GB2089862A

GB2089862A - Ground Anchors

Info

Publication number: GB2089862A
Application number: GB8040504A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-12-18
Filing date: 1980-12-18
Publication date: 1982-06-30

Abstract

An anchoring device comprises a curved pressure resistant plate which is attached to a load- transmitting flexible tendon 14 and is driven into the ground by a shaft 9 at the penetrating end of which is a mechanism connecting to the plate 1 by one or more arms 5. The arms 5 are hinged to the plate at their penetrating or leading ends 6 and have a pivot pin 7 slidably mounted in slots 10 formed at the penetrating end of the shaft 9 or in an extension 8 thereto. During the initial driving of the device the arms 5 are constrained in the slots 10 and the plate 1 is locked in a position of minimum resistance to penetration by a tapered mandril 11/12 operable within the shaft 9, after the initial driving the said mandril is withdrawn from its position 12 within the shaft 9, thereby unlocking the plate 1, and is re-inserted in the shaft 9 in the position 11 in which a tapered leading end engages with the angled edges of the arms 5. The shaft 9 may thereafter be sufficiently withdrawn to release the hinge-pin 6 from the slots 10 and the mandril used to actuate the arms 5 and cause the plate 1 to move into an operating attitude substantially normal to the penetrative axis. <IMAGE>

Description

SPECIFICATION Improvements In, or Relating To, a Method of, and Apparatus for Anchoring This invention relates to improvements in methods of and apparatus for anchoring and is particularly concerned with providing an anchor in earth or ground whose surface, or near-surface, layers have little internal cohesive strengths or permanent stability. Such anchors are commonly referred to as Earth Anchors and are used in many and varied applications. Examples of the uses to which the present invention may be put include the securing of stay-ropes, or guys, supporting masts or pylons or telegraph or electricity-supply poles, or to secure earth retaining walls, or in permanent anchoring installations below the bottom of seas.

An object of the present application is to describe a method of and apparatus whereby the principle of movement of earth-pressure resisting surfaces along pathways of minimum resistance to movement of the surfaces within an earth mass may be used, with advantage, to locate an earthpressure resisting plate or surface within an earth mass in a position such that it will maximise its resistance to displacement or extraction from the mass by a force acting on the plate or surface after its initial installation into the mass; and means whereby the plate or surface may be connected to the extraction force applied at, or above, the ground surface of the mass, for any depth of installation or positioning of the plate or surface.

In localities where the surface layers of the earth possess a sufficient internal cohesive strength to enable them to resist the extraction of an anchoring mechanism, subject to an applied extractive force, the depth to which the mechanism need be installed into the earth mass will be small in relation to the effective size or dimensions of the flukes or similar earth-resisting surfaces of the mechanism. Moreover the surfaces which may be either rigid or flexible or deformable can be easily connected to the extractive force applied at the ground level of the earth mass by a rigid bar or tube or the like, forming a part, or parts, of the anchoring mechanism, and available for its initial installation into the earth mass.

It will frequently happen however that the surface or near-surface layers of an earth mass lack either a required internal cohesive strength or a long-term stability needed to resist the extraction of an embedded anchor, by an applied force. Such cases may occur for example in regions of peats, or saturated clays, or volcanic tuffs, or in the mantles of sea-bed sediments, or, in general, where the ground layers are liable to unpredictable variations of strength or stability which would necessitate earth-pressure resisting plates or surfaces of an impractical or uneconomic size.

In such situations it follows that anchoring mechanisms must be installed in stable strata underlying the surface mantles and therefore at depths which may be great, relative to the effective dimensions of the plate, or similar earthpressure resisting surface, of the mechanism.

When an anchor is required to operate at a depth within an earth mass which precludes its installation by an effort applied to its mechanism from above ground surface level, as, for example, by the screwing or hammering or driving in of an anchor shaft, the anchor mechanism may be installed by a pneumatically operated mechanical mole, or similar earth-penetrating appliance. After installing the anchor the mole may be retracted from the earth mass, leaving the anchor connected to the ground surface by a wire or flexible tendon attached to the anchor before its installation.

Additionally, following the initial installation of the mechanism into the earth mass, the mole, or similar earth penetrating appliance, may be used to cause the earth-pressure resisting plate or surface of the mechanism to move into a position of maximum resistance to extraction, along a pathway of least resistance to movement within the mass, and carrying with it the attached flexible tendon, before detaching the plate and tendon from the mechanism which is thereafter free to also return to the ground surface level, leaving only the positioned plate and tendon and attachment within the earth mass.

