Structure of anchor and construction method thereof

Abstract: In a structure of an anchor body (1), a deformed sheath made of steel (21) and having a tubular body whose peripheral wall presents an irregular configuration (26)is inserted in an excavated bore (2). At least one tension material (3) is inserted in the deformed sheath (21). A plurality of steel pipes (22) are covered on at least an end portion of an outer peripheral wall of the deformed sheath (21) or are inserted in at least an end portion of an inner peripheral wall of the deformed sheath (21), to reinforce the same. A hardener (5) is poured into the excavated bore (2) and a space (8) within the deformed sheath (21), to form a fastening section. A method of constructing the anchor body is also disclosed.

Description: The present invention relates to a ground anchor body, comprising a deformed sheath having a tubular body whose peripheral wall presents an irregular configuration, and at least one tension member for insertion into the sheath, as well as to a method of installing such a ground anchor body. - Such a ground anchor body is known from EP-A-0 356 215 which comprises several tension members being separately anchored to a common anchor member and the free ends of which being taken up by corrugated sheaths, which sheaths are arranged in spaced relation along a bore and filled by grout. The sheaths are not reinforced so that the anchor strength may be insufficient and the sheaths may underly deformations. In recent years, in the case where a tension material such as an anchor cable or the like is fastened to a natural ground or the like, in an anchor construction, to construct an anchor, a method of construction using a sheath having a water-damming ability, rust-prevention effects and so on has widely been employed, as shown in Fig. 21, in order to improve water-tightness at a fastening section of the tension material. Specifically, a natural ground 1 is first excavated to form an excavated bore 2, and a tension material 3 consisting of a PC-steel stranded wire or the like is inserted in the excavated bore 2. The tension material 3 has its forward end 3a which serves as a fastening section A and which is covered with a tubular bond sheath 7, in order to prevent that the tension material 3 is soaked in the groundwater so as to be rusted and broken. The tension material 3 has its portion adjacent the surface of the earth, which serves as a free-length portion B and which is covered with an un-bond sheath 4 such as polyethylene or the like. Subsequently, a grout 5 is poured into a space within the excavated bore 2 and is hardened. A cement base 8 or the grout 5 is poured into the bond sheath 7 at the forward end 3a of the tension material 3 and is hardened. In this manner, the forward end 3a of the tension material 3 is fixedly fastened to form the fastening section A . Subsequently, the tension material 3 is tensioned on its extension side by a jack or the like, and is given a prestress. In the case where the anchor is constructed in this manner, however, the following disadvantages occur. That is, in the case where a straight tubular body is employed as the bond sheath 7 at the fastening section A when the prestress is given to the tension material 3, there may be a case where longitudinal cracks 9 extending along the tension material 3 and lateral cracks 6a and 6b are generated at the cement paste 8 solidified within the bond sheath 7 and at the surrounding paste 5, as shown in Fig. 21. These cracks reduce the compressive strength and the adhering strength of the anchor. In view of the above, as shown in Fig. 22, a so-called deformed sheath 10 has been developed in which the peripheral wall of the above-described bond sheath is so formed as to present a corrugated or irregular configuration The deformed sheath 10 has already been used at several scenes of labor. The deformed sheath 10 is formed such that its peripheral wall presents the irregular configuration, whereby, when the prestress is given to the tension material 3, a restricting force is loaded on the cement base 8 poured to fasten the tension material 3 and on other components, thereby compensating for reduction in the compressive strength and the adhering strength due to occurrence of the above-mentioned longitudinal cracks 9 and the lateral cracks 6a and 6b. As the deformed sheath 10, two kinds of sheaths are employed which are made respectively of steel and polyethylene. Of the two kinds of sheaths, the deformed sheath 10 made of polyethylene is superior in water-tightness and has a water-damming ability. In the case where an anchor is constructed by the use of the deformed sheath 10 made of polyethylene, however, the experiments conducted by the applicant of this invention have confirmed the fact that there are the following problems. First, the deformed sheath 10 made of polyethylene is low in elastic modulus and weak in strength as compared with the deformed sheath made of steel. For this reason, the polyethylene sheath is deformed in its outer peripheral direction by the tension force acting upon the tension material 3, so that there is a case where the grout 5 fixedly mounting the polyethylene sheath 10 is broken. In the case where such breakage occurs, it is impossible for the polyethylene sheath 10 to restrict the breaking force of the grout 5. Thus, it has been found that the adhering yield strength between the grout 5 and the tension material 3 is considerably lower than a supposed or assumed value. Secondly, in the case where the polyethylene deformed sheath 10 is deformed as described above, without being withstood, by the breaking force occurring due to the tension force of the tension material 3, the longitudinal cracks 9 and the lateral cracks 6b occur in the cement paste 8 which is solidified within the sheath 10. By occurrence of such cracks 9 and 6b, the adhering yield strength of the anchor portion is destructed or destroyed so that the anchor tension material 3 gets out of the anchor portion. The results of experiments have indicated as follows. That is, in the case where such breaking force is applied at the fastening ground which is low in restricting force of the ground, there is a problem in compressive destruction of the anchor body. Accordingly, there is a problem that the polyethylene sheath is employed as a permanent anchor at a location where the ground strength is relatively low. Thirdly, in the case where the deformed tubular body made of polyethylene is used in the bond sheath, there are the following problems. That is, since it is generally difficult to obtain deformed sheaths of sizes suitable for the bond sheath, manufacturing specially ordered is required. For this reason, in the case where various configurations, bore diameters, lengths or the like are required in view of design, it takes considerable time, and the unit cost of manufacturing becomes high. On the other hand, in the case where the deformed sheath 10 is made of steel, the following facts have been found. That is, since the elastic modulus of the deformed sheath 10 is high in material, the restricting force of the cement paste 8 or the like is strong, so that the adhering strength between the tension material 3 and the grout 5 is high as compared with the polyethylene