OPTIMIZATION OF RANDOM RUBBLE MASONRY RETAINING WALL DESIGN A. N. Santhajeewa (118633P) Degree of Master of Engineering in Structural Engineering Department of Civil Engineering University of Moratuwa Sri Lanka April 2015 OPTIMIZATION OF RANDOM RUBBLE MASONRY RETAINING WALL DESIGN Assurappulige Nalaka Santhajeewa (118633P) Dissertation submitted in partial fulfillment of the requirements for the degree Master of Engineering in Structural Engineering Design Department of Civil Engineering University of Moratuwa Sri Lanka April 2015 i DECLARATION I declare that this is my own work and this dissertation does not incorporate without acknowledgement any material previously submitted for a Degree or Diploma in any other University or institute of higher learning and to the best of my knowledge and belief it does not contain any material previously published or written by another person except where the acknowledgement is made in the text. Also, I hereby grant to University of Moratuwa the non-exclusive right to reproduce and distribute my dissertation, in whole or in part in print, electronic or other medium. I retain the right to use this content in whole or part in future works (such as articles or books). Date: 8th of April 2015 A.N. Santhajeewa The above candidate has carried out research for the Masters Dissertation under my supervision. Date: 8th of April 2015 Dr. Mrs. D, Nanayakkara ii ABSTRACT The conventional earth retaining structures built using Random Rubble Masonry (RRM) are designed as gravity retaining structures where weight of the structure is used for its stability. In Sri Lanka, RRM retaining walls is the most common type of retaining structure for low retaining heights .However; in general, engineers are reluctant to adopt RRM for retaining heights more than 3m high, due to comparatively large sections obtained as the result of conventional design practice. More optimal and creative solutions could be obtained even for low retaining heights, if design material properties of RRM are known. In this study, use of flexural strength of RRM and adopting a Reinforced Concrete (RC) Tie- back at the top of the retaining wall to optimize the conventional design was explored. The experimental investigation was carried out to find out the flexural, compressive and shear strength of RRM. Further, bond strength between Reinforced Concrete (RC) and RRM was investigated. These tests results have been used to ascertain the adoptability of suggested optimizations. From the experimental study, it was concluded that magnitude of material strengths of RRM are sufficient for considerable optimization by taking into account the effect of flexural strength of RRM and adopting a Tie- back. The width of the base of wall section reduction for 3m high retaining wall was 28% as the result of the optimization. Keywords: Random Rubble Masonry, Retaining walls, Optimization, Tie- back, Flexural Strength. iii ACKNOWLEDGEMENT There are many individuals who deserve acknowledgement for their contribution towards successful completion of this research. First, I would like to express my gratitude to my supervisor, Dr. Mrs. D. Nanayakkara for her valuable advice, guidance and assistance throughout the entire period of study. I am much grateful for sharing her vast knowledge and expertise on the field of Masonry. Secondly, my sincere acknowledgement is towards my employer, Central Engineering Consultancy Bureau for granting me the sponsorship for following the course and other assistances provided for my research works. I am much grateful to the Head of the Department of Civil Engineering, the Course Coordinator of Master of Structural Engineering, the staff of the Department of Civil Engineering and the staff of the structural laboratory for their valuable guidance and corporation related to all experimental works. The assistance rendered by undergraduate students Buddhi, Maithri and Suresh for experimental works also gratefully acknowledged. My very special thanks go to my dear wife Mahesha for her continuous encouragement, assistance and patience during the entire period. My research would never be successful without