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#6150 - 01/09/07 12:03 PM Keyway drawings/pictures
auburnbob Offline
Junior Member

Registered: 01/08/07
Posts: 6
Loc: Auburn, CA
Would a keyway reduce the hydrostatic pressure of my pond, and, hence reduce or eliminate the leaks I'm having in the berm of my pond? Does anyone have a picture or drawing of what a keyway should look like?

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#6151 - 01/09/07 12:50 PM Re: Keyway drawings/pictures
JBL Offline
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Registered: 08/21/05
Posts: 50
Loc: Missouri
This should explain everything.
http://www.cjnetworks.com/~sccdistrict/pond.htm

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#6152 - 01/10/07 12:31 AM Re: Keyway drawings/pictures
dave in el dorado ca Offline
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Registered: 04/26/06
Posts: 3260
Loc: el dorado ca
welcome to PB auburnbob, good to see another northern californian here.

a keyway will not reduce hydrostatic pressure. that is solely dictated by the volume of water in pond and the force it exerts on the substrate of pond.

nice link JBL.

auburnbob, think of a keyway as a core trench dug into the native surface (below the dam or berm that is about to be built)in which dam materials are compacted in lifts, and continue to be brought up above the core trench to form the dam or berm creating one continuous barrier that is effectively jointed into the ground.

it will help reduce seepage below (underneath) the dam. if yer seepage is from within the berm itself, you probably need to groom and repack the berms.
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#6153 - 01/11/07 08:44 AM Re: Keyway drawings/pictures
otto Offline
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Registered: 11/02/04
Posts: 1074
Loc: texas
A good keyway will reduce the pressure. You can email me at mikeotto@ottosdirtservice.com and perhaps we can help you futher.

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#6154 - 01/11/07 01:26 PM Re: Keyway drawings/pictures
dave in el dorado ca Offline
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Registered: 04/26/06
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Loc: el dorado ca
mr. otto, please educate me on this one....how does a keway reduce hydrostatic pressure?

thanks,
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#6155 - 01/11/07 07:17 PM Re: Keyway drawings/pictures
burgermeister Offline
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Registered: 02/27/05
Posts: 4025
Loc: Houston, Tx.
 Quote:
Originally posted by dave in el dorado ca:
mr. otto, please educate me on this one....how does a keway reduce hydrostatic pressure?

thanks,
Educate me too. Also the rest of the forum. Please.
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#6156 - 01/11/07 08:33 PM Re: Keyway drawings/pictures
ewest Offline
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Registered: 03/08/05
Posts: 16514
Loc: Miss.
Here is a question for the engineers and geologists. If a certain hydrostatic pressure ( water weight) is spread out over a larger surface area (bigger dam face or dam plus keyway/core) does it reduce the pressure ( as in force needed to cause failure) on the dam?
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#6157 - 01/11/07 09:11 PM Re: Keyway drawings/pictures
Theo Gallus Offline
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Registered: 05/14/04
Posts: 12285
Loc: Central Ohio
Hmmm... Pressure we measure in pounds/square inch. Spread the weight of the same number of pounds of water out over a bigger area - psi goes down.
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#6158 - 01/11/07 10:15 PM Re: Keyway drawings/pictures
TN Hillbilly Offline
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Registered: 11/23/05
Posts: 121
Loc: Greenest state in the Land of ...
Hydrostatic pressure is based on the height of a column of liquid and acts equally in all directions. You could say that a dam keyway would help the dam to resist or hold a higher hydrostatic pressure. The only way to reduce the pressure at any given point under water is to reduce the amount of water above it. The height of the water column is the only variable here. Hydrostatic pressure always acts normal to a surface. Decreasing the slope on the face of a dam changes the direction of the force the water exerts on it. A shallower slope directs the force more downward. However, the area of the face of the dam also increases as the slope decreases, so that the total sum of the force is greater. Since the change in surface area is based on the sine of the dam face angle, the net result is that there is always the same amount of force trying to push the dam away from the pond, no matter what the angle. It's the product of the pressure across the depth x the cross sectional area of the valley being dammed. Looking forward to some rain in TN this weekend.

