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Uplift Bearing Capacity and Failure Mechanism of Spread Foundations in Sand : 모래지반에 설치된 확대기초의 인발지지력과 파괴 메커니즘
| DC Field | Value | Language |
|---|---|---|
| dc.contributor.advisor | 김성렬 | - |
| dc.contributor.author | 구교영 | - |
| dc.date.accessioned | 2023-06-29T01:48:27Z | - |
| dc.date.available | 2023-06-29T01:48:27Z | - |
| dc.date.issued | 2023 | - |
| dc.identifier.other | 000000176548 | - |
| dc.identifier.uri | https://hdl.handle.net/10371/193033 | - |
| dc.identifier.uri | https://dcollection.snu.ac.kr/common/orgView/000000176548 | ko_KR |
| dc.description | 학위논문(박사) -- 서울대학교대학원 : 공과대학 건설환경공학부, 2023. 2. 김성렬. | - |
| dc.description.abstract | The shallow foundation supporting the transmission tower is subjected to uplift load due to wind load and breakage of the transmission line. Power transmission towers are mainly installed in mountainous areas, and shallow foundations are mainly applied in consideration of accessibility and construction. In addition, since the uplift resistance because the shallow spread foundation's margin of safety against uplift loads is much smaller than that against compression, research for estimation of accurate uplift resistance is important. Therefore, in this study, various centrifugal model experiments and symbolic regression analysis using machine learning techniques were performed to analyze the uplift behavior and uplift failure mechanisms of the foundation embedded in the sand.
In consideration of the realistic conditions, the experimental models target an individual shallow spread foundation of the tower legs, which is installed in sand. Tests of the full model in centrifuge were conducted under various conditions with the different sizes of the foundation and soil density. The ultimate state is reached even with a relatively small uplift displacement, and the load softening behavior is occurred after the peak load. In addition, scale effect on the uplift bearing capacity and peak displacement was confirmed according to the size of the foundation. The uplift bearing capacity became large as the embedment depth ratio and soil density increased. The vertical displacement of the ground surface due to uplift was measured and analyzed. The influence zone was proposed using the internal friction angle of the soil. In order to analyze the characteristics of the uplift behavior, half-cut model tests in centrifuge were performed to analyze the failure mechanism inside the ground. Compared to the vertical displacement of the ground surface of the half-cut foundation model with the full one, it was determined that the two experiments had the same uplift behavior. Using the PIV technique, the failure surface was analyzed in consideration of the mobilization of the vertical displacement in the ground due to uplifting the foundation. The bilinear failure surfaces were proposed by adopting the symbolic regression analysis using the machine learning technique based on the internal friction angle of soil and the foundation size ground. Finally, a semi-analytical solution for calculating uplift bearing capacity was proposed based on the limit equilibrium method and Coulombs theory. The proposed solutions adopted a slice method to estimate the shear resistance along the failure surface. The suggested solution was verified with the current centrifuge test results and previously published test results. The uplift bearing capacity was well predicted considering the foundation size and soil density. It is believed that it will be used for the preliminary design of the uplift bearing capacity proposed through the results of this study. | - |
| dc.description.abstract | 송전 철탑을 지지하는 얕은 확대기초는 풍하중, 송전선의 단선 등의 이유로 인발하중을 받게 된다. 그리고 얕은기초의 인발지지력은 압축지지력에 비해 안전율의 여유가 크지 않으므로, 정확한 인발지지력 산정을 위한 연구가 중요하다. 그러므로, 본 연구에서는 다양한 정적 원심모형실험과 머신 러닝 기법을 이용한 기호 회기 분석을 수행하여 모래지반에 설치된 기초의 인발거동 및 인발파괴 메커니즘을 분석하였다.
