JP6638312B2 - Caisson laying method - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a caisson squatting method in which a caisson is sunk to a predetermined depth and installed.

  As a method of constructing a foundation or an underground structure in the ground, a caisson method (pneumatic caisson method or open caisson method) in which a caisson (box-like structure) is settled down to a predetermined depth and installed. In order to sink the caisson smoothly and stably, the sinking resistance of the caisson (sum of the frictional force of the outer surface of the caisson, the resistance of the blade opening, and the lifting pressure) is calculated from the sinking force (self-weight of the frame, additional penetrating load, etc.). You need to keep it small. For the surface frictional force, based on past experience and actual measurement data, design guidelines and standards to be set based on the type of ground, N value, strength are indicated by public institutions and academia, and it is necessary to follow this in design estimation. General.

  If the settlement resistance exceeds the settlement force in the design estimation, countermeasures will be taken to reduce the peripheral frictional force, cutting edge resistance, and the like. As countermeasures to reduce the settlement resistance, (a) improvement of the cutting edge shape (for example, see Patent Document 1), (b) storage and laying of a friction reducing sheet, (c) application of a friction reducing base material, (D) Filling and filling of caisson peripheral surface with lubricating material (lubricant), (e) Lubricant pressure from injection hole of caisson frame, (f) Improvement and strength adjustment before caving ground around caisson Etc. have been proposed.

JP-A-8-165665

  However, in the conventional design estimation, the peripheral friction force is obtained based on the type, N value, and strength of the ground, but no consideration is given to an underground structure close to the caisson to be laid. Therefore, if there is an underground structure (underground structure or strong ground) close to the caisson when the caisson is laid, on the ground of the caisson facing the underground structure, There is a problem that a large circumferential friction force exceeding the design estimate is generated and it becomes difficult for the caisson to sink with the conventional countermeasures. Note that, even when a plurality of caissons are placed close to each other and laid simultaneously, the other caisson acts as an adjacent underground structure with respect to one caisson.

  The present invention has been made in view of such a situation, and solves the above-mentioned problems, and provides a caisson that can effectively reduce a large circumferential friction force generated on a part of the outer peripheral surface of the caisson. It is to provide a method.

The caisson squatting method of the present invention is a caisson squatting method in which a caisson is sunk down to a predetermined depth and installed, wherein the caisson's outer peripheral surface The range of the depth to reduce the stress based on one or both of the measurement result of the earth pressure from the surrounding ground acting on the ground and the measurement result of the circumferential friction force with the surrounding ground acting on the outer peripheral surface of the caisson A depth range specifying step of specifying a stress reduction depth range, a drilling hole forming step of drilling from the ground to the deepest part of the stress reduction depth range to form a drilling hole, and a multi-tube rod inserted into the drilling hole. Rotating the multiple pipe rods to break the skeletal structure of the ground while injecting water from the tip in the horizontal direction simultaneously with the air, and improving the columnar ground in the stress reduction depth range Which comprises carrying out the board reclamation process.
Further, in the caisson laying method of the present invention, in the improved ground preparation step, a sliding material may be laterally jetted from a tip of the multi-pipe rod together with the water and the air.
Furthermore, the caisson squatting method of the present invention further comprises: a caisson cutting edge; a ground pressure gauge for measuring earth pressure acting on the outer peripheral surface from the surrounding ground; and a peripheral surface friction between the surrounding ground acting on the outer peripheral surface. Either or both of the surface friction meter to measure the force is provided, in the depth range identification step, the measured value of the earth pressure by the earth pressure meter and the measured value of the circumferential friction force by the surface friction meter. The stress reduction depth range may be specified based on any one or both.
Further, in the caisson laying method of the present invention, in the excavation hole forming step, an excavation hole may be formed between the outer peripheral surface of the caisson and the facing underground structure .
Furthermore, the caisson subsidence method of the present invention provides an elasto-plastic model of the ground using the Drucker-Plager-based or Camclay-based yield criterion for the ground between the outer peripheral surface of the caisson and the opposing underground structure. By performing an analysis by the applied finite element method and verifying the effect of reducing the earth pressure by changing the number of the improved grounds formed by the stress reducing work, the number of the improved grounds formed by the stress reducing work May be set.
Furthermore, the caisson subsidence method of the present invention provides an elasto-plastic model of the ground using the Drucker-Plager-based or Camclay-based yield criterion for the ground between the outer peripheral surface of the caisson and the opposing underground structure. The design estimation of the stress reduction process may be performed based on the analysis result by the applied finite element method.

