Patent Application
20210023605
The present invention relates to the sector of interlaced metal nets. Nets of this type comprise for example double-twist hexagonal-mesh nets in which adjacent metal wires are interlaced with one another. Nets of this type are used for various civil protection works, for example as protection nets against rock falls, for constructing works in reinforced soil, for containing stone walls, riverbanks, roadbeds and trackbeds, and other works of this type.
Metal nets, in particular of the double-twist type, have long been known and are used for innumerable civil protection and containment works. They may for example be used for containing escarpments, for producing mechanically stabilised earth, for producing or reinforcing embankments. The nets may also be used for the same purposes in the form of gabions or mattress structures.
One of the basic requirements on nets of this type is to resist static forces or dynamic impacts of a predetermined magnitude. When the metal net is used as a net for protection for example from rock falls, and a significant impact event takes place, the metal net deforms and has to be replaced. However, if the forces or impacts are small in magnitude or if the deformation of the net is not permanent in nature, it is not usually possible to check visually to what extent and how frequently the metal net has been strained. Meanwhile, in works where the metal net is embedded in the ground, for example in the production of mechanically stabilised earth or green outer walls, it is not even possible to check potential permanent deformation of the net except through topographical inspection of the external wall.
In all these cases, the lack of information on the deformations undergone by the metal net in operation may bring about a risk of unexpected failure thereof, with sometimes serious consequences, for the avoidance of which it is necessary to schedule periodical inspections and planned repairs or replacements of the metal net. The frequency of the controls and repairs is a significant cost in the management of civil works.
In monitoring embankments and the banks of waterways, particular importance is placed on the possibility of keeping the saturation level of the embankments under control during flooding events and checking the presence of discontinuities created for example by burrowing animals. For this purpose, techniques are known which provide extension of geoelectric material, parallel to the waterway and completely separate from the materials used for protecting the embankments or banks.
The present invention aims to resolve the problems of the prior art and to provide a simple and effective system for monitoring the state of civil works which use interlaced metal nets. Another object is to provide a metal net the state of which can be monitored directly, preferably continuously, in normal use. Another object is to produce a metal net in which the monitoring of the strain state thereof is effective, relatively cheap, and simple to implement.
To achieve the aforementioned objects, the invention relates to a metal net as defined in the following claims. In particular, the invention provides a metal net with elongate sensor elements fixed integrally to the net.
In particular, the elongate sensor elements can detect variations in one or more parameters, for example temperature and/or deformation. Alternatively or in addition, they can detect the presence of vibrations and/or the humidity level and/or variations in pressure, electrical field, magnetic field etc.
The elongate sensor elements are integral with the net. More specifically, the elements which form the net, and in particular the metal wires, and the elongate sensor elements, which are for detecting the deformations or which are part of the geoelectric detection system, are integral with one another, in the sense that the sensor elements are inserted into the net during the production thereof. Even more specifically, the elongate sensor elements are incorporated into the meshes of the metal net. For example, the sensor elements are inserted selectively into the nodes of the meshes in the longitudinal direction of the net and/or in the transverse direction of the net. The elongate sensors may be added to the wires with which the metal mesh is produced, so as to construct three-wire nodes, or may be substituted for the wires to produce two-wire nodes at the interlacings with the adjacent metal wires. Depending on the type of strain to which the elongate sensor elements are responding, they may be incorporated into the meshes of the metal net along a substantially rectilinear path or in a wavier path with loops.
The fact that the sensor is incorporated into the metal meshes of the net causes the net itself to be the means by which the surrounding environment comes into contact with the sensors; the metal net, which is often completely embedded in a structure (reinforced earth, an embankment etc.), undergoes all the deformations and vibrations to which the structure in which it is embedded is subjected. It can thus transmit this information to the sensors with optimum effectiveness and sensitivity.
The net comprising the sensors can be used to produce an alarm system, which sends a signal when, after some event, a predetermined threshold for a parameter is exceeded. For example, it may send an alarm signal when a deviation in temperature or a deformation above a threshold considered acceptable is detected, or a vibration of an amplitude or frequency considered dangerous is detected.
