UNIVERSITY of CALIFORNIA Los Angeles Dynamic Shake Testing Of
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UNIVERSITY OF CALIFORNIA Los Angeles Dynamic Shake Testing of a Model Levee on Peaty Organic Soil in the Sacramento-San Joaquin Delta A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Civil and Environmental Engineering by Edward Thomas Reinert 2014 ABSTRACT OF THE DISSERTATION Dynamic Shake Testing of a Model Levee on Peaty Organic Soil in the Sacramento-San Joaquin Delta by Edward Thomas Reinert Doctor of Philosophy in Civil and Environmental Engineering University of California, Los Angeles, 2014 Professor Scott Brandenberg, Chair The Sacramento-San Joaquin Delta is the hub of California’s water distribution system, which consists of below sea-level islands surrounded by levees. Delta levees are constructed of local fill, have typically been unengineered and are notorious for breaching, causing flooding of the islands inside. One major concern is the seismic performance of Delta levees, which have not experienced a significant seismic event in over a century. Many of these levees are founded on local peaty organic soils, and the seismic performance of these levees is poorly understood. As part of a collaborative research investigation to study to study the seismic performance of Delta levees, a series of dynamic field tests were performed on a model levee constructed on very soft and compressible peaty organic soils on Sherman Island. This first-of- its-kind test applied dynamic loads to the model levee-peat system using the large ii NEES@UCLA MK-15 eccentric mass shaker mounted on the levee crest. Two sets of tests were performed in 2011 and 2012. Geotechnical and geophysical investigations performed at the site found a 11m thick peat deposit rests atop permeable Pleistocene sand. The peaty soils consist of 9m of soft saturated peat with a Vs of 30 m/ and a 2m stiff desiccated crust with a Vs of 60 m/s lying atop the soft peat. Artesian pressures exist in the soft saturated peat due to hydraulic connection with the nearby Sacramento River, with a zero effective stress condition existing at the peat-sand interface. Remote data monitoring measured settlement and pore pressure dissipation of the levee using embedded piezometers and a slope inclinometer. The remote monitoring found fast dissipation of pore pressures underneath the levee and continued settlement of the levee due to a high rate of secondary compression. Prior to the 2012 tests, a berm was constructed around the levee and the ground was flooded, to create more realistic soil conditions in the unsaturated crust. Dynamic base shear-displacement and moment-rotation relations were made for the levee. The model levee translated and rotated visibly during testing, demonstrating a response that differs from the one-dimensional wave propagation assumption used to analyze seismic levee response. High radiation damping was observed, and translation of the levee was found to go out-of-phase at peak shaker frequencies. Complex-valued stiffness of the levee-peat system was analyzed and compared to analytical solutions for a rigid foundation on an elastic halfspace. Little agreement was found between the field test results and the analytic solution, suggesting that the levee-peat foundation is flexible. Dynamic shear strains measured underneath the levee crest and toe measured an average value of shear strains at the bottom of the stiff crust and top of the soft peat. Peak shear strains iii measured during testing went up to 0.4%, with higher shear strains occurring underneath the levee toe, due to the rocking behavior. Comparison of residual pore pressure ratios generated during testing show a trend in increasing residual pore pressure with increasing shear strain. Comparison of field test results with dynamic laboratory testing showed very little increase in residual pore pressures from field tests, suggesting that pore pressures underneath the levee dissipated quickly due to high horizontal permeability. A series of finite element simulations were performed with elastic isotropic materials to compare different hypothetical soil conditions and loading scenarios. Good agreement in shear strains between the field test and the finite element simulations were found. Higher shear strains were found to exist beneath the levee for softer soils and uniform base excitation. A study investigated the development of shear stresses within the levee fill, and found an increase in peak shear stresses compared to shear stresses calculated for a simple shear case. This has implications for liquefaction triggering analysis, and the finite element simulations suggest that the current methodology used in evaluating seismic demand may be underestimating shear stresses within the levee fill. iv The dissertation of Edward Thomas Reinert is approved. Jonathan P. Stewart Anne