sheath. Since, however, the adhering strength is high, an increase in tension force concentrates the stress locally so that the sheath made of steel is destroyed by the breaking force. Further, the following fact has been confirmed by the experiments conducted by the applicant of the invention. That is, in the case where the sheath made of steel is employed in a pressure-support type anchor, an extremely large compressive force acts upon the end of the sheath. Accordingly, the sheath end is also destroyed by the compressive force and the breaking force. Furthermore, the following facts have been known from the experiments. That is, a winding sheath made of steel is manufactured such that both sides of a strip-like or strap-like steel sheet are bent in opposite directions respectively, and the winding sheath is wound spirally, while these both sides are superimposed upon each other. At this time, the superimposed portion is merely such that the folded parts are in mesh with each other and are staked upon each other. Because the steel sheet is small in thickness, the folded parts are not welded to each other, and are not integrated with each other. Accordingly, when the winding sheath is cut into predetermined lengths, portions of the winding sheath adjacent both ends thereof remain low in strength as a ring. For this reason, in the case where the compressive force and the breaking force are applied to the end area or region of the sheath, the winding sheath is easily destroyed at the end region, so that the meshing portion is unwound. Moreover, there are the following problems. That is, there is a case where a plurality of pressure grips are fixedly mounted to the tension material 3, in order to increase the adhering force of the tension material 3 inserted into the aforesaid deformed sheath with respect to the cement paste 8 or the like. In such construction of the anchor, since the adhering force of the tension material 3 is large, tension stress is not equally applied to the pressure grips, but concentrated stress is generated at locations respectively adjacent the pressure grips which are located nearest the surface of the earth. It is a first object of the invention to provide a structure of an anchor body, in which, even if a local stress is concentrated onto a deformed sheath, the deformed sheath is not deformed and destroyed so that the anchor body has a long service life, and in which a restricting force of a cement paste or the like poured in order to fasten at least one tension material is strong or large so that the anchor body has superior anchor strength. It is a second object of the invention to provide a structure of an anchor body which can load, in a dispersed manner, a tension stress onto each of a plurality of pressure grips fixedly mounted, in suitable intervals, to at least one tension material which is to be inserted into a deformed sheath. According to the invention, there is provided an ground anchor body of the above mentioned type which is characterized in that steel pipe sections are fixedly mounted to at least an end portion of the inner or outer side of the peripheral wall of the sheath for reinforcing said sheath, the internal diameter of the pipe sections exceeding the diameter of the tension member to allow hardener to flow beyond the pipe sections, said ground anchor body for insertion into a borehole which together with the sheath is to be filled by a hardener. The invention further concerns a method of installing such a ground anchor body which is characterized in excavating a borehole into a natural ground; reinforcing at least an end portion of the outer or inner peripheral wall of a deformed sheath having a tubular body whose peripheral wall presents an irregular configuration with a plurality of steel pipe sections; inserting the reinforced sheath into the borehole; inserting at least one tension member into the inserted sheath; pouring a hardener into the borehole and the space within the sheath to form a fastening section; and tensioning said at least one tension member to fasten said sheath. In the case where the tension material having fixedly mounted thereto a plurality of pressure grips is inserted in the aforementioned deformed sheath, the above-described object is achieved by such an arrangement that a plurality of pipes made of steel are inserted in or covered on the peripheral wall of the deformed sheath at respective parts facing to or opposed to the pressure grips, to reinforce the deformed sheath, and that a hardener is poured into the aforesaid excavated bore and the space within the deformed sheath, to form the fastening section. Furthermore, the above-described object is achieved by such an arrangement that a plurality of grip packings having compressibility and rust-prevention effects are mounted respectively adjacent said pressure grips at locations nearer the surface of the earth than the pressure grips. With the above arrangement of the invention, the steel pipes are further inserted in or covered on the irregular peripheral wall of the deformed sheath, at at least the end region of the deformed sheath. Thus, both the ends of the sheath, onto which the stress is particularly concentrated, are reinforced, and the strength of both the ends of the sheath is raised. Accordingly, the breaking force is difficult to occur in the sheath. Even if the breaking force occurs at the deformed sheath, deformation and destruction of the sheath due to the breaking force are difficult to occur, by the steel pipes which are fixedly mounted to the peripheral wall of the sheath. Thus, the restricting force of the entire sheath is compensated for, so that the strength of the anchor is made superior. Further, in the case where the deformed sheath is made of synthetic resin, the rust-prevention effects are high as compared with the steel sheath. Furthermore, since the deformed sheath made of synthetic resin has its flexibility, the practicability of the anchor cable and the execution ability such as insertion of the cable or the like are superior. Since the plurality of pressure grips are fixedly mounted to the tension material inserted in the deformed sheath, the adhering force of the tension material is large so that the concentrated stress tends to occur at locations respectively adjacent the pressure grips which are originally located at their respective positions nearest the surface of the earth. In the invention, however, the grip packings are mounted respectively adjacent the pressure grips at the location nearer to the surface of the ground than the pressure grips. Since the grip packings have flexibility, the grip packings are compressed within the fastening section under the tension force of the tension material by the pressure grips. By doing so, the pressure grips are successively moved toward the surface of the earth within the fastening section by the shrinkage allowance of each of the grip packings having the compressibility. As a result, the tension stress is loaded on the pressure grips in a dispersing manner. Thus, it is possible to prevent the deformed sheath and the steel pipes reinforcing the deformed sheath from being broken due to the concentrated stress on the steel pipes, so that it is possible to considerably improve the anchor strength. Since the grip packings have