The net comprising fixed, elongate sensor elements fixed integrally to the net itself may also be used to implement systems for monitoring a building work, which keep specified parameters, describing the state of health and state of use of the work, under continuous monitoring. The sampling frequency may be very high.
Naturally, the metal net comprising the elongate sensor elements maintains all of the properties of the net free of elements of this type, including resistance. It thus maintains all of the properties of the prior art net which make it a suitable reinforcement element in a wide variety of building works, whilst also bringing a new, important function of monitoring the conditions of the net itself, without the need to implement another separate element. Further, since the sensors are incorporated into the net itself, the monitoring is more sensitive than that which would be obtained using sensors separate from the net. In this regard, the second aspect, according to which the sensor elements are inserted into the nodes of the metal net, is particularly beneficial; this guarantees that the sensor elements cannot slide relative to the net. The elongate sensors may comprise different materials in relation to the type of measurement or detection which it is intended to carry out. In the case of evaluating deformations for example, one or more sensor wires may be used, made of a material having a low coefficient of variation of resistivity, in such a way that the variation in resistance when the temperature varies is very small. These sensor wires are integrated into the metal net so as to have a substantially rectilinear path, and preferably have a high extensometer factor (gauge factor) capable of showing a relatively high variation in resistance when the deformation which they undergo varies. A preferred material for producing elongate sensors of this type is constantan or a material having similar features, for example the copper-manganese nickel alloy known by the trade name “manganin”, the copper-zinc-nickel alloy known as “nickel brass”, and the alloy of nickel and chromium known as “nichrome”. To avoid short circuits with the metal wires in the net, or with the surrounding environment, the elongate sensors can be covered with a layer or sheath of insulating material.
For some applications, it is also possible to use elongate sensors of the composite fibre and/or optical fibre type, for example Bragg reticule sensors. Some sensors of this type make it possible to acquire information regarding localised deformation, including at predetermined intervals along the longitudinal extension of the sensor, in accordance with the construction technology of the optical fibre or composite fibre sensor.
The invention thus provides the possibility of interlacing these elongate sensor elements in a, for example double-twist, metal net during the production process of the metal net itself.
In a particularly beneficial aspect, the sensor elements are optical fibres, and preferably optical fibre sensors based on scattering phenomena. In particular, the applicant has identified an ideal sensor in optical fibre sensors which use the Brillouin effect. Brillouin scattering, as is known, brings about variation in the light frequency, caused for example by the presence of local deformation or of a variation in temperature. By analysing the light detected at the output of the fibre, it is thus possible to reconstruct the presence of local deformations or variations in temperature.
These sensors thus make it possible to detect, along a particular stretch of a single optical fibre, both variations in temperature and deformations, whilst maintaining an optimal spatial resolution, for example on the order of 1 metre over a total length of up to 100 km, if OTDR (optical time domain reflectometry) is used, or 1 cm over a total length of up to 10 km if BOCDA (Brillouin optical correlation domain analysis) is used. They are also economical, and can even be used over very long strengths in the order of kilometres.
An example of a fibre which can be used in a Brillouin effect sensor is a “telecom grade” optical fibre, in other words one of the type used for telecommunications. The fibre has a standard diameter of 125 microns. It is produced using pure siliceous material in the amorphous state, in other words in pure glass. The glass is enclosed in a protective coating.
However, the use of optical fibre sensors based on different scattering phenomena (for example Raman or Rayleigh), or other interferometric optical fibre sensors, is not excluded. It is further possible to provide distinct temperature and deformation sensors, even though detection of variations in temperature and of deformations by way of a single sensor is preferred for economic reasons and reasons of simplicity of implementation. Vibration, pressure, electric and/or magnetic field sensors etc. may further be provided.
A metal net comprising elongate sensor elements fixed integrally to the net is of use in various applications. It can be buried to produce reinforced soil, or more generally to produce support works. It can be inserted into the interior of a roadbed or a road superstructure, bound (for example bituminous) or otherwise. In all these cases, it is particularly beneficial to be able to be aware of any local deformations which may be completely invisible from the outside but may be equally dangerous for the endurance of the structure. The present invention therefore also relates to a reinforced soil or a roadbed or a road superstructure comprising a net comprising elongate sensor elements fixed integrally to the net, having some or all of the additional features described above and hereinafter.