국내의 송전 철탑은 주로 산지에 설치되고 접근성 및 시공성을 고려하여 얕은기초가 주로 적용되고 있다. 실제 시공조건을 고려하여 수평 모래지반에 얕게 근입된 기초조건에 대해 연구하였다. 기초 크기, 지반의 밀도 등을 변화시키며 다양한 조건의 전단면 기초를 이용한 원심모형실험을 수행하였다. 실험결과 기초가 인발하중을 받으면, 극한하중에 상대적으로 작은 인발변위에도 극한하중에 도달하게 되며, 극한하중 이후에 하중연화 거동을 보인다. 또한 기초의 크기에 따라서 지지력 및 인발변위가 크기효과를 받는 것을 확인하였으며, 근입비 및 지반밀도가 증가함에 따라서 인발지지력이 증가하였다. 인발에 따른 지표면 상승변위를 측정하여 분석하고 지반 내부마찰각을 이용하여 영향범위를 제안하였다. 이러한 인발지지 거동 특성을 분석하기 위하여, 반단면 조건의 원심모형실험을 수행하여 지반 내부의 파괴 메커니즘을 분석하였다. 반단면 기초의 지표면과 전단면 기초의 상승변위와 비교하여 두 실험조건이 동일한 인발거동을 갖는다고 판단하였다. PIV기법을 이용하여 기초 인발에 따른 지반의 전단 변형률 발현을 고려하여 지반의 파괴면을 분석하고, 두 직선형태의 파괴면을 제안하였다. 머신러닝 기법을 이용한 기호회기 분석법을 이용하여 기초 크기 지반 내부마찰각에 따른 파괴면을 제안하였다. 최종적으로, 전단면 및 반단면 원심모형실험 결과로부터 한계 평형 해석법을 적용한 인발지지력 산정식을 제안하였다. 파괴면에 작용하는 전단력은 절편법을 이용하여 산정하였다. 제안된 이론식은 본 연구에서 수행한 원심모형실험과 다른 연구자들에 의해 수행된 인발실험 결과를 이용하여 비교 검증하였다. 비교결과 기초 크기 및 지반 강도를 잘 반영하여, 지지력 잘 예측을 하는 것으로 나타났다. 본 연구의 결과를 통해 제안된 얕은기초의 인발지지력 산정식으로 기초의 인발하중지지 설계에 참고자료로서 이용될 것으로 판단된다. | - |
| dc.description.tableofcontents | Contents
Chapter 1. Introduction 1 1.1 Background 1 1.2 Research objectives 5 1.3 Scope of work 7 1.4 Thesis organization and structure 7 Chapter 2. Literature review 10 2.1 Introduction 10 2.2 Experimental study 11 2.2.1 1g model experimental test 11 2.3 Failure mechanism 19 2.3.1 Failure surface captured by Experimental study 19 2.3.2 Failure surface suggested by theoretical 22 2.4 Solutions for the uplift bearing capacity 25 2.4.1 Cone method 25 2.4.2 Shear method 27 2.4.3 Curved surface method 29 Chapter 3. Centrifuge test program for uplift behavior 37 3.1 Centrifuge modeling 37 3.2 Soil properties 38 3.3 Foundation model 41 3.4 Test program and layout 44 3.4.1 Test layout of centrifuge test for the uplift behavior 45 3.4.2 Test layout of centrifuge test for the uplift failure mechanisms 49 3.4.3 Genetic Programming 52 3.4.4 Particle Image Velocimetry (PIV) 55 Chapter 4. Uplift behavior of spread foundation 57 4.1 Introduction 57 4.2 Uplift load displacement curves 58 4.3 Uplift bearing capacity 60 4.3.1 Uplift resistance factor Nq 64 4.4 Influence zone 71 4.5 Peak displacement 77 4.6 Summary 81 Chapter 5. Analysis of failure mechanisms using PIV 84 5.1 Introduction 84 5.2 Test results 85 5.2.1 Load-displacement curves 85 5.2.2 Verification and comparison 85 5.3 Failure surface 88 5.3.1 Characterization of failure surface 88 5.3.2 Bilinear failure surface 90 5.3.3 Failure surface for analytical solution 92 5.4 Comparison with previous researches 98 5.5 Summary 100 Chapter 6. Semi-Analytical solution of uplift bearing capacity 102 6.1 Introduction 102 6.2 Side shear resistance of foundation slab, ff 104 6.3 Soil weight of failure zone, Ws 106 6.4 Shear resistance on failure surface 108 6.5 Verification and comparison 113 6.5.1 Verification with experimental data 113 6.5.2 Comparison with existing analytical solutions 115 6.5.3 Variation of uplift resistance factor 116 6.6 Summary 118 Chapter 7. Conclusion and Recommendations 119 7.1 Conclusions 119 7.2 Recommendations for the further studies 123 List of References 125 Appendix A: Test results of inclined loading condition 131 Appendix B: Test results considering excavation 135 Appendix C: Test results of sloping ground 139 Appendix D: Test results of different diameter of shaft 143 Tables Table 3.1 Scaling factors applied in centrifuge experiment. 38 Table 3.2 Physical properties of silica sand. 39 Table 3.3 Mechanical properties of silica sand. 40 Table 3.4 Specification of instrumentation used in this study 45 Table 3.5 Test cases for full model (in prototype scale) 47 Table 3.6 Test cases for half-cut model (in prototype scale) 52 Table 4.1 Uplift bearing capacity and corresponding uplift displacement (in prototype scale) 62 Table 4.3 Values of constant α in the determination of influence zone 75 Table 5.1 The active and passive failure surface angle 92 Table 5.2 Comparison of θa with calculated and measured value 95 Table A1 Comparison of uplift bearing capacity with different loading inclination 134 Table B1 Comparison of uplift bearing capacity with simulation of excavated condition 138 Table C1 Comparison of uplift bearing capacity with different ground slope 142 Table D1 Test results of with different foundation shaft diameter ratios. 