JPH04368516A - Structure and sinking-installation method of caisson - Google Patents

Abstract

PURPOSE:To shorten a construction period with the occurrence of heaving or swelling restrained by elevatably providing plural pressure supporting plates in the vicinities of cutting edges, and alternately elevating the pressure supporting plates, which are grounded on the ground to restrict the ground deformation, to make excavation. CONSTITUTION:A periphery is surrounded with side walls 11, a partition wall 12 integrated with the side wall 11 is provided in the inside, and plural pressure supporting plates 2 are elevatably arranged in the vicinities of cutting edges. Next, a horizontal projection 14 is fitted to the inner side lower part of the side wall 11, and plural sets of elevating jacks 3 are attached to the horizontal projection 14 to be linked with the pressure supporting plates 2. Then press-in jacks 5 are placed at regular intervals on the upper surface of the horizontal projection 14, and reaction-force anchors 4 are fixed on the inner side ground. Moreover the upper ends 3 of the anchors 4 are inserted into the horizontal projection 14 to set the press-in jacks 5. Successively the elevating jacks 3 are fitted to the horizontal projection 14, and the pressure supporting plates 2 are attached to the lower part of each elevating jack 3. Continuedly the pressure supporting plates 2 are grounded on the ground, press-in force is dispersed to restrain the ground deformation, and the pressure supporting plates 2 is alternately elevated to proceed excavation work.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a caisson structure and a method for sinking a caisson.

0002

[Prior art] In recent years, when implementing the open caisson construction method using dry excavation, if the submerged ground is soft ground, it is possible to avoid the heaving phenomenon in which the surrounding soil of the caisson wraps around to the excavated surface, and the occurrence of slab bulges due to groundwater pressure. Must. In particular, the occurrence rate of these phenomena tends to be higher as the distance between the partition walls in the caisson becomes wider, or in a caisson that does not have partition walls. Therefore, currently, an underground wall such as a continuous underground wall or an SMW wall is constructed around the outer periphery of the caisson that is scheduled to be sunk, and the caisson is sunk while shielding earth pressure and groundwater pressure with this underground wall.

0003

[Problems to be Solved by the Invention] The conventional caisson sinking described above has the following problems. <B> It has been pointed out that the construction of underground walls increases construction costs and prolongs the construction period. <B> Caissons cannot be installed close to the boundary of the site because of the underground wall, which hinders the effective use of the site. <C> When adopting a ground improvement method using chemical injection as a countermeasure against heaving, there is not only a problem of construction costs but also a concern of groundwater contamination.

0004

OBJECTS OF THE INVENTION The present invention was made to solve the above problems, and its purpose is to provide the following caisson sinking technique. <A> Caisson sinking technology that can effectively prevent the occurrence of heaving and disc bulging phenomena. <B> Caisson submersion technology that can omit the construction of underground walls, shorten construction time and reduce construction costs. <C> Caisson sinking technology that allows for effective use of land.

[0005]

[Means for Solving the Problems] The present invention provides an open type caisson with open upper and lower sides, in which a horizontal protrusion is provided at the inner lower part of the cutting edge of the caisson, and a plurality of lifting jacks are attached downwardly to the horizontal protrusion. This caisson structure is characterized by a bearing plate that is connected to the lower part of the lifting jack so as to be able to move up and down, and which is in contact with the ground near the cutting edge and restrains the deformation of the ground. Furthermore, the present invention provides a method for sinking a caisson in which the caisson is sunk while excavating inside an open type caisson with the top and bottom open. This method of sinking a caisson is characterized by excavating while alternately raising and lowering bearing plates while restraining deformation of the ground within the caisson by grounding the caisson.

