Earth Anchor and Method of Setting and Removing Same

This invention relates to an anchoring process, which comprises supporting and fixing a temporary retaining wall and a multi-tied diaphragm wall or the like constituted of sheet piles, etc., and a device therefor.

For providing a trench at the time of construction of buildings, there is provided a temporary retaining wall using sheet piles in order to prevent the land around the ground to be bored, from collapsing. This temporary retaining wall is supported by a tied-back anchor, comprising anchor steel members buried in the ground in the rear portion of the wall and hardening material applied thereto such as cement milk, mortar or the like. Such a tied-back anchor is buried outwardly of the trench ground, and hence there is a fear that it gives an obstacle in the future which remains in the base portion of another building constructed adjacent to the building which is under construction. This poses a serious problem especially in over-congested urban area and the tied-back anchor has to be removed in the future.

Referring to the embodiments, description is given to the removal processes of prior art removal of such a tied-back anchor which gives an obstacle as mentioned earlier. According to one of the prior art processes, a pressure bearing plate is disposed in the radial direction of an anchor steel member at the tip portion of the anchor steel member encompassed with a sleeve and the pressure bearing plate is secured to the sleeve, while the anchor steel member is secured to the pressure bearing plate by clip means constituted such that the anchor steel member may be detached from the pressure bearing plate when a force greater than a given level of a force is exerted. In this case, by withdrawing the anchor steel member under a force greater than a given level, the anchor steel member is detached at the clip means from the pressure-bearing plate to be brought into a condition where the sleeve and the anchor steel member are unbonded, whereby the anchor steel member can easily be withdrawn. According to this process, however, only the anchor steel member may be withdrawn, leaving alone under the ground the anchor body made of a hardening material, sleeve and pressure bearing plate which will inevitably become obstacles. Thus, the removal process as described above suffers from a disadvantage that even the removal of the anchor body cannot be achieved.

According to another process, explosives are used to break the anchor body, thereby facilitating the removal of the anchor steel member and enabling simultaneous removal of the anchor body. That is, explosive covered with a tubular body is inserted together with the anchor steel member into anchor bored hole, followed by the injection of cement milk or mortar for rigidly locating same. At the time of removal, the explosive is fired by means of load-wire running from the explosive to break the anchor body. This process has an advantage in that the tied-back anchor can no longer be an obstacle in the future, since not only the anchor steel member is removed but also the anchor body (cement, mortar) can be also broken by explosion. In this process, however, there are problems with respect to water-proof property of the tubular body covering the explosive and firing system of the explosive. Insufficient water-proof property leads to wet explosive, whereby it fails to be exploded. On the other hand, accidents such as breaking of lead-wire at the time of charging explosives are liable to occur, resulting in unsuccessful removal of the tied-back anchor. Consequently, the tied-back anchor has to remain buried under the ground without being removed. Furthermore, this process suffers from lack of convenience because special device and technique are required for handling explosives.

Further, according to another prior art, a method is known which comprises the steps of providing a plurality of pressure bearing plates arranged in a given space to each other and being in threaded engagement with anchor steel members, and disposing sheaths between each of the pressure bearing plates for surrounding the anchor steel members and embedding the anchor into filler material in unbonded condition thereto, thereby fixing the anchor steel members therein with the effect of the withdrawal resisting force. Upon removal of the anchor, the threaded engagement of the pressure bearing plates with the anchor steel members is disengaged. In this method it is required to enlarge the diameter of the pressure bearing plates so as to provide a given supporting force, resulting in the need to bore a large anchor hole in the ground. The increment in the diameter of the hole causes problems in aconomy and construction.

Accordingly, it is a principal object of the present invention to provide an anchoring process which allows the removal of an anchor steel member with ease by breaking an anchor body secured to the anchor steel member to thereby allow no rod-shaped anchor body left under the ground, with the aid of a removal device of a simple construction utilizing a wedge effect, and a hardenable filler material producing voids or a foreign material of a low rigidity which affords the similar effect to that of voids. The filler material aids in affording the wedge effect.

Another object of the present invention is to provide an anchoring process in which there are provided two or more anchor steel members which can be provided, as required depending on a supporitng force required.

Still another object of the present invention is to provide an anchoring process having a means for securing temporarily two or more anchor steel members arranged at a given spacing to outer peripheral portion of a wedge-shaped breaking means.

It is also another object of the present invention to provide an anchoring process in which there is provided a means capable of reducing frictional resistance caused between the wedge shaped breaking means and filler material at the time of withdrawing the wedge shaped breaking means.

