JP2020094434A - Face stability evaluation method and tunnel boring method - Google Patents

Abstract

To provide a method for more accurately evaluating stability of a tunnel face, and a method for boring a tunnel.SOLUTION: A face stability evaluation method includes: an information acquisition step of acquiring information on groundwater in a spring zone 3 ahead of a face 2 of a tunnel 1 and acquiring information on a distance between the face 2 and the spring zone 3 and natural ground strength information; and a stability evaluation step of evaluating stability of the face 2 on the basis of the groundwater information, the distance information and the natural ground strength information, which are acquired in the information acquisition step.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method for evaluating the stability of a tunnel face and a method for excavating a tunnel.

When excavating a tunnel, if there is a spring zone in front of the face of the tunnel, the pressure of groundwater acts on the unexcavated ground in front of the face of the face. Since the strength of the unexcavated ground decreases as the face of the face approaches the spring zone due to the excavation of the tunnel, the face of the face may be destroyed by the pressure of groundwater during the process of tunnel excavation, which may interrupt the construction. In order to avoid this situation, exploring the spring zone in front of the face, and if there is a spring zone, take countermeasures such as drilling a drain hole and draining groundwater from the spring zone through the drain hole. Construction will be performed and the tunnel will be excavated while reducing the pressure in the spring zone. Patent Document 1 discloses that a boring hole is drilled in the tunnel excavation direction to search the spring zone in front of the face and the pressure of groundwater flowing into the boring hole from the spring zone is measured. ..

JP, 2018-21315, A

Drilling a drain hole is expensive. Therefore, even if there is a spring zone ahead of the face, if the pressure of the spring zone is low enough not to damage the face and the face is stable, the tunnel should be drilled without drilling the drain hole. It is preferable to dig. Also, when drilling the water drain holes, it is preferable to minimize the number of water drain holes. For this reason, the stability of the face is evaluated based on the groundwater pressure measured by the method described in Patent Document 1, and the necessity of the drainage hole is determined based on the evaluated stability, and the drainage is performed. It is required to determine the number of holes.

However, a method for evaluating the stability of the face has not been established, and workers on site can judge the necessity of drainage holes or determine the number of drainage holes based on the measured pressure in the spring zone. It is the current situation. Therefore, although the drain holes are not necessary, the drain holes may be drilled or the drain holes may be drilled more than necessary, which may increase the cost. Therefore, it is required to accurately evaluate the stability of the face without relying on the worker.

The present invention aims to more accurately evaluate the stability of a face.

The present invention is a face stability evaluation method for evaluating the stability of a face during excavation of a tunnel, including groundwater information of a spring zone in front of the face, distance information between the face and the spring zone, and the ground. An information acquisition step of acquiring strength information, and a stability evaluation step of evaluating stability of the face based on the groundwater information, distance information and natural ground strength information acquired in the information acquisition step.

According to the present invention, the stability of the face can be evaluated more accurately.

(A) is sectional drawing when the tunnel under excavation is cut|disconnected vertically by the tunnel excavation method which concerns on embodiment of this invention, (b) is sectional drawing which follows the IB-IB line shown in (a). Is. It is a flow chart of a face stability evaluation method and a tunnel excavation method concerning an embodiment of the present invention. It is a schematic diagram for demonstrating an information acquisition step. It is a figure for demonstrating the model of the rock mass used when calculating the resistance force of an unexcavated rock mass in a stability evaluation step. It is a figure for demonstrating the model of the natural ground used when predicting the state of a spring zone in a stability evaluation step. It is a graph which shows an example of the actual pressure and the predicted pressure of groundwater in a spring zone. It is a graph which shows an example of the relationship between the flow rate of groundwater flowing out from a spring zone, and the water level in a spring zone. It is a flowchart of a countermeasure construction specification determination step. It is sectional drawing when a tunnel is horizontally cut|disconnected in the excavation step and the re-information acquisition step.