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#6159 - 01/12/07 12:41 AM Re: Keyway drawings/pictures
dave in el dorado ca Offline
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Loc: el dorado ca
great post hillbilly.

the way i see it theo, the (dam) surface area in contact with water is the same whether or not there is a keyway. since (an ideal) keyway is buried below the interface with the pond water, there is no net change of force on that part of the dam in contact with the water. it makes the dam stronger, but does not affect the force exerted by the water.

you guys are right that if the surface area is increased the pressure is decreased, but all things being equal (same size dam plus or minus keway) a keyway itself does not affect hydraulic pressure on pond side of dam.

unless i'm missin something, which is ALWAYS possible.
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#6160 - 01/12/07 08:16 AM Re: Keyway drawings/pictures
zhkent Offline
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Registered: 03/18/04
Posts: 229
Loc: Burlington, Kansas
This is one I like;
The volume in water makes no difference in preasure, only the height of the water.
If a 1 in. dia. pipe is right beside a 100 ft. dia. water tower and both are full to the same height the preasure will be equal.
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#6161 - 01/12/07 08:23 AM Re: Keyway drawings/pictures
burgermeister Offline
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Registered: 02/27/05
Posts: 4025
Loc: Houston, Tx.
If surface area is increased the pressure decreases, because the water will be shallower.
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#6162 - 01/12/07 08:35 AM Re: Keyway drawings/pictures
eddie_walker Offline
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Registered: 11/23/05
Posts: 773
Loc: Just North of Tyler, Texas
The way I understand it, the weight of the dam is what holds the water back. The deeper the water, the more force you have against the dam.

The slope of the dam is to increase the weight of the dam to hold back the water. You need so much freeboard above the water level to add more weight to the dam to keep it in place.

Without a keyway, the dam that is built on top of the soil can slide or move over time. Having the keyway locks the dam into the soil and holds in in place. In theory, you wouldn't need a keyway if the dam was so much taller that there would be no way of it ever moving, but that could make the dam twice or three times bigger. the keyway allows us to build a dam with less dirt.

Eddie
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#6163 - 01/12/07 10:28 AM Re: Keyway drawings/pictures
Theo Gallus Offline
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Registered: 05/14/04
Posts: 12285
Loc: Central Ohio
I'm gonna crawl into the pigpen all the way.

I agree with TNHB & D.I.E.D. that the amount (height) of water determines the pressure on the dam. But it seems like a keyway increases the vertical cross-sectional area of the dam (by going deeper than the bottom of the pond), thus lowering the ... let's say strain ... on an individual area of dirt in the dam.

To use a firearms analogy, a blowback action uses only the mass of the bolt to hold the cartridge being fired in place, thus limiting pistol-sized bolts to relatively weak cartridges (9mm Makarov about the maximum power) or requiring massive bolts for more powerful cartridges (like .45 ACP in a Thompson submachinegun). This is analogous to (as Eddie stated) a normal-sized unkeyed dam holding back a shallow pond, or a inordinately massive dam being needed for a deep pond.

But if we add a keyway to the dam (or a locking mechanism to the bolt) the same sized dam (or bolt) can hold back a deeper pond (or fire a more powerful cartridge - how .45 acp can be safely fired in a gun the size of a 1911 instead of a Thompson).

If water leaks through the dam, this has the effect of weakening the dam - lowering it's shear point. This is like using soft, weak steel on a bolt's locking ribs. A good keyway also helps waterproof the dam to prevent this.

----------------------------------------------

I think most misunderstandings (which may appear to be disagreements) we can have on this issue are the result of not correctly understanding terms like pressure and force wrt ponds and dams. I'm pretty sure I'm personally screwed up some on these words.
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#6164 - 01/12/07 11:05 AM Re: Keyway drawings/pictures
ewest Offline
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Registered: 03/08/05
Posts: 16514
Loc: Miss.
I see Theo picked up on my point. \:\) I agree that hydrostatic pressure is just that. You can think of it as the force exerted downward by the water in the Miss. River that keeps New Orleans from sinking in the mud. But the question assumes at least 2 types of pressure.