her tremendous support. Lastly, there are many friends and colleagues who have not been personally mentioned here that I am much indebted to their contribution at various stages of the research to make it successful. iv TABLE OF CONTENTS Declaration of the Candidate & Supervisors i Abstract ii Acknowledgements iii Table of Contents iv List of Figures viii List of Tables x List of Abbreviations xi List of Appendices xii 1. Introduction 1 1.1 General 1 1.2 Need for Research 2 1.3 Optimization of Gravity Retaining wall 3 1.3.1 Effect of Tie – back 3 1.3.2 Effect of Flexural Strength 3 1.4 Objectives of the Research Study 4 1.5 Methodology 4 1.6 Outline of the Dissertation 5 2. Literature Review 6 2.1 Introduction 6 2.2 Design of Retaining Walls 6 2.2.1 Limit State Design Method 6 2.2.2 Conventional Design Method 7 2.2.2.1 Stability Analysis in Conventional method 7 2.2.2.1.1 Stability Analysis in Craig, R.F [10] 8 2.2.2.1.2 Stability Analysis by Liu,C and Evett, J.B[11] 10 2.3 Adopting Tie back Effect in Gravity Retaining Wall Design 12 v 2.3.1 Innovative Earth Retaining System Adopted for the Proposed Printing Complex at Mawaramandiya 12 2.3.2 Wall Foundations of Proposed Block no.10- Mahinda Rajapaksha Vidyalaya, Homagama 14 2.4 British Standards relevant to Random Rubble Masonry Design 15 2.5 Standard Construction Practices of Random Rubble Masonry in Sri Lanka 16 2.5.1 Type of Stones 16 2.5.2 Sizes of Stones 16 2.5.3 Dressing of Stones 18 2.5.4 Mortar 18 2.5.5 Mortar Joints 19 2.5.6 Laying 20 2.5.7 Curing 20 2.6 Previous Experimental Investigations on Material properties of Random Rubble Masonry 20 2.6.1 Compressive Strength 20 2.6.2 Shear Strength 21 2.7 Experimental Investigations on Masonry- Concrete Interface 23 3. Different Approaches used for Design of Random Rubble Masonry 25 3.1 Introduction 25 3.2 Case 1 - Design of RRM Retaining wall using Conventional Method 26 3.3 Case 2 - Retaining Wall assuming RRM will not fail due to flexure 31 3.4 Case 3 – Design of Retaining Wall with the Tie back effect 35 3.5 Summary of the Results obtained from Three Case Studies 41 4. Experimental Study 43 vi 4.1 General 43 4.1.1 Preparation of Test Specimens 44 4.2 Experimental Set-up 45 4.2.1 Testing for Flexural Strength of RRM 45 4.2.2 Testing for Shear Strength of RRM 47 4.2.3 Testing for Shear Strength at Concrete- RRM Interface 49 4.2.4 Testing for Compressive Strength of RRM 51 5. Analysis of Test Results 52 5.1 Flexural Strength 52 5.1.1 Experimental Results 52 5.1.2 Evaluation of Results 56 5.1.3 Comparison of Test Results with Brick/ Block Masonry Flexural Strengths 58 5.2 Shear Strength 59 5.2.1 Experimental Results 59 5.2.2 Evaluation of Results 61 5.2.3 Comparison of Results with previous research findings 64 5.3 Shear Strength at Concrete- RRM interface 64 5.3.1 Experimental Results 64 5.3.2 Evaluation of Results 67 5.3.3 Comparison of Results with previous research findings on Shear strength at Concrete- Masonry interface 68 5.4 Compressive Strength 69 5.4.1 Experimental Results 69 5.4.2 Evaluation of Results 69 5.4.2.1 Compressive Strengths of each Sample 69 5.4.2.2 Mean Compressive Strength 70 5.4.2.3 Characteristic Compressive Strength 71 vii 5.4.3 Comparison of Results with previous research findings on Compressive Strength of RRM 71 5.5 Summery of Test Results obtained by the Experimental Study 72 6. Conclusions and Recommendations 73 6.1 Use of Experimental Results for the improvements of RRM Retaining wall Design 73 6.1.1 Flexural Strength 74 6.1.2 Effect of Tie back 74 6.2 Suggestions for Future Works 75 Reference List 77 Appendix A 79 Appendix B 81 Appendix C 82 Appendix D 83 Appendix E 84 viii LIST OF FIGURES Page Figure 1.1 RRM retaining wall in front of Nuwara Eliya Post Office 2 Figure 1.2 Application of Tie-back for RRM retaining walls 3 Figure 2.1 Loads and base reactions of retaining walls 8 Figure 2.2 Modified RRM retaining wall system adopted 13 Figure 2.3 Construction of Tie back arrangement at the site 13 Figure 2.4 Wall foundations at the rear side of the class block 14 Figure 2.5 Typical bond patterns and Specifications for Bushing, amount of Chips and through stone 17 