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We evaluate the dynamic response of the large (around five million cubic meters) unstable rock slope at Randa, Switzerland, based on ground-motion recordings during small earthquakes. Seismic measurements revealed strong polarization of the wavefield in the direction of maximum slope displacement with spectral amplification factors ∼5 within the unstable area. Results further highlighted resonant frequencies of both the large unstable rock mass and individual blocks within it. Block vibration was confirmed by phase analysis of in situ displacement measurements from two bounding tension fractures during a small earthquake. Numerical simulation using a discontinuous elastic model showed that the presence of steeply-dipping compliant fractures is crucial for recreating the observed site response. Such fractures are common in rock slope instabilities and are here shown to contribute to polarization and amplification of seismic shaking, site effects that are rarely considered for hard rock slopes and which may influence the potential for earthquake-triggered failure. [ABSTRACT FROM AUTHOR]

Investigating surface displacements in high alpine environments is often subject to challenges due to the difficult accessibility or harsh climatic conditions. Measurement systems have improved greatly in recent years regarding accuracy, range, or energy consumption. Continuously receiving high-precision, real-time monitoring data from a remote location can still support a better understanding of slope dynamics and risk. We present the design, construction, operation, and performance of a complex surface displacement monitoring system installed in the surroundings of the Great Aletsch Glacier in the Swiss Alps, based on two robotic total stations to continuously measure 3D displacements with high accuracies. In addition, GNSS stations are also considered in order to pass from a local to a geographic reference system, as well as to improve the measurement accuracy. The monitoring network is aimed at studying several types of deformation processes, i.e., (i) gravitationally driven and irreversible rockslide movements around the tongue of the Great Aletsch Glacier, (ii) reversible rock slope deformations caused by annual cycles of groundwater recharge and depletion, and (iii) small irreversible deformations of stable rock slopes resulting from progressive rock damage driven by glacier retreat and cyclic hydraulic and thermal loading. We describe the technical details of the monitoring system, which has been in operation successfully for 6 years, and discuss the system performance in terms of its robustness and accuracy. [ABSTRACT FROM AUTHOR]

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Most natural rock slope failures result from long-term strength degradation. It is often hypothesized that glacial retreat leads to enhanced progressive damage accumulation in adjacent rock slopes, due to mechanical unloading and changes to the thermal and hydraulic boundary conditions. However, direct observations of subsurface processes in a rock slope subject to glacial retreat are rare. In this paper, we present the design, implementation, and performance of a new borehole monitoring system installed on a rock slope in fractured crystalline rock located beside the glacier tongue of the retreating Great Aletsch Glacier (Valais, Switzerland). The three vertical, 50 m deep boreholes were instrumented to continuously monitor groundwater pressure, temperature and deformation at high resolution, in order to investigate thermo-hydro-mechanical coupled slope processes that drive progressive rock mass damage. We show that the system is capable of measuring both reversible and irreversible displacements along single fractures at magnitudes ranging between 0.001 mm to >2 mm in the studied rock slope, and that it is often possible to identify drivers of these deformation signals. The transient subsurface temperature field shows clear indications of former ice occupation in form of cold temperatures preserved at depth and superimposed annual temperature cycles penetrating down to a depth of about 17 m. The variability of the pressure head in the slope is driven by annual snowmelt infiltration cycles, rainfall events, and the assumed connection to englacial water of the temperate glacier. The new and continuously growing dataset presented here will enable us to relate the changing boundary conditions caused by glacial retreat and fatigue from daily to annual thermal and hydraulic loading cycles to progressive rock mass weakening, which may ultimately result in rock slope failure. • We installed a borehole monitoring system in a glacier adjacent rock slope. • We measure subsurface temperature, pore pressure and strain during deglaciation. • This data is used to analyze thermo-hydro-mechanical coupled rock slope processes. • We document rock mass damage at the micrometer-scale linked to deglaciation. [ABSTRACT FROM AUTHOR]

