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# Soil dynamic

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## Soil dynamic

(OP)
Hello,
What would be the effect of dynamic shear modulus and poisson coefficient , as well as , Rayleigh waves velocity on soil strain ?

### RE: Soil dynamic

A few basic issues I know:
Shear modulus and shear wave velocity are related by a simple relationship. Rayleigh wave velocity is taken approximately as 90% of shear waves velocity (Vs). Strain in a determined material is a function among other parameters of seismic stress (waves amplitude)and usually must be known a priori or is determined by iterative methods. Increasing strain has the effect to decrease shear modulus and shear waves velocity (dynamic modulus reduction or degradation if many cycles occur).

In usual geophysical investigations though strain is assumed to be zero or totally neglibile.

Which is the exact purpose of your question?

### RE: Soil dynamic

(OP)
Thank you a lot sir .
But i beg your pardon , i feel that the answer is a bit hard to understand . What i wanted to know is , if the dynamic shear modulus , shear wave velocity and compresion wave as well ( each one increase ) , does strain and deformation decrease and vice versa

Again thanks

### RE: Soil dynamic

Killswitch,
obviously, if shear modulus and Vs increase then, with the same shear stress level, the deformation decreases.

Another effect is that stiffness itself tends to decrease with increasing stress-induced strain.

So if the soil has little stiffness, as soon as the stress level increases, the tendency to deform is amplified (what is called shear modulus reduction or degradation in dynamic conditions).

### RE: Soil dynamic

(OP)
You are the man

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