Hi Qasim

Please read the following ebook:

"Unsaturated Soil Mechanics in Engineering Practice"

Delwyn G. Fredlund, Hendry Rahardjo, Murray D. Fredlund

ISBN: 978-1-118-13359-0 July 2012 944 Pages

You can carry out suction test of a soil at different water content and create SWCC or using grading of soil, you may be able to develop SWCC. The relationship between water content and suction (mainly volumetric water content vs. matric suction) is referred to be SWCC or Soil Water Retention Curve.

Best regards

Ravi

The soil-water characteristic curves (SWCC) describes the thermodynamic potential of the pore water in soil related to the free water as a function of a fraction of water consumed by the soil material (Lu and Likos, 2004). The fraction of water can be described as volumetric water content (θ), gravimetric water content (w), and level of saturation (S). The SWCC gives a conceptual comprehension of the energy state of the water phase, and the mass or volume of water in the soil. Furthermore, the SWCC is an interpretive model that uses the elementary capillary model to describe the water distribution in the voids. The effects of the soil texture, gradation, and void ratio have also become part of the measured data interpretation of laboratory SWCC. Many properties of unsaturated soils that include the coefficient of permeability, shear stress, volume strain, pore size distribution, and the quantity of water within a pores at a suction value, can be estimated from the SWCC. Figure 1 shows a typical SWCC. The graph during de-saturation exhibits three stages: capillary saturation zone, de-saturation zone, and residual saturation zone. In the capillary saturation zone, water in the pores is in tension. However, the soil remains saturated. Furthermore, the stage stops at air entry value (AEV), and the suction dominates the larger pores inside the soil material. The AEV of the soil is the value of the matric suction at which the air starts to fill the larger pores. When the suction value is higher than the AEV, the degree of saturation reduces quickly upon relatively small suction values and decreases gradually when the soil suction increases. There is a wide range of AEVs corresponding to different void ratio values. The denser the soil, the greater the AEV. Therefore, for a soil material with smaller void ratio values, a marginal variation of the degree of saturation can be considered for smaller suction values. The transition zone is an area where water is drawn from the soil matrix by evaporation on the boundary or other removal mechanisms. This stage stops at the residual water content (θr) where pore-water becomes discontinuous. At this point, the hydraulic conductivity is decreased by several orders of intensity and controlled by vapour transport and fluid transport. Inside the residual zone, water is adsorbed tightly onto soil particles, and flows occur only by vapour transport. A higher suction value change is required to pull out the extra water in the soil. This stage is attained when the moisture content is equal to the oven dryness. When the soil material is heated to 105oC, the water portion in the soil material is zero, and soil suction is approximately 1.106kPa (Fredlund and Rahardjo, 1993). Soil parameters such as the grain size distribution, void ratio, density, organic matter content, clay content, and mineralogy influence the shape and the feature of the SWCC. For example, sandy soil pores are greater than clay soil pores. During drying out, the quantity of water at a given suction value in clay soil will be greater than the quantity of water in sandy soil, due to the smaller pores diameter that exhibits a higher water retention. Figure 2 describes the typical SWCCs for sand, silt, and clay. Soil parameters such as the grain size distribution, void ratio, density, organic matter content, clay content, and mineralogy influence the shape and the feature of the SWCC. For example, sandy soil pores are greater than clay soil pores. During drying out, the quantity of water at a given suction value in clay soil will be greater than the quantity of water in sandy soil, due to the smaller pores diameter that exhibits a higher water retention. Figure 2 describes the typical SWCCs for sand, silt, and clay.

REFERENCES

Lu, N., Likos, W.J., 2004. Unsaturated soil mechanics, John Wiley & Sons. Inc, Hoboken, USA.pp. 584.

Fredlund, D.G. and Rahardjo, H., 1993. Soil mechanics for unsaturated soils. John Wiley & Sons.

Fredlund, D.G. and Xing, A., 1994. Equations for the soil-water characteristic curve. Canadian geotechnical journal, Vol. 31, No. 4, pp. 521-532. Doi: 10.1139/t94-061.

Dear Dr. Al-Obaidi

in case you mean to represent the relationship between the Suction and water content there are many empirical equations such as:

1- Brooks and Corey 1964

2- Van Genuchten 1980

3- Fredlund and Xing 1994

but in case you want to predict the curve without experimental work

there are some correlations that use the particle size distribution

such as;

1-Fredlund et al,. 1997

2-Benson et al,. 2014

in case you have one point measured you can predict the curve as by

Houston et al,. 2006

in case you have limited data you can still predict the curve ending as suggested by : Ren et al,. 2020

and there are many studies that correlate the index properties as well.

best regards

References:

Brooks, R., & Corey, T. (1964). HYDRAU uc properties of porous media. Hydrology Papers, Colorado State University, 24, 37.

