Soil Pressure Vs. Hydrostatic Pressure
Soil Pressure Vs. Hydrostatic Pressure
(OP)
I am working on retaining wall structures (2 walls forming a containment area) where the load cases are dictated to be saturated soil to a level 3 ft. above the wall OR filled with water. I understand the soil pressures are calculated using Ra = 1/2 * ka * p.soil * g * H^2, where p.soil * g = the saturated soil unit weight. What I don't understand is what equations to use for the water case. I have references that state, R = p.water * g * h, where p.water * g = the water unit weight for uniform pressure at depth, h. And R = 1/2 * p.water * g * h, for resultant force on the vertical surface.
When comparing the load cases, do water depths (h) get squared similarly to the soil depth equations? My goal is to get the governing vertical loads on the heel and toe and lateral loads. Thank you in advance.
When comparing the load cases, do water depths (h) get squared similarly to the soil depth equations? My goal is to get the governing vertical loads on the heel and toe and lateral loads. Thank you in advance.





RE: Soil Pressure Vs. Hydrostatic Pressure
RE: Soil Pressure Vs. Hydrostatic Pressure
RE: Soil Pressure Vs. Hydrostatic Pressure
The formula you showed for calculation the soil force, which i have to say is the resultant force comes from.
If its a triangular distribution with cero on the top and max on the bottom. The Lateral pressure is calculated as, P = (gamma of soil) * H * Ka. That gives you max pressure at the bottom. Now to get the soil reaction you calculate the area of the triangle and get Ra = 1/2*P*H and thats how you ended up with
Ra= 1/2 * (gamma of soil) * H^2 * Ka.
I hope that would help you calculate the water force.
RE: Soil Pressure Vs. Hydrostatic Pressure
Step 2: Know the friction angle of the soil. Let's say it's 30 degrees.
Step 3: Know the moist or saturated unit weight. Let's say it's 125 pcf.
Step 4: Know the position of the water table. Let's say it's three feet below the top of the wall.
Step 5: Know the wall height. Let's say it's 12 ft.
Step 4: Calculate the coefficient of active earth pressure - Tan^2(45-phi/2)= 1/3 (0.333333)
Step 5: Develop the stress profile.
Theoritically, the earth pressure at zero feet is zero. I usually include some measure of surcharge pressure. We'll do that later.
At zero feet - use zero psf
At the depth of 3 ft (i.e. at the ground water table) use 125 psf*1/3*3 ft = 125 psf
From 3 ft to 12 ft (i.e., below the ground water table), use [(125 pcf-62.4 pcf)*1/3*12 ft] + (62.4 pcf*12 ft) = 999.2 psf.
Connect the dots.
To allow for a surcharge pressure (i.e., let's use 200 psf at the ground surface for example), that would be a rectangular earth pressure distribution tempered by the coefficient of active earth pressure (i.e., 666 psf for the whole height of the wall).
To get force vectors, calculate the area of the stress graph and apply the vector at the centroid of the mass (or determine force vectors for each geometric area).
Hope this helps.
f-d
¡papá gordo ain't no madre flaca!
RE: Soil Pressure Vs. Hydrostatic Pressure
f-d
¡papá gordo ain't no madre flaca!
RE: Soil Pressure Vs. Hydrostatic Pressure
RE: Soil Pressure Vs. Hydrostatic Pressure
f-d
¡papá gordo ain't no madre flaca!
RE: Soil Pressure Vs. Hydrostatic Pressure