The invention relates to a foundation for fixing a mast element comprising a hollow end portion in loose ground. The invention further relates to a method for fixing a mast element comprising a hollow end portion in loose ground. Background of the invention

Electric power is mainly distributed via high-voltage line routes in the open. The high- voltage line routes typically include masts made of wood or steel. To a great extent, the establishment of new masts is done in existing high-voltage line routes. Because of lacking alternative line capacity, it is becoming more and more usual to establish new masts while there is voltage on the existing line. Substantial numbers of the high- voltage line routes are arranged in outlying fields and in rugged terrain, and the es- tablishment of new masts therefore often includes helicopter transport of masts, ma- chines, material and personnel.

Wooden masts are compact and heavy, and may, because of that, be difficult to han- die, especially near an existing high-voltage line. In addition, the great weight is a cost driver in helicopter transport. In recent years, hollow masts have been developed as an alternative to wooden masts. The hollow masts are typically made from a com- posite material and are considerably lighter than wooden masts. The low weight con- tributes to easier handling and more reasonable transport, among other things. According to the prior art, the establishment of a hollow mast in loose ground, for ex- ample moraine, bog, clay or silt, is generally done in three steps:

• The first step includes forming a recess in the loose ground, wherein a portion of the recess is arranged to receive the hollow mast, or a hollow mast element. The recess is normally formed by means of a small excavator. The forming of the recess may include explosives. As far as possible, the excavator and other material are moved in the terrain, and preferably in the high-voltage line route. If terrain transport is not possible, it is known to move the excavator and the material by means of a helicopter. In the centre of the recess, a tubular body, for example a casing pipe, is positioned. The casing pipe is typically a rigid cor- rugated plastic pipe of the type that is used for culverts and overflows. When the casing pipe has been positioned, it is fixed to the loose ground by filling supporting masses against the outside of the casing pipe. The supporting mass is typically excavation residues from the recess. The backfilled masses may possibly be compacted. If the excavation residues are unstable, like bog and clay, for example, the mass is usually replaced with more stable masses, for example moraine or mixed gravel and fines. As far as possible, nearby masses are used. A replacement of masses as described herein may entail scars in the terrain around the mast point. By a mast point may be understood the place where the mast is going to be established and the area around it.

• The second step comprises positioning the hollow mast in the recess. This is normally done by a helicopter flying the mast to the mast point, after which the helicopter lowers the mast into the casing pipe. Linesmen on the ground make sure that the mast gets a correct vertical position and fix the mast by filling an annular space formed between the mast and the casing pipe with a stabilizing material, for example gravel. When the mast has been fixed in the stabilizing material, the mast is released from the helicopter.

• The third step comprises clearing and levelling excavation residues at the mast point and repairing scars in the terrain. This is normally done with an excava- tor.

Because of the logistics associated with the prior art, the three steps are normally not carried out consecutively. When the first step has been carried out, machines and ma- terial are usually moved to the next mast point or to a base, the mast then being es- tablished at a later time. Often, a number of recesses are formed before the masts are established.

When it is time for the masts to be established, the excavator is typically moved back to the mast point, so that the linesmen can use the excavator to fill the annular space with stabilizing material and level the excavation residues after the mast has been established. In some cases, the mast is established without the use of an excavator. The excavator is then usually moved to the mast point at a later time to clear and lev- el around the mast. The use of a helicopter for the transport and establishing of masts is conditional on little wind and good visibility. A restricted weather window combined with a time- consuming method for positioning and fixing the mast contributes to a relatively low installation capacity, and high costs. Work below and near energized high-voltage lines is particularly dangerous and re- quires strict safety precautions, especially when the work includes the use of a heli copter. The trade is therefore in search of solutions that can simplify the establishing of the masts and that can reduce the flight time for the helicopter near the mast point.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved through the features that are specified in the description below and in the claims that follow.

General description of the invention

The invention is defined by the independent claims. The dependent claims define ad- vantageous embodiments of the invention.

[1] In a first aspect, the invention relates more specifically to a foundation for fixing a mast element including a hollow end portion in loose ground, the foundation including a tubular body positioned in the loose ground, and a coupling element positioned in- side the tubular body so that an annular space is formed between the coupling ele- ment and the tubular body. The annular space is arranged to receive a stabilizing ma- terial. The coupling element includes a coupling portion arranged for connection to a mast element with a hollow end portion.

