Dear Dr. Qasim Abdulkarem Al-Obaidi

I think the grain size distribution has a considerable effect on the Air Entry Value AEV of Soil Water Characteristics Curve SWCC as well as on residual suction value.

Regards

Thanks, Eng. Ali Al-Shamoosi for your valuable answer.

Regards

Qasim Abdulkarem Al-Obaidi The PSD and the shape distribution plus chemical content affects the permeability of the soil or sediment. See:

Size and shape characterization in soils and sediments

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W120209SizeShapeCharacterizationSoilSediments.html

Dear Dr. Alan F Rawle

Thanks a lot for your valuable answer and for the very useful website.

I agree with you the PSD, Shape and Chemical content such as in Gypseous soil affects the Hydro-Mechanical behavior of the soil.

Regards

Dear Dr.@ Qasim Abdulkarem Al-Obaidi

This is a very important question.

I think the SWCC curve is affected by the grain size distribution of the tested soil.

For coarse grain soil: The Air-Entry VAlue AEV will be at a low suction range (closed to y-axis of Water content).

For Fine-grain soil: The Air-Entry VAlue AEV will be at medium suction range (fare from the y-axis of Water content),

Regards

Ali

Dear Mr. Ali Al-Shamoosi

Thanks a lot for your answer.

I agree with you. These topics need more research in order to investigate all types of soils.

Regards.

Qasim

Dear Dr. Qasim

I hope u r fine;

If I want to answer u briefly, it can be said the SWCCs depends on the pore-size diameter and the air bridges between them. So, when we have sand soils, because of the shape particles, the air bridges will be more than the fin soils, like silt and clay. In the sand cases, the SWCCs are low than others, this means low matric suctions and low water volumetric content.

For more information u can see the parts 5.3 to 5.8 in Fredlund's book with the title of "Unsaturated Soil Mechanics in Engineering Practice".

Regards