Dear all,
Plaxis HS small gives us the modulus reduction curves as shown below. However, it does not give the values in tabular form. Is there any spreadsheet available to obtain the values of the curves given by plaxis?
Hi Jamal,
Indeed the values are not given in a tabular form. However, they can be obtained using the equations mentioned in Chapter 7 of the Material Models Manual.
Dear Mr. Vasileios. Thank you. I am trying to write it in an excel, I will let you know if there is place where it does not connect. My main concern is, the modulus reduction curves recommended in the literature can be used to define the G/Gmax and damping values e.g. Vucetic Dobry for clays. In plaxis we can input, the gama0.7 value by reading from the curve where the G/Gmax= to 0.722. However due to the input of the other values (E50, Eur, m...) this curve sometimes is not close to the literature recommended values.
Though I have seen different estimations of gama0.7 in the literature.
(image attached below)
Effect of Jet-Grout Columns on the Seismic Response of Layered Soil Deposits, 2016, Pouya Sedighi.
Dear Jamal,
1) The tangent curve doesn't change with Eur, apart from the fact that Eur is the cut-off of the stiffness reduction curve, so with a different Eur the strength reduction curve is only cut off at a different point. But the equation of the strength reduction curve does not contain Eur. The secant curve is of course an average stiffness over a strain interval, so that indeed changes starting from the cut-off by Eur. But again, until the cut-off the secant curve is independent of Eur. So you have to be sure what curve literature gives you: a tangent curve or a secant curve....2) I have the feeling you're mixing two things. The parameter combination G0 + gamma_0.7 describe the shape of the curve. The graph above only indicate where in the small strain range one can find loose sand and dense sand: the indicated lines are not parameters that describe the curve. On the other hand, if you would have a different value like gamma_0.2 instead of gamma_0.7 it is not so difficult to fill in the HSsmall model a gamma_0.7 and calibrate it to match your gamma_0.2. Or you do it in a spreadsheet if you find that easier. Hence, there is no need for other input parameters as the would just describe another point on exactly the same stiffness degradation curve.
With kind regards,
Dennis Waterman
Thank you Mr. Dennis. Correct, indeed I have been mixing the two.
I saw your live meetings in person in Dubai and Netherlands I guess, where, for instance parameters of HS small and many other classes are to be held. Where I am at the moment, reaching these areas is almost impossible. Is there a webinar regarding HSsmall? Are the resources given at the end of those courses available for public? Or can we purchase them?
I don't think we're having a webinar on parameters of the HSsmall model. We do indeed teach about it in in-person courses. The material of those courses are handed out to the participants, but are not publically available as we consider that just the material without hearing the explanation has less value or could even be misunderstood which will lead to the incorrect use of the model.
I understand. Thank you Mr. Dennis.
Dear Mr. Dennis,
I wanted to ask a follow on the calibration of HS model. As stated in plaxis article ´ground response analysis´ the values of γ0.7 and Go/Gs in order to match the 1D response analysis.
“The Gs/G0 curve is described in literature by Vucetic & Dorby (1991) according to different values of the plasticity index. In this example, the clay layer is characterized by a plasticity index PI of 50 % and the relative curve is displayed in blue. The value of γ0.7 has to be chosen in order to have the best fitting between the calculated Gs/G0 and the curve relative to the specific PI from Vucetic & Dorby (1991)”.
As seen in the images for γ0.7 (%) =0.07, the Go/Gs match.
And for Go=31200 kPa and Gur=4062kPa the damping curve (together with the cut off values) are argued to give the best match. According to the graph, how do you comment for the best match values? The part in red is okay too close to the reference values, but the part shaded in blue is not close to the reference value. Or we should be concerned for the region of the desired γ0.7 (%) =0.07 value and ignore the blue shaded area?
For any kind of curve in geotechnics it's almost impossible to match the entire curve. So as you say, the best fit is determined in the area of interest.