Water table depth at BRC ?

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kevinwells
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Camp Name: Firmament
Location: San Rafael, Ca.

Water table depth at BRC ?

Post by kevinwells » Wed Jul 18, 2018 9:26 pm

I know this may sound odd, but I was trying to figure out the "typical" average depth of the water table in late August on the playa. Given that the playa is a lake in the winter, and by the Burning man event the surface is rock hard, Is the water table in the hundreds of feet, or tens of feet, or even less?

I am not planning on driling for water or anything, but wondering if I drill posts or anchors for large projects, how far before i hit mud? I had heard in years past, that once you got deeper than about 6 feet, you hit mud and would break your augur. Can anyone confirm?

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Token
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Re: Water table depth at BRC ?

Post by Token » Wed Jul 18, 2018 11:14 pm

kevinwells wrote:
Wed Jul 18, 2018 9:26 pm

I am not planning on driling for water or anything, but wondering if I drill posts or anchors for large projects, how far before i hit mud?
Kevin Wells wants to drill in the Playa - he he he, funny that.

It starts to get funky right quick when drilling in the lakebed.

Regardless of where the water table is or where the mud is (which technically is surface water and not the water table) there are strict rules on drilling/digging on the Playa.

Digging is strictly forbidden.

Drilling of a 6” diameter post hole no deeper than 2’ is discouraged but permitted, provided you save and bag all removed material, then carefully pack it back in the hole good and tight, compacting mechanically and with water, when the post is removed. Once restored there must be no trace of the hole.

Bottom line - don’t do it.

There are other ways to fabricate anchors using concrete form stakes or similar that require no digging or drilling.

kevinwells
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Re: Water table depth at BRC ?

Post by kevinwells » Thu Jul 19, 2018 6:28 am

Every Dpw shade structure is built with 4x4s and augered holes. Hundreds of holes and trenches are dug every year. They are allowed, provided they are done correctly.

I am trying to do rudimentary structural calculations for a submission for very large art project for to be proposed for 2019, augurs screws are a legitimate holding strategy. Where one hits mud affects the holding power and affects difficulty of installation. Don’t worry, if we move forward with the idea, a professional engineer will be brought in, for now we are after rudimentary numbers.

Btw, my last message , the auger hole depth suggested was incorrect. Not 6 ft, more like 24-36 inches....

In 2006, for a project called the Conexus Cathedral, We relied on the the holding power of 24 inch auger screws to keep the whole 50 ft high, 20,000 sq ft structure upright.

https://images54.fotki.com/v1642/photos ... 603-vi.jpg


This project will be bigger...

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TT120
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Re: Water table depth at BRC ?

Post by TT120 » Thu Jul 19, 2018 8:03 am

Several years ago, I read that the water table was 12 to 15 feet deep. I don't know it that's where the mud starts or where the standing water starts.
Life's a bitch, then you go to Burning Man - Unjonharley
We welcome the stranger, but that doesn't mean we have to like them, nor they us, and that's alright. - AntiM

W6BJD

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torrey.smith
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Re: Water table depth at BRC ?

Post by torrey.smith » Thu Jul 19, 2018 9:55 am

It varies of course. Typically between 4 and 6 ft before the chocolate pudding starts.

When we do anchor pull tests we get a good read on it by seeing what comes up with the anchor.





Here you can see a combination of damp Playa and too-tight thread pitch on our experimental anchor (main factor) lead to a reduced holding power. The cone angle is determined by the soil type (Playa is about "1.5" on this scale with an AEA PE-46 for reference) and an optimized penetrator will get the cone starting at the end.

Image

Where else in the World do we get an empty canvas like this that renews itself every year?

Thank you, Larry.
Sarge

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Token
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Re: Water table depth at BRC ?

Post by Token » Thu Jul 19, 2018 10:06 am

kevinwells wrote:
Thu Jul 19, 2018 6:28 am
Every Dpw shade structure is built with 4x4s and augered holes. Hundreds of holes and trenches are dug every year. They are allowed, provided they are done correctly.
Correct, and the tranches are for power distribution and whatnot. Also other large camps also trench for Tesla coils etc.

You gave yourself a big hint there buddy: DPW will have the long standing experience and data on where the ground water usually lingers.

And to be clear, it is not the water table. It is ground water. If you hit the water table you get Fly ranch or Trego hot springs :)

This is where I miss the Old Couch, Bob Stahl, other than his witty charm that is. He was a living encyclopedia of Playa construction. My fav quote is “drive a truck axle in there and you’re good”

Ground water level varies by year, can be as shallow as 4’ can be 8’ etc.

It is very rarely 2’ hence the guideline of 2’ max depth for holes.

Talk to DPW, ASS team and the likes and see what they say. It is entirely likely they will approve a reasonable depth past 2’ if you have the right compacting power equipment to backfill.

If you are on the Playa this year, run an experiment.

Get some soft steel bar stock, sand it and clean it real nice and uniform, grab a big ass Jack hammer and drive the sucker in as deep as you can.

Would help if you can cut in some channels down the length to give it more surface area. Don’t know if you have acces to a maker space or whatnot.

At the end of the party, water it down then pull it out and see where the rust at.

Heck, you could repeat the test in 19 to adjust your design before building.

Good luck. Sounds like an epic build for 19.

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Token
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Re: Water table depth at BRC ?

Post by Token » Thu Jul 19, 2018 10:10 am

Ha! Sextant ninja-d me on the experiment. TS gone done it right!

kevinwells
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Re: Water table depth at BRC ?

Post by kevinwells » Thu Jul 19, 2018 12:16 pm

Torry, Thanks for the videos of the testing. Just the sort of thing I was looking for!

All the best,
Kevin.

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