The anchoring mechanism of the present invention comprises an earth-pressure resisting surface or plate which may be of any configuration and area attached to a slideable component of the mechanism relative to which the plate is also free to rotate. A tendon to communicate an extractive force is also attached to the pressure plate or to a linkage member of the associated mechanism. During the initial installation of the mechanism to its operating depth within an earth mass the pressure plate is constrained in a position relative to the direction of installation which will cause it to generate a minimum resistance to movement in the said direction of installation.

After the mechanism has reached its operating depth the pressure plate and its attached tendon are caused by the slideable and rotational components of the mechanism to move along a pathway of minimum resistance to movement and into a position such that the resultant resistance to earth pressures acting over the surface of the plate is coincident with the directional axis of an extractive force.

According to one aspect of the present invention, in which the pressure plate is to operate at a depth within an earth mass at which it can be installed by means of a shaft or tube, there is provided an anchor mechanism comprising a plate or bearing surface which forms an arc of a circle having a radius 'R' such the rise 'd' of the arc above its chord of length '2L' or, otherwise expressed, the distance 'd' between the crown of the arc and the mid-point of the chord, is equal to the breadth 'b' of the shaft, or tube. From the aforesaid circular arc form of the pressure plate it follows that it will be an arc of a circle having a radius 'R' equal to b2+L2 2d The curved pressure plate is stiffened by a central web whose shape may approximate to that of a truncated minor segment of a circle of radius 'R' and chord length '2L'.Alternatively the pressure plate may be stiffened by two such webs parallel to, and equi-distant from, the central circumferential, axis of the plate.

The pressure plate is linked to the shaft of the mechanism by activating connecting arms, pinjointed at their leading ends to the plate-stiffening web or, alternatively, by a central actuating connecting arm pin-jointed between parallel plate-stiffening webs. The arm or arms are also connected to the mechanism shaft, or to an extension thereof, by a pin-joint which, in addition to being rotational, is also free to slide relative to the shaft and in the direction of the longitudinal axis of the shaft.

The actuating connecting arm or arms are so shaped as to rotate about the pin-jointed slidable connection to the mechanism shaft when engaged by a ramrod slidable within, and driven along, the shaft.

A load-transmitting tie or rod or flexible tendon is also connected either to the joint connecting the actuating arm or arms to the pressure plate or to the slidable pin-joint connecting the actuating arms to the mechanism shaft.

A ramrod having a wedged or chisel-shaped leading end is free to slide within the mechanism shaft or tube, and to be inserted in reversed positions or, otherwise expressed, in positions which vary by 1 80 degrees in order that its tapered end may either bear upon the convex side of the curved pressure plate during the initial installation of the mechanism into an earth mass, or thereafter be withdrawn from the mechanism shaft and reversed through 1 80 degrees and reinserted into the shaft so that its tapered end will bear upon the following edges of the plate stiffening web or webs, and upon the activating connecting arms or arm.

Embodiments of the invention will now be described by way of example reference being made to the accompanying drawings in which Fig. 1 is a part-sectional, part-elevational view of an anchoring device according to the present invention, the solid lines showing the device when in its position of initial installation into an earth mass and the pecked lines showing the position of the curved pressure plate and web and attached activating connecting arms and loadtransmitting tie or flexible tendon after these parts of the mechanism have been moved into their operating positions.

Fig. 2 is a side-elevational view of Fig. 1.

Fig. 3 is a plan view of Fig. 1.

Fig. 4 is a perspective view of the anchoring mechanism when in its position of initial installation into an earth mass.

The anchoring device illustrated in Figs. 1--4 comprises a rigid curved earth-pressure resisting plate 1 which is stiffened by a central web 2, the web having a chord length approximately equal to that of the curved pressure plate 1, and being extended towards the centre of curvature of the pressure plate, the said extension forming, for example, a triangle or trapezium having a base length also approximately equal in length to that of the chord of the curved pressure plate. With advantage the leading edge of the stiffening web extension may be provided with a cutting edge 3, and the pressure plate with a tapered leading end 4 to facilitate their passage through the earth mass.

The web 2 is hinged by the pin 6 to the penetrating or leading ends of activating connecting arms 5 which may, with advantage, also be provided with cutting edges to facilitate their passage through an earth mass. The pin 6 is of sufficient length to enable it to engage in and be retained by the slots 10 formed in the plates 8 which are securely attached to the mechanism shaft 9, the said slots 10 being open-ended at their penetrating or leading ends.

The ends of the activating connecting arms remote from their penetrating, or leading, ends are also hinged by the pin-joint 7 within the slots 10, the pin 7 also being attached to a loadtransmitting rod or flexible tendon 14, by the connecting attachment 13.