the rust-prevention effects, provision of the grip packings at the locations adjacent the pressure grips does not rust the pressure grips and the tension material. Thus, it is possible to maintain the anchor body in a healthy condition. Fig. 1 is a partially cut-away, perspective view of a bond sheath which is employed in a structure of an anchor body according to a first embodiment of the invention; Fig. 2 is a cross-sectional side elevational view showing a constructing condition of the structure of the anchor body which employs the bond sheath illustrated in Fig. 1; Figs. 3 (A) through 3(C) are schematic perspective views successively showing manufacturing steps of the bond sheath according to the first embodiment of the invention; Fig. 4 is a cross-sectional side elevational view of the structure of the anchor body according to the first embodiment of the invention, which is employed in a compressive anchor; Fig. 5 is a cross-sectional side elevational view of a modification of the first embodiment; Fig. 6 is a partially cut-away, perspective view of a bond sheath which is employed in a structure of an anchor body according to a second embodiment of the invention; Fig. 7 is a cross-sectional side elevational view showing a constructing condition of the structure of the anchor body which employs the bond sheath illustrated in Fig. 6; Fig. 8(A) is a schematic perspective view showing an example of a method of manufacturing the bond sheath according to the second embodiment of the invention; Fig. 8(B) is a schematic perspective view showing another example of the method of manufacturing the bond sheath according to the second embodiment of the invention; Fig. 9 is a cross-sectional side elevational view in which the structure of the anchor body according to the second embodiment is employed in a compressive-type anchor; Fig. 10 is a cross-sectional side elevational view showing a modification of the structure of the anchor according to the second embodiment; Fig. 11 is a partially cut-away, perspective view of a bond sheath which is employed in a structure of an anchor body according to a third embodiment of the invention; Fig. 12 is a cross-sectional side elevational view showing a constructing condition of the structure of the anchor body which employs the bond sheath illustrated in Fig. 11; Fig. 13(A) is a schematic perspective view showing an example of a method of manufacturing the bond sheath according to the third embodiment of the invention; Fig. 13(B) is a schematic perspective view showing another example of the method of manufacturing the bond sheath according to the third embodiment of the invention; Fig. 14 is a cross-sectional side elevational view in which the structure of the anchor body according to the third embodiment is employed in a compressive-type anchor; Fig. 15 is a cross-sectional side elevational view showing a modification of the structure of the anchor according to the third embodiment; Fig. 16 is a schematic cross-sectional side elevational view showing a structure of an anchor body according to a fourth embodiment of the invention; Fig. 17 is an enlarged view of a principle portion of the arrangement illustrated in Fig. 16; Fig. 18 is a perspective view showing one of a plurality of grip packings which are employed in the structure of the anchor body according to the fourth embodiment; Fig. 19 is a view for explanation of a principle of the structure of the anchor body according to the fourth embodiment; Figs. 20(A) and 20(B) show the relationship between the pressure grips and the excavated bore, Fig. 20(A) being a schematic cross-sectional side elevational view showing a condition that the pressure grips are superimposed upon each other radially at the same position on the tension material in the longitudinal direction, and Fig. 20(B) being a schematic cross-sectional side elevational view showing a condition that the positions of the pressure grips are deviated in the longitudinal direction of the tension material; Fig. 21 is a cross-sectional side elevational view showing the conventional structure of the anchor body which employs a straight bond sheath; and Fig. 22 is a cross-sectional side elevational view showing the conventional structure of the anchor body which employs a deformed bond sheath. Various preferred embodiments will be described below with reference to the accompanying drawings. In this connection, components and parts like or similar to those described previously with reference to Figs. 21 and 22 are designated by like or same reference numerals, and the description of the like or similar components and parts will therefore be omitted or simplified to avoid repetition. Figs. 1 and 2 show a structure 20 of an anchor body according to a first embodiment of the invention. As shown in Figs. 1 and 2, the structure 20 of the anchor body comprises a deformed winding sheath body 21 made of steel and having both open ends or having one open end and the other closed end, and a plurality of pipes 22 made of steel and fixedly mounted to an outer peripheral wall of an end of the sheath body 21. The tension material 3 is inserted in the sheath body 21, and the cement paste 8 is poured in the sheath body 21 The grout 5 is poured into the excavated bore 2 and is hardened. Thus, the fastening section A is formed. The winding sheath body 21 made of steel is formed with a plurality of projecting stripes or ridgelines 21a which are arranged at the same intervals along the outer peripheral wall of the winding sheath body 21. The projecting ridgelines 21a are formed helically in a continuous manner so as to extend along the peripheral direction of the peripheral wall of the winding sheath body 21. The winding sheath body 21 made of steel is formed in the following manner. That is, a metallic thin plate or sheet having its thickness of, for example, about 0.5 mm is formed into an elongated strip or strap. The elongated steel strip has its central section which is pressed to form the strip-like projecting ridgelines 21a. Both sides of the steel strip is folded or bent in directions opposite to each other along the longitudinal direction. Both the sides are wound into a spiral form, while being in mesh with each other under the condition that both the folded sections project outwardly, and are staked upon each other. In this manner, a cylindrical body, whose diameter is, for example, about 80 mm, is formed. This cylindrical body is cut into predetermined lengths. Thus, the winding sheath is formed which is made of steel and which has the projecting ridgelines 21a formed at constant or equal intervals. Here, in the first embodiment, the reason why the deformed winding sheath is employed is as follows. That is, if a straight cylindrical body made of steel and having its outer peripheral surface which is formed into a smooth surface is used, the straight cylindrical body has no irregular surface. Accordingly, the straight cylindrical body is weak or low in adhering strength with respect to an anchor grout. Thus, the straight cylindrical body is unsuitable for a sheath for anchor-fastening. Further, since the straight cylindrical body is also inferior in flexibility in view of execution, work or operation is difficult to insert the tension material into the anchor bore. However, the