Hydrostatic pressure which has been well defined in the posts above. But in the context of the original question there is inferred a second type of pressure. Theo called it Shear pressure , I used dam failure pressure. I think Otto was talking about a keyway/core strengthening the dam and thus reducing the risk of a second type of pressure event i.e. reaching the breaking point pressure of the dam. Better stated as -- a core/keyway will reduce the chance of shear pressure being reached and exerted on the dam or it will reduce the pressure (chance of a leak/break) on the dam.
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#6165 - 01/12/07 11:37 AM Re: Keyway drawings/pictures
burgermeister Offline
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Registered: 02/27/05
Posts: 4025
Loc: Houston, Tx.
Shall we all agree that the core does not reduce the pressure, but reduces the chance of detrimental action of the same pressure on the base of the dam?
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#6166 - 01/12/07 11:51 AM Re: Keyway drawings/pictures
dave in el dorado ca Offline
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Registered: 04/26/06
Posts: 3260
Loc: el dorado ca
excellent discussions theo and ewest.

semantically though it still appears in my thick skull like the (ideal) keyway strengthens the ability of the dam to hold back water (increases resistive force), but by itself does nothing to change the force of the water on the dam which is a function of how much water is there and the surface area on which it acts.

so perhaps we are speaking/defining net force....if the resistive force of dam is increased (via having a keyway) the effective or acting hydraulic pressure is reduced even though the absolute hydraulic pressure remains the same....how about that?

sorry, just felt like beating a horse this morning \:\) did we scare off auburnbob? \:\)
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#6167 - 01/12/07 12:03 PM Re: Keyway drawings/pictures
Brettski Offline
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Registered: 10/07/05
Posts: 6806
Loc: Illinois
...way to go, guys; we lost another one.
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#6168 - 01/12/07 12:34 PM Re: Keyway drawings/pictures
TN Hillbilly Offline
Lunker

Registered: 11/23/05
Posts: 121
Loc: Greenest state in the Land of ...
I'd say auburnbob got his money's worth on that one. I'd like to know his ip address. \:\)

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#6169 - 01/12/07 01:30 PM Re: Keyway drawings/pictures
burgermeister Offline
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Registered: 02/27/05
Posts: 4025
Loc: Houston, Tx.
If you dont want to know the answer looked at as a thousand points of light, in 10 different dialects and/or languages. Dont ask.
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#6170 - 01/12/07 01:47 PM Re: Keyway drawings/pictures
Theo Gallus Offline
Moderator
Lunker

Registered: 05/14/04
Posts: 12285
Loc: Central Ohio
Keyway good, dam failure bad.
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Non carborundum illegitimatus!
(totus res in temperantia)

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#6171 - 01/12/07 02:40 PM Re: Keyway drawings/pictures
Brettski Offline
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Field Correspondent
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Registered: 10/07/05
Posts: 6806
Loc: Illinois
 Quote:
Dear Mr Lusk,
Constructing my own private pond has been a lifelong dream. When I happened upon the Pond Boss forum, I felt as if my dream was finally within my grasp. I spent countless hours searching through the archives and posts; my mind was reeling with input overload. Finally, I knew the only way to make that ever-so-critical first move would come to pass by starting my very first Pond Boss forum thread; “Keyway drawings and pictures”. It was shortly thereafter that I knew my dream had drastically changed. The ensuing battle of engineering wits put me into shock as I realized that simple H2O and dirt were actually complex natural wonders, requiring a masters degree in physics and engineering to even begin to understand their true reason on earth. I came to shun a glass of tap-water for fear of a gastro-explosion due to hydraulic intestinal pressure. I could no longer even look at a shovel. Life became meaningless and empty. Goodbye comrades….goodbye.
Sincerely,
Auburnbob

Ps; please feed Fluffy for me
-
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#6172 - 01/12/07 03:43 PM Re: Keyway drawings/pictures
dave in el dorado ca Offline
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Registered: 04/26/06
Posts: 3260
Loc: el dorado ca
oh brettski....i'm glad i had a glass of water nearby, darn near joined him, death by laughter.

i sure hope you have a good sense of humor mr. auburnbob....we really are nice gentle people...

edited post.....we are....arent we?
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#6173 - 01/12/07 03:49 PM Re: Keyway drawings/pictures
jeffhasapond Offline
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Registered: 07/28/06
Posts: 7608
Loc: Pond in No CA, Me in So CA
 Quote:
Originally posted by Theo Gallus:
Keyway good, dam failure bad.
Ahh, that's the way I like it. Just give me the bottom line!
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#6174 - 01/12/07 04:29 PM Re: Keyway drawings/pictures
Theo Gallus Offline
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Registered: 05/14/04
Posts: 12285
Loc: Central Ohio
 Quote:
Originally posted by Brettski:

Brettski, what are you doing with my cat? \:D
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