GB2063327A - Compound earth anchor - Google Patents

Abstract

This may consist of a clamp, coupling, or head rigidly connecting together the shafts of earth anchoring mechanisms or components. Alternatively the shaft-connector may be an integral part of one or more of the shafts to which other shafts may be secured. In the anchor, each component shaft is maintained rigidly relative to other shafts. Each anchoring component may be an anchor of known type, and the compound anchor has accordingly enhanced resistance to extraction. <IMAGE>

Description

SPECIFICATION Load-bearing heads to connect the shafts of a plurality of earth anchors to form a compound earth anchor This invention relates to improvements in methods of and apparatus for anchoring and is particularly concerned with providing a compound anchor or an anchor comprising a plurality of anchoring mechanisms in earth or ground. Such anchors are commonly referred to as Earth Anchors and are used in many and varied applications. For example they can be used for holding guy ropes supporting a telegraph or electricity pole or to hold earth retaining walls or to anchor objects to the beds of shallow seas, or to support or retain other structures or objects against displacement.

Examples of methods of anchoring and the provision of improvements of methods of anchoring in earth or ground and descriptions of devices to provide the aforesaid improved methods of anchoring are embodied in British Patent Specifications Nos. 01471/77,22037/77, 14514/78,17591/78 and 26221/78.

Several factors may operate at a particular site at which a specified anchoring resistance is required to limit the depth below ground level to which a single earth anchor can be installed, and to the size of its anchoring area against which the restraining earth pressure will act. One such factor is the length of the anchor shaft which is practical and economic without introducing undue flexure during installation. Another factor is the penetrative resistance of the anchor mechanism preventing its easy installation especially when this is to be accomplished by manual methods.

It follows that where a required anchoring force cannot be achieved by a single anchoring mechanism then the required force may be generated by a plurality of mechanisms driven into the ground so as to utilise the resistance of a greater volume of earth than can be brought to bear against a single anchor, the ends of the separate anchor shafts or similar tensile members, remote from their penetrating ends being rigidly connected to a common anchor head, which will provide: a. The means for connecting the anchoring force to its point of application such as a tie rod or eye bolt or similar attachment.

b. An end restraint of fixed alignment relative to the longitudinal axis of the anchor shafts necessary in order to maximise their resistances against extraction, by acting either as simple cantilevered beams or as cantilevers also subject to restraints at their penetrating ends induced by their anchoring mechanisms.

It is an object of the present invention to provide a load-bearing head which shall connect together the anchor shafts or such load transmitting members of a plurality of earth anchors, installed in the ground in order that the combined resistance to extraction from the ground of the said anchors shall be communicated to the point of application of a required anchoring force.

The general principle of such a plurality of connected earth anchors is illustrated in Fig. 6 of British Patent Application Nos. 01471/77 and 22037/77, although the individual anchoring mechanisms to be connected by the load-bearing head to be described herein need not necessarily each operate by extended deformable flukes as illustrated in Fig. 6 but may instead, for example, comprise a plurality of straight or curved hollow or solid beams installed in the ground by percussion or augering or screwing in a penetrating end having a fixed or moveable helical bearing surface or surfaces.Furthermore the surface or surfaces of the beams exposed to the resistive reactions of the earth may either be an integral face or faces of the beams or may be extended additionally as either fixed or moveable flanges or vanes secured to the beams in order to increase the surface area of the mechanism against which the surrounding earth may bear.

According to one aspect of the present invention there is provided a method of producing a load-bearing head to connect together the shafts or similar load transmitting members of a plurality of earth anchors which comprise a metal cone or pyramid having radial guide-ways or groves formed in its conical or tapering surface to receive the ends of the anchor shafts remote from their penetrating ends. The ends of the anchor shafts are secured in the said guide-ways or groves by an enveloping conical or pyramidical metal cap secured to the cone or pyramid by a central bolt passing through the vertical axis of the cone or pyramid or by a series of bolts or similar fastenings passing through the cap and shaft ends and into the cone or pyramid.

According to another aspect of the present invention there is provided a load-bearing anchorshaft connecting head comprising two similar metal tetrahedra, having their bases adjoining and connected together by a bolt or similar straight fastening passing through their opposing apices.

