WO2022058948A1

WO2022058948A1 - System for reducing the transmission of vibrations in the soil

Info

Publication number: WO2022058948A1
Application number: PCT/IB2021/058490
Authority: WO
Inventors: Luca D'ALESSANDRO; Simone MEDURI; Giovanni CAPELLARI; Stefano CAVERNI
Original assignee: Phononic Vibes S.R.L.
Priority date: 2020-09-18
Filing date: 2021-09-17
Publication date: 2022-03-24
Also published as: EP4214367A1; IT202000022117A1

Abstract

A device for reducing the transmission of vibrations in the ground parallel to its surface, consisting of one or more aligned elements (20; 30; 60; 70; 80), in which the external contour of each element has the shape of a parallelepiped with recesses (62, 62',...) on one of its faces or through openings (22, 22', 22",...; 31, 31',...) between two opposite faces, wherein the vibrations are produced in particular by means of transport.

Description

SYSTEM FOR REDUCING THE TRANSMISSION OF VIBRATIONS IN THE SOIL

FIELD OF THE INVENTION The present invention relates to a system which allows to limit the propagation of vibrations underground. In particular, the present invention relates to a system for attenuating Rayleigh waves propagating near the surface.

STATE OF THE ART

Vibrations generated in the ground due to natural causes or resulting from human activities, such as works or vehicle transit, are transmitted in all directions into the ground. Those propagating parallel to the ground and in the first layers of the subsoil can be transmitted to adjacent infrastructures or buildings, with the risk of damaging them (e.g. formation of cracks, destabilisation of foundations, ...) and in any case causing discomfort to the people present in the buildings. These vibrations typically have frequencies of up to a few hundred Hz; particularly vibrations at low frequencies (indicatively below 50 Hz) are harmful for the structures, and annoying to people.

Particularly relevant are the vibrations induced by the transit of means of transport, both those travelling on roads (cars, lorries, ...) and those on rails (trains, trams and underground trains); for example, intense vibrations are generated by the passage of heavy vehicles over irregularities in the road asphalt such as potholes or traces of transverse excavations; another source of intense vibrations are the increasingly widespread high-speed trains.

Several approaches have been proposed to mitigate these phenomena. A first possibility is to act directly on the source of the vibrations to reduce their initial magnitude, for example by using dampers or dissipative mats; however, this approach is very costly because, in the typical case in which the source of vibration is a stretch of road or a line of tracks, major modifications or even replacement of the infrastructure are required.

An alternative approach consists in placing isolating elements between the source of vibration and the structures to be protected, which can attenuate or completely eliminate the vibrations downstream.

Mainly trenches and barriers can be distinguished among the solutions that follow this second approach.

A trench consists of a side excavation with respect to the infrastructure, resulting in a reflection of the incident wave, with an effectiveness depending on the depth of the same trench. However, the depth that can be reached is severely limited by problems of excavation stability, combined with the risk of flooding the trench in the event of rainfall.

On the other hand, all the solutions that involve the insertion of physical elements in the ground between the source and the structures to be isolated belong to the category of barriers.

The barriers can operate according to different physical principles.

A first possible mechanism is related to the reflection of vibrational waves.

Systems of this type are described in Japanese patent application JP 63-110324 A, in which the barrier consists of two flat walls spaced apart by cross bars, and in Japanese patent JP 5747458 B2, in which two flat walls are spaced apart by tunnel-like cement structures (similar to perforated bricks) in which the direction of the opening is parallel to the ground and the outer walls.

Like in the case of open trenches, the effectiveness of the barriers operating according to this mechanism is related only to the depth of the barrier.

A second possible mechanism exploits the difference in stiffness between the ground and the barrier itself. In particular, the stiffer a barrier is and the greater the difference between the stiffnesses of the ground and of the barrier, the greater the vibration isolation effect.

A study relating to barriers produced according to the latter mechanism is reported in the article “Experimental and numerical evaluation of the effectiveness of a stiff wave barrier in the soil”, P. Coulier et al., Soil Dynamics and Earthquake Engineering 77 (2015), pp. 238- 253. According to this article (beginning of section 2.4), various techniques are available for the production of these barriers, such as deep vibro-compaction, installation of gravel or cement columns, injection of stable cement-bentonite mixtures by hydraulic fracturing of the soil, vacuum consolidation, and the “jet grouting” technique, which consists of drilling into the ground and injecting into the cavity, from the bottom upwards, a mixture that fills it and consolidates the surrounding soil. Other known techniques involve driving poles or concrete elements of other shapes into the ground. These techniques lead to the formation of very heavy and environmentally “invasive” barriers, and use large amounts of material to create a continuous structure.

