Dear Researchers,
In the HS model there is the shear modulus value (Go) that we input in the parameters tab.
The maximum shear modulus is given as Gmax=ρVs2.
But as I noticed in many papers and even plaxis tutorials is that the input value of Go is always less than Gmax in the range of approximately 80% difference.
Can anyone shed light in this matter.
Thank you.
The secant modulus is usually taken at 50% or 75% of the ultimate strength, so that it is usually smaller than the initial tangent modulus. But the ratio between the secant and tangent modulus is not defined.
Go is the initial shear modulus. It can be defined as the secant modulus rather than initial tangent. So it is smaller than Gmax.
Thank you Mohammed Yousif Fattah
How small is it? is there a ratio? or any relation?
The secant modulus is usually taken at 50% or 75% of the ultimate strength, so that it is usually smaller than the initial tangent modulus. But the ratio between the secant and tangent modulus is not defined.
Dear Ahmed Hussein Olat
The reduction of shear modulus is about 70% of the initial shear modulus has been suggested by researchers previously through the formation of the well-known S curve that represents the shear modulus-shear stain relationship in Hssmall model. This level (i.e. shear modulus = 70% of initial shear modulus is related to the threshold shear strain that represents the limit beyond which soil begins to change irreversibly. In a more practical way, the reference threshold shear strain defines the beginning of significant stiffness degradation. You could find more details in PLAXIS manual - material part - section 7.
Shear modulus is strain sensitive modulus.
Gmax is the shear modulus against minimum strain.
You can determine it for soils from resonant column tests, cyclic triaxial, bender element in laboratory mostly. In field you can determine it by geophysical tests mostly.
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