Van Genuchten, M. T. (1980). A closed‐form equation for predicting the hydraulic conductivity of unsaturated soils. Soil science society of America journal, 44(5), 892-898.

Fredlund, D. G., & Xing, A. (1994). Equations for the soil-water characteristic curve. Canadian geotechnical journal, 31(4), 521-532.

Fredlund, M. D., Fredlund, D. G., & Wilson, G. W. (1997, April). Prediction of the soil-water characteristic curve from grain-size distribution and volume-mass properties. In Proc., 3rd Brazilian Symp. on Unsaturated Soils (Vol. 1, pp. 13-23). Rio de Janeiro.

Benson, C. H., Chiang, I., Chalermyanont, T., & Sawangsuriya, A. (2014). Estimating van Genuchten parameters α and n for clean sands from particle size distribution data. In From Soil Behavior Fundamentals to Innovations in Geotechnical Engineering: Honoring Roy E. Olson (pp. 410-427).

Houston, W. N., Dye, H. B., Zapata, C. E., Perera, Y. Y., & Harraz, A. (2006). Determination of SWCC using one point suction measurement and standard curves. In Unsaturated Soils 2006 (pp. 1482-1493).

Ren, X., Kang, J., Ren, J., Chen, X., & Zhang, M. (2020). A method for estimating soil water characteristic curve with limited experimental data. Geoderma, 360, 114013.

If you want to obtain soil-water characteristic curves, based on simple physical properties of soils, I recommend Gustavo Torres Hernández's research, "Estimating the Soil–Water Characteristic Curve Using Grain Size Analysis and Plasticity Index", A Thesis Presented in Partial Fulfillment of the Requirements for the Degree Master of Science, from the University of Arizona, 2011. About it, we have prepared calculation tools for the estimation of characteristic curves of different soils in Cuba, and we are currently developing research to correlate the effectiveness of the equations proposed by Torres Hernández in different Cuban soils.

Dear Dear Dr. Al-Obaidi

In addition to my previous answer, many empirical, analytical, and statistical models can be used to fit the experimental data and describe the SWCC. The measured volumetric water content values obtained from the experiments can be compared to the predicted volumetric water content values, based on the matric suction values obtained from the models proposed by Van Genuchten (1980), Durner (1994), Fredlund and Xing (1994), Kosugi (1996) and Seki (2007). SWCC modal types are summarized in Table 1. The SWRC Fit program can be used to perform the non-linear fitting of SWCCs using the five models above mentioned, estimate the fitting parameters, determination coefficient, and Akaike information criterion (AIC). SWRC Fit program utilizes a computation language GNU Octave Seki (2007). A logarithmic scale can used because of the higher range of soil suction values. The soil water characteristic curve (SWCC) is written in θ(ψ) functional form where θ is the volumetric water content

and ψ the matric suction.

REFERENCES

Van Genuchten, M.T., 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils 1. Soil science society of America journal, Vol. 44, No. 5, pp. 892-898. Doi: 10.2136/sssaj1980. 03615995004400050002x.

Durner, W., 1994. Hydraulic conductivity estimation for soils with heterogeneous pore structure. Water resources research, Vol. 30, No. 2, pp. 211-223. Doi: 10.1029/93WR02676.

Fredlund, D.G. and Xing, A., 1994. Equations for the soil-water characteristic curve. Canadian geotechnical journal, Vol. 31, No. 4, pp. 521-532. Doi: 10.1139/t94-061.

Kosugi, K.I., 1996. Lognormal distribution model for unsaturated soil hydraulic properties. Water Resources Research, Vol. 32, No. 9, pp. 2697-2703. Doi: 10.1029/96WR01776.

Seki, K., 2007. SWRC fit–a nonlinear fitting program with a water retention curve for soils having unimodal and bimodal pore structure. Hydrology and Earth System Sciences Discussions, Vol. 4, No.1, pp.407-437. Doi: 10.5194/hessd-4-407-2007, 2007.

Dear Mr. Sir Armand Augustin Fondjo Yoermes Glez Haramboure Bashar Alibrahim Sinnappoo (Ravi) Ravindran

Thanks a lor for all of your valuable answers and literatures about the SWCC that you provide above.

It seems to be that you don't get my question correctly.

I work in the field of unsaturated and collapsible soils since more than 10 years ago, please see my publishing below.

I tried from my above question regarding to SWCC to open a scientific discussion regarding the phylosophy of representing the SWCC and methods of determention.

I try to get your opinions and answers about this issue " is any relationship between Water content and Suction of soil can be considered as SWCC irregrisive the initial suction, residual suction and AEV?"

For Example: Water content rane (10-30 %) and Suction range ( 100-10 kPa)

I hope that my question is clear now.

thanks a lot for you participation in this discussion.

Thesis Hydro-Mechanical Behaviour of Collapsible Soils

Al-Obaidi 2014, PhD Thesis