Rock slopes next to the tongue of the Great Aletsch Glacier, Switzerland are characterized by rapid environmental adjustment to non-glacial conditions. This study investigates and describes in detail the historic development of the largest rock slope instability in this area, called Moosfluh Landslide. We study in detail the structure, evolution and stability since the end of the Little Ice Age (LIA) until September 2016 and discuss their relationships with the evolution of the Great Aletsch Glacier since the Lateglacial period. In 2016 around 50 m of glacial ice thickness were left at the Moosfluh Landslide toe, where in 1850 glacial ice was >400 m thick. The changing stability conditions at the interface with the melting valley glacier are studied based on novel balanced cross sections and kinematic model of the Moosfluh Landslide dominated by toppling phenomena in metamorphic rock. The morphology and evolution of this landslide since the LIA are investigated with multi-temporal landslide maps based on aerial digital photogrammetry (ADP) applied to historic images since 1961. Internal deformation at Moosfluh is accommodated by shear slip along uphill-facing foliation and fault planes, and by extensional faulting forming tension cracks and graben-structures at the landslide head. Together with Digital Image Correlation (DIC) and total station monitoring (TPS) the Moosfluh Landslide displacement history was reconstructed, evidencing post-Egesen landslide displacements and an acceleration of movements since the LIA and especially since 2007. The displacement rates increase from few mm per year until the nineties to several meter per day in September 2016. Different kinematic models have been tested and changes in the Moosfluh rock slope stability in response to retreating glacial ice and changing groundwater conditions was explored with limit-equilibrium analysis of the stepped planar block toppling model of Goodman and Bray (1976). For the observed conditions and a toppling joint friction angle of 19° the simulated factor of safety drops non-linearly from the LIA maximum (1.12) to the year 2007 (1.02), when the height of ice above the valley bottom melted down to 100 m. This study illustrates with unprecedented detail the time scales, displacement magnitudes and structural evolutions of a large toppling mode slope instability in a paraglacial setting. The long-term cumulative slope displacements between the Egesen stadial and the LIA are of the same magnitude as the cumulative displacements between the LIA and the year 2016. As large portions of the studied slope underwent multiple retreats and advances of the Great Aletsch Glacier during the Lateglacial and Postglacial period, the observed onset of large slope displacements should be related to incremental damage (slip weakening and weathering) occurring along steeply dipping toppling fractures during the LIA. [ABSTRACT FROM AUTHOR]

We performed an extensive analysis of C-band SAR datasets provided by the European Space Agency (ESA) satellites ERS-1/2, Envisat ASAR, and Sentinel-1 in the period 1992–2020 aiming at reconstructing the multi-decadal spatial and temporal evolution of the surface displacements at the Brienz/Brinzauls landslide complex, located in canton Graubünden (Switzerland). To this end, we analyzed about 1000 SAR images by applying differential interferometry (InSAR), multitemporal stacking, and persistent scatterer interferometry (PSI) approaches. Moreover, we jointly considered digital image correlation (DIC) on high-resolution multi-temporal digital terrain models (DTM) generated from airborne surveys and InSAR results to compute 3-D surface deformation fields. The extensive network of GNSS stations across the Brienz landslide complex allowed us to extensively validate the deformation results obtained in our remote sensing analyses. Here, we illustrate the limitations occurring when relying on InSAR and/or PSI measurements for the analysis and interpretation of complex landslide scenarios, especially in cases of relevant spatial and temporal heterogeneities of the deformation field. The joint use of InSAR and DIC can deliver a better picture of the evolution of the deformation field, however, not for all displacement components. Since InSAR, PSI and DIC measurements are nowadays routinely used in the framework of local investigations, as well as in regional, national, and/or continental monitoring programs, our results are of major importance for users aiming at a comprehensive understanding of these datasets in landslide scenarios. [ABSTRACT FROM AUTHOR]

