Semi-real time systems for subsidence monitoring in areas affected by underground mining:the example of the Nuraxi-Figus coal district(Sardinia,Italy)

Underground mining can produce subsidence,which can be coincident with mining activities or delayed in response to the time-dependent deformation of the rocks.Therefore,in these cases,it is essential to effectively monitor the soil deformations at different times during and after mining activity.In the present work,an integrated approach based on geotechnical numeri-cal modeling and Advanced Differential Interferometric Synthetic Aperture Radar(A-DInSAR)method has been applied to detect,study and monitor the subsidence related to mining activity in the Nuraxi Figus coal district(Sardinia,Italy).Two datasets of high-resolution COSMO-Skymed images were acquired,respectively in two covering periods:from 2011 and 2014,and from 2013 to 2020.TheAA-DInSAR results show that the predominant displacement rates are located in correspond-ence with the panels.The cumulated satellite-based LoS displacements vary in the first period between-130 and+28 mm and-293 and+28.4 mm,while,during the second period between-6.9 and+1.6 mm and-8.72 and+4.33 mm in ascend-ing and descending geometries,respectively.The geotechnical numerical model allowed to obtain a value for the maximum expected.By using the vertical and horizontal components it was possible to reconstruct the kinematics of the deformation considering three phases:pre-mining,syn-mining,and post-mining activity.The temporal evolution of displacements started during the mining extraction in 2011,achieved the major values in correspondence of post-mining operations,during the period from 2013 to 2014 and continued slowly until 2020.The near real-time monitoring system applied in this study proved to be very useful for detecting subsidence during the mining activity and the post-mining period.

Measurement of the integrated luminosity of the Phase 2 data of the Belle Ⅱ experiment

From April to July 2018,a data sample at the peak energy of the T(4 S) resonance was collected with the Belle Ⅱ detector at the SuperKEKB electron-positron collider.This is the first data sample of the Belle Ⅱ experiment.Using Bhabha and digamma events,we measure the integrated luminosity of the data sample to be(496.3±0.3±3.0) pb-1,where the first uncertainty is statistical and the second is systematic.This work provides a basis for future luminosity measurements at Belle Ⅱ.

Prediction of the seismic behavior of an underground railway station and a tunnel in Napoli(Italy)

The assessment of the seismic safety of underground structures,either tunnels or large station boxes,should not be overlooked especially in densely populated areas,even with low to moderate seismicity.For underground structures,an important issue is the estimation of the seismic actions acting on the structure;only few experimental evidences are available for multi-level propped walls.For tunnels,it is generally assumed that their seismic behavior in soft ground is governed by the surrounding soil,while the inertial load contribution of the underground structure itself is negligible.In both cases,recent numerical studies proved that advanced dynamic analyses can provide satisfactory interpretation of non-linear soil-structure interaction during earthquakes.In this paper,a real case study,represented by a large open multi-propped excavation and a circular segmented tunnel in a densely urbanized area of the city center in Napoli,has been used to investigate some of the mentioned aspects.Accurate geotechnical characterization and choice of the reference input motions lead to a first estimate of the free-field ground motion,which was subsequently used for pseudo-static decoupled analyses.For the complexity of both excavation geometry and staged construction,a full dynamic analysis was considered neither affordable nor reliable for the multi-propped station box;thus two conventional pseudo-static analyses,applying either a displacement-based or a force-based approach,were carried out.In the case of the tunnel,the seismic increments of internal forces in the lining could be calculated through both a simplified pseudostatic analysis and a full dynamic analysis,showing a satisfying agreement.Overall,the results of the study demonstrated that the seismic increments of internal forces in the diaphragm walls of the station and in the segmented lining of the tunnel were quite significant.The case study encourages improving the reliability of simplified methods based on the more advanced dynamic approaches.