本研究藉由數值程序來建立根系在土-根系統中，提供之抗剪強度增量ΔSr與其地上部植生基徑D，地下部根系極限拉拔抗力Pu，以及土層受剪面上根系之平均拉力強度Tr等參數間之轉換模式，並用以決定植生邊坡穩定分析中，土-根系統所需之力學參數，並使穩定分析能更迅速有效。本研究首先針對台灣坡地植生工程常用之三種植物即：山黃麻(Trema orientalis (L.) Blume; India charcoal trema, ICT)、九芎(Lagerstroemia subcostata Koehne; Subcostate crape myrtle, SCM)，以及山芙蓉(Hibiscus mutabilis L.; Cotton rose, CR)，來進行根系形態調查。調查內容包含：根系幾何形狀、根徑、根面積比及根域範圍等項目。另外，再進行室內單根材料之拉力強度試驗及現地土-根系統之拉拔試驗，以決定根系材料拉力強度及土-根系統之極限拉拔抗力。最後，藉由根系形態之現地調查成果以及室內試驗所得根系材料參數，吾人即可建構土-根系統之二維數值模型，並進行土-根系統現地拉拔試驗之數值模擬及參數研究。
藉由土-根系統現地拉拔試驗數值模擬所得之拉拔抗力-拔出量關係曲線(即P-Lp曲線)，以及極限拉拔抗力值Pu與現地試驗結果之比對，吾人即可驗證上述土-根系統之二維數值模型、數值模擬程序及各項材料參數輸入值之有效性。隨之，吾人再利用上述相同之二維數值模型，來進行土-根系統現地直接剪力試驗之數值模擬，以決定根系在土-根系統中所能提供之抗剪強度增量ΔSr。最後，本研究採用(1)現地量測值：植物地下部重量Wr、側根根數NLR、植生地上部基徑D及根系極限拉拔抗力Pu；(2)室內試驗值：單根材料極限抗拉力tmax；以及(3)數值模擬值：根系極限拉拔抗力Pus，抗剪強度增量ΔSr等三組研究成果，來建立四組土-根系統抗剪強度增量之力學轉換模式，即: (1)ΔSr=f(D)，(2)ΔSr=f(Pus)，(3) ΔSr=f(D, Pu, Wr, NLR)，以及(4) ΔSr = f(Tr, Ar, As)。上述轉換模式，提供了一套快速便捷之根系力學轉換方法，其可利用土-根系統中相關之物理及力學參數，來估計由於根系所產生之抗剪強度增量，並運在植生邊坡穩定性之量化評估分析中。In this study, a mechanical conversion model was developed through numerical procedures to correlate the increased shear strength of soil-root system due to roots with plant root parameters of basal diameter of plant D, ultimate pull-out resistance of root Pu, and the average tensile strength of roots Tr. Meanwhile, the model can be used to determine the required strength parameters for the stability analysis of vegetated slope and expedite the efficiency of analysis. Firstly, three species of plants, namely, Trema orientalis (L.) Blume (India charcoal trema, ICT), Lagerstroemia subcostata Koehne (Subcostate crape myrtle, SCM), Hibiscus taiwanensis S. Y. Hu (Cotton rose, CR) commonly used for the slope vegetation in Taiwan were selected for the field investigations. In the investigation the basic properties of root system such as root morphology, root diameter, root area ratio, and root growth characteristics were surveyed in field site. Moreover, a series of laboratory tensile strength tests and in-situ pull-out tests were performed to determine the tensile strength of root material and the ultimate pull-out resistance of soil-root system respectively. Using the root morphology and root material parameters, one can establish a 2-D numerical model of soil-root system to simulate the in-situ pull-out behaviors and relevant parametric study.
