5:15 PM - 6:45 PM
[SCG44-P12] Prediction of natural fracture systems development in rock masses: recent experimental and numerical modelling results
Keywords:Geomechanics, Inelastic strain accumulation, Non-associated plasticity, Hardening
The study is devoted to the problem of prediction natural fracture systems development in rock masses. The obtained results show that usage of non-associated plastic flow law makes it possible to predict positions and spatial orientations of natural shear fractures solely from knowledge on stress changes of the rock, yet a number of special core experiments are required for the results to be reliable. The developed experimental program, theoretical methodology of experimental results interpretation, obtained experimental data, validation procedure, and numerical model of natural fractures development are covered in the study.
A series of cyclic triaxial loading tests were conducted on rock samples of variable morphology. Each cycle contained loading a sample up to a certain point above elasticity limit and unloading the sample to atmospheric conditions. Triaxial loading tests were accompanied with detailed studies of acoustic waves propagation along different directions within the sample before loading, during loading and unloading steps, and between the cycles. Difference in acoustic waves propagation was interpreted in terms of inner structure changes due to inelastic strain accumulation.
Obtained stress vs strain curves were analysed to define parameters of non-associated plastic flow law with friction hardening. Friction hardening was used to estimate orientations of optimally oriented planes for shear fractures to develop. At the same time, brittleness calculation was performed to evaluate portion of inelastic energy release to quantitatively evaluate relative free surface associated with shear fractures of different spatial orientations. Finally, results of detailed acoustic studies were used to establish relationship between inelastic strain accumulation, development of shear fractures, and their effect on effective dynamic elastic moduli. As a result, the study provides a procedure to predict development of shear fractures of rock masses based on known history of its stress state evolution.
The suggested model was incorporated into three-dimensional finite element numerical modelling software. Numerical modelling results were validated based on experimental data and proved to provide reliable estimations of different scale natural fracture systems development, granting a tool to deal with natural fractures in rocks, which can be helpful for various problems of rock mechanics, such as underground constructions risk analysis, well drilling, natural resources exploration and development, and others.
A series of cyclic triaxial loading tests were conducted on rock samples of variable morphology. Each cycle contained loading a sample up to a certain point above elasticity limit and unloading the sample to atmospheric conditions. Triaxial loading tests were accompanied with detailed studies of acoustic waves propagation along different directions within the sample before loading, during loading and unloading steps, and between the cycles. Difference in acoustic waves propagation was interpreted in terms of inner structure changes due to inelastic strain accumulation.
Obtained stress vs strain curves were analysed to define parameters of non-associated plastic flow law with friction hardening. Friction hardening was used to estimate orientations of optimally oriented planes for shear fractures to develop. At the same time, brittleness calculation was performed to evaluate portion of inelastic energy release to quantitatively evaluate relative free surface associated with shear fractures of different spatial orientations. Finally, results of detailed acoustic studies were used to establish relationship between inelastic strain accumulation, development of shear fractures, and their effect on effective dynamic elastic moduli. As a result, the study provides a procedure to predict development of shear fractures of rock masses based on known history of its stress state evolution.
The suggested model was incorporated into three-dimensional finite element numerical modelling software. Numerical modelling results were validated based on experimental data and proved to provide reliable estimations of different scale natural fracture systems development, granting a tool to deal with natural fractures in rocks, which can be helpful for various problems of rock mechanics, such as underground constructions risk analysis, well drilling, natural resources exploration and development, and others.