• In this context, a mast element may be understood as a complete mast, the mast being one undivided piece, or part of a multipart mast. The mast element may be completely or partially hollow. The mast element may include a conical portion. The mast element may include a cylindrical portion.

• The tubular body will be referred to as a pipe in what follows.

By loose ground may be understood ground comprising unconsolidated masses, for example moraine, mixed gravel and fines, bog and clay.

By establishing may be understood the positioning and fixing of a body. By po- sitioning may be understood bringing a body, for example a mast element or a coupling element or a pipe into a desired orientation or position.

• By a stabilizing material or mass may be understood a material which is sub- stantially stable in itself and which helps to stabilize adjacent elements. Exam- pies of a stabilizing material in this context are crushed stone like gravel and ballast stone, wherein the crushed material has a locking effect.

• In wat follows, the term mast point is used as a term for the place where the mast element is to be established, and the adjacent area.

The coupling element, also referred to as an adapter, is arranged to fix the mast ele- ment to the loose ground. By fixing the coupling element in the loose ground as de- scribed by the invention, the establishing of a mast element may be done more easily and more quickly than when a prior-art technique is used. The mast element may be lowered directly onto the coupling element, for example by the use of a helicopter, and immediately be placed in a correct vertical position. As soon as the mast element has been connected to the coupling element, the mast element may be released from the helicopter, and the flight time of the helicopter over the mast point can be reduced compared with that of the prior art.

The coupling element may be compact. The coupling element may be tubular. The coupling element may include a conical portion. The coupling element may be conical throughout its length. The outer shape and diameter of the coupling element may cor- respond to the inner shape and diameter of said mast element, so that the mast ele- ment may be lowered down and over a portion of the coupling element. The coupling element and the mast element may have an out-of-round shape.

In an alternative embodiment, the coupling element may include a flange arranged to receive a mast element with a corresponding flange, after which the two flanges are attached to each other in a prior-art manner, for example with bolts.

The coupling element may be arranged to position the mast element in such a way that a free height is formed between the mast element and the loose ground. The free height can be formed, for example, by arranging one or more supporting elements on the outside of the coupling element, against which the mast element may rest. Said free height eliminates the need for masses to be backfilled around the mast element after the mast element has been positioned, as is known to be done today. Excavation residues and adjacent terrain can thereby be levelled off all the way up against the coupling element before the mast element is established. The coupling element typically has a diameter of between 0.3 and 1.0 metre, and a height of up to two metres. These dimensions can make it possible to position the coupling element without using machines. The limited size of the coupling element may make it possible to transport the coupling element together with other material to the mast point.

The coupling element may be fixed to the loose ground by backfilling with a stabilizing material, for example gravel, mixed gravel and fines, ballast gravel or concrete. May- be, the stabilizing material will have to be transported to the mast point by a helicop- ter. The amount of stabilizing material should therefore be limited to a minimum. By arranging a pipe on the outside of the coupling element, as described by the inven- tion, an annular space is formed between the coupling element and the pipe. This an- nular space can be filled with the stabilizing material and thereby give the necessary fixing of the coupling element.

The pipe may be adapted for positioning in the loose ground. The pipe may be adapted for separating materials of different qualities. The pipe may help to reduce inflow of water to the coupling element and thus reduce the risk of frost weathering in the loose ground near the coupling element. It is possible to backfill against the out- side of the pipe with excavation residues from the recess.

The pipe may be formed of a rigid corrugated plastic pipe of the type that is used for culverts and overflows. A corrugated plastic pipe has the advantage of attaching bet- ter to the surrounding masses than a pipe with a smooth surface. The pipe may alter- natively be formed from concrete, composite or some other material. The pipe may have a conical shape so that a plurality of pipes can be stacked on top of each other.

The pipe may include means for connecting the pipe to the coupling element. The pipe may include means for positioning the coupling element. The means may, for exam- pie, be a rod. The rod may be extendable.

