GROUND REINFORCING METHOD

Abstract: A natural ground reinforcing construction method applied in excavation of for example a tunnel or cavern, characterized in that a ring bit (20) having a drilling function is provided at a tip end of a pipe (11) made of fiber reinforced resin, a drill rod (22) having a base end portion mounted to a rock drill (10) and having a drill bit (22a) mounted at its tip end is stored in the pipe, the bit is detachably mounted directly or indirectly to the pipe, drilling is performed into natural ground in a prescribed position at the outer periphery of the stall and/or the face in excavation of a tunnel or the like while sequentially supplying and connecting the pipes (11) and the drill rods (22), as the drill bit advances, the pipe engaged with the bit is drawn, propelled and placed into the natural ground to be laid as a reinforcing pipe in a prescribed position in the natural ground, upon or after placing the pipe, the drill rod is pulled out and retracted and then a solidifying material is injected into the surrounding natural ground through the pipe to reinforce the natural ground. In this way, the natural ground can be reinforced well without expanding the width of the tunnel cross section.

Description: Technical Field The present invention relates to a natural ground reinforcing construction method such as fore-piling and face reinforcing construction methods applied as a natural ground pre-reinforcing construction method at the time of excavating for example a tunnel or cavern. The invention particularly relates to a natural ground reinforcing construction method applicable in poor geological conditions. Background Art In conventional tunnel construction, the portal is selectively provided in a location excluding any inclined surface which is unstable for its landform and geology, but in recent years, portal positions tend to be planned regardless of the location or geology. According to conventional methods, the section of heading is small in a location in poor geological conditions, short fore-poling is employed in order to improve the self supportability of the stall crown, and short resin bolts are used for improving the self supportability of the stall face, so that the ground in the location is more stabilized. However, in recent years, in such cases, a natural ground fore-piling construction method using long fore-piling pipes or a face reinforcing construction method by resin bolts is often employed in advance to reinforce the natural ground ahead of the tunnel stall. According to these natural ground fore-piling construction method and face reinforcing construction method, the natural ground ahead of the stall is fastened for a long length, so that the ground can be prevented from being loosened in advance, and the fore-piling length is greater than the conventional short fore-poling face reinforcing construction. The natural ground fore-piling construction characterized in its various drilling methods using the long fore-piling steel pipes is performed, and the long face reinforcing construction is also provided using resin bolts in various shapes. The injection type long fore-piling construction method (AGF method or tube umbrella method) is an example of such a natural ground fore-piling construction method. According to the AGF method or the tube umbrella method, using a drill jumbo or the like for tunnel excavation, drilling is performed using a diameter widening drill bit attached at the tip end of a drill rod and having a size larger than the size of a steel pipe as water is flushed from the rock drill, steel pipes having a size of about 3 m are sequentially supplied and connected by the double-pipe method as the drilling work proceeds, and the steel pipes are placed for a long length. The steel pipes placed for a prescribed length are laid in the ground, and a solidifying material is injected into the surrounding ground through the steel pipes, so that the ground is more stabilized. Fig. 9 is a schematic view showing how the tunnel ground fore-piling construction according to the AGF method or the tube umbrella method is performed. According to the AGF method or the tube umbrella method, a steel pipe 1 is placed from the inside (the lower side in Fig. 9) of a steel tunnel support 2 at the tunnel stall F using a drill jumbo or the like which is not shown. The steel pipe 1 is placed at an angle of elevation T of about 5° so that the steel pipe 1 is positioned at a minimum distance from the back of steel tunnel supports 2 to be built ahead of the stall. In order to secure the placing angle, a width-expanded section S about as large as 6 m for the guide shell length of the drill jumbo is provided, and using the lower end of the steel tunnel support 2 already built in the immediate vicinity of the stall F as a ruler, the steel pipes 1 are sequentially placed for the entire length at prescribed intervals. Among the AGF methods or the tube umbrella methods, there is the AGF-P method according to which a resin pipe (vinyl chloride pipe) is laid as the pipe at the terminal end of the steel pipes. Fig. 10 is a schematic view showing how the tunnel ground fore-piling construction according to the AGF-P method is provided. Also according to the AGF-P method, using the drill jumbo or the like which is not shown, the steel pipe 1 is placed as it is pressed from the inside of the steel tunnel support 2 already built in the immediate