The net may also be used as a rock protection barrier or bonded rock protection net. In this case, a local deformation might be visible to the naked eye, but inspection might not be easy as a result of difficulty of access to the site. In any case, between one inspection and the next, events could take place which deform or even break the structure and of which it is advisable to be informed in a timely manner. The present invention therefore also relates to a rock protection barrier comprising a net comprising elongate sensor elements fixed integrally to the net, having some or all of the additional features described above and hereinafter.
The present invention further relates to a road or railway embankment comprising a net comprising elongate sensor elements fixed integrally to the net, having some or all of the additional features described above and hereinafter. The net may also be positioned either at the base or in intermediate positions in the embankment, including in the case of embankments on poles.
The invention comprises a net for producing escarpments and capping in a landfill, comprising elongate sensor elements fixed integrally to the net, having some or all of the additional features described above and hereinafter. In a landfill too, it is actually extremely useful to be able to have immediate feedback both in the case of structural deformations of the escarpments of the container or capping and in the case of variations in temperature, which could be due to a loss.
The invention further comprises a river bank, canal, lake or more generally water basin, or else a dam, comprising a net comprising elongate sensor elements fixed integrally to the net, having some or all of the additional features described above or hereinafter. Indeed, in the case of banks and dams it is obviously very important to have immediate feedback in the case of even a small deformation of the structure, since it could cause weakening and subsequently a break, with potentially catastrophic effects, both as a result of the flooding which inevitably follows and as a result of the difficulty in repairing a bank which has previously given way. The timeliness of the intervention is fundamental to avoiding the breaking of a bank, and thus constant, precise and punctual monitoring is of extremely great importance. In the preferred case, where the net comprises at least one elongate temperature and deformation sensor element, it is also possible to monitor the temperature, which may indicate the presence of a loss. Even a small loss, which has not yet necessarily caused a deformation in the structure of the bank itself, may nevertheless be problematic, and it is thus preferable for it to be reported. In the production of banks, the possibility of monitoring even a very long stretch with contained costs and high precision is of particular importance. Preferably, the sensor is an optical fibre sensor, and even more preferably an optical fibre sensor which makes use of the Brillouin effect.
The invention further comprises a cover structure for pipes, comprising a net comprising elongate sensor elements fixed integrally to the net, having some or all of the features described above and hereinafter. The pipes may be for gas or petroleum, or else for water, for example in the case of aqueducts or penstocks of hydroelectric plants.
In all the applications described above, and in others, the net may comprise at least one elongate temperature and deformation sensor element. For reasons of cost and of precision and reliability, the elongate sensors are preferably optical fibres, even more preferably optical fibre sensors which make use of the Brillouin effect.
Further features and advantages will be apparent from the following detailed description of preferred embodiments, referring to the accompanying drawings, given by way of non-limiting example, in which:
Referring now to
The net 1 may comprise at least one elongate sensor 5 inserted longitudinally through selected twisted portions 7′. The elongate sensor 5 may form two trapezoid meshes 6 flanked by two successive twisted portions 7′ in a longitudinal direction defined by the direction along which the elongate sensor 5 extends. The elongate sensor is preferably a wire of an alloy for extensometers, for example constantan—an alloy of copper and nickel—or any other known metal alloy having good sensitivity to deformation (gauge factor) and a relatively low sensitivity to the amplitude of the deformation and to temperature. For this purpose, other known alloys having similar features may be used, for example the copper-manganese-nickel alloy known by the trade name “manganin”, the copper-zinc-nickel alloy known as “nickel brass”, and the alloy of nickel and chromium known as “nichrome”. The elongate sensor 5 may be covered with a layer or sheath of insulating material. In some applications, it is also possible to use an optical fibre or composite fibre elongate sensor.