Using the pipe as described by the invention further has the effect of the pipe being able to prevent surrounding masses from sliding to the bottom of the recess, where the coupling element is going to be positioned. The overall effect of the features that are described above provides quick and safe establishing of a mast element including a hollow end portion, as said mast element can be connected to a coupling element belonging to a preinstalled foundation. Furthermore, the invention makes it possible to carry out all the ground work associated with the mast point continuously before the mast element is positioned, including levelling of excavation residues and repair of damage to the terrain.

[2] The coupling portion may be conical.

A conical coupling portion may make it easier for a mast element including a hollow end portion to be slipped over the coupling element, because the diameter of the end portion of the mast element may be larger than the diameter of the end portion of the coupling portion. Further, the free height of the mast element above the loose ground may be controlled through the diameters of the coupling element and the mast ele- ment. A coupling element with a large diameter will position the mast element higher above the loose ground than a coupling element with a small diameter. The end por- tion of the mast element will be positioned, in the main, at the height where the di- ameter of said end portion coincides with the diameter of the coupling element. A per- son skilled in the art will be able to calculate the height of the mast element above the loose ground. In an advantageous embodiment, the mast element has a conicity cor- responding to the conicity of the coupling element. Thereby a large contact area is achieved between the mast element and the coupling element, contributing to the mast element being wedged to the coupling element.

[3] The coupling element may include an open core portion.

An open core portion may help to reduce the weight of the coupling element in that material which is not necessary to give the coupling element strength is removed. The coupling element may include an annular end face or a partially or fully covered end face or a combination of said end faces.

[4] The open core portion may receive a stabilizing fill material.

By filling the open core portion with a stabilizing fill material, for example gravel or crushed stone, the stability of the coupling element can be increased, in that the cou- pling element is given both an external support and an internal support.

[5] The open core portion can receive a frost-proof fill material.

The effect of a frost-proof fill material is that the risk of frost weathering is reduced. The frost-free fill material may be an expanding foam material, for example polyure- thane foam. The expanding foam material has a low volume weight. By giving the coupling element an open core portion and filling this with the expanding foam mate- rial, the volume and the total weight of the coupling element may be reduced corn- pared with those of a compact coupling element. Thereby the expanding foam materi- al can contribute to easier transport and handling, while, at the same time, the risk of frost weathering is kept low.

[6] The coupling element may include a composite material.

Composite materials are known for combining strength and low weight. Low weight helps to make the coupling element easier to handle. The coupling element may be formed entirely or partially from a composite material. The mast element with the hol- low end portion which is described herein is typically formed in its entirety from a composite material. By forming the coupling element in the same way as said mast element, the coupling element and the mast element may be formed with production equipment being shared, which can be conductive to low production costs.

[7] In a second aspect, the invention relates more specifically to a method for fixing a mast element including a hollow end portion in loose ground, the method comprising the steps: a) forming a recess in the loose ground; b) positioning a tubular body in the recess; c) surrounding the tubular body with a supporting material; d) positioning a coupling element in the tubular element so that an annular space is formed between the coupling element and the tubular body; and e) adding a stabilizing material to the annular space. The ground work associated with establishing a foundation according to the invention includes, in a first step, forming a recess in a ground comprising unconsolidated mass- es. The recess is arranged to receive the pipe and the coupling element. The ground work further includes filling supporting and stabilizing masses and levelling excavation residues around the coupling element. If the mast element is to be positioned in un- stable loose ground, for example in bog or clay soil, it may be advantageous to re- place the excavated masses with more stable and draining masses.

The coupling element is normally positioned in such a way that the centre line of the coupling element is vertical, and in such a way that the centre line of the coupling el- ement is substantially in the centre of the pipe. The annular space between the cou- pling element and the pipe is filled with a stabilizing material, for example gravel, in order thereby to give the coupling element an external support and attachment to the pipe and the loose ground. The filling of the stabilizing material can advantageously be done in steps, so that the position of the coupling element can be checked and possi- bly corrected until the annular space has been filled up and the material possibly com- pacted. [8, 9] The method may further include the step of adding a fill material to an open core portion of the coupling element

The fill material may be arranged to give an internal support for the coupling element. The fill material may be a draining one, and the fill material may be frost-proof. If there is no need for an internal support of the coupling element, the open core portion may be filled with an expanding foam material, for example polyurethane foam, which prevents water from accumulating in the open core portion.

