JPS5843533B2 - Method for suppressing caisson subsidence - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for suppressing caisson settlement, which controls the initial settlement of a caisson used in the caisson construction method by widening and narrowing the bottom surface of the cutting edge of the caisson.

In recent years, shield construction work on soft ground has become more common, and as a result, more and more cases are being implemented using the caisson method for launching and arriving shafts.

In addition, as shields become larger and deeper, caissons tend to also become larger, and especially for large caissons, the most important issue is how to suppress their initial settlement.

In other words, the balance of forces that act when the caisson is in the process of sinking is the surface friction force of the peripheral wall of the caisson against the sinking blade due to the weight of the caisson, the rising air pressure (lifting force) in the working chamber, and the moon of the caisson. It is determined by the relationship between the bearing capacity of the Kusaka surface and the total subsidence resistance.

Although it varies depending on the caisson, it is generally the surface friction force and rising air pressure that show the largest values in this total sinking resistance force, but these large surface frictional forces and rising air pressure cannot be expected at the time of initial settlement. Therefore, only the supporting force of the lower surface of the moon becomes the subsidence resistance force.

Therefore, conventionally, as shown in Fig. 1, a lightweight caisson main body 2 for creating a relatively small-scale working chamber 1 is formed with a small and narrow cutting edge 4 on the bottom surface 3, and the working chamber 1 is
If the size of the caisson body 2 increases and the weight of the caisson body 2 increases, the bottom surface 3 of the cutting edge 4 should be made wider as shown in Fig. 2, and if the working chamber 1 becomes large in size, the caisson body 2 should sink. Taking this into consideration, a step-shaped cutting edge 4 as shown in FIG. 3 was provided to provide good biting performance when sinking and to secure the bottom surface 3 of the cutting edge.

However, after constructing a workroom on soft ground, when the plate was removed, rapid subsidence was observed due to the low bearing capacity of the ground.
Moreover, even after that, the amount of subsidence is large and extremely dangerous until surface friction force and rising air pressure can be expected.

For this reason, conventional ground improvement has been carried out to increase the bearing capacity of the soil, but normal ground improvement has its limits and cannot suppress rapid subsidence. , earth and sand centers are also used, but even if ground improvement and earth and sand centers are carried out in this way, it cannot be said to be safe in terms of strength, and the disadvantages are that it imposes a large economic burden and takes a long time to complete. there were.

The present invention was devised to eliminate the above-mentioned drawbacks, and focused on the fact that large caissons, which had a problem with initial settlement, have a step-shaped cutting edge. By removably fixing the auxiliary cutting edge of the required dimensions divided in the circumferential direction of the caisson working chamber, and adjusting the supporting force of the entire cutting edge by attaching and removing this auxiliary cutting edge, it is possible to prevent By attaching an auxiliary cutting edge to increase the supporting area and stably sinking to a position where surface friction force and rising air pressure can be expected, and then removing the auxiliary cutting edge and allowing the sink to sink in the same way as before, it is possible to prevent the initial settling from the conventional method. The present invention aims to provide a method for suppressing caisson settlement that can reduce the economic burden by omitting the earth and sand centers as much as possible, and at the same time significantly shorten the construction period.

The auxiliary cutting edge used in the present invention will be described with reference to the embodiment shown in the drawings.

As shown in FIGS. 4 and 5, the auxiliary cutting edge 5 is curved so as to be in close contact with the inside of the tip of the stepped cutting edge 4, that is, the step portion, and is divided into predetermined lengths in the circumferential direction. The auxiliary cutting edge 5 is made of box-shaped or lattice-shaped hardware, concrete, etc., and a mounting hole 6 is bored in each of the auxiliary cutting edges 5 to connect the inner and outer circumferential surfaces.

The auxiliary blade opening 5 configured in this way has its mounting hole 6
By screwing the bolt 7 inserted into the anchor nut 8 which has been embedded and fixed in advance into the blade main body 4, the double blade ports 4 and 5 are integrally fixed.

The basic shape of the auxiliary cutting edge 5 is as shown above.
The auxiliary blade openings 5 are formed in layers in the radial direction of the working chamber, and the auxiliary blade openings 5 are formed in layers in the radial direction of the working chamber, as shown in Fig. 6. The auxiliary cutting edge 5 may be made removable, or may be an enlarged auxiliary cutting edge 5 with a wider bottom surface, as shown in FIG.

Next, a method of suppressing the sinking of the caisson using the auxiliary cutting edge 5 configured as described above will be explained.

Taking into consideration the bearing capacity of the ground, the weight of the caisson body 2, etc., the auxiliary cutting edge 5 is fixed inside the cutting edge body 4, and the bottom surface 3 of the entire cutting edge is fixed.
Expand.

