Hi Mustafa,

A generally valid relationship between the friction angle and cohesion can not be found, because there are two different physical properties. This does not mean that one from  in situ measurements of a test field can not find an empirical, statistical relationship.

„Friction angle or angle of internal friction is the angle under which a solid or a granular material may be loaded, without to slide or to fail. It is a measure of the friction-ability of its surfaces  (friction and roughness or smoothness). The internal friction angle of granular media is not the same as the "dump angle" of bulk or the "slope angle" of a landfill."

“Under cohesion or adhesion, in the soil mechanics one understands the cohesive forces in cohesive soils. It is only in soils markedly containing which have very small grains, i.e. in which the surface properties of the individual grains are stronger as the properties that are caused by its mass, such as clay. The cohesion makes in soil or fine grain loose rock to the internal bond of the individual particles to each other.

The cohesion has mostly the character c and the physical unit of a stress; it is a shear stress. It is a special case of the shear strength."

Apparent cohesion

Once the grains of sand are surface dried, the sand has no cohesive properties longer, but is only held together by friction forces. Wet sand has an apparent cohesion. It is bonded by capillary forces between the sand grains.

Internal friction and cohesion are two different properties of loose rocks, its shear strength both together determine. Wet sand: In the determination of the apparent cohesion, can be found empirically a relationship between apparent cohesion, water content, pore pressure and angle of friction. However, this relationship is not universal. It is important amongst other things to distinguish between the individual sizing of sand at in situ conditions. In situ can be used the Cone Penetration Tests with radiometric probe, see figure.

All the best

Michael Lersow

Dear Researcher

can you elaborate your question.if it is what i am thinking then Please check this attachments if it is helpful for you.

Regards

http://phi.uhce.ox.ac.uk/pdf/ChronicConditions/DH_REVIEWS_NOVEMBER_2007.pdf

http://jpepsy.oxfordjournals.org/content/34/9/917.full

These parameters are independent, and the only way to establish those is through experimental work of the material of your concern

The phi and c are often negatively correlated, but as mentioned above testing is the best way to get reasonable value

Hi Mustafa,

A generally valid relationship between the friction angle and cohesion can not be found, because there are two different physical properties. This does not mean that one from  in situ measurements of a test field can not find an empirical, statistical relationship.

„Friction angle or angle of internal friction is the angle under which a solid or a granular material may be loaded, without to slide or to fail. It is a measure of the friction-ability of its surfaces  (friction and roughness or smoothness). The internal friction angle of granular media is not the same as the "dump angle" of bulk or the "slope angle" of a landfill."

“Under cohesion or adhesion, in the soil mechanics one understands the cohesive forces in cohesive soils. It is only in soils markedly containing which have very small grains, i.e. in which the surface properties of the individual grains are stronger as the properties that are caused by its mass, such as clay. The cohesion makes in soil or fine grain loose rock to the internal bond of the individual particles to each other.

The cohesion has mostly the character c and the physical unit of a stress; it is a shear stress. It is a special case of the shear strength."

Apparent cohesion

Once the grains of sand are surface dried, the sand has no cohesive properties longer, but is only held together by friction forces. Wet sand has an apparent cohesion. It is bonded by capillary forces between the sand grains.

Internal friction and cohesion are two different properties of loose rocks, its shear strength both together determine. Wet sand: In the determination of the apparent cohesion, can be found empirically a relationship between apparent cohesion, water content, pore pressure and angle of friction. However, this relationship is not universal. It is important amongst other things to distinguish between the individual sizing of sand at in situ conditions. In situ can be used the Cone Penetration Tests with radiometric probe, see figure.

All the best

Michael Lersow

C and Phi are two independent strength parameters.

C and phi are two independent parameters between each other. The cohesion comes from the bound between soil grains and phi comes from the friction between the grains to roll. There is not relation between C and phi, for example a cohesionless can have 5, 10, 15, 20, etc degrees of phi and a cohesive soil with for example 15° of phi can have 5-10-50-100 kPa. Of course there are some common expected values for each soil type.

In a specific soil type they depend on the degree of compactation, soil mineralogy and internal structure. Also depends if you are looking for the effective or the total parameters (drained or undrained). The most common lab tests in order to obtain and characterize the soil strenght are: direct shear test, triaxial unconsolidated undrained UU test, triaxial consolidated undrained CU test and triaxial consolidated drained CD test. You should characterize your problem (loading rate, pore pressure dissipation, drainage boundary conditions) in order to know which parameters your are looking for.

You should not to look of the corelatoon between thi two parameters.Both of them as it is explained by several researchers has different physical meaning, and depends on lot of other physical properties and contributed together on the shear strength of some soil or rock mass materials. The level of normal stress during the testing can also be very important and in general there are non linear connections between normall and shear streswhich influences the non linear character of phi.

Dear Mostafa,

I used to get baffled by this same issue but, what my experience & researches taught me later were exactly the same as what other experts have mentioned here.

The best thing is to carry out the strength tests (direct shear or others). Sandy soil can exhibit some 'c' value (very low though) & similarly, Clayey soil can exhibit low (small amount) 'phi' value. i.e., they are termed as 'c-phi' soil.

Therefore, it is always recommended to conduct the soil strength test in your study/work.

Cheers,

Sumit

C and Phi is two dependent parameter with minus correlation coefficient between -0.24 till -0.7.

Best,

Sina Sasanian

Do you have any references for your Idea?

please share it with me