vicinity of the tunnel stall F. The steel pipe 1 is provided at the back of the steel tunnel supports 2 to be build ahead of the stall, a resin pipe (vinyl chloride pipe) is laid as the pipe at the terminal end of the steel pipes 1, the resin pipe is provisionally buried in a position hindering the steel tunnel support 2 from being built in the tunnel excavation such as the range within three tunnel supports (three tunnel supports 2a, 2b, and 2c) ahead of the stall at an angle of elevation T of about 10° on the condition that it is to be removed at the time of building the tunnel supports. According to the method, the steel pipes are placed at prescribed intervals using the lower end of the steel tunnel support in the immediate vicinity of the stall F as a ruler without providing a width-expanded section in the tunnel cross section and steel pipes are used for the entire length except for the pipe at the terminal end. Meanwhile, as an example of long face reinforcing construction, when the geological conditions are poor, the walls of drilled bolt inserting holes are not self supporting, and therefore self-boring resin bolts are inserted or long hollow resin bolts are sequentially inserted as drilling is performed by a double pipe method with a dedicated machine (boring machine). The face reinforcing construction is necessarily performed using short resin bolts. The bolts used for the face reinforcing construction is glassfiber reinforced resin bolts having a diameter from 22 mm to 32 mm, and when the walls are self supporting by long-size construction for 8 m or more, couplers are used for connection. Therefore, the drilled holes often have a diameter about as large as 75 mm. Fig. 11 is a schematic view showing how face reinforcing construction is performed using a dedicated machine (boring machine), and using the dedicated machine 5, long hollow resin bolts 6 are sequentially inserted by the double pipe drilling. The outer pipe casing is retracted after the entire length of the long hollow resin bolt 6 is inserted. The inserted long hollow resin bolts 6 are laid in the natural ground, and a solidifying material is injected into the surrounding ground through the hollow resin bolts 6 in the holes H to be fixed according to this method. Incidentally, JP11-182173 discloses a modified example of the AGF-P method. In JP11-182173, the combined body comprises the steel pipe, the joint member and the resin pipe. In the state of the sheath pipe being removably fitted to the outside of the resin pipe, the drill connected with the steel pipe driving apparatus through the rod is inserted into combined body from the back end of the sheath pipe, and the combined body is set in the steel pipe driving apparatus. When the edges of the drill are located in the inside of the combined body, the diameter of the edges is reduced so that the edges can carry out attitude movement of the inside of the combined body. When the edges rush into the natural ground, the diameter of the edges is expanded larger than the outer diameter of the steel pipe. The driving load for driving the combined body added to the back end of the sheath pipe by the steel pipe driving apparatus is transmitted to the back end surface of the joint member adhered to the steel pipe via the tip end surface of the sheath pipe. After the sheath pipe is removed from the resin pipe, the resin pipe is excavated with the excavated zone ahead of the face. Further, JP9-184400 discloses the self-drilling bolt having the pipe-shaped rod made of fiber reinforced thermosetting resin. According to the above described injection type fore-piling method (AGF method or tube umbrella method), the steel pipe is placed at an angle of elevation of about 5° so that the pipe is positioned at a minimum distance from the back of the steel tunnel support ahead of the tunnel stall using the drill jumbo or the like. In order to secure the minimum placing angle, a cross section width expanded section about as large as 6 m for the guide shell length of the drill jumbo should be provided. This increases extra excavation and the amount of the material such as concrete for the expanded width of the tunnel cross section, and the workload such as tunnel excavation increases. More specifically, a space larger than the size of the cross section as exactly necessary is excavated and provided with tunnel supports and lining, which is considerably wasteful. According to the tunnel natural ground fore-piling construction by the AGF-P method (one of the tube umbrella methods), a plurality of steel pipes are placed as they are pressed at prescribed intervals along the outer periphery of the tunnel cross section ahead of the tunnel stall without providing the width expanded section in the tunnel cross section, while drilling with a diameter widening drill bit mounted at the tip end of the drill rod. At the time, the pipe at the terminal end is a resin pipe (vinyl chloride pipe) and should be placed at the angle of elevation of about 10° to be within the range of about three supports ahead of the stall, on the condition that it is to be later removed. Therefore, the distance D between the steel tunnel supports and the steel pipe in the overlapping section (the section W shown in Fig. 12) is large, the ground under the steel pipe at the part may be unfastened depending upon the circumstances of the ground, and the resin pipe (vinyl chloride pipe) at the terminal