A METHOD OF PLACING A WEB

Abstract: During the construction of an entrenchment below the ground water level in the neighbourhood of nature area's, one is not allowed to drain the entrenchment and yet it has to be ensured that a reliable watertight web is positioned on the floor of that entrenchment. The invention has solved this problem by wrapping the web (v) around a roll (3) floating in the entrenchment (4), and subsequently navigating that roll (3) to the beginning of the entrenchment (4) after which unwinding and attachment of the web (v) takes place. An important feature of the invention is that after positioning of the roll unwinding takes place by pumping water from the entrenchment at the location where the web still has to be applied, to the location between the initial edge of the web and the core (fig.3).

Description: A METHOD OF PLACING A WEB The invention relates to a method of placing a web on an entrenchment below the ground water level. Usual methods of placing such a web consist of draining such an entrenchment. Then the web can be placed in a simple way. Draining the water does however also affect the ground water level in the area outside the entrenchment and such an influence is not always admitted. One may think of for instance the provision of entrenchments for a road in the neighbour¬ hood of a nature area. The invention tends to provide a solution for the above problem. -According to the invention this is achieved by that the web is wrapped around a core or roll,floating in the entrenchment, in a water course which is in open connection with the entrenchment respectively, that subsequently said wrapped-up core or roll is navigated to the beginning of the entrenchment, after which unwinding and attachment of the web takes place. Such a web is preferably formed by connecting lengths of web material, cut off at size, substantially parallel to the center line of the core or roll, to preceding lengths of web material, which can be effected by welding or adhering. The length of the core should substantially be equal to the resultant width of the entrenchment. If a road is concerned which has to be processed in this way, it is determined according to the invention, that the resultant width of the entrenchment is realized by enlargin the projected width by applying at least one flood verge. Unwinding takes place after the core is positioned by pumping water from the entrenchment at the location where the web still has to be applied, to the location between the initial edge of the web and the core. During pumping-over a braking moment and braking force is preferably exerted on the core. In order to apply the method according to the invention also a number of installations is necessary. The floating core is for instance formed so for that purpose, that, while being pivotal about its own axis by means of moment arms, it is connected to at least one pontoon, said at least one pontoon being provided with winches to bring the core in the correct position. Furthermore means are necessary to lower compression means with the aid of guide cables to secure the web edges, provided with ring eyes, to structure parts, positioned under water. For the purpose the guide cables extend between screw eyes, present in the concrete clamping edge, to for instance auxiliary scaffolds or one or more derrick barges, dependent upon the nature of the inter¬ mediary structures. Between the guide cables and screw eyes preferably barbed bars are provided. The invention will be further elucidated hereinafter on the basis of the drawing, in which by way of example an embodiment is shown of an installation to apply the method according to the invention. In the drawing is shown by: fig. 1 an abridged cross-section by an entrenchment having some installations at the left which can be used when applying the method according to the invention, all this substantially according to the line I-I of fig. 2 and having at the right an entrenchment profile with a flood verge under the water level, fig. 2 a schematic plan view of the installations of fig. 1, fig. 3 a longitudinal section of an entrenchment at the location of a part of a structure protruding up to above the water, to elucidate the beginning of the web placing process, fig. 4 a detail of the guide means of fig. 3, and fig. 5 a longitudinal section of an entrenchment at the location of a structure which does not protrude up to above the water level, on the basis of which the end of the web placing process is elucidated. The installations indicated in fig. 1 and 2 consist substantially of a working floor 1 having a length which is equal to the resultant width of the web, wound on a reel 2. Said resultant width may have a length of the magnitude of 175 meters. Along the working floor a core 3 can be moored, on which the web is wound. This is effected by winding the complete web V, necessary for one section, i.e. a part of the entrenchment between for instance two structures, including the triangle as a consequence of a possible oblique crossing of one of the structure parts, and the prefabricated web edges. It goes without saying that the said entrenchment need not be rectangular in plan view, but may have any shape. The roll is moored as closely as possible against the working floor, and the working floor may be over the slope 4. For the roll 3 is thought of a steel tube having a diameter of approximately 1 meter and a wall thickness of approximately 12.5 millimeters. On the other hand the web is very thin (up to a magnitude of 1 millimeter) by which only an increase in radius of some tens of centimeters is developed for an entrenchment of approximately 400 meters. With respect to the location of the working floor may be thought of the bank of the section to be dredged or a small channel, communicating with said section. The roll 3 is connected to two small pontoons 7 via two moment arms which are connected to the roll via a hydromotor 6. Said constructions cause the total width of the roll with pertaining par