Time dependent behaviour of Class II rocks under the confining pressure

Research Project

Project/Area Number	61460192
Research Category	Grant-in-Aid for General Scientific Research (B)
Allocation Type	Single-year Grants
Research Field	資源開発工学
Research Institution	The University of Tokyo
Principal Investigator	NISHIMATSU Yuichi The University of Tokyo, 工学部, 教授 (70010741)
Co-Investigator(Kenkyū-buntansha)	AKIYAMA Masao The University of Tokyo, 工学部, 助手 (00011172) OKUBO Seisuke The University of Tokyo, 工学部, 助教授 (90092155)
Project Period (FY)	1986 – 1987
Project Status	Completed (Fiscal Year 1987)
Budget Amount *help	¥4,700,000 (Direct Cost: ¥4,700,000) Fiscal Year 1987: ¥1,400,000 (Direct Cost: ¥1,400,000) Fiscal Year 1986: ¥3,300,000 (Direct Cost: ¥3,300,000)
Keywords	Rock / Visco-elasticity / Time-dependent behaviour / Constitutive equation Finite element method / cOnfining pressure / 周圧 / post-failure領域 / 三軸圧縮試験 / 応力緩和試験 / クリープ試験
Research Abstract	Triaxial compression tests were performed upon 5 sample rocks to investigate the effect of loading rate by constant-strain-rate method for a Class I rock and stress- feedback method for the other Class II rocks. Results show that strength increases with loading rate, and that stress-strain curve in the post-failure region at a higher loading rate encloses those at lower rates. Also, the unloading compliance of rock specimen in the post-failure region was investigated by repeated unloading-loading cycles. It is found that the inverse of comliance decreases linearly with stress at which the unloading cycle starts. Based on the test results a simple model which explains the effect of loading rate and the compliance change in the post-failure region was proposed, the model can also explain behaviours under constant strain (relaxation) and constant stress (creep) qualitatively, though it has some incompletenesses such as the inability of explaining strain hardning phenomenon. The model was applied to simulate the time-dependent behaviour of underground roadway in mine. In the calculation, FEM techinique was used with paeameters assumed on the basis of test results of sample rock. The calculated results are compared with those of field measurement conducted at two nines located in Akita. The roadways considered in this study are U-shaped and supported by rock bolts or steel arch sets. The calculated results of convergence and extension in the rock wall indicate a fairly good coincidence at least in qualitative means, with measured ones, It can be said that the model showed a good potential for application purpose. However, for quantitative discussion, more accurate estimation of rock pressure and strength of rock mass may be inevitable.