JP2015151813A - Frost heaving load suppressing method for freezing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a frost heaving load suppressing method for a freezing method, which can reliably and effectively suppress generation of a frost heaving load at a relatively low construction cost by discharging groundwater on the periphery of a frozen area.SOLUTION: A frost heaving load suppressing method for a freezing method includes: a boring step of boring long and short boreholes 1 and 2 into natural ground G from inside a tunnel T; a first freezing step of arranging a freezing pipe in the short borehole 2 and forming a frozen area R2 on the periphery of the inside of the tunnel while discharging groundwater from the long borehole 1; and a second freezing step of arranging a freezing pipe in the long borehole 1 in the stage of the completion of the first freezing step and forming a frozen area on the periphery of the outside of the tunnel.

Description

  The present invention relates to a method for suppressing frost heave pressure in a freezing method.

  Conventionally, when tunnel construction is performed by the shield method or mountain method, excavation work is performed while applying the ground reinforcement method to irregular cross sections such as widened parts, joints between shield pits and shafts, and geological defects. Like to do. In addition, as a natural ground reinforcement method, a boring hole is drilled in the natural ground (ground, bedrock), and a cooling liquid (refrigerant) is supplied and circulated through this boring hole to freeze the natural ground. A freezing method that increases the strength is frequently used (see, for example, Patent Document 1).

  Furthermore, for example, when building a tunnel with a desired diameter by excavating a surrounding natural ground from within a small-diameter shield, such as when constructing a branching / merging part of a tunnel or a station building in a tunnel of a railway tunnel, etc. In many cases, the freezing method is selected as the ground reinforcement method.

JP 07-216865 A

  Here, when freezing a natural ground around an existing structure by the freezing method, a freezing expansion pressure (freezing up pressure) generated due to freezing may act on the existing structure. Also in tunnel construction, there is a risk that frost heave pressure acts on existing structures such as segments and lining concrete, causing displacement. For this reason, conventionally, as measures against frost heave pressure, a method of reinforcing a structure to be installed in the freezing range in advance or a method of suppressing the frost heave pressure are taken.

  However, there is a problem that the cost increases when a method of reinforcing a structure to be installed in the freezing range in advance is applied.

  On the other hand, the groundwater in the surrounding natural ground moves near the freezing line (0 ° C isotherm in the ground temperature distribution map) and freezes in the vicinity to form an "ice lens". It is considered. It is known that the frost heave pressure can be suppressed by blocking the entry of moisture into the vicinity of the freezing line.

  For this reason, conventionally, as a technique for suppressing the frost heave pressure, a water-blocking method for suppressing the frost heave pressure by blocking the intrusion of moisture near the freezing line is frequently used.

  However, in the method of forming a water-impervious layer in the ground by grouting or the like, there are problems that the larger the frozen region, the higher the cost and the more reliable water-impervious becomes difficult.

  Further, in the method of suppressing the frost heave pressure by draining groundwater, it is necessary to use a deep well method or the like when draining the underground around the tunnel in the deep underground, and there is a problem that the cost is further increased.

  The present invention, in view of the above circumstances, drains groundwater around a freezing area, and is capable of reliably and effectively suppressing the occurrence of frost heave pressure at a relatively low construction cost, and a method for suppressing frost heave pressure in a freezing method. The purpose is to provide.

  In order to achieve the above object, the present invention provides the following means.

  The method for suppressing frost heave pressure in the freezing method according to the present invention includes a boring drilling step of drilling a long boring hole and a short boring hole from a tunnel to a natural ground, and placing a freezing pipe in the short boring hole. A first freezing step for forming a freezing region around the inside of the tunnel while draining groundwater from the long boring hole, and a freezing pipe is disposed in the long boring hole when the first freezing step is completed And a second freezing step for forming a frozen region around the outside of the tunnel.

  In the frost heave pressure suppression method in the freezing method of the present invention, the ground is frozen in two steps, the first freezing step and the second freezing step, so that groundwater in the vicinity can be reliably and effectively removed. By draining, the generation of frost heave pressure (freezing expansion pressure) can be suppressed, the external force acting on the existing structure can be reduced, and the natural ground can be suitably reinforced using the freezing method.

  In addition, the generation of frost heave pressure (freezing expansion pressure) can be easily suppressed and the external force acting on the existing structure can be reduced. Therefore, compared with the conventional design, the design can be streamlined and the construction cost can be reduced. It becomes possible.

  Furthermore, by using the borehole (long boring hole) where the freezing pipe is inserted and used for groundwater drainage, it is not necessary to use a water-blocking method such as grout or to provide a dedicated drainage hole. In view of this, it is possible to reliably and effectively suppress the occurrence of frost heave pressure at a low construction cost.

It is a tunnel cross-sectional view which shows the condition of a 1st freezing process in the freezing-up pressure suppression method in the freezing method which concerns on one Embodiment of this invention. It is a tunnel longitudinal cross-sectional view which shows the condition of a 1st freezing process in the freezing-up pressure suppression method in the freezing method which concerns on one Embodiment of this invention. It is a tunnel cross-sectional view which shows the condition of a 2nd freezing process in the freezing-up pressure suppression method in the freezing method which concerns on one Embodiment of this invention. It is a tunnel longitudinal cross-sectional view which shows the condition of a 2nd freezing process in the freezing-up pressure suppression method in the freezing method which concerns on one Embodiment of this invention.