Each activating connecting arm is provided with one edge forming an angle with the line joining the centres of pin 6 and pin 7 and of such length that the edge may form a minor chord within the arc of the curved pressure plate 1, when the pins 6 and 7 are both engaged in the slots 10 during the initial penetration of the mechanism into an earth mass, the pressure plate itself being held in a position where its principal chord is parallel to the longitudinal axis of the mechanism shaft 9 by the ramrod 11 having its tapered leading end 12 engaged with the convex curved surface of the pressure plate, the ram-rod 11 and the mechanism shaft 9 being locked together by means of a pin or similar attachment removable from above ground level after the initial installation of the mechanism.

It will be apparent that when the pins 6 and 7 are engaged within the slots 10 formed in the plates 8 and the principal chord of the curved pressure plate 1 is either coincident with or parallel to the longitudinal axis of the mechanism shaft 9 the mechanism will be in a position which will present a minimum resistance to the penetration of the mechanism into the earth mass.

After the mechanism has been installed to its operating depth the locking pin or similar device operable from above ground level and which connects the ram-rod 11 to the shaft 9 is removed or otherwise released. The ram-rod may then be withdrawn from the shaft and after being rotated through 1 80 degrees about its longitudinal axis may be reinstalled in the shaft so that its tapered or chisel-edged leading end 12 now bears upon the inclined edges of the activating connecting arms 5 and the plate stiffening web 2 as shown in the hachured position of the ram-rod in Fig. 1.

An initial effort applied to the ram-rod 11 will cause an incremental rotation of the curved pressure plate 1 and the stiffening web 2 about the pin 6 with a corresponding incremental increase in earth pressure against the leading convex surface of the pressure plate.

While maintaining the aforesaid initial ram-rod effort upon the pressure plate and activating connecting arms the mechanism shaft 9 may be sufficiently withdrawn from the earth mass to cause the pin 6 to disengage from the open leading ends of the slots 10.

After the pin 6 has been disengaged from the slots 10 a further effort applied to the ram-rod 11 will induce a further incremental increase in the earth pressure acting over the leading convex surface of the plate, and since the pressure upon the convex surface of the plate will now be greater than the pressure on its concave side, shielded during the initial installation of the mechanism, the pressure plate, while rotating further about the pin 6, will also cause the freed activating connecting arms 5 to rotate about the pin 7, thereby causing the leading end of the arms to move in a direction lateral to that of the longitudinal axis of the mechanism shaft and ramrod.

It will be apparent that the separate movements of the mechanism as heretofore described as separate steps may, with advantage, be combined into compound or simultaneous movements concurrently induced for example by means of a lever and parallel linkage connected above ground level to the following end of the mechanism shaft and the following end of the ram-rod after its re-insertion into the shaft.

It also follows that after pin 6 has moved clear of the plates 8, a combined further effort of the shaft 9 applied through its attached plates 8 upon the pin 7, and of the ram-rod 11 upon the pressure plate support web 2, and the following angled edges of the activating connecting arms 5, together with the induced earth reactive pressure upon the convex side of the pressure plate will cause the pin 6 to move along a pathway within the earth mass which is lateral to the longitudinal axis of the mechanism shaft and which may approximate to an arc of a circle, concentric with that of the curved pressure plate.

In this manner the pressure plate 1, following initial penetration to its operating depth within an earth mass in a locked position offering a minimum resistance to installatidn, may thereafter be rotated about the pin 6, while the pin 6, itself, is rotated about the pin 7, along a pathway within the earth mass which offers a minimum resistance to the movement of the pressure plate, until the plate occupies a position in which it will maximise the resistance of the earth mass to an extractive force applied to the plate through the rod or flexible tendon 14 attached to the activating connecting arms 5, by the attachment 13 and the pin 7.

When the mutually relative positions of the following ends of the ram-rod and the mechanism shaft and the ground surface demonstrate that the pressure plate 1 has completed its movement along its pathway of minimum resistance to such movement within the earth mass and has reached its operating position, the ram-rod 11 may be withdrawn from the shaft 9 and the shaft itself, together with the attached plates 8, may also be withdrawn from the ground thereby disengaging the pin 7 from the slots 10 in the plates 8.

It will be evident that, following the operational positioning of the pressure plate 1 by the mechanism, the withdrawal from the earth mass of the mechanism shaft 9 and attached plates 8 will leave the flexible tendon 14 lying within a columnar zone of earth which will have a diminished resistance to any lateral movement of the tendon.

An extractive force applied to the flexible tendon 14 at ground surface level will cause the tendon and the line joining the centres of pins 6 and 7 to mutually move towards a common line of action, or line of resistance to extraction of the pressure plate 1, the final operating positions of the tendon and line, or otherwise expressed the final angle included between the tendon and line, being determined by the combined effects of the extractive and resistive forces, and the resistances to lateral movement through the earth mass of the tendon 14 and of the activating connecting arms 5, rotating about the pin 6.