deformed sheath is employed for the following reasons. That is, the outer peripheral surface of the deformed sheath presents the irregular different form, is rich in flexibility, and is superior in execution ability. Further, in the case where the straight cylindrical bodies made of steel are bonded to each other, the bonding is made by welding or by a threaded joint. Since, however, the winding sheath is processed spirally, it is made possible to employ, as a sheath for the joint, a sheath whose diameter is slightly larger than the winding sheath. Thus, the winding sheath is advantageous in that adjustment in length is free. By the way, in the winding sheath employed in the first embodiment, the meshing sections 21b of the steel strip cannot be welded to each other and be united or integrated together, because, as described above, one used as the steel strip is small in thickness. That is, the thickness of the steel strip employed as the winding sheath is so restricted that a maximum thickness is 0.5 mm, in the case where a cylindrical body having its diameter of, for example, 80 mm is formed. An increase in the maximum thickness to a size of the order of 2 mm to 5 mm is impossible in view of spiral processing. Further, even if welding can be made to the steel strip, there is nothing in reliability considered technically. For this reason, a location adjacent the cut part of the end as the winding sheath is low in strength as a tubular body. Accordingly, in the case where the compressive force and the breaking force act upon the end section, the end is easily broken or destroyed. Thus, there may be a case where the meshing section 21b gets loose. In view of the above, the pipes 22 made of steel similar to the sheath body 21 are fixedly mounted to both outward ends of the deformed outer peripheral wall of the sheath body 21. By doing so, the sheath end is reinforced, so that it is possible to prevent the meshing section 21b from being loosened. In the illustrated embodiment, not only the pipes 99 made of steel are fixedly mounted to both the ends of the outer peripheral wall of the sheath body 21, but also a suitable number of pipes 22 are fixedly mounted to the intermediate section of the sheath body 21 in the longitudinal direction. In the case where the pipes 22 made of steel are fixedly mounted to the sheath body 21, the fixed mounting is practiced as illustrated in Figs. 3(A), 3(B) and 3(C), for example. The deformed sheath body 21 made of steel is first prepared, which is formed as described above and which has a suitable diameter. Further, apart from the deformed sheath body 21, a straight cylindrical body made of steel whose tube thickness is larger than the tube thickness of the sheath body is cut into suitable lengths and is prepared, as illustrated in Fig. 3(A). At this time, the bore diameter of the cylindrical body is selected to be a diameter sufficient that the outer peripheral wall of the sheath body 21 including the projecting ridgelines 21a can loosely be fitted in the bore diameter of the cylindrical body. As shown in Fig. 3(B), the steel pipes 22 formed by cutting or shivering into the suitable lengths as described above are inserted in and fitted in the winding sheath body 21 from the one end thereof. At this time, since the inner diameter of each of the pipes 22 is slightly larger than the outer periphery of the winding sheath 21, the steel pipe 22 is fitted in the winding sheath 21 under a loosely fitted condition. Subsequently, adhesives 23 are applied to the circumference of the outer peripheral wall of the sheath body 21, to a width corresponding substantially to the length of the pipe 22, at a position on the winding sheath body 21 to be reinforced, under the condition that the steel pipe 22 is slightly deviated from the reinforcing position. After application of the adhesives 23, as shown in Fig. 3(C), the piped 22 are deviated and are positioned respectively on the adhesives 23. The adhesives 23 are bonded to the sheath 21 and are hardened. Thus, the bond sheath according to the first embodiment has been completed. The above description has taken the tension-type anchor as an example. If is needless to say, however, that the present embodiment can be applied to a compressive-type anchor 30 as shown in Fig. 4. The compressive-type anchor 30 is arranged as follows. That is, a plurality of un-bond PC strands 3 are inserted in the winding sheath body 21. The compressive-type anchor 30 is fixedly mounted, by the pressure grips, to a pressure support plate 31 which is provided at the end of the sheath body. At tensioning or stretching, the tension force acting upon the tension materials 3 is transmitted to and supported by the anchor body as a compressive force. In this case, a large compressive force acts upon the end of the winding sheath 21, particularly, on the end thereof adjacent the pressure support plate 31. By this high compressive force and the breaking force of the grout, there may be a case where the winding sheath 21 is broken. In view of the above, the steel pipes 22 are covered respectively on portions where the stress is locally concentrated, particularly, on the end region of the winding sheath 21, whereby the end region of the winding sheath 21 is reinforced. Thus, the sheath 21 is prevented from being destroyed by the stress concentration. At this time, a long pipe is covered on the end region of the sheath, and a plurality of pipes shorter than the long pipe are covered respectively on the intermediate sections other than the end region, where the stress is concentrated, at suitable intervals and at required numbers. Thus, the reinforcing is further enhanced. Furthermore, a modification of the present embodiment is illustrated in Fig. 5. In the modification, a plurality of tension materials 3 are inserted in the winding sheath body 21 made of steel. A plurality of pressure grips 33 are mounted to the forward ends of the respective tension materials 3 at suitable intervals. These tension materials and pressure grips 3 and 33 are fastened within the sheath 21 by the cement paste 8 or the like. A plurality of pipes made of steel are covered on suitable locations including the end of the deformed outer peripheral surface of the winding sheath body 21. Thus, the modification illustrated in Fig. 5 is formed. In the manner described above, even if the stress is concentrated on the winding sheath body 21 when the prestress is given to the tension materials 3, the winding sheath body 21 is reinforced by the steel pipe covered on the winding sheath body 21, so that the destruction of the sheath is not caused. Further, pressure bonding of the grips 33 improves an adhering stress between the tension materials 3 and the anchor grout 8. Thus, it is possible to construct the anchor which is superior as a whole. As described above, according to the construction of the anchor body of the first embodiment, the following advantages can be produced. That is, the winding sheath made of steel is employed, and the steel pipe is covered on the end of the winding sheath and, if necessary, the pipes are covered on the intermediate section thereof at which the stress is concentrated. Accordingly, the strength is rapidly or considerably improved. Thus, it is possible to secure that the destruction or