Development Of Advanced Geotechnical Test Technology And Experimental Investigation On Dynamic Characteristic Of Gravelly Soil

Laboratory test is one of the basic means to solve the problems in soil dynamics,also is an important research issue. To meet the needs of research advancing, new testtechniques must be constantly developed and innovated. In the2008China Wenchuanearthquake, large-scale gravelly soil liquefaction was surveyed. Up to date, however,research reports on gravelly soil liquefaction are still limited. One of fundamental topicsis gravelly soil dynamic characteristics. In this dissertation, two aspects are focused on,that is, to develop soil dynamics experimental techniques, and to investigate gravellysoil dynamic characteristics.The effects of gravel content on shear wave velocity are rarely published, althoughgravel content is the groundwork for liquefaction estimation based on shear wavevelocity for gravelly soil sites. Therein, a combined test system of shear wave velocityand relative density of cohesionless soil, which was established by measuring shearwave velocity of a steel bearing cylinder using bending element technique and thenapplied on samples with different relative densities prepared by vertical vibrationtriggered by a shaking table, was developed. Using this system, gravelly soil sampleswith different gravel contents were tested. Experimental results showed that shear wavevelocities of samples vary exponentially with respect to relative densities. Meanwhile,samples reconstituted according to average grain-size distribution of liquefied gravellysoil in Wenchuan earthquake show similar pattern. A general relation of the shear wavevelocities between gravelly soil and standard sand under the same relative density wasfound, and a mathematical formula to describe the effect of gravel content on thesample shear wave velocity was proposed.A large-diameter dynamic triaxial test system imported from GDS, England, wasinstalled in IEM, and the function of measuring large sample shear wave velocity wasachieved. Liquefaction testing results of gravelly soil samples and standard sandsamples using this system were compared, indicating that the shear wave velocity ofgravelly soil is noticeably higher than that of standard sand under condition of the sameCSR so that it provides experimental evidence for the current debate about theapplicability of sand liquefaction estimation methods on the gravelly site. Moreover,modeling of pore water pressure progress for gravelly soil samples was studied that apolynomial model was proposed to describe pore water pressure buildup, and thedifference of pore water pressure increasing progress between gravelly soil and standardsand was analyzed. And then, a trilinear model was suggested to describe therelationship between the progress of pore water pressure and the shear modulus. Thedifference between gravelly soil and standard sand was also showed in the proposedmodel. A measurement system using the FBG sensing technology is designed to assess theone-dimensional distribution of lateral deformation of model soils in the shaking tabletests. This measurement system is tested and verified through the shaking table tests andcompared with other measurements.The experimental techniques presented in this dissertation were developed for theresearch of gravelly soil dynamic characteristics, but the test techniques and methodsare also feasible to other soil categories.