WO2008084510A1

WO2008084510A1 - Anti-vibration system

Info

Publication number: WO2008084510A1
Application number: PCT/IT2008/000017
Authority: WO
Inventors: Vitantonio Roma
Original assignee: Roma E Assoicati S.R.L.
Priority date: 2007-01-11
Filing date: 2008-01-10
Publication date: 2008-07-17
Also published as: EP2104770A1; ITTO20070015A1

Abstract

Anti-vibration system for mitigating the vibrations transmitted through the ground by an emitter means to a receiver means comprising a plurality of modular elements made of plastic, metal or another suitable material, vertically buried underground and positioned between said emitter means and said receiver means and characterised in that each of said modular elements achieves an air interspace at its interior, made impermeable with lasting effect over time.

Description

Anti-vibration system

DESCRIPTON

The object of the present finding is an anti-vibration system for insulating a receiver from the vibrations emitted by a source and which are propagated in the ground.

As is known, the vibrations which travel in the ground are propagated both inside the medium in the form of compression waves and shear waves, and on the surface of the same in the form of compression waves, shear waves and above all in the form of Rayleigh waves.

The state of the prior art, in the field of insulation of external receivers, such as buildings, plants and the like, first of all proposes anti- vibration systems positioned near the source which emits the vibrating waves. Such is the case, for example, in the anti-vibrating mattresses placed in the railway superstructure that have the object of attenuating the vibrations emitted upon the passage of trains, also underground trains. These systems have the disadvantage of being exposed to outside environmental conditions, like rain. Hence, with use, they tend to become impregnated with water and increasingly less effective, since the presence of water worsens the damping capabilities of the mattress. Moreover, they tend to be potentially dangerous, since they can amplify the motion field at the resonance frequencies of the system itself. Another significant disadvantage of these systems is represented by the impossibility of installing them without having to interrupt the operations of the source. Vibration removal systems are also known, positioned between the emitting source and the receiver. These are based on the known principle according to which a vibrational wave upon meeting a barrier is partly reflected and partly transmitted beyond the barrier itself. There is total reflection and zero transmission when there is a maximum difference of rigidity between the barrier and the medium from which the vibrations arise. This signifies that an ideal barrier would be that composed of an open trench or by an extremely rigid medium. The open trench solution is not feasible for most applications, since it creates conditions of instability in the long term both for the walls of the excavation and for the ground adjacent to the trench. One object of the finding, object of the present invention, is to provide a solution to the technical problem of vibration insulation which is at the same time both effective and economically sustainable. The finding, object of the present invention, is therefore an anti-vibration system according to the characteristics specified in claim 1, whose installation process is specified in claim 12. More in particular, the system is based on the fact that it interposes between the vibration source and the external receivers, in a ground excavation, a barrier consisting of a panel of suitable shape in order create an air interspace which is impermeable to the fluids present in the ground, such as water, and remains impermeable over time.

These and other advantages will be evident from the detailed description of the invention, which will make specific reference to the tables 1/2 and 2/2 in which an absolutely non-limiting preferential embodiment is represented of the present finding. In particular:

• Fig. 1 schematises an application example of the anti- vibration system in the railway field;

• Fig. 2 is an axonometric view of a slat according to the invention;

• Fig. 3 is a section of the slat of Fig. 2;

• Fig. 4 is a panel, as a result of the assembly of several slats;

• Fig. 5 is a detail which illustrates a possible connection between two adjacent slats; • Fig. 6 is a cross section of the single slat;

• Fig. 7 illustrates an alternative embodiment of the liquid- resistant/waterproofing system of the panel of Fig. 4, with a detail (Fig. 7a) and overall (Fig. 7b) view;

• Finally, Fig. 8 schematises an embodiment of the anti- vibration system in case of rocky terrain.

