Pore pressure due to capillary rise

[tzx9633]

Homework Statement

Why there's no pore pressure due to capillary rise at point A and point D ? There's only pore pressure due to capillary rise at B ..

Homework Equations

The Attempt at a Solution

i think the author is wrong . There's should be also ore pressure due to capillary rise at A and D . Because the capillary rise can occur anywhere in the soil .

 

[Chestermiller]

Homework Statement

Why there's no pore pressure due to capillary rise at point A and point D ? There's only pore pressure due to capillary rise at B ..

Homework Equations

The Attempt at a Solution

i think the author is wrong . There's should be also ore pressure due to capillary rise at A and D . Because the capillary rise can occur anywhere in the soil .

Can you please define the variables in your equations.

 

[tzx9633]

Can you please define the variables in your equations.

Huh , what do you mean ?

It's the pore water pressure due to capillary rise , u = -s(yw)(H2)

 

[Chestermiller]

There is no water in the pores at A; it is above the saturation zone. At D, the pores are all fully saturated, because it is below the water table, and there is no capillary pressure there because there is no free surface (between air and water) in this zone. So the author is correct.

 

[tzx9633]

there is no capillary pressure there because there is no free surface (between air and water) in this zone. So the author is correct.

Having said that there's capillary rise at B , means that there is free surface (between air and water) in this zone ?

I didnt see there's air at B , can you explain further ?

 

[Chestermiller]

Having said that there's capillary rise at B , means that there is free surface (between air and water) in this zone ?

Sure.

I didnt see there's air at B , can you explain further ?

What do the words "50% saturated" mean to you?

 

[tzx9633]

Sure.

What do the words "50% saturated" mean to you?

ok , noted . Why there is no pore pressure due to capillary rise at C ?

 

[Chestermiller]

ok , noted . Why there is no pore pressure due to capillary rise at C ?

At C and below, the pores are completely full of water.

 

[tzx9633]

There is no water in the pores at A; it is above the saturation zone. At D, the pores are all fully saturated, because it is below the water table, and there is no capillary pressure there because there is no free surface (between air and water) in this zone. So the author is correct.

How do you know that there's no water at A ? How do you know that there's water at B ?

 

[Chestermiller]

How do you know that there's no water at A ? How do you know that there's water at B ?

The figure implies that, between A and B, there is dry sand and between B and C, there is partially saturated sand. So, B is the top of the region containing water in some of the pores.