JPH0338396B2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field This invention is based on the Natom construction method (New Austrian construction method).
In order to evaluate the properties and stability of the ground in front of the excavation and the shotcrete lining, especially the upper part, when constructing tunnels using the Tunneling Method, it is necessary to This article relates to a method of measuring and managing the ground properties above the shotcrete lining and in front of the excavation, which is carried out to evaluate the ratio of support to the supporting lining.

Conventional Technology Conventionally, tunnel construction using the NATM construction method has already been carried out and is well known (for example, pages 33 to 44 of Nippon Kogyo Shuppan's "Construction Machinery" April 1980 issue). NATM
When constructing tunnels using this construction method, construction is proceeding while measuring the behavior (stability evaluation) of the surrounding ground and shotcrete lining. When designing and analyzing underground cavities such as tunnels, it is economical and rational to evaluate the proportion of underground stress supported between the ground around the tunnel and the lining that supports the tunnel. This is because it is extremely important when designing and constructing a lining.

However, the current measurement management method is based on the measurement items stipulated in Article 6 of the NATM Construction Method Construction Regulations, which can be roughly divided into: () Measurement of the behavior of the ground around the tunnel.

() Measuring the behavior of various lining components.

() Shape measurement of tunnel structure.

It is only supposed to be carried out either by in-situ surveys or by using ground samples.

Problems to be Solved by the Present Invention As mentioned above, the measurement items in the current measurement management method mainly measure the tunnel cross-sectional direction (radial direction), and the tunnel longitudinal cross-sectional direction (tunnel The measurement items in the axial direction are as follows:
Only a small amount of ground surface subsidence measurement was carried out, and the effectiveness of measurement management is questionable when it comes to tunnel construction in deep layers.

Tunnel stability, especially how the shotcrete lining and the ground in front of the face (ground in front of excavation) behave in the longitudinal cross-sectional direction (axial direction) of the tunnel, depending on the progress of tunnel construction using the NATM construction method. This is extremely important for safety evaluation. Therefore, it must be said that the fact that the current measurement control method does not substantially perform measurement control in the longitudinal cross-sectional direction (axial direction) of the tunnel as described above is a serious flaw, and this point needs to be resolved. This has become an important issue.

Therefore, an object of the present invention is to continuously monitor changes in the behavior of the ground in front of excavation and the shotcrete lining in the longitudinal cross-sectional direction of the tunnel (tunnel axis direction) in accordance with the progress of tunnel construction using the NATM construction method over time. The object of the present invention is to provide a measurement management method that can be measured in real time and can evaluate stability with high accuracy based on the measurement.

Means for Solving the Problems As a means for solving the above-mentioned problems of the prior art, a method for measuring and managing the top part of the shotcrete lining and ground properties in front of excavation in tunnel construction using the Natom construction method according to the present invention is shown in the drawings as an example. As shown in (a), a horizontal borehole is constructed from a position corresponding to the cross section of the shotcrete lining of the face 3 toward the ground 4 in front of the excavation, approximately parallel to the axis of the tunnel; A detector tube 2 with a detector 7 attached at each measurement point position is inserted into the hole with approximately the same length as the horizontal borehole,
(b) The lead wire 5 of the detector tube 2 led out from the face portion 3 is connected to measurement recorders 9 and 10, and A step in which the axial force, shear force, bending stress, etc. applied to each measurement point of the pipe 2 is measured and recorded as the amount of strain by each detector 7; The pipe 2 is sequentially buried within the cross section of the shotcrete lining 1; (d) the measurement values obtained by the measurement recorders 9 and 10 are evaluated and the construction is managed in accordance with the management standards; It is characterized by becoming.

Function Each detector 7 of the detector tube 2 installed in the ground 4 in front of the excavation detects the behavior and stability of the ground in front of the face during subsequent ground excavation, expressing axial force, shear force, and bending stress. The amount of strain is measured in real time, and the soil properties can be managed and evaluated in real time based on the results.