  According to the present invention, by performing stress reduction work on the ground facing a part of the outer peripheral surface of the caisson where a large peripheral surface frictional force is generated, a large circumferential surface formed on the part of the outer peripheral surface of the caisson is obtained. There is an effect that the surface frictional force can be effectively reduced.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows schematic structure of the caisson laying method which applies the caisson laying method which concerns on this invention. FIG. 2 is an enlarged view of a cutting edge portion shown in FIG. 1. It is a ground map in this embodiment. It is a graph which shows the measured value of the earth pressure by the earth pressure gauge shown in FIG. 3 is a graph showing a measured value of a peripheral friction force by the peripheral friction meter shown in FIG. 2. It is process drawing which shows the process of the stress reduction in the caisson squatting method which concerns on this invention. 5 is a graph obtained by superimposing an analysis result of earth pressure by a finite element method on the graph shown in FIG. 4. It is a figure which shows the enforcement example which examines the countermeasure effect by the stress reduction construction of the caisson sinking method based on this invention. 9 is a graph showing the effect of reducing the earth pressure according to the embodiment shown in FIG. 8. It is a figure showing the example of application to the uneven ground of the sinking method of the caisson concerning the present invention.

  Next, embodiments for implementing the present invention (hereinafter, simply referred to as “embodiments”) will be specifically described with reference to the drawings.

  In this embodiment, as shown in FIG. 1, the caisson laying method according to the present invention is applied to a caisson laying method in which a caisson 1 and a caisson 2 are simultaneously laid close to each other to construct an underground structure. Will be described. 1A and 1B show a state of a caisson setting process, in which FIG. 1A is a plan view, and FIG. 1B is a sectional view taken along line XX in FIG.

  The shapes of the caisson 1 and the caisson 2 are rectangular cylinders extending in the up-down direction. An outer peripheral surface of the caisson 1 facing each other (hereinafter, referred to as a close opposing surface 1a) and an outer peripheral surface of the caisson 2 (hereinafter, referred to as a close opposing surface 2a) are parallel to each other at a distance L (for example, L = several meters). It sinks in a state of facing and approaching. As for the timing at which the caisson 1 and the caisson 2 are laid, only one may be laid alternately or both may be laid at the same timing (at the same speed). In each case, caisson 1 and caisson 2 act as adjacent underground structures to each other. In addition, the ground facing the other outer peripheral surfaces of the caisson 1 and the caisson 2 (hereinafter, referred to as the non-opposing surface 1b and the non-opposing surface 2b, respectively) can be regarded as an infinite ground having no adjacent underground structure.

  Referring to FIG. 2, the cutting edge 10 of the caisson 1 and the caisson 2 has a peripheral surface of an earth pressure gauge 11 that measures the earth pressure acting on the outer peripheral surface from the surrounding ground, and a peripheral surface that acts on the outer peripheral surface. A peripheral friction meter 12 for measuring frictional force and a blade reaction force meter 13 for measuring a ground reaction force (support force) acting on the blade 10 are provided. Although not shown in FIG. 2, an earth pressure gauge 11 and a peripheral friction meter 12 are also provided on the non-opposing surfaces 1b and 2b, respectively. Further, the caisson 1 and the caisson 2 are provided with a measuring device (not shown) for measuring other information such as water pressure, lift pressure, inclination of the caisson 1 and the caisson 2. The earth pressure measured by the earth pressure gauge 11, the surface friction force measured by the surface friction meter 12, the ground reaction force measured by the blade reaction force meter 13, and other (water pressure, lifting pressure, caisson 1 And the inclination of the caisson 2) are input to an information processing device such as a computer (not shown). Then, the work manager refers to the information of the earth pressure, the peripheral frictional force, the ground reaction force, and other information (water pressure, lift pressure, inclination of the caisson 1 and the caisson 2) input to the information processing apparatus, and performs the subsidence work. Manage.

