EP1253252A1

EP1253252A1 - High voltage pylon with strengthened foundation

Info

Publication number: EP1253252A1
Application number: EP02076679A
Authority: EP
Inventors: Joseph Fransiscus Van Wolven; Jacobus Fredericus Rikken
Original assignee: Kema NV
Current assignee: Kema NV
Priority date: 2001-04-27
Filing date: 2002-04-29
Publication date: 2002-10-30
Also published as: NL1017953C2

Abstract

The invention relates to a method for increasing the permissible load of the foundation of a pylon provided with a number of legs, wherein at least one tie anchor is arranged in the ground in the vicinity of the foundation of the pylon, and the tie anchor is connected to the relevant foundation.

Experience has shown that the existing foundations can generally absorb the great pressure load, but that the tensile stress of the foundation is much more critical.

By arranging a tie anchor the permissible tensile strain of a foundation is therefore also greatly increased, while there is not generally a very great need to increase the pressure load, so it can suffice to demonstrate the pressure capability.

Description

As a result of economic, political and environmental conditions there is a need to increase the transport capacity of existing high-voltage lines. This is caused by the liberalization of the energy sector, cost considerations and the lack of space for routes for new high-voltage lines.
Increasing the transport capacity generally entails increasing the load on the pylons; it will be wished to increase the conductor cross-section or the number of conductors of a line, or to increase the height of the pylon so as to increase the permissible sag of the conductors. In all these cases the mechanical load on the pylon will increase. This will of course involve an increase of the load on the foundation of such a pylon. The foundation of such a pylon, which is usually provided with four legs, consists of four foundation elements, one for each of the legs, each resting on a number of piles present in the ground.
Such a foundation element is dimensioned to absorb pressure forces and to absorb tensile forces. The tensile strain is generally caused by the wind, the pressure force by own weight and the vertical load of conductors and insulators.
When a new high-voltage line is erected, soil-drilling tests are carried out in the ground, wherein a foundation is dimensioned on the basis of the results of these soil-drilling tests. A safety factor is herein taken into account which depends per se on the ground characteristics and the variance in soil qualities which can hereby be anticipated, and the distance between the soil-drilling tests.
When faced with having to increase the load-bearing capacity of the foundations, the problem has to be confronted that the pylons are often placed in poorly accessible locations. They are in any case often placed a great distance from roads which can be used for heavy equipment, so that large investment is necessary to reach the locations with this heavy equipment.
The object of the present invention is to provide a method wherein it is possible to increase the load-bearing capacity of the foundations with a relatively small amount of machinery. This entails that both the pressure capability and the tensile capability must be increased or demonstrated. The invention comprises of increasing the tensile capability by means of arranging a tie anchor and demonstrating that sufficient pressure capability is available.
This object is achieved by a method wherein at least one tie anchor is arranged in the ground in the vicinity of the foundation of the pylon, and the tie anchor is connected to the relevant foundation.
Experience has shown that the existing foundations can generally absorb the great pressure load, but that the tensile stress of the foundation is much more critical.
By arranging a tie anchor the permissible tensile strain of a foundation is therefore also greatly increased, while there is not generally a very great need to increase the pressure load, so it can suffice to demonstrate the pressure capability.
An advantage hereof is that a tie anchor can easily be arranged without employing particularly heavy equipment; it is possible to transport the means required for this purpose to the relevant location using for instance a wheelbarrow or a rowing boat.
According to a preferred embodiment the permissible load of the tie anchor is tested before the tie anchor is connected to the relevant foundation.
Certainty is hereby obtained concerning the permissible load of the tie anchor.
According to another preferred embodiment the pressure load of the foundation is investigated during testing of the tensile strain of the tie anchor, and a new value of the permissible pressure load of the foundation is obtained from the obtained result.
In this embodiment use is made of the situation that it is possible to mutually connect the tie anchor and the foundation via a force-generating device, wherein a load is applied by the force-generating device, which load acts as a pressure load on the side of the foundation and acts as a tensile strain on the side of the tie anchor. It is therefore possible here to test both loads simultaneously using a relatively simple device. It is not necessary for this purpose to bring in heavy equipment which would have been necessary if only the pressure load of the foundation were to be tested.
The testing is of course continued up to a force which, while taking a safety factor into account, corresponds with the load calculated for a heavier line. When no displacement of the foundation of the pylon is detected here, the relevant load can be permitted.
Although the actual capability for pressure load does not change, the load or safety factor can be decreased because the strength has been demonstrated.
Use is preferably made of a hydraulic cylinder in testing of the tensile strain of the tie anchor and the pressure load of the foundation.
This entails a relatively simple device, which can be brought in without heavy machinery, and which is suitable for generating great forces by means of a simple pump.
Of course not only the foundation of a high-voltage pylon will usually have to be strengthened, but also the construction of the pylon itself.
Experience has shown that it is usually the corner posts or other components of the pylon extending substantially vertically which are under the heaviest load, namely buckling load. It is therefore attractive to reduce the buckling length by arranging appropriate elements. This can also be realized in simple manner without heavy equipment or hoisting equipment being necessary.
The invention further relates to a device for testing the pressure load of a foundation and the tensile strain of a tie anchor arranged in the ground in the vicinity of the foundation, comprising a linear drive element, one side of which is adapted for connection to the foundation and the other side of which is adapted for connection to the tie anchor, and a measuring device for measuring the force exerted by the linear drive element on the foundation and the tie anchor.
Such a device can advantageously be used in applying the method as described in the foregoing. Such a device is not very voluminous and does not weigh very much, so it can be arranged at the relevant location without many transport problems.
According to a preferred embodiment the linear drive element is formed by a hydraulically drivable cylinder.
It hereby becomes possible, by causing a pump to operate for a long time, to build up sufficient pressure to perform the test. Such a cylinder and the pump for use therein are furthermore not very heavy or bulky.
Finally, the invention relates to a high-voltage pylon, the permissible load of which is increased, which is characterized by at least one tie anchor which is arranged in the ground in the vicinity of one of the foundations and which is connected to the foundation, wherein the foundation of the pylon otherwise remains unchanged.
It will be apparent that such a pylon results from applying a method according to the invention.
The present invention will be elucidated hereinbelow with reference to the annexed drawing, which shows a schematic cross-sectional view of a pylon during performing of a method according to the present invention.
Figure 1 shows a pylon 1 which is provided with four legs, only two of which, numbers 2 and 3, are visible. Leg 2 is placed on a foundation plate 4 and leg 3 is placed on a foundation plate 5. Foundation plate 4 is placed on a foundation pile 6 and foundation plate 5 is placed on a foundation pile 7. The existing foundation piles 6 and 7 extend through a loose soil stratum 8 into a firm soil stratum 9, for instance consisting of sand.
In order to increase the permissible tensile forces on foundation pile 6 by pylon 1, there is arranged according to the invention a tie anchor 10 which is per se known in the prior art. Tie anchor 10 is connected to a space above the ground surface by means of a rod or tube 11. Tie anchor 10 can be connected to foundation plate 4 by means of a connecting construction 12. Greater tensile forces can hereby be exerted on the foundation by the pylon, which in most cases is the most critical when the pylon load is increased.
For the purpose of investigating the permissible load of the tie anchor use is made of a cylinder 13, preferably a hydraulic cylinder 13. The connection 12 is of course broken here and tie rod 11 is directly connected to the suction position 14 of hydraulic cylinder 13. Hydraulic cylinder 13 is connected to a pump 16 by means of a hose 15. The force exerted by hydraulic cylinder 13 can be increased to a desired value by switching on the pump. Use is of course made herein of measuring means (not shown in the drawing) for measuring the force in question.
It will be apparent that the force exerted by the cylinder forms a pressure load for foundation plate 4 and a tensile strain for tie anchor 10. Both elements can hereby be tested for their respective loads so that certainty can be obtained regarding the actual load-bearing capacity of these elements and, while of course applying a certain safety factor, whether the pylon can be loaded up to such loads in the future.
Account is of course taken of the fact that in the construction of the line in question considerable safety and load factors are usually observed. It will therefore only occur in exceptional cases that the pressure load of the foundation is insufficient for the proposed increase in weight and that the foundation will have to be strengthened. Since it only need be applied in the necessary cases, a great saving is obtained.
It is finally pointed out that as the case arises it may be advantageous to increase the buckling load of for instance the posts 17 of the pylon construction by arranging anti-buckling elements 18. Posts 17 are after all usually the most heavily loaded elements of the pylon construction, while the buckling load of these elements can be increased using relatively simple means.
The arranging of anti-buckling elements is per se known, but in combination with the measure according to the invention the advantage is obtained that the use of heavy equipment for the purpose of strengthening the pylon becomes wholly unnecessary.
It will be apparent that this invention is applicable not only to pylons for carrying high-voltage lines, but also to other types of pylon, such as for instance masts for transmitters, particularly transmitters for the purpose of mobile telephony.

