BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates in general to ground anchors used in construction of underground continuous wall in building works or public works and, more particularly, to an improved structure in such ground anchors for facilitating the removing of the ground anchors after grouting.

Description of the Prior Art In construction of underground parts of large-sized structures such as of high-storied buildings or of the subway, it is required to form underground walls for stopping of underground water or prevention of landslide. In order to form the water stopping walls or the landslide prevention walls, the ground is dug to a depth so as to form an underground cavity and a plurality of H beams are vertically driven in the ground about the bottom side of the underground cavity. Here, it is preferred to drive the H beams in the ground such that they are spaced out at regular intervals. Thereafter, a plurality of wall panels are placed between the H beams, thus to form the underground walls for stopping of underground water or prevention of landslide. However, the wall panels supported by the vertically driven H beams should be applied with higher soil pressure, often higher than several hundred tons, as the underground cavity is more deepened. In this regard, the water stopping walls or the landslide prevention walls may not withstand the higher soil pressure and unfortunately collapse, thus to cause a big accident.

In order to combat such collapse of the underground walls, those underground walls may be reinforced by

connecting the walls in lattice type using a plurality of large-sized H beams. Otherwise stated, the underground walls may be reinforced by forming a lattice type reinforcing structure. The lattice type reinforcing structure using the large-sized H beams, while successfully preventing the collapse of the underground walls, nevertheless is very complex in its construction and inevitably disturbs movement of construction vehicles in the underground cavity. This causes deterioration of work efficiency, extension of term of works and increase of cost. The cost problem of the above reinforcing structure becomes worse due to the fact that the reinforcing structure should waste a great number of H beams.

Underground continuous walls have been proposed to be used as the water stopping walls and the landslide prevention walls. In order to form a typical underground continuous wall, the ground is dug to a depth so as to form a groove. The groove is, thereafter, continuously charged with concrete to form the underground continuous wall. After curing of the concrete, the earth inside the underground continuous wall is excavated, thus to define an underground cavity inside the underground continuous wall. However, this typical underground continuous wall is uneven on its exposed side surface, which surface thus additionally needs finishing such as by grinding. The finishing of the uneven side surface of the typical underground continuous walls causes environmental pollution since it inevitably generates considerable noise and dust.

In an effort to overcome the above problems, various types of ground anchors have been wide used in construction of the underground walls.

It has been noted that use of the ground anchors as the reinforcing structure of the underground walls is more effective when the walls should be formed at a deeper position underground.

As well known to those skilled in the art, the ground anchors used in construction of underground continuous

walls are classified into two types, that is, permanent anchors and removable anchors. The permanent anchors, particularly used in construction of a building on soft ground, permanently anchor themselves in the ground. Meanwhile, the removable anchors, which are concerned with the present invention, are temporarily anchor themselves in the ground and drawn out after grouting so as to be removed.

U.S. Patent No. 4,592,178 discloses a ground anchor which comprises a drill bit and an anchor head to which a plurality of swingable arms are pivoted. This ground anchor is driven into a depth and slightly pulled backward so that the swingable arms stretch out, thus to be anchored in the ground. U.S. patent No. 4,832,535 discloses process for soil treatment and successive installations of a plurality of equipments at different locations and apparatus for implementing the process. This process comprises the steps of drilling the soil by driving a tubular stem, introducing one equipment inside the tubular stem tool, removing from the soil the tubular stem tool while leaving the equipment within the soil, modifying the soil compaction around the equipment by mechanical action during removal of the tubular stem tool. However, the process disclosed in U.S. Patent No. 4,832,535 remains the equipments in the ground after finishing the work and this sometimes causes serious problems.

Japanese Patent Publication Nos. Heisei. 3-77891 and Heisei. 2-5206 disclose removable ground anchors respectively. In each of the above removable ground anchors, a removable mandrel is received in a vertically excavated ground hole and a plurality of tensile members are coupled to about the mandrel with interposition of spacers. The mandrel is removed from the anchor after grouting so as to destroy the coupling structure between the spacers and the mandrel, so that the tensile members can be easily pulled out so as to be removed. However, the coupling structure comprising the spacers and the tensile

members about the mandrel may achieve no desired coupling force.

