JP2018035506A - Construction method for underground structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a construction method for an underground structure that facilitates construction.SOLUTION: A pneumatic caisson 5 is installed, and a bottom end thereof is set in an impermeable stratum 3 of a ground. When installing the caisson 5, pressure in an excavation part 11 underneath a bottom slab 7 of the caisson 5 is kept at a high pressure state of a pressure higher than groundwater pressure, and automatic excavation is performed using an excavator and the like provided on an undersurface of the bottom slab 7 of the caisson 5. After installing the caisson 5 at a prescribed position, a low-temperature antifreeze liquid is circulated through a frozen duct embedded in a side wall 9 or the like of the caisson 5 for forming a frozen part 33 by freezing a boundary between the caisson 5 and the impermeable stratum 3 outside, thus water-sealing the boundary between the caisson 5 and the impermeable stratum 3. Then, the pressure in the excavation part 11 underneath the bottom slab 7 is lowered gradually to an atmospheric pressure, for casting concrete in the excavation part 11 and filling a gap under the atmospheric pressure.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a construction method for an underground structure using a caisson.

  As construction methods for deep underground structures such as shield tunnel shafts and sewage treatment plant buildings, there are methods using caisson such as pneumatic caisson method and open caisson method. These construction methods have many construction results because they do not require a water-impervious wall.

  FIG. 9 is a diagram showing an outline of the pneumatic caisson method. In the pneumatic caisson method, as shown in FIG. 9 (a), a pneumatic caisson 103 (hereinafter sometimes simply referred to as caisson) having a bottom plate 105, a side wall 107, and a blade edge 125 is constructed near the ground surface. 9 (b), the excavation of the ground under the bottom slab 105 and the caisson 103 are repeated while the side wall 107 is added to the upper part.

  The side wall 107 is provided in a cylindrical shape on the upper surface of the bottom plate 105 along the outer peripheral portion of the bottom plate 105, and the blade edge 125 is provided on the lower surface of the bottom plate 105 along the outer peripheral portion of the bottom plate 105. The bottom plate 105 is provided with openings such as a manlock 109a and a material lock 109b. The manlock 109a is used for workers to enter and leave the excavation section 111 below the bottom slab 105, and the material lock 109b is used to input equipment to the excavation section 111 below the bottom slab 105 and carry out excavation soil.

  When excavating the ground and laying the caisson 103, the bottom plate is prevented from invading groundwater by using high-pressure air, helium gas, or the like to make the pressure of the excavation part 111 below the bottom plate 105 higher than the groundwater pressure. The excavation part 111 below 105 is a dry work space without water.

When caisson 103 is deeply submerged, the pressure of the excavation part 111 reaches 5-7 kgf / cm ² (equivalent to a water depth of 50-70 m), which makes it difficult for workers to enter the excavation part 111. A lot of excavation is done. This is because an excavator (not shown) is attached to a traveling rail disposed on the lower surface of the bottom slab 105, and the excavator is operated with an operation panel on the ground to excavate the ground. It is to do soil. By performing automatic excavation, the cost can be increased, but the work can be performed safely.

  As shown in FIG. 9 (c), after excavating the ground and completing the caisson 103 to a predetermined position, an operator enters the excavating part 111 in a high-pressure air state on the floored ground 110 to dismantle and remove the excavator and the like. Then, the floored ground 110 is shaped. And as shown in FIG.9 (d), concrete is cast in the excavation part 111 and it fills up. Thereafter, the openings of the bottom plate 105 such as the manlock 109a and the material lock 109b are closed with concrete.

  FIG. 10 is a diagram showing an outline of the open caisson method. As shown in FIG. 10A, the open caisson method is constructed as shown in FIG. 10B after constructing an open caisson 117 having a side wall 119 and a blade edge 127 in the vicinity of the ground surface. As shown in the figure, the underwater excavation of the ground inside the caisson 117 and the caisson 117 are repeated while the side wall 119 is added to the upper part (see, for example, Patent Documents 1 and 2).

  The side wall 119 is a cylindrical structure, and the blade edge 127 is provided on the lower surface of the side wall 119 along the circumferential direction of the side wall 119. In this example, the anchor 115 is installed on the ground, and the caisson 117 is press-fitted with the jack 116 by using the anchor 115 as a reaction force to perform the sinking. However, the caisson 117 may be sunk by its own weight without using the anchor 115 or the jack 116.