Claims

Method for increasing the permissible load of the foundation of a pylon provided with a number of legs, characterized by arranging at least one tie anchor in the ground in the vicinity of the foundation of the pylon, and connecting the tie anchor to the relevant foundation.
Method as claimed in claim 1, characterized in that the permissible load of the tie anchor is tested before the tie anchor is connected to the relevant foundation.
Method as claimed in claim 2, characterized in that the pressure load of the foundation is investigated simultaneously during testing of the tensile strain of the tie anchor, and a new value of the permissible pressure load of the foundation is obtained from the obtained result.
Method as claimed in claim 3, characterized in that testing of the tensile strain of the tie anchor takes place simultaneously with the investigation of the pressure load of the foundation.
Method as claimed in claim 3 or 4, characterized in that use is made of a hydraulic cylinder in testing the tensile strain of the tie anchor and the pressure load of the foundation.
Method as claimed in any of the foregoing claims, characterized in that the pylon is a lattice mast and that the permissible load of the pylon construction is increased by reducing the buckling length of substantially vertically extending elements.
Method as claimed in any of the foregoing claims, characterized in that the pylon is a high-voltage pylon.
Device for testing the pressure load of a foundation and the tensile strain of a tie anchor arranged in the ground in the vicinity of the foundation, comprising a linear drive element, one side of which is adapted for connection to the foundation and the other side of which is adapted for connection to the tie anchor, and a measuring device for measuring the force exerted by the linear drive element on the foundation and the tie anchor.
Device as claimed in claim 8, characterized in that the linear drive element is a hydraulically drivable cylinder.
Pylon, the permissible load of which is increased, characterized by at least one tie anchor arranged in the ground in the vicinity of one of the foundations, wherein the foundation of the pylon otherwise remains unchanged.