Extremely-rapid, flowlike landslides can impact people and property far from their source, and predicting the initiation and runout of these events remains a challenging task. The ongoing risk analysis of the Schlucher Landslide, located near the town of Malbun, Liechtenstein, highlights the uncertainties associated with this type of analysis. This landslide, composed of clayey sand and clayey gravel, has accumulated 10s of meters of displacement in the last 3 years. Managing the risk posed by this unstable colluvial mass requires addressing the following questions: Can the Schlucher Landslide transition into an extremely-rapid flowlike landslide? If such a transition were to occur, what would be the consequence for the community located at the outflow of the Schlucher Catchment?Addressing these questions requires an understanding of potential mechanisms that can lead to catastrophic failure of the unstable mass. A number of mechanisms, including static and dynamic liquefaction, loss of true and/or apparent cohesion and shearing to residual strength have been well documented in literature, and can be identified by routine geotechnical analyses. The focus of this work is on macroscopic brittleness, a poorly understood mechanism that may have governed the failure of a number of well documented case histories that were composed of fine grained colluvium, similar to the Schlucher Landslide. Here we present detailed field observations and 3D numerical runout modelling of three extremely-rapid, flowlike landslides that occurred in fine grained colluvium: The 2014 Oso Flowslide, the 2012 Johnsons Landing Landslide and the 1973 Attachie Slide. These analyses reveal that the catastrophic runout of all three cases can be explained by the landslide debris undergoing a large, undrained strength loss. The potential for this mechanism to occur at these sites would have been difficult to identify by conventional geotechnical analyses. We then compare surface and subsurface data obtained for the Schlucher Landslide to these three cases to qualitatively assess the potential that this landslide could experience a similar undrained strength loss. The results of this work have significant implications for understanding catastrophic failure potential of fine grained colluvium, and highlight the need for further research on the mechanism of macroscopic brittleness. [ABSTRACT FROM AUTHOR]

The Moosfluh slope, located in the vicinity of the current tongue of the Great Aletsch glacier, Switzerland, hosts one of the largest active instabilities of the European Alps. Despite at this location accelerated slope displacement has been detected over the past decade, the rapid evolution observed between September and November 2016, locally reaching tens of meters, was largely unexpected. During this "crisis phase", the rock mass experienced substantial internal deformation mainly composed of toppling, formation of tensile scarps, and basal sliding. The large internal deformation caused also several local failure events in the form of single block falls and/or rock mass collapses of moderate size. Here we focus on the post-crisis, i.e. the period going between spring 2017 until today. The deformation occurring at the Moosfluh slope is still consistent and rock failure events are regularly going on, however, not in a dramatic fashion as observed in fall 2016. We show the results obtained by jointly investigating satellite, airborne, and ground based imagery, exploiting optical and radar sensors, as well as the data recorded from a local seismic network. In particular, we focus on the joint analysis of the information obtained from the optical imagery acquired with high temporal frequencies and the seismic waveforms associated to rock failure events. The combined remote sensing and geophysical dataset presented here is unique, and allows for a detailed interpretation of the rapid spatial and temporal rock mass disintegration in an alpine slope. Our results are of interest to understand mutual influences between predisposing slope instability factors (i.e., mainly due to geological, structural, and geomorphological conditions), and external driving factors (i.e., seismicity and meteo-climatic effects) on the progressive evolution of rock mass, specifically at the Moosfluh slope but also in similar case scenarios. [ABSTRACT FROM AUTHOR]

This study is based on detailed monitoring data from a large DSGSD called Moosfluh instability, located at the current glacier tongue of the Great Aletsch Glacier (Switzerland). This about 100 Mm³ large, and up to 170 m deep toppling mode instability started to accelerate around 1990, presumably caused by increased rates of glacier ice downwasting at the landslide toe. In 2013 and 2014, when average velocities reached about 500-700 mm/a, we installed a high accuracy displacement monitoring system, composed of 2 robotized total stations measuring displacements at about 15 reflectors positioned within the active landslide, 4 GNSS stations, and 2 Time-Lapse cameras. In the fall of 2016 a dramatic increase in acceleration occurred, leading to velocities of individual landslide compartments of up to 12 m in 6 weeks. Optical imagery and digital image correlation revealed that this acceleration was caused by the rapid development of three secondary rockslide scarps, and that movement initiated at the toe of the slope and evolved upslope. To investigate the depths of movements and the subsurface kinematic mechanism in detail, we developed a new analytical model, which considers the time series of three-dimensional displacements and plunge angles of discrete points within the landslide. The application of this model leads to the conclusion that a transition from primarily toppling to sliding mode displacements occurred during fall 2016. We can trace the detailed evolution of individual compartments, showing that toppling/sliding ratios varied in both space and time. The secondary rockslides forming during this period have a depth of about 30-40 meters and volumes ranging between 1 and 5 Mm³. Planar sliding surfaces are expected to have developed at a major kink zone within the large toppling rock mass.This kinematic evolution observed at Moosfluh significantly impacts the corresponding hazard and risk assessment, as flexural toppling tends to be a self-stabilizing mechanism, whereas planar rockslides can potentially transition into catastrophic failures. The estimated potential runout length probabilities show that the main hazard would be created by the formation and subsequent breach of a rock avalanche dam in the Massa gorge below the tongue of the Great Aletsch Glacier. [ABSTRACT FROM AUTHOR]