It is still another object of the present invention to provide an anchoring process in which a tension steel member is inserted into through-hole along the center axis of the wedge shaped breaking means and secured by clamping means to the diverging end portion of the breaking means wherein the breaking means gradually acts along the direction of the anchor steel member to be pulled, without departing from the axis of the anchor body.

It is also still another object of the present invention to provide an anchoring process having a foreign material of a low rigidity for forming a filler material which is readily broken by the wedge shaped breaking means.

Furthermore, still another object of the present invention is to provide an anchoring device which can remove an anchor steel member with ease and also break an anchor body.

FIG. 1 shows a longitudinal cross-sectional view in which a supporting wall is supported by a tied-back anchor;

FIG. 2 a side view of a wedge shaped breaking means, as viewed from the diverging end portion thereof;

FIG. 3 a view of appearance of a wedge-shaped breaking means;

FIG. 4 a side view of an anchor steel member and a breaking means in the fixed condition;

FIG. 5 a view of a partial appearance of an anchor steel member and a breaking means in the fixed condition;

FIG. 6 a side view of a breaking means having blade shaped projections;

FIG. 7 a view of appearance of the breaking means shown in FIG. 6;

FIG. 8 a side view of a breaking means, exhibiting another embodiment of a means for securing tension steel member in position;

FIG. 9 a view of appearance of the breaking means shown in FIG. 8; and

FIG. 10 through FIG. 14 longitudinal cross-sectional views shown in the order of steps of the anchoring process of the present invention.

With reference to the preferred embodiment as illustrated in the drawing, the present invention will be described in more detail as below. FIG. 1 shows a longitudinal cross sectional view of a supporting wall 10 such as temporary retaining wall illustrative of the supported condition according to the anchoring process of the present invention. The supporting wall 10 is supported and fixed by a tied-back anchor 12 buried in a ground 11. The tied-back anchor includes an anchor steel member 14 and an anchor removing means 15, inserted into an anchor bored hole 13 bored in the ground 11, and an anchor body 17 of a hardenable filler material 16 injected into the anchor bored hole 13 to be solidified therein.

The anchor steel member 14 to be used is preferably a strand wire of steel and secured by a fastening piece 19 on a pressure bearing block 18 provided on the outer surface of the supporting wall 10. The number of the anchor steel member may be either single or plural, depending on the supporting force required. Depending on whether the anchor steel member 14 is single or plural, the constitution of the anchor removing means 15 as hereinafter described is somewhat different; but it should be noted that there is no fundamental difference between these embodiments. In the present embodiment, description is given with reference to plural anchor steel members.

FIG. 2 and FIG. 3 show one embodiment of the constitution of the anchor removing means 15. The anchor removing means 15 is equipped with a wedge-shaped breaking means 20 tapered in the direction to be pulled (namely, toward the opening side of the anchor hole 13) and a tension steel member 22 encompassed with a sheath 21 to be insulated from the filler material 16. In the central portion along the axis of the wedge-shaped breaking means 20, there is provided a through-hole 23. As shown in FIG. 4 and FIG. 5, the tip portion of the tension steel member is inserted into this through-hole 23 and secured by a fixing means 24 to the diverging end portion of the breaking means 20. The inner diameter of the tension steel member 22 and hence the tension steel member 22 is loosely fitted in the through-hole 23 so as to be movable in the directions except for the direction to be pulled. The tension steel member 22 is preferably made of a strand wire of steel having flexibility in order to avoid stress concentration due to a tension when pulled. In the peripheral surface of the wedge-shaped breaking means 20, there are provided grooves corresponding in number to the anchor steel members 22 to be fitted therein in parallel with the axis direction of the breaking means 20. The gradient of the peripheral surface of the breaking means 20 is suitably determined, depending on the soil of the ground 11 surrounding the anchor body 17, a side arresting force determined by the soil, a frictional resistance with the anchor body 17, a breaking strength of the anchor body 17, etc. Alternatively, the breaking means may also be constituted as shown in FIG. 6 and FIG. 7. That is, in order to reduce the frictional resistance on the outer periphery of the breaking means 20, there radially project blade-shaped projecting portions 26 on the peripheral surface of the breaking means 20. The projecting portions 26 may be tapered at a certain gradient. Another embodiment of fixing means for securing the tension steel member 22 to the breaking means 20 is shown in FIG. 8 and FIG. 9, in which a wedge part 24A fittable in the through-hole 23 is used in place of the fixing means 24.

