Laboratory test for EPB tunnelling assessment:results of test campaign on two different granular soils

Earth Pressure Balanced shields are currently the most utilized tunnelling machines throughout around the world. The possibility of using conditioning agents that change the mechanical and hydraulic behaviour of a soil, changing it into a plastic paste and thus permitting soil pressure applications at the tunnel face, is the key point to explain the increasing utilization of this technology. Despite its great importance, not much laboratory researches can be registered on soil conditioning, particularly for cohesionless soils. The conditioning criterion is usually defined on the basis of a trial-and-error procedure developed directly at the job sites. A test that is able to simulate the extraction of soil from the bulk chamber with the screw conveyor inclined upwards, as in real machines, can offer a quantitative indication of the conditioned soil behavior for EPB use. The characteristics of the device and the results obtained on many different types of soil are discussed in order to point out the great importance and quality of results that can be achieved using the proposed test devic

The behaviour of a two-component backfilling grout used in a Tunnel-Boring Machine

The instantaneous filling of the annulus that is created behind the segment lining at the end of the tail during the TBM advance is an operation of paramount importance. Its main goal is to minimize the surface settlements due to any over-excavation generated by the passage of the TBM. To correctly achieve the goals, a simultaneous backfilling system and the injected material should satisfy the technical, operational and performance characteristics. A two-component system injection for the back-filling is progressively substituting the use of traditional mortars. In this paper different systems of back-filling grout and in particular the two-component system are analyzed and the results of laboratory tests are presented and discusse

QuaRRi: a new methodology for rock-fall risk analysis and management in quarry exploitation

Rockfall is one of the most critical geological events that can affect quarrying activities. Nevertheless, few tools are currently available to help designers and managers correctly define the risk conditions and quantify the advantages, in terms of workers' safety and quarry management, that can be obtained using suitable prevention devices. For this reason it is necessary to evaluate the various parameters that are involved, and to define the most important and which have the greatest influence on rock-fall phenomena, taking into account the Prevention through Design approach. A risk evaluation systemwhich is able to support decision makers in the critical rockfall risk assessment phase, and offer decision makers the updated information that is necessary for a continuous and dynamic operation design during exploitation activities is here presented and discusse

How tunnel boundary irregularities can influence the stresses in a shotcrete lining

The shape of a tunnel boundary excavated by drill & blast in fractured rock masses is influenced by geological conditions and blasting operations. The overbreaks, apart from influencing the construction times and costs, also have an important influence on the stresses acting in the shotcrete lining, particularly when it is used as the final lining. These effects have been analyzed, on the basis of a parametric numerical analysis, and the results have shown that if the boundary shape is more irregular there are traction stresses. These tractions are not evident if a regular shape of the boundary is considered in the numerical mode

High Risk of Secondary Infections Following Thrombotic Complications in Patients With COVID-19

Background. This study’s primary aim was to evaluate the impact of thrombotic complications on the development of secondary infections. The secondary aim was to compare the etiology of secondary infections in patients with and without thrombotic complications. Methods. This was a cohort study (NCT04318366) of coronavirus disease 2019 (COVID-19) patients hospitalized at IRCCS San Raffaele Hospital between February 25 and June 30, 2020. Incidence rates (IRs) were calculated by univariable Poisson regression as the number of cases per 1000 person-days of follow-up (PDFU) with 95% confidence intervals. The cumulative incidence functions of secondary infections according to thrombotic complications were compared with Gray’s method accounting for competing risk of death. A multivariable Fine-Gray model was applied to assess factors associated with risk of secondary infections. Results. Overall, 109/904 patients had 176 secondary infections (IR, 10.0; 95% CI, 8.8–11.5; per 1000-PDFU). The IRs of secondary infections among patients with or without thrombotic complications were 15.0 (95% CI, 10.7–21.0) and 9.3 (95% CI, 7.9–11.0) per 1000-PDFU, respectively (P = .017). At multivariable analysis, thrombotic complications were associated with the development of secondary infections (subdistribution hazard ratio, 1.788; 95% CI, 1.018–3.140; P = .043). The etiology of secondary infections was similar in patients with and without thrombotic complications. Conclusions. In patients with COVID-19, thrombotic complications were associated with a high risk of secondary infections

