JPH0432919B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a shield construction method used in tunnel construction, etc., in which a function is added to detect soil at risk of ground collapse.

Conventional technology In shield work for subways, tunnels, etc., if the ground is predicted to be soft, the ground is hardened by chemical injection and freezing methods, and the work is carried out by using a shield excavator to dig. However, even if the general strata of the ground to be constructed are known, there are areas where the strata are locally complex and it is not possible to predict the details of the construction site before excavation. Accidents where the ground collapses occur. Conventionally, as a measure to prevent such accidents, a mechanical method has been proposed in which weaknesses or holes (voids) are detected using a plate liquid pressed by a spring. This is because, for example, if the plate-like body is installed on the upper part of the outer shell of a shield excavator, and when the weak ground is reached during excavation, the earth pressure that has been holding down the plate-like body will decrease, so the plate-like body Detection is performed by utilizing the fact that one end of the body rises upward. However, this method is extremely unreliable and has the disadvantage that the plate-shaped body is easily damaged mechanically during excavation, so it is not very practical.

On the other hand, Japanese Patent Application Laid-Open No. 58-181999 discloses a configuration in which pulse radio waves are transmitted from an antenna provided at the tip of the shield outer shell of a shield excavation machine, and the geology of the excavation point is detected by the reflected reception signal obtained. is disclosed.

In general, the reflected reception signal depends on three factors: the geology (such as dielectric constant) of the soil existing between the reflecting object and the reflecting object, the reflectance of the reflecting object, and the distance to the reflecting object. Here, the reflective object is an underground object,
Considering the fact that it is the ground surface or the boundary between different types of soil, the above three elements can be combined in a wide variety of ways.

Therefore, as disclosed in the above patent publication,
If a single antenna is used to detect the geology, only the differences from other locations can be determined, and there is a disadvantage in that it is not possible to make correct judgments about changes in the geology based on absolute criteria.

OBJECT OF THE INVENTION Therefore, an object of the present invention is to provide a new geological exploration shield construction method that solves the disadvantages of the above-mentioned prior art.

Composition of the Invention The present invention is a shield construction method for detecting the geology of the soil at an excavation point using a reflected reception signal obtained by transmitting pulse radio waves from an antenna provided at the tip of the shield outer shell of a shield excavation machine, By installing multiple antennas, installing a different dielectric material for each antenna on the side that transmits the pulse radio waves of each antenna, and comparing the reflected received signals obtained from each antenna, geological information can be determined. It is designed to be detectable.

In other words, as the dielectric constants of the dielectric material and the soil get closer, the level of radio waves induced at the interface between the two increases, and as a result, the radio waves are reflected from buried objects, the ground surface, etc., and then follow the opposite path and are received by the antenna. The level of the reflected received signal increases. Therefore, the permittivity (geology) of the soil at the current excavation point was determined to be close to the permittivity of the dielectric material installed in the antenna that received the reflected reception signal with a large intensity, and the reflected reception signal with a small intensity was obtained. By determining that the dielectric constant is far from the dielectric constant of the dielectric member provided in the antenna, the geology can be determined more absolutely.

The principle of the present invention will be explained using the model shown in FIG. The antenna 1 is in contact with soil 3 having a dielectric constant K ₁ outside the shield via a dielectric member 2 having a dielectric constant K ₀ .
The transmitted pulse wave 4a from the antenna penetrates into the soil 3, is reflected by the ground surface 5, etc., becomes a reflected pulse 4b, and is received by the antenna 1. The relationship between the amplitude of this received signal and time is shown in Figure 2, where t ₂
(round trip time) later, it is received as a strong reflected pulse 4b from the ground surface 5. In this figure, pulse a at t ₀
is a transmitted pulse, and a small reflected pulse c at t ₁ is reflected by debris in the soil 3. And the strength of the radio waves that penetrate into soil 3 is
It varies depending on the ratio of K ₀ and K ₁ . Therefore, when the intensity of the reflected radio wave is changed by changing the dielectric constant K ₀ of the dielectric member 2, received signals, that is, reflected received pulses having different reflected strengths can be obtained for the soil 3 having the same dielectric constant K ₁ . Further, even if the dielectric constant K ₀ of the dielectric member 2 is the same, if the dielectric constant K ₁ of the soil 3 changes, reflected reception pulses with different reflection intensities can be obtained. Taking advantage of this fact, if multiple antennas are installed to transmit and receive, each received signal will receive a different reflected reception pulse depending on the ratio of K ₀ /K ₁ , and this difference can be compared. Therefore, the difference in quality of _K1 , that is, soil 3, can be estimated.

Specific Structure FIG. 3 is a diagram showing an embodiment of the present invention, in which a radar antenna head 8 is shown which has a plurality of antennas having different dielectric members 2 near the upper end of the face 7 side of the shield shell 6. It is placed. During shield excavation, it is desirable to predict the risk of soil collapse as close to the front as possible.

Now, as shown in FIG. 3, it is assumed that there are three geological formations in the lower part of the ground surface 5, which are complicated, and that the shield excavator 18 advances in the direction of the arrow 19. The geology is wet and the dielectric constant is K _A ,
is clayey and has a dielectric constant K _B , and is dry soil and has a dielectric constant KK _C. A single transmission pulse a is given from the transceiver 20 to each of the three different antennas A, B, and C of the dielectric member 2 of the radar antenna head 8, and its reflected reception pulses b,
c is given from the transceiver 20 to the display 21, so that mono-pulse radar detection signals from each antenna A, B, and C can be observed. FIG. 4 shows the status of the transmitted pulse and received pulse at each point P ₁ , P ₂ , and P ₃ of this detection signal. The permittivity K ₀ of each dielectric member 2 of antenna A, antenna B, and antenna C is, for example, K ₀ ¹ , K ₀ ² ,
^Therefore , for the reason mentioned _above , the shield excavator 18 excavates and the radar antenna head 8 reaches the points P ₁ , P ₂ , and
When P ₃ is reached, the detection signals A ₁ , B ₁ , and C ₁ are detected with different signal waveforms as shown in FIGS. 4(a), (b), and (c).

