EP4685335A1

EP4685335A1 - System and method of protection against detachments of portions of the roof of a tunnel

Info

Publication number: EP4685335A1
Application number: EP25191598.9A
Authority: EP
Inventors: Alessandro LACAVA
Original assignee: Alisea Srl; Iniziative Nazionali Autostradali - SINA SpA Soc
Current assignee: Alisea Srl; Iniziative Nazionali Autostradali - SINA SpA Soc
Priority date: 2024-07-25
Filing date: 2025-07-24
Publication date: 2026-01-28

Abstract

System for protecting against detachment of portions of the roof (20) of a tunnel, comprising a plurality of ropes (10) which extend longitudinally with respect to the tunnel, and are positioned transversely to it, so as to cover all potentially unstable portions of the roof (21) and intercept any detachments of concrete, said ropes (10) being anchored to the roof (20) by means of end and possibly intermediate restraints or anchors (30).

Description

The present invention relates to a system for protecting tunnel users from detachment of portions of the roof.
The techniques currently in use basically involve the prevention of the problem of detachment of portions of the roof through the (more or less extensive) demolition and subsequent (more or less invasive) reconstruction of entire portions of the tunnel where surveys show damage to the cladding (due to faulty construction or degradation developed over time) and where detachments can therefore potentially occur.
For example, depending on the extension of the damaged areas and the depth of potential detachments, the following techniques can be used:

1. For limited extensions and depths up to a maximum of 20 cm, as shown as an example in Fig. 1, where some dimensions in centimetres are also indicated: scaling of the potentially unstable portions of the roof and smoothing of the surface by hydro-milling or other fit-for-purpose systems; restoration of the thickness with a double layer of gunite 1 suitably reinforced with electro-welded nets 2, 3 connected with bars 4 and/or steel dowels 5 to the intact roof 6;
2. For larger extensions and/or depths up to a maximum of 40 cm (see Figure 2 as an example): scaling of the potentially unstable portions of the roof and smoothing of the surface by hydro-milling or other fit-for-purpose systems; restoration of the thickness with several layers of gunite 1 having a maximum thickness of 20 cm suitably reinforced with electro-welded net 2, connected with dowels to the intact roof 6, and electro-welded net 3 fixed by radial bolting with self-drilling bolts having an appropriate diameter and pitch, anchored in the rock mass 7 behind the cladding roof 6.

Although these intervention techniques solve the problem of detachments, they have the following disadvantages:

The intervention is applied evenly to all areas to which possible detachments are ascribed, as it is difficult to distinguish areas where the likelihood of the event occurring is greater than others;
The consequence referred to in the previous point is that interventions may affect large portions of the tunnel resulting in it being unfit for use for a longer period of time the greater the longitudinal extension of the intervention;
Interventions can also be very invasive, particularly when they involve the "hanging" of the cladding to the rock mass behind (self-drilling bolts), with possible modification of the equilibrium state that has been determined.

The object of the invention is thus to try to eliminate the aforementioned drawbacks.
In particular, an object of the invention is to provide a system for protecting against detachments of portions of an existing roof of a tunnel that limits any invasive demolition-reconstruction work only where actually necessary.
Another object of the invention is to provide a system that reduces the period during which tunnel is unfit for use to a minimum in order to carry out the planned interventions.
A further object of the invention is to provide a system that can be installed with quick and easy operations.
These objects are achieved by the system for protecting against detachments of portions of an existing roof of a tunnel according to the invention which has the features of the appended independent claim 1.
Advantageous embodiments of the invention are expressed in the dependent claims.
Substantially, the system for protecting against detachments of portions of the roof of a tunnel according to the invention comprises a plurality of ropes that extend longitudinally with respect to the tunnel, and are positioned transversely to it, so as to cover all potentially unstable portions of the roof and intercept any concrete detachments, said ropes being anchored to the roof by means of end and possibly intermediate restraints or anchors.
Further features of the invention will become clearer from the detailed description that follows, referring to a purely exemplary and therefore non-limiting embodiment thereof, illustrated in the accompanying drawings, wherein:

Figures 1 and 2 are schematic cross-sectional views of restoration work on a deteriorated tunnel roof using the prior art;
Figures 3 and 4 are schematic cross-sectional and longitudinal views, respectively, of a portion of a tunnel, to which a system for protecting against the detachment of portions of the roof according to the invention is applied;
Figures 5 to 8 show in more detail a possible embodiment of the anchors of the system to the tunnel vault, and in particular: Figure 5 shows the embodiment of a groove made by mechanical demolition, Figure 6 the embodiment of a new constraining beam, Figure 7 the connection of a longitudinal rope to the new beam, Figure 8 an enlargement of the detail of Figure 7 at the connection plate.

