Correlation between undrained shear strengh Cu and Permeability

[Lovi]

Hey all, im designing a cofferdam. We have to quantify the seepage but we are missing permeability values.

what Ive got here is a soft clay (Cu=30kN/m2), a firm clay (Cu=60kN/m2), stiff clays(100kN/m2). These values have been estimated from SPT N values. We also have the densities for each soil layer. I need to estimate the vertical and horizontal pearmeability for each layer.

Is there a relationship between Cu and permeability?
if not, is there a relationship between density and permeability?

 

[dgillette]

Everything that governs permeability is second-order compared to grain sizes and clay plasticity, and their variation with depth. For a given soil, there is a decrease in permeability with increasing density, but that effect is relatively small compared to variability from soil to soil. As horizontal permeability is driven by stratification (e.g., the thin sand partings that sneaked into the clay), I don't think it's a good idea to try to estimate it from any single parameter. There is no reason to expect much of a correlation between strength and permeability.

That said, the permeability of clay is pretty darned low, unless it has cracks or sand partings.

Regards,
DRG

 

[fattdad]

run the numbers at 1x10-6 and 1x10-7 cm/sec and see just how they look. parametric evaluations are a good thing.

+1 to dgillette too.

f-d

¡papá gordo ain’t no madre flaca!

 

[YannisChasiotis]

You could make a rough estimate of permeability by soil classification, the existence of cracks, sand-silt layers, but...not strength

 

[BigH]

Do you have layerings or partings in your clay? Some clay have very fine sand partings - sometimes a mm or so thick. Such partings can have a drastic effect on the operative permeability.

 

[Lovi]

its been a long time since this post and I appreciate the help. We gave a vertical and horizontal permeability value to each layer.

Flownet was looking wierd with the three layers and artesian condition at the bottom. so we also used a modified fdm of laplace equation for validation