GB2115856A - Earth Anchor - Google Patents

Abstract

This is of the type having anchoring element(s) 4 which on being driven down a hollow shaft 2 with an earth-penetrating head 3, and out through an opening 6, in shaft 2, or formed by shaft 2 and head 3, is deflected and deformed to form an anchoring fluke. The initial insertion forces necessary for the deformation are reduced by a reduction in the member's cross- section towards its leading end. The element may also have a portion of reduced cross-section between its strongest, intermediate portion and its trailing end to reduce the final insertion forces required for deformation. <IMAGE>

Description

SPECIFICATION Improvements in or relating to earth anchors This invention relates to improvements in or relating to earth anchors.

An earth anchor is known which comprises a hollow shaft to be driven into the ground or earth, a penetrating head at the leading end of the shaft, a deflecting surface arranged for the purpose of deflecting an anchoring element driven relative to the shaft, and an anchoring element initially having a configuration to be received within the hollow shaft and which on being driven through an opening in the shaft, or formed by the shaft and the earth penetrating head, is deflected to form an anchoring fluke. Such an earth anchor is hereinafter referred to as "an earth anchor of the type herein defined".

One prior art earth anchor of the type herein defined has an anchoring element or elements (often anchor elements are installed in diametrically opposed pairs) which, apart from a penetrating tip portion, has a uniform cross-section and the material from which the anchoring element is formed is homogeneous in composition. Thus, with respect to bending or deforming the anchoring element to form an anchoring fluke, the elastic modulus of the anchoring element is substantially constant along the length of the anchoring element. In consequence, the initial forces, which are required to drive the anchoring element through the opening and to commence bending of the element, are much higher than at subsequent stages in the driving and bending of the anchoring element.In practice, much greater resistance to the driving of the anchoring element is experienced in the initial stages of installing the anchoring element in the earth or ground, than the later stages.

One method of bending a straight bar of substantially constant elastic modulus throughout its length into a curved form of substantially constant radius is to force it lengthways through a series of three deflecting surfaces comprising two outer ones bearing upon one side of the bar and an intermediate one bearing upon the diametrically opposite side, so positioned normal to the axis of the bar at a distance from that axis that the bar cannot pass through the series without assuming a curved form. The deformation of the bar into a curved form is achieved by the imposition of bending moments of such magnitudes as to produce stresses in the material of the bar beyond the yield point of the material of which it is made.

With such a series of deflecting surfaces it is believed that the maximum bending moment exerted upon the bar is at or near the point of contact between the bar and the intermediate deflecting surface. The force normal to the axis of the bar required to produce deformation is related to the distance between the outer deflecting surfaces and to the position of the intermediate deflecting surface relative to the outer deflecting surfaces. It is also believed that the situation in which a required bending is achieved by the least pressure upon the intermediate deflecting surface is when that surface is midway between the outer deflecting surfaces. The force required to bend the bar increases progressively as the intermediate deflecting surface is moved to approach one or other of the outer deflecting surfaces.The friction resisting movement lengthways of the bar through the series of deflecting surfaces is dependent upon the forces required to bend the bar, and is thus related to the relative positions of the deflecting surfaces.

To equate the mechanism of an earth anchor of the type herein defined with the series of deflecting surfaces previously described, the one outer deflecting surface is represented by that part of the inside of the shaft tube wall or the corresponding end of another element if it is one of an opposed pair which restrains that part of an anchoring element remote from its earth penetrating end. The second outer deflecting surface is the deflecting surface at the earth penetrating end arranged to deflect the anchoring element outwardly through its associated opening in the tube wall or an opening defined by the tube wall and the earth penetrating point of the anchor. This deflecting surface may continue externally of the tube or be reintroduced as a continuation in the form of an external support to the anchoring element.The intermediate deflecting surface is represented by the inner surface of the shaft tube wall above the slot through which the anchoring element emerges.

The distance apart of the outer deflecting surfaces remains constant as the anchoring element is driven downwards for as long as the anchoring element is supported at both ends, but the intermediate deflecting surface, which is close to one outer deflecting surface at the commencement of driving, will move towards a central position relative to the outer deflecting surfaces as driving progresses, thereby reducing the amount of force required to bend the bar if it is of constant elastic modulus throughout its length.

