JPS62138779A - Surveying method for cavity in natural ground outside tunnel protection wall - Google Patents

Abstract

PURPOSE:To survey a cavity in the natural ground outside a tunnel protection wall by sending out an elastic wave from inside the tunnel projection wall to the natural ground and using the return propagation time of the reflected elastic wave. CONSTITUTION:When the elastic wave signal is sent out of a transmitter 12 to the natural ground 3, this elastic wave signal is propagated in the protection wall 1 and natural ground 3, and the elastic wave signal reflected by the natural ground surface 3a is inputted to a receiver 13 and converted into an electric signal, which is sent to an unshown arithmetic recording device. The arithmetic recording deice measures the propagation time from the transmission of the elastic wave from the transmitter 12 to the input to the receiver and this propagation time is used to survey whether there is the cavity or not. If the cavity 5 is found, the propagation time becomes longer because of the presence of the air or water in the cavity, thereby confirming the presence/absence state and its size.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a method for exploring cavities in the ground outside the lining wall of a tunnel, particularly a shield tunnel.

[Prior art]

When excavating a tunnel using the shield method, segments are sequentially assembled behind the shield machine as it excavates, and backing concrete is placed in the annular gap between the segments and the ground, and the segments and backing concrete are This forms the lining wall.

It would be ideal if the annular gap had a size equal to the outer diameter of the shield machine body, but cavities with a diameter larger than the outer diameter of the shield machine body may partially occur due to over-excavation or collapse of the ground, etc. It often happens. Cavities caused by such over-excavations are likely to occur near the top of the tunnel, and even when the backing concrete is poured, it is difficult for the concrete to go around into the cavities, and the cavities may remain as they are. The existence of such a cavity.

This means that the lining wall and the ground are not in close contact.

Not only is it impossible to expect the lining wall to have the specified strength, but it can also cause ground subsidence.

For this reason, conventionally, after the lining wall is formed, polling is performed at multiple locations from the inner surface toward the ground, and the core of one wall is taken to check whether there is a cavity.

[Problem that the invention seeks to solve]

The conventional method described above not only reduces the strength of the lining wall, but also requires filling the holes with mortar etc. after exploration, since holes are drilled in multiple locations in the lining wall. The problem was that exploration could not be carried out because groundwater gushed out through the hole.

An object of the present invention is to provide an exploration method that can solve the problems of the conventional methods described above.

[Means for solving problems]

In order to solve the above problems, this invention sends out elastic waves from the inside of the tunnel lining wall toward the ground, and calculates the propagation time of the elastic waves from the inside of the tunnel lining wall to the time it returns to the ground. The method is characterized by exploring a cavity in the ground outside of.

〔Example〕

Figure 1 shows a longitudinal section of the tunnel after the lining wall has been formed. The concrete has not completely gone around the ground on the outside of the concrete 4, and a cavity 5 remains. A guide rail 6 having a similar shape to the inner surface of the lining wall 1 is arranged inside the lining wall 1, and a mount 7 for the guide rail 6 is arranged.
is placed on a rail 9 on a truck 8, and the guide rail 6 moves on the truck 8 in the tunnel excavation direction. Furthermore, the trolley 8 is a board 9 installed at the bottom of the lining wall 1.
The carriage 8 is placed on the rails 10 of the board 9 and moves on the base plate 9 in the tunnel excavation direction.

A pedestal 11 is placed on the guide rail 6 so as to move along it, and an elastic wave transmitter 1 is mounted on the pedestal 11.
2 and a receiver 13 (see Figure 2).
is listed.

When an elastic wave signal is transmitted from the transmitter 12 toward the ground 3, this elastic wave signal propagates through the lining wall 1 and the ground 3, and the elastic wave signal reflected at the ground surface 3a is Receiver 13
The wave receiver 13 converts this into an electrical signal and sends it to an arithmetic and recording device (not shown). 1 in an arithmetic recording device
The propagation time from when the elastic wave signal is sent out from the wave transmitter 12 until it is input to the wave receiver is measured, and the presence or absence of a cavity is detected based on this propagation time. In other words, if there is no cavity in the ground 3, the propagation time will be short, but if there is a cavity 5, as shown near the top of the tunnel, the propagation time will be longer due to the presence of air or water in the cavity. The presence or absence of the cavity 5 and its size are confirmed by this. Such exploration is carried out at many points in the circumferential direction of the tunnel by moving the probe 14 along the guide rail 6 at predetermined pitches (several centimeters). The rail 6 is moved in the excavation direction, and similar exploration is repeated on other cross sections. After confirming the existence of the cavity 5, a hole is made in the lining wall 1 towards the cavity,
The cavity 5 is filled with mortar or the like through this hole.

The presence or absence of a cavity can also be confirmed from the attenuation rate of the elastic wave signal level when input to the receiver 13, but since this attenuation rate is proportional to the propagation time, it can be confirmed based on the propagation time. It can be said that it is synonymous with

As the elastic wave signal, a sound wave signal or an electromagnetic wave signal is used, and the frequency thereof is from several H2 to several 100 Mz, and an appropriate value is used depending on the soil quality of the ground.

This invention is applicable not only to shield tunnels but also to other tunnels.

〔Effect of the invention〕

As described above, according to the present invention, the presence or absence of a cavity in the ground outside the lining wall is detected by sending out elastic waves from the inside of the tunnel toward the ground. There is no need to drill holes in the wall, so there is no need to reduce its strength, and there is no need to fill the lining wall with mortar, etc., allowing exploration work to proceed quickly. Furthermore, since there is no need to drill holes in the lining wall, it can be carried out even in areas where there is a lot of groundwater.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view showing one embodiment of the method of this invention;
The figure is a plan view of the spacecraft.

Claims (1)

[Claims] 1. Send an elastic wave toward the ground from inside the tunnel lining wall, and search for cavities in the ground outside the lining wall based on the propagation time until the elastic wave is reflected from the ground and returns. An exploration method characterized by: