Patent Publication Number: US-6702522-B2

Title: Foundation for a tower and a method for its deployment on site

Description:
FIELD OF THE INVENTION 
     The present invention relates to foundations for towers in general and, in particular, to a foundation for telecom towers and similar applications. 
     BACKGROUND OF THE INVENTION 
     In the implementation of a telecom network, a power transmission network or a similar network, first, sites are selected and planned, then building permits for the sites, including the tower sites, are obtained, and afterwards, the sites are built. In the conventional case, a concrete foundation is cast at the tower site. A normally prefabricated steel tower is assembled, erected and affixed to the foundation, in any of a number of known fashions, generally including screwing or bolting the tower base to the foundation. This provides a permanent tower facility, but takes a relatively long time to deploy, due to the fact that the foundation concrete must cure sufficiently to withstand the tower base loads before the tower can be erected and affixed to it. 
     Increasingly, new Telecom Networks (primarily mobile telephone networks) tend to be built under fast roll-out constraints. On the other hand, it is increasingly hard to obtain building permits for the sites (primarily the tower sites) of such networks. 
     Accordingly, there is a long felt need for, and it would be very desirable to have, a rapidly deployable telecom or similar tower, which would utilize a prefabricated foundation solution. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a foundation for a tower, the foundation comprising a plurality of prefabricated slabs coupled together so as to function as a monolithic foundation. 
     According to one embodiment of the present invention the shape of the surface area of the foundation can be substantially square, rectangular, circular, octagonal or any other geometrical shape. 
     According to another embodiment of the present invention the foundation includes a plurality of layers, each layer including a plurality of adjacent slabs joined transversely to adjacent layers, wherein the thickness of each slab in a layer is substantially the same. 
     According to one embodiment of the invention the surface area of each slab is one half of the surface area of each said layer. 
     According to a preferred embodiment of the invention, each slab includes a plurality of horizontally spaced throughgoing substantially vertical bores for accepting long bolts or elongated connecting members having threaded at least end portions. Said bores further include lining sleeves. 
     According to yet another preferred embodiment of the invention, at least each slab at the bottom layer of said foundation, further comprises substantially vertical recesses at one end of said throughgoing vertical bores, wherein said recesses have a cross-section which is larger than the cross-section of said bores. 
     Further according to a preferred embodiment of the invention, the recesses have a specially shaped non-circular cross-section for housing said long bolts or connecting members, securing nuts, locking nuts, plate washers and non-rotating nut holding devices for preventing rotation of said connecting members when tightening said securing nuts. 
     According to a preferred embodiment, said recesses are arranged for snug fit housing of said heads of long bolts and securing nuts. 
     According to yet another preferred embodiment, said recesses further house non-rotating nut holding devices which have a non-circular cross section equal to or larger than the cross section of said securing and locking nuts, and are adapted to snug fit into said recesses and snug hold said locking nut, for preventing rotation of said connecting members. Said non-rotating nut holding devices comprise a substantially flat surface having surface area dimensions and contour suitable for snug fitting into said recesses, a circular hole suitable for inserting said connecting member and co-axial thereto, and two parallel walls projecting from said flat surface substantially perpendicularly thereto, wherein each wall is positioned at an equal distance from the center of said circular hole and spaced apart at a distance substantially equal to the length between two opposite ribs of said locking nuts for snug fit housing and holding of said locking nut. According to another preferred embodiment, said bottom layer slab further comprises a metal plate including holes co-axial with said recesses and bores, for distributing loads created by tensioning of said long bolts or connecting members and providing a support surface against which said heads of long bolts or securing nuts abut when said connecting members are tightened. 
     According to yet another preferred embodiment, all of said long bolts or connecting members or at least some of them, protrude from the top layer of the foundation for joining together all said layers of the foundation and connecting said tower to said long bolts or connecting members. According to still another preferred embodiment, each said layer includes slabs substantially similar to said bottom layer slab. According to one embodiment, the top layer includes slabs substantially similar to said bottom layer slabs turned upside down. 
     There is also provided in accordance with the present invention a method of preparing a foundation for a tower, the method comprising: 
     preparing prefabricated slabs including throughgoing substantially vertical bores for receiving elongated connecting members; 
     preparing a site having a desired area; 
     placing a first layer of said prefabricated slabs on the site; 
     placing a second layer of said prefabricated slabs transversely on said first layer, while; 
     aligning said throughgoing receiving bores; and 
     joining together said first and second layers by means of said elongated connecting members passing through said aligned throughgoing receiving bores. 