At the heads of the elongate sensor 5, with variable spacing, a known data acquisition system is provided comprising an electronic device which detects, in the case of the use for example of a constantan wire, the electrical potential at the heads of the elongate sensor 5, and is capable of reporting and/or storing a variation in said electrical potential.
In the case of the use of optical fibres or composite fibres, an equivalent data acquisition system in the use of these fibres is provided in the installation step on a building site, in a spacing which is variable as a function of the subdivisions in individual homogeneous stretches to be monitored. The system normally provides at least one light source and a photodetector.
Referring now to
It should be noted that the net portions depicted in
A net 1 as described above with reference to
Referring to
In
A net as described above with reference to
Referring now to
In a known manner, the bank 30 comprises an embankment having two flanks 32 and 34: an inner flank 32, facing towards the water, and an outer flank 34, facing the opposite side. The net 1 may be used to reinforce only one of the flanks 32, 34 or both. For this purpose, it is placed on the previously compacted ground. Subsequently, it may also be covered, for example with soil, as in the example case of
The net 1 is placed on the ground with the elongate sensor elements 5 preferably arranged parallel to the direction of the river or parallel to the shore, in the case of a water basin, or in other words parallel to a primary direction of the bank itself. In this way, a single sensor element monitors long stretches of the bank 30. The bank further comprises a communication backbone 36, preferably positioned on the summit 38 of the bank.
The bank 30 may further comprise a rain sensor 40, which is particularly beneficial in the case where at least one of the two elongate sensors 5 detects humidity or temperature. Indeed, it is clear that in the case of rain an increase in humidity and probably also a variation in temperature, which however are not attributable to a loss of the bank, will be detected. The possibility of monitoring the presence of rainwater thus makes it possible to interpret correctly the values detected by the sensors 5.
The bank 30 may also comprise a hydrometer 44, to monitor the height of the water. It may also comprise a surveillance video camera 42. The communication backbone 36 transmits the information received from all of the equipment, as well as the signals detected by detection control units 46, positioned a predetermined distance apart. The detection control units 46 may comprise a data acquisition system for acquiring the signal from the elongate sensor elements 5.
In use, the elongate sensors 5 monitor at least one parameter, for example deformation, temperature, humidity and vibration. It should be noted in particular that the fact that the sensors 5 are fixed at the nodes 7′ of the net 1 causes the net itself to be the means by which the surrounding environment comes into contact with the sensors 5. The metal net 1, which in the illustrated example is completely embedded in the bank, undergoes all the deformations and vibrations to which the structure in which it is embedded is subjected, and therefore transmits them highly efficiently to the sensors.
The bank 30 is thus an intrinsically monitored bank. Naturally, the type of monitoring may be modified depending on the requirements of the particular stretch and on multiple variables, such as the atmospheric conditions, the detected height of the water etc. For example, it is possible to vary the sampling frequency, but also to set different alarm thresholds for each monitored parameter.
It should be emphasised that the net 1 maintains the functions of a conventional metal net for erosion control and for reducing the risks associated with the presence of burrowing animals. Further, the net 1, being provided with elongate sensors 5, also performs a further function of hydraulic and geotechnical monitoring.
For producing the bank 30 of
Referring now to
A first net 60 comprising elongate sensor elements is positioned at the base 56 of the road embankment 50, 54. A second net 62 comprising elongate sensor elements is positioned at the base of the foundation 58. A third net 63 comprising elongate sensor elements is positioned in the interior of the foundation 58, which may be bound or unbound. A fourth net 64 comprising elongate sensor elements is positioned in the interior of the road pavement 59, which may optionally comprise bituminous macadam. In the examples illustrated, both of the road embankments 50 and 54 comprise four nets 60, 62, 63, 64, comprising elongate sensors, even though it is naturally possible to use one net comprising elongate sensors in only one of the described positions, using nets free of elongate sensors in the other positions or alternative reinforcement structures.
Naturally, without prejudice to the principle of the invention, the embodiments and the implementation details may vary considerably from what is described and illustrated, without departing from the scope of the present invention as a result.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102018000004022 | Mar 2018 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2019/052534 | 3/28/2019 | WO | 00 |