  As shown in FIG. 3, the ground in the present embodiment is as follows: the ground surface to the depth D1 is the upper layer G1, the depths D1 to D2 are the Yurakucho layer / low overconsolidation soil G2, and the depths D2 to D3 are the Yurakucho layer and the high overconsolidation soil. G3, depths D3 to D4 are composed of sand G4 mixed with Tokyo layer and silt, depths D4 to D5 are composed of Tokyo layer and gravel G5, and depths D5 to D6 are composed of sand G6 mixed with Tokyo layer and silt. The upper layer G1 is a loose sand ground, and the Tokyo layer / silt sand G4, the Tokyo layer / sand gravel G5, and the Tokyo layer / silt sand G6 are dense sand (sand) ground.

  FIG. 4 shows measured values of earth pressure by the earth pressure gauge 11 provided in the caisson 1 when the caisson 1 and the caisson 2 are settled down to the sand G6 mixed with the Tokyo layer and silt at the depths D5 to D6. . In FIG. 4, the solid line A is the earth pressure from the surrounding ground acting on the proximity opposing surface 1 a of the caisson 1, and the dotted line B is the earth pressure from the surrounding ground acting on the non-opposing surface 1 b of the caisson 1. The dashed line C is the initial earth pressure in the design estimate. According to FIG. 4, the earth pressure acting on the non-opposite surface 1b is almost equal to the initial earth pressure in all the layers, whereas the earth pressure acting on the close opposing surface 1a is a high overconsolidation soil G3. The layer and the G4 to G6 layers made of dense sand (sand and gravel) are higher than the initial earth pressure. The measured values of the earth pressure by the earth pressure gauge 11 provided in the caisson 2 were almost the same.

  FIG. 5 shows that the caisson 1 and caisson 2 are settled down to the sand G6 mixed with the Tokyo layer and silt at the depths D5 to D6, and the surface friction is measured by the surface friction meter 12 provided on the adjacent facing surface 1a of the caisson 1. Force measurements are shown. In FIG. 5, the solid line A is the peripheral frictional force acting on the proximity facing surface 1 a of the caisson 1. According to FIG. 5, the peripheral frictional force acting on the proximity opposing surface 1a is high in the G3 layer made of highly over-consolidated clay and the G4 to G6 layers made of dense sand (sand) as in the case of earth pressure. Has become. The measured values of the peripheral friction force by the peripheral friction meter 12 provided in the caisson 2 were almost the same.

  As shown in FIGS. 4 and 5, when the earth pressure and the peripheral frictional force acting on the proximity facing surface 1a, which is a part of the outer peripheral surface of the caisson 1, are higher than those of the other non-facing surface 1b, the balance is lost. This makes caisson 1 difficult to sink. Therefore, as a countermeasure to reduce the earth pressure and the peripheral frictional force acting on the adjacent facing surface 1a, the stress of the confined ground between the adjacent facing surface 1a of the caisson 1 and the adjacent facing surface 2a of the caisson 2 is taken as a measure. Implement stress reduction to reduce the stress. This stress reduction also reduces the earth pressure and the peripheral frictional force acting on the proximity facing surface 2a of the caisson 2.

  In the stress reduction work, first, as a depth range specifying step, a depth range (hereinafter referred to as a depth range) in which stress is reduced based on a measured value of earth pressure by the earth pressure gauge 11 or a measured value of circumferential friction force by the circumferential friction meter 12. , The specified range is referred to as a stress reduction depth range). For example, in the present embodiment, the depth range that is higher than the initial earth pressure of the G3 to G6 layers is determined based on the earth pressure from the surrounding ground acting on the proximity facing surface 1a of the caisson 1 shown by the solid line A in FIG. Specified as the stress reduction depth range.

  Next, as a drilling hole forming step, using a boring machine, as shown in FIG. 6A, the caisson 1 and the caisson 2 acting as an underground structure adjacent to the proximate facing surface 1 a as shown in FIG. The hole 20 is formed by drilling from the ground to the deepest part of the stress reduction depth range.

  Next, as an improved ground formation step, as shown in FIG. 6B, a multi-pipe rod 21 is inserted into the excavation hole 20, and ultra-high pressure water is supplied from the tip of the multi-pipe rod 21 simultaneously with the compressed air in the lateral direction. While spraying, the multi-pipe rod 21 is rotated by the column machine, and the multi-pipe rod 21 is pulled up by the crane. The injection of the ultra-high pressure water and the compressed air destroys the skeletal structure of the ground, thereby forming the columnar improved ground 23. The slime 22 generated in the course of the destruction of the skeletal structure of the ground is discharged to the ground surface between the excavation hole 20 and the multiple pipe rod 21.