In order to combat this possible problem of deficient coupling force, the removable anchor disclosed in Japanese Patent Publication No. Heisei. 3-77891 comprises an unbonded type mandrel having a tapered cone consisting of two separate parts, a plurality of tensile members vertically placed about the mandrel such that their distal ends are inserted in the tensile member holes of the tapered cone of the mandrel. A pair of cavity forming members of the unbonded type are vertically placed in opposed sectorial spaces between the two parts of the tapered cone of the mandrel. With the above structure of the removable anchor, the cavity forming members can be drawn out after grouting so as to form their cavities in the grouting material before drawing out the mandrel. In drawing out the mandrel, the tapered cone is pulled up along the length of the anchor so that the tensile members are extruded from the flat sections of the tapered cone to the outside or into the cavities formed by the removed cavity forming members. The tensile members are thus free from the grouting material and removed.

The removable anchor disclosed in Japanese Patent Publication No. Heisei. 2-2056 comprises an unbonded type mandrel and a plurality of comber spacers. The spacers are placed about the mandrel and decomposed when the mandrel is removed after grouting. A tensile member is placed at the outside of each comber spacer. When the mandrel is drawn out of the anchor after grouting, the comber spacers about the mandrel will be decomposed so as to allow the tensile members to be extruded into the cavities formed by decomposed spacers. The tensile members can be thus removed from the cured grouting material.

However, the above Japanese patents have problems as follows. That is, the tensile members can not sufficiently withstand the soil pressure in the ground. In addition, it is very difficult to insert and place the anchor in the

ground hole while retaining its assembled shape. After grouting, the tensile members are firmly fixed to the cured grouting material or to the cured mortar so that they are scarcely separated from the grouting material. These problems make the above removable anchors not practically used in construction work.

In order to overcome the above problems caused by the above removable ground anchors, the present inventors proposed a removable anchor in Korean Patent Application No. 93-17615. In this removable anchor of these inventors, a tapered pressure split cone 2 is inserted in a cylinder 1 and in turn receives a split spacer 3 therein as shown in Fig. 1. A tapered coupling cone 4 having a tensile member 5 is inserted into the spacer 3 such that the tensile member 5 passes through all the cylinder 1, the tapered cone 2 and the spacer 3. The cylinder 1 is, thereafter, covered with a cap 6 by screw type fitting. After covering the cap 6 on the cylinder 1, the tensile member 5 is strongly tensioned in order to exhibit a desired anchor function. The anchor is in turn disassembled by vibration so as to be removed. However, this removable anchor has a problem in that it comprises a plurality of parts to be coupled to each other and, as a result, it may be entangled in its structure. Furthermore, the anchor can not be desirably disassembled since it should be extremely overloaded when the anchor needs disassembling using vibration load.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a removable ground anchor in which the above problems can be overcome and which comprises a cylinder, an anchor disassembling cone placed at the center of the cylinder and a plurality of anchor tensioning cones placed about the anchor disassembling cone and is easily removed after grouting and curing of grouting material.

It is another object of the present invention to provide a method for anchorage using the above removable ground anchor and removing the ground anchor after grouting and curing of the grouting material.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is an exploded perspective view of a removable ground anchor of the prior art;

Fig. 2 is an exploded perspective view of a removable ground anchor in accordance with an embodiment of the present invention;

Fig. 3 is a sectional view of the removable ground anchor anchored in the ground in accordance with the present invention; Fig. 4 is a sectional view of the removable ground anchor of the present invention after assembling;

Fig. 5 is a partially broken perspective view of a cylinder of the removable ground anchor of the present invention; Figs. 6A and 6B are perspective views of a tensile member coupling cone of the removable ground anchor of the present invention in the closed state and in the opened state respectively;

Figs. 7 to 9 are sectional views of the removable ground anchor of the present invention, showing the process for disassembling and removing the ground anchor;

Fig. 10 is a sectional view showing the disassembling of the removable ground anchor of the present invention after grouting and curing of the grouting material; Figs. 11 to 13 are plan views of removable ground anchors in accordance with other embodiments of the present invention respectively; and