An aperture or orifice is formed in each of the six tapering faces of the head each in such similar position in the faces as to form three mutually inclined holes or guideways connecting opposing faces of the head, each hole or guide-way being also tangential to the central connecting bolt and of such diameter or shape as to accommodate the shaft of one of the anchoring mechanisms. Each tetrahedron comprising the head may be formed either from a shaped metal plate or as a solid casting in which the three guide-ways are each semi-cylindrical. If the tetrahedra are formed from plates and are hollow their junction may lie in a single plane which is equi-distantfrom their opposing apices and at right-angles to the longitudinal axis of the connecting bolt.When the tetrahedra are formed as solid castings their junction must lie in three mutually inclined planes each including the longitudinal axis of one anchorshaft guide-way or hole and a diameter or crosssection of the guide-way, common to both castings. In both the plate or hollow head and the cast or solid head the tetrahedra are of such size as to cause them to rigidly secure the anchor shafts when the central connecting bolt or similar fastening is tightened, and the divided guide-ways are accordingly closed. Although a connecting head formed from two tetrahedrons has been described to rigidly secure the ends of three mutually inclined anchor shafts, it will be evident that similar heads formed from suitably divided parts capable of mutually securing a different number of shafts could be described and produced.

According to a preferred embodiment of the invention there is provided a load-bearing connecting head comprising four identical metal plates each provided with a central hole and with three slots each equal in width to the diameter or width of the anchor shafts. The axies of the said three slots form an equilateral triangle having the central hole in the plate at its centre. The size of the equilateral triangle is such that the projection of the inner sides of the slots are all tangential to the central hole of the plate and triangle. Each of the three slots extends from the edge of the plate to a point which is conditioned by the diameters or shape of the anchor shafts and the thickness of the plate and the range of angles in which the three anchor shafts may be mutually inclined to the plate.The inner end of each slot is also modified in size and shape in order that a second plate, when reversed or turned up-side-down will also contain three inclined anchor shafts in its slots when the shafts are mutually inclined to an unreversed identical plate. The reversed and unreversed plated will therefore lie together and are secured by a bolt or similar fastening passing through their coincident central holes and will form a single element by which the three anchor shafts will be constrained in position but not in angular relationship.If however a second element comprising a further two reversed and un-reversed plates is secured to the central bolt at some distance from the first element, and the three mutually inclined anchor shafts be also constrained by a corresponding slot in the upper element then the three anchor shafts will be constrained in a mutually angular position dependent upon the distance apart of the two constraining elements. The effect of drawing together the two elements by tightening the central bolt will be to rigidly lock together the three anchor shafts.

Although the preferred embodiment of the invention has been described for the connecting together of three mutually inclined anchor shafts it will be evident as stated heretofore that a greater number of anchor shafts could be connected together by a similar combination of suitably shaped plates arranged as restraining elements in pairs.

When ground or site conditions are such that the anchor shafts of only two anchoring elements are required to be rigidly connected together to provide a compound anchor having a sufficient strength, the end rigidity of the connection may be achieved either by directly bolting together the shaft ends or by providing a connecting head secured internally or externally to one or both shafts and also providing with either method, a tie rod or strut passing either through or around both shafts and secured to each so as to form with the apex connection at the ends of the shafts a rigid triangular or three-point connection whose tie or strut will also be available as an adjustable member of the compound anchor to which may be secured the load or force which the compound anchor is required to resist.Alternatively the ends of the two anchor shafts may be connected by either a single or compound gusset plate or plates secured to one anchor shaft either before or after the anchor has been installed in the ground, and to a sleeve tube or clamp, through which the second anchor is free to pass and to which the end of the shaft may be secured after the anchor has been installed in the ground.

Embodiments of the invention will now be described by way of example, reference being made to the accompanying drawings in which: Fig. 1 and Fig. 2 are respectively a plan view and a part-elevational and part-sectional view of an anchoring mechanism and shaft, which together comprise one form of one anchoring element of a compound earth anchor. The element included herewith by way of example and for ease of reference is in all respects similar in principle to the anchor described in British Patent Application No. 01471/77.