end cannot be strong enough to hold, or the degree of ground improvement could adversely be affected. In this case, separate fore-piling reinforcement should be necessary, which increases the amount of the reinforcing material and the workload. In the face reinforcing construction in worse geological conditions, the walls of the drilled bolt insertion holes are not self supporting, and therefore a dedicated machine (boring machine) is necessary. Using the machine, a plurality of long hollow resin bolts are sequentially inserted into the casings by the double pipe drilling, and then the casing pipes are sequentially pulled out. The process has a problem of increasing the construction cost and period. The present invention is directed to a solution to the above described disadvantages associated with the conventional technique, and provides an efficient natural ground reinforcing construction method which always allows stable tunnel excavation to proceed without expanding the tunnel cross section at the time of performing long fore-piling construction at the minimum distances between the pipes and tunnel supports for reinforcing the natural ground, and without a dedicated machine in the face reinforcing construction method. Disclosure of the Invention The natural ground reinforcing construction method according to the present invention is directed to a solution to the above-described disadvantages and has the following features. More specifically, according to the present invention, a drill rod having a base end portion mounted to a rock drill and having a drill bit mounted at its tip end is stored in a pipe, drilling is performed into natural ground in a prescribed position at the outer periphery of the stall and/or the face in excavation of a tunnel or the like while sequentially supplying and connecting the pipes and drill rods, the pipe being propelled and placed into the natural ground as the drill bit advances, the pipes are laid as a reinforcing pipe in a prescribed position in the natural ground, upon or after placing the pipe, the drill rod is pulled out and retracted and then a solidifying material is injected into the surrounding natural ground through the pipe to reinforce the natural ground, characterized in that the pipe is made of fiber reinforced resin, that a ring bit having a drilling function and having a diameter larger than the outer diameter of the pipe is provided just after the end of pipe and outside the pipe, and that the pipe detachably engaging directly or indirectly with the drill bit is drawn into the natural ground by the drill bit. In another aspect of the invention, there is provided the natural ground reinforcing construction method, wherein a tunnel is excavated forward into the reinforced natural ground, the reinforcing pipe exposed into the tunnel space formed at the time is sequentially cut away, as a tunnel support is built along the inner surface of the tunnel, the pipe is propelled and placed into the natural ground as the pipe is directed to the front side at a prescribed angle to the excavation advancing direction from the tunnel space on the inner side than the tunnel supports already built. In another aspect of the invention, there is provided the natural ground reinforcing construction method, wherein the pipe is propelled and placed into the natural ground from the face toward the front side in the excavation advancing direction of the tunnel, and the placed reinforcing pipe including a plurality of pipes is sequentially cut away and removed entirely as the excavation proceeds. In another aspect of the invention, there is provided the natural ground reinforcing construction method, wherein the pipe is made of resin and reinforcing fiber, the resin is non-saturated polyester, epoxy, vinyl ester or the like, and the reinforcing fiber is glassfiber or carbon fiber or aramid fiber or the like. In another aspect of the invention, there is provided the natural ground reinforcing construction method, wherein the reinforcing pipe is attached with the ring bit having a drilling function at its tip end and includes a plurality of pipes threaded at both ends and connectable with one another, an adhesive is applied to the threaded parts at the time of connection and then a coupler is used for connection. In another aspect of the invention, there is provided the natural ground reinforcing construction method, wherein the reinforcing pipe is made of a pipe having an outlet hole for an injection material and has an inner diameter in the range from 60 mm to 120 mm, and a length in the range from 1 m to 12 m. In still another aspect of the invention, there is provided the natural ground reinforcing construction method, wherein when said reinforcing pipe is propelled, the base end portion of said drill rod is mounted to said rock drill through a swivel capable of supplying an injection material, a cement-based injection material is flushed through the swivel to reinforce the natural ground surrounding the reinforcing pipe, and said reinforcing pipe is laid in a prescribed position in the natural ground. Brief Description of the Drawings Fig. 1 is a schematic longitudinal sectional view showing a fore-piling reinforcing construction method using a high-strength glassfiber reinforced resin pipe according to a first embodiment of the present invention; Fig. 2 is a transverse sectional view showing fore-piling reinforcing at the tunnel stall