Slope Stability of Open Pit Mine in 2D & 3D

Transcription

1 Slope Stability of Open Pit Mine in D & D MIDASoft Inc. Angel Francisco Martinez Civil Engineer a.martinez@midasit.com Integrated Solver Optimized for the next generation64-bit platform Finite Element Solutions for Geotechnical Engineering

2 Contents Part. Part. Part. Part 4. Part 5. Objectives Introduction D case D case Conclusion Integrated Solver Optimized for the next generation64-bit platform Finite Element Solutions for Geotechnical Engineering

3 Objectives GTS NX Importing Terrain and Strata Meshing Higher Order Elements Importing materials from excel Water surface levels Generating D model out of D slice Excavation by stages Pseudo Seismic Results Interpretation SAM (LEM) vs SRM Results Interpretation in D vs D

4 Contents Part. Part. Part. Part 4. Part 5. Objectives Introduction D case D case Conclusion Integrated Solver Optimized for the next generation64-bit platform Finite Element Solutions for Geotechnical Engineering

5 Introduction GTS NX In sequential excavation, the stability analysis of a shoring wall, slope and the effects on the adjacent ground and structures are crucial. Accurate ground material properties and geometry must be reflected. In addition, the analytical model needs to closely reflect the excavation sequence. Stage Analysis by FEM The analysis is carried out by the FEM and is applied to large scale, deep excavations in the design and construction of shoring wall and support systems. This method calculates displacements and stresses reflecting the elasto-plastic behavior of ground and interaction with the shoring wall and support structures as well as the deformations in the surrounding ground. Slope stability by strength reduction method is also necessary. 7

6 Strength Reduction Method In the strength reduction method, the shear strength c, (φ ) of the sloped ground material is gradually reduced until the point of divergence in calculation at which point slope failure is assumed to have taken place. The maximum strength reduction ratio at that point is considered to be the minimum safety factor. Such methods require iterative nonlinear analyses consuming significant analysis time, but they are manageable through the advancement in computing speed.

7 Element shapes Mesh (Elements) For more accurate prediction of results in D analysis, use hexahedral element dominated mesh Tetra elem. Pyramid elem. (connect hexa and tetra) Tetrahedral Hexahedral Hybrid [Hexa dominated mesh] Hexa elem. Good for displacement Good for stress as well

8 Terrain Import CAD-like features to generate/import terrain surface. Import elevations of grids in sequence to create D terrain. /tutorial_list.asp?ncat=

9 Topography and Boring Hole Import [Puntos de mapa topografico se usan para crear superficie] [Superficies geológicas D generadas automáticamente a través de la información de campo real

10 Tools to check or verify mesh quality Inspect and fix imported geometry Check Mesh Connections

11 Contents Part. Part. Part. Part 4. Part 5. Objectives Introduction D case D case Conclusion Integrated Solver Optimized for the next generation64-bit platform Finite Element Solutions for Geotechnical Engineering

12 Materials and Properties Procedure Mesh > Material Import from excel Create D solid properties

13 Import terrain DXF to TGM GTS NX Procedure Download contour DXF map (Google Earth, Web Database, Etc) cadmapper.com Geometry > Tools > Terrain Geometry Maker Import DXF file into Terrain Geometry Maker 4 Select lines and area for topography surface Save file to be exported topography surface back to GTS NX Topography Map (DXF contour lines) Extract geometry from DXF Extracted surface of topography 4

14 Import bedding planes GTS NX Procedure Geometry > Surface & Solid > Bedding Plane Import > mine boring hole Excel file Leave X & Y distance as 0 4 Press Apply 4 4

15 Divide solid by surfaces GTS NX Procedure Geometry > Surface & Solids > Box Generate D Box with dimensions shown to serve as terrain solids. Geometry > Divide > Solid Select Extra geometries and press DELETE Check Duplicates 4 4

16 Mesh layers GTS NX Procedure Mesh > Generate > D Select top geometries Size 0 Hybrid Mesh Material Top Rock Layer Advanced >> Check Higher Order Element Uncheck Register sets independent > Ok > Apply 4 Mesh nd layer as Top Weak Layer Mesh rd layer as Bottom Weak Layer 5 Mesh 4 th Layer as Bottom Rock Layer *note each layer has geometries Top rock layer Top weak layer 4 5 Bottom weak layer Bottom rock layer

