[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] According to a preferred embodiment the permissible load of the tie anchor is tested
before the tie anchor is connected to the relevant foundation.
[0012] Certainty is hereby obtained concerning the permissible load of the tie anchor.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] Although the actual capability for pressure load does not change, the load or safety
factor can be decreased because the strength has been demonstrated.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] According to a preferred embodiment the linear drive element is formed by a hydraulically
drivable cylinder.
[0024] 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.
[0025] 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.
[0026] It will be apparent that such a pylon results from applying a method according to
the invention.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. Method as claimed in any of the foregoing claims, characterized in that the pylon is a high-voltage pylon.
8. 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.
9. Device as claimed in claim 8, characterized in that the linear drive element is a hydraulically drivable cylinder.
10. 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.