  As shown in FIG. 10 (c), after the caisson 117 has been set up to a predetermined position and the ground is excavated to the floored position, the underwater concrete 123 is placed on the floored ground 110. Thereafter, as shown in FIG. 10 (d), the drainage inside the caisson 117 is performed, and the bottom plate 121 is constructed by placing concrete on the underwater concrete 123. The underwater concrete 123 is provided so that groundwater does not enter the inside of the caisson 117 when draining inside the caisson 117.

Patent No. 3926804 Patent No. 5670595

  In the above example, caisson is embedded in the permeable layer of the ground, and in order to prevent infiltration of groundwater, the excavation part 111 under the bottom plate 105 is in a high-pressure air state in the pneumatic caisson method, and the underwater concrete 123 is used in the open caisson method. It is laid. This is the same when the caisson is embedded in the impermeable layer 3 such as a soft rock layer under the permeable layer 2 of the ground as shown in FIG. That is, when the caisson is set up, the impervious layer 3 outside the caisson may collapse due to the blade edge, and a water channel may be formed, and the same treatment is required to prevent infiltration of groundwater. FIG. 11 shows an example of a pneumatic caisson method, which shows a pneumatic caisson 103 having a bottom plate 105, a side wall 107, and a blade edge 125, but the same applies to the open caisson method.

  However, such a treatment for preventing intrusion of groundwater leads to difficulty in construction. For example, in the pneumatic caisson method, in order to place concrete in the excavation part 111 in a high-pressure air state, an ultra-high-pressure concrete pump truck that does not lose the pressure of the excavation part 111 is required, and bubbles in the concrete are crushed by pressure. Since the air volume decreased, the fluidity of the concrete decreased, and it was difficult to place the concrete in a stable state.

  Furthermore, it is difficult to put a concrete hose around the excavation part 111 in a high-pressure air state, and to perform the placement and vibration compaction while visually observing. The excavation part 111 under the bottom plate 105 is completely filled with concrete. It is difficult to do. Therefore, it was necessary to close the space left after placing concrete with mortar injection.

  Further, when automatic excavation of the ground is performed, the floored ground 110 tends to be deeply dug, and there is a problem that the amount of concrete to be placed in the excavation part 111 is increased by the deep dug. In addition, in the automatic excavation, the caisson 103 may be difficult to sink. In this case, the caisson 103 is subtracted from the flooring position to sink the caisson 103 and then backfilled to the flooring position, leaving loose soil. There was a problem in terms of supportability.

  In addition, dismantling and unloading of excavators, etc. are dangerous because the workers enter the excavation section 111 in a high-pressure air state, and the time required for one operation is extremely short, so it takes time to complete the operation. It was hanging.

  On the other hand, in the case of the open caisson method, since the underwater concrete 123 is placed to prevent the ingress of groundwater, the ground for the thickness of the underwater concrete 123 must be excavated. Although it depends on the design, the thickness of the underwater concrete 123 is required to be about 2 to 4 m in order to withstand the load (water pressure from below the underwater concrete 123) that acts during drainage inside the caisson 117. I need a long one.

  Furthermore, in order to place the underwater concrete 123, it is necessary to use a tremy tube or underwater non-separable concrete, which increases the construction cost. Further, in order to maintain the water tightness of the boundary between the inner surface of the caisson 117 and the underwater concrete 123 and to transmit the above load from the underwater concrete 123 to the side wall 119, it is necessary to clean the inner surface of the side wall 119 and to arrange a shear key in advance. there were.

  Furthermore, since it is underwater excavation, it is difficult to manage the excavation depth, and it is easy to excavate deeper than planned. Further, the floor-equipped ground 110 is likely to be uneven, and the floor-equipped ground 110 may be damaged and it may be difficult to obtain a supporting force.

  This invention is made | formed in view of the above problem, The objective is to provide the construction method of an underground structure with easy construction.

  In order to achieve the above-described object, the present invention includes a step (a) of rooting a lower end portion of a caisson in an impermeable layer below the water permeable layer of the ground, and the impermeable water outside the caisson and the caisson. A method of constructing an underground structure, comprising: a step (b) of freezing a boundary portion with a layer and impermeable to water; and a step (c) of placing concrete inside the caisson. is there.