17 Loads and BC GTS NX Procedure Static/Slope> Boundary> Constraints Self Weight > Z = -

18 Analysis Cases Procedure Analysis > General > Analysis Case > SRM - Activate All - Output Control > Check on Strains Name SRM Run Analysis

19 D Results GTS NX With HOE With LOE FOS.56 FOS.8 Iso-Volume Slices of critical slopes

20 Contents Part. Part. Part. Part 4. Part 5. Objectives Introduction D case D case Conclusion Integrated Solver Optimized for the next generation64-bit platform Finite Element Solutions for Geotechnical Engineering

21 Export from GTS NX to SoilWorks

22 Limit Equilibrium Method (LEM) A method for analyzing the stability of a slope in two dimensions. The sliding mass above the failure surface is divided into a number of slices. The forces acting on each slice are obtained by considering the mechanical equilibrium for the slices.

23 D Slope Stability Strength Reduction Method (SRM): The strength reduction method gradually decreases the shear strength and friction angle until the calculation does not converge, and that point is considered to be the failure point of the slope. Stress Analysis Method (SAM): This method first uses the finite element method to perform stress analysis on the slope and the safety factor for each various virtual slip surface, created from the assumptions of the limit equilibrium theory, is calculated based on the stress analysis results SRM SAM

24 D CAD Slice Export GTS NX Procedure Export CAD from D to D Geometry > Point & Curve > Rectangle Draw Rectangle Larger than geometry side Geometry > Transform > Translate - Move rectangle 0 meters in Y Menu > Export > Soilworks Neutral Format D Target > 4 solids Tool > new surface

25 New D file GTS NX Procedure New > D Menu > Import < Neutral Format Geometry > Transform > Rotate > -90 degrees about X Translate > point vector > Select bottom corner to origin (0,0,0)

26 Import Materials Procedure Mesh > Material GTS NX Import from excel Create D Plane Strain properties

27 Mesh all d layers GTS NX Procedure Mesh > Generate > D Mesh the layers in same sequence as D model Size: 0 Activate Higher Order Element

28 Boundary conditions for SAM Procedure Static / Slope > Boundary conditions Auto Generate Water Level 4 Gravity Load > Y = - Slip Surface Left 5 Slip Surface right 4 5

29 SRM Analysis Cases Procedure Analysis > General > Analysis Case > SRM - Activate All - Output Control > Check on Strains Name SRM DRY Analysis Case > SRM - Activate All - Output Control > Check on Strains - Analysis Control > Define Water Level Name SRM Saturated

30 SAM Analysis Cases Procedure Analysis > General > Analysis Case > SAM - Activate All except SAM Right Name SAM Left Analysis Case > SAM - Activate All ecept SAM Left - Analysis Control > Define Water Level Name SAM Right Run All 4 analysis

31 D Results GTS NX Dry Season FOS:.4 Rainy Season FOS: 0.7 Left Slip Surface FOS.4 Right Slip Surface FOS.

32 Bench Cuts in Stages Construction Stage Analysis for Sequential Excavation Stability Inpsection

33 Draw and Mesh D Bench Cuts GTS NX Procedure Geometry > Point & Curve > Lines Draw lines for Cute Intersect All Mesh D > Remesh Draw 5 lines for cuts as shown following grid and remesh

34 D Stages and Seismic Coeff. Procedure Static Slope > Load > Gravity Use Gx and Gy as seismic Coefficients Define Stages as shown, 4 excavations and last stage as seismic coefficient load Construction Stage Analysis Case > Run

35 D Sequential Excavation Results GTS NX Construction stage analysis can give FOS for each stage of excavation. Exca : FOS. Exca : FOS.0 Exca : FOS. Exca 4: FOS.8 Stage 5 Seismic FOS.0

36 Contents Part. Part. Part. Part 4. Part 5. Objectives Introduction D case D case Conclusion Integrated Solver Optimized for the next generation64-bit platform Finite Element Solutions for Geotechnical Engineering

37 Conclusion GTS NX In D models it is possible to review in detail the stress distributions on cross-sections, which is not possible in D models. Give more accurate and less conservative results. Failure surfaces need not be assumed with SRM. Failure takes place when the shear strength of the soil is less than the shear stress due to the internal and external loads on the soil. The finite element method does not require the data or concept of slices and satisfies the equilibrium state until failure. Stresses, deformations and stability of the excavation sequences can be obtained through construction stage analysis.

38 Questions? Integrated Solver Optimized for the next generation64-bit platform Finite Element Solutions for Geotechnical Engineering