Fig. 14 is a view corresponding to Fig. 10, but showing another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to Fig. 2, there is shown a removable ground anchor in accordance with an embodiment of the present invention. As shown in this drawing, the removable anchor comprises a tensile member coupling cone 20 for anchor disassembling which is placed at the center of a cylinder 10. A plurality of spacers 30 are placed about the outer surface of the above coupling cone 20. In addition, a plurality of tensile member coupling cones 20' for anchor tensioning are tightly placed on the cylinder 10 about the anchor disassembling cone 20 with interposition of the spacers 30. The parts, that is, the cylinder 10, the anchor disassembling cone 20, the anchor tensioning cones 20' and the spacers 30 are integrated into the removable anchor body of the present invention. With the above structure of the anchor body, the spacers 30 are collapsed inwardly by tensile force applied thereto by the tensile members for tensioning anchor W of the anchor tensioning cones 20' when the anchor disassembling cone 20 is pulled out or remained broken in the cylinder. Hence, the coupling force of the coupling cones 20' is removed by vibrating or pulling the anchor tensioning cones 20', thus to let the tensile members for tensioning anchor W' be easily drawn out so as to be removed from the soil.

Fig. 3 shows the removable ground anchor of the present invention anchored in the ground. Fig. 4 shows the ground anchor after assembled and Fig. 5 shows the cylinder 10 of the ground anchor. As shown in these drawings, the cylinder 10 having a center through hole 11 is provided with a plurality of peripheral holes 12 which are vertically formed about the center hole 11 on a middle partition ring 14. These peripheral holes 12 are spaced out at regular angles. Here, there is a height difference

"d" between the center through hole 11 and the peripheral holes 12. Between the top surface 13 and the middle partition ring 14 of the cylinder 10, there is provided the same number of semicircular recesses 16 as that of the tensile member coupling cones 20' for anchor tensioning. The recesses 16 are formed along the inner surface 15 of the cylinder 10 and receive therein the anchor tensioning cones 20' respectively. The cylinder 10 is simply hollowed at its lower section from the lower surface of the middle partition ring 14 to the bottom edge 13'. The top section of the cylinder 10 has a smaller outer diameter and is threaded on its outer surface, thus to form an outer threaded part 17 thereon.

As shown in Figs. 6A and 6B, the anchor disassembling cone 20 or the anchor tensioning cone 20' of the ground anchor of this invention comprises a plurality of sectorial pieces 20a, 20b and 20c. The plurality of sectorial pieces 20a, 20b and 20c are integrated into the coupling cone 20 or 20' which shows a truncated and hollowed conical shape. Each of the sectorial pieces 20a, 20b and 20c are uneven on their inner surfaces 18 for tightening the tensile members W and W when the cone 20 or 20' is closed as shown in Fig. 6A. The larger diameter top section of each cone 20 or 20' is provided with an annular groove 19 on its outer surface for elastically receiving an elastic ring 21 therein. The elastic ring 21 tightens the top sections of the sectorial pieces 20a, 20b and 20c, thus to integrate the sectorial pieces 20a, 20b and 20c into the reversed cone 20 or 20' in such a manner that the side end surfaces of the pieces 20a, 20b and 20c come into contact with each other. As a result of integration of the sectorial pieces 20a, 20b and 20c into the cone 20 or 20', there is provided a center through hole 23 for receiving the tensile member for dissembling anchor W. Here, the diameter of the center through hole 23 of the cone 20 or 20' is slightly smaller than that of the tensile member W and W' , thus to achieve the desired airtightness between the cone 20 or 20' and the tensile

member W and W' when inserting the tensile member in the center through hole 23.

It is preferred to produce both the anchor disassembling cone 20 and the anchor tensioning cones 20' such that they are equal to each other in their sizes and widths. This makes both the productivity and using efficiency of the coupling cones 20 and 20' improved. However, it should be understood that the coupling cones 20 and 20' may be different in their sizes, thus to be changed in their strengths and assembling efficiencies. Even when the coupling cones 20 and 20' are different in their sizes, they are tightened by the elastic ring 21.

