Thursday, July 2, 2015

Effective Stress - Part 4

Ok, enough of the basics, it'll just zoom over the heads of all those 'non-math' scientists who seem to control our lives through oral skills.

Let's get down to injection.  If I insert my hose into a bed of clay, nothing much happens.  The water stops, since the clay is impermeable, that is, a very low permeability.  I can pump up the water, which produces a very high pressure gradient in the clay, but no work is done (work is energy, or force times distance).

I can then put my hose into a bed of gravel.  I can turn up the pumps, and get a huge flow.  However, there is virtually no pressure gradient, because the gravel is extremely permeable.  The gravel doesn't move.

Weird things only happen when I get a pressurized channel, which happens when I inject into shale.  In that case, I get the best of both worlds, the channel is permeable (but blocked at the end), and the shale is not.  There is a high pressure gradient, and available energy.  The shale parts on a bedding plane, and my pumps are howling with the flow.  Tremendous work is being done, as I crack apart the rock.

So, seismologists are lost when you have a real situation, such as a fault.  To pry the fault apart, and allow slip, you need a pressure gradient, normal to the fault (right angles to).  If the rock is as permeable as the fault, then you can't get a pressure gradient no matter what you do.  The losers at my old company unnecessarily anchored lots of dams because they measured water pressure under the dam.  But the concrete was as permeable as the rock, so no pressure gradient.  They thought the water pressure would lift the dam, and send it down the river.  Just one more thing that contributed to my breakdown.  :)

In the Precambrian rock under Oklahoma, you either have open-channel flow, or the rock is tight.  You can't form any gradients in open channels.  That is why they are able to inject huge amounts of water.  No pressure gradient, no effect on faults.  The granite will never act like shale being fractured and pried apart.

There you have it.  The USGS and 'consensus science' has it all wrong.  That is why you have earthquakes where there aren't any high-flow injection wells.  There is another reason, and I've gone over it enough -- stress corrosion.

End of lecture

Effective Stress - Part 3

All those points contacting the grain express the full vector surface forces including shear.  Since the grain is at rest, the forces sum to zero.  When the beaker is filled with water, there is a hydrostatic pressure gradient.  Within the water itself, these forces balance to zero, and there is no flow, but the grain is exposed to a gradient.

The pressure is greater on the bottom than on the top.  So if sum the forces, there is uplift, which is called buoyancy.  The skeleton stresses on the grains are reduced, that is, the effective stress is reduced.  Now, here's the thing that loses seismologists.  If we filled the beaker with more water, or we attach a big pressure hose, there is no difference.  The gradients remain the same.

If we attach a hose to the bottom, and start injecting water, we get an unbalanced pressure gradient in the water, and it begins to flow upward (if we allow it to).  If we sum the forces on the grain, we find the balance goes to zero if the gradient keeps increasing, until it becomes zero, and the grain has no effective stress.  That is quick sand.  (Let's ignore viscous drag.)

If we reverse the pressure gradient downwards, then the effective stress increases, and the sand becomes as hard as rock.

Wednesday, July 1, 2015

Effective Stress - Part 2

This is physics as I love it - primal.  The most important formula of physics is F=ma.  Force is mass times acceleration.  For us, it is better to invert it a bit -- a=F/m  or zero acceleration means zero force.

Of course, nothing is simple since force and acceleration are vectors and everything must be summed.  This leads to the first study in engineering, that of statics and a force-balance diagram.  For, if you want something to stay still, like a building, you must balance all the forces.

You calculate it with a force-balance diagram, and if you want to learn anything here, go off and study it.  Then come back.  You couldn't believe the anguish in my Statics class.  Some people just couldn't get it, and had to drop out of engineering.  They went on to be seismologists and climate scientists.  :)

So, we'll start with a soil particle, a nice shiny grain of quartz, since I like quartz.  How does it live down there?

This grain does not live by himself.  He is squished by the other grains.  If he turned colour by the amount of squeezing, this would reflect the 'effective stress'.  There could come a point where the effective stress is very high, and he could crack.

There is one thing that could relieve him of some cracking pressure (stress), and that's water.  As I said in my Wikipedia explanation, we would have these quartz grains in a beaker, and fill it with water.  Those seismologists would do well to read this.  :)  They are bitching about the lack of references, but there's nothing!  Filling with water introduces some very interesting physics.