Fig. 3 is a part-elevational and part-sectional view of a cone and cap connecting head, and includes some examples of anchoring elements whose shafts are connected by the head and which are capable of resisting extraction from the earth, either 1, by web supported extended metal flukes or 2, as a simple inclined rigid bar or tube or 3 through fixed or moveable pressure plates or vanes secured to the anchor shaft and having a shape or shapes which will cause the shaft to be uniformly loaded throughout its length or which will otherwise maximise available earth resistance, or 4 by a screw anchoring element.

Fig. 4 is a plan view of the cone 5 with the cap 6 removed and showing the radial guide-ways 7 in.

which the anchor shafts are located.

Fig. 5 is a pictorial representation of a connecting head formed to connect the ends of three anchor shafts 1,2 and 3 by two tetrahedrons 4 and 5 formed either from shaped plates or from castings, and connected by a central locking bolt 6. The heavy continuous black line in the figure represents the outline, in pictorial representation, of the planometric shape of each of the tetrahedrons when formed from plates and bent about the line A-B, and C-D and E-F shown in Fig. 6 and the heavy broken lines in Fig. 5 represent the junction planes of the two tetrahedrons when cast and which also are shown at G-H and l-J and K-L in Fig. 6.

Fig. 6 is a planometric drawing of the configuration of a plate, prior to being bent along the lines A-B, and C-D and E-F to form a tetrahedral shell capable of accepting the three anchor shafts centred at 1,2 and 3. The Figure is also the envelope of a cast of a tetrahedron whose reverse image is joined to it along planes passing through the lines G-H and l-J, and K-L.

Fig. 7 is an elevational view of the preferred embodiment of the invention heretofore described in which the configuration of the plate 1 is shown in plan at Fig. 8 in heavy black continuous line.

The geometrics leading to the configuration of the plate are also included in Fig. 8. A second plate, identical with plate 1 is shown at 2 in Fig. 7 by broken or pecked lines when turned up-side-down and is also shown in plan by similar pecked lines in Fig. 8, the said pecked lines being slightly offset from those defining plate 1 for reasons of clarity.

The coincident central bolt holes in both plates is shown at 3. The unreversed plate 1 and the reversed plate 2 when secured together by the bolt 4 form one element by which the three inclined anchor shafts 5, 6 and 7 are constrained in position. The second anchor tube constraining element of the connecting head comprise the unreversed plate 8 and the reversed plate 9 also secured together by the central bolt 4 at a distance "D" from the first element of the head.

The three mutually inclined anchor shafts 5, 6 and 7 are shown in Figs. 7 and 8 by the same form of broken line in both Figures. The effect of drawing together the two constraining elements 1 and 2 and 8 and 9 of the head by tightening the central bolt 4 is to secure in position and inclination the three anchor shafts 5, 6 and 7.

Figs. 9 and 10 are respectively a part-plan, part-section and an elevational section of one method of providing a connecting head for two anchoring elements whose shafts 1 and 2 are connected by a head and spigot 3 secured to the anchor shaft 1 and capable of restraining shaft 2 when installed in the ground within the angular range 0. The tie-bar 4 passing through the anchor shafts 1 and 2 and secured by the screw-threadec quadrant 5 and the locking nut 6 complete the head connection.

Figs. 11 and 12 are respectively a part-plan, part-section and an elevational section of an alternative load-bearing head connecting together the ends of two earth anchor shafts 1 and 2. The head comprises a bar 3 which passes into the shaft 1 and is secured within the shaft by the tierod 4 after both anchors 1 and 2 have been installed in the ground. The bar 3 also lies against the outer face of shaft 2 to which it is also secured by the tie-rod 4 which passes through elongated holes in the bar 3 and the shafts 1 and 2 and is secured by the quadrant block 8 and the lock-nut 9. The tie-rod also passes through a spacing sleeve 10 inserted between the shafts 1 and 2. A metal thrust block 11 is inserted between the bar 3 and the end of shaft 2 and if necessary a bearing plate or sleeve tube 12 is added to shaft 1 against which the quadrant 8 can bear.The tie-bar 4 being screw-threaded and adjustable in length is available after being locked to the connecting head to transmit the anchor resistance P to the required point of application of the force.

