氏名　アラジヤワンナ　モホッタララジ　ナヤナ　アラジヤワンナ
学位の種類　博士（工学）
学位記番号　博乙第187号
学位授与の日付　平成14年3月25日
学位論文題目　Study on mechanism of mobilizing reinforcing effect of geogrid by pullout test and numerical analysis　（引張試験と数値解析によるジオグリッドの補強効果発現メカニズムに関する研究）
論文審査委員
　主査　教授　杉本　光隆
　副査　教授　海野　隆哉
　副査　教授　鳥居　邦夫
　副査　教授　丸山　暉彦
　副査　助教授　岩崎　英治
　副査　助教授　豊田　浩史

• 論文目次
• 論文要旨

［平成13（2001）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

Title Page　p.i
Abstract　p.ii
Acknowledgements　p.iv
Table of Contents　p.vi
List of Notations　p.ix
List of Tables　p.xi
List of Figures　p.xii

CHAPTER I　INTRODUCTION
1.1　General　p.1
1.2　Scope and objectives of the study　p.4
1.3　Organization of the dissertation　p.5

CHAPTER II　LITERATURE REVIEW ON REINFORCED SOIL
2.1　General　p.6
2.2　Materials　p.7
　2.2.1　Backfill materials　p.7
　2.2.1.1　Types of backfill soils used in reinforced soil　p.7
　2.2.2　Reinforcements　p.9
　2.2.2.1　Geosynthetic reinforcements used in reinforced soil　p.9
　2.2.3　Facings used in reinforced soil　p.10
2.3　Common applications of reinforced soil　p.11
　2.3.1　Reinforced embankments and retaining walls　p.11
　2.3.2　Steep reinforced slopes　p.12
2.4　Concepts and behavior of reinforced soil　p.12
　2.4.1　Concepts　p.12
　2.4.2　Behavior of reinforced soil　p.13
2.5　Soil-reinforcement interaction mechanisms　p.15
　2.5.1　Direct shear mechanism　p.15
　2.5.1.1　Factors affecting direct shear resistance　p.15
　2.5.1.2　Models to estimate direct shear resistance　p.17
　2.5.1.3　Direct shear test　p.17
　2.5.2　Pullout mechanism　p.17
　2.5.2.1　Factors affecting pullout resistance　p.18
　2.5.2.2　Models to estimate pullout resistance　p.20
　2.5.2.3　Pullout test　p.22
2.6　Finite element analysis of reinforced soil　p.23
　2.6.1　Discrete representation　p.24
　2.6.2　Composite representation　p.26
2.7　Summary　p.27

CHAPTER III　MODEL PULLOUT TESTS
3.1　Details of experimental set-up　p.28
3.2　Pullout test parameters and measurements　p.29
3.3　Materials used in pullout tests　p.30
　3.3.1　Sand　p.30
　3.3.2　Geogrids　p.30
3.4　Methodology for pullout tests　p.30
　3.4.1　General pullout tests　p.30
　3.4.2　Pullout tests for x-ray radiographs　p.31
3.5　Methodology for data analysis　p.32
　3.5.1　Analysis of pullout test results　p.32
　3.5.2　Analysis of x-ray radiography data　p.34
3.6　Summary　p.35

CHAPTER IV　INFLUENCE OF THE BOUNDARY CONDITIONS
4.1　General　p.36
4.2　Bond stress distribution　p.37
4.3　Pullout force　p.40
4.4　Friction on the side wall　p.41
4.5　Influence of overburden pressure　p.41
4.6　Influence of relative density　p.41
4.7　Influence of geogrid stiffness　p.42
4.8　Ultimate bond stress　p.42
4.9　Summary　p.43

CHAPTER V　INFLUENCE OF MEMBERS OF GEOGRID
5.1　General　p.45
5.2　Influence of longitudinal members　p.46
5.3　Influence of transverse members　p.48
5.4　Summary　p.52

CHAPTER VI　FINITE ELEMENT ANALYSIS OF PULLOUT TEST
6.1　General　p.53
6.2　Examination of pullout test results for FEM simulation　p.54
　6.2.1　Bond stress distribution　p.54
　6.2.2　Pullout force　p.58
　6.2.3　Lateral force on front face　p.58
　6.2.4　Relationship between bond stress and strain　p.59
　6.2.5　Ultimate bond stress　p.60
6.3　Finite element analysis of pullout test　p.61
　6.3.1　Geometrical modeling　p.61
　6.3.2　Material modeling　p.62
6.4　Comparison of pullout test results with FEM result　p.62
　6.4.1　Bond stress distribution　p.62
　6.4.2　Pullout force　p.64
　6.4.3　Lateral force on front face　p.64
6.5　Summary　p.64

CHAPTER VII　CONCLUSIONS
7.1　Conclusions　p.66

REFERENCES　p.69
LIST OF AUTHOR'S PUBLICATIONS　p.73
TABLES　p.75
FIGURES　p.82
APPENDIX A　Model pullout test results
APPENDIX B　Curve fittings of model pullout test results
APPENDIX C　X-ray analysis results
APPENDIX D　Tested geogrid specimens
APPENDIX E　Photographs of test apparatus

　A series of laboratory pullout tests is carried out to make clear the mechanism of mobilization of reinforcing effect of geogrid. For this purpose, the pullout behavior of geogrid in sand is investigated under rigid （RF test） and flexible （FF test） boundary conditions at the front of the pullout test apparatus, and the influence of the longitudinal and transverse members of a highly extensible geogrid on the pullout behavior is also examined. In addition to them, the influence of overburden pressure, relative density and the stiffness of geogrid on the pullout behavior of geogrid is also investigated using both types of pullout tests. Furthermore, non-destructive x-ray radiography method is used to examine the sand behavior during the pullout of the geogrid. Then, an attempt is made to simulate the pullout behavior of geogrid using finite element method focusing mainly on the interface behavior.
　The mechanism of mobilization of bond stress in explained based on the results of pullout tests and FEM analysis. The mechanism of mobilization of pullout resistance is identified in three ways as Type A, B and C. In Type A, the geogrid does not show the elongation and the slippage along the entire length. In such a case, the bond stress is maximum at the loaded end and decreases away from the front face. In Type B, the geogrid shows the elongation and the bond stress distribution shows a peak and is localized near the front face. In such a case, the mobilized bond stress in the elongation range depends on the strain and does not depend on the overburden pressure. In Type C, the geogrid shows the slippage along the entire length and depend on the overburden pressure. The mathematical models are presented to determine the distributions of strain, tensile force and bond stress along the geogrid length and the stress-strain relationship of the geogrid using the measured pullout force and the geogrid displacement. Based on the test results, it is made clear that the geogrid pullout behavior with the rigid front face is different from that with the flexible front face. It is found that the bond stress distribution is localized more near to the front face in RF test due to densification than that in FF test.
　From the results of pullout tests on highly extensible geogrids with different percentage of longitudinal and transverse members, it is made clear that the influence zones of longitudinal members become isolated with the increase of the longitudinal member spacing and the mobilization of transverse member resistance depends on the displacement of the geogrid at the location of that transverse member. Furthermore, it is found that the contribution of longitudinal members to the pullout force is more significant than that of transverse members in case of highly extensible geogrid.
　FEM analysis showed that the Bond-slip model for interface between sand and geogrid can give reasonable results when the geogrid shows the elongation and the Coulomb friction model for interface can reasonably simulate the geogrid behavior when the geogrid slips along the entire length.