Abstract

Hydropower plays an important role in the context of the energy transition contributing to the reduction of the CO2 emission through a permanent power production as run-of-river scheme as well as for energy storage as pump-storagescheme. Nowadays large hydropower plant designs comprise tunnel, cavern and shaft excavation work known as head race and pressure tunnel or pressure shaft. The powerhouse is often placed within a large underground cavern. The results of a ground investigation phase including the determination of in-situ parameters derived from tests in boreholes drilled from the surface are crucial for a preliminary design of the hydropower plant. Additional in-situ measurements are frequently carried out within an exploratory tunnel to confirm the first predictions and to characterize in detail the mechanical and hydraulic properties of the rock mass. Solexperts portfolio of in-situ well tests comprise the assessment of hydraulic properties vs. depth through hydraulic testing of isolated borehole sections along the borehole axes, the determination of geomechanical parameters like deformation- and Young’s modules through borehole dilatometer tests and rock stress measurements conducting hydraulic mini-frac tests. Plate load tests which use surficial loading are performed in small tunnels or test adits to measure the deformation characteristics of a rock mass on a larger scale.

Abstract

Because soil resists applied stresses in the x, y, and z directions, the ratio of horizontal to vertical stresses, ko, determines the soil stress distribution. The dilatometer test predicts the unit weight of the soil and the horizontal stress ratio at rest, ko, providing the necessary input to determine the stress increase applied to the soil. The Boussinesq stress distribution assumes the soil has a linear elastic stress-strain relationship. This distribution has no input from the soil’s material properties. Harr (1977) proposed using the normal probability distribution with ko input to more accurately compute stress distribution. The authors show the Harr stress distribution for different values of ko and compares them with the Boussinesq stress and Westergaard stress distributions. The authors also present some case studies of stress distribution measurements and proposes modern instrumentation needed for additional research to determine the best prediction method.

Abstract

The definition of the shear wave velocity profile is a fundamental step for the seismic characterization of a site in the context of Eurocode 8 and for the conduction of earthquake geotechnical engineering efforts such as site response analysis. Shear wave velocity profiles can be obtained: (1) directly from seismic geophysical and seismic geotechnical tests; or (2) indirectly, from “static” in-situ geotechnical tests such as dilatometer tests (DMT) and cone penetration tests (CPT). In the latter approach, shear wave velocity is estimated by using transformation models which are typically derived from data collected at other sites. This paper illustrates the procedures and main results of the comparative assessment of the performance of existing DMT-based and CPT-based transformation models to estimate shear wave velocity at two adjacent spatial locations in a rural site in the region of Tuscany in central Italy. Model-predicted shear wave velocity profiles were compared with direct measurements obtained by geophysical seismic dilatometer (SDMT) testing. The comparative assessment involved the definition, calculation, and assessment of quantitative performance statistics. The paper provides a critical analysis and a discussion of the outcomes with respect to soil type.

Abstract

The quantification of the spatial variability of soil properties allows the enhanced engineering modelling, analysis, and design of geotechnical systems. Evolutionary design codes such as Eurocode 7 are awarding spatial variability an increasing central role in geotechnical design. The spatial variability of geotechnical properties is often investigated using a random field approach. Among the defining parameters of a random field is the scale of fluctuation, which describes the extent of significant spatial correlation in a specific spatial direction. The scale of fluctuation can be estimated quantitatively using a variety of methods relying on statistical approaches. The scale of fluctuation is not an inherent property of a soil. Existing studies demonstrate its dependency from numerous factors including the spatial direction, measurement interval, and user-defined modelling options. This paper illustrates the procedures and main results of the comparative estimation of the vertical scale of fluctuation of undrained shear strength of a layer of silty clay from piezocone (CPTU) and dilatometer (DMT) testing at a rural site in the region of Tuscany in central Italy. Vertical scales of fluctuation were calculated using two methods available in the geotechnical literature. Quantitative estimates are compared and analysed critically.