In addition, the detector tubes 2 excavated one after another by ground excavation are continuously buried in the upper part of the lining and its surroundings until they are buried in the shotcrete lining 1 of the tunnel, and even after they are buried. The behavior of the ground is also measured moment by moment by the same detector tube 2 as the amount of strain indicating axial force, shear force, and bending stress. Based on the results, the properties of the shotcrete lining 1, Enables management and evaluation of stability, etc.

In other words, the detector tube 2 measures the behavior and properties of the ground 4 in front of the excavation and the shotcrete lining 1, such as the axial force, shear force, bending stress, etc. applied to each measurement point where the individual detectors (strain gauges) 7 are located. Continuously measure with high precision. In this case, since the detector tube 2 is used, the installation work of each detector 7 and the stress measurement can be made extremely easily and reliably.

Example Next, illustrated embodiments of the present invention will be described.

Figures 1 and 2 briefly show the general state of tunnel construction using the NATM construction method, in which the measurement management method according to the present invention was implemented. In the figure, 1 is the shotcrete lining of the tunnel, and 2... is the position within the cross section of the shotcrete lining 1 from the face 3 toward the excavated front ground 4 in front of the face 3 of the tunnel. This is a detector tube that is placed approximately parallel to the axis and deep enough to be unaffected by ground excavation. 5 are lead wires led out from the end of the detector tube 2 on the face side into the tunnel hollow part 6, respectively.

As shown in Figs. 3 and 4, the detector tube 2 has a diameter d≒5 cm and a module length l.
It is said to be made by adding the required number of elongated modular tubes approximately 5 meters in length. The length of each detector tube 2 is usually ~2.2 times the diameter of the tunnel cross section.
It is said to be about 3.0 times the actual size, and the actual length is about 15m to 25m. A thin-walled steel tube with appropriate hardness and bending rigidity is used for the tube body of the detector tube 2, and one tube is placed at each measuring point position determined in a predetermined arrangement in the circumferential direction and axial direction of the inner diameter surface. It has a configuration in which a detector (strain gauge) 7 is attached. A large number of dowels 8 protrude from the outer diameter surface of the detector tube 2 to ensure integration when buried in the cross section of the shotcrete lining 1, as will be described later. Lead wires 5 are individually led from each detector (strain gauge) 7 of the detector tube 2, and these are led out from the end of the detector tube 2 on the face side. Note that the lead wires are not shown in FIGS. 3 and 4.

As described above, since it is necessary to attach the detector (strain gauge) 7 to the inner diameter surface of the long and narrow detector tube 2, the detector tube 2 is made by dividing the module tube vertically as shown in Fig. 4. It has a structure divided into two equal parts, and a detector 7 is attached to each measurement point position on the inner diameter surface of each divided tube body 2a, 2b. Thereafter, the divided tube bodies 2a and 2b are again butted against each other to form a single modular tube body, and the butted edges are fastened together by brazing, clamping, or the like.

Next, the position and installation method of the detector tube 2 will be explained.

As described above, the detector tube 2 is installed from the face portion 3 toward the excavation front ground 4 in front of the face portion 3. In particular, the detector tube 2 is located at a position (approximately at the center) where sufficient concrete coverage within the wall thickness section of the shotcrete lining 1 is obtained. and,
Due to the need to evaluate the true state and change of stress in the ground 4 ahead of excavation, the detector tube 2 is moved sufficiently deep from the face 3 towards the ground 4 ahead of excavation to a part of the ground that is not affected by the excavation. , specifically the tunnel diameter
2.2 times to 3.3 times, length from face 3 to 15 m
It will be installed approximately parallel to the tunnel axis to a depth of approximately 25m. Furthermore, in light of the purpose of measuring and managing the stress state, change, and stability in the longitudinal cross-sectional direction (tunnel axis direction) of the shotcrete lining 1, the detector tube 2 is installed at the upper half of the shotcrete lining 1. be done.

In the case of tunnel construction using the short bench cut method shown in Figures 1 and 2, the method for installing the detector tube 2 is to excavate the ground in the upper half of the face.
After constructing the upper half of the shotcrete lining 1, horizontal boring is carried out from the upper half face and the position within the cross section of the tip of the shotcrete lining 1 (Fig. 2) toward the ground 4 in front of the excavation. Construct the hole. The horizontal borehole is constructed with a hole diameter and depth (length) that allows the detector tube 2 to be inserted, the detector tube 2 is inserted into this horizontal borehole, and then the detector tube 2 is injected with mortar. is firmly fixed in the ground.