Through the comparisons of the simulated pull-out force versus pull-out displacement curves (or P-Lp curves) and the ultimate pull-out resistance of soil-root system Pu with those from measurements, the validities of the numerical model, simulation procedures and various input material parameters can be verified. Subsequently, the identical 2-D numerical model of soil-root system with that used in pull-out test was repeatedly adopted for the simulation of direct shear test to estimate the increased shear strength ΔSr of soil-root system due to roots. Eventually, integrating the data from : (1) field measurements: the dry root weight Wr, number of lateral root NLR, basal diameter of plant D, ultimate pull-out resistance Pu, (2) laboratory tests: the maximum tensile load of single root tmax, and (3) numerical simulations: the simulations of ultimate pull-out resistance Pus , increased shear strength due to roots ΔSr, one can propose four mechanical conversiton models for soil-root system: (1)ΔS r=f(D), (2)ΔSr=f(Pu), (3) ΔSr=f(D, Pu, Wr, NLR), and(4) ΔSr = f(Tr, Ar, As). The above four conversion models play an important role in the quantitative analyses of the stability of vegetated slope in which the models enable a fast estimation for the increased shear strength due to roots ΔSr through the associated physical and mechanical parameters of soil-root system.ABSTRACT I
摘 要 II
Chapter 1 Introduction 1
1.1 Motivation of study 1
1.2 Objective of study 2
1.3 Framework of study 2
Chapter 2 Literatures Review 6
2.1 Classification of root patterns 6
2.2 Soil-root system reinforcement model 9
2.3 Mechanical test and numerical simulation of Soil-root system 14
2.3.1 Laboratory/In-situ test 14
2.3.2 Numerical simulation 21
2.4 Statistic model 28
2.4.1 Bivariate correlations 28
2.4.2 Linear Regression 29
2.5 Finite element method – c-phi strength reduction method (SRM) 31
Chapter 3 Investigation and Experiments 32
3.1 Basic information of study site 32
3.2 Investigation of vegetation 34
3.2.1 Vegetation species 34
3.2.2 Investigation methods 34
3.2.3 Root system measurement 38
3.2.3.1 Measurement methods 38
3.2.3.2 Root morphology 40
3.2.3.3 Root parameter 45
3.3 Roots mechanical test 46
3.3.1 Direct shear test of soil 47
3.3.2 Tensile strength of root 47
3.3.3 In-site pull-out test of soil-root system 50
3.3.3.1 Test procedure 50
3.3.3.2 Test results 51
Chapter 4 Numerical Analysis of Soil-Root System 53
4.1 Simulation and verification of pull-out test of soil-root system 53
4.1.1 Numerical model 53
4.1.1.1 Geometry model 53
4.1.1.2 Boundary condition 54
4.1.2 Input material model parameter 54
4.1.2.1 Soil material model parameter 54
4.1.2.2 Root material model parameter 56
4.1.3 Implementation of the numerical simulation 61
4.2 Parametric study of root morphology in pull-out test 62
4.2.1 Numerical model 62
4.2.1.1 Geometry model 62
4.2.1.2 Boundary condition 64
4.2.2 Input material model parameter 64
4.2.2.1 Soil material parameter 65
4.2.2.2 Root material parameter 65
4.2.3 Implementation of parametric study 65
4.3 Direct shear test of soil-roots system 65
4.3.1 Numerical model 65
4.3.1.1 Geometry model 65
4.3.1.2 Boundary condition 67
4.3.2 Input material model parameter 67
4.3.3 Implementation of the numerical simulation 67
Chapter 5 Results and Discussions 69
5.1 Statistic analyses 69
5.1.1 Field investigation 69
5.1.2 Experiments 69
5.1.2.1 Tensile strength 69
5.1.2.2 Pull-out resistance of soil-root system 72
5.2 Verification of numerical procedures of pull-out test 78
5.2.1 Pull-out resistance versus pull-out displacement 78
5.2.2 Ultimate pull-out resistance 90
5.2.2.1 Comparison between in-situ test and numerical simulation 90
5.2.2.2 Statistical analysis 93
5.2.2.3 Summary and comments 100
5.3 Parametric study of root morphology 101
5.3.1 Pull-out behaviors 101
5.3.2 Ultimate pull-out resistance 110
5.4 Numerical simulation of direct shear test 116
5.4.1 Numerical simulation results 116
5.4.2 Statistic analyses 128
5.4.3 Summary and comments 131
5.5 Conversion model of increased shear strength due to roots 132
5.5.1 Increased shear strength due to roots versus ultimate pull-out resistance 132
5.5.2 Increased shear strength due to roots versus basal diameter 135
5.5.3 Increased shear strength due to roots versus plant parameters 138
5.5.4 Summary and comments 139
5.5.4.1 Application of conversion model in stability analysis of vegetated slope 139
5.5.4.2 Comparison of conversion model with previous root reinforcement models 140
Chapter 6 Conclusions 146
6.1 Conclusions 146
6.1.1 Field investigation and in-situ test 146
6.1.2 Numerical simulation and parametric study of pull-out test 146
6.1.3 Numerical simulation of direct shear test of soil-root system 146
6.1.4 Conversion model of increased shear strength due to roots 147
6.1.5 Summary and comments 147
6.2 Suggestions 148
6.2.1 Influence of soil type 148
6.2.2 Influence of root reinforcement behaviors in soil other than tap roots 149
6.2.3 In-situ test for soil-root system other than pull-out test and direct shear test 149
References 15