146 Figures Fig. 1.1 Overview of transmission tower system: (a) transmission tower, (b) force on transmission tower(Kulhawy et al., 1983), (c) resultant force on foundations (Kulhawy et al. 1983), and (d) spread foundation (KEPCO 2013) 2 Fig. 1.2 Failure mechanism of spread foundation under uplift loading 3 Fig. 2.1 Typical test layout of the model test in 1g by Kulhawy et al. (1987). 12 Fig. 2.2 Typical test layout of the model test in centrifuge by Dickin (1988) 13 Fig. 2.3 Results of 1g model tests with anchors performed by Baker and Konder (1966). 14 Fig. 2.4 Results of centrifugal tests with three different model anchors corresponding to a prototype, embedment depth=3.70m and width=1.77m by Ovesen (1981) 15 Fig. 2.5 Relationship between peak Nq and D on 1g model tests by Sakai and Tanaka (1998) 16 Fig. 2.6 Variation of net uplift resistance with displacement for models of different diameter ratio by Dickin and Leung (1992) 17 Fig. 2.7 Variation of relative failure displacement Df/bb with diameter ratio bb/bs in centrifuge tests by (Dickin & Leung, 1992) 17 Fig. 2.8 Delineation of failure surface in half-cut model test on shallow anchor in dense sand by (Ilamparuthi et al., 2002). 20 Fig. 2.9 Volume change of soil during anchor uplifting in fine sand by (Liu et al., 2012): (a) loose sand; (b) dense sand 21 Fig. 2.10 influence of anchor embedment depth on the shear strain field: (a) loose; (b) dense 22 Fig. 2.11 Failure surface proposed by (Meyerhof & Adams, 1968) 23 Fig. 2.12 Shape of the failure surface in half-cut model: (a) experimental result by (Balla, 1961); (b) suggested failure surface 23 Fig. 2.13 Determination of failure surface of spread foundation by (Matsuo, 1967) 25 Fig. 2.14 failure mode of strip foundation under uplift load by (Meyerhof & Adams, 1968) 28 Fig. 2.15 Kotter's equation for a curved failure surface (adopted from (Deshmukh et al., 2010)) 30 Fig. 2.16 Coefficients of uplift resistance by (Balla, 1961) 32 Fig. 2.17 Geometry of failure surface by (Matsuo, 1967) 33 Fig. 2.18 Free body diagram of the rectangular anchor by (Deshmukh et al., 2010) 35 Fig. 2.19 Free body diagram of logarithmic failure surface by (Chattopadhyay & Pise, 1986) 36 Fig. 3.1 Centrifuge test machine 37 Fig. 3.2 Grain size distribution curve of silica sand. 39 Fig. 3.3 Evaluation of normalized roughness Rn of soil–foundation interface based on surface profile measurement: (a) definition (adopted from Han et al. 2018), (b) measured profile and result 42 Fig. 3.4 Evaluation of soil−foundation interface friction angle (δ) from direct shear tests 43 Fig. 3.5 Typical layout of centrifuge test for the uplift behavior: (a) front view, (b) plan view (dimensions in prototype scale and units in m) 48 Fig. 3.6 Test layout of centrifuge test for the uplift failure mechanisms: (a) plan view; (b) front view; (c) side view (dimensions in prototype scale and units in m) 50 Fig. 3.7 Tree structure of genetic programming 54 Fig. 3.8 Principles of PIV analysis (adopted from White and Take, 2002) 56 Fig. 4.1 Load–displacement curves obtained from centrifuge tests with different slab width Bf 59 Fig. 4.2 Comparison of Qnet between measurement and calculation by existing methods 63 Fig. 4.3 Effect of (a) slab width Bf, (b) embedment depth ratio Ds/Bf on uplift resistance factor Nq in dense sand. 66 Fig. 4.4 Procedure for developing empirical equation of target object (Nq) using genetic programming 68 Fig. 4.5 Comparison of Nq between measurement and calculation by proposed equations 70 Fig. 4.6 Evaluation of influence zone based on measurement of surface uplift displacement for Case 12 with Bf=6.5 m, Ds/Bf=1.07, and Dr=80%. 