     There is further provided in accordance with the present invention a method of preparing a foundation for a tower, further comprising placing additional layers of prefabricated slabs on said second layer and joining together all the layers by means of elongated connecting members passing through said aligned throughgoing bores in all the slabs. 
     The method according to another preferred embodiment of the present invention, further comprises placing prefabricated slabs having substantially vertical recesses at one end of said throughgoing vertical bores, at the bottom layer. According to a preferred embodiment, the method further comprises placing slabs substantially similar to said bottom layer slabs at any of the layers. 
     The method according to yet another preferred embodiment, further comprises placing slabs substantially similar to bottom layer slabs turned upside down at the top layer. 
     According to another preferred embodiment, said method further comprises the step of assembling onto bottom end portions of connecting members said securing nuts, said non-rotating nut holding devices and said locking nuts before inserting connecting members through said first layer, extending upwardly. 
     According to yet another preferred embodiment of the present invention, said method further comprises the step of inserting connecting members through said first layer, extending upwardly, before the step of placing the slabs of the first layer on the ground. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be further understood and appreciated from the following detailed description taken in conjunction with the drawings in which: 
     FIG. 1 is a perspective view of a tower mounted on a foundation constructed and operative in accordance with one embodiment of the present invention; 
     FIG. 2 is a schematic plan view of the tower of FIG. 1; 
     FIG. 3 is a plan view of a slab constructed and operative in accordance with one embodiment of the invention; 
     FIG. 4 is a partial sectional view of the slab of FIG. 3; 
     FIG. 5 is a partial sectional view of a bottom slab with recesses and bottom end portions of elongated connecting members, constructed and operative in accordance with an alternative embodiment of the invention; 
     FIG. 6 is a sectional view of a preferred metal liner for the bores and recesses shown in FIG. 5, constructed and operative in accordance with a preferred embodiment of the invention; 
     FIG. 7 is a partial sectional view of the foundation constructed and operative in accordance with an alternative embodiment of the invention; 
     FIG. 8 is a partial sectional view of the upper part of the foundation and partial sectional view of a leg of a tower and structural interface element, constructed and operative in accordance with an alternative embodiment of the invention; 
     FIG. 9 is a plan view of two layers of the foundation constructed and operative in accordance with an alternative embodiment of the invention; 
     FIG. 10 is a plan view of two layers of the foundation constructed and operative in accordance with an alternative embodiment of the invention; 
     FIG. 11 illustrates the non-rotating nut holding device, constructed and operative in accordance with an alternative embodiment of the invention; and 
     FIG. 12 is a partial sectional view of the upper part of the foundation, constructed and operative in accordance with an alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a foundation for towers of telecom sites, power transmission lines, and the like, which facilitates rapid deployment due to the fact that the foundation is completely prefabricated. Except for a possible thin layer of lean concrete, which has no structural significance, no other on site casting is required in order to form a solid, stable foundation for the tower. Thus, one purpose of the invention is to provide a solution for the tower sites of telecom and similar networks that require rapid deployment due to fast roll-out constraints. 
     The foundation according to the invention is formed of a plurality of prefabricated slabs. The heart of the invention is the method used to connect together the components of the foundation, and make them function effectively and safely as if they were one monolithic foundation. The foundation according to the invention can be permanent, or can be removable after temporary deployment, as preferred by the network builder. It is a particular feature of the invention that the foundation is very big and heavy in its entirety, so as to provide stability for the tower, yet its components can be prefabricated in dimensions and weights which are transportable by conventional means. 
     Referring now to FIGS. 1 and 2, there are shown respective perspective and plan views of a tower foundation and tower constructed and operative in accordance with one embodiment of the present invention. As can be seen, a conventional prefabricated tower  10  is mounted on a foundation  20 . Tower  10  can be any telecom tower or similar tower requiring a firm foundation to carry and stabilize it. Tower  10  can be of various conventionally required shapes (i.e. Lattice Tower or Monopole type), heights, or dimensions. The tower illustrated in FIGS. 1 and 2 is a Lattice Tower with three legs  12 , which are affixed to the foundation  20 , as described below. A ladder  14  for climbing the tower, and a fence  16  or other security measures, may be optionally provided, as known. 