  The columnar improved ground 23 is formed in a stress reduction depth range as shown in FIG. The radius of the improved ground 23 is preferably set to be shorter than the distance between the proximity opposing surface 1a and the excavation hole 20 in order to prevent damage to the proximity opposing surface 1a. In addition, the radius of the improved ground 23 can be appropriately set according to the pressure of the water and air to be injected, and the rotation and lifting speed of the multiple pipe rod 21. Further, a lubricant such as bentonite may be injected and mixed into the improved ground 23.

  The number and intervals of the improved ground 23 to be formed are set by analysis using an elasto-plastic model described later. Then, the drilling hole forming step and the improved ground formation step are repeated until the set number is reached. Since the skeletal structure of the ground is destroyed by the improved ground formation process, the ground adjacent to the improved ground 23, that is, the confined closed ground between the adjacent facing surface 1a of the caisson 1 and the adjacent facing surface 2a of the caisson 2 is restricted. Is reduced, and the earth pressure and the peripheral frictional force acting on the proximity facing surface 1a of the caisson 1 are also reduced.

  Referring to FIG. 3 to FIG. 5, when the underground structure (caisson 2) close to the caisson 1 is laid on the ground (G3 to G6) of dense sand (gravel) or over-consolidated clay, A large earth pressure and a circumferential friction force greater than the design estimate are generated on the near-facing surface 1a of the caisson 1 facing the structure (caisson 2). This is considered to be due to the constraint of the ground between caisson 1 and the underground structure (caisson 2). However, it cannot be explained only by the constraint of the ground, and the present inventors assume that the ground (G3 to G6) of dense sand (gravel) or over-consolidated cohesive soil is positive due to shearing when the caisson 1 and caisson 2 are settled. It was considered that dilatancy (expansion of volume) was also caused.

  Therefore, an elasto-plastic model of the ground using the Drucker-Prager yield criterion is applied to the ground between caisson 1 and the underground structure (caisson 2), and the surface friction meter 12 The frictional force measured on the peripheral surface was applied as a set load, and a reproduction analysis of the earth pressure measured on the adjacent facing surface 1a of the caisson 1 by the finite element method (FEM) was performed. The elasto-plastic model of the ground using the Drucker-Plager yield criterion is a model that can take into account the stress conditions of the ground when the caisson 1 is laid and the expansion due to shearing (positive dilatancy. The analysis target is In addition, G4 to G6 sand and gravel layers, which are considered to be greatly affected by dilatancy, were analyzed by the finite element method (FEM). In addition to the elasto-plastic model using the yield criterion described above, an elastic body model was used, and the two cases were compared.

  FIG. 7 is a graph in which the analysis result of earth pressure is superimposed on FIG. According to FIG. 7, in the elasto-plastic model using the yield criterion of the Drucker-Plager system in consideration of dilatancy, there is an increase in earth pressure from the initial earth pressure. Was obtained. On the other hand, in the elastic body model without considering the dilatancy, the increase of earth pressure was not obtained, and the result was distributed near the initial earth pressure. Therefore, it is considered that the increase in the earth pressure on the proximity facing surface 1a of the caisson 1 is due to the influence of dilatancy (volume expansion).

  Next, in order to examine the effect of countermeasures by stress reduction, a finite element using the elasto-plastic model using the Drucker-Plager system yield criterion was applied to the ground between caisson 1 and underground structure (caisson 2). As shown in Fig. 8, the number of the improved ground 23 to be created is gradually increased in the first, second, and third terms to verify the effect of reducing the earth pressure of each of the grounds, as shown in FIG. did. As a result, as shown in FIG. 9, as the number of the first term, the second term, the third term, and the number of the improved ground 23 increased, the effect of reducing the earth pressure became large.

  As described above, the number and interval of the improved ground 23 to be formed can be determined by the analysis by the finite element method (FEM) to which the elasto-plastic model using the yield criterion of the Drucker-Plager system is applied. That is, referring to FIG. 9, the earth pressure acting on the near opposing surface 1a is still higher than the other non-opposing surface 1b at the time of the first term construction, and is applied to the other non-opposing surface 1b at the time of the second term construction. It is lower than that. Therefore, it can be seen that the number of the improved grounds 23 that is smaller than that at the time of the second term construction and larger than that at the time of the first term construction should be created. Thus, the balance of the earth pressure acting on each outer peripheral surface of the caisson 1 can be easily adjusted.

