Triaxial Tests on Soft Rocks
Dr. An-Bin Huang
|Keywords:||軟弱岩石;三軸試驗;應力應變關係;小應變;soft rock;triaxial test;stress-strain relationship;small strain|
The mechanical properties of very soft to soft rock are between soil and rock. It is not easy to determine these properties using the conventional soil or rock testing equipment. A new triaxial testing system specifically developed for soft rocks has been developed. The new system is capable of applying up to 20 MPa confining stress to the specimen and measure local strains. Earlier reports have indicated that the deformability of soft rock at strains less than about 0.01% appears to be linear, elastic, and strain rate-independent. Under very small strains, the Young's modulus referred to as Emax, is mainly dependent on the consolidation pressure. The rock coring process is likely to cause fractures in the rock samples due to the loss of confining stress. Thus, it is advisable to re-apply the in situ stress upon the specimen in the triaxial tests. A series of consolidated undrained triaxial tests were performed on specimens cored from rock blocks obtained in Dakeng, Taichung. Results indicate that closure of cracks originally existed in the Dakeng rock block occurred when the confining stress exceeded 3MPa. Under a consolidation stress of 3MPa the Emax was approximately 4000MPa, was 1500, and was about 320. As strain increases, the Young's modulus decreases significantly, indicating a non-linear deformability. Under the same confining stress, high porosity soft rock specimens with a higher porosity had a more ductile behavior and lower shear strength. The stress-strain curve had an upward concave shape if the soft rock specimen was tested under low confining stress and cracks were present within the specimen. Under low confining stress, the peak and residual strength of the soft rock increased linearly with the confining stress.
|Appears in Collections:||Thesis|