Lastnosti dvokomponentnega utrjevalnega materiala pri vrtanju predora s TBM

The instantaneous filling of the annulus that is created behind the segment lining at the end of the tail during the TBM advance is an operation of paramount importance. Its main goal is to minimize the surface settlements due to any over-excavation generated by the passage of the TBM. To correctly achieve the goals, a simultaneous back-filling system and the injected material should satisfy the technical, operational and performance characteristics. A two-component system injection for the back-filling is progressively substituting the use of traditional mortars. In this paper different systems of back-filling grout and in particular the two-component system are analyzed and the results of laboratory tests are presented and discussed.Eden od najpomembnejših postopkov pri uporabi mehanizirane metode izkopa predora je takojšnje polnjenje praznega prostora, ki se ustvari za segmentno oblogo na koncu stroja za vrtanje polnega profila (TBM). Njegov glavni cilj je zmanjšati usedanje površine nad predorom, ki ga povzroča rezanje hribine s TBM. Da bi natančno dosegli cilje, morata simultani sistem polnjenja z zadnje strani z vtiskanjem utrjevalnega materiala zadovoljiti tehnične, operacijske in izvedbene zahteve. Predstavljen dvokomponentni sistem vtiskanja utrjevalnega materiala v praksi postopoma zamenjuje uporabo tradicionalne malte. V pričujočem prispevku so analizirani različni sistemi takšnega načina vtiskanja malte, še posebej pa je predstavljen dvokomponentni sistem skupaj z rezultati in analizami laboratorijskih preizkusov

Analisi mediante modellazione numerica e modelli analitici di un presostegno con infilaggi in gallerie superficiali

Il lavoro presenta i risultati del confronto tra un modello numerico tridimensionale sviluppato mediante il codice di calcolo FLAC 3D ed un modello analitico che si basa sull'approccio della trave su appoggi cedevoli, in termini di sollecitazioni e spostamenti che si generano negli elementi resistenti (tubi) di un presostegno con infi laggi per una galleria superfi ciale con copertura pari a tre volte il diametro della stessa, per due diversi tipi di terreno. I risultati consentono di valutare quale carico agente nel modello analitico meglio permetta di riprodurre i risultati del modello numerico e quindi fornire indicazioni utilizzabili in sede di progettazione. Analysis of a pre-reinforcement umbrella-arch in shallow tunnels through numerical modelling and analytical approaches. This paper shows the results of a comparison between a three-dimensional numerical model developed with the code FLAC 3D and an analytical model based on the approach of a beam on yielding supports, in terms of stresses and displacements induced within the resistant elements (tubes) of a pre-reinforcement structure for a shallow tunnel, with a coverage equal to three times its diameter, for two different types of soil. The results permit to defi ne which is the load applied in the analytical model that reproduces the results of the numerical model and then provide suggestions for the design phas

Using the slump test to assess the behavior of conditioned soil for EPB tunnelling

In order to extend the application field of Earth Pressure Balance (EPB) tunnel machines to various soil conditions, the soil to be excavated has to be treated with additives in order to modify its mechanical properties, changing it into a plastic paste. Sometimes the grain size distribution is also changed with the use of fine-sized materials. The performance of the conditioned soil should be evaluated with tests that are able to describe its mass behavior, but very little research has been carried out in this field. Often the choice of the conditioning agent set and its control during the excavation is made on a trial-and-error basis during the excavation process. The slump cone test performed on conditioned material is a fast and lowcost way of checking this behavior both in the laboratory and on the job site. The results of a test program on different conditioned non-cohesive soils using the slump cone test are presented and discussed. The influence of the water content and the amount of conditioning foam has been studied, and the feasibility of this type of test for the control of EPB conditioned soil has been assesse