Mixed barrier/trench solutions have also been proposed, such as the one described in the Japanese patent JP 2932012 B2, in which a barrier consisting of two flat walls spaced apart by means of balloons filled with compressed air is inserted into a trench constructed with cement walls. A similar system is described in patent application CN 111379279 A relative to a modular system for the construction of barriers that are hollow in their inside and with continuous walls. Systems of this type are clearly more complex and costly to construct than in the case of simple barriers or trenches.

An object of the present invention is to provide a device for attenuating the transmission of vibrations in the ground, which maximises the induced stiffening effect of the ground and consequently the isolation of vibrations, while maintaining a structure as light and slender as possible.

SUMMARY OF THE INVENTION

This object is achieved by the present invention, which relates to a system for reducing the transmission of vibrations in the ground parallel to its surface, consisting of one or more aligned elements, in which the external contour of each element has the shape of a parallelepiped with recesses on one of its faces or through openings between two opposite faces of the same, and in which said one or more elements are formed by a material having a Young’s modulus between 10⁵ Pa and 10¹² Pa and a density between 1,000 kg/m³ and 15,000 kg/m³.

In a preferred embodiment, the basic element of the system of the invention has the shape of a grid formed by essentially coplanar and non-adjacent beam parts, so as to define openings. The present invention enables an effective reduction of the surface transmission of the vibrations in the ground. In particular, the present invention is particularly effective for attenuating Rayleigh waves propagating near the surface.

The physical principles that govern the operation of the technical solution and determine its effectiveness in reducing the vibrations are:

1. the existence of a critical bending frequency of each parallelepiped-shaped element: the lower the stiffness of the barrier made up of one or more aligned elements, the better the attenuation performance of the vibratory wave, particularly in the 20-50 Hz frequency range. In particular, the one or more aligned elements define a critical frequency of the system and thus lead to a stiffening of the ground;

2. the depth of the system in the ground, starting from the surface: the one or more aligned elements delimit a zone of attenuation of the transmission of vibrations in the ground, and a greater depth reached by the lower portion of the installed elements corresponds to a better functioning in intercepting the non-surface portion of the wave.

In general, the system for reducing the transmission of vibrations has elements with a substantially planar geometry. The system for reducing the transmission of vibrations has a stiff structure, consisting of structural beams arranged to identify a grille in the plane defined by the single element. Preferably, a continuous panel may be superimposed and fixed to the structural beam assembly to close all, or part, of the through openings defined by the system of structural beams arranged in a grille as above. This panel further contributes to reducing vibrations, due to the plate-like elastic stiffness behaviour that occurs in the free portions of the panel, reached through the defined through openings of the structural beam system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in the following with reference to the figures, in which:

- Fig. 1 schematically shows the positioning of the system of the invention between a vibration source and a building;

- Fig. 2 shows an element suitable for constituting, alone or in a side-by-side arrangement with other elements, a system of the invention, wherein the element has a generic geometry and through openings;

- Figs. 3a and 3b show, in a perspective view and a front view respectively, an element suitable for constituting, alone or alongside other elements, a system of the invention, wherein the element has a grid geometry and through openings;

- Fig. 4 shows a possible way of constructing the element of Figs. 3a and 3b;

- Fig. 5 shows various possible cross-sections of beam parts for the construction of the element of Figs. 3a and 3b;

- Figs. 6a, 6b and 6c show, in a perspective view, a front view and a side view respectively, an element similar to that of Figs. 3a and 3b but has recesses instead of through openings;

- Figs. 7a, 7b and 7c show, in a perspective view, a front view and a side view respectively, an element suitable for constituting, alone or alongside other elements, a system of the invention, wherein the element is formed by two semi-elements of the type shown in Figs. 3a and 3b coupled by means of a continuous connecting element along one side of said two semi-elements;

- Figs. 8a and 8b show, in a perspective view and a front view respectively, an element suitable for constituting, alone or alongside other elements, a system of the invention, wherein the element is formed by two semi-elements of the type shown in Figs. 3a and 3b coupled by means of a series of connecting elements arranged along one side of said two semi-elements;

- Fig. 9 shows possible cross-sections of the connecting elements of the elements of Figs. 7a, 7b, 8a and 8b;

- Fig. 10 shows in a schematic manner a system of the invention, consisting of several elements of the previous figures placed side by side;

- Fig. 11 shows a possible method for mounting acoustic insulation panels on a system of the invention;

- Fig. 12 reproduces two frequency-dependent vibration damping graphs obtained with a system of the invention.