72 Fig. 4.7 Simplified empirical influence zone: (a) medium sand, (b) dense sand 74 Fig. 4.8 Relationship between simplified empirical influence zone and failure surface recommended by existing studies (Dr = 40% at left side and Dr = 80% at right side, foundation dimensions not to scale) 76 Fig. 4.9 Effect of relative shaft diameter Bs/Bf on dimensionless uplift displacement wp/Bf at peak load Qu in dense sand 78 Fig. 4.10 Verification of developed formulation to estimate the uplift displacement wp at peak load Qu 80 Fig. 5.1 Load-displacement curves of Half-cut model in centrifuge 85 Fig. 5.2 Comparison with full model and half-cut model of load-displacement curves 86 Fig. 5.3 Comparison with vertical displacement of full model and half-cut model in centrifuge 87 Fig. 5.4 Determination of failure surface based on vertical displacement profile from Case 13 and 16 with Bf=3.5 m, Ds/Bf=1.09, and Dr=40 and 80%. 89 Fig. 5.5 Defined failure surface based on the vertical displacement from Case 13 and 16 with Bf=3.5 m, Ds/Bf=1.09, and Dr=40 and 80 %. 91 Fig. 5.6 Suggested bilinear failure surface. 94 Fig. 5.7 Derivative of suggested bilinear failure surface. 97 Fig. 5.8 Comparison of failure surface and Qnet between the proposed and existing analytical solutions: (a) small-scale test of Balla (1961) and (b) large-scale of this study. 99 Fig. 6.1 Proposed bilinear Failure mechanism 103 Fig. 6.2 Soil mass bounded by the suggested bilinear failure surface in three dimensions. 107 Fig. 6.3 Forces acting on the failure surface of a typical slice of the soil mass. 108 Fig. 6.4 Calculation of Qnet with θa determined by genetic analysis (a) in comparison with measured data and (b) Spearman correlation test on the model factor (M=Qnet-measured/Qnet-calculated) against embedment depth Ds. 113 Fig. 6.5 Comparison of Qnet between previously published data and calculation by proposed semi-analytical solution. 114 Fig. 6.6 Comparisons with theoretical results proposed by other researchers 115 Fig. 6.7 Variation of uplift resistance factor Nq with respect to foundation width Bf, embedment depth ratio Ds/Bf, and soil states. 117 Fig. A1 Schematic diagram of inclined loading tests. 131 Fig. A2 Load-displacement curves under different loading direction 133 Fig. B1 Schematic diagram of loading tests considering excavation condition. 136 Fig. B2 Load-displacement curves of loading tests considering excavation condition 136 Fig. B3 Comparison of test results with different excavation condition in Dr = 40% 137 Fig. C1 Schematic diagram of tests on sloping ground. 139 Fig. C2 Load-displacement curves of sloping ground. 140 Fig. C3 Comparison of load-displacement curves with sloping and horizontal ground. 141 Fig. D1 Schematic diagram of tests for different diameter of foundation shaft. 143 Fig. D2 Load-displacement curves with different diameter of shafts including Case 4 and 7. 144 Fig. D3 net uplift bearing capacity with different foundation shaft diameter ratios. 145 Fig. D4 peak displacement with different foundation shaft diameter ratios. 146 | - |
| dc.format.extent | xiii, 146 | - |
| dc.language.iso | eng | - |
| dc.publisher | 서울대학교 대학원 | - |
| dc.subject | spread foundation of transmission tower | - |
| dc.subject | uplift bearing capacity | - |
| dc.subject | centrifuge test | - |
| dc.subject | failure surface | - |
| dc.subject | shear resistance | - |
| dc.subject.ddc | 624 | - |
| dc.title | Uplift Bearing Capacity and Failure Mechanism of Spread Foundations in Sand | - |
| dc.title.alternative | 모래지반에 설치된 확대기초의 인발지지력과 파괴 메커니즘 | - |
| dc.type | Thesis | - |
| dc.type | Dissertation | - |
| dc.contributor.AlternativeAuthor | Kyo-Young Gu | - |
| dc.contributor.department | 공과대학 건설환경공학부 | - |
| dc.description.degree | 박사 | - |
| dc.date.awarded | 2023-02 | - |
| dc.contributor.major | 지반공학 | - |
| dc.identifier.uci | I804:11032-000000176548 | - |
| dc.identifier.holdings | 000000000049▲000000000056▲000000176548▲ | - |
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