the like of the sheath is prevented from being caused, and the anchor body can be manufactured at relatively low cost. Further, since various sizes of the winding sheaths made of steel come into market in plenty, the winding sheaths are easily available as compared with the deformed sheath made of polyethylene. Accordingly, the steel winding sheaths are superior in execution ability. At the execution, it is possible to assemble the steel winding sheaths not only at the factory, but also at the scene of labor. Thus, there is provided the structure of the anchor body which is high in the practical-use advantages. Referring next to Figs. 6 and 7, there is shown a structure 40 of an anchor body according to a second embodiment of the invention. As shown in Figs. 6 and 7, the structure 40 of the anchor body comprises a deformed winding sheath body 21 made of steel, whose both ends are open or whose one end is open and the other end is closed, and a plurality of pipes 22 made of steel, which are fixedly mounted to an inner peripheral wall of the sheath body 21 at an end thereof. A tension material 3 is inserted in the sheath body 21 which has mounted therein the steel pipes 22. The cement paste 8 is poured into the sheath body 21. The grout 5 is poured into the excavated bore 2 and is hardened. Thus, the fastening section A is formed. That is, in the second embodiment, the steel pipes 22 fixedly mounted to the outer peripheral wall of the winding sheath body 21 in the aforesaid first embodiment are fixedly mounted to the inner peripheral wall of the sheath body 21. In the illustrated embodiment, a suitable number of steel pipes 22 is fixedly mounted not only to both the ends of the inner peripheral wall of the sheath body 21, but also to the intermediate section thereof in the longitudinal direction. In the second embodiment, fixed mounting of the steel pipes 22 to the sheath body 21 is practiced as follows, for example, as shown in Figs. 8(A) and 8(B). The steel winding sheath body 21 formed as described above and having its desirable bore diameter is first prepared. Apart from the winding sheath body 21, a steel straight cylindrical body having its tube thickness larger than that of the sheath body 21 is cut into desired lengths and is prepared, as shown in Fig. 8(A). At this time, the cylindrical body is selected to have its outer diameter sufficient to be inserted into the tube of the sheath body 21. The adhesives 23 are applied to the outer peripheral wall of the steel pipe 22 formed in shivering to the desired size as described above. The steel pipe 22 is inserted in and fitted in the interior of the winding sheath body 21 from the one end thereof. At this time, the outer diameter of the pipe 22 is slightly smaller than the inner diameter of the winding sheath body 21, and the projecting ridgelines 21a do not project from the inner periphery of the pipe 22 unlike its outer peripheral wall. Accordingly, it is possible to easily insert and fit the pipe 22 into the winding sheath 21 without catching. Particularly, as compared with the fact that the steel pipes 22 are covered on the outer peripheral wall of the winding sheath body 21 like the aforesaid first embodiment, the following advantage can be produced. That is, in the case where the steel pipes 22 are inserted in and fitted in the inner peripheral wall of the winding sheath body 21, the steel pipes 22 are fixed naturally as a whole by the hardener such as the cement paste 8 or the like poured into the winding sheath 21. Thus, it is possible to easily manufacture the steel pipes 22. Furthermore, since the inner peripheral wall of the winding sheath body 21 has a certain degree of irregularities, no problem occurs regarding the adhering yield strength. In the case where the anchor construction is executed, the steel pipes 22 are fixedly mounted respectively to the locations within the winding sheath 21. Accordingly, when the winding sheath is inserted in the anchor excavated bore, the winding sheath can extremely easily be executed without catching to a drill pipe. Further, as shown in Fig. 8(B), it is also possible to beforehand apply the adhesives 23 to a location on the winding sheath 21 to be reinforced and, subsequently, to insert and fixedly mount the steel pipe 22 to a location within the sheath body 21. The deformed bond sheath according to the second embodiment is completed in the manner described above. It is suitably decided depending upon the conditions such as the bore diameter, length and the like of the sheath body 21 by which one of the methods illustrated in Figs. 8(A) and 8(B) the deformed bond sheath is manufactured. The above description has been made to the tension-type anchor taken as an example. As shown in Fig. 9, however, it is needless to say that the second embodiment is applicable to a compressive-type anchor 50 similarly to the first embodiment. Furthermore, a modification of the second embodiment is shown in Fig. 10. In the modification, a plurality of tension materials 3 are inserted in the winding sheath body 21 made of steel. A plurality of pressure grips 33 are mounted respectively to portions of the tension materials 3 adjacent the forward ends thereof, at suitable intervals Thus, all of the pressure grips 33 are fastened within the sheath 21 by the cement paste 8 or the like. A plurality of steel pipes 22 are inserted respectively in suitable locations including the end of the inner peripheral surface of the winding sheath body 21. In this manner, the winding sheath body 21 is constructed. Thus, even if the stress is concentrated onto the winding sheath body 21 when the prestress is given to the tension materials 3, the winding sheath body 21 is reinforced by the fact that the steel pipes 22 are inserted in the winding sheath body 21, so that breaking of the sheath is not caused. Further, bonding of the grips 33 improves the adhering stress between the tension materials 3 and the anchor grout 8, so that it is possible to construct the anchor which is superior or good as a whole. As described above, the second embodiment can produce the functional advantages similar to those of the first embodiment. Particularly, however, as compared with the case where the steel pipes are covered on the outer peripheral wall of the winding sheath, the following advantages can be produced. That is, in the case where the steel pipes are inserted in the inner peripheral wall of the winding sheath, the steel pipes are naturally fixed as a whole by the hardener such as cement paste or the like poured into the sheath body. Thus, it is possible to easily manufacture the steel pipes. Furthermore, since the inner peripheral wall of the sheath body has a certain degree of irregularities, no problem occurs regarding the adhering yield strength. In the case where the anchor construction is executed, the following advantage can be produced. That is, since the steel pipes are fixedly mounted within the sheath body, insertion of the winding sheath into the anchor excavated bore does not catch the winding sheath to the drill pipe. Thus, the anchor construction can extremely easily be executed. In connection with the above, a modification of the embodiment illustrated in Figs. 1 and 2 can produce the following advantage. That is, a case is considered where the