  In the present invention, after the lower end portion of the caisson is embedded in the impermeable layer of the ground, the boundary portion between the caisson and the impermeable layer outside thereof is frozen to perform water shielding. As a result, the water channel formed in the impermeable layer outside the caisson when the caisson is set up can be blocked, and groundwater can enter the caisson from the upper permeable layer, hindering the construction of underground structures. Can be prevented.

For example, the caisson is a pneumatic caisson having a bottom slab, and in the step (a), excavation of the ground below the bottom slab is performed while setting the pressure of the excavation part to be higher than the groundwater pressure, and the caisson is laid down, In the step (c), the concrete is placed in the excavation part with the excavation part at atmospheric pressure. In the step (c), after setting the excavation part to atmospheric pressure, an operator is put into the excavation part, and the ground below the bottom slab is excavated to the floor position.
In the case of the pneumatic caisson method, after the excavation part under the bottom slab is returned to atmospheric pressure by blocking the boundary part between the caisson and the impermeable layer as described above, various operations in the excavation part by workers are performed. It becomes possible to pack the excavated part with concrete. Therefore, the excavator and the like can be disassembled and carried out in an efficient and safe state. In addition, since concrete is placed under atmospheric pressure and clogging is performed, the properties of the concrete, such as the amount of air, do not change, allowing workers to enter and perform placement work, and compaction by using a vibrator Therefore, high-quality concrete can be easily placed using a normal concrete pump car. In addition, it is possible to excavate to the floored position by human power under the bottom plate, and it is easy to prevent deep excavation. If there is any loose soil left during the automatic excavation, it can be removed to secure the bearing capacity of the floored ground. Moreover, since an operator puts in the excavation part, it is also possible to measure the supporting force of the ground with a floor by performing a flat plate loading test or the like.

Alternatively, the caisson is an open caisson, and in the step (a), the caisson is submerged while excavating the ground inside the caisson, and the caisson is drained inside the caisson in the step (c). The bottom plate is constructed by placing the concrete inside. In the step (c), after draining the inside of the caisson, an operator is put inside the caisson, and the ground inside the caisson is excavated to a floored position.
In the case of the open caisson method, by blocking the boundary between the caisson and the impermeable layer as described above, it is not necessary to place underwater concrete that is expensive, and the bottom plate can be constructed directly. Therefore, construction becomes easy, the excavation depth is shallow, and the caisson can be shortened, thereby reducing the construction cost. In addition, it becomes possible to perform excavation near the floored position in the atmosphere by human power or a small excavator, and it is easy to prevent deep digging and prevent the ground with ground from being damaged. Moreover, it is possible to remove the loose soil generated by underwater excavation and secure the supporting force of the ground with floor, and it is also possible to measure the supporting force of the floor with ground by a flat plate loading test or the like.

The caisson is preferably provided with a freezing pipe for circulating a freezing fluid.
In this way, water can be easily shielded by freezing using a freezing tube provided in the caisson in advance.

The caisson is preferably provided with a temperature sensor.
It can be confirmed whether the frozen part is formed in the predetermined position using the measurement data by the temperature sensor.

  ADVANTAGE OF THE INVENTION According to this invention, the construction method of an underground structure with easy construction can be provided.

The figure shown about the construction method of an underground structure by a pneumatic caisson method. The figure which shows the freezing tube 20. FIG. The figure shown about the construction method of an underground structure by a pneumatic caisson method. The figure shown about the construction method of an underground structure by a pneumatic caisson method. The figure shown about the construction method of an underground structure by an open caisson method. The figure which shows the freezing tube 60. FIG. The figure shown about the construction method of an underground structure by an open caisson method. The figure shown about the construction method of an underground structure by an open caisson method. The figure which shows the outline | summary of a pneumatic caisson method. The figure which shows the outline | summary of an open caisson method. An example in which the caisson 103 is embedded in the impermeable layer 3.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First embodiment]
The construction method of the underground structure of the 1st Embodiment of this invention is demonstrated with reference to FIGS. 1-4. In the pneumatic caisson method, the first embodiment is an example in which an underground structure is constructed by rooting a lower end portion of a pneumatic caisson into an impermeable layer below the permeable layer of the ground.