shown in Fig. 1; Fig. 3 is an overview showing a high-strength glassfiber reinforced resin pipe and a drill machine according to one embodiment; Fig. 4 is a partially sectional view showing an example of the connection portion of a high-strength glassfiber reinforced resin pipe and a coupler; Fig. 5 is a schematic longitudinal sectional view showing an example of a face reinforcing construction method using a high-strength glassfiber reinforced resin pipe; Fig. 6 is a transverse sectional view showing how the face of the tunnel stall shown in Fig. 5 is reinforced; Fig. 7 is a transverse sectional view showing a valve injection method; Fig. 8 is a transverse sectional view showing a swivel injection method; Fig. 9 is a schematic view showing an example of a steel pipe fore-piling construction method according to a conventional AGF method; Fig. 10 is a schematic view showing an example of a steel pipe fore-piling construction method according to a conventional AGF-P method; and Fig. 11 is a schematic view showing an example of a conventional face reinforcing construction method using a dedicated machine. Best Mode for Carrying Out the Invention The natural ground reinforcing construction method according to an embodiment of the present invention shown in the drawings will now be detailed. Fig. 1 is a schematic view showing how the top section of a tunnel is subjected to fore-piling reinforcing construction by the fore-piling reinforcing construction method according to a first embodiment of the natural ground reinforcing construction method according to the present invention, and there is a drill jumbo 10 provided in the vicinity of the tunnel stall in the hanging wall of the tunnel. The tip end of the guide shell 10a of the drill jumbo 10 is set at the lower end of a steel tunnel support 12 built in the immediate vicinity of the stall face 15 after the excavation. According to the embodiment, the excavated wall surface between the face 15 in the direction of the longitudinal section of the tunnel and steel tunnel support (H-200x200) 12a in the immediate vicinity is lined with primary shotcrete (t=50 mm) 13, and then secondary shotcrete (t=200 mm) 14 is also provided in a prescribed lining thickness further at the back between the steel tunnel supports 12 already built at a pitch of 1 m. The stall face 15 is provided with shotcrete (t=100 mm) 16, and the face 15 is provided with a hole (not shown) drilled in advance and having a diameter of about 120 mm and a depth of about 300 mm in the ground in a prescribed position (see Fig. 2) at the lower end of the steel tunnel support 12a positioned along the outer periphery of the stall. Note that the hole dilled in advance is used to provide a leakage preventing gap larger than the steel pipe at the mouth portion surrounding the steel pipe where a solidifying material could be leaked to seal against the leakage, when the solidifying material is injected into the ground surrounding the pipe through a reinforcing pipe placed as will be described. The guide shell 10a shown in Fig. 1 is attached with a reinforcing pipe 11 made of fiber reinforced resin (FRP), particularly glassfiber reinforced resin (GFRP) according to the embodiment. At the tip end of the reinforcing pipe 11, a ring bit (not shown) having a diameter larger than the size of the reinforcing pipe 11 and a drilling function is attached, while the drill rod having the function of transmitting the striking force and pivoting force to the ring bit, and a function of drilling aid, is placed in the reinforcing pipe 11 and coupled to the rock drill, which will later be described. The guide shell 10a is set at such an angle of elevation (from 3° to 6°, preferably about 5°) that the reinforcing pipe 11 passes on the fourth steel tunnel support ahead of the stall counting from the one at the leading drilling position of the stall face 15. In the ground ahead of the stall where the tip end of the guide shell 10a is set, a series of four coupled reinforcing pipes 11 are placed. According to the embodiment, a plurality of reinforcing pipes 11 each as long as 3 m are coupled, and the reinforcing pipe is made of glassfiber reinforced resin for the entire length. In the ground around the reinforcing pipes 11 already placed, an improved zone is formed by injecting a solidifying material for the entire length, and a natural ground reinforcing effect as a result of fore-piling construction can be expected. The natural ground injection will later be detailed. Fig. 3 is a view for use in illustration of how drilling with the reinforcing pipe 11 made of the glassfiber reinforced resin is propelled to carry out the method according to the invention. According to the embodiment, the reinforcing pipe 11 having an outer diameter of 70 mm, an inner diameter of 60 mm, and a length of 3 m is used. A ring bit 20 having a drilling function is attached through a casing shoe 21 to the tip end of the reinforcing pipe 11 at the head, while a drill rod 22 having a drilling aiding function is stored in the reinforcing pipe 11 as it has a bit 22a mounted at the tip end protruded from the ring bit 20 toward the front side. The bit 22a of the drill rod 22 is detachably engaged with the ring bit 20 and the casing shoe 21, while the base end side of the drill rod 22 is connected to the shank rod 23a of the rock drill 23 by a shank sleeve 24. Thus, when the drilling work is performed, the striking force and