pressure grips 33 are fixedly mounted to suitable locations on the tension materials 3 inserted in the winding sheath 21. In this case, if the steel pipes 22 are covered on the locations on the outer peripheral wall or are inserted in the location on the inner peripheral wall of the winding sheath, which are located in opposite relating to the pressure grips 33, even it the stress is concentrated locally onto the pressure grips 33, destruction of the winding sheath 21 can be prevented from occurring, because the the winding sheath 21 at the locations where the pressure grips 33 are provided is reinforced by the steel pipes 22. Referring next to Figs. 11 and 12, there is shown a structure 60 of an anchor body according to a third embodiment of the invention. As shown in Figs. 11 and 12, the structure 60 of the anchor body comprises a deformed sheath body 61 made of synthetic resin, whose both ends are open or whose one end is open and the other end s closed, and a plurality of steel pipes 22 fixedly mounted to the inner peripheral wall of the end region of the sheath body 21. The tension material 3 is inserted in the sheath body 61 having mounted therein the steel pipes 22. A hardener such as the cement paste 8 or the like is poured into the sheath body 61, and the grout 5 is poured into the excavated bore 2 and is hardened. Thus, the fastening section A is formed. That is, the third embodiment employs the deformed sheath body 61 made of synthetic resin, in substitution for the steel winding sheath body 21 employed in the first and second embodiments. The steel pipes 22 are fixedly mounted to the inner peripheral wall of the deformed sheath body 61. The sheath body 61 made of synthetic resin is formed with a plurality of projecting ridgelines 61a at constant intervals along the outer peripheral wall of the sheath body 61. The deformed sheath includes a sheath in which the projecting ridgelines 61a are continuously formed in a spiral manner along the peripheral wall of the deformed sheath in the peripheral direction, and a sheath in which the projecting ridgelines 61a are discontinuously formed in a spiral manner along the peripheral wall of the deformed sheath in the peripheral direction. In the third embodiment, the reason why the deformed sheath is made of synthetic resin is that the resinous deformed sheath is higher in rust-prevention effects than the steel deformed sheath, As a result of various experiments conducted by the applicant of the present invention, the following facts have been found. That is, the restricting effects of the steel pipes 22 are considerably higher than those expected or anticipated originally. Accordingly, even in the case of the deformed sheath made of synthetic resin, which has been considered unusable because of being low in restricting effects, the deformed sheath can sufficiently withstand the use, if the deformed sheath is used with the steel pipes mounted to the sheath. Accordingly, in the third embodiment, in view of the considerably high restricting effects of the steel pipes 22, the deformed sheath made of synthetic resin having the rust-preventing effects is daringly used even if the restricting effects are low. In the illustrated embodiment, the desirable numbers of steel pipes 22 are fixedly mounted not only to both the ends of the inner peripheral wall of the sheath body 61, but also to the intermediate section thereof in the longitudinal direction. Here, the length of each of the steel pipes 22 is not particularly limited. In view of the execution ability and the restricting effects, however, it has been confirmed by experiments that the steel pipe of the order of 20 cm to 50 cm is preferable in length. That is, if the length of the steel pipe is less than 20 cm, it is difficult to obtain a sufficient restricting force, while, if the length of the steel pipe is too excessive, the characteristic of elasticity that is the characteristic of the deformed polyethylene sheath is lost, and the pouring ability of the grout poured into the sheath is deteriorated. Further, since, generally, the inner surface of the steel pipe 22 is brought to a smooth surface, excessive length of the steel pipe 22, will cause reduction of the adhering force. Thus, it is preferable that the steel pipe is confined to the length of the order of 50 cm to the maximum. In this connection, if the steel pipe having formed therein a plurality of bores is used, it is possible to prevent the adhering force to be reduced even if the steel pipe is formed long more or less. As shown in Figs. 13(A) and 13(B), fixed mounting of the steel pipe 22 to the sheath body 61 is practiced by an execution method similar to that of the second embodiment. In this case, as shown in Fig. 13(A), the deformed sheath 61 made of synthetic resin and having its suitable bore diameter, formed in the summer described above, is prepared. Apart from the above, the steel straight cylindrical body, whose tube thickness is larger than that of the sheath body, is cut into desired lengths, for example, into 20 cm to 50 cm, and is prepared. At this time, the cylindrical body is selected to have its bore diameter which is sufficient that the inner peripheral wall of the sheath body 61 is loosely fitted in the cylindrical body, The above description has been made taking the tension anchor as an example. As shown in Fig. 14, however, it is needless to say that the third embodiment is applicable to the case of a compressive-type anchor 70, similarly to the first and second embodiments. Further, a modification of the third embodiment is shown in Fig. 15. In the modification, a plurality of tension materials 3 are inserted in the deformed sheath body 61 made of synthetic resin. A plurality of pressure grips 33 are mounted to portions of the respective tension materials 3 adjacent the forward ends thereof in suitable intervals. All of these tension materials 3 and pressure grips 33 are fixedly mounted in the sheath 61 by the cement paste 8 or the like. A plurality of steel pipes 22 are inserted in and fitted in suitable locations including the end of the inner peripheral surface of the winding sheath body 21. in this manner, the compressive-type anchor 70 is formed. As described above, the third embodiment indicates functional advantages principally similar to those of the second embodiment. As a result of repeated experiments described previously, however, in view of the fact that the restricting effects of the steel pipe 22 are considerably higher than those expected, the deformed sheath made of synthetic resin and having rust-prevention effects is daringly used even if the restricting effects are low. Thus, the third embodiment provides the synthetic or composite effects in a series of experimental results. Referring next to Fig. 16, there is shown a structure 80 of an anchor body according to a fourth embodiment of the invention. As shown in Fig. 16, the structure 80 of the anchor body is formed in the excavated bore 2 which is formed by excavation of the natural ground 1. A plurality of tension materials 3 each consisting of the PC stranded wire or the like are inserted in the excavated bore 2. Portions of the respective tension materials 3 at the forward ends thereof, which are brought to the fastening section A , are covered by a deformed