Dear all,
I am new to unsaturated soil mechanics, I am working on rainfall induced landslides.
Modeling of soil slopes involves modeling of unsaturated part of soil slope. Now I have a SWCC plot please tell me how to get the van Genuchten parameters. Procedures for determining van Genuchten parameters (Alpha, n, m...).
I kindly request please suggest any reading material as mentioned above.
Thank you in advance
Using Microsoft Excel Solver?
Chen et al., 2014. Gas and water relative permeability in different coals: Model match and new insights. International Journal of Coal Geology 122, 37–49.
Brown, A.M., 2001. A step-by-step guide to non-linear regression analysis of experimental data using a Microsoft Excel spreadsheet. Comput. Methods Prog. Biomed. 65, 191–200.
Dear Sir,
Thank you for the help. I will go though the study material.
Thank you once again.
Have you carried out grain size distribution ? I suggest you search for articles by Fredlund a Canadian Professor.
I have grainz size distribution data, but was unaware on how to find the parameters (alpha, m and n).
Plot the grain-size distribution (GSD) data and determine whether the soils are well graded or gap graded. From the GSD curve you could determine the soil particle shape factor alpha which ranged from 1.1 for fine-textured soils to 2.5 for coarse-textured soils (Arya et al 1999). Now did you estimate SWCC empirically or obtain from experiment ? Are the SWCCs adsorption or desorption curves ? If experimentally, then you can deduce n (rate of desaturation of the soil as suction exceeds the air-entry value) and may require finding the intermediate suction which could be obtained by subtracting the suction at air-entry value point on SWCC (the first point of inflection on SWCC ) from soil residual suction on SWCC (the second inflexion point where SWCC curve is about becoming flat and parallel to the horizontal axis). This intermediate suction is associated with desaturation region of SWCC and could be inserted into van Genuchten equation and subsequently solved to obtain n. This would only be possible after obtaining m from GSD curve fitting. You may also find the attached articles useful.
Adarsh,
One of the best references for unsaturated soil mechanics in general is "Unsaturated Soil Mechanics in Engineering Practice" By Fredlund Rahardjo and Fredlund. Here's a link http://www.amazon.ca/Unsaturated-Soil-Mechanics-Engineering-Practice/dp/1118133595
As for the van Genuchten parameters, I recommend using SoilVision software (here is a link (http://soilvision.com/subdomains/soildatabase.com). This knowledge based software helps you estimate unsaturated soil properties through 11 theoretical methods including van Genuchten method by inputting your SWCC data.
Moreover, since you are focused on rainfall induced landslides I highly recommend reading the extensive work done by Dr. Harianto Rahardjo.
Finally one of the best tools for numerical simulations of rainfall induced landslide scenarios is SVSlope coupled with SVFlux so I also recommend checking it out.
Hope this helps
Ahlam
Dear Mr. Moruffdeen A. Adabanija, could you write the exact citation of those two papers, please? They are obviously parts/chapters of a bigger book/proceedings.
Below are the exact citations of the papers:
Fredlund M.D., Wilson G.W. and Fredlund D.G. 2002. Use of grain-size distribution for estimation of soil-water characteristic curve. Canadian Geotech. Joournal 39:1103-1117 DOI:10.1139/T02-049
Fredlund D.G., Sheng D and Zhao J. 2011. Estimation of soil suction from the soil-water characteristic curve. Canadian Geotech. Journal 48:186-198 DOI:10.1139/T10-060
Fredlund M.D., Fredlund D.G. and Wilson G.W. 2000. An equation to represent grain-size distribution. Canadian Geotech. Journal 37:817-827
Validate your SWCC by fitting it to the Van-Genuchten equation. Assume different values for aplha, m and n. Once you get the best fit, this confirms the values of Alpha, m and n. It is quite straightforward procedure. Hope this helps.
Dear Sir,
Thank you for the suggestion, I will try it.
Thank you once again.
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