This document summarizes a study on modeling the structural integrity of bench formations for cable shovels operating in oil sands. It outlines the objectives, methodology, and results of developing a 3D finite element model of shovel crawler-oil sand interactions using ABAQUS. The model examines stresses and deformations on the formation from excavation loads. It represents the oil sand as an elastic-plastic material and crawler tracks as rigid strips. Results show deformation concentrates under and spreads from the tracks, with plastic failure zones forming below and around the tracks. The analysis can predict formation response to static loads.

1. BENCH STRUCTURAL INTEGRITY
FOR OPTIMUM PERFORMANCE OF
CABLE SHOVELS
Eric Gbadam,
PhD Student, Department of Mining & Nuclear Engineering
Missouri S&T, Rolla, MO
Samuel Frimpong, PhD, PEng
Prof. & Chair, Department of Mining & Nuclear Engineering
Missouri S&T, Rolla, MO
September, 12 2013

2. PRESENTATION OUTLINE
Introduction
Objectives
Methodology
 Finite Element Model
Results and Discussions
Conclusions
Source: P&H, 2010
Source: Jacque & Riesland, 2013

3. INTRODCUTION
 Primary choice of equipment for oil sands
excavation
 The loads are transferred to formation
via the crawlers
 This cyclic loading reduces the oil sand
shear strength & causes instability (failure)
 Bench failure leads to lost in production
and increase in downtime
Source: Frimpong, 2012

4. INTRODCUTION Cont’d
 Load bearing capacity oil sands is low due
to bitumen (8% to 15%)
 Temperature changes during summer and
winter
 Average stress due to machine weight on
crawlers be smaller to prevent sinkage
 Shovel sinkage leads:
carbody and side frame cracks
associated increased downtime
Increased maintenance cost
Subsequent reduced availability
Source: Grondin, 2008

5. OBJECTIVES
 To develop 3D Finite Element (FE) model
shovel crawler-oil sands interactions using
ABAQUS
 To examine the average stresses and
deformations on the formation during
excavation

6. METHODOLOGY
The FE model were developed based on the principle of soil
mechanics by assuming that:
the oil sand is homogeneous, isotropic undergoing elasticplastic deformation;
the crawler tracks were treated as a rigid strip footing
resting on the oil sand; and
the pressure distribution underfoot the tracks were
uniform.
The oil sand formation was modeled as elastic-plastic
material with strain-softening Mohr-Coulomb criterion.

7. Shovel Crawler-Oil Sands Interactions
Table 1 Physical Dimensions of 3-D cable shovel crawler-oil sand model
L (m)
B (m)
H (m)
S (m)
W(m)
b (m)
h (m)
25
20
10
10.5
2.21
4.5
1
 Dimensions (Table 1) chosen to minimize
boundary effect on formation behavior
 Half symmetry model (Fig. 1) is used in the
simulation to reduce computational time
 Crawler track is modeled as a rigid
rectangular footing
 Contact interaction is modeled using
Coulomb friction criterion (eqn 1)
Fig. 1 3D half model

8. FE Model of Crawler-Oil Sands Interaction
Elastoplastic model of the oil sand under strain softening
Mohr-Coulomb’s failure (eqn. 2)
Table 2 gives the parameters used for the oil sand model
and simulation
ρ1
E1
ET1
T1
c2
Ψ2
(kg/m3)
(MPa)
(MPa)
(°C)
(kN/m2)
(°)
0.1
25
10
10
1600
0.1
10
0.3
Source: 1Li et al (2012) and 2Anochie-Boateng (2008)
30.67

9. FE Model of Crawler-Oil Sands Interaction
 Meshes under the tracks are
finer (Fig.2) to account for high
stress concentration zone
 The elements selcted for both
oil sand and tracks was C3D8R,
3D, 8-node linear brick
 This elements uses reduced
integration technique which
greatly reduces computation
time
Fig. 2 FE mesh and boundary condition for 3D
oil sand-crawler model

10. FE Model of Crawler-Oil Sands Interaction
 The base of the model is fixed in
all directions
 All vertical boundaries are fixed
in the perpendicular direction
but free in the vertical direction
 All nodes along the plane of
symmetry given ZSYMM
condition
Fig. 2 FE mesh and boundary condition for 3D
oil sand-crawler model

11. FE Model of Crawler-Oil Sands Interaction
Terzaghi’s classical bearing capacity equation forms the
foundation for this model
Overburden pressure used to account for depth of
influence

12. FE Model of Crawler-Oil Sands Interaction
The loads are applied very slowly to avoid exciting the
model
Gravity and surcharge loads are applied to initiate the
induced stresses

13. FE Model of Oil Sands Deformation
(a)
(b)
(d)
(c)
Fig. 3 Deformation contour plot of oil sand-crawler interface, (a) 3-D isometric view showing
maximum deformation (b) Deformation under the tracks (c) deformation along the symmetry
plane in 2-D and (d) Top view of oil sand deformation

14. FE Model of Oil Sands Deformation
 Deformation of the oil sand occurs underfoot the tracks and
spreads laterally to the surface of the oil sand (Fig 3a), the
maximum deformation of 2.497 cm under the tracks.
 The deformation increases nonlinearly from the top surface to the
(a)
bottom of the formation as shown in Fig. 3(c).
(b)
 The top view (Fig. 3(d)) presents deformation spreading concentric
with maximum occurring at the edges of the track and beyond.
 Vertical displacement of the oil sand below the track is shown
plotted in Fig.4 at a time of 0.13 seconds.
(c)

15. FE Model of Oil Sands Deformation
 This figure depicts nonlinearly behavior of the formation under
static loads
Fig. 4 Displacement-time graph of oil sand-track interface

16. FE Model of Oil Sands Deformation
(a)
Fig. 4 Zones of elastic and
plastic strain at failure for oil
sand,
(a) maximum principal elastic
strain, (b) 2-D elastic strain and
(c) plastic strain
(b)
(c)

17. CONCLUSIONS
The following conclusions are made based on the FE
simulation results from ABAQUS:
 FE analysis has been implemented successful to fully
produce 3-D oil sand-track interaction that reasonably
predicts formation response to a static load.
 Three distinct oil sand regions were observed from the
plastic strain failure pattern: the region below the tracks
recording larger strain at failure, region adjacent the tracks
and expanding dipper and wider in all directions.