sheath 81 whose tube peripheral wall presents an irregular configuration. As the deformed sheath 81, a deformed sheath made of synthetic resin or steel, whose both ends are open or whose one end is open and the other end is closed, is used, or a winding sheath similar to the deformed sheath is employed. Further, a portion of each of the tension materials 3 adjacent the surface of the earth, which is to be brought to a free length portion B , is covered with an un-bond sheath 4 made of synthetic resin. Furthermore, a plurality of pressure grips 33 for increasing the adhering force between the tension materials 3 and the hardener such as the grout 5 or the like are fixedly mounted, at suitable intervals, to the portions of the tension materials 3 which are brought to the fastening section A . A plurality of steel pipes 22 are covered on or inserted in portions of the peripheral wall of the deformed sheath 81, which face toward the pressure grips 33 fixedly mounted to the tension materials 3. The steel pipes 22 are provided for compensating for the restricting force of the deformed sheath 81 with respect to the tension materials 3 and prevent the deformed sheath 81 from being broken. In the illustrated embodiment, the steel pipes 22 are covered on the outer peripheral wall of the deformed sheath 81 at respective locations facing toward the pressure grips 33. The steel pipes 22 are so positioned as to reinforce portions of the deformed sheath 81 adjacent the pulling side more than the pressure grips 33, front the outside. Further, the previous experiments indicate that the length of each of the steel pipes 22 is not particularly limited or restricted. It has been confirmed, however, that, in the case where the execution ability and the restricting effects are taken into consideration, it is preferable that the length of the steel pipe 22 is of the order of 20 cm to 50 cm. As shown in Figs. 16 and 17, a grip packing 82 is interposed at or mounted to a location nearer the surface of the earth than each of the pressure grips 33 on the tension material 3, and is located adjacent the pressure grip 33. The grip packing 82 is made of a material having compressibility and rust-prevention effects, such as rubber, synthetic resin or the like. As shown in Figs. 17 and 18, the grip packing 82 is formed into a ring-shaped configuration. The grip packing 82 has its outer diameter D which is substantially equal to the outer diameter R of the pressure grip 33. The inner diameter d of the grip packing 82 is substantially equal to the outer diameter r of the tension material 3. Furthermore, the grip packing 82 is set to have its adequate thickness depending upon the length extending from the pressure grip 33 on which the grip packing 82 is mounted, to the forward end of the fastening section, and the magnitude of the tension force of the tension material 3. Specifically, the thickness t of the grip packing 82 can be obtained by the following equation: In σ PM · s = E· ε, where, for example, σ PM : PC stranded wire breaking force = 19,000 Kg/cm² s: Safety factor = 0.6 E: Elastic modulus = 2.0 x 10⁶ ε: Distortion factor. Then, 19,000 x 0.6 = 2.0 x 10⁶ x ε ε = 1.14 x 10⁴/2.0 x 10⁶ = 0.57 x 10² ≒ 0.006 Thus, 100 x 0.006 = 0.6 cm = 6 mm. As a result of the experiments, 3 mm/m that is half of the above value is employed as the thickness t of the grip packing 82. For example, as shown in Fig. 19, if the designed fastening length of the anchor body in the PC stranded wire breaking force = 19,000 Kg/cm² is 6 m, and if there are provided three pressure grips A , B and C , the following equation can be obtained: 3 mm/m x 4 m = 12 mm because the length from the pressure grip A to the forward end of the fastening section is 4 m. Thus, the grip packing having its thickness t = 12 mm is interposed at or mounted to a location on the pressure grip A on the side of the surface of the earth and adjacent the pressure grip A . Likewise, the grip packing having its thickness of t = 3 mm/m x 2 m = 6 mm is mounted to a location on the pressure grip B on the side of the surface of the earth and adjacent the pressure grip B . The pressure grip C is brought to its thickness t = 3 mm/m x 0 m = 0 mm. Thus, the grip packing is not required. The cement paste 8 is poured into the space within the excavated bore 2 and is hardened, and the cement paste 8 or the grout 5 is poured into the deformed sheath 81 at the forward ends of the tension materials 3 and is hardened. Thus, the forward ends of the tension materials 3, on which the pressure grips 33 are fixedly mounted, are fastened and fixed so that the fastening section A is formed. Subsequently, the extension sides of the tension materials 3 are tensioned by a jack or the like, whereby a prestress is given to the tension materials 3, If the tension stress is loaded on the tension materials 3, the adhering force of the tension materials 3 is large because the plurality of pressure grips 33 are fixedly mounted to the tension materials 3 which are inserted in the deformed sheath 81. Thus, a concentrated stress tends to occur at a location adjacent each of the pressure grips 33a which are originally located nearest the surface of the earth. In the embodiment, however, the ring-like grip packing 82 is mounted to a location nearer the surface of the earth than each of the pressure grips 33 and adjacent the latter. Since the grip packing 82 has compressibility, the grip packing 82 is pushed by the pressure grip 33 under the tension force of the tension material 3, and is compressed within the fastening section A . By doing so, the pressure grips 33 are successively moved toward the surface of the earth within the fastening section A by the shrinkage allowance of the grip packings 82 which have the compressibility. As a result, the tension stress is loaded on the pressure grips 33 in a dispersed manner. Now, an example of the experimental results will be indicated. As described with reference to Fig. 19, if the thickness t of the grip packing 82 is successively thinned toward the forward end, in the case where the tension stress of 100 t is loaded on the tension material, the stress is loaded on the pressure grips A , B and C by approximately 33.3 t in a dispersed manner substantially equally. By doing so, it is possible to prevent the deformed sheath 81 and the steel pipes 22 reinforcing the same from being broken due to the concentrated stress. Thus, the anchor strength can considerably be improved. Further, since the grip packing 82 is made of the material such as rubber, synthetic resin or the like, the grip packing 82 has rust-prevention effects. Even if the grip packing 82 is provided adjacent each of the pressure grips 33, the pressure grip 33 and the tension material 3 are not corroded, making it possible to maintain the anchor body in a healthy condition. In the case where, in the present embodiment, the plurality of tension materials 3 are inserted in the deformed sheath 81 in a bundled manner, as shown in Fig. 20(A), if the pressure grips 33 provided on the tension materials 3 are superimposed upon each other in the radial direction at the same locations on the tension materials 3 in the longitudinal direction, the outer diameter D₁ of the bundled tension materials 3 is correspondingly increased. As a result, the