## Calculating modulus from stress-strain curves in triaxial UU tests

## Calculating modulus from stress-strain curves in triaxial UU tests

(OP)

Hi, for UU triaxial tests (saturated ML), I have 3 stress-strain curves for different confined pressures. In my case, these pressures are around 50 kPa, 100 kPa and 200 kPa. So, I had 3 different modulus.

For example, if I want to calculate the secant modulus at a certain depth, say around 6m. Is it correct to use the modulus obtained from the stress-strain curve for the 50 kPa of confined pressure? Effective stresses at 6m for a typical soil (wet density of 18 kN/m3) with water table at the surface will be around 50 kPa.

Also, should the modulus be similar for these 3 curves since the shear strength is constant at any vertical stress?

I will check my soil mechanics books tomorrow, but if you can provide some guidance here, it will be greatly appreciated.

For example, if I want to calculate the secant modulus at a certain depth, say around 6m. Is it correct to use the modulus obtained from the stress-strain curve for the 50 kPa of confined pressure? Effective stresses at 6m for a typical soil (wet density of 18 kN/m3) with water table at the surface will be around 50 kPa.

Also, should the modulus be similar for these 3 curves since the shear strength is constant at any vertical stress?

I will check my soil mechanics books tomorrow, but if you can provide some guidance here, it will be greatly appreciated.

## RE: Calculating modulus from stress-strain curves in triaxial UU tests

## RE: Calculating modulus from stress-strain curves in triaxial UU tests

Mike Lambert

## RE: Calculating modulus from stress-strain curves in triaxial UU tests

## RE: Calculating modulus from stress-strain curves in triaxial UU tests

As for maximum pile deflection, all depends on the structure. I've seen everything from "well of course none", to 1-inch for structures; and up to a foot for landslide repairs.

Mike Lambert

## RE: Calculating modulus from stress-strain curves in triaxial UU tests

## RE: Calculating modulus from stress-strain curves in triaxial UU tests

I prefer to use the modulus from 50Kpa confined stress, if you did not use back pressure.

If the sample were homogen, the higher confining stress you will get the higher modulus value as well.

## RE: Calculating modulus from stress-strain curves in triaxial UU tests

## RE: Calculating modulus from stress-strain curves in triaxial UU tests

Your sample is 6m depth with the gwl on the surface and wet density of 18 kN/m3, so confining stress of 50 kPa represents the actual condition.

## RE: Calculating modulus from stress-strain curves in triaxial UU tests

## RE: Calculating modulus from stress-strain curves in triaxial UU tests