  Hereinafter, with reference to FIG. 1 to FIG. 4, a frost heave pressure suppressing method in a freezing method according to an embodiment of the present invention will be described.

  First, the frost heave pressure suppression method in the freezing method of the present embodiment is applied to the area around the freezing area when applying the freezing method for the purpose of water stoppage or reinforcement of tunnel widening, unhealthy parts, etc. by shield method or mountain method. It is related with the method of suppressing generation | occurrence | production of frost heave pressure by draining the groundwater of this, and reducing the external force which acts on existing structures, such as a segment and a lining.

  Specifically, in the method for suppressing frost heave pressure in the freezing method according to the present embodiment, as shown in FIGS. 1 and 2, first, a boring hole (inserted) is drilled at a predetermined position of a natural ground (ground) G by boring. Holes 1 and 2 are drilled (boring drilling step). At this time, the bore holes are arranged at equal intervals in the circumferential direction S1 of the tunnel T with a predetermined interval. Further, the long boring holes 1 and the short boring holes 2 are alternately arranged in the tunnel circumferential direction S1. In addition, it is preferable to arrange the long boring holes 1 and the short boring holes 2 substantially alternately in the tunnel axis O1 direction S2.

  Next, a freezing tube for circulating brine (coolant) for freezing the natural ground G is inserted into the short boring hole 2. And while draining from the long boring hole 1, it cools by circulating a brine through the freezing pipe | tube arrange | positioned in the short boring hole 2 (1st freezing process).

  As a result, the drainage from the long boring hole 1 forms an unsaturated region R1 around the outside of the tunnel T, and the freezing region R2 around the inner side of the tunnel T in which the short inner boring hole 2 is disposed. Is formed. And by forming the unsaturated region on the outside and the frozen region on the inside in this way, the movement of groundwater is suppressed and the generation of frost heave pressure is suppressed.

  Next, in the freezing-up pressure suppression method in the freezing method of the present embodiment, as shown in FIGS. 3 and 4, the freezing region R2 is sufficiently formed around the inner side where the short boring holes 2 are disposed. Then, a freezing tube is inserted into the long boring hole 1 and cooled (second freezing step). At this time, since the ground strength of the freezing region R2 around the tunnel inner side has already increased, when the brine is circulated through the freezing pipe of the long boring hole 1 and the outer periphery is frozen, the freezing region around the inner periphery R2 suppresses the frost heave pressure from acting on existing structures 3 such as segments and linings.

  In the frost heave pressure suppression method in the freezing method of the present embodiment, as described above, in applying the freezing method for the purpose of water stoppage and reinforcement of the widened portion of tunnel construction by the shield method and the mountain method, the poor portion of the ground, etc. The long boring hole 1 and the short boring hole 2 are drilled alternately, and a freezing pipe is arranged in the short boring hole 2 in the first stage (first freezing step), and groundwater is discharged from the long boring hole 1. A freezing region R2 is formed around the inside of the tunnel while draining, and a freezing tube is disposed in the long boring hole 1 in the second stage (second freezing step), and a freezing region R3 is formed around the outside of the tunnel.

  Thereby, in the freezing-up pressure suppression method in the freezing method of the present embodiment, the generation of freezing-up pressure (freezing expansion pressure) can be suppressed reliably and effectively by draining the nearby groundwater, which acts on the existing structure 3. The external force to be reduced can be reduced, and the natural ground G can be suitably reinforced using the freezing method.

  In addition, according to the frost heave pressure suppression method in the freezing method according to the present embodiment, the freezing pressure (freezing expansion pressure) can be easily achieved by dividing the construction process of the freezing method into the first stage and the second stage as described above. Generation can be suppressed, and the external force acting on the existing structure 3 can be reduced. Therefore, it is possible to rationalize the design and reduce the construction cost as compared with the conventional case.

  Furthermore, by using the boring hole (long boring hole 1) for inserting and placing the freezing pipe as a drainage for groundwater, there is no need to use a water shielding method such as grout or to provide a dedicated drainage hole. Also from this point, it is possible to reliably and effectively suppress the occurrence of frost heave pressure at a low construction cost.

  As mentioned above, although one embodiment of the frost heave pressure suppression method in the freezing method according to the present invention has been described, the present invention is not limited to the above-described one embodiment, and can be appropriately changed without departing from the gist thereof. .

DESCRIPTION OF SYMBOLS 1 Long boring hole 2 Short boring hole 3 Existing structure G Ground mountain O1 Tunnel axis R1 Unsaturation area R2 Freezing area R3 Freezing area S1 Tunnel circumferential direction S2 Tunnel axial direction T Tunnel

Claims (1)

A boring drilling process in which a long boring hole and a short boring hole are drilled from a tunnel to a natural ground;
A first freezing step in which a freezing pipe is disposed in the short boring hole, and a freezing region is formed around the inside of the tunnel while draining groundwater from the long boring hole;
A freezing-up pressure in a freezing method comprising: a second freezing step in which a freezing pipe is disposed in the long boring hole and a freezing region is formed around the outside of the tunnel when the first freezing step is completed. Suppression method.

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