Vibration-damping arrangement

Abstract

A vibration-damping arrangement intended to be placed in a slot-like shaft or trench in earth layers, or in water masses, wherein the arrangement includes a flexible container (1) which is pressurised by a gas in its operative state, and wherein the container has an associated gas generating device (2) which is adapted to generate a predetermined gas volume in the container at a given time delay. The vibration-damping arrangement can be used to reflect the propagation of vibrations or to restrict the occurrence of the quicksand phenomenon in water-containing ground in the event of cyclic pressure variations, e.g. in earthquake or landslip conditions. The arrangement can be conveniently combined with means for draining water from the ground in the near proximity of the container.

Description

The present invention relates to a vibration-damping arrangement of the kind defined in the preamble of claim 1, and also to the use of such an arrangement.

It is known that the propagation of ground vibrations, for example vibrations originating from a railroad, can be prevented, and thus also subsequent damage to nearby buildings for instance, by providing a vertical slot-like trench or shaft in the ground down to an appropriate depth, for instance a depth of 10 metres, wherein the extension surface of the slot-like shaft or ditch is orientated at right angles to the direction between the vibration source and those installations to be protected against vibrations. There can be inserted into such a shaft a container that has generally the same extensional measurements as the shaft and that includes flexible walls. The container is conveniently pressurised with a gas so that it is capable of supporting the shaft walls. The pressurised gas in the container dampens or refracts sound transmission. Variants of this technique allow the container to include cellular plastic bodies or the like in addition to a pressurised gas. The container-formed screen can be cast firmly in place in the shaft, for instance by filling the shaft with a hardenable or a curable liquid mass, into which the container is submerged and the mass then allowed to harden.

The submersion of the vibration-damping screen into such a liquid-like mass in a slot-like shaft can be facilitated by mounting/fastening a major surface of the container to a plate, for instance a concrete plate of the same size and area as the container. Alternatively, the vibration-damping screen can be fitted to a frame structure that facilitates submersion of the screen in the liquid-like mass against the action of the buoyancy forces of the screen/container in said casting mass. Another alternative in this regard involves connecting the lower edge of the screen container to a heavy horizontal bar whose mass is sufficiently great to draw the gas-filled container into the liquid mass in the shaft. It is, of course, conceivable to first insert the screen-forming container into the shaft in an inflated and sealed state, and then introduce the liquid hardenable mass into the shaft.

Alternatively, the screen may, of course, be placed in the shaft and anchored therein in a non-inflated/non-pressurised state and then inflated/pressurised in the presence of or in the absence of a flowable hardenable mass.

However, the flexible vibration-damping screen is subjected to high internal gas pressures in its operative state, and the container is expected to remain sealed over a long period of time under the influence of the vibrations whose propagation shall be refracted or absorbed by the screen.

Consequently, high demands are placed on the impermeability of the container. A screening container of this kind is usually manufactured from thin plastic sheeting, metallised sheeting or plastic sheeting laminates of a flexible nature and of high mechanical strength, high impermeability and that can be welded effectively. The weld seams are, of course, critical and are preferably welded at the plant producing said containers, with no part being produced in the field itself.

Accordingly, conventional vibration-damping screens of this particular type have been delivered from a plant in a ready-welded sealed stated and pressurised with a gas filling that is adapted to the application in question. Alternatively, the damping screen may be provided with inflation valves for inflation of the container in the location in which it shall be used, whereafter the valves are closed or the container is sealed-off prior to finally placing the device in its position of use, either in the ground or in a water mass.

The transportation of inflated containers from the factory to their place of use is expensive and problematic with respect to handling of the containers. Transportation also involves damage risks. Furthermore, the possibility of then lowering the screening container into the shaft or trench when the container is empty of gas is, of course, excluded in practice.

Accordingly, one object of the present invention is to provide a flexible container intended to form a vibration-damping or vibration reflecting screen in water or earth layers, where said container is produced in the absence of pressurising gas so that it can be transported in a non-inflated state, for example in a rolled-up state or a coiled state, to the location in which the screening container shall be installed, and where said container can be pressurised non-invasively with a predetermined gas volume prior to, during or subsequent to inserting the container into said shaft/place of use.