rotating force from the rock drill 23 are transmitted to the bit 22a and the ring bit 20 through the drill rod 22, and the drilling is performed by the drill rod 22 sliding on the guide shell 10a integrally with the rock drill in association of the feeding operation of the rock drill 23. As the drilling work proceeds, the bit 22a draws the reinforcing pipes 11 engaged therewith through the ring bit 20 and the casing shoe 21 and thus the reinforcing pipe 11 is propelled and placed. Note that the above bit 22a may directly draw the reinforcing pipes. During the above drilling work, the ring bit 20 drills a hole having a larger size than the outer diameter of the reinforcing pipe 11, and the reinforcing pipe 11 is therefore smoothly drawn. As a result, despite its inferiority in terms of rigidity to a steel pipe and its long length, the reinforcing pipe 11 made of fiber reinforced resin can readily be placed at a prescribed angle of elevation (which is smaller than that according to the conventional AGF method or tube umbrella method) in a prescribed position in the ground by the drawing operation of the bit 22a positioned at the head of the hole and by the function of the leading ring bit 20 to ream the diameter. Therefore, when the tunnel supports 12 are sequentially built in the process of excavating the tunnel to the position of a new face 15' denoted by the broken line in Fig. 1, the supports can built at the minimum distance without expanding the width of the cross section unlike the conventional technique, so that the tunnel excavation can be stable. The reinforcing pipes 11 thus placed are made of fiber reinforced resin for the entire length, and therefore the part impeding the supports from being built can readily be cut and removed as required as the drilling work proceeds. Note that after the reinforcing pipes 11 are placed, the bit 22a can be reversely rotated, so that the engagement between the ring bit 20 and the casing shoe 21 is released, the drill rod 22 is detached from them, and the drill rod 22 including the above bit 22a is pulled out and retracted from the reinforcing pipes 11. The space created in the reinforcing pipes 11 after the drill rod 22 is pulled out is used as an injection path for a solidifying material. Fig. 4 shows an example of how the reinforcing pipes 11 for carrying out the method are connected. According to the first embodiment, the headmost pipe, the following intermediate pipes, and the terminal pipe are glassfiber reinforced resin pipes having an outer diameter of 70 mm, an inner diameter of 60 mm, and a length of 3 m. There is a connection portion 11a provided with a cutting thread having a V-shaped cross section to minimize cross section defects at both ends, a connection coupler 25 is made of aluminum and provided with a V-shaped raised cutting thread, and a resin-based adhesive is applied at the time of connection to improve the strength of the connection portion. A plurality of drill rods 22 and reinforcing pipes 11 of glassfiber reinforced resin are sequentially connected, propelled and placed for the entire length simultaneously with the drilling work, so that the reinforcing pipes of high-strength glassfiber reinforced resin can be laid for the entire length. Figs. 5 and 6 are schematic views showing how face reinforcing construction is performed at the top section of the tunnel in a face reinforcing construction method according to a second embodiment of the natural ground reinforcing construction method according to the present invention. As shown Fig. 5, there is a drill jumbo 10 in the vicinity of the stall in the hanging wall of the tunnel. The tip end of the guide shell 10a of the drill jumbo 10 is set at the stall face 15 after the tunnel excavation. According to the embodiment, the face 15 in the direction of the longitudinal section of the tunnel is provided with shotcrete (t=100 mm) 16 and there is a hole (not shown) drilled in advance having a diameter of about 120 mm and a depth of about 300 mm in the ground in a prescribed position at the face. The guide shell 10a shown in Fig. 5 is attached with the reinforcing pipe 11 made of glassfiber reinforced resin mounted with a ring bit (not shown) having a drilling function at the tip end similarly to the first embodiment shown in Fig. 1 described above, and a drill rod having a function of transmitting the rotating force and the striking force to the ring bit and aiding the drilling is attached to the rock drill. The guide shell 10a is provided at such an angle of elevation that slime is not kept from being let out at the time of drilling from the leading drilling position of the stall face into the natural ground ahead of the stall. In the natural ground ahead of the stall where the tip end of the guide shell 10a is set, a series of four connected reinforcing pipes are already placed. Also according to the embodiment, a plurality of reinforcing pipes each as long as 3 m are coupled, and the reinforcing pipe is made of glassfiber reinforced resin for the entire length. In the ground around the reinforcing pipes 11 already placed, an anchorage zone is formed by injecting a solidifying material for the entire length, and a natural ground reinforcing effect as a result of the face reinforcing construction can be expected. The natural ground injection will later be detailed. The method of propelling/drilling with the reinforcing pipes 11 and the method of connecting