JPS63206527A - Settling promoting work for caisson - Google Patents

Abstract

PURPOSE:To raise the efficiency of construction work by a method in which the surrounding ground of the lower inside of a caisson is excavated by jet air, and the excavated soil is discharged from an air lift to promote the settlement of caisson. CONSTITUTION:A caisson 1 is lowered to the bottom under water, and the water surface of a shaft 8 is detected by a water pressure guage 13 and controlled to stabilize the caisson 1. When air is jetted from an air jet nozzle 3 into the caisson 1, the surrounding of the ground 15 is excavated and the excavated soil is dispersed into water. When the valve of an air tube 10 is opened, soil os discharged by air and water from the tube 10. An excavating bucket 7 is put in the shaft 8 to excavate the heaved ground 15. Excavation is repeatedly made by jet air and the bucket 7, and the caisson 1 is slowly settled down into the ground 15.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a construction method for promoting the sinking of a caisson installed in the ground at the bottom of water.

[Conventional technology]

Generally, a caisson is lowered by mechanically excavating the ground inside the caisson.

[Problem that the invention seeks to solve]

Therefore, excavation must be carried out with care so that the entire caisson sinks evenly, which not only takes time and construction period, but also requires a lot of labor, large cranes, machinery, etc. There was a problem.

[Means for solving problems]

This invention was devised for the purpose of solving the problems of the above-mentioned conventional method.
An air injection part is constructed by arranging the required number of air injection holes at regular intervals in the circumferential direction. In addition to dividing the area watertightly, an air lift pipe communicating with the lower part of the caisson is provided, and when the caisson is grounded on the water bottom and excavated into the ground, the surrounding area of the ground inside the lower part of the caisson is excavated with air injection, The above problem is solved by discharging the excavated earth and sand from the air lift pipe to promote the sinking of the caisson.

(Function) In the above construction method, the excavation of the ground occurs from the surrounding area by air injection, and since the amount of air injection is constant in any part, there is no big difference in the excavation around the ground.
The caisson sinks evenly throughout. Further, the amount of sinking is controlled by changing the amount of air injection, the amount of air discharged from the air lift tube, and the height of the water surface inside the shaft.

(Example) In the figure, 1 is a caisson, in which a plurality of air pipes 2 are arranged inside the wall. A large number of air injection holes 3.3 are connected to an annular pipe 4 for supplying air.

Reference numeral 5 denotes a bottom plate which also serves as an over-settling prevention plate, which is mounted with a stopper 6 in the caisson above the air injection part where the large number of air injection holes 3.3 are present, and partitions the lower part of the caisson in a watertight manner.

A shaft 8 of a required height is provided in the center of the bottom plate 5 to accommodate an excavation bucket 7 (see FIG. 3) in a manner that allows it to be raised and lowered and opened and closed. An air lift pipe 10 is provided in communication with the lower part of the caisson.

A drain pipe 11 is connected to the lower part of the shaft 8,
Further, a water supply pipe 12 is connected to the upper part.

Note that 13 is a water pressure pipe attached to the lower surface of the bottom plate 5, 14 is a cover plate of the shaft 8, and 15 is the ground at the bottom of the water.

In order to lower the caisson 1, the caisson 1 is first lowered vertically to the bottom of the water, touches down φ, then the water pressure gauge 13 detects the water surface, and the water surface of the shaft 8 is controlled within a set range to stabilize the caisson 1 underwater. Plan. This water level control is performed by supplying or draining water to the shaft 8.

Excavation of the ground 15 in the lower part of the caisson 1 is performed using both the air injection force and the excavation bucket 7 in the shaft 8, but if the ground 15 is soft, the excavation bucket 7 can be omitted.

When air is injected inside the caisson with the lower end of the caisson in contact with the ground 15, the area around the ground in contact with the caisson is excavated all at once due to the injection force, and the excavated earth and sand are thrown up into the water. The water pressure in the lower part of the caisson increases due to the injection of air, but this pressure is released by opening the valve 9 of the air lift pipe 10, and excavated earth and sand are discharged from the air lift pipe 10 together with the air and water.

When the resistance in the lower part of the caisson decreases due to this discharge, the caisson 1 sinks and the unexcavated ground W15 is raised up to the opening of the shaft 8 because the ground inside the lower part of the caisson 1 has been removed.

Therefore, the excavation bucket 7 is inserted into the shaft 8, and the raised ground 15 is excavated.

The caisson 1 is gradually lowered into the ground by repeatedly performing such injection of air and excavation by the excavation bucket 7. In addition, the excessive settling of caisson 1 is due to the fact that the ground 15 is lower than the bottom plate 5.
The amount of subsidence can be controlled arbitrarily by opening and closing the valve 9 of the air lift pipe 10, changing the amount of air injection, and the height of the water surface inside the shaft.

〔Effect of the invention〕

As mentioned above, this invention injects air from inside the lower part of the caisson to promote the sinking of the caisson.
It is possible to expect a significant improvement in construction efficiency compared to the case where only mechanical excavation is performed, and it is possible to shorten the construction period and save on labor, machinery, etc. In addition, since air excavation is even, the precision of caisson sinking is further improved, eliminating the need for large-scale excavation using machinery, and because excavation can be done inside the shaft, the occurrence of excavation troubles is reduced. have

[Brief explanation of the drawing]

The drawings show an embodiment of the method for promoting caisson settlement according to the present invention, in which Fig. 1 is a longitudinal cross-sectional view of the caisson, Fig. 2 is a horizontal and vertical plan view of the lower part of the caisson, and Figs. 3 and 4 show the subsidence state. FIG.

Claims (2)

[Claims] (1) An air injection part is provided by arranging the required number of air injection holes at regular intervals in the circumferential direction inside the lower part of the caisson, and above the air injection part, the inside of the lower part of the caisson is placed in the center. It is divided watertightly by a bottom plate with a shaft for excavation, and an air lift pipe that communicates with the inside of the lower part of the caisson is installed. A caisson settlement promotion method characterized by excavating the caisson using air jets and discharging the excavated earth and sand from an air lift pipe to promote the caisson settlement. (2) The caisson settlement promotion method according to claim 1, wherein the excavation settlement is carried out by an excavation bucket provided in the shaft so as to be able to rise and fall freely.