  In addition, the above analysis results show that when there is an underground structure (underground structure or strong ground) close to the caisson at the time of caisson subsidence, By applying the elasto-plastic model of the ground using the yield criterion of the Drucker-Plager system to the ground between structures and analyzing it by the finite element method (FEM), it is possible to predict the increase in earth pressure. means. This makes it possible to predict the required stress reduction work, and to add the stress reduction work to the budget in the design estimation.

  In the present embodiment, the method of laying the caisson to reduce the earth pressure and the circumferential frictional force acting on the proximity facing surface 1a of the caisson 1 has been described, but the earth pressure and the circumferential force acting on the proximity facing surface 1a of the caisson 1 are described. It goes without saying that by reducing the surface frictional force, the earth pressure and the peripheral surface frictional force acting on the adjacent facing surface 2a of the caisson 2 are also reduced.

  Further, in the present embodiment, the elasto-plastic model using the yield criterion of the Drucker-Plager system is used for the analysis by the finite element method (FEM), but the elasto-plastic model using the yield criterion of the Cam-Clay system is used. A model may be used. The elasto-plastic model using the Drucker-Plager yield criterion is suitable for sand ground, and the elasto-plastic model using the Cam-Clay yield criterion is suitable for clay ground.

  Furthermore, as shown in FIG. 10, the stress reduction work of the present embodiment can also be used when laying the caisson 3 on irregular ground where the hard ground layer 30 crosses obliquely. The hard ground layer 30 is made of, for example, high-density sand / gravel, hard clay, or the like. For the hard ground layer 30 facing the outer peripheral surface of the caisson 3, as a stress reduction operation, the layer thickness of the hard ground layer 30 is set as a stress reduction depth range, and a columnar improved ground 23 is formed in this stress reduction depth range. Thereby, reduction and leveling of the earth pressure and the peripheral frictional force on the outer peripheral surface of the caisson 3 can be realized.

As described above, the present embodiment is a method of laying down the caisson 1 by sinking the caisson 1 to a predetermined depth, and reducing the stress of the ground facing the outer peripheral surface (the proximity facing surface 1a) of the caisson 1. As a stress reducing step for reducing the stress, a depth range specifying step of specifying a range of the depth for reducing the stress as the stress reducing depth range, and a drilling hole for drilling from the ground to the deepest part of the stress reducing depth range to form the drilling hole 20. In the forming step, the water is jetted from the tip of the multiple pipe rod 21 inserted into the excavation hole 20 in the horizontal direction simultaneously with the air, and the multiple pipe rod 21 is rotated to destroy the skeletal structure of the ground. An improved ground formation step of forming the columnar improved ground 23 is performed.
With this configuration, the ground facing the part of the outer peripheral surface of the caisson 1 (proximal facing surface 1a) in which a large peripheral frictional force is generated is subjected to a stress reduction work from the ground, so that the outer peripheral part of the caisson 1 is partially removed. The large peripheral frictional force generated on the surface (proximal facing surface 1a) can be effectively reduced. In addition, since the stress reduction work can be performed from the ground regardless of the structure of the caisson 1, it is not necessary to previously provide a structure (piping or the like in the caisson 1) for causing a circumferential frictional force to the caisson 1. , Cost can be reduced.

Further, in the present embodiment, in the improved ground preparation step, a lubricant (such as bentonite) is jetted laterally from the tip of the multiple pipe rod 21 together with water and air.
With this configuration, it is possible to set the improved ground 23 formed by the stress reduction work to an appropriate strength, depending on the material of the lubricating material (such as bentonite) and the injection amount.

Further, in the present embodiment, the blade 10 of the caisson 1 has an earth pressure gauge 11 for measuring earth pressure acting on the outer peripheral surface from the surrounding ground, and a peripheral friction force between the surrounding ground acting on the outer peripheral surface. And a peripheral friction meter 12 for measuring the surface pressure is measured. In the depth range specifying step, the measured value of the earth pressure by the earth pressure gauge 11 and the peripheral friction force by the peripheral friction meter 12 are used to reduce the stress reduction depth based on the measured value. Identify the range.
With this configuration, the improved ground 23 can be formed at an appropriate depth by the stress reduction work.