Rapid mapping of event landslides is crucial to identify the areas affected by damages as well as for effective disaster response. Traditionally, such maps are generated with visual interpretation of remote sensing imagery (manned/unmanned airborne systems or spaceborne sensors) and/or using pixel-based and object-based methods exploiting data-intensive machine learning algorithms. Recent works have explored the use of convolutional neural networks (CNN), a deep learning algorithm, for mapping landslides from remote sensing data. These methods follow a standard supervised learning workflow that involves training a model using a landslide inventory covering a relatively small area. The trained model is then used to predict landslides in the surrounding regions. Here, we propose a new strategy, i.e., a progressive CNN training relying on combined inventories to build a generalized model that can be applied directly to a new, unexplored area. We first prove the effectiveness of CNNs by training and validating on event landslides inventories in four regions after earthquakes and/or extreme meteorological events. Next, we use the trained CNNs to map landslides triggered by new events spread across different geographic regions. We found that CNNs trained on a combination of inventories have a better generalization performance, with a bias towards high precision and low recall scores. In our tests, the combined training model achieved the highest (Matthews correlation coefficient) MCC score of 0.69 when mapping landslides in new unseen regions. The mapping was done on images from different optical sensors, resampled to a spatial resolution of 6 m, 10 m, and 30 m. Despite a slightly reduced performance, the main advantage of combined training is to overcome the requirement of a local inventory for training a new deep learning model. This implementation can facilitate automated pipelines providing fast response for the generation of landslide maps in the post-disaster phase. In this study, the study areas were selected from seismically active zones with a high hydrological hazard distribution and vegetation coverage. Hence, future works should also include regions from less vegetated geographic locations. [ABSTRACT FROM AUTHOR]

We use multitemporal analyses based on Synthetic Aperture Radar differential interferometry (DInSAR) to study the slope adjacent to the large Punatsangchhu-I hydropower plant, a concrete gravity dam under construction in Bhutan since 2009. Several slope failures affected the site since 2013, probably as a consequence of toe undercutting of a previously unrecognised active landslide. Our results indicate that downslope displacement, likely related to the natural instability, was already visible in 2007 on various sectors of the entire valley flank. Moreover, the area with active displacements impinging on the dam site has continuously increased in size since 2007 and into 2018, even though stabilization measures have been implemented since 2013. Stabilisation measures currently only focus on a small portion of the slope, however, the unstable area is larger than previously evaluated. Highly damaged rock is present across many areas of the entire valley flank, indicating that the volumes involved may be orders of magnitude higher than the area on which stabilisation efforts have been concentrated after the 2013 failure. The results highlight that satellite-based DInSAR could be systematically used to support decision making processes in the different phases of a complex hydropower project, from the feasibility study, to the dam site selection and construction phase. [ABSTRACT FROM AUTHOR]

