Failure and convergence criteria for bolts in DDARF

The simulation of the whole process of initiation, propagation, penetration and breaking of rock cracks has been successfully realized by DDARF, while the effective failure and convergence criteria of bolts are scarce. For the tensile failure of the bolts, the maximum tensile stress criterion is adopted and the program is realized on VC++ platform. For the slippage failure of the bolts, grouting body's strength is judged by Moore-coulomb criterion, and the program is realized. For the convergence criterion of the program, a method for the ratio of the displacement difference of two adjacent steps to the displacement of the current step which is less than a certain minimum value is adopted, and the program is realized. At the same time, the effect of the relaxation factor on the convergence is studied. The failure and program convergence criteria for the bolts in DDARF are compared with those of the laboratory tests and applied in engineering examples. The results show that the failure and program convergence criteria of DDARF are effective, and can improve the efficiency and precision of the calculation, which may provide reference for engineering support of special positions. Reasonable relaxation factor is benificial to the convergence calculation. It is suggested that the relatively reasonable relaxation factor should be 1.4 ~ 1.8.