Abstract

Structural geological models are used to understand and visualize how geological materials are organized below the Earth surface. This technique is crucial in different fields of geomechanics such as mining to identify mineral deposits and to plan mining operations, environmental engineering to assess the contamination of soil and groundwater and to design remediation strategies, and civil engineering to design foundations, tunnels and other underground structures. In this sense, ground models allow the engineer to understand and to visualize the spatial organization of subsurface geological structures and, additionally, it is possible to evaluate the spatial distribution of material properties which is essential in any geomechanical study prior to any project. In this context, SAALG Geomechanics through DAARWIN web platform provides a suitable software tool for the geotechnical engineer to perform the complete ground model workflow. The process starts introducing borehole data from different sources and then, the engineer can visualize and interpret borehole logs, define geomechanical units and assign parameters from in-situ and laboratory tests, as well as assign units’ geometry from geological layers. Finally, the user can feed this information to the system to obtain a 2D cross-section, that can be exported to the commercial Finite Element software PLAXIS and use this PLAXIS model for geotechnical design and more advanced analyses such as Sensitivity analysis and Back-Analysis, which are also implemented in DAARWIN.

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

The weathering profile in mudstone outcrops can range from weathered clay to unweathered mudstone. The strength and small-strain stiffness of these materials, and of stiff clays and weak rocks in general, is critical to the design of geotechnical structures. Monitoring data and ground investigation data were gathered during the construction of a trial embankment founded on weathered, Jurassic-aged mudstone, for the HS2 high-speed railway project (UK). These data included outputs from in-situ downhole geophysical tests and extensometers at the embankment location. These were compared to ground investigation data from the wider mudstone outcrop over an 18.2 km stretch of the route. The installation of extensometers prior to loading by the embankment construction enabled the measurement of in-situ strains for a range of small and medium strains. It was therefore possible to characterise the stress-strain behaviour of the individual layers within the ground profile. The results showed that stiff clays derived from weathered mudstone at shallow depth (<10 mbgl) are characterised by low undrained shear strength (<300 kPa) and by maximum stiffness values that are comparable to laboratory measurements from fine-grained soils. However, the unweathered mudstone at greater depth (>15 mbgl) showed higher strength (>300 kPa) and higher maximum stiffness than the overlying clay. Both the strength and stiffness profiles showed a transition zone between the weathered clay and the unweathered mudstone. This zone included a partially weathered mudstone that had the visual appearance and index properties of a mudstone, but the strength of a stiff clay (i.e. τu < 300 kPa).