Compressive stress on piece of rock

In summary, the conversation discusses the stress on a rock under hydrostatic pressure and the boundary conditions on the steel end plates. The calculations show a compressive stress of 1027 psi in the axial direction, but there is uncertainty about whether the force due to 5,850 psi in the rock should be taken into account. The conversation also raises the possibility of other forces acting on the rock, such as shear or friction, and discusses the unbalanced forces on the end plates.
  • #1
vtmike
7
0
Hi,
I have a configuration in which a piece of rock is under hydrostatic pressure (see attached figure) and I'm trying to figure out what the stress on this rock will be.
The boundary conditions on the Steel end plates are such that the right and left plates are restricted to move in the -ve X and +ve X directions respectively.

According to my calculations:From FBD, -(6000 X 41.3) + (6500 X 31.6) = -42,400 lbf
Stress = 42400/41.3 = 1027 psi Compressive in axial direction

But I'm not sure about my approach here. I did not account for the force due to 5,850 psi in the rock because it cancels out but I am not sure if it should cancel out or taken into account as an additional compressive load on the rock?

Thanks,
Mike
 

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  • #2
Hello VTmike.

I would start by considering the fact that your rock would be proceeding leftwards rather rapidly if the pressures were indeed what you have written.

Forces driving the rock rightwards = 6500*31.6 = 205400 lbs

Forces driving the rock leftwards = 6000*41.3 = 247800 lbs

So there is a net force driving leftwards of 42400 lbs.

For this to be true there must be other forces acting, eg shear or friction at the horizontal surfaces.
 
  • #3
Is it really supposed to by under hydrostatic compression? ie the same pressure over all the surface. From your diagram it looks like biaxial compression, which could lead to shear failure.

And, yes, as StudioT said, the forces don't balance. Another example is the unbalanced force on the right-hand end plate. That means the plate is accelerating.
 

1. What is compressive stress on a piece of rock?

Compressive stress on a piece of rock is a type of force that acts on a rock by pushing or squeezing it inwards. This type of stress causes the rock to deform and become shorter and wider.

2. What causes compressive stress on a piece of rock?

Compressive stress on a piece of rock can be caused by tectonic forces, such as the collision of two continental plates, or by the weight of overlying rocks. It can also be caused by human activities, such as mining or construction.

3. How is compressive stress measured on a piece of rock?

Compressive stress on a piece of rock is typically measured in units of pressure, such as megapascals (MPa) or pounds per square inch (psi). This can be done using specialized equipment, such as a load cell or a hydraulic press.

4. What are the effects of compressive stress on a piece of rock?

The effects of compressive stress on a piece of rock depend on the rock's strength and composition. In general, it can cause the rock to fracture or deform, leading to changes in its shape and volume. It can also create folds and faults in the rock.

5. How can compressive stress on a piece of rock be mitigated or controlled?

In certain situations, such as in mining or construction, it may be necessary to mitigate or control compressive stress on a piece of rock. This can be done by using support systems, such as rock bolts or steel beams, to help distribute the stress and prevent the rock from collapsing or fracturing.

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