slope stability of open pit mine in 2d & 3d

Integrated Solver Optimized for the next generation 64-bit platform

Finite Element Solutions for Geotechnical Engineering

MIDASoft Inc.

Angel Francisco Martinez

Civil Engineer

Email : [email protected]

Slope Stability of Open

Pit Mine in 2D & 3D

mailto:[email protected]



ContentsPart 1.

Part 2.

Part 3.

Part 4.

Part 5.

Objectives

Introduction

3D case

2D case

Conclusion

GTS NX

3

✓ Importing Terrain and Strata

✓ Meshing Higher Order Elements

✓ Importing materials from excel

✓ Water surface levels

✓ Generating 2D model out of 3D slice

✓ Excavation by stages

✓ Pseudo Seismic

✓ Results Interpretation SAM (LEM) vs SRM

✓ Results Interpretation in 2D vs 3D

Objectives



ContentsPart 1.

Part 2.

Part 3.

Part 4.

Part 5.

Objectives

Introduction

3D case

2D case

Conclusion

GTS NX

7

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.

Introduction

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.

• For more accurate prediction of results in 3D analysis, use hexahedral element

dominated mesh

HexahedralTetrahedral Hybrid [Hexa dominated mesh]

Element shapes

Mesh (Elements)

Good for displacement Good for stress as well

Hexa elem.

Pyramid elem.

(connect hexa and tetra)

Tetra elem.

Terrain Import

• CAD-like features to generate/import terrain surface.

Import elevations of grids in sequence to create 3D terrain.

1

2 31

http://en.midasuser.com/training/tutorial_list.asp?nCat2=132

Topography and Boring Hole Import

[Puntos de mapa topografico se usan para crear superficie]

[Superficies geológicas 3D generadas

automáticamente a través de la

información de campo real

12

3

1

2

3

Tools to check or verify mesh quality

• Inspect and fix imported geometry

2

3

1

• Check Mesh Connections



ContentsPart 1.

Part 2.

Part 3.

Part 4.

Part 5.

Objectives

Introduction

3D case

2D case

Conclusion

Materials and Properties

Mesh > Material

Import from excel

Create 3D solid properties

2

Procedure

1

3

2

1

3

GTS NX

32

Import terrain DXF to TGM

Extract geometry from DXF

Topography Map (DXF contour lines)

Extracted surface of topography

1

Download contour DXF map

(Google Earth, Web Database,

Etc)

Geometry > Tools > Terrain

Geometry Maker

Import DXF file into Terrain

Geometry Maker

Select lines and area for

topography surface

Save file to be exported

topography surface back to

GTS NX

2

2

Procedure

1

3

4

3

4

3

cadmapper.com

GTS NXImport bedding planes

1

Geometry > Surface & Solid >

Bedding Plane

Import > mine boring hole

Excel file

Leave X & Y distance as 0

Press Apply

2

Procedure

1

3

4

2

3

4

4

2

3

4

GTS NXDivide solid by surfaces

1

Geometry > Surface &

Solids > Box

Generate 3D Box with

dimensions shown to serve

as terrain solids.

Geometry > Divide > Solid

Select Extra geometries and

press DELETE

Check Duplicates

2

2

Procedure

1

3

4

GTS NX

3

2

Mesh layers

Top rock layer

Bottom weak layer Bottom rock layer

Top weak layer

1Mesh > Generate > 3D

Select top 2 geometries

Size 20

Hybrid Mesh

Material Top Rock Layer

Advanced >>

Check Higher Order Element

Uncheck Register sets

independent > Ok > Apply

Mesh 2nd layer as Top Weak

Layer

Mesh 3rd layer as Bottom Weak

Layer

Mesh 4th Layer as Bottom Rock

Layer

*note each layer has 2

geometries

Procedure

1

5

3

4

2

5

3

4

2

GTS NXLoads and BC

1

Static/Slope> Boundary>

Constraints

Self Weight > Z = -12

2

Procedure

1

2

1

Analysis Cases

1

Analysis > General >

Analysis Case > SRM

- Activate All

- Output Control > Check on

Strains

Name SRM

Run Analysis2

Procedure

1

2

2

GTS NX

32Iso-Volume Slices of critical slopes

3D Results

FOS 1.81FOS 1.56

With HOEWith LOE



ContentsPart 1.

Part 2.

Part 3.

Part 4.

Part 5.

Objectives

Introduction

3D case

2D case

Conclusion

Export from GTS NX to SoilWorks

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.

• 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

2D Slope Stability

GTS NX

Export CAD from 3D to 2D

3D CAD Slice Export

1Geometry > Point & Curve >

Rectangle

Draw Rectangle Larger than

geometry side

Geometry > Transform >

Translate

- Move rectangle 330 meters in Y

Menu > Export > Soilworks

Neutral Format 3D

Target > 4 solids

Tool > 1 new surface

2

2

Procedure

1

3

3

GTS NXNew 2D file

New > 2D

Menu > Import < Neutral

Format

Geometry > Transform >

Rotate > -90 degrees about X

Translate > 2 point vector >

Select bottom corner to origin

(0,0,0)

2

Procedure

1

3

2

1

3

GTS NX

1

2

3

Import Materials

Mesh > Material

Import from excel

Create 2D Plane Strain

properties

2

Procedure

1

3

GTS NXMesh all 2d layers

1

Mesh > Generate > 2D

Mesh the layers in same

sequence as 3D model

Size: 10

Activate Higher Order

Element

2

2

Procedure

1

3

3

Boundary conditions for SAM

1

Static / Slope > Boundary

conditions

Auto Generate

Water Level

Gravity Load > Y = -1

Slip Surface Left

Slip Surface right

2

2

Procedure

1

3

4

3

4

5

5

SRM Analysis Cases

1

2

3


Analysis Case > SRM

- Activate All


Strains

Name SRM DRY

Analysis Case > SRM

- Activate All


Strains

- Analysis Control > Define

Water Level 1

Name SRM Saturated

2

Procedure

1

SAM Analysis Cases

1

2

3


Analysis Case > SAM

- Activate All except SAM

Right

Name SAM Left

Analysis Case > SAM

- Activate All ecept SAM

Left

- Analysis Control > Define

Water Level 1

Name SAM Right

Run All 4 analysis

2

Procedure

1

3

GTS NX

Dry Season FOS: 1.34

Left Slip Surface FOS 1.42

2D Results

Rainy Season FOS: 0.72

Right Slip Surface FOS 1.13

Construction Stage Analysis for Sequential Excavation Stability Inpsection

Bench Cuts in Stages

GTS NX

Draw 5 lines for cuts as shown following grid and remesh

Draw and Mesh 2D Bench Cuts

1

Geometry > Point & Curve >

Lines

Draw lines for Cute

Intersect All

Mesh 2D > Remesh

2

2

Procedure

1

3

3

2D Stages and Seismic Coeff.

1

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

2

2

Procedure

1

3

3

GTS NX

Construction stage analysis can give FOS for each stage of excavation.

Exca 1: FOS 1.32

2D Sequential Excavation Results

Exca 2: FOS 1.30

Exca 4: FOS 1.18Exca 3: FOS 1.21

Stage 5 Seismic

FOS 1.01



ContentsPart 1.

Part 2.

Part 3.

Part 4.

Part 5.

Objectives

Introduction

3D case

2D case

Conclusion

GTS NXConclusion

• In 3D models it is possible to review in detail the stress distributions oncross-sections, which is not possible in 2D 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.



Questions?https://midassupport.jitbit.com/helpdesk/KB

[email protected]

https://midassupport.jitbit.com/helpdesk/KB

slope stability of open pit mine in 2d & 3d

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