Lemnitzer David D. Jackson Daniel Pradel Scott J. Brandenberg, Committee Chair University of California, Los Angeles 2014 v To my parents, family, and friends. vi Table of Contents Abstract ii Committee v Dedication vi Table of Contents vii Acknowledgments ix Vita xii 1. Introduction 1 1.1 Introducing the Delta 1 1.2 Historical Background 2 1.3 Dissertation Organization 9 2. Technical Background and Project Motivation 12 2.1 Flooding Hazards in the Delts 12 2.2 Seismic Events and Flooding 22 2.2.1 Seismic Hazards in the Delta 24 2.2.2 Studies on Levee Vulnerability 33 2.3 Peaty Organic Soils 41 2.3.1 Dynamic Properties of Delta Peat 43 2.4 Project Motivation 46 3. Site Identification and Investigation 51 3.1 Site Identification and Selection 52 3.2 Sherman Island Geophysical and Site Investigations 55 3.2.1 March 2010 Geophysical Investigation 55 3.2.2 June 2011 Geotechnical Site Investigation 72 3.2.3 August 2nd, 2011 Investigation 73 3.2.4 August 24th Site and Geophysical investigation 74 3.2.5 September 2012 Site Investigation 79 3.3 Interpretation of Site Stratigraphy 82 4. Model Levee Design, Construction, and Testing 84 4.1 Model Levee Design 84 4.1.1 Design of Model Levee and Shaker Platform Dimensions 85 4.1.2 Modeling and Development of Dynamic Stresses During Shaking 92 4.1.3 Fill selection, compaction specifications, and geosynthetic selection 99 vii 4.2 Model Levee Construction, Repair, and Long-Term Remote Monitoring 101 4.2.1 Model Levee Construction and Repair 101 4.2.2 Long-Term Remote Monitoring of Model Test Levee 110 4.3 Shake Testing of Model Test Levee 117 4.3.1 Instrumentation of Model Levee for Dynamic Testing 118 4.3.2 Dynamic Shake Testing and Data 129 4.3.3 Calculation of Shaker Force 141 5. Interpretation of Dynamic Test Data 147 5.1 Measurements of Dynamic Translational and Rotational Impedance Functions 147 5.1.1 Calculation of Impedance Functions 148 5.1.2 Measured Shear-Displacement and Moment-Rotation Responses 151 5.1.3 Impedance Functions for Frequency-dependent Stiffness 156 5.2 Development of Shear Strains from Dynamic Testing 166 5.2.1 Calculation of Dynamic Shear Strains 166 5.2.2 Dynamic Shear Strains During Shake Testing 168 5.3 Residual Pore Pressure Response and Dynamic Shear Strains 175 5.3.1 Calculation of Residual Pore Pressure Ratio 175 5.3.2 Shear Strain and Pore Pressure Response 179 5.4 Dynamic Finite Element Model Testing 182 5.4.1 Construction of Finite Element Model 182 5.4.2 Comparison of Finite Element Shear Strains with Shear Strains from Field Tests 188 5.4.3 Comparison of Shear Strains Between Top-Down and Bottom-Up Excitation 192 5.4.4 Dynamic Stresses Within and Beneath the Levee Fill 198 6. Summary and Conclusions 213 6.1. Geotechnical and Geophysical Investigations at the Sherman Island Test Site 213 6.2. Design, Construction, Monitoring, and Testing of the Model Levee 214 6.3. Interpretation of Dynamic Test Data 216 6.4. Finite Element Simulations 218 6.5. Recommendations for Future Research 219 Bibliography 222 viii Acknowledgments As I approach the end of my long career as a student at UCLA, I would like to acknowledge the help, support, and guidance I received from a number of people over the last four and a half years. The research and this dissertation would not have been possible without them, and I am simultaneously humbled and grateful for all of the assistance they have provided. First of all, I would like to thank my advisor, Professor Scott Brandenberg, for helping me with all stages of this project and supported me throughout my doctoral studies. It has been an honor and pleasure to work with him throughout the entire duration of this project. He has worn many hats during the last four and a half years: performing as a teacher, a researcher, a project manager, and a mentor, and he has done all of these superbly. He has helped me to become a better engineer and has helped guide me through all of the various technical challenges that have come up in the duration of this project. His ability as a mentor has been second-to- none, and I come away from my time with a greater understanding and heightened passion for this career field. I would like to acknowledge the help of the various researchers and state officials that have been gotten their hands dirty with me and have been instrumental in putting this project together. First, I would like to thank the entire staff of the NEES@UCLA team that provided the muscle and man hours during the construction and field testing of our model levee. Without the help of Bob Nigbor, Steve Keowen, Alberto Salamanca, Andrey Kozhukovskiy, Erica Eskes, Sophia Poulos, Jackson English, Estefan Garcia, Charys Clay, and Jasmin Sadegh, none of this would have been remotely possible. I would like to thank the tireless efforts of the staff at Gornto Ditching in providing excellent contracting services in building the model levee.