Laboratory and In-Situ Assessment of Liquefaction of Gravelly Soils

cyclic simple shear;gravel;shear wave velocity;liquefaction;Civil and Environmental Engineering;Engineering;Civil Engineering

Hubler, JonathanZekkos, Dimitrios ;

University of Michigan

关键词: cyclic simple shear;    gravel;    shear wave velocity;    liquefaction;    Civil and Environmental Engineering;    Engineering;    Civil Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/138786/jhubler_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

To date, most research in soil liquefaction has focused on sands, as they have been observed to liquefy in the field and can be readily tested under controlled conditions in the laboratory. However, the response of gravelly soils during earthquake loading is not well understood due to fewer well-documented case histories of field liquefaction as well as the unavailability of large-scale laboratory test devices that can accurately capture material response of large-size particles. This thesis presents the results of laboratory and in-situ field tests of gravelly soils. A prototype large-size Cyclic Simple Shear (CSS) device was utilized to perform constant volume monotonic, cyclic, and post-cyclic shear tests of uniform gravels and gravel-sand mixtures. Bender elements and miniature accelerometers were used to measure shear wave velocity for every tested specimen. Three uniform gravels (Pea Gravel, 8 mm Crushed Limestone, and 5 mm Crushed Limestone) were first tested at loose and dense states and a range of initial vertical stresses (100 to 400 kPa) to evaluate the effects of particle morphology on shear response. Particle angularity was shown to be an important parameter that affects peak, phase transformation (PT), and ultimate state (US) response of uniform gravels. As particle angularity increased, peak, PT, and US friction angles increased. Particle size was shown to have a lesser impact on these friction angles. Results of cyclic tests on uniform gravels in this study showed that gravels will liquefy at normalized shear wave velocities (Vs1) of up to approximately 230 m/s. Increasing particle size, angularity, and relative density led to an increase in post-cyclic shear strength. Monotonic, cyclic, and post-cyclic tests were also performed for mixtures of Pea Gravel and Ottawa C109 Sand and 8 mm Crushed Limestone and Ottawa C109 Sand. Mixtures of varying percent sand and gravel compositions were tested at loose and dense states and at vertical stresses from 100 kPa to 400 kPa. Test results showed that there is an optimum mixture percentage (40% Sand for Pea Gravel mixtures and 60% Sand for 8 mm Crushed Limestone mixtures) that exhibits the highest Vs value, peak shear strength, and liquefaction resistance. Results also showed that gravels will liquefy at Vs1 values of up to approximately 240 m/s. Post-cyclic tests revealed that particle morphology and density of the gravel skeleton has a significant effect on the post-liquefaction undrained shear strength as well as the post-liquefaction volumetric strain (found to be less than that expected for sands).The field testing component of this study focused on three sites where gravelly soils were present, and in the case of Cephalonia, liquefied during the 2014 earthquakes (Ports of Lixouri and Argostoli in Cephalonia, Greece and Millsite Dam in Ferron, Utah). The field tests included the Chinese Dynamic Penetration test (DPT) and the Multi-Channel Analysis of Surface Waves (MASW) test. A correlation was developed between DPT and Vs combining data from this study and data from the literature. Furthermore, new DPT and Vs-based liquefaction triggering charts were developed based on laboratory CSS test data for uniform gravels and gravel-sand mixtures from this study, field data collected in this study from the sites in Cephalonia, Greece, and existing data for gravelly soil liquefaction from the literature.