stratum wanted to drop as the excavation advanced, the water could not drop as expected but would hit one of these finer lenses and then move horizontally to the excvation face - blowing out the edge and then working its way back into the slope at many "levels". This is my way of saying that you need good people on the drill logging - not drillers who do not know, usually, the nuances that you would find important. (see oldest guy's comments on supervision and not informing those above.

Thanks for letting me "blow off a bit of energy"!!

 

[Kevin9679]

BigH,

Your observation of anisotropy in the layers is the reason I asked about the sampling in the soil and not just the rock. Actually I'm concerned about the exact situation (in the soil). I will look into your Terzhagi reference.

 

[Kevin9679]

When you guys say spend time "behind the rig" do you mean inspecting or drilling/helping?

 

[Kevin9679]

I have looked for the "scraper bucket" as described by Terzhagi. It doesn't seem to be on the market? Does it go by a different name now?

 

[oldestguy]

Say Kevin: Pay attention to engineers like BigH. He has years of experience both in the field "behind the rig" and writing reports. If you don't know "behind the rig" you have much to learn.

 

[Kevin9679]

I know "out in the field." I've inspected for a bunch of borings. I've never operated the machines. I'm sure I do have a lot to learn, but the lingo is just what it is. Oldestguy I'm sure it doesn't mean much to you but I've been in the industry for 8 years and I do have my PE in geotech.

 

[MTNClimber]

Also we've all experienced boreholes collapsing even when the mud tub is up to the top.

The amount in the mud tub is important but doesn't impact the pressure head in the casing. If you're having trouble keeping the hole open, make sure the casing is full of drilling fluid as they are pulling rods. When they pull the rods out, the water level in the casing will drop below the natural groundwater level on the outside of the casing. The hole will have trouble staying open under that condition and you could get material blowing up into the casing. This requires an ample source of water if you want to drill a full day.

When it comes to drive and wash and mud rotary drilling techniques, it takes a lot of time behind the drill rig (inspecting) to understand the little tricks. Unfortunately, a few borings isn't enough time. You need time, experienced drillers, and a wide variety of site conditions. Then, even after you get a full grasp of whats going on, in a few years a new tool or product comes out that changes how they do things.

 

[BigH]

The side sampler is an old device - and I am not sure that it is made any longer but I doubt it would not be difficult to find someone in your area to manufacture it. It would come in handy for certain situations - espeially if you continue to have poor recovery.

Keven 9679 - I've never operated a rig either but I have sure helped drilled break a lot of H and P pipes in -20 degC weather! Getting a bit 36 inch pipe wrench on the pipe, add a 1.5 m pipe to gain more leverage . . . Sadly, I have some great pictures of the investigation I was mentioning but they have been in storage in Toronto for the last 25 years as I and my wife (and daughter) traipsed all around Asia and SE Asia.

 

[1503-44]

Speaking of storage. This tip could save you $Ks ~~ Tip: Sell it all.
Be extremely selective as to what you put in storage. I recently opened our storage containers, one since 20yrs, after transporting them via air and sea from Dubai, London and Spain, to our hopefully final, retirement home destination on a relatively remote island in the Atlantic. Storage bills got to be $500/mo. Just reunification transport alone was a major expense. Almost nothing with now weakened or crumbling plastic, rubber, elastomers, or leather in it was of any use. TV, "sound system" and everything electronic were hopelessly out of date. Other stuff was simply not needed today. [pre][/pre]Some stuff worked, but not for long. With what we paid over the years for storage, we could have purchased most of it new today, which we have now done anyway. Sell it for whatever you can get and ... move on.

 

[BigH]

1503-44 - I understand your dilemma on storage - mine has been in for 25 years. Household items, 1000+ vinyl records, a very large geotech library but important, about 30 years worth of original draft drawings that had been tossed into garbage which I retrieved and paid for .. . original cross sections and boring plans for many of the major long span bridges in a Canadian province - but what to do with them as I never plan to return and live in North America ...

 

[1503-44]

You might be able to sell the vinyls on ebay; but bridge plans .. yeah, their going to have a limited market. Donate to a local historical museum?

An ex sold my library and other stuff she got her hands on a long time ago, so there weren't any books to speak of. Miss that library a lot. I had many books dating back to my father's metallurgy collection and other engineering and math courses he took in the late 40's. Those textbooks were great. They were entirely understandable reading them on the first pass. Don't write them like that anymore. Good thing I was far away from her...

Crumbling rubber drive belts, degenerating, sticky, black rubber appliance handle pads, some "softer plastics" and leather were the worst offenders, other than lack of USB, HDMI and Bluetooth compatibility in the electronics. I managed to find and fit some BT adapters, but that's not great. Some humming going on there with a TV. Works OK, but the speakers are vibrating and it only plug and plays with OEM outdated devices. Think I'm going to pop the hood and rewire the speaker output. NO! Why mess with it. There are 52" screens selling for 400€ now and its ! I'll dedicate the old TV to the PlayStation II. They deserve each other.