Water infiltration into fractures is ubiquitous in crustal rocks. However, little is known about how such a progressive wetting process affects fracture stiffness and seismic wave propagation, which are highly relevant for characterizing fracture systems in situ. We study the acousto‐mechanical behavior of a free‐standing fractured granite subjected to gradual water infiltration with a downward‐moving wetting front over 12 days. We observe significant differences (i.e., by an order of magnitude) in wave amplitudes across the fractured granite compared to an intact granite, with both cases showing a strong correlation between wave amplitudes and wetting front movement. Effects of water infiltration into the fracture and surrounding matrix on seismic attenuation are captured by a numerical model with parameters constrained by experimental data. Back‐calculated fracture stiffness decreases exponentially with the wetting front migration along the fracture. We propose that moisture‐induced matrix expansion around the fracture increases asperity mismatch, leading to reduced fracture stiffness. Plain Language Summary: In the shallow layers of the Earth, hydrological cycles such as snowmelt, fog, dew, and rain have been shown to change the moisture content of crustal rocks, which can alter the elastic properties of natural fractures and affect the propagation of seismic waves. Understanding how seismic waves propagate in the near‐surface environment is crucial for the assessment of earthquake hazards and the characterization of geologic heterogeneities. In this work, we perform well‐controlled laboratory experiments to study the acousto‐mechanical behavior of a single fracture in granitic rock subjected to progressive wetting over 12 days. We report that the fracture stiffness decreases exponentially as the wetting front advances along the fracture. Our research sheds light on an important question in fracture characterization: how elastic waves propagate across a fracture undergoing moisture‐induced expansion. Key Points: A laboratory study establishes a relationship among water imbibition, seismic attenuation, and stiffness evolution in a wetted fractureWave amplitudes across a fracture correlate strongly with the wetting front movement of infiltrated water within the fractureFracture stiffness exponentially decreases with the advance of the wetting front along the fracture [ABSTRACT FROM AUTHOR]

The paper represents a summary about our research projects conducted between 2003 and 2015 related to the mechanical behaviour of Opalinus Clay at Mont Terri. The research summarized covers a series of laboratory and field tests that address the brittle failure behaviour of Opalinus Clay, its undrained and effective strength, the dependency of petro-physical and mechanical properties on total suction, hydro-mechanically coupled phenomena and the development of a damage zone around excavations. On the laboratory scale, even simple laboratory tests are difficult to interpret and uncertainties remain regarding the representativeness of the results. We show that suction may develop rapidly after core extraction and substantially modifies the strength, stiffness, and petro-physical properties of Opalinus Clay. Consolidated undrained tests performed on fully saturated specimens revealed a relatively small true cohesion and confirmed the strong hydro-mechanically coupled behaviour of this material. Strong hydro-mechanically coupled processes may explain the stability of cores and tunnel excavations in the short term. Pore-pressure effects may cause effective stress states that favour stability in the short term but may cause longer-term deformations and damage as the pore-pressure dissipates. In-situ observations show that macroscopic fracturing is strongly influenced by bedding planes and faults planes. In tunnel sections where opening or shearing along bedding planes or faults planes is kinematically free, the induced fracture type is strongly dependent on the fault plane frequency and orientation. A transition from extensional macroscopic failure to shearing can be observed with increasing fault plane frequency. In zones around the excavation where bedding plane shearing/shearing along tectonic fault planes is kinematically restrained, primary extensional type fractures develop. In addition, heterogeneities such as single tectonic fault planes or fault zones substantially modify the stress redistribution and thus control zones around the excavation where new fractures may form. [ABSTRACT FROM AUTHOR]

Catastrophic landslides characterized by runaway slope failures remain difficult to predict. Here, we develop a physics‐based framework to prospectively assess slope failure potential. Our method builds upon the physics of extreme events in natural systems: the extremes so‐called "dragon‐kings" (e.g., slope tertiary creeps prior to failure) exhibit statistically different properties than other smaller‐sized events (e.g., slope secondary creeps). We develop statistical tools to detect the emergence of dragon‐kings during landslide evolution, with the secondary‐to‐tertiary creep transition quantitatively captured. We construct a phase diagram characterizing the detectability of dragon‐kings against "black‐swans" and informing on whether the slope evolves toward a catastrophic or slow landslide. We test our method on synthetic and real data sets, demonstrating how it might have been used to forecast three representative historical landslides. Our method can in principle considerably reduce the number of false alarms and identify with high confidence the presence of true hazards of catastrophic landslides. Plain Language Summary: Catastrophic slope failures that pose great threats to life and property remain difficult to predict due to the strong variability of slope behavior. As a result, only a limited number of large rock slope failures have been so far successfully forecasted with associated risks mitigated. Here, we propose a novel predictive framework to prospectively and quantitatively detect slope failure precursors with high confidence. Our research sheds light on one of the most challenging questions in landslide prediction: Would an active landslide slowly move or catastrophically fail in the future? Our method adds a new conceptual framework and operational methodology with a significant potential to support existing early warning systems and hence reduce landslide risks. Key Points: Tertiary creeps of catastrophic landslides accommodate dragon‐kings showing statistically different properties than secondary slope creepsA predictive framework is developed to forecast catastrophic landslides by detecting signatures typical of the emergence of dragon‐kingsA phase diagram characterizes the detectability of dragon‐kings against black‐swans and discriminates catastrophic and slow landslides [ABSTRACT FROM AUTHOR]