Hereinafter, a face stability evaluation method and a tunnel excavation method according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIGS. 1( a) and 1 (b ), when there is a spring zone 3 in front of the face 2 of the tunnel 1, the pressure of groundwater in the zone 3 is between the face 2 and the zone 3. It acts on unexcavated ground (hereinafter referred to as "unexcavated ground UEG"). Since the strength of the unexcavated ground UEG decreases as the cutting face 2 approaches the spring zone 3 due to the excavation of the tunnel 1, the cutting face 2 may be destroyed by the groundwater pressure during the excavation of the tunnel 1. As a method to prevent the destruction of the face 2 due to the pressure of groundwater, countermeasures such as drilling the drainage hole 5 and draining groundwater from the spring zone 3 through the drainage hole 5 were performed, and the pressure of the groundwater in the spring zone 3 There is a way to reduce.

Drilling the drain hole 5 is costly. Therefore, it is required to evaluate the stability of the face 2 and determine the necessity of the water drainage holes 5 based on the evaluated stability and to determine the number of the water drainage holes 5.

As shown in FIG. 1 and FIG. 2, the face stability evaluation method according to the present embodiment acquires groundwater information of the spring zone 3 and also information on the distance between the face 2 and the spring zone 3 and the ground. An information acquisition step S201 for acquiring strength information, and a stability evaluation step S202 for evaluating the stability of the face 2 based on the acquired groundwater information, distance information and ground strength information. The evaluation result changes according to groundwater information, distance information, and ground strength information. Therefore, the stability of the face 2 can be evaluated more accurately.

In addition, the tunnel excavation method according to the present embodiment is a measure for determining the number of drain holes 5 as a specification of a countermeasure work for the spring zone 3 based on the stability of the face 2 evaluated by the face stability evaluation method. The engineering specification determination step S203 is included. Therefore, the necessity of the water drainage holes 5 can be appropriately determined, and the number of the water drainage holes 5 can be appropriately determined. Therefore, it is possible to prevent the cutting face 2 from being broken and suppress an increase in cost.

In addition, the tunnel excavation method according to the present embodiment includes the excavation step S204 of excavating the tunnel 1 while excavating the drainage holes 5 of the number determined in the countermeasure construction specification determination step S203, and the spring after the excavation step S204. The re-information acquisition step S205 of acquiring the groundwater information of the water zone 3 again is included. Therefore, the effect of the countermeasure work for draining groundwater from the spring zone 3 through the drainage hole 5 can be confirmed, and the face 2 is more reliably prevented from being destroyed when excavating the ground near the spring zone 3. be able to.

Hereinafter, the information acquisition step S201 and the stability evaluation step S202 of the face stability evaluation method, the countermeasure construction specification determination step S203, the excavation step S204, and the re-information acquisition step S205 of the tunnel excavation method will be described in detail.

<Information acquisition step>
First, the information acquisition step S201 will be described with reference to FIGS. 1 and 3. In the information acquisition step S201, as shown in FIG. 1, the first boring hole 6 is bored in the natural ground, and the groundwater pressure in the spring zone 3 and the spring zone 3 are utilized by using the first boring hole 6. Measure outflow of groundwater. Further, when the first boring hole 6 is drilled, the distance L between the face 2 and the spring zone 3 is acquired, and the ground resistance coefficient as the ground strength in front of the face 2 is acquired.

The procedure for measuring the pressure and flow rate of groundwater using the first boring hole 6 and the procedure for acquiring the distance L and the resistance coefficient of the ground will be described with reference to FIG.

First, as shown in FIG. 3A, the first boring hole 6 is drilled in the tunneling direction of the tunnel 1 by using the drilling rod 10. The drilling rod 10 includes a cylindrical tubular body 11 and a drilling bit 12 detachably attached to one end of the tubular body 11. The drill bit 12 is used in a state of being attached to the pipe body 11 when drilling the first boring hole 6, and is used when inserting the intake pipe 20 into the first boring hole 6 as described later. Removed from body 11.

