Numerical Analysis of a Deep Excavation in Front of MarmorKirken, Copenhagen

In this paper, the main results of a numerical geotechnical analysis of the deep excavation carried out in front of MarmorKirken in Copenhagen are presented and compared with the observed performance. The excavation has a maximum depth of about 35 m; a full top-down construction technique was adopted in order to minimize the effects induced by the excavation works on the monument. Foundation soils are characterized by the presence, starting from a depth of about 13 m, of a limestone formation. The comparison between predicted and observed performance shows that a significant amount (about 50%) of the maximum settlements experienced by the church occurred during the construction stage of the retaining wall panels in front of the church. Numerical analyses got the order of magnitude of displacements, but underpredicted both panel construction and excavation induced settlements of the church, while a better agreement was found for horizontal displacements

Dynamic soil-structure interaction: A three-dimensional numerical approach and its application to the Lotung case study

This paper presents a three-dimensional non-linear finite element (FE) approach to analyse the dynamic soil-structure interaction (SSI) phenomena observed at the Lotung Large-Scale Seismic Test (LSST) site. The numerical study is carried out in the time domain by a commercial FE code, taking into account the non-linear behaviour of soil and the multi-directional nature of real seismic events. The soil response is simulated by an isotropic hardening elasto-plastic hysteretic model (HSsmall) implemented in the material model library of the code. This model allows to describe the non-linear cyclic response ranging from small to large strain amplitudes and to account for the variation of the initial stiffness with depth. In the paper, the FE numerical approach is first validated through a series of parametric analyses simulating simplified cases (i.e. linear visco-elastic structures founded on a homogeneous linear visco-elastic soil deposit) for which analytical solutions exist. Then, it is adopted to back-analyse the behaviour of the 1/4-scale nuclear power plant containment structure constructed at the Lotung LSST site which was shook by several earthquakes of different intensities and frequency contents. The FE results are thus compared to the recorded in-situ free-field and structural motions, highlighting the satisfactory performance of the numerical model in replicating the observed response. The overall outcome of this research proves that nowadays complex dynamic SSI phenomena can be tackled by direct approach, overpassing the strong simplifications of the well-established substructure approaches

Seismic ground response at Lotung: Hysteretic elasto-plastic-based 3D analyses

This paper presents a non-linear finite element study to back-interpret the free field seismic response recorded at the Lotung Large-Scale Seismic Test site. The study is carried out in the time domain by the Finite Element (FE) code PLAXIS 3D, considering the vertical wave propagation of both the horizontal components of motion. The non-linear soil behaviour is simulated through a constitutive model, the Hardening Soil model with Small-Strain Stiffness (HSsmall), capable of describing the cyclic response of the material at different strain levels. In the paper, the constitutive response of the HSsmall model is firstly investigated through numerical simulations of strain-controlled cyclic shear tests under single and multi-directional conditions at low strain levels. Then, it is adopted to back-analyse the recorded free field seismic response, comparing the FE numerical results to the in-situ down-hole and surface signals recorded during two earthquakes occurred on May 20th and July 17th 1986, characterized by different peak ground accelerations

3D numerical modelling of a compensation grouting field trial in alluvial soils

The underground bypass of the new high-speed and high-capacity railway line in Florence (IT) involves the construction of about 7 km of twin tunnels beneath the historic city centre. To minimise the impact of tunnelling works, mitigation measures using the compensation grouting technique were integrated into the design stage with the aim of limiting the induced settlements and the risk of damage to nearby structures. A field trial near the Campo di Marte railway station was carried out to assess the efficiency of the compensation measure and establish a successful grouting strategy. This paper presents a three-dimensional numerical model of the field trial, explicitly implementing both the grouted volumes and the injection sequence. The grouted area is represented by non-porous soil bulbs with enhanced stiffness properties and the expansion process is simulated through imposed volumetric strains. The injections from each valve of the sleeved pipes (tubes-à-manchettes) are activated in a stepwise procedure, mirroring the injection sequence. The effectiveness of the proposed strategy is validated against recorded displacements in the field trial, demonstrating that the application of non-isotropic volumetric strains (i.e., vertical strains larger than horizontal ones) is able to accurately reproduce the observed heave

Exploitation of drainage water heat: A novel solution experimented at the Brenner Base Tunnel

