Alternative Approach for Predicting Modulus of Deformation Using Fem
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ALTERNATIVE APPROACH FOR PREDICTING MODULUS OF DEFORMATION USING FEM A DISSERTATION Submitted in partial fulfillment of the requirements for the award of the degree of MASTER OF TECHNOLOGY in CIVIL ENGINEERING (With Specialization in Geotechnical Engineering) By KALE LAKSHMI GAINESH DEPARTMENT OF CIVIL ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY ROORKEE ROORKEE - 247 667 (INDIA) JUN E,, 2007 INDIAN INSTITUTE OF TECHNOLOGY ROORKEE ROORKEE CANDIDATE'S DECLARATION I hereby certify that the work which is being presented in the dissertation entitled, "ALTERNATIVE APPROACH FOR PREDICTING MODULUS OF DEFORMATION USING FEM" in partial fulfillment of the requirements for the award of the degree of Master of Technology with specialization in Geotechnical Engineering, submitted in the Department of Civil Engineering, Indian Institute of Technology, Roorkee, is an authentic record of my own work carried out during the period from August 2006 to June 2007 under the guidance of Prof. M. N. Viladkar, Department of Civil Engineering, IIT Roorkee. The matter presented in this report has not been submitted by me for the award of any other degree of this or other Institute/ University. Date: VS-06-04 K. L .6Cx1A-Q11/4 (KALE LAKSHMI GANESH) This is to certify that the above statement made by the candidate is correct to the best of my knowledge. Date: 2_c51 0 6 I 67 (M. N. VILADKAR) Professor Department of Civil Engg, IIT Roorkee Roorkee-247 667(India) ABSTRACT Modulus of deformation is an important parameter which defines the engineering behaviour of rock mass. It is generally determined by in-situ methods like Plate Loading Test, Plate Jacking Test etc. Due to difficulties encountered while conducting in-situ tests, modulus of deformation is often estimated by design engineers on basis of empirical correlations developed for the purpose on the basis of available field test data. For the interpretation of in-situ test data, the rock mass behaviour is assumed to be elastic which does not represent the actual behaviour of rock mass in nature. In the present work, simulation of plate jacking test conditions has been carried out for five different dam sites for which field data was readily available in the literature (Mehrotra, 1992). The analysis considers the elasto-plastic response of the rock mass through Drucker-Prager yield criterion and the theory of cyclic plasticity. The analysis has been performed using the finite element method with the help of ANSYS 10.0. The modulus of deformation of rock mass has been determined from load intensity versus strain response of rock mass corresponding to different loading and unloading cycles for various stress ranges. It has been observed that modulus of deformation is greatly affected by geological conditions and the geotechnical properties of rock mass and its degree of saturation. The analySis also provides an alternate means for predicting the modulus of deformation, which would be useful in situations where it is difficult to conduct such tests. ACKNOWLEDGEMENT I would like to express my deep sense of gratitude and sincere thanks to Dr. M. N. VILADKAR, Professor, Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, for his expert guidance, invaluable suggestions and keen interest throughout the period of this dissertation work. In fact, words would fail to describe the invaluable help and the unending encouragement which I am highly privileged to receive from him on many occasions. I am extremely grateful to Dr. Priti Maheshwari, Lecturer, Department of Civil Engineering, IIT Roorkee, for her valuable suggestions and invaluable help during this work without which, it would not have been possible to compile this report in the present form. I am also thankful to all my teachers and staff of Geotechnical Engineering, Deptt. of Civil Engineering for their help and cooperation. I specially thank Mr. Rajib Sarkar, Research scholar, Deptt. of Earthquake Engineering, IIT Roorkee, for his help during my work. My sincere thanks to my parents and my brother who have been a constant source of inspiration to me and I am also grateful to my friends who have provided suggestions at different stages of my work. (KALE LAKSHMI GANESH) ii CONTENTS Title Page No. ABSTRACT ACKNOWLEDGEMENTS ii LIST OF FIGURES vi LIST OF TABLES ix NOTATIONS CHAPTER-I INTRODUCTION 1.1 UNDERGROUND SCENARIO 1 1.2 NEED AND IMPORTANCE OF MODULUS 2 1.3 BRIEF REVIEW OF EARLIER WORKS 2 1.4 DEFINITION OF PROBLEM 3 1.5 ORGANISATION OF DISSERTATION 3 CHAPTER-II LITERATURE REVIEW 5 2.1 GENERAL 5 2.2 EXISTING