Figs. 1 3 and 14 are respectively a plan and elevational section of an alternative load-bearing head connecting together the ends of two earth anchor shafts 1 and 2 and comprises a "U" shaped gusset or cleat 3 passing around shaft 1 and secured to the shaft by the tie-rod 4. The two arms of the "U" gusset plate are welded or otherwise permanently secured to a guide tube 5 through which the shaft 2 is free to pass. The guide tube 5 and anchor shafts 1 and 2 are provided with elongated holes through which the tie-rod 4 may pass thereby securing shaft 2, when driven into the ground, to the guide-tube 5. The "U" shaped gusset plate is also provided with a welded bottom stiffening plate 6 which also acts as a bearing plate for shaft 1 if necessary and as protection for the tie-rod screw thread. The anchor resistance is transmitted by the tie-rod 4 screwthreaded to the quadrant block 7 which bears against the base of the "U" gusset 3.

Claims (9)

1. A method of producing an earth anchor which comprises the steps of installing into the ground a plurality of earth-anchoring components, or mechanisms, each of which includes at least a rigid anchor shaft and the capability of imposing a compressive force or resistance upon the ground mass in contact with, or adjacent to, the component in order that the component shall resist extraction from the ground mass, the ends of the anchoring component shafts, remote from their penetrating ends, being connected to, and restrained by, a coupling or clamp or single or multiple slotted guide head or similar mechanical device so arranged as to enable the separate anchoring components to mutually maximise their resistances to extraction from the ground mass and to transfer these resistances to a common point of application of an external extractive force applied to the coupling or head.

2. A method according to Claim 1 in which the end of each anchoring component shaft, remote from its penetrating end, is secured in position and direction relative to the position and direction of the other connected shaft or shafts by being rigidly clamped within split guide-ways provided in the coupling or head, the parts of the head forming the guide-ways being held together by one or more screws or bolts or similar fastenings.

3. A method according to Claim 1 in which the end of each anchoring component shaft, remote from its penetrating end, is located in position and direction relative to the position and direction of the other connected shaft or shafts by one or more slots or guide-ways formed in the head through which the anchor component shaft or shafts may pass and within such slots or guide-ways the shaft or shafts may thereafter be fixed by locking nuts or pins or similar means.

4. A method according to Claim 1 in which the directions and positions of a plurality of anchor component shafts, mutually inclined to, and mutually touching, in a common plane near to their ends remote from their penetrating ends, are maintained by sets of metal plates, preferably all similar and reversible and interchangable, each set being shaped to engage with, and to secure, the plurality of anchor component shafts at points where the shafts are converging towards, and diverging from, their common plane of inclination and contact, the sets of plates being thereafter locked together and upon the shafts by means of a bolt or bolts or similar fastenings connecting the sets and to which an extractive force may be applied.

5. An anchoring device being a clamp or head which may be either integral with, or attachable to, a plurality of earth anchoring components each of which comprises at least a rigid anchor shaft whose position and direction relative to the position and direction of an adjacent attached shaft or shafts is rigidly maintained by the device and to which an external force to be resisted by the combined anchoring components can be applied.

6. An anchoring device according to Claim 5 in which the ends of each anchoring component shaft remote from its penetrating end is located in position and direction within split guide-ways provided in the head, the split parts of the head being held together by means of one or more screws or bolts or similar fastenings.

7. An anchoring device according to Claim 5 in which the ends of each anchoring component shaft remote from its penetrating end is located by one or more slots or guide-ways formed in the device through which the anchor component shaft or shafts may pass and within which each shaft may thereafter be fixed by locking nuts, or pins, or similar means.

8. An anchoring device according to Claim 5 in which the directions and positions of a plurality of anchor component shafts, mutually inclined to, and mutually touching in a common plane near to their ends remote from their penetrating ends, are maintained by sets of metal plates preferably all similar and reversible and interchangeable, each set being shaped to engage with, and to secure, the plurality of anchor component shafts at points where the shafts are converging towards, and diverging from, their common plane of inclination and contact, the sets of plates being thereafter locked together and upon the shafts by means of a bolt or bolts or similar fastenings connecting the sets and to which an extractive force may be applied.

9. An anchoring device constructed, arranged and adapted to operate substantially as herein described and illustrated.