This object is achieved either completely or partially by means of the present invention.

The invention is defined in the accompanying independent Claim.

Further embodiments of the invention will be apparent from the accompanying dependent Claims.

The invention is based on the concept of placing a gas-generating device in the container in conjunction with the manufacture and permanent sealing of said container. The gas-generating device is of a kind that can be activated without penetrating the container wall. For example, according to one simple embodiment of the invention, the gas generating device may include a sealed plastic film cushion that is divided into two spaces which are mutually separated by a membrane that can be ruptured by applying an external force mechanically via the container wall and the walls of said cushion. The spaces provided in the cushion may include respective suitable chemical substances which when brought together generate a pre-chosen gas volume, wherewith the gas thus generated ruptures the cushion packing so as to allow the gas to be emptied into the container and pressurise said container to a predetermined extent that depends on the nature of the chemical substances involved and the amounts in which they are present. In another embodiment, a container made, for instance, of heat insulating material is filled with gas in a solid or liquid state and then placed in the cushion. The purpose of the heat insulating material is to delay the transition of the gas from a solid state to a gaseous state. n certain cases, the heat insulating material may be surrounded by a gas-tight container that may be provided with valve means or closure means that can either be opened by remote control or may be adapted to be opened automatically by the gas pressure when said pressure reaches a given level. This enables a pre-chosen volume of gas (in liquid or solid state) to be metered in a simple and convenient fashion, while providing sufficient time for effective closure of the container of the gas-generating device, since the loss of gas during closure of said container is practically negligible. Moreover, there is obtained a selectable time period for placing the gas-generating device in position before inflating the container arrangement.

There are, of course, other alternative embodiments of the gas-generating device. For example, the device may include a pressurised container comprised of suitable material (a gas tank, gas flask) that can be opened from outside the wall of the closed container, without penetrating said wall. The gas-generating device may, of course, be activated by mechanical action, by heating said device or by remote control, for instance by wireless actuation, such as via radio waves and with a selected time delay with regard to gas development in relation to the time of actuation.

The present invention enables the flexible container for the vibration-damping screen to be manufactured in a permanently sealed state in the absence of any substantial internal free gas volume, so that the container will require only a small storage and transportation space and so that the container can be folded together or coiled into a transport-friendly and handling-friendly form with regard to its transportation to the location at which the container shall form the vibration-damping screen, by virtue of its flexible wall material. The invented container can be inflated at its place of use, by activating the gas generating device before or after inserting the container into the slit-like shaft or trench, either before or after optional filling of the shaft with a floatable, hardenable mass. The container may be carried by a structure that keeps the container in an outwardly tensioned state. Alternatively, the container may be coupled to a heavy body, for instance at the bottom edge surface of the container, so as to hold down the container in its inflated state in a liquid non-hardened mass.

In one preferred embodiment of the invention, an inventive container is mounted on at least one side of a concrete structure, such as a concrete plate, having essentially the same area as the container, to enable the container to be readily inserted into the slot-like shaft or trench and held therein in connection with bringing the vibration-damping screen into its final position.

Thin plastic sheeting that can be used for the manufacture of a screening container arrangement according to the invention consists of a laminate or metallised foil of the kind typically used for vacuum packaging in the food industry.

An application of the present invention is found within earthquake technology, to reduce or to eliminate the effect of cyclic loading in water-saturated sand. In the case of cyclic loading of water-saturated sand there occurs a pore water pressure that promotes the quicksand phenomenon (liquefaction). The water-saturated sand gradually looses its strength, which can result in significant reduction in the bearing capacity of foundations and piles, or trigger a slope failures. It is well known that the build-up of pore water overpressure is already reduced by small gas quantities (less than 1%) in a water-saturated sand. This effect can be achieved by installing gas-filled flexible containers (cushions) in an earth layer beneath the groundwater surface. When the earth layer is subjected to cyclic loading, the pore water overpressure is compensated for by a reduction in the volume of gas in the cushions (the cushions are compressed), as in the case of a shock absorber. The volume of the cushions increases when the earthquake or landslip has ceased and the pore water pressure diminishes.

