Use of the event tree to assess the risk reduction obtained from rockfall protection devices

Abstract. The paper presents and discusses a procedure for the evaluation of the collective risk that can affect a road subjected to rockfalls, with and without protection measures, by means of the event tree analysis. This tool is useful to show designers whether the rockfall protection structures are located in the correct positions, whether they are the correct technological choice and what level of reduction of risk can be obtained. Different design options can therefore be compared on the same bases

Technical Note: Design of rockfall net fences and the new ETAG 027 European guideline

Abstract. The need for protection against rockfall has led to the development of different types of technological solutions that are able to both prevent blocks from detaching from rock walls and to control, intercept or deviate the blocks during movement. Of the many devices that are able to intercept and stop a block, one of the most frequently used is net fence. Many different types of full-scale tests have been carried out, with different test site geometries and procedures to study their behaviour and to certify these devices. This has led to a series of data and information that are not easy to compare. The recent endorsement, by the European Organization for Technical Approvals (EOTA), of a European Technical Approval Guideline (ETAG), which defines how to test and assess the performance of a net fence, is therefore a great innovation that will change both the market and the design procedures of these devices. The most important innovations introduced by this new guideline are here presented and discussed and a net fence design procedure for protection against rockfall is provided

design of reinforced ground embankments used for rockfall protection

Abstract. The prediction of the effects of rockfall on passive protection structures, such as reinforced ground embankments, is a very complex task and, for this reason, both full-scale tests and numerical dynamic modelling are essential. A systematic set of numerical FEM models, developed in the dynamic field, has been implemented in this work to evaluate the conditions of an embankment that has been subjected to the impact of rock blocks of various sizes at different speeds. These analyses have permitted design charts to be obtained. Furthermore, a simplified analytical approach, based on an equilibrium analysis, has been proposed and its results are compared with numerical data in order to assess its feasibility. A good correspondence between the results has been obtained

Comparison of the Results of Analytical and Numerical Models of Pre-Reinforcement in Shallow Tunnels

AbstractThe steel pipe umbrella is a widely used technology when tunnelling in weak soils in order to create pre-support ahead of the tunnel face. The design of steel pipes is frequently done through simplified analytical approaches which are easy to apply but require proper assessment of the loads acting on the pipe. To provide information on this key design aspect, the results of the 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 is presented and discussed. The comparison refers to a shallow tunnel with an overburden of three times its diameter for two different types of weak rock masses. The obtained results provide suggestions about the load that has to be applied in the analytical model for the design phase

Long-term durability assessment of PVC-P waterproofing geomembranes through laboratory tests

Waterproofing heavily influences the operation and maintenance costs of underground structures. Currently, the most commonly used technology for tunnel waterproofing is plasticized polyvinyl chloride (PVC-P) geomembranes. However, not much is known about the long-term durability of these geomembranes, especially in relation to the long expected lifespan of new tunnels (i.e. 100–150 years). Therefore, in this paper, the durability of two commercially available PVC-P geomembranes is studied with the help of a specifically designed accelerated ageing device in addition to mechanical and absorption tests. The degradation resulting from plasticizer loss is extrapolated to the long term, and a threshold value for the end-of-life of the PVC-P geomembrane is estimated from the mechanical tests

A More Comprehensive Way to Analyze Foam Stability for EPB Tunnelling—Introduction of a Mathematical Characterization

In the tunnelling industry, a large share of the market is occupied by EPB (Earth Pressure Balance) machines. To operate this kind of machine, a radical change in the rheological behaviour of the excavated soil must be performed, and this is achieved by adding water, foam, and, eventually, polymers. The stability of the foam is assessed through a half-life test. The main limitation of this test is that only one value is used in the characterization of the foam degradation process, which is insufficient to describe the whole evolution of the phenomenon. The results of more than 270 tests were modelled through a five-parameter mathematical formulation that suited the experimental data. The results show that the influence of concentration on the stability of the foam is not always present and that the flow rate used during production bears an influence on the characteristics of the foam

Evaluation of the geo-mechanical properties property recovery in time of conditioned soil for EPB-TBM tunneling

The soil conditioning is a process of fundamental importance during the excavation of tunnels with Earth Pressure Balance full face machine. The soil conditioning is achieved through the addition of foam at the excavation face and in the bulk chamber that modifies the natural soil properties from solid-like to fluid-like with a pulpy behavior. Clearly, a material with a pulpy or fluid-like consistency is not suitable for the construction of embankments of landfill or for other civil purposes. It is therefore important to have a procedure able to identify how long it is necessary before the conditioned soil recovers its geo-mechanical properties, since this knowledge is needed at the design stages from a logistic point of view. The paper proposes and discusses a procedure to find out whether and when the conditioned soil gets back to its original properties. The procedure foresees direct shear tests, vane tests, Proctor tests, and rotational mixer tests at different time schedules from the production of the conditioned soil in the laboratory. The conditioned soil samples have been cured in a controlled environment up to 60 days from the conditioning. Thanks to these tests, it is possible to assess if and when the soil recovers its natural behavior or if a permanent alteration is induced. The proposed procedure has been applied to a standard alluvial soil showing that most of the original properties of the soil are recovered already after seven days from the conditioning. The carried-out tests have shown that the procedure is feasible and easy to apply

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