[0006]

[Structure of the present invention] The present invention will be explained below with reference to the drawings. <A> Structure of the caisson Fig. 1 shows a central vertical sectional view of the caisson 1, and Fig. 2 shows an enlarged view of the blade end of the caisson 1. The caisson 1 is a vertically open type caisson that is surrounded by a side wall 11 and has a partition wall 12 integrated with the side wall 11 inside. One of the features of the present invention is that a plurality of bearing plates 2 are arranged in the vicinity of the cutting edge 13 of the caisson so as to be movable up and down. <B> Bearing pressure plate The bearing pressure plate 2 is a plate body intended to increase the ground contact area of the cutting edge 13 portion of the caisson 1. FIG. 3 illustrates the arrangement position of the bearing plate 2 when the caisson 1 is viewed from the blade mouth 13 side. The bearing plate 2 is the side wall 11
or, if necessary, between the side wall 11 and the partition wall 12, or between the partition walls 12 and 12 so as to be movable up and down. <C> Elevating means for the bearing plate The elevating means for the elevating plate 2 will be explained based on FIG. If the lower part of the support plate 2 is connected to the support plate 2 via a ball seat, the support plate 2 can be raised and lowered by extending and contracting the elevating jack 3. The means for lifting and lowering the bearing pressure plate 2 is not limited to a jack, and any known lifting means such as a screw feeding mechanism can be used. Further, each bearing plate 2 is configured so that its elevation can be controlled individually by remote control. <D> Caisson sinking method Although the caisson 1 may be sunk using its own weight or load, in this example, the caisson 1 is forcibly pressed through an anchor 4 and a press-fit jack 5, as shown in FIG. The case of adding input will be explained. The press-fitting jacks 5 are center-hole type jacks, and are mounted at regular intervals on the upper surface of the horizontal protrusion 14 inside the side wall 11 in consideration of the press-fitting balance.

[0007]

[Function] Next, the method of sinking the caisson will be explained. <B> Anchor installation As shown in Figure 4, anchor
Anchor 4 for reaction force is fixed. Next, the upper end 3 of the anchor is inserted into the horizontal protrusion 14 at the bottom of the caisson 1 constructed on site, and the press-fit jack 5 is set. When constructing the lower part of the caisson 1, attach the lifting jacks 3 downward to the horizontal protrusion 14 near the cutting edge 13, and attach each lifting jack 3
Attach the bearing plate 2 to the bottom of the. The bearing plate 2 is directly under the side wall 11 near the cutting edge 13 of the caisson and the partition wall 12 near the cutting edge 13.
It is important to position it directly below the <B> Sinking of the caisson As shown in Figure 1, the process of press-fitting the caisson 1 by obtaining a reaction force from the anchor 4 with the press-in jack 5 while paralleling the excavation work of the exposed ground inside the caisson 1, and Repeating the process of extending caisson 1 is the same as the previous construction method. In the process of sinking the caisson 1, the present invention dissipates the pressing force by placing a large number of bearing plates 2 on the ground, and at the same time prevents deformation of the ground exposed inside the caisson 1 (soil blistering, heaving). Then, with the bearing plates 2 restraining the deformation of the ground, the bearing plates 2 are lifted one by one to proceed with the excavation work. Even if some of the bearing plates 2 are temporarily lifted for excavation, there is no fear of ground deformation because the other bearing plates 2 remain in contact with the ground.

[0008]

