NHPC Intern Report

7/30/2019 NHPC Intern Report

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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!

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