In one aspect the present invention seeks to provide an improved earth anchor which is designed to reduce the driving force required for driving the anchoring element to form an anchoring fluke, and which thereby provides an earth anchor far more readily and easily installed.

According to one aspect of the present invention there is provided an earth anchor of the type herein defined in which the anchoring element is adapted towards its leading end to reduce the initial insertion forces necessary to produce an anchoring fluke.

The invention encompasses an earth anchor in which the anchoring element is of reduced cross-section towards its leading end.

The anchoring element may also be of reduced cross-section between its trailing end and its strongest, intermediate section thereby to reduce the later insertion forces necessary to produce the anchoring fluke of required form.

Tests have established that an anchoring element so adapted requires lower applied force at the initial stages (and final stages in the case of an element according to the immediately proceeding paragraph) of driving and bending.

If the modulus of the anchoring element is selectively weakened, for instance in a direction towards its trailing end from its strongest intermediate part as mentioned in the two immediately preceeding paragraphs, bending of the element can be made to occur at positions along its length other than that in contact with the intermediate deflecting surface. By this means an anchoring element which is in part stronger in resistance to bending than the strongest section which could be bent by the mechanism of the anchor, even when the element is in its most favourable position for bending, can be made to pass between the deflecting surfaces.

Considering the known earth anchor, the anchoring element in its final position forms a cantilever, notionally uniformly loaded when an extractive load is applied to the anchor.

The maximum bending moment exerted by an extractive force occurs at the outer-most point of support for the element, this being the wall of the anchor tube of the extremity of any external support provided. From this point in both directions along the length of the element the bending moment decreases. However, with the known element of constant cross-section, it has to be so dimensioned that its elastic modulus is limited to a value which, at all stages of installation, enables it to be deformed to the required curvature of an anchoring fluke. According to the invention the element may be progressively weakened from this point without detriment to the magnitude of extractive force which the element as a whole will resist without bending.

Thus, an embodiment of the present invention provides an improved earth anchor which is designed to reduce the driving force required to drive and deform an anchoring fluke and to provide improved resistance to extractive forces.

Further, according to the present invention there is provided an earth anchor of the type herein defined in which the anchoring element is adpated to be preferentially deformable in the direction of bending to form an anchoring fluke.

The invention also encompasses an earth anchor in which the anchoring element is so constructed at a portion thereof rearwardly of its leading end, as to be preferentially deformable in that portion with respect to the direction of bending required to provide an anchoring fluke.

The invention also encompasses an earth anchor in which the anchoring element is formed of material of heterogeneous composition, such that a portion thereof rearwardly of its leading end is preferentially deformable with respect to the direction of bending required to provide an anchoring fluke.

The invention also encompasses an earth anchor in which the anchoring element is adapted to exhibit a preferential tendency to bend in the direction of bending required for forming an anchoring fluke by virtue of selective treatment of the anchoring element. Such selective treatment will alter the physical and mechanical properties of the anchoring element at selected locations thereon. Such treatment may include hardening and tempering the anchoring element.

The invention also encompasses an earth anchor in which the anchoring element has a combination of two or more of the features of the preceding paragraphs.

Many earth anchor are required to withstand an extractive force applied at an angle of elevation which is less than vertical, hereinafter referred to as an oblique loading. Nevertheless it is often advantageous to install an earth anchor vertically rather than with its axis coincident with the direction of the oblique loading.

A preferred embodiment of the invention provides an earth anchor designed for oblique loading at an angle of 15 to 45 to its axis.

This anchor is provided with additional strengthening webs extending outwardly from side walls of its hollow shaft, these side walls being those which join side walls in one or both of which there is a said opening for the emergence of an anchoring element.

An earth anchor according to the invention may also be provided with a ground bearing plate or plates of flexible material, wider than the anchoring element or elements, and associated with the or each element. Such plates are held external to and parallel with the anchor shaft during installation of the anchor in the ground by means of guides or brackets attached to the anchor shaft or its associated side webs, and after the anchoring fluke elements have been driven to their final position the plates are driven downwardly to adopt the configuration of the anchoring fluke or flukes and to lie immediately above them to increase their ground bearing area and resistance to movement through the ground under extractive loading.

