It  decreases the stability especially when it saturated with water as it makes a soap like inter-layers. clay has the ability of swelling  when it absorbs water....

Dear Mr. Azimian,

I can support the comment of Dr. Diabat. But I encourage you to disclose your precise issue to the audience and the type or assemblage of phyllosilicates. If this has not yet been done describe the outward appearance of the clay-bearing rocks as to their morphology and  position. Please be more detailled as to the rocks associated with the argillaceous rocks and the structural environment. I can imagine that there may a solution to your problem.

I refer to this paper of mine:

DILL, H.G., HAHNE, K. and SHAQOUR, F. (2012) Anatomy of landslides along the Dead-Sea-Transform Fault System in NW Jordan.- Geomorphology, 141-142: 134-149.

Should you have further questions as to the composition of the argillaceous rocks, feel free to raise your questions.

Best regards

Harald G. Dill

Thanks Dr. Harald G. Dill and Dr. Abdullah Diabat for your comments. I search this issue for my phd thesis. I have not considered special location yet. Taking account consideration that Major engineering projects such as dams, roads, and

tunnels are now under construction in argillaceous rocks, there is less knowledge concerning the behavior of this type of material and role of them in slope instability. Therefore, I want work my thesis in PH.D on this issue and I search this subject for obtain paper  and ... that previous work on this subject. 

See also the paper of Erdal Unal (Modified- Rock Mass Rating): Ünal, E., 1996. Modified rock mass classification: M-RMR system. In: Bieniawski, Z.T.

(Ed.), Milestone in Rock Engineering: A Jubilee Collection. InBalkema, pp. 203–223.

ypou can find some special refernece for clay-bearing strata and rock mass behaviour for both underground and surface mines.

Youcan also contact Marco Barla from Politecnico di Torino, he worked on clay bearing rock and swelling condition in tunnelling.