Advances in Civil Engineering | Volume 2018 ,2018-04-03 |
The Numerical Simulation of Hard Rocks for Tunnelling Purposes at Great Depths: A Comparison between the Hybrid FDEM Method and Continuous Techniques | |
Research Article | |
Nicholas Vlachopoulos ^{1} Ioannis Vazaios ^{1} | |
Show affiliations | |
DOI：10.1155/2018/3868716 | |
Received 2017-12-01, accepted for publication 2018-02-27, Published 2018-02-27 | |
摘要
Tunnelling processes lead to stress changes surrounding an underground opening resulting in the disturbance and potential damage of the surrounding ground. Especially, when it comes to hard rocks at great depths, the rockmass is more likely to respond in a brittle manner during the excavation. Continuum numerical modelling and discontinuum techniques have been employed in order to capture the complex nature of fracture initiation and propagation at low-confinement conditions surrounding an underground opening. In the present study, the hybrid finite-discrete element method (FDEM) is used and compared to techniques using the finite element method (FEM), in order to investigate the efficiency of these methods in simulating brittle fracturing. The numerical models are calibrated based on data and observations from the Underground Research Laboratory (URL) Test Tunnel, located in Manitoba, Canada. Following the comparison of these models, additional analyses are performed by integrating discrete fracture network (DFN) geometries in order to examine the effect of the explicit simulation of joints in brittle rockmasses. The results show that in both cases, the FDEM method is more capable of capturing the highly damaged zone (HDZ) and the excavation damaged zone (EDZ) compared to results of continuum numerical techniques in such excavations.
授权许可
Copyright © 2018 Nicholas Vlachopoulos and Ioannis Vazaios. 2018
This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
图表
Schematic of the Hoek–Brown criterion strength envelope and the composite strength envelope of the DISL model [16] (modified after [17]).
Tunnel model configuration created in Irazu (left) and in RS2 (right). The geometrical characteristics of the excavation and the applied geostatic stresses correspond to the ones recorded and monitored at the URL Test Tunnel.
Unconfined compressive strength (UCS) test for the calibration of the FDEM elastic microparameters based on the deformability properties of the LdB granite. (a) The initial UCS configuration and (b) the UCS specimen at its postpeak condition. Black fractures indicate failure in tension (Mode I), and yellow fractures indicate failure in shear (Mode II).
Unconfined compressive strength (UCS) test for the calibration of the FDEM elastic microparameters based on the deformability properties of the LdB granite. (a) The initial UCS configuration and (b) the UCS specimen at its postpeak condition. Black fractures indicate failure in tension (Mode I), and yellow fractures indicate failure in shear (Mode II).
Axial stress-axial strain and axial stress-lateral strain curves obtained from UCS testing of the calibrated FDEM model. Recording of stress-strain results ceased once the peak strength was achieved, as the UCS numerical model is used only for the calibration of the elastic parameters of the model.
(a) Photograph of URL Test Tunnel (after [16] modified from [24]) showing the damage profile observed in situ. (b) Damage profile from the FDEM model (highlighted black) after the completion of the numerical analysis.
(a) Photograph of URL Test Tunnel (after [16] modified from [24]) showing the damage profile observed in situ. (b) Damage profile from the FDEM model (highlighted black) after the completion of the numerical analysis.
Calibration process employed for determining the required input parameters in the FDEM model. The microscopic Young’s modulus E and Poisson’s ratio ν refer to the elastic constants of the triangular elements (E and ν at element scale). The macroscopic values refer to the Young’s modulus and Poisson’s ratio obtained from the UCS testing in Figures 2 and 3 (Erm and νrm at 7.5 m height specimen scale). For more information, the reader is referred to [46].
Major principal stress σ1 contours of the intact FEM model using the Hoek–Brown criterion (GSI = 80). (a) Elastic response of the model at 60% of the induced stresses (tunnel advancing) and (b) final model state after the completion of the excavation. Yielded elements in shear (×) and in tension (○) are plotted.
Major principal stress σ1 contours of the intact FEM model using the Hoek–Brown criterion (GSI = 80). (a) Elastic response of the model at 60% of the induced stresses (tunnel advancing) and (b) final model state after the completion of the excavation. Yielded elements in shear (×) and in tension (○) are plotted.
Major principal stress σ1 contours of the intact FEM model using the DISL approach [16]. (a) Elastic response of the model at 60% of the induced stresses (tunnel advancing), and (b) final model state after the completion of the excavation. Yielded elements in shear (×) and in tension (○) are plotted. Yielded elements in tension at the crown and floor of the excavation are the result of extensile fracturing. Numerical results are consistent with the results by [16].
Major principal stress σ1 contours of the intact FEM model using the DISL approach [16]. (a) Elastic response of the model at 60% of the induced stresses (tunnel advancing), and (b) final model state after the completion of the excavation. Yielded elements in shear (×) and in tension (○) are plotted. Yielded elements in tension at the crown and floor of the excavation are the result of extensile fracturing. Numerical results are consistent with the results by [16].
Major principal stress σ1 contours of the intact FDEM model. (a) Elastic response of the model at 60% of the induced stresses (tunnel advancing), and (b) final model state after the completion of the excavation. Cohesive elements failing in tension (Mode I fractures) are coloured red, and cohesive elements failing in shear (Mode II fractures) are coloured yellow.
Major principal stress σ1 contours of the intact FDEM model. (a) Elastic response of the model at 60% of the induced stresses (tunnel advancing), and (b) final model state after the completion of the excavation. Cohesive elements failing in tension (Mode I fractures) are coloured red, and cohesive elements failing in shear (Mode II fractures) are coloured yellow.