Embodiments of the invention will now be described, by way of example only, with refer ence to the accompanying drawings, in which: Figure 1 shows a perspective elevation of an earth anchor; Figure 2 shows double anchoring element prior to installation; Figure 3 shows another embodiment of part of an anchoring element and, in section, part of the other anchor components, with the anchoring element illustrated before and after driving thereof; Figure 4 shows a side elevation of part of another embodiment of a ground anchor according to the invention with an anchoring element similar to that of Fig. 3; Figure 5 is a front elevation of the anchor of Fig. 4; Figure 6 is a rear elevation of the anchor of Fig. 4; Figure 7 is a view from below of the anchor of Fig. 4; Figure 8 is a view similar to that of Fig. 4 showing a means for driving the groundbearing plate;; Figure 9 is a front elevation of the anchor of Fig. 8; Figure 10 is a perspective view of part of a tool for facilitating the installation of a groundbearing plate of Fig. 4.

In Fig. 1 there is shown an earth anchor 1, which comprises a hollow shaft 2 of rectangular cross-section which has been driven into the ground or earth. A penetrating head 3 is attached to the leading end of the shaft 2.

The penetrating head 3 projects upwardly within shaft 2 and is provided internally of the shaft with a deflecting surface 5 (not shown) arranged for the purpose of deflecting an anchoring element 4 driven relative to the shaft 2. A double anchoring element 4 initially has a configuration to be received within the hollow shaft 2. On being driven through an opening 6 in the shaft 2, the anchoring element 4 is deflected to form an anchoring fluke. This embodiment illustrates a pair of anchoring elements 4 (formed initially as a single component as illustrated in Fig. 2) which are installed in diametrically opposed positions and which have reduced penetrating tip portions 7.

By virtue of the cross-section of the elements 4 (which, as will be described with reference to Fig. 2, diminishes towards the tip portions 7), the initial bending or deforming of the anchoring element 4 to form an anchoring fluke is accomplished more readily than if the anchoring element had a uniform crosssection of its largest section. In consequence, the anchoring element 4 may be more readily bent outwards and driven through the opening 6 in the hollow shaft 2 to commence bending of the anchoring element 4. At this initial driving stage, the anchoring element 4 is constrained by the other earth anchor components. The broken lead line 5 indicates the approximate location of one deflection surface 5 within the shaft 2 (see also Fig. 3). The other deflection surfaces are within the tube 2 and may be appreciated by viewing the points marked 8, 9 of Fig. 3.In this case point 9 is in contact with the lower surface 4a of the limb 4. The relative expressions 'lower surface' and 'upper surface' relate to the respective surfaces 4a, 4b of the anchoring element 4 when it adopts the configuration of an anchoring fluke. An anchoring fluke extends from an earth anchor 1 by which it is supported in cantilever manner and curves upwardly thus exhibiting 'upper' and 'lower' surfaces. The deflecting surface 8 is provided internally of the hollow shaft 2 and as driving proceeds moves closer to the upper extremity of the opening 6 through which the anchoring element 4 emerges. The lower deflecting surface 5 is provided by the deflecting head within shaft 2 which the leading end 7 of the anchoring element 4 contacts when fully advanced within the hollow shaft 2 and before driving commences.During initial driving of the anchoring element 4 deformation or bending of the anchoring element 4 occurs due to the constraints applied at just these points 5, 8 and 9. The spacing between these points is important and the configuration of the element 4 allows the initial position of the point 8 to be well within the shaft 2. This reduces the initial driving forces required. When the anchoring element 4 is advanced sufficiently, the anchoring element 4 extending through an opening 6 in the hollow shaft 2 also contacts and follows a deflecting surface 1 9 of a support web 10. Since this embodiment has double anchoring elements 4, a pair of oppositely directed support webs 10 extends radially outwardly of the penetrating head 3.