[Display omitted] • We explore THM coupled processes in a new TBM tunnel in the Opalinus Clay shale. • We present the evolution of in-situ state variables acquired over four years. • Radial total pressures (RTP) on the tunnel support are heterogeneous. • RTP reflect construction activities and long-term tunnel climate variations. • RTP reveal swelling, gap grout yielding, and are consistent with lab swelling tests. The old Belchen tunnel tubes in the Swiss Jura Mountains were excavated with drill-and-blast in swellable sedimentary rocks, i.e., anhydrite-rich marls (Gipskeuper) and Opalinus Clay shale (OPA). Already during construction in the 1960s both rock formations caused substantial damage to the tunnel support through high swelling pressures and heave, and in later years the tubes had to be refurbished again. Important maintenance and repair prompted the construction of a new, third Belchen tunnel tube (2016–2021) with a tunnel-boring machine (TBM). In this study we present in-situ datasets acquired to investigate the stress evolution and controlling mechanisms over more than four years at a monitoring section located in a strongly faulted OPA section of the new Belchen tunnel tube. The main datasets include time series of total radial pressure, radial strain, rock water content, rock and concrete temperatures, as well as details of the geological structures obtained from analyses of borehole logs and three-dimensional photogrammetric excavation face models. Finally, a series of idealised numerical simulations explore the impact of measured temperature variations on the measured total pressures, which confirm a strong temperature effect on radial pressures related to the setting of concrete and seasonal climatic variations. We find that in our monitoring section radial pressures on the tunnel support are very heterogeneous, i.e., they range between 0.5 MPa and 1.5 MPa, and still gently increasing 4 years after excavation. The measured pressures are 2–5 times greater than measured in the old Belchen tunnel tubes and similar in magnitude to swelling pressures obtained in laboratory tests. EDZ permeability measurements, water content evolution, and radial strain data from the tunnel invert suggest that swelling processes contribute to the long term radial pressure build-up. Thermo-elastic deformation and swelling might be superimposed by local reactivation of tectonic faults and gap grout cracking at crack-initiation stress levels. [ABSTRACT FROM AUTHOR]

We present a combined experimental and numerical study of failure and damage in faulted Opalinus Clay shale around an opening at the Mont Terri Rock Laboratory, Switzerland. An experiment borehole with a diameter of 0.6 m and a length of 12.9 m intersecting a major fault zone at an acute angle of ∼ 40 ° was drilled, with subsequent overbreaks closely monitored. To investigate the underlying mechanisms that lead to the observed overbreaks, we developed a 3D geomechanics model to simulate the deformation and failure behaviour of faulted Opalinus Clay shale. To represent geological structures including the major fault zone and secondary fracture sets, a site-specific fracture network was constructed. Our model captured many important geomechanical properties and responses of the faulted Opalinus Clay shale, such as anisotropy of the shale matrix, deformation of the fault zone, dislocation of secondary fractures, and growth of new cracks as well as generation of overbreaks around the opening. We compared our simulation results with in-situ experimental observation of short-term overbreak patterns along the borehole and found that the overbreak occurrence is strongly controlled by both stress conditions and geological structures. Our results indicate that the damaged zone is characterised by an inner shell and an outer shell, where the former (dominated by extensive tensile/shear cracks) has a thickness of about one quarter of the borehole diameter and the latter (dominated by sparse shear cracks) extends by half to one borehole diameter into the surrounding rock. We further elucidated the impacts of the major fault zone and secondary fracture sets as well as the borehole–fault intersection angle on the deformation, damage, and failure characteristics. The findings and insights obtained in this study have important implications for the stability evaluation of waste emplacement drifts and long-term safety assessments of nuclear waste galleries in faulted argillaceous rocks. • 3D simulation captures overbreak and damage of Opalinus Clay around an opening. • Interplay of stress and heterogeneity drives overbreak formation and pattern. • Damaged zone of a two-shell structure rotates with the distance to a fault zone. • Acute angled faults exert strong controls on overbreak and damage generation. [ABSTRACT FROM AUTHOR]