The drill bit 12 drills the first boring hole 6 by rotating while being pressed against the natural ground. In the following, the direction in which the pipe body 11 and the drill bit 12 move along with the drilling of the first boring hole 6 is referred to as "front", and the opposite direction is referred to as "rear".

The drilling bit 12 is not rotatable with respect to the pipe body 11 when mounted on the pipe body 11, and rotates together with the pipe body 11. The pipe body 11 is supported by a boring machine (not shown). The boring machine presses the pipe body 11 forward and rotates the pipe body 11. As a result, the drill bit 12 is rotated while being pressed against the natural ground, and the first boring hole 6 is drilled.

The first boring hole 6 is drilled with an inner diameter larger than the outer diameter of the pipe body 11. The gap formed between the inner peripheral surface 6s of the first boring hole 6 and the outer peripheral surface of the tubular body 11 is used as a passage for discharging the excavation deviation caused by the drilling. Specifically, when drilling the first boring hole 6, water for sludge drainage is supplied from the rear end of the pipe body 11 to the rear end of the drill bit 12 and through the hole 13 formed in the drill bit 12. It is ejected in front of the drill bit 12. Excavation caused by drilling is discharged from the mouth of the first boring hole 6 through the gap between the inner peripheral surface 6s of the first boring hole 6 and the outer peripheral surface of the pipe body 11, together with water ejected from the boring bit 12. It

At the time of drilling the first boring hole 6, the resistance coefficient of the natural ground is acquired. Specifically, the drilling data such as the drilling speed and the drilling torque is measured, and the resistance coefficient of the ground is calculated using the measured drilling data. Since the drilling speed, drilling torque, etc. change according to the resistance coefficient of the rock mass, the relationship between the drilling speed, drilling torque, etc. and the resistance coefficient of the rock mass is obtained in advance by experiments, The resistance coefficient of the natural ground can be calculated by using the obtained relationship and the drilling speed and the drilling torque measured during drilling of the first boring hole 6.

The ground strength is not limited to the resistance coefficient of the ground, and may be uniaxial compression strength or triaxial compression strength. For the uniaxial compressive strength and the triaxial compressive strength, a part of excavation gap generated at the time of drilling the first boring hole 6 is taken as a sample, and the uniaxial compressive strength test or the triaxial compressive strength test is performed on the sample. Can be obtained by

Further, at the time of drilling the first boring hole 6, the drilling length of the first boring hole 6 is measured, and when the first boring hole 6 reaches the spring zone 3 as shown in FIG. The distance L between the face 2 and the spring zone 3 is calculated based on the drilled length. Whether or not the first boring hole 6 has reached the spring zone 3 is determined based on, for example, the flow rate of water flowing out from the mouth of the first boring hole 6.

Specifically, in a state where the first boring hole 6 does not reach the spring zone 3, groundwater does not flow from the spring zone 3 into the first boring hole 6, and is discharged from the mouth of the first boring hole 6. Muddy water contains almost no groundwater. On the other hand, when the first boring hole 6 reaches the spring zone 3, the groundwater in the spring zone 3 flows into the first boring hole 6. Therefore, groundwater is added to the water for sludge discharge ejected from the boring bit 12. Therefore, the water content in the mud water discharged from the mouth of the first boring hole 6 increases.

Thus, when the first boring hole 6 reaches the spring zone 3, it is discharged from the mouth of the first boring hole 6 as compared with when the first boring hole 6 does not reach the spring zone 3. The flow rate of water increases. In other words, it can be determined that the first boring hole 6 has reached the spring zone 3 when the flow rate of water flowing out from the mouth of the first boring hole 6 increases.

If the position of the spring zone 3 is known in advance, the distance L between the face 2 and the spring zone 3 may be calculated based on the position of the face 2.

When the first boring hole 6 reaches the spring zone 3, the boring of the first boring hole 6 is completed. Next, as shown in FIG. 3C, the drilling rod 10 is retracted, and the drilling bit 12 is moved from the spring zone 3 to the front. As a result, a space is formed between the front end of the first boring hole 6 and the drill bit 12.