Further, in the present embodiment, a stress reduction work is performed on the ground between the outer peripheral surface of the caisson 1 (proximal facing surface 1a) and the opposing underground structure (proximal facing surface 2a of the caisson 2).
With this configuration, it is possible to effectively reduce a large peripheral friction force generated on a part of the outer peripheral surface (the proximity opposing surface 1a) of the caisson 1 facing the underground structure (the proximity opposing surface 2a of the caisson 2).

Further, in the present embodiment, the ground between the outer peripheral surface of the caisson 1 (proximal facing surface 1a) and the opposing underground structure (proximal facing surface 2a of the caisson 2) has a Drucker-Plager system or a camclay system. By performing the analysis by the finite element method applying the elasto-plastic model of the ground using the yield criterion, and by changing the number of the improved grounds 23 created by the stress reduction work, the effect of reducing the earth pressure of each is verified. The number of the improved grounds 23 to be created by the reduction work is set.
With this configuration, the number of man-hours for the stress reduction work can be grasped in advance.

Further, in the present embodiment, the ground between the outer peripheral surface of the caisson 1 (proximal facing surface 1a) and the opposing underground structure (proximal facing surface 2a of the caisson 2) has a Drucker-Plager system or a camclay system. Based on the analysis results by the finite element method applying the elasto-plastic model of the ground using the yield criterion, the design estimation of the stress reduction work is performed.
With this configuration, it is possible to grasp the necessity of the stress reduction work in advance and prepare equipment for performing the stress reduction work.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to the combination of the components, and that such modifications are also within the scope of the present invention.

1, 2, 3 Caisson 1a Proximity facing surface 1b Non-facing surface 2a Proximity facing surface 2b No-facing surface 10 Blade port 11 Earth pressure gauge 12 Surface friction meter 13 Blade port reaction force meter 20 Drilling hole 21 Multi-pipe rod 22 Slime 23 Improvement Ground 30 Hard ground layer

Claims (6)

A caisson squatting method in which a caisson is sunk down to a predetermined depth and installed,
As a stress reduction work to reduce the stress of the ground facing the outer peripheral surface of the caisson,
Reduces stress based on one or both of the measurement result of earth pressure from the surrounding ground acting on the outer peripheral surface of the caisson and the measurement result of the peripheral surface frictional force acting on the outer peripheral surface of the caisson A depth range specifying step of specifying a depth range to be used as a stress reduction depth range,
A drill hole forming step of drilling from the ground to the deepest part of the stress reduction depth range to form a drill hole,
While spraying water simultaneously with air from the tip of the multiple pipe rod inserted into the drilling hole and in the horizontal direction, the multiple pipe rod is rotated to destroy the skeletal structure of the ground, and the cylindrical shape is improved in the stress reduction depth range. A method for laying a caisson, comprising performing an improved ground preparation step of forming a ground.   The caisson laying method according to claim 1, wherein in the improved ground formation step, a sliding material is jetted laterally from a tip of the multiple pipe rod together with the water and the air. There are two types of caisson blades: a soil pressure gauge that measures the earth pressure acting on the outer peripheral surface from the surrounding ground, and a peripheral tribometer that measures the peripheral friction force between the surrounding ground acting on the outer peripheral surface. Or both are provided,
In the depth range specifying step, the stress reduction depth range is specified based on one or both of the measured value of the earth pressure by the earth pressure gauge and the measured value of the surface friction force by the surface friction meter. 3. The method of laying a caisson according to claim 1, wherein 4. The method according to claim 1, wherein in the excavation hole forming step, an excavation hole is formed between an outer peripheral surface of the caisson and an underground structure facing the caisson. 5.   For the ground between the outer peripheral surface of the caisson and the opposing underground structure, an analysis was performed by the finite element method applying an elasto-plastic model of the ground using the yield criterion of Drucker-Plager system or Camclay system, The number of the improved grounds formed by the stress reduction work is set by changing the number of the improved grounds formed by the stress reduction work and verifying the effect of reducing the earth pressure of each of the improved grounds. 5. The method for setting a caisson according to any one of claims 4 to 4.   Based on the analysis results by the finite element method applying the elasto-plastic model of the ground using the yield criterion of Drucker-Plager system or Camclay system to the ground between the outer peripheral surface of the caisson and the opposing underground structure 6. The caisson laying method according to claim 1, wherein a design estimate of the stress reducing work is performed.

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