<p>One of the most important but still unknown destabilizing factors of rock faces in periglacial environments is the contribution of water in terms of hydrostatic pressure (e.g. Piz Cengalo in 2017). Its presence has often been registered in major rock failures, but it has never been quantified. Perched water table >>20m above virtually impermeable permafrost bedrock can cause excessive hydrostatic stress on affected rockwalls. Climate change related intensification of rainstorms as well as permafrost degradation promote water accumulation. An increase in rockfall activity due to higher water pressure peaks is therefore expected, thus intensifying the risk for humans and infrastructures.</p><p>Here we conduct a hydromechanical stability analysis at two study sites in the Northern Calcareous Alps where this effect has been observed. We use the distinct element method developed in the software UDEC (Itasca); the required geometric and mechanical model input parameters were obtained from previous studies with direct investigations and laboratory tests in frozen/unfrozen conditions. Infiltration from rainfall or snow/ice melting is expected to create extreme pressure peaks, especially when permafrost seals fractured rock.</p><p>Here we present results from:</p><ol><li>the permafrost affected Zugspitze summit (Wetterstein Range), where sealing permafrost allows the meltwater to accumulate in the active layer. This causes high hydrostatic pressure, evaluated by relative gravimetry methods and with the help of a fracture mapping.</li> <li>a preparing high-magnitude rock fall at the Hochvogel (Allg&#228;u Alps), where perched water could destabilize up to 260&#8217;000 m&#179;. Displacement measurements on the summit showed acceleration following intense precipitation.</li> </ol><p>Our model proves that a column of water can bring the Zugspitze north face to instable equilibrium. This happens with different intensities according to frozen/unfrozen conditions and various depth of the active layer, if the hydrostatic pressure is adequate (0.2-0.4 MPa = 20-40 m water column).</p><p>Water could also increase the destabilization rates of the south-east face of Hochvogel by adding hydrostatic pressure. A Factor of Safety < 1 is reached when other water-related factors are considered, like: (i) reduction of cohesion in saturated joints, (ii) decrease of the interface friction angle in fractures and (iii) accelerates weathering along the shear plane</p>
We describe the case of a patient who underwent craniectomy for hemorrhage of the left parietal lobe. Three weeks later, orthostatic memory impairment was detected as initial symptom of sinking skin flap syndrome (SSFS). This deficit was examined by neuropsychological testing and associated with a posture-dependent increase in the delta/alpha ratio at the F3 electrode, an electroencephalographic (EEG) index related to brain hypoperfusion. This EEG spectral alteration was detected in a brain region that includes the left dorsolateral prefrontal cortex, an area known to be involved in memory processing; therefore we hypothesize that SSFS induced reversible hypoperfusion of this otherwise undamaged cortical region. Neither of these findings was present after cranioplasty. This case suggests that SSFS may induce neuropsychological deficits potentially influencing outcome in the postacute phase and is further evidence supporting the clinical benefits of early cranioplasty.
Hydrostatic pressure is one of the most important but still not fully understood destabilising factors of bedrock slopes. Water presence has often been recorded in major rock failures like at Piz Cengalo in 2017 but still its quantification and its effective destabilizing role remain unsolved issues in rockfall forecasting. Intensification of rainstorms due to climate change will enhance hydrostatic pressures in fractured bedrock, which will likely lead to increase in rockfall activity and connected risks for humans and infrastructures. Here we present a hydro-mechanical stability analysis of the Hochvogel summit (2,592 m AA) in the Northern Calcareous Alps. At this site, an imminent high-magnitude rockfall could destabilise up to 260,000 m3 and is therefore acutely monitored. Displacement measurements on the summit showed daily acceleration following intense precipitation. With the help of direct investigations and laboratory tests from previous studies, we implemented the Hochvogel SE slope and its mechanical parameters in the 2D Universal Distinct Element Code (UDEC). Our model shows that the presence of water columns of 10 m decreases the factor of safety (FoS) on average by 11 % and can increase the max displacement by up to 70 %. When including the effects of cleft weathering in the model, FoS < 1 can be reached. The friction angle of clefts has a key role in this destabilization process. This study provides key elements for interpreting the mechanical behaviour of this imminent rockfall in connection with hydrostatic pressures, helping to improve hazard forecasting at the Hochvogel and at similar sites.
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