Effect evaluation of grass on infiltration and seepage of volcanic soil ground

NguyenThanhBinh TV pdf Effect evaluation of grass on infiltration and seepage of volcanic soil ground By Thanh Binh Nguyen A thesis submitted in partial fulfillment of the requirements for the degree[.]

Effect evaluation of grass on infiltration and seepage of volcanic soil ground ⅆᒣ⅊㉁ᆅ┙ࡢᾐ㏱≉ᛶ࡟ཬࡰࡍ᳜⏕ࡢᙳ㡪ホ౯ By Thanh Binh Nguyen A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering Professor Tatsuya Ishikawa Supervisor Laboratory of Analytical Geomechanics Division of Field Engineering for the Environment Graduate School of Engineering Hokkaido University Sapporo, Japan ABSTRACT Vegetation can be considered as a sustainable and environmentally friendly reinforcement method It has been widely applied in engineering design in order to reduce the amount of water infiltration on the soil However, the understanding and studies related to vegetation have been limited Therefore, vegetation effect on rainfall water infiltration should be studied elaborately In this study, a column test apparatus is used to investigate the differences in the amount of infiltration and runoff water between bare soil and grassed soil Test results reveal that the grass cover plays an important role in minimizing the water infiltration Furthermore, soil-water retention and seepage behavior under unsaturated condition of grassed soil differ from bare soil Finite element (FE) numerical seepage analyses were performed for column test experiments in order to clearly understand the mechanism of grass influence on rainfall water infiltration The numerical analyses show a reasonable agreement with actual test results ii ACKNOWLEDGEMENT First and foremost I would like to express my sincere gratitude to my supervisor Prof Tatsuya Ishikawa for his consistent support, guidance, and understanding throughout my master course I want to express my sincere thanks to Associate Prof Koichi Isobe and Assistant Prof Shoji Yokohama for their support and advice I gratefully acknowledge the students of Laboratory of Analytical Geomechanics for their help during a period of two years The MEXT scholarship provided by Japanese Government through English Engineering Education (E3) Program, Graduate School of Engineering, Hokkaido University, is also gratefully acknowledged Finally, I would like to express my personal thanks to my family members for their consistent support and encouragement throughout this study iii TABLE OF CONTENTS ABSTRACT ii ACKNOWLEDGEMENT iii TABLE OF CONTENTS iv LIST OF FIGURES vi LIST OF TABLES ix INTRODUCTION 1.1 General background 1.2 Research objectives 1.3 Outline of thesis LITERATURE REVIEW 2.1 Unsaturated soil 2.2 Slope failures due to rainfall 2.3 Vegetation’s effects on infiltration SOIL SLOPE MEASUREMENT 3.1 Outline of cut slopes 3.2 Field instrumentation 12 3.2.1 Soil moisture meter 12 3.2.2 Tensiometer 13 3.2.3 Temperature and humidity sensor 14 3.2.4 Solar radiation meter 15 3.2.5 Wind speed and wind direction sensors 16 3.2.6 Rain gauge 17 3.3 Results and discussions 19 3.3.1 Climate data 19 3.3.2 Volumetric water content 19 3.3.3 Matric suction 22 3.3.4 Ground temperature 23 3.3.5 Summary 25 COLUMN TEST 26 4.1 Materials 26 4.2 Methods 28 4.2.1 Column test apparatus 28 4.2.2 Experimental procedures 37 4.2.3 Approximated profile method 42 4.3 Results and discussions 44 iv NUMERICAL ANALYSIS 48 5.1 Axis-symmetric model 48 5.2 Van Genuchten and Mualem model 49 5.3 Simulation of column test 50 5.3.1 Numerical model 50 5.3.2 Soil properties 50 5.3.3 Analytical conditions 50 5.4 Results and discussions 53 CONCLUSIONS AND RECOMMENDATIONS 55 6.1 Conclusions 55 6.2 Recommendations 55 REFERENCES 57 v LIST OF FIGURES Figure 2.1 Subdivisions of unsaturated soil zone on the local and regional basis (Fredlund et al 2012) Figure 2.2 Element of unsaturated soil with a continuous air phase (Fredlund et al 2012) Figure 2.3 Global susceptibility map of rainfall-induced landslides (Hong, Y et al, 2008) Figure 2.4 The landslides occurred in La Conchita, California (a) The March 4, 1995, rainfall-triggered La Conchita, California, landslide (Courtesy of Robert L Schuster, US Geological Survey.) (b) The