Time-dependent ground movements induced by shield tunneling in soft clay: a parametric study

In this work, the effects of coupled hydromechanical (consolidation) processes associated with shield tunneling excavation in soft clays are investigated with particular attention to the prediction of ground movements at the ground surface. A series of 2d FE analyses have been carried out in parametric form in order to investigate the effects of tunnel excavation velocity relative to the soil consolidation rate and the hydraulic boundary conditions at the tunnel boundary. The shield advancement process has been simulated with a simplified procedure incorporating both volume loss and ovalization of the tunnel section. In order to investigate the relative importance of soil consolidation during the excavation process, different characteristic times for the tunnel face advancement and for the consolidation process around the tunnel have been considered, for the two limiting conditions of fully permeable liner and impervious liner. The potential damage induced by the tunnel excavation on existing structures, based on computed ground surface distortions and horizontal deformations, has been found to vary significantly with time during the consolidation process. The results of the simulations allowed to obtain useful information on the minimum tunnel face advancement speed for which the assumption of fully undrained conditions for the soil during the excavations is acceptable, as well as on the speed range for which solving the fully coupled hydromechanical problem is necessary.     

Timing of diagenesis and very low‐grade metamorphism in the eastern sector of the Sierra de Cameros (Iberian Range,Spain): a U–Pb SHRIMP study on monazite

The Sierra de Cameros is an intracontinental orogen and represents the north‐western part of the Iberian Range in Northern Spain. It comprises a thick sequence of syn‐rift continental sediments (mainly sandstones and carbonates) deposited during lower Cretaceous times. A unique characteristic of the Sierra de Cameros in relation to the rest of the Iberian Range is the presence of low‐grade metamorphism in certain parts of the basin, an event that predates basin inversion. This paper describes the presence, textural relationships and geochemical aspects of authigenic and/or metamorphic monazite within different lithologies from the deepest parts of the basin. Sensitive high resolution ion microprobe (SHRIMP) U–Pb dating of monazite records the presence of two age populations: the first with ²⁰⁶Pb/²³⁸U ages ranging from 122 to 116 Ma which is considered as diagenetic in origin, whilst the second is dated at 99 ± 2 Ma and postdates the metamorphic climax.     

Correction to: Rip current hazard assessment on a sandy beach in Liguria,NW Mediterranean

Natural Hazards - The article was published showing the first two author names in the wrong order.     

Rip current hazard assessment on a sandy beach in Liguria,NW Mediterranean

Natural Hazards - Rip currents are one of the most significant environmental hazards for beachgoers and are of interest to coastal scientists. Several studies have been conducted to understand rip...     

Magnetized relativistic jets and long-duration GRBs from magnetar spin-down during core-collapse supernovae

We use ideal axisymmetric relativistic magnetohydrodynamic simulations to calculate the spin-down of a newly formed millisecond,   B ∼ 10¹⁵ G  , magnetar and its interaction with the surrounding stellar envelope during a core-collapse supernova (SN) explosion. The mass, angular momentum and rotational energy lost by the neutron star are determined self-consistently given the thermal properties of the cooling neutron star's atmosphere and the wind's interaction with the surrounding star. The magnetar drives a relativistic magnetized wind into a cavity created by the outgoing SN shock. For high spin-down powers  (∼10⁵¹–10⁵² erg s⁻¹)  , the magnetar wind is superfast at almost all latitudes, while for lower spin-down powers  (∼10⁵⁰ erg s⁻¹)  , the wind is subfast but still super-Alfvénic. In all cases, the rates at which the neutron star loses mass, angular momentum and energy are very similar to the corresponding free wind values (≲30 per cent differences), in spite of the causal contact between the neutron star and the stellar envelope. In addition, in all cases that we consider, the magnetar drives a collimated  (∼5–10°)  relativistic jet out along the rotation axis of the star. Nearly all of the spin-down power of the neutron star escapes via this polar jet, rather than being transferred to the more spherical SN explosion. The properties of this relativistic jet and its expected late-time evolution in the magnetar model are broadly consistent with observations of long duration gamma-ray bursts (GRBs) and their associated broad-lined Type Ic SN.     

Crystal chemistry, surface morphology and X-ray photoelectron spectroscopy of Fe-rich osumilite from Mt. Arci, Sardinia (Italy)

Microprobe analysis, single crystal X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray absorption spectroscopy were applied on Fe-rich osumilite from the volcanic massif of Mt. Arci, Sardinia, Italy. Osumilite belongs to the space group P6/mcc with unit cell parameters a = 10.1550(6), c = 14.306(1) Å and chemical formula (K_0.729)_C (Na_0.029)_B (Si_10.498 Al_1.502)_T1 (Al_2.706 Fe _0.294 ²⁺ )_T2 (Mg_0.735 Mn_0.091 Fe _1.184 ²⁺ )_AO₃₀. Structure refinement converged at R = 0.0201. Unit cell parameter a is related to octahedral edge length as well as to Fe²⁺ content, unlike the c parameter which does not seem to be affected by chemical composition. The determination of the amount of each element on the mineral surface, obtained through X-ray photoelectron spectroscopy high-resolution spectra in the region of the Si_2p, Al_2p, Mg_1s and Fe_2p core levels, suggests that Fe presents Fe²⁺ oxidation state and octahedral coordination. Two peaks at 103.1 and 100.6 eV can be related to Si⁴⁺ and Si¹⁺ components, respectively, both in tetrahedral coordination. The binding energy of Al_2p, at 74.5 eV, indicates that Al is mostly present in the distorted T2 site, whereas the Mg peak at 1,305.2 eV suggests that this cation is located at the octahedral site. X-ray absorption at the Fe L_2,3-edges confirms that iron is present in the mineral structure, prevalently in the divalent state and at the A octahedral site.     

Monitoring, prediction, and early warning using ground-based radar interferometry

In order to define adequate prevention measures and to manage landslide emergencies, real-time monitoring is required. This paper presents two different applications of the remote sensing technique: the ground-based synthetic aperture radar interferometry, here proposed as a monitoring and early warning support for slope instability. Data acquisitions carried out through a ground-based synthetic aperture radar interferometer, operating in K_u band, installed in front of the observed slopes, are discussed. Two case studies, based on the use of the same apparatus (formerly developed by the Joint Research Center of the European Commission and by Ellegi-LiSALab srl), are reported: the first one concerns the monitoring of a large landslide, named Ruinon (Valfurva, Italy). The second one deals with the monitoring of the NW unstable slope in the Stromboli island aimed to implementing an early warning system. Acquired interferometric data are processed to provide displacements and velocity maps of the monitored area. The monitoring services ongoing on the Ruinon landslide and on Stromboli demonstrate the capability of this technique to operate in different operative settings (i.e., different phenomena and geological framework) and for different aims (monitoring for prevention, early warning, and emergency assessment). This methodology has also been proved by national and regional authorities of civil protection in order to provide a real-time monitoring for emergency management.     

Preliminary paleolimnological study of rocha lagoon, SE Uruguay

Physical, chemical and biological data from a sedimentary profile of Rocha lagoon (Uruguay) are presented. Analyses of silica remains showed that opal phytoliths, diatoms, sponge spicules and chrysophyte cysts were the most important contributors to biogenic silica. Organic matter, total nitrogen and total phosphorus were used to infer past trophic development. Physical analysis of sediments allowed us to identify five lithological units related to sea level variation and climatic events.