DETAILED DESCRIPTION OF THE INVENTION The inventors observed that it is possible to achieve very good damping properties of the transmission of vibrations by using a system consisting of one or more elements placed side by side, wherein the elements are lighter and thinner than elements that constitute barriers of the prior art, for example made of cement columns placed side by side.

Although in one of the embodiments described below (Figs. 6a and 6b) the element constituting the system of the invention may have blind recesses, generally said system does not constitute a continuous barrier, but rather a device with openings which provides a stiffening for the ground and enables the vibration isolation to be maximised. This is an important technical aspect, as it offers a great flexibility in the design in the event of external constraints, and for example the openings can be exploited in order not to interrupt anthropogenic substructures in the subsoil, or to avoid dangerous localised accumulations of water in the subsoil potentially induced by an impermeable barrier.

Each single element forming (alone or together with other elements) a system of the invention has a shape inscribed in a parallelepiped, i.e. in views perpendicular to its three faces, each of them will have a shape that is rectangular or inscribable in a rectangle; within this parallelepiped, however, the faces of the element may be, but are not necessarily, flat, and the geometry of their surface depends on that of the beams that make up the element, as described below. Typically, although not necessarily, two sides of this parallelepiped have comparable length to each other (e.g. the longest side is not longer than ten times, preferably no more than five times the length of the shortest side), while the third side has a significantly shorter length, e.g. less than a quarter, and preferably less than a tenth, of the first two sides. Under these conditions, an element of the invention typically has a planar geometry, with two larger faces and four side faces with a much lower surface. In this more typical case (element of essentially planar geometry) the openings in the element pass through between the two larger faces.

The system of the invention may consist of a single element of those shown in Figures 2, 3a and 3b, 6a, 6b and 6c, 7a, 7b and 7c, and 8a and 8b, but more commonly it consists of a series of such elements placed side by side along one of the faces with a lower surface, as shown schematically in Fig. 10. The positioning in the ground of a system of the invention (consisting of one or more elements) is shown schematically in Fig. 1: the system, 10, is arranged transversely between the source of the vibrations (in this case represented by a train on rails, 11) and the structure to be protected from the vibrations, 12.

In particular, the one or more elements are vertically driven in the ground, between the source of the vibrations and the structure to be protected; the one or more elements may be driven for their entire extension, thus being underground, or be partially driven in the ground, having an erected portion outside the ground.

Each element intended to constitute (if alone) or construct (if placed side by side to other elements) a system of the invention is formed by a material having a Young’s modulus between 10⁵ Pa and 10¹² Pa and a density between 1,000 kg/m³ and 15,000 kg/m³. Preferred materials for the construction of the elements of the invention are metallic materials such as iron and steel, preferably treated to make them more resistant to the aggressive environment of the subsoil (humidity, acid or basic compounds, ...), for example by galvanisation, or alternatively plastic materials, for example regenerated plastics.

Fig. 2 shows an element 20 suitable for constituting (if alone) or constructing (if placed side by side to other elements) a system of the invention, in the most general embodiment of such elements. The element has the planar geometry that is most common for the elements of the invention, with two larger faces 21 and 21’ (the latter not visible in the figure) having through openings 22, 22’, 22”, the openings have a generic, regular or non-regular shape (for example, regular or non-regular polygons), not necessarily equal to each other, and arranged on the faces 21 and 21 ’ in an unordered arrangement.

In the most common case, however, the elements of the invention have openings with regular shape and arranged in a regular arrangement; for example, the openings may be square, rectangular or circular, with the centres arranged in a square lattice or, for example in the case of circular openings, in a hexagonal lattice. In the simplest case (also in view of its industrial realisation) the openings are rectangular (or, as a sub-case, square) and arranged in a rectangular (or, as a sub-case, square) arrangement, i.e., such that the centres of the openings define a rectangular (or, as a sub-case, square) lattice; for simplicity’s sake, in the following description reference will be made to elements with square openings arranged in a square arrangement, but everything said below applies to elements of any geometry.

Figs. 3a and 3b show, in a perspective view and a front view respectively, the element 30 according to this simpler embodiment, in which, as said above, the openings 31, 31 ’, ..., are square and arranged in a square arrangement. The total surface of the openings can vary within wide limits, typically between 20 and 80%, preferably between 40 and 60%, of the surface of the face on which they are present. For example, in the front view of Fig. 3b the openings have a total surface which is equal to about 50% of the surface of face 32. The solid parts that separate two adjacent openings may be spaced apart by a value between 0.01 m and 20 m.