Figure 2.6 Types of Stones used in RRM 18 Figure 2.7 Types of Joints used in RRM 19 Figure 2.8 Triplet setup by Milosevic J. [17] 22 Figure 2.9 Relationship between Normal stress and Shear stress of samples 23 Figure 2.10 (a): Testing Setup 24 (b): Shear deformation while applying the load 24 Figure 3.1 Loadings acting on Retaining wall for Case 1 26 Figure 3.2 Loadings acting on Retaining wall for Case 2 31 Figure 3.3 Assumed Base Pressure Variation for Case 2 33 Figure 3.4 Loadings acting on Retaining wall for Case 3 36 Figure 3.5 Possible Shear Failure Planes of RRM for Case 3 40 Figure 4.1 (a): Preparing samples for Flexural Strength Test 44 (b): Pre-Compressed Specimens 45 Figure 4.2 (a): The Plane of Bending is Vertical 45 (b): The Plane of Bending is Horizontal 45 Figure 4.3 The test set up for Specimens bent about Vertical Axis (Plane of Bending is horizontal) 46 Figure 4.4 The test set up for Specimens when the plane of bending is vertical 46 Figure 4.5 Set up for Triplet tests as in [3] 47 ix Page Figure 4.6 Set up adopted for Shear Strength Test 48 Figure 4.7 Test set up for Shear Strength Test 49 Figure 4.8 Set up for investigating Shear Strength at Concrete-RRM Interface Test 50 Figure 4.9 Set up for Compressive Strength Test 51 Figure 5.1 Failure patterns of Specimens (When the Plane of Bending is horizontal) (a): Specimen 1 53 (b): Specimen 2 53 (c): Specimen 3 53 Figure 5.2 Failure Patterns of Specimens (When the Plane of Bending is Vertical) (a): Specimen 4 54 (b): Specimen 5 55 (c): Specimen 6 55 Figure 5.3 (a): Failure Patterns of Specimens – Specimen 1 59 (b): Failure Patterns of Specimens – Specimen 2 59 (c): Failure Patterns of Specimens – Specimen 3 60 (d): Failure Patterns of Specimens – Specimen 4 60 (e): Failure Patterns of Specimens – Specimen 5 60 (f): Failure Patterns of Specimens – Specimen 6 60 Figure 5.4 Variation of individual Shear Strength values with the Pre- Compressive Stresses 62 Figure 5.5 Failure Pattern of Specimens for Shear Test (a): Specimen 1 65 (b): Specimen 2 65 (c): Specimen 3 66 (d): Specimen 4 66 (e): Specimen 5 66 (f): Specimen 6 66 x LIST OF TABLES Page Table 2.1 Summary of guidance on British and British European Standards relevant to Natural Stone 15 Table 2.2 Characteristic Compressive Strength of RRM for Mortar designation of 1:5 21 Table 2.3 Comparison of Characteristic Compressive Strength of RRM and Brick work for Mortar designations of 1:5 and 1:8 21 Table 3.1 Summary of results obtained from Three Case Studies 41 Table 5.1 Results of the test on Flexural Strength (When the Plane of Bending is horizontal) 52 Table 5.2 Results of Flexural Strength Test (When the Plane of Bending is Vertical) 54 Table 5.3 Flexural Strength of RRM specimens 56 Table 5.4 Characteristic Flexural Strength of RRM 57 Table 5.5 Flexural strength of Brick and Block Masonry as per BS 5628-1:1992 58 Table 5.6 Results of the Test on Shear Strength 59 Table 5.7 Shear Strength results for different Pre-Compressive Stresses 62 Table 5.8 Results of Shear Strength Test 65 Table 5.9 Results of test carried out for Shear Strength at Concrete- Masonry Interface 68 Table 5.10 Results of Compressive Strength Test 69 Table 5.11 Compressive Strength Results of each sample 70 Table 5.12 Characteristic Compressive Strength of RRM for Mortar designation of 1:5 71 Table 5.13 Summery of Strength Parameters of RRM 72 Table 6.1 Results obtained through different Design Approaches 73 Table 6.2 Extent of Optimization for 1-3m Retaining Heights 75 xi LIST OF ABBREVIATIONS Abbreviation Description RRM Random Rubble Masonry RC Reinforced Concrete BS British Standard ICTAD Institution of Construction Training & Development HM Hydraulic Mortar AM Air Lime Mortar ASTM American Society for Testing and Materials xii LIST OF APPENDICES Appendix Description Page Appendix – A Flexural Strength -Experimental Data and Results 79 Appendix – B Shear Strength -Experimental Data and Results 81 Appendix – C Shear Strength at Concrete Masonry Interface – Experimental Data and Results 82 Appendix – D Compressive Strength – Experimental Data and Results 83 Appendix – E Calibration Reports of Proving Rings 84