The system according to the invention comprises a plurality of ropes to be applied at the tunnel roof in order to intercept any detachments of portions of the concrete roof for the purposes of creating a safety guard for the traffic below.
With reference to Figures 3 and 4, the ropes, indicated by reference number 10, extend longitudinally with respect to the tunnel, and are positioned transversely to it, at preferably constant spacing, so as to cover the entire area of the roof or cladding 20 affected by potential detachments. In the figures, some potentially unstable portions of the roof, indicated by reference number 21, are shown in hatching.
The ropes 10 are suitably pre-tensioned and anchored to the roof 20 at a maximum longitudinal distance L equal to about 15÷20 m, by means of end and intermediate restraints or anchors, all indicated by reference number 30 in Figure 4.
The ropes 10 (and related anchors 30), are sized so as to bear the weight of the portion of concrete that may possibly detach, preventing it from falling onto the road surface 22, with such vertical displacements that the useful section of the tunnel is not reduced.
The longitudinal ropes 10 are connected to each other by a small-mesh net 11, or equivalent means, so as to intercept even the detachment of small portions of concrete.
With reference to Figures 5-8, a possible embodiment of anchors 30 of the ropes is described in more detail.
At the established end and intermediate points, where the anchors 30 are to be arranged, a groove 23 with an indicative size of 70x25 cm, shown in hatching in Figure 5, is initially made by mechanical demolition.
Then, a reinforced concrete arch or beam 24 connected vertically and laterally, by means of groutings 25 to the roof 20, and suitably anchored to the base 26 (Figure 6), is made.
Each of the ropes 10 is connected, at its ends, to the beams 24 by means of a fixed cable lug 12 and an adjustable cable lug 12' to allow for tensioning (Figure 7).
The cable lugs 12, 12' are fixed to a steel plate 31, which is constrained by means of dowels 32 to the beam 24, the relative reinforcement 33 of which is shown schematically in Figure 8; in this figure groutings 25 connecting the beam 24 to the existing roof 20 are also indicated.
As an alternative to constructing the reinforced concrete beam 24, after the groove 23 has been made, a rib, suitably anchored to the base to which the longitudinal ropes 10 can be connected, can be installed in it.
In case concrete with sufficient strength is present, a direct connection of the ropes 10 to the existing roof 20 of the tunnelcan be provided.
From the foregoing, it can therefore be stated that the system object of the present invention can be installed by means of simple and rapid operations and can consequently limit the period of the tunnel being unfit for use; in addition, the tension state of the rock mass behind the cladding is not affected.
In other words, the proposed protection allows to apply demolition-reconstruction interventions referred to in the introduction, not indiscriminately to all potentially unstable situations, but only to those situations in which the detachment will actually take place, allowing a more rational use of resources, ensuring greater eco-sustainability of the process (more invasive interventions only where actually necessary) and at the same time guaranteeing the safety of users.
The present invention is not limited to the particular embodiment previously described and illustrated in the accompanying drawings, but numerous modifications can be made to it in detail, within the reach of the person skilled in the art, without thereby departing from the scope of the invention itself, as defined in the appended claims.

Claims

System for protecting against detachment of portions of an existing roof (20) of a tunnel, comprising a plurality of ropes (10) which extend longitudinally with respect to the tunnel, and are positioned transversely to it, so as to cover all potentially unstable portions of the roof (21) and intercept any detachments of concrete, said ropes (10) being anchored to the roof (20) by means of end and possibly intermediate restraints or anchors (30).
System according to claim 1, characterised in that said longitudinal ropes (10) are connected to each other by a small-mesh net (11), so as to intercept even the detachment of small portions of concrete.
System according to any one of the preceding claims, characterised in that these anchors (30) are arranged at a maximum longitudinal distance L equal to about 15÷20 m.
System according to any one of the preceding claims, characterized in that said ropes (10) are pre-tensioned.
System according to any one of the preceding claims, characterized in that said anchors (30) are provided directly in the existing roof (20) of the tunnel, in the case of concrete with sufficient strength.
System according to any one of claims 1 to 4, characterised in that said anchors (30) are provided in reinforced concrete beams (24) made in grooves (23) made transversely to the tunnel.
System according to any one of claims 1 to 4, characterized in that said anchors (30) are provided in ribs installed in grooves (23) made transversely to the tunnel.
Method of protection against detachment of portions of an existing roof (20) of a tunnel, consisting in fixing to the roof (20), by means of end and possibly intermediate constraints or anchors (30), a plurality of ropes (10) extending longitudinally with respect to the tunnel, and positioned transversely to it, so as to cover all potentially unstable portions of the roof (21) and intercept any detachments of concrete.
Method according to claim 8, comprising the following steps:
- making, by mechanical demolition, a groove (23) at the established end and intermediate points, where said anchors (30) are to be arranged;

- making a reinforced concrete arch or beam (24) in said groove (23) by means of grouting;

- connect the ends of each rope (10) to adjacent beams (24) using respective cable lugs (12, 12').
Method according to claim 8 or 9, characterized by providing for the connection of said longitudinal ropes (10) by means of a small-mesh net (11), so as to intercept even the detachment of small portions of concrete.