the reinforcing pipes 11 are the same as the case of the fore-piling natural ground reinforcing construction method according to the first embodiment shown in Figs. 1 to 4, and the methods are not detailed. The reinforcing pipes 11 according to the first and second embodiments described above are subjected to the same injection process. As an example of the injection method at the tunnel stall position according to the present invention, a subsequent injection, valve injection method and a prior injection, swivel injection method will be described. Fig. 7 shows an example of the valve injection method and the gap (mouth portion) between the rear end portion of the terminal one of the reinforcing pipes 11 laid for the entire length described above and the leading drilling portion described above is sealed with waste cloth 28 or the like impregnated with a urethane-based chemical agent, so that a solidifying material can be prevented from leaking. The solidifying agent is injected using the reinforcing pipes 11 laid for the entire length described above as the injection pipe. The reinforcing pipes 11 are therefore provided with strainer holes 11c at prescribed intervals as shown in Fig. 4 (b). At the rear end of the terminal one of the reinforcing pipes 11, an injection valve 29 is attached as shown in Fig. 7, and the solidifying material is introduced into the reinforcing pipes 11 through the injection valve 29 described above from an injection hose 31 connected to an injection device 30. The solidifying material introduced into the reinforcing pipes 11 is sequentially discharged from the strainer holes 11c of the reinforcing pipes 11, injected into the natural ground and solidified, so that the reinforcing pipes 11 and the surrounding ground are integrally reinforced. Meanwhile, Fig. 8 shows an example of the swivel type injection method, and the reinforcing pipes 11 are attached with the ring bit 20 described above having the drilling function at the tip end. A plurality of rods 22 and the reinforcing pipes 11 are sequentially connected for the entire length, propelled and placed as the drilling work proceeds. In the case of the valve injection, the drilling work is performed as water or air is flushed from the rock drill through the drill rods 22 having a drilling aiding function. In contrast, when the injection is performed by the swivel type method as shown in Fig. 8, a cement-based injection material is flushed through a swivel 33 provided in front of the rock drill during the drilling work, the wall surrounding the reinforcing pipes during the drilling work is stabilized for reinforcing the natural ground, and the reinforcing pipes 11 are laid for the entire length. Then, the gap (mouth portion) between the rear end of the terminal one of the reinforcing pipes 11 and the leading drilling portion described above is sealed by waste cloth 28 impregnated with a urethane-based chemical agent similarly to the case as shown in Fig. 7, so that the solidifying material can be prevented from leaking, and the solidifying material is injected. For injecting the solidifying material, the reinforcing pipes 11 laid for the entire length described above are used as the injection pipe. The injection valve is attached at the rear end of the terminal one of the reinforcing pipes 11, and the injection material is passed through the injection valve from the injection hose set at the injection device (not shown), discharged from the strainer holes 11c of the reinforcing pipes 11, injected into the ground and solidified, so that the reinforcing pipes 11 and the surrounding ground are integrally reinforced. Industrial Applicability As in the foregoing, according to the present invention, a plurality of pipes such as high-strength glassfiber reinforced resin pipes which can be cut are laid in the ground as a reinforcing pipe for long fore-piling for the entire length without using a dedicated machine and a solidifying material can be injected for the entire length into the ground surrounding the pipes through the reinforcing pipe. As a result, the placement angle of the reinforcing pipe can be restricted to a small value, the size of the tunnel cross section is not expanded, while the long fore-piling reinforcing construction can be provided as the distance between the reinforcing pipe and the tunnel supports is minimized. Since the fore-piling reinforcing pipe in the excavation range during the excavation of the tunnel can be cut, steel tunnel supports can readily be built in the same cross section. Therefore, the period and cost for an auxiliary construction method of the reinforcing construction method can be reduced, and the work efficiency can be improved. In the face reinforcing construction, a plurality of pipes such as high-strength glassfiber reinforced resin pipes which can be cut are laid in the ground as a reinforcing pipe for reinforcing the face for the entire length without using a dedicated machine, and a solidifying material can be injected for the entire length into the natural ground surrounding the pipes through the reinforcing pipe. As a result, it is not necessary to pull out the casing pipes by the double pipe drilling using the dedicated machine at the time of the face reinforcement as is with the conventional case. This allows the method to be easily and stably performed, the work efficiency to be improved and the construction period and cost to be reduced.