  In this embodiment, as shown in FIG. 1, a pneumatic caisson 5 (hereinafter sometimes simply referred to as a caisson) having a bottom plate 7, a side wall 9, and a blade edge 19 is used. The bottom plate 7 and the side wall 9 are constructed by cast-in-place concrete or precast concrete. The bottom plate 7, the side wall 9, and the blade edge 19 have substantially the same configuration as the bottom plate 105, the side wall 107, and the blade mouth 125 described with reference to FIG. 9. As in the above, the bottom plate 7 includes a manlock 13 a and a material lock 13 b. An opening is provided.

  However, in the present embodiment, a freezing tube 20 is provided on the outer periphery of the caisson 5 as shown in FIG. The freezing pipe 20 circulates a low-temperature antifreeze which will be described later. The freezing pipe 20 has a substantially annular horizontal pipe 23 along the circumferential direction of the caisson 5 (corresponding to the left-right direction in FIG. 2), an inlet-side vertical pipe 25 and an outlet. It has a vertical pipe 27 on the side. The freezing pipe 20 is embedded in concrete such as the side wall 9 of the caisson 5.

  The horizontal pipe 23 is disposed at the lower end of the caisson 5, and for example, a pipe having a diameter of about 75 mm is used. The horizontal pipe 23 is embedded at a position where the fog from the outer peripheral surface of the caisson 5 is 25 cm or less, for example. In the present embodiment, the freezing tubes 20 are used in three stages, and the horizontal pipes 23 are arranged in three upper and lower stages at a predetermined interval. This interval is, for example, about 50 cm, but is not limited thereto.

  A temperature sensor 29 is disposed near the center between the upper and lower horizontal pipes 23. The temperature sensor 29 is also embedded in the concrete such as the side wall 9 of the caisson 5. In the example shown in the figure, one temperature sensor 29 is provided in the circumferential direction of the caisson 5, but a plurality of temperature sensors 29 can be arranged at intervals along the circumferential direction of the caisson 5.

  The vertical pipes 25 and 27 are provided so as to extend upward from the end of the horizontal pipe 23 and reach the upper surface of the side wall 9 of the caisson 5.

  The caisson 5 is laid out in a manner substantially the same as that described with reference to FIG. 9 and the like, and the excavation of the ground under the bottom slab 7 and the caisson 5 are repeated while the side wall 9 is added to the upper part as described above. When excavating the ground, automatic excavation is performed by an excavator or the like provided on the lower surface of the bottom slab 7 while the atmospheric pressure of the excavation part 11 below the bottom slab 7 is in a high-pressure air state higher than atmospheric pressure and groundwater pressure. The vertical pipes 25 and 27 described above are added in accordance with the addition of the side wall 9 when the caisson 5 is set, and are extended upward.

  However, in the present embodiment, the caisson 5 is laid down to a predetermined position as shown in FIG. 1, and the lower end of the caisson 5 is rooted in an impermeable layer 3 such as a soft rock layer. A frozen portion 33 is formed at the boundary with the outer impermeable layer 3 to shield water between the caisson 5 and the impermeable layer 3.

Here, the water-impermeable layer 3 refers to a water-impermeable layer in a broad sense including what is called a hardly water-permeable layer. In the present embodiment, the impermeable layer 3 is a soft rock layer such as Dotan, and the permeability coefficient is 1 × 10 ⁻⁵ cm / sec or less, for example, about 1 × 10 ⁻⁶ to 1 × 10 ⁻⁸ cm / sec. . The soft rock layer also has a role as a support layer for the underground structure, and its uniaxial compressive strength is, for example, 5 to 20 kgf / cm ² or more. In addition, although the penetration length to the impermeable layer 3 of the caisson 5 shall be 4-5 m or more, for example, it is not restricted to this.

  Such an impermeable layer 3 does not collapse due to water pressure, but if the impermeable layer 3 is scraped and broken by the blade 19 when the caisson 5 is set, the boundary between the caisson 5 and the outer impermeable layer 3 outside thereof. There is a possibility that a gap is formed in the portion, and the gap becomes a waterway, and the groundwater of the permeable layer 2 enters the excavation portion 11 inside the caisson 5.

  Therefore, in this embodiment, the antifreezing liquid of −20 to −30 ° C., which is a freezing fluid, is circulated through the above-described freezing pipe 20 (horizontal pipe 23, vertical pipes 25 and 27) by a pump (not shown) or the like. Thereby, the boundary part of the caisson 5 and the impermeable layer 3 outside thereof is frozen to form a frozen part 33, and the caisson 5 and the impermeable layer 3 are insulated. Nybrine (registered trademark) or the like can be used as the antifreeze.