As shown in Figs. 2, each spacer 30 comes into contact with both the outer surface of the center member 31 and the outer surfaces of the neighboring anchor tensioning cones 20' at its side surfaces 30a, 30b and 30c. In this case, it is preferred to make the spacer 30 and the outer surfaces of both the center member 31 and the cones 20' coming into airtight contact with each other. In order to achieve the above object, the three surfaces 30a, 30b and 30c of each spacer 30 are preferably smoothly concaved. However, it should be understood that each spacer 30 may have a simple rod profile or a polyhedral profile. Alternatively, the spacer may be more widened in its width so as to support at least two coupling cones. As a further alternative, each spacer 30 may be constructed such that it simply spaces the anchor tensioning cones 20' apart from the center member 31 at a predetermined interval as shown in Figs. 11 to 13. Each spacer 30 is gradually reduced in its thickness from the top to the bottom and, in this regard, it achieves the perpendicularity when it comes into contact with the outer surface of the center member 31.

As best seen in Fig.4, the center member 31 is seated on an annular ring or a snap ring lib. The ring lib is fitted in an annular groove 11a formed in the bottom section of the center through hole 11. The bottom diameter of the center member 31 should be thus slightly smaller

than that of the center through hole 11. The outer diameter of the center member 31 is gradually reduced from the bottom to the top so that its flat side surface meets with its bottom at an acute angle. The tensile members used in the present invention are conventional strands or PC steel wires. The tensile members w are inserted into the coupling cones 20 and 20' respectively, thus to be coupled to their coupling cones 20 and 20'. When coupling the tensile members to their coupling cones 20 and 20', the uneven surface 18 of each coupling cone 20 or 20' comes into tight contact with the outer surface of the tensile member.

The top surface 13 of the cylinder 10 is provided with at least two inner threaded holes 13b for receiving their respective bolts 42. In the same manner, the bottom edge 13' of the cylinder 10 is provided with at least two inner threaded holes 13b. With the inner threaded holes 13b provided on both the top surface 13 and the bottom edge 13' of the cylinder 10, the cylinder 10 is detachably coupled to and covered with a top cover 40 and a bottom cover 41 on its top and bottom ends respectively. Here, each of the top and bottom covers 40 and 41, which is provided with the same number of tensile member guide openings 13" as that of the coupling members 20,20' is provided with bolt receiving holes at positions corresponding to the inner threaded holes 13b of the cylinder 10 and detachably screwed to the top and bottom ends of the cylinder 10 using bolts 42. The diameter of each tensile member guide opening 13" of the top and bottom covers 40 and 41 is slightly larger than that of each tensile member w.

In order-to achieve a more stable disassembling of the anchor, it is preferred to provide a projecting guider boss 43 for each of the tensile member guide openings 13" of the bottom cover 41 as shown in Fig. 4. The cylinder 10 is covered with a domed cap 50 on its outer threaded top section by fitting the domed cap 50 to the top section by screw type fitting. This domed cap 50

defines therein a cavity 52 which allows the coupling cones 20 and 20' to be played without restriction. In order to achieve the screw type fitting of the cap 50 to the outer threaded top section of the cylinder 10, the cap 50 is threaded on its inner surface about its opening, thus to form an inner threaded part 51 which will be engaged with the outer threaded part 17 of the top section of the cylinder 10.

Hereinbelow, the process for anchorage using the above ground anchor and for removing the ground anchor after grouting and curing will be given.

1. Excavation of a predetermined depth of hole in the ground: The predetermined depth of vertical hole 61 is excavated in the ground 60 using appropriate holing means, such as casing pipes and a ground hole excavator.

2. Assemblage of parts into ground anchor body: At first tensile member for dissembling anchor W is inserted in each anchor disassembling cone 20 at its end prior to seating of the center member 31 on the snap ring lib of the center through hole 11 of the cylinder 10. After seating the center member 31 on the snap ring lib, the anchor disassembling cone 20 having the tensile member for dissembling anchor W is inserted into the center through hole of the center member 31. The same number of spacers 30 as that of the semicircular recesses 16 of the cylinder 10 are placed about the center member 31 such that they are spaced out at regular angle intervals. In this case, the bottoms of the spacers 30 are laid on the top surface of the middle partition ring 14 between the center through hole 11 and the peripheral holes 12 of the cylinder 10 while the surfaces 30a of the spacers 30 come into contact with the outer surface of the center member 31. After placing the spacers 30, the tensile members for tensioning anchor W are inserted in their respective anchor

