ISSN:
1082-5010
Keywords:
creep
;
dilatancy
;
damage
;
stability
;
failure
;
galleries
;
Engineering
;
Civil and Mechanical Engineering
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Architecture, Civil Engineering, Surveying
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
An analysis of stability of rectangular-like galleries or caverns is developed from the point of view of creep, creep failure and short-time failure. The initial stress distribution around the cavern just after excavation is obtained with an exact elastic solution. Further this solution is used in conjunction with an elastic/viscoplastic non-associated constitutive equation to determine first the domains around the excavation where the rock becomes dilatant, where compressible, and where a short-time failure is expected. This constitutive equation is further used to determine the creep of the rock around the opening, and where and when a creep failure is to be expected due to excessive dilatancy. It is shown that the location of the incipient creep failure depends on the stress concentration due to the presence of the ‘corners’, on the possible elongated shape of the cavern, and also to the stress concentration induced by the far field stresses. This location also depends on the internal pressure and on depth, and it can be determined quite accurately. Thus the location of incipient creep damage depends on a variety of parameters and the determination of this exact location is very important, and is described in this paper. It is shown that the evolutive damage is spreading mainly in the direction of minimum far field stresses or in the direction of greater elongation of the cross-section. The same constitutive equation allows us to determine the creep convergence (or divergence) of the walls, where this creep is quite fast and when for the first time the incipient creep failure due to dilatancy is to be expected. This timing depends primarily on the magnitude of octahedral shear stress. The time up to creep failure is shorter if this stress is larger (close to the short-term failure value), but tends towards infinity if the stress is relatively small (close but still above the compressibility/dilatancy boundary). Once the various failure modes are well understood the orientation and magnitude of far field stresses can be determined by this analysis if not known a priori. Also, once the location of losing the stability and that of the volume of rock involved in fast creep and creep failure are determined, one can suggest the optimal design of a support. The way in which the stress variation is influencing the above mentioned problem will be discussed in forthcoming papers. While the authors recognize the importance of the pre-existing rock discontinuities in the overall cavern stability, it was thought that a better understanding of this stability starts from analyzing a rock without such pre-existing discontinuities. The examples are given for rock salt.
Additional Material:
24 Ill.
Type of Medium:
Electronic Resource
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