[Other Embodiments] FIG. 5 shows an embodiment in which the ground pressure of the bearing pressure plate 2 and the pressing force of the caisson 1 are automatically controlled in response to changes in soil quality and the weight of the caisson 1. Each lifting jack 3 and each anchor 4 are connected to a hydraulic unit 5, and a control device 7 is connected to the hydraulic unit 6. The information necessary for calculating the stability of the ground surrounding the caisson, such as the weight of the caisson, the frictional force on the circumferential surface, the unit volume weight of the soil, the uniaxial substructure strength, and the adhesion force, is input into the control device 7 in advance. Furthermore, in order to automatically control the expansion and contraction of the lifting jack 3, information regarding the ground pressure of the bearing pressure plate 3 can be controlled by attaching a pressure sensor to a part of the hydraulic system of the lifting jack 3 or to the bottom surface of the bearing pressure plate 3. It is necessary to input it into the device 7. In order to automatically control the tension force of the anchor 4 by the press-fitting jack 5, for example, a sensor for detecting the penetration force of the caisson 1 is installed in the press-fitting jack 5 or a part of the caisson 1 body, and information regarding the press-fitting force of the caisson 1 is provided. It is also necessary to input the information to the control device 7. Figure 6 is a model diagram of the occurrence of the heaving phenomenon, in which the weight of the overlaid soil mass W on the outer periphery of the caisson 1, which is the cause of the heaving phenomenon, is deformed from the cutting edge 13 of the caisson 1 to the inside of the caisson 1 along the sliding circle radius R. Indicates the condition. According to this embodiment, the occurrence of a heaving phenomenon is predicted by calculation using a computer or the like based on geological data inside and outside the caisson 1, and when the occurrence of a heaving phenomenon is predicted, the lifting jack 3
is extended to pressurize the excavated surface with the press plate 2. In this state, the partial pressure load w from the pressing plate 2 causes stress distribution to the excavated ground, countering the heaving phenomenon. The load applied to the press plate 2 at this time uses the weight of the caisson 1 and a part of the press-fitting reaction force. When sinking the caisson 1, the caisson 1 is sunk by increasing the press-fitting load while keeping the load on the press plate 2 constant in principle. According to this embodiment, the following advantages can be obtained. One of these is the ability to accurately predict the occurrence of disc bulges and heaving phenomena. Furthermore, if these phenomena are predicted, the ground pressure of the bearing plate and the pressing force of the caisson 1 can be automatically controlled to avoid the occurrence of these phenomena.

[0009]

[Effects of the Invention] Since the present invention is as explained above, the following effects can be obtained. <A> By installing a plurality of bearing pressure plates on the ground, it is possible to substantially increase the ground contact area of the cutting edge. As a result, even if the ground in which the caisson is to be sunk is soft, it is possible to effectively prevent the occurrence of rock bulges and heaving phenomena, and to safely sink the caisson. <B> Since there is no need to construct an underground wall around the outer periphery of the caisson as in the past, it is possible to reduce construction costs and shorten the construction period. Furthermore, the caisson can be sunk close to the boundary of the site, allowing for effective use of the site. <C> Conventionally, ground improvement by chemical injection has been proposed as a countermeasure against slab blistering and heaving, but the present invention does not use any such chemical. Therefore, there is no need to worry about groundwater contamination.

[Brief explanation of drawings]

[Fig. 1] Longitudinal cross-sectional view of a caisson according to the present invention

[Figure 2
] Enlarged view of the caisson blade part

[Figure 3] Explanatory diagram of an example of deployment of a bearing pressure plate as seen from the cutting edge side

[Figure 4] Longitudinal section of a caisson to explain the initial process of sinking

[Figure 5] Conceptual diagram of another embodiment that automatically controls caisson sinking

Claims (2)

[Claims] Claim 1: In an open type caisson with the top and bottom open, a horizontal protrusion is provided at the inner lower part of the cutting edge of the caisson, a plurality of lifting jacks are attached downward to the horizontal projection, and a plurality of lifting jacks are attached to the lower part of the lifting jack near the cutting edge. A caisson structure characterized by a bearing plate connected to the ground that can be raised and lowered to restrain the deformation of the ground. [Claim 2] In a caisson-sinking method in which the caisson is sunk while excavating inside an open-type caisson with its top and bottom open, a plurality of bearing plates are arranged near the cutting edge inside the caisson so as to be movable up and down, and the bearing plates are placed in the ground. A method for sinking a caisson, which is characterized by excavating while alternately raising and lowering bearing plates while restraining the deformation of the ground within the caisson.