The element 30 can be assembled starting from beams, as shown in Fig. 4: three equally spaced beams 42, 42’ and 42” are fixed perpendicularly to a first beam 41; then, additional beams 41’, 41 ”, ..., similar to the first beam 41, are fixed equally spaced apart along the beams 42, 42’ and 42”, finally obtaining an element of type 30.

The beams of type 41 and 42 may be connected to each other with mechanical elements (for example, nuts and bolts) or welded; in a preferred embodiment, these are shaped so as to allow the assembly of the element 30 by interlocks.

The beams of type 41 and 42 (or other similar construction elements) can conveniently be transported separately to the site where the system of the invention is to be positioned, and the element constructed in said site, facilitating and reducing the costs of transporting the parts that will constitute the system. When the beams are connected by interlocking, this can be done by positioning the first beam 41 horizontally at the bottom of the excavation, anchoring the beams 42, 42’ and 42” thereto in a vertical position, and then fixing (again by interlocking) the other beams 41’, 41 ”, ... thereon.

Fig. 5 shows various possible cross- sections of beams of type 41 or 42: this may be a solid section of any shape, simple or complex solid (51, 52, 54 and 58), hollow (53 and 55), or with specific profiles, for example a ‘C’ profile (56) or the common ‘double T’ profile beam (57); in each of these sections, the overall contour of each side may be between 0.01 m and 5 m, and in the case of hollow cross-section beams the wall thickness may be between 1 and 100 cm.

Another possible geometry of an element useful for realising the system of the invention is a parallelepiped with two sides with significantly greater length than the third one, and which has a series of recesses on one of its two largest faces. This geometry can be obtained by moulding or by casting a molten material in a mould, as described above for element 30. Preferably, however, this configuration is obtained by coupling a part of type 30 with a continuous panel. This preferred possibility is depicted in Figs. 6a, 6b and 6c showing, in a perspective view, a front view and a side view respectively, an element of the invention 60 formed by an element of type 30 connected on one of its two larger faces to a continuous panel 61, defining a series of recesses 62, 62’, ...

Figs. 7a, 7b and 7c show, in a perspective view, a front view and a side view respectively, a further element suitable for constituting, alone or placed side by side to other elements, a system of the invention. In this case, the element, 70, is formed by two semielements 71 and 71’, each one similar to element 30 described above; said semi-elements are parallel, spaced apart and connected to each other by a continuous connecting element 72 along one of the longer sides of the two semi-elements.

Alternatively, a similar structure, element 80 (Figs. 8a and 8b, perspective and top views respectively), may be obtained by connecting two semi-elements 81 , 81’ to each other, each one similar to element 30, with a series of connecting elements 82, 82’, 82”, ..., arranged along one side of said two semi-elements.

Some possible cross-sections of the connecting elements 71 or type 81 are shown in Fig. 9; the cross-section of these elements can be solid (91 and 94), hollow (92) or open (93). In the case of the discrete connecting elements 82, 82’, 82”, ..., they can be arranged in the element 80 in such a way that the faces seen in cross-section in Fig. 9 are those in contact with, or perpendicular to, the semi-elements 81 and 81’.

As mentioned above, a complete system of the invention can be obtained by placing side by side smaller faces of elements of type 20, 30, 60, 70 or 80 (referred to generically in the figure as element 100), as shown in Fig. 10; although the elements making up the system (when it is made up of several elements) are preferably the same, this condition is not necessary, and the system of the invention may consist of elements of different type placed side by side.

A system of the invention may be combined with acoustic insulation systems. Typically, in fact, the causes that cause the production of vibrations and their propagation in the ground also produce noise, which, although not harmful to the structures hit, is as much a cause of discomfort to people as the vibrations (if not more). For this purpose, it is possible to produce an integrated system for reducing both ground and sound vibrations by using the system described above as a basis for mounting acoustic insulation panels. This possibility is illustrated schematically in Fig. 11, in which an integrated element 110 is shown which consists of an element 100 (indicating by this reference number any of the elements described above) intended to be inserted in an excavation in the ground, on the upper side of which an acoustic insulation panel 111 is fixed, intended instead to emerge from the ground level. In the insert in the figure it is shown a possible way of coupling the element 100 to the panel 111, in which the upper side of the element 100 has a housing 112 (for example, a continuous groove) for the insertion of the base of the panel 111; the coupling between element 100 and panel 111 can then be made stable for example with known fixing systems, such as screws or the like. This integrated system also offers the advantage that the elements for reducing the transmission of vibrations replace the foundation for the acoustic panelling, which would otherwise have to be specially prepared.