     The tower foundation according to the present invention is formed of several layers  22 , preferably at least four layers, as illustrated in FIGS. 1 and 2. Each of the layers consists of at least two concrete slabs  24  (rectangular if the foundation is substantially square). It will be appreciated that each layer of the foundation according to the present invention consists of a plurality of slabs that are either identical or not identical in surface area shape and dimensions, depending on engineering choices or constraints. Also, the slabs of each layer may differ in surface area shape and dimensions from one layer to another. However, the slabs in each layer must be of suitable surface area dimensions and shape to cover the overall area of that layer, and the thickness of each slab within a given layer must be substantially equal. Still, the thickness of each layer may vary, also depending on engineering choices or constraints. It will be further appreciated that the surface area of the foundation according to the present invention can be of various geometrical shapes, such as substantially square, rectangular, circular, octagonal, etc. 
     Referring now to FIG. 9, there is shown a substantially square foundation wherein each layer consists of 3 rectangular slabs  25 ,  26  and  27 , which can differ from one another in surface area dimensions. Slabs  25  and  27  have different dimensions than slab  26 , and slabs  25  and  27  may be identical or not identical. 
     Referring now to FIG. 10, there is shown a substantially octagonal foundation wherein each layer consists of 3 slabs. Slabs  28  are identical but are of different surface area dimensions and shape from slab  29 . During the process of assembling the foundation on site, the slabs are stacked in layers in a criss-cross fashion, so that their long dimensions are arranged in alternating transverse directions. Thus, in FIG. 2, the two slabs  24  of the top most layer are indicated by a solid line, while the slabs  24 ′ of the layer beneath it are indicated by a broken line. In FIG. 9, slabs  25 ,  26  and  27  of the top most layer are indicated by a solid line, while the slabs  25 ′,  26 ′ and  27 ′ of the layer beneath it are indicated by a broken line. In FIG. 10, slabs  28  and  29  of the top most layer are indicated by a solid line, while the slabs  28 ′ and  29 ′ of the layer beneath it are indicated by a broken line. When the slabs are all tightly fastened together, they form a monolithic “Raft” type foundation for the tower. 
     Referring now to FIG. 3, there is shown a plan view of a slab  30  constructed and operative in accordance with one embodiment of the invention. Slab  30  is an elongate slab having a pre-selected dimensions and thickness, which depend on the design constraints of the particular tower. A plurality of substantially vertical throughgoing bores  32  are provided through slab  30 , as seen in FIGS. 3 and 4. Bores  32  are arranged to allow long bolts or elongated connecting members which may be threaded or have threaded end portions, to pass through said bores  32  for coupling the slabs of all the layers together. Bores  32  are preferably lined with a metal or other liner or sleeve  34  during casting, so as to facilitate accurate placing of all designed bores  32  in the slab. Accurate placing of the bores is imperative for alignment of each respective bore  32  in all the layers of the foundation, thus allowing insertion of said long bolt or elongated connecting member through respective bore  32  of all the layers. Typically slab  30  is for use in layers of the foundation other than the bottom layer. 
     Referring to FIG. 5, there is shown a sectional view of a bottom slab  40  including the bottom end portions of the long bolts or elongated connecting members  47  and  47 ′, constructed and operative in accordance with an alternative embodiment of the invention. According to a preferred embodiment of the invention, slab  40  turned upside down can be used at the top layer as well as at the bottom layer. Although not necessarily economical, slab  40  can also be utilized as any internal layer. Slab  40  includes throughgoing bores  42  and  42 ′ merging into specially shaped and substantially vertical cylindrical recesses of non-circular cross-section  44  and  44 ′ at one end of bores  42  and  42 ′, respectively. According to a preferred embodiment, recesses  44  and  44 ′ are shaped and sized for snug fit housing and holding of the bottom heads of the long bolts or of securing nuts  45  and  45 ′ screwed on to the end portions of elongated threaded connecting members  47  and  47 ′, which are inserted into bottom slab  40  and extend upwardly for connecting the layers of the foundation. Alternatively, the recesses may be shaped and sized for snug fit housing and holding of non-rotating nut holding devices  50  and  50 ′, which have a non-circular cross section equal to or larger than the cross section of the securing nuts  45  and  45 ′ and locking nuts  52  and  52 ′, and are adapted to snug hold the locking nuts. Referring to FIG. 11, there is shown a non-rotating nut holding device  120 , comprising a substantially flat surface  122  having surface area dimensions and contour suitable for snug fitting into the recesses  44  and  44 ′ in slab  40 , and a circular hole  124  having a diameter which is equal to or larger than the diameter of connecting member  47  and  47 ′ and is co-axial with the connecting members, recesses  44  and  44 ′ and bores  42  and  42 ′. Non-rotating nut holding device  120  further comprises two parallel walls  126  and  126 ′ projecting from flat surface  122  substantially perpendicularly thereto, and each wall is positioned at an equal distance from the center of circular hole  124  and spaced apart at a distance substantially equal to the length between two opposite ribs of the locking nuts for snug fit housing and holding of said locking nuts, thus preventing the nuts from rotating. 