The embodiment of Fig. 1 provides an earth anchor 1 designed for oblique loading at angles 15 to 45 to the axis of the hollow shaft 2. For this purpose the upper end 1 2 of the hollow shaft 2 is provided with a coupling bracket 1 3. As shown, bracket 1 3 is substantially U-shaped and may be fixedly connected to shaft 2 e.g. by bolting or welding. It has a surface 14 disposed to co-operate with a plate 15 of a load attachment means 16. Load attachment means 1 6 comprises the forged steel eyebolt 17, the plate 1 5 and a pair of locking nuts 1 8. The load is represented by the cable 1 7a.In order to provide further resistance to the pull of extractive forces on the cable 1 7a (in addition to the extractive resistance of the flukes 4), the hollow shaft 2 is provided with strengthening webs 21 (only one of which is seen in Fig. 1). Webs 21 extend outwardly from the side walls 22 of the hollow shaft 2. Side walls 22 interconnect side walls 23. An opening 6 is provided in each of the side walls 23 for the emergence of the anchoring elements 4. A pair of oppositely directed strengthening webs 24 on the penetrating head 3 are aligned with the webs 21.

As already mentioned the double anchor elements 4 of Fig. 2 are designed to reduce the driving force required at the initial and later stages of driving the anchor elements.

The penetrating end 7 of each anchoring element 4 adjoins a portion 25 of a configuration tapering towards it penetrating end which adjoins a portion 26 tapering away from its penetrating end, with intermediate portion 27 of maximum lateral dimension in between.

Portion 25 is about one third the length of portion 26. The thickness of the portion 25 (i.e. the lateral dimension of surface 4c) increases from its junction with penetrating end 7 to its junction with portion 27.

Portions 26 are of rearwardly reducing thickness. It will be seen that the opposed surfaces 4a in the region of the junction 27 of portions 25, 26 abut. This is achieved by presing after the contour of surfaces 4a is determined, for example by flame cutting. The width of the elements 4 (i.e. the lateral dimension of surfaces 4a, 4b) is constant.

In respect of the anchoring element of Fig.

2, one practical embodiment has a length of 45cm and is formed from a bar having a width of 4.8 cm at its leading end tapering to 4cm at its trailing end. This is slotted from the penetrating end to form the penetrating edges and to form the portions 25, 26. The portions 27, now separated by a gap of 8 cm and intermediate the portions 25, 26 of each limb, are then pressed together. Portions 27 have a width of 2 cm each. Portion 25 is tapered internally over a length of 10 cm from the intermediate portion where it has a width of 2 cm down to 1.2 cm at a location 5 cm from the end of the penetrating edge, this taper continues to the point where the penetrating edge is rounded. Portion 26 is tapered rearwardly of the portion 27 from a lateral dimension 2 cm down to 1.6 cm.

In the embodiment of Fig. 3 the earth anchor 1 is shown partially with the anchoring element 4 (in full line) within the shaft 2 prior to driving and the anchoring element 4 (in broken line) extending from the shaft after driving. In this embodiment portion 25 of the anchoring element 4 has a taper such that the lateral dimension of surface 4c diminishes from the junction with portion 27 towards the leading end 7 (for similar reasons as the tapering of portion 25 in Fig.2). The 'lower' and 'upper' surfaces 4a and 4b respectively in the portion 25 are curved 'convexly' and 'concavely' respectively to enable the element 4 to pass through the opening 6 with little bending. The anchoring element 4 is also preferentially deformable in the region of a portion 30.Portion 30, which is interposed between portions 27 and 26, enables by virtue of its reduced thickness, the curvature of the element 4 to form an anchoring fluke to be accomplished more readily; a substantial part of the bending taking place in this portion 30. At the same time, portion 27 which is at the shaft end of the fluke (when driven) is of maximum thickness and provides greater resistance to the extractive forces acting on the cable 19 (Fig. 1). The portion 26 has a cross-sectional area almost as great as the internal dimensions of the shaft tube 2 to provide a striking surface for a ramrod used to drive the element 4 downwardly and to locate the rearward end of the element 4 in the tube 2 when driven to its final position. Deflecting head 20 having deflecting surface 5 and located within the shaft 2 can be seen in Fig.

3.

Referring to Figs. 4 to 7 there is shown a ground anchor 40 as if in position in the ground. It comprises a hollow shaft 2 and penetrating head 3 generally similar to those previously described and an anchoring element 4 generally similar to the one described in relation to Fig. 3 and driven to its final position. Further explanation of this part of the anchor is unnecessary.

