I am trying to model a stone column in loose sand. To apply gravity loading for initial stresses in the domain, it is required to input elastic shear modulus and bulk modulus in gravity analysis. These parameters will be changed later on to required values in pushover/dynamic analysis.
My problem is what values of these elastic gravity parameters (E and mu, or G and B) shall be chosen for stone column and soil so as to have more effective stress in stone column as compared to soil at same depth.
Dear Tanmay,
Which software are you using in your analysis, to obtain elastic parameters lot of literatures are available. you have to choose correct elastic modulus form the literature or it is better to conduct the laboratory test to obtain the stress - strain characteristics of soils. The elastic modulus can be obtained from stress - strain characteristics of stone used for the analysis. You can conduct triaxial test to obtain the elastic properties of stone..ok all the best..
Dear Karthigeyen Sir,
Thanks for your reply. I am using OpenSees software for modelling liquefaction. In any geotechnical software, we apply gravity loading to generate the initial stresses before our intended pushover or dynamic loading is applied. As mentioned by you, for behaviour of soil in pushover/dynamic analysis, we can use parameters from literature based on SPT, CPT etc. but my question is about generation of initial stresses.
By default, this value is taken as high as E=600 MPa in some softwares. This value gives correct gravitational stresses i.e. (gamma'*z) for the soil domain considered (even if different soils are layered in the domain).
However, I have stone column in my model which means there are two different soil with different unit weight present at same depth. By theory, we should have initial effective stresses more in stone column zone as compared to soil zone at same depth. My issue is to specify Elastic parameters in gravity step for soil and stone column so as to have representative initial stresses at the end of gravity analysis.
Thanks in advance...
Dear Tanmay,
I understand your theory but you tell me that in the initial gravity analysis stage is it required to use separate elastic properties for soil and stone. As, i understood that gravity analysis in initial stage is to predict the stress - strain characteristics of soil alone and now, stone column is used to improve its characteristics. So, in the initial stage you assign elastic properties are the same for both soil and stone. Then, in the second stage while need to know the modified characteristics of composite ground, assign the respective elastic properties of soil and stone. I have explained to you for obtaining the elastic properties of both soil and stone. It is very simple and easy to work sequences of analysis in a phased manner. ok all the best..
Dr. Karthigeyan, @Karthigeyan . S
I am simulating the stone column in liquefiable sand. I used PDMY for materials. How I can use the sand material for whole model and elements at initial state (first stage) and after that (for dynamic stage) change the parameters of columns elements to stone material? Should I again define the element by stone material with the same numbers of elements? or I should change the parameter of material?
in other words, I don't know how I enter, at first, sand parameter for the column area and after that replace that area by stone material.
would you please describe for me?
Thank you in advance.
Best,
Atefe