total normal stresses of 110 and 40 kpa are applied to two planes at right angles in an element of soil. the shear stress acting on those palnes is 20 kpa. what must be the value of the pore pressure in the element if the minor principle stress in the elemnt is to be zero?
a. 15.4%
b.2038.5 kg/m^3
c.1766.5kg/m^3
It's been a while since I worked with Mohr's circle. Hope I still remember enough to help you.
If σ1 and σ3 are 40 and 110 respectively, with τ being 20, you can draw the Mohr's circle, with centre at (40+110)/2=75 and radius = √((110-75)²+20²)=40.3 kpa
The principal stresses are therefore
=75 ± 40.3
=34.7/115.3
Remembering that pore pressure shifts the Mohr's circle to the left, what would be the magnitude of the pore pressure to reduce the minor principal stress to zero?
a large soil sample obtained from a borrow pit has a wet mass of 26.50kg. the in place volume occupied by the sample is 0.013 m3. a small portion of the sample is used to determine the water content; the wet mass is 135g, and after drying in an oven, the mass is 117g.
a) determine the soil's water content.
b) determine the soil wet and dry density for conditions at the borrow pit.
To find the value of the pore pressure in the element when the minor principle stress is zero, we need to understand some concepts from soil mechanics and stress analysis.
In soil mechanics, the principle stresses are the maximum and minimum normal stresses acting on a plane inside a soil element. The difference between these stresses defines the shear stress acting on that plane.
In this problem, we are given the following information:
Total normal stress on one plane (σ_1) = 110 kPa
Total normal stress on the other plane (σ_3) = 40 kPa
Shear stress on both planes (τ) = 20 kPa
To find the value of the pore pressure (u), we can use Terzaghi's effective stress principle, which states that the effective stress on a soil is equal to the difference between the total stress and the pore pressure:
σ' = σ - u
Here, σ' is the effective stress, σ is the total stress, and u is the pore pressure.
To find the value of the pore pressure (u) when the minor principle stress is zero, we can assume that the effective stress on the plane with the minor principle stress is zero:
σ_3' = 0
Using the effective stress principle, we can rewrite this equation as:
σ_3 - u = 0
Rearranging the equation, we get:
u = σ_3
Therefore, the value of the pore pressure (u) in the element must be equal to the total normal stress on the plane with the minimum stress:
u = 40 kPa