to be approximately 2 meters larger than the length of the core or roll itself. On the pontoons winches 8 are provided, which are controllable both with respect to their tensile force and holding force. With the aid of said winches the core or roll can be introduced into and maintained in any position within the dredged section. The initial and final operations when placing the web at the beginning and end of the entrenchment are most simple, as the web needs not be arranged under water then. However, the situation at the location of the structures is completely different, which structure parts do, as in fig. 3, or do not, as in fig. 5, protrude above the water surface P. In the event the structure obliquely intersects the entrenchme the roll 3 can be manoeuvered to the extreme corner point of the respective section, and then the partly unwound point can be drawn onto an auxiliary scaffold 10 (fig. 3) , secured to a viaduct 9, and temporarily anchored. By further unwinding the roll and navigating it parallel to the viaduct, the total web edge can be brought onto said auxiliary scaffold. One will note then, that the complete triangle is between the roll and the viaduct in a folded manner, which, however, is no disadvantage. Before the roll or core is navigated against the viaduct, then for instance each 3 meters vertical guide cables 11 are pre-arranged from screw eyes 13 (fig. 3 and 4) , present in a concrete clamping edge 12, to the auxiliary scaffold to be arranged. Said guide cables are laced through the (not shown) ring eyes, present in the web edge. Furthermore said web edge is provided with some ballast, with the aid of which the web edge can be lowered along the guide cables. Between the guide cable and the concrete a barbed bar 14 (fig. 4) is planned, which should prevent the web, when passed over said barb, from sliding, back. With sensors one can control whether the web edge is in the required position and if not, is brought in said position. Before the clamping construction 15, weighing about 1 ton, can be arranged, it has to be certain that on its track along the guide wires 11 it does not meet a web V, as this will undoubtedly cause dammage. In fig. 3 two clamping constructions 15 are visible, the one on the clamping edge 12, already provided, and the construction, which is drawn somewhat more to the top, is on its way to be arranged next to the first one. Securing said clamping constructions 15 next to each other takes place by turning nuts 23 (fig. 4) over the screw eyes 13. The guarantee that the web will not be dammaged by the clamping constructions can be achieved by further turning the core or roll in a position perpendicular to the axis of the entrenchment, keep them under control, and then introducing a slight difference in water pressure by means of pumping over water. This exerts a pressure on the web, which pressure is indicated by arrows A in fig. 3. Care should be taken, however, that the water that flows in causes as less disturbance as possible, and that is the reason that for instance a long (not shown) spray pipe must be used. After having checked first whether the web indeed almost horizontally leaves the clamping edge 12, the clamping units 15, which have a length of approximately 6 meters, can be payed out one by one from the auxiliary scaffold 10 along the guide wires 11 and screwed on with the aid of divers. The web can now be further payed out under a certain braking moment and braking force by pumping-over water, while care is furthermore taken that the core or roll will not become clamped against one of the banks. It has to be remarked, that a leak flow around the core heads or roll heads has an erosive effect, therefore a light erosion protection of 0.1 meters of gravel on the slope is necessary. Furthermore one should realize that the resultant length may be approximately 5 meters longer than the projected one, which requires the provision of a flood verge, indicated at the right in fig. 1 by means of a dashed line 16. It is also possible to solve this problem by including a fold on the core or roll. In order to ensure that the web edge does not disappear under water, it is advisable to fix it with for instance pegs 17 (fig. 1) , which can then be connected by wires 22 to a (not shown) ring eye, which is included in the reinforced web edge. In a later stage the web edge has to be brought above the water and the flood verge has to be completed. This can be done by locally withdrawing the web edge from the opposite side of the section of the entrenchment and thereby enabling re-profiling the verge. The connection of the web at the end of the respective section of the entrenchment takes place in a similar manner as described for the connection at the beginning at the location of a structure. O PI A difference is, however, that a water enclosure 18 (fig. 5) is introduced between the web and the bottom, i.e. under the fold, which can, however, be discharged by creating an overpressure relative to the ground water. In order to ensure that the fold will be on the bottom, a sausage¬ like ballast could be used, at one side connected to the guide wires 11, which can then be lowered parallelly to the axis of the entrenchment. The connection to the structure 19 (fig. 5) , which does not extend through the water level, is additionally complicated, so that one has to work from the water with a derrick barge 20. The guide wires 11 can then be tensioned by means of somewhat more robust floats 21. Although the invention is elucidated hereabove on the basis of an application to an entrenchment for a road for automobile traffic, it is remarked that the invented method and the pertaining installations can also be used in similar cases if the fact is concerned that during and/or after the construction of a project no influence of the ground water level in the direct neighbourhood is admissible. In this respect one may think of large closed reservoirs, like rubbish tips, water basins, swimming pools and the like reservoirs.

