The Buoyancy of the Tunnel Segmental Lining in the Surrounding Filling Material and its Effects on the Concrete Stress State

Segmental lining is subject to significant upward buoyancy forces when a grouting material (slurry), initially fluid, is adopted to fill the gap between its external profile and the wall of a tunnel excavated with a TBM machine. The analysis of the effects of these forces is important in order to correctly dimension the segmental lining and avoid damage to the lining and subsequent costly maintenance and restoration actions. Given the complexity of the behavior of a segmental lining consisting of segmental rings and circular joints that alternate in the longitudinal direction of the tunnel, a specific numerical model has been implemented, adopting the Finite Element Method (FEM). This model is able to obtain the development of the vertical displacements of the segmental lining starting from the TBM tail, together with the bending moments and the shear forces induced inside it. The developed model is able to assess the risks of breaking and damaging the concrete and steel bolts that are used to connect the segmental rings at the circular joints; therefore, it represents a useful design tool for being able to correctly dimension the segmental lining also in relation to the risks produced by the appearance of considerable buoyancy forces around it, due to the presence of the initially fluid filling material. The proposed numerical model was applied to a real case (Ningbo metro tunnel) and allowed to obtain satisfactory results from the comparison of the calculated displacements with in situ measurements. Some sensitivity analyzes developed on the studied case have made it possible to detect which are the influencing parameters that have the greatest impact on the behavior of segmental lining in the presence of the studied buoyancy forces

The important role of stiffnesses values of circular joints on the stress state developed in the tunnel segmental lining

Under the application of the fluctuating Tunnel Boring Machine (TBM) jack thrust and the non-uniformly distributed total pressure of the slurry around the lining, the bending and the shear deformation occur on the segmental lining along the longitudinal direction, which cause a stress concentration and increase the damage risk of the segmental tunnel lining. The analysis of the circular joint stiffness is a critical step during the evaluation of the stress state of the segmental lining so as to decrease the associated risk of damage. In order to investigate the lining rings and the circular joint separately, an integrated numerical model which is composed of segment elements and joint elements was developed. Furthermore, stiffness equations for describing in the detail the circular joint behaviour of the tunnel segmental lining are derived. The new stiffness equation of the circular joint is also used to analyse the segment lining behaviour based on a well-known indoor test result by the scientific literature, and satisfactory results were obtained. A simplified estimation of the bending stiffness of the circular joint based on the Boltzmann equation is then suggested in order to obtain quickly its calculation. Finally, based on a specific numerical model, the calculated joint stiffnesses are adopted to analyse the vertical displacement of a real case (The Ningbo metro tunnel in China). Through a developed sensitivity analysis, some useful suggestions are proposed to reduce the damage risk of the segmental lining

Genetic variability in three Italian beef cattle breeds derived from pedigree information

The aim of the present work was to estimate genetic variability in Chianina (CH), Marchigiana (MC) and Romagnola (RO) breeds using pedigree information. Different approaches based on probability of identity-by-descent (effective population size through an increase in inbreeding Ne) or probability of gene origin (total number of founders f, effective number of founders fe, ancestors fa and founder genomes fg) were used. Reference populations were defined using female animals born between 1996 and 2000 where both parents are known. Generation intervals were 5.35, 4.93 and 5.15 years for CH, MC and RO, respectively. The total number of founders were 7092, 11947, 3928, for CH, MC and RO, respectively. Complete generation equivalent showed the relative high quality of pedigree information: 5.66 for CH, 4.54 for MC and 4.95 for RO. For CH, MC and RO, respectively, a fe value of 152.1, 70.9 and 89.8, a fa value of 73.6, 48.0 and 59.5 and a fg value of 39.5, 25.0 and 38.5, were calculated. When inbreeding was used effective population sizes were 138, 122 and 124 for CH, MC and RO, respectively. Parameters derived from the probabilities of gene origin were variable among the investigated breeds and the results for MC demonstrate the need to pay specific attention to breeding strategies

Rodoretto talc mine (To, Italy): studies for the optimizationof the cemented backfilling

The underground talc mine of Fontane (Prali, near Torino, North West of Italy) has been exploited for decades by conventional cut and fill method using loose fill and, in the last 30 years, using cemented backfill and exploiting the orebody downwards. With this exploitation approach, the orebody recovery and the safety of the mining operations have been greatly improved. In the new mine section, located in Rodoretto, a detailed numerical modelling has been carried out to simulate the various geometrical and mining conditions and the fill properties. In the meantime an experimental research carried out to check the possibility of using the waste rock for the fill mix have been carried out in order to establish a procedure able to reduce the filling cost

Theoretical and Experimental Results from Laboratory Tests by ILCM

The Intermediate Linear Cutting Machine (ILCM) is a machine designed to work on an intermediate scale between the full- and the small-scale. The reduced scale involves several advantages compared to full-scale tests, especially in terms of sample supplying and transportation. On the other hand, it has an impact on the testing conditions, resulting in a limitation of the cutting penetration and spacing during the test, as well as in a smaller disc cutter. This affects most of the results, which cannot be directly used for the on-site machine performance prediction. However, some experimental results provided in the literature show that the optimal spacing/penetration ratio is not significantly affected by the changes involved. On this basis, the results obtained from ILCM tests should provide reliable information about the optimal cutting conditions of a tunnel boring machine (TBM) in massive rock mass. The work performed included the development of some improvements of the testing rig, as well as a modified ILCM testing procedure, according to the one typically used in standard LCM tests. The results provide information about the attitude of the tested lithotypes to mechanical excavation by means of disc tools, including the optimal cutting conditions. Additional work was developed in terms of detailed characterization of the rock samples involved and assessment of the size distribution of the debris produced during the ILCM tests. Nevertheless, further tests are necessary, in order to assess the consistency of the experimental procedure employed and to investigate the scale effect

Dynamics of Elastic Excitable Media

The Burridge-Knopoff model of earthquake faults with viscous friction is equivalent to a van der Pol-FitzHugh-Nagumo model for excitable media with elastic coupling. The lubricated creep-slip friction law we use in the Burridge-Knopoff model describes the frictional sliding dynamics of a range of real materials. Low-dimensional structures including synchronized oscillations and propagating fronts are dominant, in agreement with the results of laboratory friction experiments. Here we explore the dynamics of fronts in elastic excitable media.Comment: Int. J. Bifurcation and Chaos, to appear (1999

Rodoretto talc mine (To, Italy): studies for the optimizationof the cemented backfilling

The underground talc mine of Fontane (Prali, near Torino, North West of Italy) has been exploited for decades by conventional cut and fill method using loose fill and, in the last 30 years, using cemented backfill and exploiting the orebody downwards. With this exploitation approach, the orebody recovery and the safety of the mining operations have been greatly improved. In the new mine section, located in Rodoretto, a detailed numerical modelling has been carried out to simulate the various geometrical and mining conditions and the fill properties. In the meantime an experimental research carried out to check the possibility of using the waste rock for the fill mix have been carried out in order to establish a procedure able to reduce the filling costs