co efficient of friction between concrete blocks

[jacs127]

Dear friends,

I have to check the existing stability of a block wall and it is constructed using precast blocks more than 15 years ago on the sea front. Now in sliding stability checking what should be the co-efficient of friction adopted. Considering the old concrete, some silt diposition and other factor if any ref is available than please share.. i also request all of you to kindly share your views also..

regards,

jacs127

[ynopum]

It will be useless to check the stability without any real data for your structure, but only using some literature and advices (it could be illegal, depending of the regulations).

My advices (except of testing) are:
Do not include cohesion at all, as the structure is not monolithic. So at zero stress - "zero strength". No tension of course!
The weak planes are the contacts between the blocks, so check only them. Check only sliding through these contacts and the base.
Check overturning safety at the base, and at each contact (you don't need the contact strength.
Include water penetrating the contact!
Don't forget the wave action!

The friction angle depends on the surface smoothness and the aggregate material of the concrete. Usually testing gives values between broad range - 30~50 degrees. The lower is for high paste concrete. I expect that during the years and the water abrasion there should be some "penetration" of the surfaces, with washing of the fine material, and leaving the coarse aggregate "interlocked". But the actual strength depends on the contact surface, the aggregate shape and its bond-strength with the paste.

If it is impossible (whatever reason) to test the blocks, then do a back calculation - to find what friction between blocks is enough to keep the wall still standing on water, waves, some other forces, which you should know better than me. Then if the necessary friction is very low - (i.e. below 35 degrees) - it seems the wall should be safe.

[jacs127]

thanks

but i am just checking the sliding stability at some base section (not at the interface betwn wall and foundation soil/rock but at intermediate block joints)... in order to get FOS i want to calculate the friction resistance at that section and for that i need frictional coefficient (mue) ... some say take it 0.6 but it will be optimestic to adopt that as it is recommanded for fresh precast joints... another it is in saturated condition and silt deposition is also expected... anyone know any study carried out...