[10] The method may further include the step of levelling excavation residues from the recess on the outside of the coupling element.

By excavation residues from the recess being levelled on the outside of the coupling element after the annular space has been filled with the stabilizing material, all the ground work at the mast point may be completed before the mast element is estab- lished. This gives a more efficient utilization of machines and personnel, and the over- growing of terrain touched can start earlier than with current methods.

[11] The method may further include the step of compacting one or more of the materials. Compacting makes the material more compact and more stable. Thereby the stability of the pipe and the coupling element can increase as well. Besides, a compacted ma- terial has less space for water, so that the risk of frost weathering is reduced.

[12] The method may further, after step e), include the step of connecting the mast element including the hollow end portion to the coupling element. By the fact that the foundation and the ground works may be completed consecutively as described by the invention, the hollow mast element may be connected to the cou- pling element without any subsequent need for mechanical ground work at the mast point. By the mast element being lowerable directly onto the coupling element, the flight time of the helicopter over the mast point can be reduced. By the masts being connected to preinstalled coupling elements, several masts can be established in a shorter time than today. It is particularly favourable when masts are to be established in areas with changing weather and periodically much fog and wind. While current establishing methods require a favourable weather window for both po- sitioning and fixing the mast, the invention only requires a favourable weather window for the actual connection of the mast and the coupling element.

In what follows, an example of a preferred embodiment is described, which is visual- ized in the accompanying drawings, in which:

Figure 1 shows a cross section of a foundation for a mast element including a hollow end portion arranged in loose ground;

Figure 2 shows the foundation of figure 1 seen from above; and

Figure 3 shows a mast element including a hollow end portion arranged on the foundation of figure 1.

Figures 1 and 2 show, respectively, a cross section and a top view of a foundation 1 for a mast element 20 (see figure 3) comprising a hollow end portion (22) in loose ground 99. The foundation 1 is arranged in the loose ground 99 by a recess 91 being formed. The recess 91 is so deep that the bottom 92 is frost-free. The recess 91 is advantageously formed by the use of an excavator. In the recess 91, a tubular body 30, referred to as a pipe in what follows, is arranged first. On the outside of the pipe 30, a supporting material 52 has been added. In the drawing, the pipe 30 is shown with a smooth surface. The supporting material 52 is typically excavation residues from the recess 91. A coupling element 40 is then positioned inside the pipe 30. The centre axis 40C of the coupling element is arranged vertically, and the coupling ele- ment 40 is, in the main, positioned in the centre of the pipe 30. In an annular space 35 formed between the coupling element 40 and the pipe 30, a stabilizing material 51 has been added. The stabilizing material 51 is typically a draining and crushed materi- al, for example gravel. Excavation residues 97 from the recess have been levelled around the coupling element 40 and have been given a fall carrying surface water away from the coupling element 40. The supporting material 52 and the stabilizing material 51 have been compacted to give increased stability to the pipe 35 and the coupling element 40.

Figure 3 shows a mast element 20 arranged on the foundation 1. More specifically, a coupling portion 21 belonging to the mast element 20 has been lowered over the out- side of a coupling portion 41 belonging to the coupling element 40. The centre axis 40C of the coupling element coincides with the centre axis 20C of the hollow mast el- ement. The two coupling portions 21, 41 have corresponding conical designs arranged to give a stable and locking connection of the hollow mast element 20 and the cou- pling element 40. The mast element 20 has a free height h over the loose ground, determined by the conicity and diameter of the coupling element 40. By the mast el- ement 20 being arranged on the coupling element 40 with a free height h as shown in figure 3, excavation residues 97 may be filled all the way up to the coupling element 40 before the mast element 20 is established.

It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art may construct many alternative em- bodiments without departing from the scope of the attached claims. In the claims, reference numbers in brackets are not to be regarded as restrictive. The use of the verb "to comprise" and its different forms does not exclude the pres- ence of elements or steps that are not mentioned in the claims. The indefinite article "a" or "an" before an element does not exclude the presence of several such elements.

The fact that some features are indicated in mutually different dependent claims does not indicate that a combination of these features cannot be used with advantage.