In the case of this use application, cylindrical or spherical containers (cushions) are installed in shafts narrow trenches or predrilled holes. The shaft or the drill hole may be filled with suitable container-protecting material. When the containers are buried in the ground, the effect afforded by the containers can be enhanced by combining the containers with draining means. In certain cases, it may be meaningful to fasten the cushions to prefabricated elements (piles or plates) that may include or be provided with draining means which function to reduce the amount of ground water present in the close vicinity of the containers, in a known manner.

In a further embodiment, vibration-damping devices are installed in water masses to reduce the propagation of shock waves. The technology applied is similar to that employed in the case of ground-installed insulating screens, although with the screen anchored either to a wall or to some other installation to be protected against the influence of vibrations.

The invention will now be described by way of example with reference to the accompanying drawings, in which

FIG. 1 is a schematic illustration of a container constructed in accordance with the invention;

FIG. 2 is a schematic sectional view taken on the line II-II in FIG. 1 (See the mistake in FIG. 1);

FIG. 3 is a sectional view of a ground-installed slot-like shaft in which an inventive container has been inserted, said container being mounted on a supporting structure and cast in a hardened mass in the shaft;

FIG. 4 is a view taken on the line IV-IV in FIG. 3;

FIG. 5 is a variant in a reproduction corresponding to FIG. 2; and

FIG. 6 illustrates a further variant in a reproduction corresponding to FIG. 2.

FIG. 1 illustrates a generally parallelepipedic, sealingly closed container 1, which is formed by the sealed connection of flexible gas-impervious foil sheets. The container 1 has height and width dimensions A, B in the order of metres, and a thickness or diametrical dimension C in the order of decimetres.

The container may be produced by laying two sheets of foil material on one another and joining said sheets together with a weld seam. The container 1 is essentially empty when in a closed state, with the exception of a gas generating device 2 enclosed in the container 1, wherewith the container can be rolled up, folded up, etc., to facilitate transportation of the container from its place of manufacture to its place of use. It will be seen from FIG. 2 that according to one embodiment of the gas generating device 2 the device includes a closed plastic foil cushion 21 of significantly smaller volume than the volume of the container 1. The cushion 21 is divided by a membrane 22 into two spaces 23, 24 which contain respectively a first chemical substance (e.g. an acid) 25 and a second chemical substance (e.g. a salt) 26. The membrane 22 can be caused to burst, by applying external forces F against the cushion 21 via the container walls. As a result, the first chemical substance will come into contact with the second chemical substance and therewith generate gas in the cushion 21, which is gradually burst by the established gas pressure so that gas will flow out into the interior of the container 1 and therewith fill the same. The volume of gas generated can be predetermined by appropriate dosing of the chemical substances, so that the container 1 will be given a predetermined gas filling that is well adapted to the use conditions.

The container 1 may be conveniently mounted on a supporting structure, for instance on a concrete slab 3, having the same area as the main surfaces of the container 1, for insertion into a slot-like shaft or narrow trench formed in the ground 5. The supporting structure 3, which is shown to have a container 1 on each main surface thereof, can be lowered into a can be caused to harden. It can be assumed that the containers 1 are pressurised with a predetermined gas volume, either before or after positioning the supporting structure 3 in the shaft or trench 4. The shaft or trench 4 may have a depth of 10 m, for instance. The liquid mass 6 exerts pressure against the containers 1, wherein the magnitude of said pressure depends on the depth and the density of the mass 6. The mass 6 hardens in its state of pressure equilibrium. The pressurised gas in the containers 2 provides effective screening/dampening of vibrations that propagate generally in the direction x and can be assumed to propagate in a direction normal to the extensional plane of the containers 1./?/

FIG. 4 illustrates a series of structures 3 with containers 1 cast in the mass b in a slot-like shaft or trench 4 formed in the ground.