During the initial installation of the anchoring mechanism an alternative method of restraining the pressure plate 1 relative to the longitudinal axis of the shaft 9 by the ram-rod 11 in its initial position 12, is to enclose the shaft 9 within an outer shaft within which the shaft 9 is free to slide, the said outer shaft having its leading or penetrating end shaped so as to engage upon and restrain the following end of the pressure plate 1 in its initial penetrating position.After the mechanism has penetrated to its operating depth, a force applied only to the shaft 9 will cause a further penetration of the mechanism sufficient to disengage the following end of the pressure plate 1 from the penetrating end of the outer shaft, following which the wedged or chisel-shaped end of the ram-rod 11 already bearing upon the following edges of the stiffening web 2 and the activating connecting arms 5 may be driven against the said edges to bring about the operational positioning of the pressure plate as heretofore described.

The use of this alternative method of initially restraining the pressure plate by means of a shaft, concentrically external to shaft 9, is preferred when an anchoring mechanism is to be positioned within an earth mass at a depth which can only be reached by attaching the mechanism to a pneumatically or hydraulically operated mechanical mole, or similar earth penetrating appliance, adapted to transport the anchoring mechanism and to thereafter cause the pressure plate 1 to move along its pathway of minimum resistance to movement within the earth mass and into its operating position of maximum resistance to extraction from the mass, before the mole and the outer shaft and the inner shaft 9 with the attached plates 8 and the ram-rod 11 return, under the pneumatic or hydraulic or similar energy, to the surface of the ground.

Claims

1. An anchoring device comprising a curved or bent earth-pressure resistant plate or shoe having means for the attachment of a cable or flexible tendon through which an extractive force may be applied to the said plate or shoe after it has firstly been driven into the ground and secondly been moved into an operating attitude of maximum resistance to extraction from the ground-mass, by a mechanism which comprises an arm or link whose penetrating or leading end is hinged or pinjointed to the said plate or shoe and whose following end is slideable in, and rotateable relative to, an open-ended slot, or slots, formed at the penetrating end of a shaft or tube or in an extension thereto, by which the said anchoring device and mechanism are driven into the ground, during which initial installation the said arm or link is constrained by the said slot or slots so that the line joining the said leading hinge and following slideable end is parallel to the penetrative axis of the said driving shaft, and with the said plate or shoe retained in a position of minimum resistance to penetration by a tapered or chisel-ended mandril which is moveable in, and operable in conjunction with, the said driving shaft, after which said initial installation the said tapered mandril is withdrawn from the said driving shaft to release the said plate or shoe and after being semi-rotated about the penetrative axis is re-inserted in the said driving shaft and used as a ram-rod to disengage the leading end of the said arm or link from the open leading end of the said slot or slots and thereafter to cause the said plate or shoe to move along a pathway of minimum resistance to movement and into the said operational attitude within the ground-mass, under the rotational and slideable constraints of the said arm or link, following which said positioning of the said plate or shoe, the said slotted driving shaft and mandril may be withdrawn from the said arm or link.

2. An anchoring device according to Claim 1 in which the earth-pressure resisting plate or shoe is provided with one or more web plates, to which the penetrating or leading end of the arm or link is hinged or pin-jointed.

3. An anchoring device according to Claim 1 or 2 in which there is provided a plurality of arms or links, hinged or pin-jointed at their penetrating or leading ends to the earth-pressure resisting plate or shoe and with their following ends slideable in and rotateable relative to one or more openended slots formed in the penetrating end of the driving shaft or in an extension thereto.

4. An anchoring device according to Claim 1 or 2 or 3 in which the one or more arms or links are provided with one edge or side inclined to the line joining the centres of the leading and following hinge positions or pin-joints the said inclined edge or edges being engageable with the tapered leading end of the mandril when the said mandril is positioned in the driving shaft as a ram-rod.

5. An anchoring device according to Claim 1 or 2 or 3 or 4 in which either one or both pins of the hinges or joints at the penetrating or leading end, and at the following end of the arm or arms are extended to engage in the slot or slots formed at the penetrating end of the driving shaft.

6. An anchoring device according to any one of the preceeding claims in which the cable or flexible tendon is attached to the arm or arms.

7. An anchoring device according to any one of the preceeding claims in which the earth-pressure resisting plate or shoe is curved or contoured to the curve of a curved pathway of minimum resistance to the movement of the said plate or shoe within the ground-mass.

8. An anchoring device according to any one of the Claims 1 to 6 inclusive in which the earthpressure resisting plate or shoe is curved or contoured to an arc of a circle.

9. An anchoring device according to any one of the preceeding claims in which the anchoring device and associated driving and platepositioning mechanism are installed into the ground-mass by means of a mechanically operated "mole", or similar earth penetrating appliance.

10. An anchoring device constructed, arranged and adapted to operate substantially as herein described with reference to the accompanying drawings.