Next, as shown in FIG. 3D, the water intake pipe 20 is inserted into the pipe body 11 of the drilling rod 10. By pushing the intake pipe 20 with the front end of the intake pipe 20 in contact with the rear end of the drill bit 12, the drill bit 12 is removed from the pipe body 11 and provided on the outer periphery near the front end of the intake pipe 20. The packed packer 24 is taken out from the pipe body 11. Then, the packer 24 is expanded on the face 2 side of the tunnel 1 with respect to the position of the spring zone 3 to close the space between the outer peripheral surface of the intake pipe 20 and the inner peripheral surface 6s of the first boring hole 6. Thereby, the groundwater in the spring zone 3 can be taken into the intake pipe 20 through the hole 13 of the drill bit 12.

By mounting the pressure gauge 21 near the rear end of the intake pipe 20 and attaching the flowmeter 22 at the rear end of the intake pipe 20, it is possible to measure the pressure and flow rate of groundwater in the intake pipe 20. With the above, the installation of the intake pipe 20 and the like is completed.

The intake pipe 20 is installed across the spring zone 3 and the mouth of the first boring hole 6. Therefore, the groundwater flowing from the spring zone 3 into the intake pipe 20 is guided to the mouth of the first boring hole 6 through the intake pipe 20. Therefore, the groundwater flowing in from the inner peripheral surface 6s of the first boring hole 6 flows in from the tip of the intake pipe 40, and the groundwater of the spring zone 3 permeates the ground from the inner peripheral surface 6s of the first boring hole 6. Therefore, it is possible to prevent the occurrence of the occurrence of water, and it is possible to measure the flow rate and the pressure, which are information of groundwater, with higher accuracy.

A space between the outer peripheral surface of the water intake pipe 20 and the inner peripheral surface 6s of the first boring hole 6 is closed by a packer 24. Therefore, the groundwater in the spring zone 3 can be prevented from being discharged from the mouth of the first boring hole 6 through the space between the outer peripheral surface of the intake pipe 20 and the first boring hole 6, and the flow rate and pressure of the groundwater can be further improved. It can be measured with high accuracy.

Further, the pipe body 11 of the drilling rod 10 is left inside the first boring hole 6. Therefore, the tube body 11 can prevent the first boring hole 6 from collapsing. Therefore, the water intake pipe 20 can be easily inserted into the first boring hole 6.

Note that the pipe body 11 may be extracted from the first boring hole 6 after the water intake pipe 20 is installed. When the ground is stable and there is no risk of the first boring hole 6 collapsing, the pipe 11 is completely removed from the first boring hole 6 and then the intake pipe 20 is inserted into the first boring hole 6. May be.

The pressure and the flow rate measured using the pressure gauge 21 and the flow meter 22 are fetched as groundwater information into the microcomputer 30 as a stability evaluation means for evaluating the stability of the face 2. In addition to the groundwater information, the microcomputer 30 receives the calculated distance L and the calculated resistance coefficient of the natural ground as distance information and natural ground strength information, respectively.

With the above, the information acquisition step S201 is completed.

<Stability evaluation step>
Next, the stability evaluation step S202 will be described with reference to FIGS. 4 to 7. The stability evaluation step S202 is executed by the microcomputer 30.

The microcomputer 30 includes a CPU (Central Processing Unit) that performs arithmetic processing, a ROM (Read-Only Memory) that stores a control program executed by the CPU, and a RAM (Random Access Memory) that stores the arithmetic result of the CPU. ) And, including. The microcomputer 30 may be one or plural.