The lead wire 5 is guided into the tunnel hollow part 6 from the end of the detector tube 2 fixed in the excavation front ground 4 on the face side, and the switchbox 9 is carried into the appropriate position in the tunnel hollow part 6. It is connected to the automatic recorder 10 (or an automatic sampling, analysis, and plotting system using a microcomputer) as shown in FIG. 5, and the underground stress in the ground 4 in front of the excavation is immediately measured and recorded.

Meanwhile, in parallel with these measurement records, the tunnel construction work included excavating the ground 4 in front of the excavation face 3, constructing the upper half shotcrete lining (primary lining), excavating the lower half bench, and excavating the side wall. Construction will proceed in the following order: partial shotcrete lining (primary lining), excavation of the tunnel bottom, and invert construction.

Therefore, as the ground 4 in front of excavation is excavated in front of the face 3, the detector tube 2 fixed in the ground
are excavated one after another, and the impact of these excavations on the ground (changes in underground stress) is measured in real time. Subsequently, the excavated detector tube 2 is buried in the cross section of the shotcrete lining 1 as the shotcrete lining 1 is constructed. Therefore, from now on, what kind of change the impact of excavation brings on the stress of the shotcrete lining 1 supporting the tunnel is measured in real time every moment.

Next, the evaluation of the measured values of the detector tube 2 installed as described above and the management method based thereon will be explained.

Axial force and shear force applied to each measurement point of the detector tube 2,
Bending stress and the like are measured as strain amounts by individual detectors (strain gauges) 7, and these are recorded in the automatic recorder 10 as a graph as shown in FIG. The point at which the detector tube 2 is buried and fixed in the ground 4 in front of the excavation is set as the zero point (measurement reference value), and thereafter, the strain value that changes every moment as time passes is measured and recorded. For one detector tube 2, the same number of graphs as the number of measurement points will be created.

The meaning of the graph shown in FIG. 6 is evaluated as follows.

First, it is possible to continuously grasp the magnitude (change) of the total strain value occurring in any detector 7 of the detector tube 2 fixed in the ground over time. Second
The strain in the ground and the strain in the shotcrete lining at the position where the detector tube 2 (each detector 7) is installed can be grasped in series.

Specifically, the strain value ε _{1 from the time when the detector tube 2 was installed (zero point) to the elapsed time T 1 is} the strain in the ground due to tunnel excavation, and T ₁
At this time, the portion of the detector 7 is located at the face. Thereafter, the portion of the detector tube 2 where the detector 7 is located is embedded within the cross section of the shotcrete lining 1.
Therefore, strain in the ground and lining is detected after _T1 . The strain value ε ₂ at the elapsed time T ₂ represents the total amount of strain in the ground and the shotcrete lining 1 at that time. Therefore, the elapsed time T ₂
The strain ε _a of the shotcrete lining 1 at that point in time is finally understood as ε _a =ε ₂ −ε ₁ .

Therefore, by analyzing all the similar graphs measured at each measurement point position, we can find that, in particular, the ground 4 in front of the excavation and the shotcrete in the longitudinal cross-sectional direction (axial direction) of the tunnel, depending on the progress of excavation of the tunnel construction. It is possible to continuously measure and manage changes in the ever-changing properties and behavior of the lining 1 in real time. As a result, the properties of the ground 4 in front of the excavation and the shotcrete lining 1, that is, the ratio of underground stress (stress in the ground) between the ground around the tunnel and the shotcrete lining 1 that supports the tunnel, are determined. It is possible to continuously evaluate whether or not it is supported. Of course, if a large number of detector tubes 2 are installed in the circumferential direction of the tunnel cross section, measurement in the tunnel cross section direction can also be managed using exactly the same paragraphs.

The management method based on the above-mentioned evaluation of the graph shown in Figure 6 is that the Young's modulus of the ground and the shotcrete lining 1 are different, and that the strain in the ground is less mass than that of the shotcrete lining 1. Taking into consideration the fact that the substance may be detected in some parts of the country, the management standard values are set as follows.