Correction to: I Scientific Reports i https://doi.org/10.1038/s41598-021-89015-8, published online 06 May 2021 The original version of this Article contained an error in Table 1, where the formula given for the MCC score was incorrect. [Extracted from the article]

Abstract: In this study, the rock mass response ahead of an advancing test tunnel in the Opalinus Clay at the Mont Terri Rock Laboratory (Switzerland) was investigated. Characterisation of the excavation-induced damage zone at Mont Terri is a challenging task due to the anisotropic and heterogeneous nature of the shale: pronounced bedding leads to intact rock anisotropy and prevalent small-scale tectonic shears lead to rock mass heterogeneity. Rock mass damage ahead of an experimental tunnel or niche was characterised through single-hole seismic wave velocity logging, borehole digital optical televiewer imaging, and geological drillcore mapping. Three-dimensional elastic stress analyses were completed and showed that rock mass degradation can be correlated to changes in the maximum to minimum principal stress ratio (i.e., spalling limit). Numerical results showed that close to the niche boundary, unloading lowers stress ratios, which correspond with decreasing seismic wave amplitudes and velocities; thus, indicating that strength degradation resulted from increasing crack-induced damage. Considerations of tectonic shears and distance from a previously stressed volume of rock were necessary in understanding both the damage state and extent ahead of the face. By integrating field and numerical data, the investigation showed that geological structures (i.e., bedding and bedding-parallel tectonic shears) were most influential near the entrance but played a lesser role as the niche deepened. Additionally, a portion of the niche is located in the perturbed zone of the intersecting Gallery04. [Copyright &y& Elsevier]

The Gotthard Base Tunnel (GBT), constructed between 2000 and 2011, is a 57 km long and up to 2.5 km deep high-speed railway tunnel located in the Swiss Alps. Significant ground surface displacements reaching about 10 cm were observed during and after the tunnel construction. To gain a better understanding of the causal mechanism of such conspicuous ground deformations, we develop a three-dimensional (3D) fully-coupled hydro-mechanical model to simulate GBT-induced groundwater drainage, stress redistribution, rock mass consolidation, and fault zone deformation at the regional scale. First, we construct a geological model with topographical features, lithological units, and natural faults realistically represented. We constrain the material properties of fault zones and rock masses based on available extensive laboratory testing results and site characterisation datasets. We then simulate the tunnelling process over time, with the resulting coupled hydro-mechanical responses of faulted rock masses well captured and ground surface/subsurface displacements quantitatively analysed. The simulation results in general show a good agreement with the field monitoring data of ground surface displacement, subsurface tunnel settlement, and groundwater inflow into the tunnel. Our model indicates that ground surface displacements originate from GBT-induced water drainage and rock mass consolidation in the deep subsurface. Our results also show that the GBT construction could trigger faults to shear via drainage-induced pressure diffusion and poroelastic stressing. The research findings from our work have important implications for many groundwater drainage-related geoengineering activities such as underground excavation in alpine mountains and fluid withdrawal in subsurface reservoirs. [Display omitted] • 3D simulation captures tunnelling-induced groundwater flow and rock mass deformation. • The simulation explains ground subsidence in crystalline rock during deep tunnelling. • Drainage and consolidation in deep subsurface cause ground surface displacements. • Tunnelling-induced pressure diffusion and poroelastic stressing drive fault movement. [ABSTRACT FROM AUTHOR]