The hardenable filler material 16 is composed of a hardenable material such as cement milk, mortar or others, which contains ingredients producing a plurality of voids or a plurality of a foreign material of a low rigidity, which affords an effect similar to that of voids. Induced by foreign materials of low rigidity are rubber granules, hollow synthetic resin granules, synthetic resin foams, cork granules and so on, which are capable of forming discrete cells in the filler material 16. Alternatively, there may also be used a cylindrical body having continuous void, such as polyvinyl chloride pipe or a paper cylinder as foreign material of a low rigidity. Owing to the effect of the void or foreign material thus incorporated into the filler material 16, a stress concentration tends to take place in the filler material 16 when an external force is imposed thereon, resulting in a lowered strength. This is related with the supporting strength of the tied-back anchor. As a matter of course, the strength achieved in the presence of voids or in the case of the use of foreign materials of low rigidity is greater than the supporting strength required by the fixing anchor 12.

Turning now to FIG. 10 through FIG. 14, an anchoring process and anchor removing process according to the present invention are described. First, as shown in FIG. 4 and FIG. 5, two or more anchor steel members 14 are fitted in grooves 25 in the breaking means 20 and a binding band 27 of relatively low strength is wound around the entire circumference of the anchor steel members 14 to have the breaking means 20 temporarily integrally secured to the tip portion of teh anchor steel member group 14. Wound around the entire peripheral surface of the breaking means and the anchor steel members 14 is a tape 30 for insulating same from the filler material 16. However, the tape 30 is provided not only for the purpose of insulating from the filler material 16, but also preventing the sheath 21 from permeation of the filler material 16 from the joint portion between the breaking means 20 and the sheath 21 and other gaps. In this respect, the filler material is injected into the anchor hole under such a high pressure to be flown into the sheath 21 if it finds a small gap. If the filler material is flown into the sheath 21 and hardened therein, the starting tension load should be increased upon removal of the anchor steel members 14, thus requiring a large sized jack, which is an undesirable situation. In the drawings, shown at 28 is a ring inserted between the breaking means 20 and the anchor steel member 14 to hold the anchor steel member 14 in parallel with the center axis of the breaking means.

Then, as shown in FIG. 10, the assembled anchor steel member 14 and anchor removing means 15 encased in a cylindrical casing 29 are inserted into the anchor bored hole 13. Subsequently, as shown in FIG. 11 and FIG. 12, the hardenable filler material 16 is injected under a high or low pressure according to the ground condition into the bored hole 13 while pulling the casing 29. And, while leading out the anchor steel member 14 and the tension steel member 22 outwardly, the edge portions thereof are secured by a fastening means 19 on a pressure bearing block 18 provided on the outer surface of the supporting wall 10. According to such a procedure, the tied-back anchor 12 is set, whereby the supporting wall 10 is supported by a bonding force created between the anchor steel member 14 and the filler material 16.

Upon removing the tied-back anchor 12, the breaking means 20 is withdrawn by applying a tension load therein by means of a jack (not shown), as shown in FIG. 13 and FIG. 14. At this time, due to the wedge-shaped breaking means 20, a breaking stress acts on the surrounding filler material 16, namely the anchor body 17 so as to produce cracking. The voids or foreign materials of a low rigidity incorporated in the filler material 16 greatly contribute to production of such cracks. Furthermore, the breaking means 20 gradually acts along the direction of the anchor steel member 14 to be drawn, without departing from the axial line of the anchor body 17, thus causing cracks. On the withdrawal of the breaking means 20 in the aforesaid manner, the anchor body 17 is broken to detach the anchor body 17 from the anchor steel member 14, thereby placing the anchor steel member 14 in a condition independent of the anchor body 17.

After the breaking means 20 have been taken out, the anchor steel member 14 can manually be pulled out from the ground with ease.

Though the specific description is given to the embodiment using a plurality of the anchor steel members, it will be appreciated that single anchor steel member is also applicable to the present invention. Within the range of the required supporting force, a single anchor steel member will be used. In this case the diameter of the anchor hole 13 can be lessened, resulting in saving of the expenses in the construction.

As described above, according to the present invention, the anchor steel member can be taken out, and the anchor body may be broken of the anchor. As the result, no fixing anchor will not be left alone as a rod-shaped body under the ground. Furthermore, the anchor steel member may be pulled and the anchor body broken as described above without very a special device in a simple manner, as best. This greatly contributes to an efficient operation and saving in operational expense.