That is, at point _P1 , for example at _C1 , the radio wave of the transmitted pulse reaches the ground surface 5 and is reflected, and the intensity of the reflected pulse b is also large. At _A1 , the radio waves of the transmitted pulses hardly penetrate into the soil 3, and therefore no reflected received pulses are observed. In B ₁ , a weak reflected reception pulse b is observed between the cases of A ₁ and C ₁ . Comparing these reflected received pulses b with those at points _P2 and _P3 , the changes are different, and from these different trends, it is possible to estimate the dielectric constant of the geology, that is, to determine the geology.

In other words, it is determined that the geological feature at point _P1 has a dielectric constant close to the dielectric constant K ₀₃ of the dielectric member of antenna C. Similarly, it is found that the geological feature at point _P2 has a dielectric constant close to the dielectric constant K ₀₁ of the dielectric member of antenna A. Also, at point _P3 , the dielectric constant K ₀₂ of the dielectric member of antenna B and antenna C
Since the dielectric constant K ₀₃ of the dielectric member is close to both of these, for example, it is determined that the geology has a dielectric constant between these.

Next, each antenna A of the radar antenna head 8,
Examples B and C are shown in FIG. antenna element 9
is formed on a printed circuit board 13, in which two triangles are arranged facing each other as shown in FIG. along with giving
The reflected wave signal is extracted. This triangular antenna has radiation characteristics with wide-angle directivity.
It was chosen so that the search range by radar would be wide. The upper part of the antenna element 9 is filled with a dielectric material 14 corresponding to the dielectric member 2, and these members are housed in a box-shaped body 15 with a concave structure provided at the tip of the shield outer shell 6. A radio wave absorbing material 16 such as a ferrite core is placed on the bottom of the box-like body 15, the printed circuit board 13 and the dielectric material 14 are fixed to the top of the material, and an insulating cover made of epoxy resin is placed over this. 17 to form a waterproof contact surface with the soil 3.

The thickness of the insulating cover 17 is the same as that of the dielectric member 14 as shown in the figure.
Since the value is set to be sufficiently small compared to the thickness of the dielectric member 14, the dielectric member 14 is replaced with a dielectric member having approximately the same dielectric constant and total thickness as the dielectric member 14 as a whole. In other words, the presence of the insulating lid 17 can be ignored.

The dielectric material 14 is different for each antenna A, B, and C, for example, a liquid dielectric material such as pure water or oil, a powder dielectric material such as glass powder or plastic resin powder, a plastic resin plate, a paraffin plate, etc. Solid dielectric materials with different dielectric constants are used.

In addition, by changing the pointing direction of each antenna A, B, and C so that it tilts forward, it is possible to detect the geology as far in front of the excavation point as possible, and by changing the shape of the antenna element 9, pulse radio waves can be transmitted. or convert the amplitude values of each reflected reception pulse signal A ₁ , B ₁ , C ₁ displayed on the display 21 into shading or color signals to make it easier to compare differences in reflected signal waveforms. It is possible to modify the method to suit the purpose of detection, such as by

Effects of the Invention As explained in detail above, according to the geological detection shield construction method of the present invention, a plurality of antennas provided with different dielectric members are installed and the reflected reception signals of each antenna are compared. The geology (permittivity) of the excavation point can be known more absolutely as the value closest to the dielectric constant of the dielectric material installed in the antenna that received the reflected reception signal of great strength, and the risk of ground collapse etc. The effect is that it can more accurately prevent.

[Brief explanation of drawings]

The drawings show an embodiment, and FIG. 1 is a cross-sectional configuration diagram for explaining the principle of the present invention, FIGS. 2 and 4 are waveform diagrams of detection signals, FIG. 3 is a longitudinal sectional view of the overall configuration, and FIG.
The figure is a sectional view of the structure of the radar antenna head portion. DESCRIPTION OF SYMBOLS 1... Antenna, 2... Dielectric member, 3... Soil, 4a... Transmitted pulse wave, 4b... Reflected pulse wave, 5... Ground surface, 6... Shield shell, 7...
Cutting surface, 8... Radar antenna head, 9... Antenna element, 10... Insulating body, 11... Insulation holding, 12... Terminal, 13... Printed circuit board, 14
... Dielectric material, 15 ... Box-shaped body, 16 ... Radio wave absorbing material, 17 ... Insulating lid, 18 ... Shield tunneling machine,
19...Drilling direction, 20...Transmitter/receiver, 21...
display.

Claims (1)

[Scope of Claims] 1. A shield construction method that detects the geology of the soil at an excavation point using a reflected reception signal obtained by transmitting pulse radio waves from an antenna provided at the tip of the shield outer shell of a shield excavator, In addition to providing multiple antennas, a dielectric material with a different permittivity is provided for each antenna on the pulse radio wave transmitting side of each antenna to perform transmission, and each reflected reception signal obtained from each antenna is compared. A geological detection shield construction method characterized by making it possible to detect the geological feature.