Also, can we say that a rock mass with highly fractured closely spaced parallel joints will behave as a jointed rock?
A fractured rock mass, is called rift which.The more fragmented rock is found, you have less compressive resistance and minor tensile strength.
On the other hand, the more fractured rock mass, more plastic will be.
Dear Koushik,
the strength of a jointed rock is only relevant for observations in the rock mechanics lab. I would say. For geomechanics and civil/mining applications youi always would consider the rock mass, e.g. larger rock volumes, of course,
In a fractured rock mass which include fractures with variable orientation, the strength is controlled by the strength and frictional properties of the fractures. The strength of the pre-existing fractures usually is less than the undeformed rock itself. Exceptions may occur if the fractures are healed by re-mineralisation (calcite or quartz). In this case the healed fractures may be even stronger than the undeformed rock.
However, if you have only a 1-2 dominant fracture system characterised by parallel fracture sets in the rock mass, fracture strength is only the controlling factor of rock mass strength if they are oriented favourable in the in-situ stress field (highly oblique to maximum principal stress sigma 1). If not, fracture strength does not have an effect.
Last point regarding strength on rock sample scale are mechanical anisotropies on sample scale like cleavage and foliations. For example in a slate or shale with a well-developed mechanical or compositional foliation, rock strength parallel to the foliation may be weaker as well than in other directions. In this case, the styrength of the rock sample again depends on the orientation of the acting stress field similar to rock masses with only one dominant fracture set (see above).
I hope this helps. Kind regards, Jürgen
There are several discontinuities you can find in rocks and rockmasses. They affect them diffrently. If you have joints in a system then its not rock, its rockmass. So, you can explain more to get better answer.
I highly agree with the very clear answer to sir Adam. Thank you for the question Mr. Pandit and Mr. Adam, your session has made me clear as well.
Rock mass is different in its behavior in comparison to rocks. Rock mass is more deterministic than rocks. Rock is a sample drawn from rock mass to represent a rock mass. However, a rock mass may be jointed, the rock sample drawn from the rock mass may be incidentally free from any joints and discontinuities. As such, the rock mass will provide more reliable results of mechanical properties of rock as compared to a sample rock drawn from the same rock mass. The differences may be positive or negative, meaning thereby that the actual mechanical properties of rock mass may be higher or lower in magnitudes. Nevertheless, it is arduous and sometimes almost impossible to conduct the tests on rock masses, which calls for bringing the rock samples and preparing their specimens for testing in the labs to give fairly close idea of rock mass properties. However, a design engineer must try to correlate rock properties with rock mass properties for efficient design and also must give a factor of safety for engineering design for safety of structures in rock mass.
Hi Piyush Rai,
You can understand as jointed rock a single joint or a joint area/ or you can understand as jointed rock a obtained sample from a jointed rock mass.
I have enclosed for you the standard literature : "Strength of jointed rock masses" in which you could find the answer to your question.
Good luck
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