Adopted damage mechanics, constitutive relation and damage evolution equation of jointed rockmass are presented and used to evaluate the deformation behavior and stability of jointed rockmass. The application to engineering shows that the model presented is reasonable and practical.
A great number of engineering practices have indicated that the failures of rockmass are mostly because of the evolution of internal deficiency such as joints and cracks, so it's quite necessary to study the weaken and damage-evolution effects of such joints and cracks in rockmass. Commonly we use anchor to reinforce rock mass and restrict its deformation and failure. To study the deformation character of such anchored rockmass, we have to establish an effective model, which can describe the reinforcement effect of the anchor in jointed rockmass. In this paper, a constitutive model and damage evolution equation of joint-crack rockmass is established, and a kind of anchored- damage rock clement is devised to evaluate the stability and deformation of the rockmass. At last, an engineering application of stability analysis in an underground workhouse is presented.
Assuming that there are M groups of generalized joints.
After being added into rockmass, anchor and its surrounding jointed rockmass form a kind of anchor-damage column element (see Fig.1), it is built in jointed rockmass, and formulated column element of damage rockmass with bolts (CEDRB). In order to describe restricting effect of the bolt on deformation of surrounding rockmass, the stiffness of CEDRB will be added into the stiffness matrix of jointed rockmass elements in computing process. Assuming that CEDRB is a kind of orthography damaged medium and on the basis of energy equivalent theory.
Considering main workhouse of a power station, the upper span of its anchored rock beam is 3 1.60m, the bottom span is 30.00m. The maxim height of its excavated sidewall is 88.62m, and the upper sidewall's height of draft tube is 58.12m, the total length of this power station is 352.60m, where the underground workhouse part is 280.60m. The ground elevation of underground main workhouse is generally 190–200m and the bedrock is mainly composed of amphibole plagioclase granite and anorthosile enclosure. There are three sets of faults in the area of workhouse: NNN, NE and NEE-EW, among which the NNW fault angle with middle line of workhouse greater than 50°, the other two faults are poorly cementation, comprising with some substance, locally with soil. Fissures in workhouse area are fully developed, mainly composed of steep dip fissures, which takes a fraction of 61.5% of all fissures, and moderate dip fissures take 24.7%, low dip fissures take 13.7%. Surrounding rock are slightly fresh rock, mainly belongs to I, II block type.
The calculating range of main workhouse includes No.2, 3, 4, 5, and 6 of machine units.