Damage profiles obtained from each intact numerical model (DFN geometries are not integrated in the models): purple continuous line—FEM Hoek–Brown model, red dashed line—FEM-DISL model, blue dotted line—collapsed material of the FDEM model (HDZ), blue dash-dotted line—damaged (fractured) material of the FDEM model (EDZ). In Figure 8, it can be observed that the collapsed material is detaching from the rockmass. On the contrary, the damaged material fractures but maintains its integrity and does not collapse. The results are compared to the actual damaged profile as observed at the URL Test Tunnel [48], and acoustic emission (AE) and microseismic (MS) events are also plotted for comparison [49].
Major principal stresses σ1 monitored along the line (AB) (Figure 12) for the intact FEM Hoek–Brown model (purple line), the intact FEM-DISL model (red line), and the intact FDEM model (blue line). In situ stress measurements (stress cell SM-5) are plotted for comparison [50]. The purple hatched area indicates the extent of the damaged zone (yielded elements) for the FEM Hoek–Brown model along line (AB). The red hatched area indicates the extent of the damaged zone (yielded elements) for the FEM-DISL model along line (AB). The blue hatched area indicates the extent of the damaged zone (failure of cohesive elements) for the FDEM model along line (AB). The blue dashed line indicates the ending point of the collapsed material and the starting point of the damaged zone in the FDEM model. The red dashed line indicates the ending point of the HDZ and the starting point of the EDZ in the FEM-DISL model. The red continuous line indicates the ending point of the EDZ in the FEM-DISL model.
Monitoring line along the Y axis placed at the crown of the tunnel within the intact FDEM (left) and FEM (right) models for monitoring the principal stresses. The symbols (A) and (B) indicate the starting and ending point of the monitoring line, respectively. The obtained stress results are shown in Figures 11 and 13 for the major and minor principal stresses, respectively. (Left) Cohesive elements failing in tension (Mode I fractures) are coloured red, and cohesive elements failing in shear (Mode II fractures) are coloured yellow. (Right) Yielded elements in shear (×) and in tension (○) are plotted.
Minor principal stresses σ3 monitored along the line (AB) (Figure 12) for the intact FEM Hoek–Brown model (purple line), the intact FEM-DISL model (red line), and the intact FDEM model (blue line). In situ stress measurements (stress cell SM-5) are plotted for comparison [50]. The purple hatched area indicates the extent of the damaged zone (yielded elements) for the FEM Hoek–Brown model along line (AB). The red hatched area indicates the extent of the damaged zone (yielded elements) for the FEM-DISL model along line (AB). The blue hatched area indicates the extent of the damaged zone (failure of cohesive elements) for the FDEM model along line (AB). The blue dashed line indicates the ending point of the collapsed material and the starting point of the damaged zone in the FDEM. The red dashed line indicates the ending point of the HDZ and the starting point of the EDZ in the FEM-DISL model. The red continuous line indicates the ending point of the EDZ in the FEM-DISL model.
Major principal stress σ1 contours of the fractured FEM model using the Hoek–Brown criterion (GSI = 80). Yielded elements in shear (×) and in tension (○) are plotted. The dashed black line indicates the damage profile based on the recorded yielded elements. White lines indicate the contributing joints to the obtained damage profile.
Major principal stress σ1 contours of the fractured FEM model using the DISL approach [16]. Yielded elements in shear (×) and in tension (○) are plotted. The dashed black line indicates the damage profile based on the recorded yielded elements. White lines indicate the contributing joints to the obtained damage profile.
Major principal stress σ1 contours of the fractured FDEM model. Cohesive elements failing in tension (Mode I fractures) are coloured red, and cohesive elements failing in shear (Mode II fractures) are coloured yellow. The dashed black line indicates the damage profile based on the monitored fractures. The continuous black line indicates the collapsed material. White lines indicate the contributing joints to the obtained damage profile.
Comparison between damage profiles for (a) the FEM Hoek–Brown intact (purple continuous line) and fractured (black dashed line) models, (b) the FEM-DISL intact (red dashed line) and fractured (black dashed line) models, and (c) the FDEM intact (blue dotted line-collapsed material and blue dash-dotted line-damaged material) and fractured (black continuous line-collapsed material and black dashed line-damaged material) models.
Comparison between damage profiles for (a) the FEM Hoek–Brown intact (purple continuous line) and fractured (black dashed line) models, (b) the FEM-DISL intact (red dashed line) and fractured (black dashed line) models, and (c) the FDEM intact (blue dotted line-collapsed material and blue dash-dotted line-damaged material) and fractured (black continuous line-collapsed material and black dashed line-damaged material) models.
Comparison between damage profiles for (a) the FEM Hoek–Brown intact (purple continuous line) and fractured (black dashed line) models, (b) the FEM-DISL intact (red dashed line) and fractured (black dashed line) models, and (c) the FDEM intact (blue dotted line-collapsed material and blue dash-dotted line-damaged material) and fractured (black continuous line-collapsed material and black dashed line-damaged material) models.
通讯作者
Nicholas Vlachopoulos.Department of Civil Engineering, Royal Military College of Canada, Kingston, ON, Canada, rmc.ca.vlach@rmc.ca
推荐引用方式
Nicholas Vlachopoulos,Ioannis Vazaios. The Numerical Simulation of Hard Rocks for Tunnelling Purposes at Great Depths: A Comparison between the Hybrid FDEM Method and Continuous Techniques. Advances in Civil Engineering ,Vol.2018(2018)
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