soil lateral pressure in multi-layered condition

[citywall]

Hello,
Assuing overberdon = 80psf, Rankine theory.
1st layer: ϒ1,Ka1, h1 (layer thickness)
2nd layer: ϒ2,Ka2, h2
3rd layer: ϒ3,Ka3, h3

Lateral earth pressure at [highlight #FCE94F]to of each layer[/highlight]
80 x Ka1 ------------- 1st layer
(80 + ϒ1 x h1) x Ka2 -----2nd layer
(80 + ϒ1 x h1 + ϒ1 x h1) x Ka3 ----- 3rd layer
For each layer, take the upper layers as surcharges in the calculation.
Please tell me if this calculation is right.

Thanks.
Tony

 

[citywall]

Hi, anybody can tell me?
Lateral earth pressure at the [highlight #FCE94F]top[/highlight] of each layer.

Thanks.

 

[PEinc]

Looks correct but you also need the pressure at the bottom of each layer. This is covered in most soil mechanics text books. However, you really should check the soils books before asking online if half of your pressure calculatios are correct. I hope you know that you can't just connect the pressures you calculated at the top of each layer in order to form a pressure diagram.

http://www.PeirceEngineering.com

 

[citywall]

Thanks, PEinc.
Example in 'Trench & Shoring Manual' by state of Califonia department of transportation doesn't count ALL the layers' weight. Page 6-19.
It's surprising.

 

[BigH]

Why not look at the old NAVDOC 7.1 Slope Stability analysis for wedge failure - they have an example of how to compute the driving force (the lateral earth force) for the various layers involved - the principal would be the same.

 

[fattdad]

effective vertical stress at any depth times the layer's horizontal earth pressure coefficient equals the horizontal stress.

f-d

¡papá gordo ain’t no madre flaca!