By using mechanical analysis software, the inventors carried out simulations of the vibration reduction performance by a system of the invention. The results are shown in graphical form in Fig. 12, which shows the trend of the Insertion Loss (IL) value as a function of the vibration frequency, respectively at a distance of 10 m (solid line) and 20 m (dashed line) from the vibration source; the IL value measures the vibration reduction at these points by comparing the configuration without the system of the invention with the configuration with the system present. An important reduction (up to more than 8 dB) can be noted in the frequency range from 16 Hz to 160 Hz, and in particular it is interesting to underline a significant mitigation even at low frequencies (16-40 Hz), which are particularly harmful to structures and people and difficult to counteract with traditional solutions. Another advantage that is achieved with the system of the invention (except for the case illustrated in Fig. 6) compared to those of the prior art is that, since its main faces are not continuous but have through openings, it is compatible with the presence of other underground structures such as electricity, telephone or gas lines, water pipes, sewerage elements, ... A system of the invention can be constructed starting from beams of type 41 and 42 as described above around these pre-existing underground structures and be crossed by them (or, these structures can be constructed later by crossing the vibration damping system of the invention), whereas the continuous wall systems of the prior art cannot be crossed by said underground structures and therefore pose greater difficulties in positioning. The project leading to this patent application has received funding from the European

Union's Horizon 2020 research and innovation programme under grant agreement No

863179.

Claims

CLAIMS System for reducing the transmission of vibrations in the ground parallel to its surface, consisting of one or more aligned elements (20; 30; 60; 70; 80), in which the external contour of each element has the shape of a parallelepiped with recesses (62, 62’, . . .) on one of its faces or through openings (22, 22’, 22”, 31, 31’, ...) between two opposite faces of the same, and in which said one or more elements are formed by a material having a Young’s modulus between 10⁵ Pa and 10¹² Pa and a density between 1,000 kg/m³ and 15,000 kg/m³. System according to claim 1 , in which said material is selected from metallic materials, possibly treated to make them resistant to humidity and acid or basic agents, and plastic materials. System according to any one of claims 1 or 2, in which said parallelepiped has two sides in which the longer one has a length not exceeding 10 times the length of the shortest one, and a third side has a length not exceeding a quarter of the shortest of the first two sides, defining a parallelepiped with two faces with a larger surface and four side faces with a lower surface, in which said recesses are present in one of the faces with a larger surface or said openings are through openings between the two faces with a larger surface. System according to any one of the preceding claims consisting of one or more elements (20) in which said through openings (22, 22’, 22”, ...) have regular or nonregular shapes, not necessarily equal to each other, and are arranged on two opposite faces (21, 21 ’) of said parallelepiped in an unordered arrangement. System according to any one of claims 1 to 3 consisting of one or more elements in which said recesses or through openings have a regular shape and are arranged in a regular arrangement. System according to claim 5 consisting of one or more elements (30), in which said through openings (31, 31’, ...) are square and arranged in a square arrangement, and the overall surface of said through openings is between 20% and 80% of the surface of the parallelepiped faces in which they are present. System according to claim 6, in which said one or more elements (30) are produced by assembling a first series of equally spaced beams (41, 41’, 41”) with a second series of equally spaced beams (42, 42, 42”) perpendicular to the beams of the first series. System according to claim 7, wherein said beams have a solid of simple or complex shape (51, 52, 54, 58), hollow (53, 55), with a “C” profile (56) or with a “double T” profile (57) cross-section, the overall contour of each side of the beam is between 0.01 m and 5 m, and in the case of hollow cross-section beams the wall thickness is between 1 and 100 cm. System according to claim 5 consisting of one or more elements (70; 80) each formed by coupling two parallel semi-elements (71, 71’; 81, 81’), spaced apart and connected to each other by a continuous connecting element (72) or by a series of discrete connecting elements (82, 82’, 82”, ...) arranged along one of the longer sides of said two semi-elements. System according to claim 9, in which said connecting elements have a solid (91, 94), hollow (92) or open (93) cross-section. System according to claim 5 consisting of elements (60) that have recesses (62, 62’, ...) on one face, formed by coupling a part that has through openings with a continuous panel (61). 14 System according to any one of claims 5 to 11, wherein in each element the solid parts that separate two adjacent recesses or openings are spaced apart by a value between 0.01 m and 20 m. System for reducing the transmission of vibrations in the ground and for acoustic insulation, consisting of one or more panels of any one of the previous claims on the upper surface of which an acoustic insulation panel (111) is fixed.