STRENGTH AND DEFORMATION PROPERTIES OF SAMPLES UNDER DIFFERENT LOADING PATHS

1. STRENGTH ANDDEFORMATION PROPERTIES OF SAMPLES UNDER DIFFERENTLOADING PATHS By Cheng Zhao and Mingrong Shen Tongji University, China 2005.8 in Nagasaki University

2. Presentation Outline • Introduction • Normal trialxial test • Different loading paths • Comparing of strength • Deformation properties • Conclusions

3. Introduction • In underground excavation conditions，rock often undergoes very complicated loading and unloading process. However，in laboratory tests on rock，such as normal triaxial test，the loads are usually exerted gradually and continuously, which cannot simulate the real stress state of rock precisely.

4. Introduction • It is capable of supplying axial loading or confining pressure or both of them simultaneously. The maximum capacity is 5000 kN in axial loading and 150 MPa in confining pressure.

5. Introduction .Controlling system .Controlling system Controlling system Some of the rock samples

6. Normal trialxial test

7. Normal trialxial test

8. Different loading paths Two kinds of different loading paths

9. Comparing of strength Mohr-Coulomb theoryNormal test: where Different loading path: where

10. Deformation properties The hysteretic loop can be divided into 3 steps: 1.The beginning step 2. All the cracks are clogging 3.The cracks developed quickly

11. Conclusions • Comparing the curves with it in the normal triaxial tests, though loading path has an effect on the stress-strain behaviour of rocks, the loading paths have little effect on the strength of rock samples. They all follow the Mohr-Coulomb theory.

12. Conclusions • In the normal traixail tests, the hysteretic loop can be divided into 3 steps: (1) we call it the beginning step, the direct-pressure decreased a lot while the deformation’s recovery is very finite, for the internal friction must be overcome firstly. (2) Almost all the cracks are clogging, so the curve just shows us the natural Young’s modulus of the sand rock samples. (3) In this step The cracks developed quickly, and the residual deformation with different axial-stresses and confining pressures can be judged by the areas of the hysteretic loops .

13. Thank You! Any questions?