The microcomputer 30 evaluates the stability of the face 2 at the time when the pressure gauge 21 performs the measurement based on the acquired groundwater information, the distance information and the ground strength information, and the measurement is performed by the pressure gauge 21. The stability of the face 2 after being broken is evaluated. Here, as shown in FIG. 4, the cutting face 2 is circular, and the unexcavated ground UEG in front of the cutting face 2 is regarded as a columnar soil mass (also referred to as “bulkhead”), and a force Fw exerted on the soil mass by groundwater is The stability of the face 2 is evaluated from the relationship of the resistance Fg of the clod. Further, the central axis of the unexcavated ground UEG extends horizontally, and a horizontal plane passing through the central axis of the unexcavated ground UEG is defined as a reference plane DL.

The force Fw exerted on the soil mass by the groundwater is calculated by using the groundwater pressure P in the spring zone, which is the pressure of the groundwater on the reference plane DL in the spring zone 3, and the diameter R of the face 2.
Fw=P×π(R/2)^2 (1)
Is expressed as

Further, assuming that the outer circumferential surface of the clod corresponds to the force received from the inner circumferential surface of the ground contacting the outer circumferential surface of the clod, the resistance Fg of the clod is equivalent to the distance L, the diameter R of the face 2, and the resistance coefficient C of the ground. Using,
Fg=L×πR×C (2)
Is expressed as

From the equations (1) and (2), the groundwater pressure Pi of the spring zone when the force Fw applied to the soil mass and the resistance force Fg of the soil mass are equal to
Pi=4CL/R (3)
Is expressed as

It has been found that the face 2 maintains a stable state even if it receives a pressure that is higher than the groundwater pressure Pi of the spring zone expressed by the equation (3) to some extent. In other words, the stable water pressure Ps capable of maintaining the stable state of the face 2 can be a pressure obtained by adding a predetermined pressure Pc to the groundwater pressure Pi of the spring zone expressed by the equation (3). ,
Ps=4CL/R+Pc (4)
Is expressed as

In Expression (4), the diameter R of the face 2 is a value determined by the specifications of the tunnel 1, the predetermined pressure Pc is a predetermined value, and the natural resistance coefficient C and the distance L are obtained in the information acquisition step S201. This is the value to be acquired. Therefore, the stable water pressure Ps can be calculated by using the equation (4).

The microcomputer 30 evaluates the stability of the face 2 by comparing the groundwater pressure P in the spring zone with the stable water pressure Ps. Specifically, when the groundwater pressure P in the spring zone is equal to or lower than the stable water pressure Ps, it is evaluated that the face 2 is stable. When the groundwater pressure P in the spring zone exceeds the stable water pressure Ps, the face 2 is evaluated as unstable.

The groundwater pressure P in the spring zone can be calculated based on the pressure information acquired in the information acquisition step S201. Specifically, as shown in FIG. 5, the rear end of the intake pipe 20 is closed to stop the flow of groundwater in the intake pipe 20. In this state, no friction loss occurs in the water intake pipe 20. Therefore, the groundwater pressure P in the spring zone is measured pressure Pm measured using the pressure gauge 21, the vertical distance Hc between the pressure measurement point Pp and the reference plane DL, the groundwater density ρ, and the gravity acceleration g. And using P=Pm−ρgHc (5)
Is expressed as

In Expression (5), the interval Hc is a value determined by the installation of the intake pipe 20, the density ρ and the gravitational acceleration g are known values, and the measured pressure Pm is a value acquired in the information acquisition step S201. Therefore, the groundwater pressure P in the spring zone can be calculated by using the equation (5).

As described above, the microcomputer 30 calculates the stable water pressure Ps, the groundwater pressure P in the spring zone, and compares the stable water pressure Ps with the groundwater pressure P in the spring zone to measure by the pressure gauge 21. The stability of the cutting face 2 at the time when is performed is evaluated.

By the way, the water intake pipe 20 installed in the information acquisition step S201 also functions as a drain hole. Therefore, when the rear end of the intake pipe 20 is open, the groundwater in the spring zone 3 flows out from the intake pipe 20. With the outflow of groundwater, the water level in the spring zone 3 decreases with time, and the groundwater pressure P in the spring zone decreases. That is, the state of the spring zone 3 changes with the passage of time.

