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, PEngProf. & Chair, Department of Mining & Nuclear Engineering

Missouri S&T, Rolla, MO

September, 12 2013

PRESENTATION OUTLINE

IntroductionObjectivesMethodology

Finite Element ModelResults and DiscussionsConclusions

Source: P&H, 2010

Source: Jacque & Riesland, 2013

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

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

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

METHODOLOGYThe FE model were developed based on the principle of soil mechanics by assuming that: the oil sand is homogeneous, isotropic undergoing elastic-

plastic 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.

Shovel Crawler-Oil Sands Interactions

L (m) B (m) H (m) S (m) W(m) b (m) h (m)

25 20 10 10.5 2.21 4.5 1

Table 1 Physical Dimensions of 3-D cable shovel crawler-oil sand model

Fig. 1 3D half model

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)

𝝉𝒄𝒓𝒊𝒕=𝝁𝑷 (𝟏)

FE Model of Crawler-Oil Sands InteractionElastoplastic 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

𝝉=𝒄−𝝈𝒕𝒂𝒏∅ (𝟐)

ρ1 (kg/m3)

1

(MPa)E1

(MPa)

1 ET1

(MPa)

T1

(°C)

2

(°)c2

(kN/m2)Ψ2

(°)

1600 0.1 10 0.3 0.1 25 30.67 10 10

Source: 1Li et al (2012) and 2Anochie-Boateng (2008)

FE Model of Crawler-Oil Sands InteractionMeshes 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

FE Model of Crawler-Oil Sands InteractionThe 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

FE Model of Crawler-Oil Sands InteractionTerzaghi’s classical bearing capacity equation forms the

foundation for this model

Overburden pressure used to account for depth of influence

𝒒𝒖=𝒄𝑵𝒄+𝒒𝒔𝑵𝒒+𝜸 𝑩𝟐

𝑵𝜸 (𝟑)

(4) and depth of influence is

FE Model of Crawler-Oil Sands InteractionThe loads are applied very slowly to avoid exciting the

model

Gravity and surcharge loads are applied to initiate the induced stresses

FE Model of Oil Sands Deformation

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

(a) (b)

(c)(d)

FE Model of Oil Sands Deformation

(a) (b)

(c)

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 bottom of the formation as shown in Fig. 3(c).

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.

FE Model of Oil Sands Deformation

Fig. 4 Displacement-time graph of oil sand-track interface

This figure depicts nonlinearly behavior of the formation under static loads

FE Model of Oil Sands Deformation

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

(a) (b)

(c)

CONCLUSIONSThe 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.