At this time, if the strata are simple and the soil bearing capacity is relatively large, the auxiliary cutting hole 5 shown in Figures 4 and 5 should be installed. By attaching an enlarged auxiliary cutting edge 5 as shown in Fig. 7, the bottom surface 3 of the cutting edge body can be further enlarged.Also, when the strata are complex and it is desired to change the supporting force of the cutting edge into multiple stages. teeth,
A laminated auxiliary cutting edge 5 as shown in FIG. 6 is attached.

When the auxiliary cutting edge 5 is attached inside the cutting edge main body 4 in this way, the bottom surface 3 of the cutting edge is enlarged by the auxiliary cutting edge 5, and its supporting area increases.

Therefore, even if the ground is soft, where earth and sand centers were conventionally used, if the auxiliary cutting edge 5 is installed, there is no need to use earth and sand centers, and even if earth and sand centers are used, initial settlement will be reduced. Even if the ground is extremely soft, as in the case where the ground is being subsided rapidly, it is possible to increase the supporting force of the entire cutting edge at the initial stage of subsidence, so that the caisson body 2 can be further stabilized by the combined use of the earth and sand center.

When the sinking progresses and the surface friction force and rising air pressure become sufficiently stable, the auxiliary blade opening 5 is removed from the working chamber 1 to smoothen the sinking of the caisson body 2.

In addition, if sufficient surface friction force and rising air pressure cannot be obtained during sinking, it is not necessarily necessary to remove this auxiliary cutting edge 5, and it is necessary to increase or decrease the supporting force of the cutting edge depending on changes in the strata. In such a case, the auxiliary cutting edge 5 may be attached or detached as necessary.

Therefore, in such a case, it is preferable to use a laminated auxiliary cutting edge 5 as shown in FIG.

In addition, when attaching and detaching the auxiliary cutting edge 5 as described above, since the auxiliary cutting edge 5 is divided in the circumferential direction and fitted into the step part of the cutting edge main body 4, it is easy to attach and remove the auxiliary cutting edge 5.
Moreover, the attached auxiliary cutting edge 5 is maintained in a stable state.

In addition, in the above embodiment, the shape of the working room frame is circular, but the shape is not limited to this, and it may be angular, and the shape of the caisson also has a circular cross section. It is not limited to those of
It may be of quadrilateral or other shape.

In summary, the present invention provides for detachably fixing auxiliary cutting holes of required dimensions divided in the circumferential direction of the working chamber to the inside of the stepped tip of the caisson working chamber. By adjusting the sinking resistance force, the support force of the entire cutting edge can be adjusted to increase or decrease the support force of the entire cutting edge, not only at the beginning of the caisson sinking, but also during the sinking process, by adjusting the sinking resistance force to increase or decrease the support force that is most suitable for each process. Therefore, it is possible to stabilize large caissons even in soft ground, and it is possible to reduce the frequency of ground improvement or the use of earth and sand centers as much as possible, which was previously considered impossible. This is an extremely useful new effect that can significantly shorten the construction period of the caisson construction method and significantly reduce construction costs, as it is possible to stably sink the caisson even in extremely soft ground that has been previously used in combination with ground improvement or earth and sand centers. It is something that plays.

[Brief explanation of the drawing]

The drawings show an embodiment of the method for suppressing caisson settlement according to the present invention, and FIGS. 1 to 3 are longitudinal cross-sectional views of essential parts illustrating the caisson cutting edge, respectively. FIG. 4 is a longitudinal sectional view of the main part used in the present invention. FIG. 5 is a longitudinal cross-sectional view of the main parts showing an improved mounting condition, and FIG. 6 is a perspective view of the main parts showing another example of the auxiliary cutting port used in the present invention in an installed state. FIG. 7 is a vertical cross-sectional view of a main part showing a mounting state of yet another example of the auxiliary cutting edge used in the present invention. In the figure, 1 is a caisson working chamber, 2 is a caisson main body, 4 is a cutting edge main body, and 5 is an auxiliary cutting edge.

Claims (1)

[Scope of Claims] 1. An auxiliary blade opening of a required size divided in the circumferential direction of the caisson working chamber is removably fitted and fixed inside the tip of the moon body formed in a step shape, and the auxiliary blade opening is removably fitted and fixed. A method for suppressing sinking of a caisson, characterized in that the supporting force of the entire cutting edge can be increased or decreased by attaching and detaching the blade. 2. The caisson according to claim 1, wherein the auxiliary cutting edge has a laminated structure, and the supporting force of the entire cutting edge can be increased or decreased in multiple stages by attaching and detaching the auxiliary cutting edge of each layer. Subsidence control method.