The distance L between the face 2 and the spring zone 3 becomes shorter as the tunnel 1 advances. Therefore, the stable water pressure Ps (see the equation (4)) decreases as the tunnel 1 advances.

The microcomputer 30 predicts the groundwater pressure P and the distance L of the spring zone after the measurement by the pressure gauge 21, and the stability of the face 2 based on the predicted groundwater pressure P and the distance L of the spring zone. Evaluate. A method for predicting the groundwater pressure P and the distance L in the spring zone will be described in detail.

Here, as shown in FIG. 5, it is assumed that the horizontal cross-sectional area S of the spring zone 3 is a constant solid regardless of the vertical position, and that groundwater in the spring zone 3 flows out only through the intake pipe 20. I assume. Further, the distance from the reference plane DL to the water surface of the groundwater is the water level H in the spring zone 3.

First, the horizontal sectional area S is calculated. The amount V of groundwater flowing out from the spring zone 3 is V=ΔH×S (6) using the decrease amount ΔH of the water level H and the horizontal sectional area S.
Is expressed as

The amount V of groundwater flowing out can be calculated based on the flow rate Qm measured using the flow meter 22, and the decrease amount ΔH of the water level H is calculated based on the pressure Pm measured using the pressure gauge 21. be able to. Specifically, as shown in FIG. 6, during the period from time T0 to time T1, the flow rate Qm of groundwater flowing out from the spring zone 3 is closed to 0 (zero) during the time T1. At, the rear end of the intake pipe 20 is opened and groundwater is discharged from the spring zone 3 through the intake pipe 20. Then, at time T2, the rear end of the intake pipe 20 is closed again, and the flow rate Qm of groundwater flowing out from the spring zone 3 is set to 0 (zero). By using the flow rate Qm measured over the period from the time T1 to the time T2, the amount V of groundwater flowing out from the spring zone 3 can be calculated. Further, by calculating the pressure difference using the pressure Pm measured before the time T1 and after the time T2, the decrease amount ΔH of the water level H can be calculated. The horizontal cross-sectional area S can be calculated by using the calculated amount V of groundwater and the decrease amount ΔH of the water level H and the equation (6).

Next, using the calculated horizontal cross-sectional area S, the water level H at time T and the groundwater pressure P in the spring zone are predicted. Here, it is assumed that the rear end of the intake pipe 20 is opened at time T3, and the water level H and the groundwater pressure P in the spring zone after time T3 are predicted. In the following, the time after the elapse of a predetermined period from time T3 is referred to as "time T".

Using the water level H3 at time T3, the water level H at time T, and the horizontal cross-sectional area S, the amount V of groundwater flowing out of the spring zone 3 in the period from time T3 to time T is V=(H3-H)× S... (7)
Is expressed as

Further, the amount V of groundwater flowing out is equal to a value obtained by integrating the flow rate Q of groundwater flowing into the intake pipe 20 from time T3 to time T,

と表される。式（７）及び（８）から、次の式（９）が得られる。

Is expressed as The following expression (9) is obtained from the expressions (7) and (8).

The flow rate Q of groundwater flowing into the intake pipe 20 decreases as the water level H decreases. The relationship between the flow rate Q and the water level H can be obtained by using, for example, the Manning formula. FIG. 7 is an example of a graph showing the relationship between the flow rate Q and the water level H obtained using the Manning formula.

It is known that the relationship between the flow rate Q and the water level H changes depending on the inner diameter of the intake pipe 20 and the roughness coefficient of the inner wall surface of the intake pipe 20. In FIG. 7, the relationship between the flow rate Q and the water level H obtained by changing the roughness coefficient with the same inner diameter is shown. The dotted line shows the relationship obtained by setting the roughness coefficient as RC1, and the one-dot chain line shows the roughness. The relationship is obtained by setting the degree coefficient as RC2 (where RC2>RC1 and the roughness coefficient is rougher than the inner wall surface having RC1).