Claims: 1. A natural ground reinforcing construction method, wherein a drill rod (22) having a base end portion mounted to a rock drill (23) and having a drill bit (22a) mounted at its tip end is stored in a pipe (11), drilling is performed into natural ground in a prescribed position at the outer periphery of the stall and/or the face in excavation of a tunnel or the like while sequentially supplying and connecting the pipes (11) and drill rods (22), the pipe (11) being propelled and placed into the natural ground as the drill bit (22a) advances, the pipes (11) are laid as a reinforcing pipe (11) in a prescribed position in the natural ground, upon or after placing the pipe (11), the drill rod (22) is pulled out and retracted and then a solidifying material is injected into the surrounding natural ground through the pipe (11) to reinforce the natural ground, characterized in that the pipe (11) is made of fiber reinforced resin, that a ring bit (20) having a drilling function and having a diameter larger than the outer diameter of the pipe (11) is provided just after the end of pipe (11) and outside the pipe (11), and that the pipe (11) detachably engaging directly or indirectly with the drill bit (22a) is drawn into the natural ground by the drill bit (22a). The natural ground reinforcing construction method according to claim 1, wherein the tunnel is excavated forward into said reinforced natural ground, said reinforcing pipe (11) exposed into the tunnel space formed at the time is sequentially cut away, as a tunnel support (12) is built along the inner surface of the tunnel, said pipe (11) is propelled and placed into the natural ground as said pipe (11) is directed to the front side at a prescribed angle to the excavation advancing direction from the tunnel space on the inner side than the tunnel supports (12) already built. The natural ground reinforcing construction method according to claim 1, wherein said pipe (11) is propelled and placed into the natural ground from the face toward the front side in the excavation advancing direction of the tunnel, and the placed reinforcing pipe (11) including a plurality of pipes (11) is sequentially cut away and removed entirely as the excavation proceeds. The natural ground reinforcing construction method according to claim 1 characterized in that said pipe (11) is made of resin and reinforcing fiber, the resin is non-saturated polyester, epoxy, vinyl ester or the like, and the reinforcing fiber is glassfiber or carbon fiber or aramid fiber or the like. The natural ground reinforcing construction method according to claim 1 characterized in that said reinforcing pipe (11) is attached with the ring bit (20) having a drilling function at its tip end and includes a plurality of pipes (11) threaded at both ends and connectable with one another, an adhesive is applied to the threaded parts at the time of connection and then a coupler (25) is used for connection. The natural ground reinforcing construction method according to claim 1 characterized in that said reinforcing pipe (11) is made of a pipe (11) having an outlet hole (11c) for an injection material and has an inner diameter in the range from 60 mm to 120 mm, and a length in the range from 1 m to 12 m. The natural ground reinforcing construction method according to claim 1 characterized in that when said reinforcing pipe (11) is propelled, the base end portion of said drill rod (22) is mounted to said rock drill (23) through a swivel (33) capable of supplying an injection material, a cement-based injection material is flushed through the swivel (33) to reinforce the natural ground surrounding the reinforcing pipe (11), and said reinforcing pipe (11) is laid in a prescribed position in the natural ground.

Inventors: HABA TORU, KAKIUCHI YUKIO, MATSUO TSUTOMU, MITARASHI YOSHIO, HABA, TORU, KAKIUCHI, YUKIO, MATSUO, TSUTOMU, MITARASHI, YOSHIO
Applicants: KFC LTD, KFC LTD.
Application year: 1999
Main classification: E21D9
IPC codes: E21D20, E21D9