3 - Numerical Modelling of Shallow and Deep Underground Caverns-20201020
RSE3010 MINING GEOTECHNICAL ENGINEERING SECOND SEMESTER 2020 Assignment 3 - Numerical Modelling of Shallow and Deep Underground Cavern Student's Name : John Smith ID Number : 20160666 Main Component Sub - components Marks (%) Remarks Allocated Obtained Original format .cad/.fez Accuracy, comprehensive 10 Introduction Introduction of shallow and deep tunnel, in particular the Melbourne Metro 2 Geological information Introduction of geological longitudinal section 3 Cavern excavation and support design (1) FEM model 10 (2) Material parameters of rock mass 5 (3) Constitutive model 5 (4) Rock bolt, liner/lining, and column support 10 (5) Underground water level 5 (6) In-situ stress 5 (7) Surface building modelling 5 (8) 6 stages of excavation 5 Results of shallow tunnel (1) Vertical displacement/stress of each stage 5 (2) Force of column (3) Bending moment of lining (4) Yield zone of elements 5 . Results of deep tunnel (1) 1,000m overburden pressure 5 (2) Vertical displacement/stress of each stage 5 (3) Force of column (4) Bending moment of lining (5) Yield zone of elements 10 Conclusion and reference Clear, convincing 5 Total 100 RSE3010 MINING GEOTECHNICAL ENGINEERING SECOND SEMESTER 2020 Page 1 Assignment 3: Numerical Modelling of Shallow and Deep Underground Cavern using FEM software Numerical modelling has been widely used in underground engineering in the past few decades. Researchers and engineers have been using numerical modelling in almost every stage of an underground engineering project, from designing, monitoring to maintaining and back analysis. With the help of numerical modelling, it is possible to analysis the underground excavation with complex geometry and geological condition, which is hard to do with empirical or analytical methods. The State Library Station of Melbourne Metro Project is one of such examples. Melbourne Metro Tunnel project aims to upgrade the existing railway network with a pair of new nine-kilometre twin tunnels, which pass underneath the Melbourne CBD region. The project promised to enable 39,000 more passengers to use the railway system during each the peak period, and it would be the first step for Melbourne’s ‘metro style’ rail network. For the State Library Station, the design of tri-arch caverns is proposed for the station platform and the twin railway tunnels, and the tri-arch caverns will further intersect with passenger adits, results in a rather complex underground structure. Furthermore, the presence of geological structures like fault zones and dykes, make it even more technically challenging. More details, please refer to the https://metrotunnel.vic.gov.au/construction/cbd/state-library The following files are required for the submission. 1. The final models with the original format of your software (1) The AutoCAD Model (2) RS2 software, and the format is ****.fez 2. Please complete a technical report by following the below steps. https://metrotunnel.vic.gov.au/construction/cbd/state-library RSE3010 MINING GEOTECHNICAL ENGINEERING SECOND SEMESTER 2020 Page 2 1. Geological longitudinal section of State Library Station, please do not consider the fault in your modelling and the bedding planes can be assumed to the horizontal only. (F1-9: faults; D1-2: Dyke; A5: Anticline; MF1: slightly weathered or fresh; MF2: slight weathered; MF3: moderately weathered; MF4: highly weathered Melbourne formation; blue line indicates the underground water table level; the green zone is the state library station.) 