     Also, the recesses prevent the ends of said bolts or connecting members  47  and  47 ′ from protruding downwards from the lower surface of the bottom layer. This feature of said recesses is imperative for even contact between the underside of the foundation and the soil sub-base prepared for erection of the foundation and thus for even load distribution of the weight of the foundation and tower on said sub-base. 
     Preferably, only the recesses in the slabs of the bottom layer need have a non-circular cross section of compatible shape and size of the bolt head or securing nut in the absence of access to these bottom heads or nuts. According to a preferred embodiment, the recesses can be of non-circular substantially cylindrical shape and size, through which the securing nuts can be indirectly held. As shown in FIG. 5, recesses  44  and  44 ′ can have a substantially cylindrical non-circular cross section larger in size than the securing nuts  45  and  45 ′. According to this embodiment, elongated connecting members which may be threaded or have threaded end portions are used to join the layers of the foundation. When threaded connecting members  47  and  47 ′ are used, before they are inserted into bottom slab  40 , securing nuts  45  and  45 ′ are screwed on to the bottom end portions of the connecting members, with or without plate washers  54  and  54 ′. Thereafter, non-rotating nut holding devices  50  and  50 ′, are slipped, respectively, onto bottom end portions of connecting members  47  and  47 ′ followed by locking nuts  52  and  52 ′ which are screwed on to the bottom end portions of the connecting members, abut against non-rotating nut holding devices  50  and  50 ′ and slide them up along the connecting members until they abut against securing nuts  45  an  45 ′. Once non-rotating nut holding devices  50  and  50 ′ are locked between locking nuts  52  and  52 ′ and securing nuts  45  and  45 ′, the top portions of connecting members  47  and  47 ′ are inserted respectively into recesses  44  and  44 ′ and bores  42  and  42 ′ of bottom slab  40 , and securing nuts  45  and  45 ′, non-rotating nut holding devices  50  and  50 ′ and locking nuts  52  and  52 ′ are placed in recesses  44  and  44 ′, respectively. Thus, when securing nuts  74  and  74 ′ are screwed on the end portions of the connecting members (shown in FIG. 7) for joining together all the layers of the foundation, non-rotating nut holding devices  50  and  50 ′ abut against recesses  44  and  44 ′ respectively and prevent the rotation of connecting members  47  and  47 ′. It will be appreciated, that locking non-rotating nut holding devices  50  and  50 ′ between locking nuts  52  and  52 ′ and securing nuts  45  and  45 ′, respectively, can also be accomplished by tightening securing nuts  74  and  74 ′ which may rotate connecting members  47  and  47 ′, respectively, until locking nuts  52  and  52 ′ cause non-rotating nut holding devices  50  and  50 ′ to abut against securing nuts  45  an  45 ′, thus preventing further rotation of the connecting members. 
     According to an alternative embodiment, wherein recesses  44  and  44 ′ snug fit bottom heads of the long bolts or of securing nuts  45  and  45 ′, the locking nuts or non-rotating nut holding devices or both, may not be required. According to this embodiment, long bolts or connecting members  47  and  47 ′, which have threaded end portions only, can be used to join the layers of the foundation. Thus, when these connecting members are used, securing nuts  45  and  45 ′, with or without plate washers  54  and  54 ′, are screwed on to the bottom end portions of the connecting members before their top end portions are inserted into bottom slab  40 . When securing nuts  74  and  74 ′ are tightened, connecting members  47  and  47 ′, respectively, may rotate until securing nuts  45  and  45 ′ reach the end of the threaded bottom end portion of the connecting members, thus preventing them from further rotation. When long bolts are used, no securing nuts are required at their bottom portions and their top end threaded portions are inserted into the recesses in bottom slab  40  and extend upwardly while their heads are snug fitted in recesses  44  and  44 ′ which prevent the rotation of the long bolts when securing nuts  74  and  74 ′ are tightened. 