Control criteria for ground 4 in front of excavation The fracture strain ε _f varies greatly depending on whether the ground is sandy soil, clay soil, or rock, so conduct a mechanical test in advance to evaluate ε _f . , contrast with the strain value ε ₁ at T ₁ .

Control standards for shotcrete lining 1 Based on the design standards, control standards up to 300 microstrains (unit: ^10-6 ) are defined as control standards 1, and up to 500 microstrains are defined as control standards 2, and the above criteria are applied to these standards 1 and 2. The strain ε _a = ε ₂ − ε ₁ value of the shotcrete lining 1 is compared.

ε _a value is control standard 1 (300 microstrain)
Even if the slope of the strain curve (dε/dt=ε) shown in Figure 6 is small, the situation is not particularly dangerous and there is no need to worry even if special reinforcement measures are taken, so be careful for a while. Construction will continue. However, when the slope of the curve is large, the change is sudden and dangerous, so reinforcement measures such as locking bolts should be taken.

If the ε _a value approaches control standard 2 (500 microstrain), it is dangerous, so reinforcement should be carried out by using additional lock bolts, additional spraying of shotcrete, etc.

Effects of the Invention As described above in detail together with the embodiments, the method for measuring and managing the ground properties in front of the shotcrete lining and in front of excavation in tunnel construction using the Natom construction method according to the present invention has the following effects: , Ground 4 in front of the excavation that has not yet been excavated
Starting with the measurement and management of the properties and behavior of the current ground, the excavation of the ground, and the formation of the shotcrete lining 1 are successive steps to determine the longitudinal cross-section of the tunnel according to the progress of the tunnel construction construction. Changes in properties and behavior in the direction (tunnel axis direction) can be continuously measured and managed in real time, and the behavior and stability of the ground and shotcrete lining 1 can be evaluated in real time. What ratio of underground stress (stress in the ground) is supported between the ground surrounding the tunnel and the shotcrete lining that supports the tunnel? In other words, the stress in the ground is supported by the concrete lining. It is possible to evaluate the rate at which the underground stress acts (the rate of release of underground stress caused by ground excavation). Therefore, it is possible to provide extremely important data for designing and constructing an economical and rational shotcrete lining, and in particular, to predict construction risks and take appropriate safety measures against them. This will also contribute to improving the safety and economic efficiency of tunnel construction using the Natom method.

Second, the use of the detector tube 2 makes it easy to install the detectors 7, and the accuracy of setting each measurement point position is high. This makes it possible to perform highly accurate measurement management.

[Brief explanation of drawings]

Figures 1 and 2 are a bird's-eye view and a sectional view showing an overview of tunnel construction in which the measurement management method of the present invention was implemented, Figures 3 and 4 are a perspective view and an exploded perspective view of the detector tube, and Figure 5 The figure is a connection diagram between a detector tube and an automatic recorder, etc., and FIG. 6 is a graph showing measured and recorded values. 3... Face portion, 4... Ground in front of excavation, 1... Shotcrete lining, 7... Detector, 2... Detector pipe, 5... Lead wire, 9, 10... Measurement recorder.

Claims (1)

[Scope of Claims] 1. A method for measuring and managing ground properties above a shotcrete lining and in front of excavation in tunnel construction using the Natom construction method, comprising the following steps (a) to (d). (b) A horizontal borehole is constructed from a position corresponding to the cross section of the shotcrete lining of the face toward the ground in front of the excavation in a position approximately parallel to the axis of the tunnel, and the horizontal borehole is placed in the horizontal borehole. A step of inserting a detector tube with a detector attached to each measuring point position and fixing the detector tube in the ground by pouring mortar. (b) The lead wire of the detector tube led out from the face is connected to a measurement recorder, and the axial force, shear force, bending stress, etc. applied to each measurement point of the detector tube is measured by each detector as a strain amount. The stage of measuring and recording. (c) A step in which the detector tubes dug out as the ground excavation progresses are sequentially buried within the cross section of the shotcrete lining. (d) The stage of evaluating the measured values obtained with the measuring recorder and managing the construction in accordance with the management standards.