The anti-vibration system according to the invention can be applied in order to actively insulate any type of source that interacts with the ground or in order to passively insulate the potential receivers reachable by the vibrations. With reference to the abovementioned figures and according a preferred embodiment example, a receiver building or plant to be protected from the vibrations which are propagated through the ground is indicated with 1, 2 is the source which generates vibrations, according to a non-limiting example two trains, 3 is a schematisation of the vibrations that are propagated on the ground surface, essentially composed of Rayleigh surface waves, 4 is the flat countryside, 5 generally represents the anti-vibration system according to the invention, 6 is the temporary excavation subsequently filled with the same excavated earth, making up part of the manufacturing process of the anti- vibration system. In addition, with 7 a slat is indicated which represents the modular element of the system, while 8 and 9 are respectively the upper and lower portions of the aforesaid slat made impermeable to liquids, 10 is the liquid-resistant/waterproofing foam (or equivalent device), 11 is the stiffening separator of the slat and 12 indicates a connection example between adjacent slats. Finally, an assembly of several slats to form a panel is indicated with 13 in Fig. 4. The finding consists of the installation, in the ground, of a barrier 5 with an air interspace made impermeable to possible liquids present in the ground, positioned vertically or horizontally according to the system of vibrations to be intercepted (undulatory, sussultatory, etc.) made by means of several panels 13 adjacent to each other. Each panel 13 is composed of elementary units called slats 7, which have a limited thickness and are formed by two flat, thin and parallel faces of any material, for example plastic, cement or metal, connected with each other through transverse stiffening separators 11 of suitable section and placed at an appropriate interaxis. Inside the interspace, a liquid-resistant/waterproofing foam 10 or equivalent device is inserted in the upper 8 and lower 9 portions of the single slat, for a limited height. The liquid- resistant/waterproofing foam has the functioning of blocking the infiltrations of water or another liquid inside the interspace, a drawback which would increase the equivalent mass density of the barrier and reduce its effectiveness.

Schematically, the installation process of the anti-vibration system comprises the following phases: excavation of a trench at an appropriate distance from the vibrating source and at an appropriate depth; insertion of a barrier constituted by the assembly of a plurality of panels; filling the trench with soil or another appropriate material.

According to a preferential embodiment, the panel has a width of 2.3 m - 2.4 m, a thickness of about 4 cm and an appropriately sized depth H; the panel is composed of several 20 cm - width slats, held together by taping carried out with 1 m pitch along the depth of the panel.

According to an alternative embodiment, the panel is made impermeable to the fluids due to a U-shaped plastic material closure system 14 placed at the two ends, upper and lower; such U-shaped closure system is integrally fixed to the panel by pasting or another suitable system. In addition, liquid resistance/waterproofing is provided at possible holes, made for binding the panel to a moving system, by means of pasting small plastic material cylinders inside the 4 holes.

Also concerning the installation process of the finding, as previously described, several variants are clearly possible which are comprised within the protective scope of the present patent. For example, it is possible to make the anti-vibration system by using normal or plastic concrete as trench filling, rather than excavated soil; the plastic cement is composed of a mixture of cement, bentonite and water, which is characterised by a specific weight equal to about 1200 kg/me. Such expedient is optional and can serve to avoid possible secondary consolidation creep of the soil used for the filling; in reality, such circumstance rarely occurs, only in fact in the presence of soils with particular volume expansion tendencies.

Moreover, the anti-vibration system can be made along the designed alignment, according to a "section" procedure and by using normal or plastic cement for the filling of the trenches: a trench is excavated which is 0.6m - 0.8m wide, 2.5m long and H depth, according to appropriate sizing, the panel is inserted and the trench refilled by casting the cement on both sides of the panel. Once the casting is executed, another section of anti- vibration system is made of 2.5 m length, not adjacent to the just-executed section, but leaving 2.5 m of ground free; one then proceeds in an alternating manner. Subsequently, following the setting of the plastic cement, one returns to complete the barrier in the sections of ground left free between the already made sections.

Regarding the movement of the panel, 4 metal guides can be used, vertically arranged on the sides of the panel, 2 guides for each side; the guides are connected by another horizontal guide. The system of 4 vertical guides plus horizontal guide serves to move the panel during the insertion inside the trench and to keep it in centred position inside the trench. The guides are immediately recovered after the filling of the trench with the plastic cement. The 4 guides are connected with the panel by means of 4 holes placed at the 4 corners of the panel. Finally, in the case of rocky terrain where an excavation is not easily made, it is advisable to perforate the rock 15 with drillings typically used for the installation of micropiles, with diameter less then 40cm, inside of which plastic or metal material tubes 16 are inserted, for example PVC tubes, made appropriately impermeable at the upper 17 and lower 18 ends by means of pasted and/or threaded covers.