FIELD METHODS 5 2.3 REVIEW OF EARLIER WORK 7 2.4 CRITICAL COMMENTS 9 2.5 JUSTIFICATION OF PROBLEM 11 2.6 OBJECTIVES AND SCOPE OF WORK II CHAPTER-III FIELD GEOLOGICAL DATA 13 3.1 IMPORTANCE OF GEOLOGY 13 3.2 GEOLOGY OF JAMRANI DAM SITE 14 3.3 GEOLOGY OF KOTLIBHEL DAM SITE 14 3.4 GEOLOGY OF LAKHWAR DAM SITE 15 3.5 GEOLOGY OF SRINAGAR HYDEL DAM SITE 15 3.6 GEOLOGY OF TEHRI DAM SITE 16 CHAPTER-IV FIELD GEOTECHNICAL DATA 22 4.1 IMPORTANCE OF GEOLOGICAL DATA 22 iii 4.2 ROCK MASS PROPERTIES 23 4.3 MODULUS OF DEFORMATION 23 4.3.1 Details of Field Tests 23 4.3.2 Test Data 25 4.3.3 Interpretation of Test Data 25 4.4 CONCLUDING REMARKS 26 CHAPTER-V NUMERICAL SIMULATION OF PLATE JACKING TESTS 33 5.1 GENERAL 33 5.2 GEOMETRICAL IDEALIZATION 33 5.2.1 PLANE82 Element Description (ANSYS 10.0) 34 5.2.2 Description of Model 34 5.3 BOUNDARY CONDITIONS 34 5.4 LOADINGS 34 5.5 MATERIAL PROPERTIES 35 5.6 YIELD CRITERION 35 5.7 PLASTIC STRESS - STRAIN RELATIONS - FLOW RULE 37 5.8 SOLUTION ALGORITHM 38 5.8.1 Overview 38 5.8.2 Convergence 41 5.8.3 Line Search Algorithm 41 5.8.4 Program Developed in ANSYS 10.0 for Present Study 42 CHAPTER-VI DISCUSSION OF RESULTS 51 6.1 GENESIS OF THE PROBLEM 51 6.2 VERIFICATION OF THE SOLUTION ALGORITHM 52 6.3 LOAD INTENSITY VERSUS STRAIN RESPONSE OF JAMRANI DAM SITE 53 6.4 LOAD INTENSITY VERSUS STRAIN RESPONSE OF KOTLIBHEL DAM SITE 54 iv 6.5 LOAD INTENSITY VERSUS STRAIN RESPONSE OF LAICHWAR DAM SITE 55 6.6 LOAD INTENSITY VERSUS STRAIN RESPONSE OF SRINAGAR HYDEL DAM SITE 55 6.7 LOAD INTENSITY VERSUS STRAIN RESPONSE OF TEHRI DAM SITE ZONE 55 6.8 ESTIMATION OF LOADING AND UNLOADING MODULII FOR DIFFERENT CYCLES OF LOADING 56 6.9 COMPARISON OF MODULII WITH THE FIELD TEST DATA 56 6.10 CONCLUDING REMARKS 57 CHAPTER-WI CONCLUSION 81 7.1 SUMMARY OF WORK DONE 81 7.2 CONCLUSIONS 81 7.3 SCOPE FOR FUTURE WORK 82 REFERENCES 83 APPENDIX-1 85 LIST OF FIGURES Figure No. Title Page No. Fig. 2.1 Principles of Three Main Methods for In Situ Deformation 12 Measurement Fig. 3.1 Geological Section Along the Axis of Jamrani Dam Project 17 Fig. 3.2 Geological Section Along the Axis of Kotlibhel Dam Project 18 Fig. 3.3 Geology Below Spillway Section of Lakhwar Dam 19 Fig. 3.4 Cross Section of the Deepest Block Showing Foundation Geology of Srinagar Dam 20 Fig. 3.5 Geological Section Along Tehri Dam Project 21 Fig. 4.1 Set-up of Equipment for Uni-axial Jacking Test in Vertical Direction in a Drift 27 Fig. 4.2 Typical Pressure-Settlement Curve for Poor Quality Rock Mass (RMR=25) Obtained from Uni-axial Jacking Test 28 Fig. 4.3 Typical Pressure-Settlement Curve for Poor Quality Rock Mass (RMR=31) Obtained from Uni-axial Jacking Test 29 Fig. 4.4 Typical Pressure - Settlement Curve for Fair Quality Rock Mass (RMR=43) Obtained from Uni-axial Jacking Test 30 Fig, 4.5 Typical Pressure - Settlement Curve for Fair Quality Rock Mass (RMR=54) Obtained from Uni-axial Jacking Test 31 Fig. 4.6 Correlation Between Rock Mass Rating (RMR) and Modulus of Deformation (Ea) 32 Fig. 5.1(a) Finite Element Model Developed in ANSYS with Full Meshing 44 Fig. 5.1(b) Zoomed View of Finite Element Mesh near the Loaded Area 45 Fig. 5.2 Boundary Conditions Applied Along Three Sides of Finite Element Mesh 46 Fig. 5.3 Geometrical Representation of Mohr-Coulomb and Drucker-Prager Yield Surfaces in Principal Stress Space 47 vi Two-Dimensional 7r - Plane Representation of Mohr-Coulomb Fig.5.4 and Drucker-Prager Yield Criteria 47 Fig.5.5 Drucker-Prager Yield Criterion in Terms of Stress Variants 48 Fig.5.6 Drucker-Prager and Von-Mises Yield Surfaces in Principal Stress Space 48 Fig.5.7 Newton-Raphson Solution-One Iteration 49 Fig.5 .8 Newton-Raphson Solution-Next Iteration 49 Fig.5.9 Incremental Newton-Raphson Procedure 50 Fig.5.10 Initial - Stiffness Newton — Raphson Solution 50 Load intensity vs Deformation Response for Verification of Fig 6.1 Solution Algorithm 62 Fig. 6.2(a) Variation of Vertical Stress Along the Plate Width for Jamrani Dam Site 63 Fig.6.2(b) Variation of Vertical Deformation Along Plate Width for Jamrani Dam Site 63 Fig. 6.3(a) Variation of Vertical Stress Along Line of Symmetry for Jamrani Dam Site 64 Fig. 6.3(b) Variation of Vertical Deformation Along Line of Symmetry for Jamrani Dam Site 64 Fig.6.4 Spread of Plastic Zone for Different Load Increments at Jamrani Darn Site(Eioading = 2000 MPa, Eunloading = 2500 MPa, = 0.33, c = 0.33 MPa and 0 = 45°) 65 Fig.6.5. Deformations in Rock Mass at Different Load Increments for Jamrani Darn Site(Eloacting = 2000 MPa, Eunloading = 2500 MPa, = 0.33, c = 0.33 MPa and = 45°) 66 Fig.6.6(a) Load Intensity vs Strain Response at Jamrani Dam Site for 2-Cycles of Loading (Natural Moisture Condition) 68 Fig.