     Non-rotating nut holding devices  50  and  50 ′ are shaped so that, when inserted into recesses  44  and  44 ′, any rotation of non-rotating nut holding devices  50  and  50 ′ is prevented. It will be appreciated by those skilled in the art that the alternative arrangements described above are preferred for the bottom most layer of the foundation, on top of which all the other layers are placed, and to which there is no access once the slabs are in place. 
     The depth of recesses  44  and  44 ′ from the bottom end of slab  40  is substantially smaller than the thickness of said slab but sufficiently deep to prevent the long bolts or connecting members from protruding downwards from the bottom layer. 
     The bores and recesses are formed during the casting of slab  40 , preferably through use of a metal “cast-in” type liner, one embodiment of which is more clearly illustrated in FIG.  6 . Said liner may be provided in individual segments, each forming a single bore and a single recess in the casted slab. Preferably, the lining of said bores and recesses is formed by grouping together a large number of bores and recesses. Such grouping together of two horizontally spaced apart bores and recesses is illustrated in FIGS. 5 and 6. Grouping of more than two bores and recesses can be accomplished in the same manner. 
     Referring now to FIG. 6, there is shown a base plate  48  including holes  49  and  49 ′ of a diameter equal to the diameter of bores  42  and  42 ′, respectively, and located directly thereunder. Bore liners or sleeves  46  and  46 ′, for forming bores  42  and  42 ′ respectively, are attached on one side of plate  48  and larger substantially cylindrical recess liners or sleeves  43  and  43 ′ for forming recesses  44  and  44 ′, respectively, are attached on the other side of plate  48 . Liners or sleeves  43  and  43 ′,  46  and  46 ′ and holes  49  and  49 ′ are arranged, respectively, substantially co-axially; the two axes being spaced apart at a pre-selected distance. Metal plate  48  serves also as a base against which the securing nuts or heads of the long bolts abut directly or through washers or plate washers  54  and  54 ′, as known in the art and as shown in FIG.  5 . Thus, plate  48  serves to distribute the concentrated loads created by the tensioning of the long bolts or elongated connecting members. 
     A plurality of selected long bolts or elongated connecting members must protrude upward from the top surface of the top layer for connecting the tower to the foundation, whereas the remaining long bolts or connecting members, preferably, do not protrude from said top surface. 
     Now referring to FIG. 7, there is shown one preferred embodiment of the invention, wherein a bottom slab turned upside down is used to form the top layer. In this embodiment, recesses  72  and  72 ′ are sized to allow the use of a fastening tool, such as a deep ring-wrench or the like, for tightening the securing nuts  74  and  74 ′ on top of said non-protruding long bolts or connecting members  76  and  76 ′. The recesses  72  and  72 ′ in the top layer, which house, respectively, said non-protruding long bolts or connecting members  76  and  76 ′, may be filled in with any type of grout material, if desired, to provide a smooth upper surface finish for the foundation. FIG. 7 further shows a partial cross section of internal layers  78 , bottom layer  80  and full length of non-protruding long bolts or connecting members  76  and  76 ′. 
     In another preferred embodiment shown in FIG. 12, a bottom slab  140  is turned upside down and used as a top layer of the foundation. According to this embodiment, the size of recesses  142  and  142 ′ does not allow the insertion and use of a fastening tool for tightening securing nuts  144  and  144 ′ inside the recesses. Thus, there is provided a plate  146  comprising a plurality of holes having a diameter which is equal to or greater than the diameter of connecting members  148  and  148 ′ and arranged substantially co-axially with the long bolts or connecting members which are inserted through said holes in plate  146 . Securing nuts  144  and  144 ′ are screwed on to the top end portion of connecting members  148  and  148 ′ and abut against plate  146  directly or indirectly through plate washers  150  and  150 ′, when tightened. 