The use of the anti- vibration system, object of the present invention, offers the following advantages: • The anti-vibration system with cell barriers can be carried out at any time during the useful life of the railway line, even during operation, without having to interrupt the transit of the trains;

• Such system acts as a low-pass filter, attenuating the vibrations above a certain filter frequency, without amplifying any frequency of the train source spectrum; there is therefore no risk of resonance phenomena and/or amplifications of particular frequencies;

• It can be localised both near the railway line (active system) and near the receiver (passive system) as a function of the constraints and conditions of the surrounding environment;

• The barriers ensure a lifetime equal to at least the useful lifetime of the works.

As practical embodiment example, the vibrational impact generated by a moving train is described below on a potential building situated near the railway line. Naturally, it is specified that there are numerous other conditions in which the system, object of the patent, can be successfully employed. For example, such conditions include vibrational impact due to trams, underground trains, vibrating machines of an industrial plant, and generally all those situations which cause vibrations that are propagated through the ground. In the current example, the vertical barrier is composed of a PVC insulating element of about 4 cm thickness, inserted in the ground through an appropriately supported excavation for a depth and a linear extension which depend on various factors: dynamic characteristics of the ground through which the surface vibrations are propagated (essentially Rayleigh waves); dynamic, geometric (length) and velocity characteristics of the train source; dynamic and geometric characteristics of the receiver (building); position of the receiver with respect to the source; maximum levels of vibrational disturbance permitted by law. For the characterisation of the soil, the transfer functions were calculated at the receiver on the basis of experimental tests, in order to carry out a more precise forecast of the vibrational impact of the moving trains on the receiver. For the characterisation of the train source, reference was made to a design spectrum based on experimental investigations conducted on several train lines. The forecast model of the vibrational impact is a complex transfer function, which resulted from the sum of different transfer functions, representative of the different aspects and/or phenomena of the model: a) Dynamic characterisation of the train source; b) Vibration propagation in the ground; c) Vibration propagation in the "ground/foundation" system; d) Vibration propagation between the floors of the building; e) Effects of the mitigation system.

The mathematical formula of the calculation model of the vibration level at the receivers is reported below: L (f,d) = L₀(f) + A₁ + A₂(f,d) + A₃ + A₄ + A₅(f) + A₆ + A₇ [dB] Where: f = frequency; d = distance;

L₀ : reference acceleration spectrum of the source; Ai: amplification created by wheel-rail interface alteration;

A₂ : transfer function of the ground;

A₃ : transfer function of the "ground-foundations" system;

A₄ : transfer function inside the building;

A₅ : amplification at the natural frequency of the building (for precautionary reasons assumed to be equal to 5 dB/floor at

16 Hz for cement buildings);

A₆ : correction which takes into account the different actual velocity of the train in the investigated section with respect to the maximum running speed; A₇ : beneficial effects of the mitigation system, object of the patent.

The criteria adopted for the legal verification are referred to the night period, since the reference limits are narrower with respect to those of the day period. For the dynamic characterisation of the train source, trains were considered in the day period with maximum set speed of 300

Km/h and in the night period LC. trains and freight trains having maximum set speeds respectively of 220 Km/h and 120 Km/h.

The reference acceleration spectrum of the vibrational source was determined on the basis of: • typology, frequency and velocity of the trains moving on the line

• analysis of the vibrational level experimental measurements. In order to estimate the attenuation of the vibrations during the propagation through the ground, the MASW seismic tests (Multichannel Analysis of Surface Waves) were undertaken at the site affected by the "critical" receiver. The MASW tests are specific geotechnical investigations of dynamic characterisation of the soils, which permit determining various aspects of the wave propagation in the soils:

• surface propagation velocity

• velocity profile of the vertical shear waves of the shear waves Vs

• attenuation of the surface vibrations, essentially composed of Rayleigh surface waves.

The MASW test active on site consists of:

• energising the ground in one point on the free surface;

• measuring the vibrations generated from the source (harmonic or impulsive) along a linear extension, generally of 12 or 24 sensors.