Claims: CLAIMS : 1. A method of placing a web on an entrenchment below the ground water level, characterized in that the web (V) is wrapped around a core or roll (3) floating in the entrenchment, in a water course which is in open connection with the entrenchment respectively, that subsequently said wrapped-up core or roll is navigated to the beginning of the entrenchment, after which unwinding and attachment of the web takes place. 2. A method according to claim 1, characterized in that the web is formed by connecting lengths of web material, cut off at size, substantially parallel to the center line of the core or roll, to preceding lengths of web material. , 3. A method according to claim 1 or 2, characterized in that the connection consists of welding or adhering. 4. A method according to any of the claims 1-3, characterized in that the length of the core is substantially equal to the resultant width of the entrenchment. 5. A method according to any of the claims 1-4, characterized in that the resultant width of the entrenchment is realized by enlarging the projected width by applying at least one flood verge. 6. A method according to any of the claims 1-5, characterized in that after positioning the core the web edge, provided with ring eyes, is lowered over guide cables to the structures- positioned under water. 7. A method according to any of the claims 1-6, characterized in that after lowering the web edge the unwinding of the web takes place substantially by pumping water from the entrenchment, at the location where the web still has to be applied, to the location between the initial edge of the web and the core. 8. A method according to claim 7, characterized in that during pumping-over a braking moment and braking force is exerted on the core. 9. A method according to any of the claims 1-8, characterized in that the connection of the'web to structures, positioned under water, takes place with the aid of compression means which are lowered along guide cables. 10. A method according to claim 9, characterized in that the connection fold at the end of the web is folded back along the web, already applied, by creating an overpressure relative to the ground water. 11. A method according to claim 10, characterized in that the overpressure is assisted by a sausage-like ballast. 12. A floating core for use in the application of the method according to any of the preceding claims, characterized in that, while being pivotal about its own axis by means of pivotal moment arms (5) , it is connected to at least one pontoon (7) , said at least one pontoon being provided with winches (8) to bring the core in the correct position. 13. A core according to claim 12, characterized in that the rotation of the core is controllable by a hydromotor (6) . 14. Means to lower compression means with the aid of guide cables to secure the web edges, provided with ring eyes, to structure,paefes, ^J E O PI positioned under water, characterized in that the guide cables (11) extend between screw eyes (13) , present in the concrete clamping edge (12), to auxiliary scaffolds (10). 15. Means according to claim 14, characterized in that the auxiliary scaffolds are placed on one or more derrick barges (20) . 16. Means according to claim 14 or 15, characterized in that between guide cables and screw eyes a barbed bar (14) is provided. 17. Method and installations as shown in the drawing and/or discussed on the basis thereof.

Inventors: KRUYT J, NETTE A
Applicants: HOLLANDSCHE BETONGROEP NV, KRUYT J, NETTE A, HOLLANDSCHE BETON GROEP NV
Application year: 1980
Main classification: E02B3
IPC codes: E02B3, E02D27