In areas where there is a risk of earthquakes, the concrete sheet or slab 3 can be replaced by a column-like element (pile or drain) and the container 1 can be installed directly in a slot 4 or a drill hole. In some cases, the liquid mass b may be replaced with drainage material.

FIG. 5 illustrates an alternative gas generating device 2 which may include a pressure gas vessel 121 having an emptying valve 122 which can be opened with the aid of a drive element 123 that can be activated by a receiver 124 capable of receiving a signal from an externally located operator-controllable transmitter 125.

FIG. 6 illustrates a further alternative gas generating device 2 that may include gas in a liquid or a solid state 126. In certain cases, the gas can be placed in a heat insulating casing 127 which may surround a gas-tight vessel 128 or which may itself form a gas-tight vessel 128. The gas-tight vessel 128 may include valve means 129 where the valve is triggered at a chosen overpressure to allow the gas to fill the container 1. The heat insulation 127 enables dosing of the liquid or solid gas volume to be readily achieved in a convenient fashion and also to retain the dosage of cooled liquid or solid gas to be retained over a relatively long period of time sufficient to enable the casing 127 with a possible vessel 128 to be inserted into the container 1 with a good margin, before any significant amount of gas has time to leave the casing 127 or the vessel 128. Moreover, the heat insulation 127 or a possible valve means 129 can be chosen to delay the actual inflation of the container 1 for a selected period of time, so as to provide sufficient time for comfortable transportation of a selected period of time, so as to provide sufficient time for comfortable transportation of the container 1 and its insertion into its position of use prior to inflating the container 1 with said gas. The valve means 129 may be opened by remote control.

The gas-generating device may, of course, include known means for delaying gas generation subsequent to triggering the gas-generating device.

Claims

1. A vibration-damping arrangement for ground or water installation, wherein the arrangement includes a flexible container (1) which is gas inflated in an operative state and in its position of use, characterised in that the container (1) includes an associated gas generating device (2) which is adapted to delay the delivery of gas to the container.

2. An arrangement according to claim 1, characterised in that the gas generating device (2) is adapted to slowly release the gas in the container (1) so as to enable the closed container including said gas delivering and gas generating device to be placed in an essentially non-inflated state in its place of use in which the gas generating device fully inflates the container.

3. An arrangement according to claim 1 characterised in that the gas generating device (2) contains a volume of gas in liquid or solid, preferably cooled, state, wherein the container (1) includes a gas inlet opening that can be closed, preferably by welding, subsequent to the introduction of a gas volume into the container, wherein the transition of the gas volume to a gas phase requires a predeterminable time period.

4. An arrangement according to claim 1, characterised in that the container (1) is supported by a structure (3) with which the container (2) can be mounted in a ground-formed shaft or in a water mass.

5. An arrangement according to claim 4, characterised in that the structure (3) is adapted to drain water from the ground in the close vicinity of the container.

6. An arrangement according to claim 4 characterised in that the container (2) is surrounded by ground-installed drainage material.

7. An arrangement according to claim 1, characterised in that the structure (3) has a mass which prevents the structure-connected inflated container from floating up from liquid present in a ground-formed shaft in which the container and the structure are placed.

8. An arrangement according to claim 7 characterised in that the structure (3) is sheet-like and keeps the container extended and is placed in a slot-like shaft to form a vibration-damping screen.

9. An arrangement according to claim 8, characterised in that the liquid in said shaft is a hardening mass; and in that a container (1) is placed on each side of the sheet-like structure (3).

10. An arrangement according to claim 3, characterised in that the liquid or solid gas volume is encased by heat insulation that delays the transition of said gas volume to a gas phase.

11. An arrangement according to claim 1 characterised in that the gas generating device (2) as connected to the closed container (1) is adapted for activation at a freely selective time point.

12. An arrangement according to claim 1, characterised by draining means for draining water present in the ground in the proximity of the container (1).

13. The use of an arrangement according claim 1 for reducing the quicksand phenomenon in water-containing ground/soil in the case of cyclic pressure variations in the ground, for instance as a result of earthquakes.