  During freezing by the freezing tube 20, the measurement data measured by the temperature sensor 29 is transmitted to a computer (not shown), and heat conduction analysis is performed by the computer, so that the frozen portion 33 is formed at a desired position. Make sure. For example, as described above, when the vertical distance between the horizontal pipes 23 is about 50 cm, if the maximum distance r from the outer peripheral surface of the caisson 5 to the outer edge of the frozen portion 33 reaches 1 m, the caisson 5 and the impermeable layer 3 It is judged that the water barrier between the two was secured.

  After forming the frozen portion 33 and water shielding, the pressure of the excavating portion 11 below the bottom slab 7 is gradually lowered, and the excavating portion 11 is enlarged while confirming that the amount of water leakage is small (the water shielding effect due to freezing). Return to atmospheric pressure.

  After returning the excavation part 11 to atmospheric pressure, workers and heavy machinery are put into the excavation part 11 and the excavator etc. is removed, the ground is excavated to the floored position, and the loose soil generated during automatic excavation remains. In that case, the removal is also performed, and concrete is placed in the excavation part 11 on the ground with ground 30 inside the caisson 5 as shown in FIG. Further, the openings of the bottom plate 7 such as the manlock 13a and the material lock 13b are closed with concrete.

  The operation of circulating the antifreeze liquid in the freezing pipe 20 is performed at least until completion of placing the concrete on the excavation part 11, and during this time, temperature measurement by the temperature sensor 29 and confirmation of water shielding based on measurement data are also performed. After completion of placing the concrete, the antifreeze circulating operation is stopped at an appropriate time, and the freezing of the freezing portion 33 is naturally released. After the circulation operation is stopped, the antifreeze liquid is extracted from the freezing tube 20 and filled with a grout material or filled with an inert gas such as nitrogen gas.

  As described above, in the first embodiment, after the lower end portion of the caisson 5 is embedded in the impermeable layer 3 of the ground, the boundary portion between the caisson 5 and the outer impermeable layer 3 on the outside thereof is frozen to provide water shielding. Do. As a result, when the caisson 5 is set up, the impermeable layer 3 outside the caisson 5 is scraped to become a water channel, and groundwater enters from the upper permeable layer 2 into the caisson 5, thereby obstructing the construction of the underground structure. Can be prevented.

  In the case of the pneumatic caisson method as in the present embodiment, by blocking the boundary between the caisson 5 and the impermeable layer 3 as described above, the excavation part 11 below the bottom slab 7 is returned to atmospheric pressure, Various kinds of work in the excavation part 11 by an operator and clogging of the excavation part 11 by concrete can be performed. Therefore, the excavator and the like can be disassembled and carried out in an efficient and safe state.

  In addition, since concrete is placed under atmospheric pressure and clogging is performed, the properties of the concrete, such as the amount of air, do not change, allowing workers to enter and perform placement work, and compaction by using a vibrator Therefore, high-quality concrete can be easily placed using a normal concrete pump car.

  In addition, it is possible to excavate to the floored position by human power under the bottom plate 7, and since it can be visually confirmed, it is easy to prevent deep excavation. Moreover, if the loose soil produced at the time of automatic excavation remains, this can be removed and the supporting force of the floor ground 30 can also be ensured. Moreover, since an operator puts in the excavation part 11, it is also possible to measure the supporting force of the floor ground 30 in an original position by performing a flat plate loading test or the like.

  However, the present invention is not limited to this. For example, in this embodiment, the excavation part 11 is padded with concrete, but the material used for the padding of the excavation part 11 is not limited to concrete. Since the manlock 13a and the material lock 13b of the bottom plate 7 are finally closed with concrete, the excavation part 11 can be filled with an inexpensive material such as crushed stone or soil mortar.

  The impermeable layer 3 is not limited to a soft rock layer, and may be a clay layer, a silt layer, a hard rock, or the like. Furthermore, the uniaxial compressive strength and water permeability coefficient of the impermeable layer 3 are not limited to those described above. If it is confirmed by design calculation that the stability of the water-impermeable layer 3 to the water pressure and the amount of spring water will not interfere with the construction, the implementation will be carried out even in the water-impermeable layer 3 having a smaller uniaxial compressive strength and a larger water permeability. The construction method of the underground structure in the form can be applied.