diameter of the excavated bore becomes excessively large, and this is uneconomical. In view of the above, as shown in Fig. 20(B), the pressure grips 33 adjacent each other in the radial direction of the excavated bore 2 are provided in slight deviation toward the surface of the earth in the longitudinal direction of the tension materials 3 by, for example, the length of each of the pressure grips 33, such that the pressure grips 33 are not superimposed upon each other, whereby it is possible to reduce the outer diameter D₂ of the bundled tension materials as a whole, that is, D₁ > D₂. Thus, the excavated bore can be reduced in size and reduction of the cost of construction can be achieved. In the case where the position of the pressure grip 33 is deviated and the tension materials 3 are bundled to each other in the manner described above, it is preferable that the steel pipes 92 inserted in or covered on the peripheral wall of the deformed sheath 33 are formed slightly long. Figs. 20(A) and 20(B) show the case where the steel pipes 22 are inserted in the interior of the peripheral wall of the deformed sheath 81. In connection with the above, the applicant of the present invention has already filed an application relating to a technique associated with the above-technique, in which an un-bond sheath is employed along the entire length of the tension material other than its portion at which the pressure grip is fixedly mounted. In the prior technique, however, the tension stress tends to be concentrated onto the pressure grip at a location nearest the surface of the earth. As a result of the practical execution and experiments, an adequate proposal has not yet been made as a method of reinforcing the pressure grip. In view of the above, like the present invention, the entire length of the tension material 3 is not brought to the un-bond sheath, and almost all portions except for the grip packing 82 are adhered by the hardener. Thus, the tension stress can be dispersed on the pressure grips 33, making it possible to improve the prior application. In connection with the above, in the fourth embodiment, description has been made to the case where the plurality of tension materials 3 are inserted in the deformed sheath 81. It is needless to say, however, that the invention can equally be applied to a case where a single tension material 3 is employed, and the plurality of pressure grips 33 are fixedly mounted to the single tension material 3. As described above, according to the structure of the anchor body of the fourth embodiment, the tension stress is loaded, in a dispersed manner, on the plurality of pressure grips which are fixedly mounted to the at least one tension material to be inserted in the deformed sheath, at suitable intervals. By doing so. it is possible to prevent breakage of the deformed sheath and the steel pipes reinforcing the deformed sheath. Thus, there is produced an extremely superior advantage that the anchor strength can considerably be improved. In connection with the above, the first through fourth embodiments are arranged as follows. That is, the excavated bore 2 is first excavated in the natural ground 1 or the like by an excavator such as a rotary percussion or the like. Subsequently, the deformed sheath 21, 61 or 81 is reinforced by the steel pipes 22. The deformed sheath 21, 61 or 81 reinforced by the steel pipes 22 is inserted in the excavated bore 2. The at least one tension material 3 or the at least one tension material 3 having fixedly mounted thereto the pressure grips 33 is inserted in the deformed sheath 21, 61 or 81 within the excavated bore 2. Subsequently, the cement paste 8 is poured in the deformed, sheath 21, 61 or 81, and the grout 5 is poured in the excavated bore 2 and is hardened. Thus, the fastening section A is formed to construct the anchor body.

Claims: Ground anchor body, comprising a deformed sheath (21) having a tubular body whose peripheral wall presents an irregular configuration; and at least one tension member (3) for insertion into the sheath (21); characterized in that steel pipe sections (22) are fixedly mounted to at least an end portion of the inner or outer side of the peripheral wall of the sheath (21) for reinforcing said sheath (21), the internal diameter of the pipe sections (22) exceeding the diameter of the tension member (3) to allow hardener to flow beyond the pipe sections (22), said ground anchor body for insertion into a borehole which together with the sheath (21) is to be filled by a hardener. Ground anchor body according to claim 1, characterized in that the tension member (3) is provided with at least one pressure grip (32, 33) fixedly mounted thereto. Ground anchor body according to claim 2, characterized in that the pressure grips (33) are positioned within the pipe sections (22). Ground anchor body according to anyone of the claims 1 to 3, characterized in that the sheath (21) is of steel, especially a winding body of steel, or of synthetic resin. Ground anchor body according to anyone of the claims 2 to 4, characterized in that a plurality of grip packings (82) having compressibility and rust-prevention effects is mounted respectively to portions of the tension members (3) nearer the earth surface than the pressure grips (33, 33a) and respectively adjacent said pressure grips (33a). Ground anchor body according to claim 5, characterized in that each of the grip packings (82) has a thickness which is suitably set depending upon a length from a position of a corresponding one of the pressure grips (33a) being mounted thereto the grip packing (82), to a forward end of the section to be filled by the hardener, and a magnitude of a tension force on the tension members (3). Method of installing a ground anchor body according to anyone of the claims 1 to 6, characterized in excavating a borehole (2) into a natural ground (1); reinforcing at least an end portion of the outer or inner peripheral wall of a deformed sheath (21) having a tubular body whose peripheral wall presents an irregular configuration with a plurality of steel pipe sections (22); inserting the reinforced sheath (21) into the borehole (2); inserting at least one tension member (3) into the inserted sheath (21); pouring a hardener into the borehole (2) and the space within the sheath (21) to form a fastening section; and tensioning said at least one tension member (3) to fasten said sheath (21). Method according to claim 7, characterized in that a plurality of pressure grips (32, 33) are fixedly mounted onto the plurality of tension members (3) in a configuration facing to the pipe sections (22). Method according to claim 8, characterized in that a plurality of grip packings (82) are mounted respectively at locations adjacent said pressure grips (33a) and at locations on said tension members (3) nearer to the earth surface than the pressure grips (33a). Method according to anyone of the claims 7 to 9, characterized in that the pipe sections (22) are fixed to the sheath (21) by an adhesive.

Inventors: YAMADA KUNIMITSU, YAMADA YASUHIRO, YAMADA, KUNIMITSU, YAMADA, YASUHIRO
Applicants: KENSETSU KISO ENG, STRONGHOLD INT JAPAN, KENSETSU-KISO ENGINEERING CO., LTD., STRONGHOLD INTERNATIONAL JAPAN CO., LTD.
Application year: 1990
Main classification: E02D5
IPC codes: E02D5, A47K3