Sensitivity Analysis and 3 D-displacement Inversion of Rock Parameters for High Steep Slope in Open-pit Mining
Due to the complexity of multiple rocks and multiple parameters circumstance, various parameters are often reduced to only one parameter empirically to generalize geological conditions, ignoring the really influential parameters. A developed method was presented as a complement to 3D displacement inversion to obtain the relative important parameters under complex conditions with limited computational work. Furthermore, this method was applied to a high steep slope in open-pit mining to investigate field applicability of the developed system. Back analysis was conducted in the reality of the east open-pit working area of Daye Iron Mine and propositional steps were presented for parameters solving in complex circumstance. Firstly, multi-factor and single-factor sensitivity analysis were carried out to classify rock mass and mechanical parameters respectively according to the extent of their effects on deformations. Secondly, based on the results, main influence factors were selected as inversion parameters and taken into a 3D calculating model to get the displacement field and stress field, all of which would be the artificial network training samples together with inversion parameters. Thirdly, taking the real deformations as input for the trained back propagation (BP) neural network, the real material mechanical parameters could be obtained. Finally, the results of trained neural network have been confirmed by field monitoring data and provide a reference to obtain the matter parameters in complicated environment for other similar projects.
Long term stability assessment of Siah Bisheh powerhouse cavern based on displacement back analysis method
Siah Bisheh pumped storage powerhouse cavern with complex geometry, changeable geological formations and diverse geotechnical properties of rocks, is under construction on the Chalus River at the north of Iran. Powerhouse cavern is located near the lower dam reservoir and its crown is more than 30 m down the lower dam maximum lake level. After impounding of lower dam, powerhouse region will be located under saturated condition. Therefore long term stability assessment of the powerhouse cavern under saturated condition is unavoidable. In this study, displacement based direct back analysis using univariate optimization algorithm were applied and geomechanical properties of rocks, stress ratio and joints parameters were identified. Numerical modeling results are in good agreement with measured displacements using extensometers which confirm the numerical modeling accuracy and back analysis results. Then ordinary analysis of powerhouse cavern under natural condition using back analysis results were carried out. Results of analysis shows that powerhouse cavern is stable under natural condition and existing support system has suitable efficiency and could effectively control displacements. Finally, powerhouse cavern long term stability under saturated condition was analyzed. Results of analysis shows that after lower dam impounding, pore water pressure and uplift pressure in discontinuities around powerhouse cavern will arose and tend to local failure of powerhouse cavern in region 2nd and 3rd instrumentation arrays. To obtain powerhouse long term stability, it is recommended to construct a cutoff curtain around powerhouse cavern.
Numerical analysis of initiation and progressive failure in natural rock slopes—the 1991 Randa rockslide
The 1991 Randa rockslide in the Swiss Alps involved several complex mechanisms relating to geological, mechanical and hydrological processes for which no clear trigger can be asserted. This paper investigates the concept of progressive failure and the numerical modelling of rock mass strength degradation in natural rock slopes using the Randa rockslide as a working example. Results from continuum (i.e. finite-element) modelling are presented to illustrate a hypothesis, suggesting that initiation of a progressive rock mass degradation process, ultimately leading to failure, began following deglaciation of the valley below. Discontinuum (distinct-element) modelling is then applied to investigate the underlying mechanisms contributing to the episodic nature of the rockslide. Finally, the use of a hybrid method that combines both continuum and discontinuum techniques to model fracture propagation are discussed in the context of modelling progressive slide surface development linking initiation and degradation to eventual catastrophic failure. r 2003 Elsevier Ltd. All rights reserved.