January 10, 2005, remobilization of part of the 1995 landslide Figure 2.5 Slope failure at Route No 38, Hikachi Pass, Hokkaido, Japan on 31 August, 2016 Figure 2.6 Measured variations of the cumulative volume of water infiltrated and infiltration rate with time for bare, grass-covered and tree-covered soil (Leung et al, 2015) Figure 2.7 Pore-water pressure measurement at various depths of: (a) original slope, (b) the slope with Orange Jasmine, (c) the slope with Vetiver grass, (d) factor of safety variation and (e) rainfall intensity from 7/29/2010 12:00 to 1/5/2011 17:50 (Rahardjo et al, 2014) Figure 3.1 Bare soil slope and grassed soil slope (a) before spraying grass seed and (b) when the grass growing Figure 3.2 (a) Location and (b) depth of installed instruments into two soil slopes 10 Figure 3.3 Overviews of instruments measuring climate variables .11 Figure 3.4 Soil moisture meter 12 Figure 3.5 Tensiometer 13 Figure 3.6 Temperature and humidity sensor 15 Figure 3.7 Solar radiation meter 15 Figure 3.8 Wind speed and wind direction sensors 16 Figure 3.9 Rain gauge 17 Figure 3.10 Climate data observed in field 19 Figure 3.11 Change in the volumetric water content at different depths in the lower side of bare and grassed soil slopes 20 Figure 3.12 Comparison in the volumetric water content at different depths in upper side of bare and grassed soil slopes 21 vi Figure 3.13 Change in the matric suction at different locations in bare and grassed soil slopes 22 Figure 3.14 Change in the ground temperature at different depths at the upper side of bare and grassed soil slopes 23 Figure 3.15 Change in the ground temperature at different depths at the lower side of bare and grassed soil slopes 24 Figure 4.1 Sampling Komaoka soil at field cut slope in Hokkaido, Japan 26 Figure 4.2 Grain size distribution of Komaoka soil and Toyoura sand 27 Figure 4.3 Schematic diagram of column test apparatus 28 Figure 4.4 Schematic diagram of the tensiometer 29 Figure 4.5 Soil moisture sensor 30 Figure 4.6 Drilled holes to collect runoff water 31 Figure 4.7 Valve to collect outflow water 32 Figure 4.8 Electric balances (a) GP-20K and (b) GX-8000 32 Figure 4.9 Measurement screen of RsCom 34 Figure 4.10 Power supply 34 Figure 4.11 Terminal block 36 Figure 4.12 Data Logger 36 Figure 4.13 (a) Toyoura sand layer and (b) installing soil moisture sensor 38 Figure 4.14 Grassed soil specimen (a) in mold and (b) after releasing mold 39 Figure 4.15 (a) Placing grassed soil specimen on column test and (b) treatment for soil moisture sensors 40 Figure 4.16 Inserting two tensiometers into grassed soil layer 40 Figure 4.17 Column test after setting up (a) bare soil specimen and (b) grassed soil specimen 41 Figure 4.18 (a) Change in volumetric water content and (b) water pressure head with time 44 Figure 4.19 (a) Change in water content when using bare soil and (b) grassed soil 44 Figure 4.20 Comparison of surface runoff and outflow water 45 Figure 4.21 (a) Soil water characteristic curves and (b) coefficient of permeability 46 Figure 4.22 Cross-sectional illustration of capillary rise (a) within a single cylinder and (b) within concentric cylinders 47 Figure 5.1 Representation of axis-symmetric problem 48 Figure 5.2 FE mesh and contour of (a) pore-water pressure, (b) volumetric water vii content in the initial steady state model 51 Figure 5.3 Comparison of initial volumetric water content 52 Figure 5.4 Boundary condition setting in transient analysis 52 viii LIST OF TABLES Table 3.1 Specification of soil moisture sensors 13 Table 3.2 Specification of the tensiometer 14 Table 3.3 Specification of temperature/humidity sensor 14 Table 3.4 Solar radiation meter 16 Table 3.5 Specification of wind direction and wind speed sensor 17 Table 3.6 Specification of rain gauge 18 Table 4.1 Soil properties 27 Table 4.2 The specifications of the tensiometer 30 Table 4.3 The specifications of soil moisture sensor 31 Table 4.4: The specifications of electric balances 33 Table 4.5: The performance specifications of the power supply 35 Table 4.6 General specifications of data logger 37 Table 4.7 Experimental conditions of column tests 42 Table 5.1 Soil properties used for the simulation 50 ix