Once the vibrations are measured along the extension, the weighted acceleration was calculated and the corresponding vibrational level was calculated at the different distances from the source. Knowing the vibrational level at the different distances, the transfer functions were calculated of the ground in the various investigated sites.

The transfer functions regarding the propagation of the vibrations from the ground to the receiver and inside the receiver were determined through regression analyses conducted on the average differential spectra measured in the field between a fixed position and a movable position. In the case of propagation in the ground, the fixed position was found near the source and the movable position on the ground at various distances from the source. In the case of transmission of the vibrations from the ground to the receiver, the fixed position was situated near the receiver and the movable position at different positions inside the receiver. The frequency range considered is in the range of 1 - 80 Hz. Without a mitigation system, such as that which is the object of the present patent, the movement of the train generates a field of vibrations upon contact between the wheels of the train and the rails of the line that is propagated in the ground, both inside and through the surface, towards the receiver (building). The waves which are propagated inside the ground, unlike the Rayleigh waves which travel on the surface, are characterised by a lesser attenuation with distance and thus potentially harm the building. In order to evaluate the vibrational impact of the train on the receiver, reference is made to the abovementioned formula, where the term A₇, representative of the mitigation effects of the anti-vibration system, does not appear.

On the basis of the undertaken tests, it results that the analysed receiver, placed at about 30m from the railway line, requires mitigation operations.

The applied anti-vibration system is composed of cell barriers inserted in the ground, in a position comprised between the railway line (source) and the receivers. The fundamental aspects in the sizing of the anti-vibration system with cell barriers are reported below:

• its effectiveness in terms of mitigation is based on the impedance ratio (the impedance of a material is equal to the product between mass density and shear wave velocity in the material itself) between the cell barrier composing the anti- vibration system and the surrounding soil. The stronger the impedance contrast between cell barrier and soil, the more effective the mitigation operated by the system: the overall performance of the anti-vibration system therefore depends on the dynamic characteristics (shear wave velocity, mass density and damping) of the material forming the barrier- system and the dynamic characteristics of the soil;

• the height of the anti-vibration system affects the filter frequency of the system itself, above which the barrier- system attenuates the vibratory intensity. The attenuation size depends on the dynamic characteristics of the material composing the barrier-system. Finally, the deeper or higher the barrier, the greater the vibratory wavelength intercepted and thus the lower the filter frequency above which the vibrations are attenuated. In the current case, a height of 6-7 m permits intercepting and removing all of the wavelengths less than or equal to 6-7 m and thus intercept and remove all frequencies above about 20Hz. Of course, in addition to the filter frequency, above which the vibrations are attenuated, the effectiveness and mitigation power of the barrier-system has importance, operating frequency being equal. Hence, the overall effectiveness of the anti-vibration system in terms of attenuation is the combined effect of its height and its composing material;

• in the case of trenches, and hence also in the case of anti- vibration system with cell barriers, the thickness does not have a very significant affect on the attenuation effectiveness or power of the system itself;

• the length of the anti-vibration system is sized so as to project a shadow cone of protection on the receiver and depends on the wavelength of the vibratory motion and on the length of the train;

• the localisation of the anti-vibration system in the space comprised between the source and receiver has a fundamental role for the effectiveness of the mitigation system. If the anti-vibration system is close to the source, then this is an active insulation system; if the anti-vibration system is close to the receiver then this is a passive insulation system. The position of the anti- vibration system with respect to the source and receiver significantly affects the insulation power of the anti- vibration system and hence the sizing of the anti- vibration system height. Naturally, the preferable solution is that which provides the anti-vibration system near the source;

• the dynamic characteristics of the soil propagation medium, in particular the propagation phase velocity of the vibrations

(dispersion curve), which are essentially composed of surface waves or Rayleigh waves propagated on the ground surface. Conditions (position and size of the anti-vibration system, source type, receiver type) being equal, the propagation velocity of the vibrations as a function of the excitation frequency (dispersion curve) determines the filter frequency of the anti-vibration system and thus its mitigation capacity. This implies that for sizing the anti-vibration system, the dispersion curve of the Rayleigh waves must be measured directly on the ground;