tensioning cones 20' at its end. The anchor tensioning cones 20' are in turn fitted in their respective spaces defined between the semicircular recesses 16 and the spacers 30 such that their tensile members for tensioning anchor W are received in the peripheral holes 12 of the cylinder 10 so as to project out of the bottom edge 13' of the cylinder 10 respectively. The tensile members for tensioning anchor W are in turn pulled, thus to achieve the assembled state of the cylinder 10 as shown in Fig. 4. Thereafter, the top and bottom covers 40 and 41 are screwed to the top and bottom ends of the cylinder 10 prior to screw type fitting of the cap 50 to the top section of the cylinder 10. Here, the top cover 40 is screwed to the top surface 13 of the cylinder 10 using the bolts 42 such that both of the tensile members W and W' of the coupling cones 20 and 20' are partially exposed to the outside. In the same manner, the bottom cover 41 is screwed to the bottom edge 13' of the cylinder 10 using the bolts 42 such that the tensile members W and W' of the cones 20 and 20' are partially exposed to the outside. The above screwing of the top and bottom covers 40 and 41 to the cylinder 10 is followed by the screw type fitting of the inner threaded domed cap 50 to the outer threaded top section of the cylinder 10. Thus, the assembling of ground anchor body of the present invention is achieved.

3. Placing of the above anchor body in the ground hole:

The anchor body, prepared by the above step 2, is inserted into the ground hole 61 of the above step 1 until it reaches the bottom of the ground hole 61. At this time, it needs to not only prevent entangling of the tensile members W and W using both a packer 64 and a tensile member spacer 65 but also let the tensile members W and W' be surrounded by a seize pipe 66 as shown in Fig. 3. A conventional grouting is carried out so as to fill the ground hole 61 with the grouting material. The anchor body

is fixed in the grouting material after curing of the grouting material.

4. Anchor tensioning: A base 62 is fixed to a plate 67 and, thereafter, the tensin members for tensioning anchor W' except the tension member for dissembling anchor W are tightly fixed to the base 62 at their ends using their respective fixtures as shown in Fig. 10.The tightening force can be as much as several thousands Kg per sqare centimete in each strands.

5. Disassembling and removing the anchor:

First of all,the tensile member for dissembling anchor W of the anchor disassembling cone 20 which is received in the center member 31 is strongly pulled up so that the snap ring lib of the cylinder 10 can not withstand the higher pressure of the center member 31 and is broken as shown in Fig. 7. Therefore, the center member 31 and the anchor disassembling cone 20 are drawn by the high power pulling or vibration force out of the anchor body through the seize pipe 66 or remained broken or spread out randomly in the inner space of cylinder. After the breakage of center member 31 and anchor dissembling cone, the anchor tensioning cones 20' which have been tensioned at several thousand kg to several ten tons are instantaneously collapsed while being biased inwardly due to removing of the center member 31 which has supported them. At this time, the tensile members for tensioning member W' are strongly vibrated using a vibrator or pulled by the usual mechanical force so that the lower sections of the anchor tensioning cones 20' are opened as they come into contact with the peripheral holes 12 or stop rings 12a as shown in Fig. 8. The anchor tensioning cones 20' are thus separated from their tensile members for tensioning anchor W' . In this regard, the tensile members for tensioning anchor W' of the anchor tensioning cones 20' can be removed from the anchor by drawing out them as shown in Fig. 10.

As described above, a removable ground anchor in accordance with the present invention is easily assembled and disassembled. When disassembling and removing the ground anchor after grouting and curing of the grouting material, the anchor tensioning cones are easily disassembled by simply removing the anchor disassembling cone placed at the center of the cylinder of the anchor. Thus, the tensile members of the wire type of this ground anchor are free from the cured grouting material and easily pulled out so as to be removed. In addition, the ground anchor of this invention increases the tensile force to several times or several ten times in comparison with the prior art anchor. In this regard, the number of ground holes per unit area is remarkably reduced so that the construction cost is saved.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.