UBC Theses and Dissertations
An evaluation of seismic flat dilatometer and lateral stress seismic piezocone Rivera Cruz, Ivan
The flat dilatometer (DMT) and piezocone penetration (CPTU) tests are likely to be among the most widely used in situ testing methods for soil characterization and indirect determination of geotechnical design parameters such as: strength, stiffness, permeability and compressibility. The flat dilatometer has proved to be a reliable, robust and adaptable tool, and the data obtained with this instrument is very repeatable, and easy to reduce and process. Furthermore, the addition of a seismic module to the standard flat dilatometer (SDMT) to measure the shear wave velocity (Vs) significantly complements the set of data typically obtained with a standard DMT test. Nonetheless, the experience in interpreting the combination between Vs and DMT data is fairly limited due to the recent introduction of the SDMT for commercial applications. Additionally, the estimation of the coefficient of earth pressure at rest (K₀) has been the most important application of the DMT since its introduction. However, a potential weakness of the DMT is that the derivation of K₀ is based upon empirical correlations developed some time ago and neither improvement work nor upgrade of these approaches has been performed in the last 10 years. Throughout the years several additional sensors have been developed in order to supplement the data collected with the CPTU test. Among the wide variety of sensor developed, the lateral stress module mounted behind a piezocone represents a promising tool for estimation of in situ lateral stress conditions from the interpretation of lateral stress penetration data. However, the popularity of the so called lateral stress cone has declined over the years due to constraints in both the instrumentation and the interpretation of measured data. Also, the application of this instrument remains limited to specific soils conditions and specific projects. However, the valuable experience gained throughout the years in the development and application of several lateral stress cones in combination with developments in electronics and understanding of soil behaviour allow the improvement of this type of technology. This thesis presents the results of a comprehensive laboratory and field testing programs performed by the author at several research sites located in the Lower Mainland of BC, undertaken in order to assess the performance of the seismic flat dilatometer and lateral stress seismic piezocone (LSSCPTU), built and develop at UBC. Firstly, the analysis of field measurements with the SDMT collected at several sites have demonstrated the potential for an improved soil characterization through the combination of DMT parameters and the small strain shear modulus (G₀). Additionally the usefulness of the DMT-C closing pressure for soil identification is shown. On the basis of several relationships identified from this data, a new soil type behaviour system based upon SDMT measurements is proposed. Furthermore, empirical correlations based upon fairly large and updated databases have been developed to estimate K₀ and Vs values from DMT parameters.
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