In addition, there is provided a groundbearing plate 42 shown in full lines in Fig. 4 in the position it takes substantially parallel to the shaft 2 while the anchor 40 is being driven into the ground. The plate 42 is maintained in this position during installation of the anchor by means of brackets 44 fixedly secured as by rivets or screws 46 to two side webs 48 which increase the surface area of the anchor.

After the anchoring fluke 4 has been driven to its final position as shown in Figs. 4 to 7, the plate 42, which is easily deformable relative to the fluke 4, is driven downwardly guided by brackets 44 so that its tip 42a generally follows the curve 4b of the fluke 4 and the plate 42 adopts a configuration as shown by the broken line in Fig. 4.

Figs. 8 to 10 show one means of driving the plate 42. A pile driver 46 terminates at its lower end in a plate 50 having a recess 50a dimensioned to receive the upper end of the plate 42; the end 46a of the rod 42 extending over the recess a short distance so that the end of the plate 42 is received therebetween. The other end of the pile driver 46 is provided with a head 48. In use when the fluke has been driven downwardly by hammer blows applied to the head 48. When the plate is positioned as shown by the broken line in Fig. 4, the pile driver 46 can be removed for re-use.

The plate 42 being of greater superficial area than surface 4b of the anchoring fluke 4 provides a greater resistance to extractive forces applied to the anchor.

While the embodiments of the invention as described with reference to Figs. 3 to 10 have been shown with a single anchoring element, they can, of course, be provided with more than one, for example, two diametrically opposed elements in a similar fashion to the embodiment of Figs. 1 and 2.

The elements 4 disclosed in relation to the drawings have been provided with portions of reduced cross-section which reduce the force required to drive them into position and deform them to their final shape. Alternatively, or additionally, the elements may be formed of a material of heterogeneous composition or a material which has been selectively treated, for example as by hardening and tempering, whereby its resistance to bending at selected portions along its length is reduced.

Claims (11)

1. An earth anchor comprising a hollow shaft to be driven into the ground or earth, a penetrating head at the leading end of the shaft, a deflecting surface for deflecting an anchoring element driven relative to the shaft, an anchoring element having an initial configuration to be received within the shaft and which on being driven down the shaft and out through an opening in the shaft, or formed by the shaft and the earth penetrating head, is deflected to form an anchoring fluke, wherein the anchoring element is adapted to reduce the initial insertion forces necessary to produce an anchoring fluke.

2. An earth anchor according to claim 1, wherein the anchoring element is of reduced cross-section towards it leading end.

3. An earth anchor according to claim 1 or 2, wherein the cross-sectional area of the anchoring element is progressively reduced in a direction along its length from an intermediate portion to its leading end.

4. An earth anchor according to claim 3, wherein the anchoring element is so formed that the portion of progressively reduced cross-section has a convex 'lower' surface and a concave 'upper' surface.

5. An earth anchor according to claim 1, 2, 3 or 4, wherein the anchoring element is of reduced cross-section between an intermediate portion and its trailing end.

6. An earth anchor according to any one of the preceding claims, wherein the anchoring element is adapted to be preferentially deformable in the direction of bending to form an anchoring fluke.

7. An earth anchor according to claim 6, wherein the anchoring element is formed of a heterogeneous material, such that at least one portion is preferentially deformable in the direction of bending.

8. An earth anchor according to claim 6, wherein the anchoring element is adapted to exhibit a preferential tendency to bend in the direction of bending required for forming an anchoring fluke by selective treatment of the anchoring element.

9. An earth anchor according to claim 8, wherein said treatment comprises hardening and tempering.

10. An earth anchor according to any one of the preceeding claims further comprising at least one elongate web extending outwardly from said shaft to provide additional resistance to movement of the anchor in the ground at an angle to its axis.

11. An anchoring element according to any one of the preceding claims, further comprising a ground bearing plate member of deformable material and having a superficial area greater than that of said anchoring element, means for slideably supporting the plate member above said opening, substantially parallel to and externally of the shaft while the shaft is driven into the ground and means for driving the plate downwardly so that its distal end contacts and follows the upper surface of the anchoring fluke towards the tip of the fluke and the plate when installed in position lies over the upper, external surface of the fluke.

1 2. An anchoring element substantially as herein before described with reference to and as illustrated in Figs. 1 to 3 or Figs. 4 to 7 or Figs. 4 to 7 with Figs. 8 to 1 0.