  In this embodiment, three freezing tubes 20 and three horizontal pipings 23 are provided, but at least one freezing tube 20 may be provided. Further, the structure of the freezing pipe 20 is not limited to this embodiment, such as one in which a three-stage horizontal pipe 23 is branched from one vertical pipe 25 and these horizontal pipes 23 are connected to one vertical pipe 27. The piping method of this is also possible. In this embodiment, the freeze pipe 20 is embedded in the concrete such as the side wall 9 of the caisson 5, but the freeze pipe 20 may be disposed on the inner peripheral surface or the outer peripheral surface of the caisson 5. In addition, after the caisson 5 is laid, a freezing tube 20 can be separately installed on the ground. Further, the side wall 9 of the caisson 5 is not limited to a concrete one, and for example, a steel material such as a steel shell may be used.

  Further, the shape of the caisson 5 is not particularly limited. For example, the side wall 9 may have a cylindrical shape, and the planar shape thereof may be a substantially circular shape, a substantially rectangular shape, or another substantially polygonal shape.

  Next, another example of the present invention will be described as a second embodiment. The second embodiment will mainly describe differences from the first embodiment, and the same points will be denoted by the same reference numerals in the drawings and the like, and description thereof will be omitted.

[Second Embodiment]
5-8 is a figure shown about the construction method of the underground structure of the 2nd Embodiment of this invention. In the open caisson method, the second embodiment is an example in which an underground structure is constructed by rooting the lower end portion of the open caisson into an impermeable layer below the permeable layer of the ground.

  That is, in the present embodiment, as shown in FIG. 5, an open caisson 45 having a side wall 47 and a blade edge 55 (hereinafter sometimes simply referred to as caisson) is used. The side wall 47 is constructed of cast-in concrete or precast concrete. The side wall 47 and the blade edge 55 have substantially the same configuration as the side wall 119 and the blade edge 127 described with reference to FIG.

  However, also in this embodiment, the freezing pipe 60 for circulating the antifreeze liquid is embedded in the concrete of the side wall 47 of the caisson 45 as shown in FIG. The freezing pipe 60 has a substantially annular horizontal pipe 63 along the circumferential direction of the caisson 45 (corresponding to the left-right direction in FIG. 6), an inlet-side vertical pipe 65, and an outlet-side vertical pipe 67. These configurations, arrangements, and the like are the same as those of the horizontal pipe 23 and the vertical pipes 25 and 27 of the freezing pipe 20 described above. Also in this embodiment, the temperature sensor 69 is arranged near the center between the upper and lower horizontal pipes 63. The temperature sensor 69 is embedded in the concrete of the side wall 47 of the caisson 45 in the same manner as the temperature sensor 29 described above.

  The caisson 45 is laid down in a manner substantially the same as that described with reference to FIG. 10 and the like, while the ground inside the caisson 45 is excavated underwater, the caisson 45 is pressed and set by the jack 54 with the anchor 53 as a reaction force. The anchor 53 and the jack 54 are the same as the anchor 115 and the jack 116 described with reference to FIG. In some cases, it is possible to set the caisson 45 by its own weight without using the anchor 53 or the jack 54. As in the first embodiment, the vertical pipes 65 and 67 described above are added in accordance with the addition of the side wall 47 when the caisson 45 is set, and are extended upward.

  However, also in this embodiment, after caisson 45 is laid down to a predetermined position as shown in FIG. 5 and its lower end is rooted in impermeable layer 3 such as a soft rock layer, caisson 45 and its A frozen portion 73 is formed at the boundary with the outer impermeable layer 3 to shield water between the caisson 45 and the impermeable layer 3. Thereby, when the caisson 45 is set, the impermeable layer 3 is cut by the blade 55, and the groundwater of the permeable layer 2 enters the inside of the caisson 45 through a gap formed at the boundary between the caisson 45 and the impermeable layer 3. prevent.

  Also in this embodiment, the antifreeze is circulated through the freezing pipe 60 by a pump (not shown) or the like, and the boundary between the caisson 45 and the impermeable layer 3 outside thereof is frozen to form the frozen part 73. Water is blocked between the layers 3. The heat conduction analysis is performed using the temperature data measured by the temperature sensor 69, and it is the same as described above to confirm that the frozen portion 73 is formed at a desired position and the water shielding is ensured.

