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Geotechnical Analysis of
Powerhouse Cavern
(Finite Element Method)
Summer Internship Report
Vijay Nehra
09113102
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Objectives
Understanding the basics of Rock Engineering and the Structural
Components of a Hydroelectric Power Project.
Geotechnical Analysis of Underground Power House Caverns via:
1. Finite Element Method.
2. Tunnel Support Measures at excavations in weak rock classes:I. Rock Bolts.
II. Shotcrete.
Modeling various structural Elements using Auto-Cad.
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Geological Strength Index
Devepoled by Hoek and Brown (1994) and is based on the Index that they invented
Geological Strength Index (GSI) . It is the same index on which present day calculationsare performed assuming the practical conditions.
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Excavations in the Weak Rock
Support Measures Applied a combination of - Rock Bolts Shotcrete
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The Analysis using FEM Analysis and Software
Phase2
The Software provides us an interface to analyze the
caverns or tunnels either considering rock to be
plastic or elastic. The corresponding residual values
can be mentioned if the bolt, lining or the rockelements yield.
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Finished modelPhase2
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Steps
1. Create boundaries
2. External boundaries
3. Discretize
4. Meshing
5. Define Boundary conditions6. Define Field Stresses
7. Define Material properties
8. Excavate
9. Compute
10. Interpret
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Material Properties:
Elastic properties:
Poissons ratio =0.2
Cohesion =12 Mpa
Initial element loading =Field stresses only
Youngs modulus =20,000 Mpa
Strength Parameters:
Failure Criterion =Mohr Coulomb
Material Type =Elastic
Field Stresses:
Sigma 1 =20,Sigma 3 =10
Sigma Z =10
Angle =(+)30
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Stress block
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1. Principal Stresses:
Contours of Major Principal Stress
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Principal stress on excavation boundary
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Principal stress on excavation boundary
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2. Strength Factor:
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Total displacement contours, with deformation vectors and deformed boundaries displayed.
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Excavation in Weak Rock-
This will be illustrated by the following support conditions
I. Unsupported Excavation
II. With Bolts only
III. With Bolts & Shotcrete
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Data Assumed:
Sigma 1 =12 MPaSigma 3 =8
Sigma Z =10
Angle =()35 degrees
Elastic Properties:Rock Type =Phyllite
Initial Element Loading =Field Stresses only
Youngs Modulus =1120 Mpa
Poissons Ratio =0.3
UCS (Compressive Strength) =50 Mpa
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Define Material PropertiesDialog Box
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Finished modelPhase2
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Strength Factor Contours (elastic analysis)
Elastic Analysis
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Displacement contours (Elastic Analysis)
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Plastic Analysis
Strength factor contours and yielded elements, for unsupported excavation.
583 yielded finite elements, after Plastic Analysis.
Maximum Total
Displacement = 0.0961 m
Yielded Elements= 583
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Case II: With Bolts.
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Bolt properties
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Bolt pattern used (Radial outwards)
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Strength factor contours and yielded elements, for excavation with pattern bolt support Only.
547 yielded finite elements, after Plastic Analysis.
Maximum Total
Displacement = 0.080 m
Yielded Elements= 547
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Case III: With Bolts & Shotcrete.
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Comparison: Strength factor contours and yielded elements
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Comparison: Total displacement contours and vectors
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Comparison:
Unsupported 583 ---
With Bolts 547 205
With Bolts & Shotcrete 367 161
Yielded finite
elements
Yielded bolt
elements
Maximum Total
Displacement
9.61 mm
8.00 mm
5.39 mm
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Conclusions
Got exposure to my fields of interest, that is, Rock Engineering
and non-conventional sources of energy.
Understood the concept of finite element method.
Moreover, training provided me with an opportunity to be
among the countrys most hardworking and knowledgeable
engineers.
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Thank You!