Deep tunnels in permeable fractured rock-masses and under high piezometric levels can drain notable volumes of warm water, which are collected under gravity in specific conduits towards the portals, where heat can be exploited. The utilization of this energy source is generally narrowed by the limited presence of end-users near the portals, while other promising heating and cooling needs can be found directly along the tunnel length. The work presents the design, construction and installation of a geothermal system prototype exploiting the drainage water heat directly inside the tunnel. The prototype was named Smart Flowing due to the peculiarity of its heat exchange process. The system was realized and installed inside the exploratory tunnel of the Brenner Base Tunnel, near the border between Italy and Austria. The Smart Flowing modules were built outside and later moved inside the tunnel, where they were placed and assembled concurrently to the advancement of the Tunnel Boring Machine. A design procedure was proposed and validated against a testing and monitoring campaign. The data from the experimental activity confirmed that the drainage water flow guarantees long-term stabilization of circulating water temperature and fast heat recovery afterwards, thus securing the considerable power and performance values of a water-water heat pump connected to the system. A sensitivity analysis allowed the reproduction of different working scenarios, in order to generalize the application of Smart Flowing beyond the specific installation context

A new in situ test for the assessment of the rock-burst alarm threshold during tunnelling

Rock-burst is one of the most serious risks associated with hard rock tunnelling and mining at high depths. Monitoring of acoustic emissions emitted by the rock-mass during excavation and their interpretation now permits the early assessment of failure events and makes the safe management of the construction works possible. A reliable set-up of the alarm threshold is thus fundamental for the correct implementation of the procedures planned to minimise rock-burst related risk. This paper focuses on a novel in situ test specifically developed to provide an experimental basis for a more accurate assessment of the alarm threshold during tunnelling, representative of the local geomechanical conditions. The test, thanks to the compression induced by two flat jacks at the tunnel side wall, produces an artificial failure process during which acoustic emissions are measured and correlated to the mechanical response of the rock-mass, without the typical limitations of scale that characterised the laboratory experiments. The new methodology, named the Mules method, was successfully tested during the excavation of some stretches of the Brenner Base Tunnel in the Brixner granite, affected by mild spalling episodes. The case-history is fully described in the paper to illustrate the practical application of the proposed approach

Performance of the CMS Cathode Strip Chambers with Cosmic Rays

The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device in the CMS endcaps. Their performance has been evaluated using data taken during a cosmic ray run in fall 2008. Measured noise levels are low, with the number of noisy channels well below 1%. Coordinate resolution was measured for all types of chambers, and fall in the range 47 microns to 243 microns. The efficiencies for local charged track triggers, for hit and for segments reconstruction were measured, and are above 99%. The timing resolution per layer is approximately 5 ns

Class A predictions of damage level in an historical fortress induced by twin tunnelling

Tunnelling below historical city centres requires the accurate analysis of the impact of construction works on cultural heritage monuments, which need to be preserved from any possible damage. In this paper, the undercrossing of an historical masonry structure in the city of Florence (Italy), the Fortezza da Basso, by two tunnels of the new high-speed railway underground line is analysed. The interaction problem is studied by a 3D class-A finite element numerical model. Advanced constitutive laws are adopted to describe the key features of the mechanical behaviour of both soil layers and masonry structures. The results of the analyses show that the excavation process is likely to induce a negligible to slight damage in the historical fortress when a typical surface volume loss of 0.5% is considered in greenfield conditions

Performance and Operation of the CMS Electromagnetic Calorimeter

The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons are described. These muons were recorded after the closure of the CMS detector in late 2008. The calorimeter is made of lead tungstate crystals and the overall status of the 75848 channels corresponding to the barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented

3D modelling of soil-rock mixtures considering the morphology and fracture characteristics of breakable blocks

Failure mechanisms of a soil-rock mixture (S-RM) can be efficiently investigated by the discrete element method (DEM). This paper proposes a stochastic approach for 3D DEM modelling of S-RM samples accounting for morphological features and internal fractures of blocks and their potential breakage. The research refers to the case-history of an artificial S-RM filling slope, mainly containing highly-weathered shale blocks, constructed at the ±500 kV electronic converter station in the Funing County, Yunnan Province, China. The 3D morphological features of the blocks and the characteristics of their internal fractures were obtained by CT technology and image processing. A stochastic method based on harmonic series was developed starting from the real blocks, allowing the generation of random block clusters with characteristics similar to the original ones. Another stochastic approach was implemented for the creation of the internal fractures, simulated as voids in the block clusters, following the characteristic of the real fractures. Finally, the procedure was applied for the definition of a 3D S-RM DEM model with 40% block proportion, whose meso-parameters were determined for simulating direct shear tests. These latters were also useful to explore the mechanical response of the sample at the mesoscale, including the formation and development of the localization band. The numerical results showed that the generated random S-RM DEM model well reproduced the experimental behaviour of S-RM samples with breakable blocks. Also, they highlighted the importance of modelling the block breakage and internal fractures; in fact, companion simulations with unbreakable blocks and breakable blocks without fractures were all characterised by increased shear strength with higher friction angle but reduced cohesion