     Now referring to FIG. 8, as aforesaid, some of the throughgoing long bolts or elongated connecting members  90  and  90 ′ are utilized to affix the base plate  95  of the leg of the tower, either directly or indirectly to the long bolts or connecting members. As known in the art, due to design, manufacturing or construction imperfections, it is generally impossible or very difficult, to affix base plate  95  directly to the long bolts or connecting members. Thus, in the embodiment seen in FIG. 8 (as well as in FIG.  2 ), leg  94  of the tower is engaged to a structural interface element  96  by conventional bolts  100 . In turn, said interface element  96  is affixed to the long bolts or connecting members  90  and  90 ′, which also serve to couple the layers of the foundation underneath. Thus it may be further appreciated that the long bolts or connecting members can vary in length, whereas long bolts or connecting members  90  and  90 ′ will be longer while used to affix the base of the tower to the foundation then the others which have no such role. There are further shown in FIG. 8 the top ends of the long bolts or connecting members protruding from slab  102 , which is a bottom layer slab turned upside down. Also seen in FIG. 8 are ends of long bolts or connecting members  90  and  90 ′ secured by securing nuts  98  which abut optionally against plate  92  and secure the joining of the foundation layers by securing plate  92 . Conventional bolts  100  are used for affixing interface element  96  to leg  94 . It will be appreciated by those skilled in the art, that the coupling of the tower to the foundation is shown in FIG. 8 by way of an example only. 
     The dimensions of the slabs can vary somewhat, according to the type and size of the tower to be supported, the size of the site, and the design standards and norms required to be followed in the specific country in which the site is to be erected. Preferably, the foundation is symmetrical in the horizontal plane, e.g., square or circular, to permit ease of fabrication and layering in the transverse orientation, and since the direction of the force acting on the tower (e.g., wind or earthquake) cannot be normally predicted. The foundation can, alternatively, be asymmetrical. Most preferably, the foundation is substantially square and the slabs are standardized for groups of towers having similar construction requirements. The horizontal dimensions of the slabs should normally be limited by the constraints of conventional transportability (i.e. width and length not exceeding those of conventional truck pallets). Preferably, the foundation according to the present invention comprises at least 4 layers, whereas the thickness of the slabs is determined by the overall design of the “Raft” type foundation and by constraints of the weight of each slab, which is a function of its thickness. On one hand, the thickness of the slab cannot be less than a minimum thickness that provides the required stiffness of the slab, and on the other hand, it cannot exceed a maximum thickness that will raise the weight of each slab beyond the capacity of locally available cranes. 
     Once the dimensions of the foundation, the number of layers, the number, shape and thickness of the slabs, and the number and location of bores for the long bolts or connecting members, have been decided upon (all depending upon construction calculations), the required slabs can be prefabricated. When it is desired to deploy the tower in a specific site, preparation works need to be done according to the conditions of the site, including soil conditions. Said site preparation works are normally limited to shallow excavation (normally up to 50 cm), compaction of the natural soil bed and backfill with granular material compacted in two or three layers. Thus, the preparation works take only a short while. For permanent deployment, casting a thin, well-leveled layer of lean concrete on top of the compacted sub-base is preferable. The prefabricated slabs are then transported to the construction site, and rapidly assembled to form the finished foundation. The long bolts or connecting members  47 , washers  54 , nuts  45 , locking washers  50  and locking nuts  52  are assembled together and inserted into the recesses, holes and bores of slabs  40  of the bottom most layer (FIG.  5 ), from underneath the slabs while they are securely held at an appropriate height above the ground, before it is laid down in its final position. The middle and upper layers are carefully placed transversely over the preceding layers, while being laced onto the upwardly projecting long bolts or connecting members  76  (FIG. 7) and  90  (FIG.  8 ). When the top most layer is laid, securing nuts are applied and tightened onto the threaded top end portions of long bolts or connecting members  76  and  90 . Thereafter, the tower itself can be assembled, erected and secured onto said selected protruding long bolts or connecting members  90 . When it is desired to remove the tower and its foundation, this process can be reversed. Alternatively, if the tower site is permanent, recesses in top slab  40  are preferably filled with any type of grout material. 
     It will be appreciated that the invention is not limited to what has been described hereinabove, merely by way of example. Rather, the invention is limited solely by the claims, which follow.