2. Concept Design of State Library Station (refer to the attached PDF design figure) 3. Material properties of intact rock and GSI values for Melbourne Formation Rock γ (kN/m3) σci (MPa) Ei (MPa) v Φ (°) c (kPa) mi GSI Fill 19 0.05 10 30 30 0 N/A N/A MF4 22.5 19 100 0.3 30 37 13 N/A MF3 23 6 200 0.25 34 60 13 35 MF2 24 2 800 0.2 43 115 13 45 MF1 25.5 1 2500 0.2 54 270 N/A 55 RSE3010 MINING GEOTECHNICAL ENGINEERING SECOND SEMESTER 2020 Page 3 4. The maximum overburden of tri-arch station platform is around 25m, so the entire State Library Station is a shallow excavation and the vertical in-situ stress is considered as lithostatic (caused by weight of overburden only). According to results from field measurement, the horizontal in-situ stress is represented as ratio of vertical stress (σh/σv), and this ratio is around 1.5. 5. State Library Station is excavated under the Melbourne CBD with the presence of many surface buildings. The load from surface building is modelled by applying a vertical stress at the top boundary of the model. The value of the applied stress is estimated as 15kPa per 10m of building height. 6. The underground excavation at State Library Station follows NATM method, which includes temporary support and permanent support. As shown in Figure. 1.5m of rock is excavated by roll header for each excavation cycle, followed by installation of temporary supports, which include rockbolts, shotcrete and central steel column. For central cavern, the excavation face is divided into topheading, bench and invert (excavation sequences: 1-3); for side caverns, only topheading and invert (excavation sequences: 4-5). The excavation is conducted in drained condition, so the effect of groundwater is ignored. Figure 3: Design of supports for the tri-arch cavern and excavation sequences Construction sequence: the following 6 stages with corresponding support 1) Top Heading of central cavern with the support of rock bolt and liner 2) Bench of central cavern with the support of liner 3) Invert of central cavern with the liner support 4) Column support in platform 5) Top Heading of two sides cavern with the support of rock bolt and liner 6) Invert of two sides cavern with the liner support RSE3010 MINING GEOTECHNICAL ENGINEERING SECOND SEMESTER 2020 Page 4 Support type Parameters Rockbolt (Rb) Steel Spacing: 1.5m x 1.5m Length: 4m Elastic modulus: 200GPa Cross sectional area: 4.91cm2 Grout perimeter: 20m Grout stiffness: 103kN/m Grout friction angle: 20° Shotcrete lining Concrete Unit weight: 2500kN/m3 Thickness: 30cm Elastic modulus (E): 3GPa Poisson’s ratio: 0.2 Central Columns Steel column Cross-section area: 1m2 Elastic modulus (E): 200GPa Area Moment of inertia-y: 3.81x106cm4 Area Moment of inertia-x: 1.70x105cm4 Poisson’s ratio (v): 0.27 7. Numerical results: (1) Vertical displacement and stress of each stage of the above shallow tunnel (2) Support information: (1) Force of column and (2) Bending moment of lining (3) Yield zone of elements in this model 8. Please use the same model but increase the depth of this caverns to an additional 1,000 m to obtain vertical displacement and Sigma 1. (4) Use granite material (get any one of granite parameters from RocData or publications) to calculate the 1,000m overburden pressure (5) Horizontal in-situ stress is 1.5 times higher than the vertical in-situ stress. (6) If the same support system is used as the shallow caverns, is that stable? If no, please propose an optimised support system (e.g., simply upgrade the dimension and mechanical properties) State Library Station Geological Profile.pdf FI LL LE GE ND : IN FE RR ED G RO UN D W AT ER L EV EL M F4 T YP IC AL G RO UN D M F2 T YP IC AL G RO UN D M F1 T YP IC AL G RO UN D IN FE RR ED G EO LO GI CA L BO UN DA RY QP E FA UL TS DY KE S FR AN KL IN A DI T M F3 T YP IC AL G RO UN D M F3 a TY PI CA L GR OU ND D1 D YK E ST S UP PO RT T YP E F3 FA UL T F2 FA UL T F1 FA UL T F7 F AU LT A1 A NT IC LI NE A2 A NT IC LI NE A3 A NT IC LI NE A4 A NT IC LI NE A5 A NT IC LI NE S1 S YN CL IN E S2 S YN CL IN E S3 S YN CL IN E RA IL L EV EL EX IS TI NG S UR FA CE L EV EL 0.00 CH AI NA GE OV ER BU RD EN TU NN EL C RO W N (T C) T O .5 D AB OV E TC W IT HI N TU NN EL SE CT IO N PR ED IC TE D GR OU ND S UP PO RT DA TU M M M RL 6 0. 0m A HD -4 0. 0m 70809010 0 11 0 12 0 13 0 22 - 24