• the dynamic characterisation of the source (in this case, the train), with particular reference to the frequency energy content and thus to the spectrum;

• the distance from the railway line and the receiver size, aspects which affect the extension or length of the anti- vibration system, since they affect the minimum shadow cone of protection from the vibrations, projected by the anti- vibration system and inside of which the receiver must be situated. Based on the considerations set forth above for the critical receptor, it was possible to calculate the term A₇ of the formula, in order to evaluate the vibrational impact on the critical receptor in the presence of the anti-vibration system with cell barriers and verify its acceptability with respect to the current laws on the matter. For the analysed critical receiver, the anti-vibration system with cell barrier permits attenuating the vibratory level below the limit thresholds indicated by law. The overall length of the anti-vibration system with cell barriers is equal to about 330 m.

Claims

1) Anti-vibration system (5) for mitigating the vibrations transmitted through the ground by an emitter means to a receiver means comprising a plurality of modular elements (7, 16) made of plastic, metal, cement or another appropriate material, buried underground and positioned between said emitter means and said receiver means and characterised in that each of said modular elements makes an air interspace at its interior.

2) Anti-vibration system according to claim 1, characterised in that said modular elements are slats (7).

3) Anti-vibration system according to claim 2, characterised in that said slats are composed of two thin faces, parallel to each other, at whose interior an air interspace is created.

4) Anti-vibration system according to claim 2 or 3, where said slats (7) are flanked with respect to each other and are connected together to form a panel (13) of modulatable length, and several adjacent panels form the barrier (5), it too of modulatable length. 5) Anti-vibration system according to one of the claims 2 - 4, where said slat (7) has at least one transverse stiffening separator (11).

6) Anti-vibration system according to one of the preceding claims, where inside said slat, in its upper (8) and lower (9) portions, and in any case at all communication pathways with the outside environment, a waterproofing or other liquid- resistant means is housed so that liquids do not penetrate inside the interspace.

7) Anti-vibration system according to claim 6, where said liquid-resistant/waterproofing means is a foam (10).

8) Anti-vibration system according to claim 6, where said liquid-resistant/waterproofing means is a U-shaped plastic material closure system (14) placed at the two ends, upper and lower, of the panel (13) and pasted thereto, as well as, possibly, in another suitable shape for sealing further communications pathways of the interspace with the outside environment.

9) Anti-vibration system according to one of the preceding claims, where the connection between two consecutive slats is a dovetail connection (12).

10) Anti-vibration system according to one ^{^}of the preceding claims, where the panel (13) has a width from 1 m to 5 m, a thickness of about 4 cm and an appropriately sized depth H and is composed of several slats (7) of about 20 cm length, held together by a suitable taping carried out with 1 m pitch along the depth of the panel. l l) Anti- vibration system according to claim 1, characterised in that said modular elements are tubes made of plastic, metal or another suitable material (16), made impermeable to liquids at the upper (17) and lower (18) ends by means of pasted and/or threaded covers.

12) Installation process of an anti-vibration system, as specified in one of the claims 1 - 11, comprising the following steps: excavation (6) of a trench at a suitable distance from the vibrating source and at a suitable depth; insertion of a barrier

(5) composed of the assembly of a plurality of panels (13); filling of the trench with soil or with another suitable material.

13) Installation process of an anti-vibration system, according to claim 12, according to which cement is used in place of excavated soil as trench filling.

14) Installation process of an anti-vibration system, according to claim 13, according to a "section" procedure which consists of making a plurality of longitudinal portions of the system which are not adjacent to each other, and subsequently, after the setting of the cement, one achieves the completion of the system in the ground sections left free between the already made portions.

15) Installation process of an anti-vibration system according to claim 13 or 14, where for the movement of the panel, metal guides are used which are vertically arranged along the sides of the panel and connected by another horizontal guide, guides which are immediately recovered after the filling of the trench with the plastic cement. 16) Installation process of an anti- vibration system, as specified in one of the claims 10 or 11, comprising the following steps: perforation of the rock (15) by drilling means similar to that used for installing micropiles, insertion of tubes made of plastic, metal or another suitable material (16), and making the communication pathways between the tube and surrounding rock impermeable to liquids.