  After forming the frozen portion 73 and blocking the water, draining the water inside the caisson 45 and gradually lowering the water level, confirming that the amount of water leakage is small (freezing and water blocking is made). Complete draining inside 45. After the drainage is completed, workers and heavy machinery are put inside the caisson 45 to excavate the ground to the floored position and remove soft earth and sand such as soil that has collapsed during underwater excavation. As shown in FIG. 8, after finishing the floored ground 30, a crushed stone 81 is spread on the ground, and a bottom plate 83 is constructed on the crushed stone 81. The bottom plate 83 is constructed by placing concrete.

  The operation of circulating the antifreeze liquid in the freezing pipe 60 is performed at least until the construction of the bottom plate 83 is completed, and during this time, the temperature measurement by the temperature sensor 69 and the water shielding based on the measurement data are also confirmed. After the construction of the bottom plate 83 is completed, the antifreezing liquid circulation operation is stopped at an appropriate time, and the freezing of the freezing unit 73 is naturally released. After the circulation operation is stopped, the antifreeze liquid is extracted from the freezing tube 60 and an inert gas such as a grout material or nitrogen gas is sealed in the same manner as described above.

  As described above, in the second embodiment as well, the boundary portion between the caisson 45 and the impermeable layer 3 outside thereof is frozen and water shielding is performed, so that groundwater enters the caisson 45 from the upper permeable layer 2. In addition, it is possible to prevent an obstacle during construction of the underground structure.

  In the case of the open caisson method as in the present embodiment, by blocking the boundary between the caisson 45 and the impermeable layer 3 as described above, it is not necessary to place underwater concrete which is expensive, and the bottom plate 83 is directly attached. Can be built. Therefore, construction becomes easy, the excavation depth is shallow, and the caisson 45 can be shortened, so that the construction cost can be reduced. In addition, excavation in the vicinity of the floored position can be performed in the atmosphere by human power or a small excavator, and it is easy to prevent deep digging, and it is possible to prevent the floored ground 30 from being damaged. Further, it is possible to remove the loose soil generated by the underwater excavation to secure the supporting force of the floored ground 30 and to measure the supporting force of the floored ground 30 in the original position by a flat plate loading test or the like. .

  As mentioned above, although embodiment of this invention was described referring an accompanying drawing, the technical scope of this invention is not influenced by embodiment mentioned above. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the technical idea described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

3: Impermeable layer 5, 103: Pneumatic caisson 7, 83, 105, 121: Bottom plate 9, 47, 107, 119: Side wall 11, 111: Excavation part 13a, 109a: Manlock 13b, 109b: Material lock 19, 55, 125, 127: Cutting edge 20, 60: Freezing pipe 23, 63: Horizontal piping 25, 27, 65, 67: Vertical piping 29, 69: Temperature sensor 30, 110: Ground with floor 33, 73: Freezing section 45 117: Open caisson 53, 115: Anchor 54, 116: Jack 81: Crushed stone 123: Underwater concrete

Claims (7)

A step (a) of rooting the lower end of the caisson into the impermeable layer below the permeable layer of the ground;
Freezing a boundary portion between the caisson and the impermeable layer outside the caisson, and performing water shielding (b);
Placing concrete inside the caisson (c);
The construction method of an underground structure characterized by comprising. The caisson is a pneumatic caisson with a bottom plate;
In the step (a), excavation of the ground below the bottom slab is performed while the pressure of the excavation part is higher than the groundwater pressure, and the caisson is laid down,
The method for constructing an underground structure according to claim 1, wherein, in the step (c), the concrete is placed in the excavation portion with the excavation portion as an atmospheric pressure.   3. The underground according to claim 2, wherein, in the step (c), after setting the excavation part to atmospheric pressure, an operator is put into the excavation part and the ground below the bottom slab is excavated to a floored position. Construction method of the structure. The caisson is an open caisson,
In the step (a), the caisson is submerged while excavating the ground inside the caisson underwater,
The method for constructing an underground structure according to claim 1, wherein, in the step (c), drainage inside the caisson is performed and the concrete is placed inside the caisson to construct a bottom plate.   5. In the step (c), after draining the inside of the caisson, an operator is put inside the caisson, and the ground inside the caisson is excavated to a floored position. Construction method for underground structures.   The construction method for an underground structure according to any one of claims 1 to 5, wherein the caisson is provided with a freezing pipe for circulating a freezing fluid.   The construction method for an underground structure according to any one of claims 1 to 6, wherein a temperature sensor is provided in the caisson.

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