The water levels H1 and H2 and the flow rates Q1 and Q2 at the times T1 and T2 can be calculated using the pressures Pm and Qm measured by the pressure gauge 21 and the flowmeter 22 at the times T1 and T2. Therefore, by using the Manning formula and the water levels H1 and H2 and the flow rates Q1 and Q2, the roughness coefficient of the inner wall surface of the intake pipe 20 can be calculated, and the relationship between the flow rate Q and the water level H can be calculated. (The relationship shown by the solid line in FIG. 7) can be acquired.

By using the equation (9) and the relationship between the flow rate Q and the water level H shown in FIG. 7, the water level H at the time T can be predicted, and the groundwater pressure P in the spring zone at the time T can be predicted. be able to.

From the above, the groundwater pressure P of the spring zone as the state of the spring zone 3 after time T3 is predicted.

Next, the stable water pressure Ps at time T is predicted. Here, it is assumed that the tunnel 1 is dug at a constant speed. The distance L between the face 2 and the spring zone 3 at time T is calculated by using the distance L3 at time T3 and the excavation speed Vt of the tunnel 1,
L=L3-Vt×(T-T3) (10)
Is expressed as From equations (4) and (10), the stable water pressure Ps at time T is
Ps=4C{L3-Vt*(T-T3)}/R+Pc (11)
Is expressed as FIG. 6 also shows the stable water pressure Ps after time T3.

The groundwater pressure P and the stable water pressure Ps in the spring zone are predicted until time T6 when the tunnel 1 is predicted to reach the spring zone 3. The time T6 can be calculated based on the distance L3 at the time T3 and the excavation speed Vt.

Next, the stability is evaluated by comparing the predicted stable water pressure Ps with the predicted groundwater pressure P of the spring zone. In the example shown in FIG. 6 (see the solid line with 0 drainage holes), the predicted groundwater pressure P in the spring zone is lower than the stable water pressure Ps during the period from time T3 to time T5. Therefore, the face 2 is stable until time T5. On the other hand, after time T5, the predicted groundwater pressure P in the spring zone is higher than the stable water pressure Ps. Therefore, the face 2 becomes unstable after the time T5. In such a case, the microcomputer 30 evaluates that there is a period during which the face 2 becomes unstable.

Although illustration is omitted, in the period from time T3 to time T6, when the predicted groundwater pressure P in the spring zone is lower than the stable water pressure Ps, the microcomputer 30 determines that the face 2 is stable. Evaluate.

With the above, the stability evaluation step S202 ends.

In the above-described face stability evaluation method, the stability of the face 2 is evaluated based on the acquired groundwater information, distance information, and ground strength information. Therefore, the stability evaluation changes according to the acquired groundwater information, distance information, and ground strength information. Therefore, the stability of the face 2 can be evaluated more accurately.

In the stability evaluation step S202, the groundwater pressure P in the spring zone after the time T3 is predicted, and the stability of the face 2 is evaluated based on the predicted groundwater pressure P in the spring zone. Therefore, the stability evaluation changes according to the predicted value of the groundwater pressure P in the spring zone after time T3. Therefore, the stability of the face 2 after the time T3 can be more accurately evaluated in advance.

In the stability evaluation step S202, the distance L between the face 2 and the spring zone 3 after the time T3 is predicted, and the predicted distance L, the predicted groundwater pressure P of the spring zone, and the acquired rock mass strength are predicted. The stability of the face 2 is evaluated based on the information. Therefore, the stability evaluation changes according to the predicted value of the distance L and the groundwater pressure P of the spring zone after the time T3. Therefore, the stability of the face 2 after the time T3 can be more accurately evaluated in advance.

<Steps for determining countermeasure construction specifications>
Next, step S203 of determining the countermeasure work specification of the tunnel excavation method will be described with reference to FIG. The countermeasure engineering specification determining step S203 is executed by the microcomputer 30, similarly to the stability evaluating step S202. The countermeasure engineering specification determining step S203 may be executed by a microcomputer other than the microcomputer 30 that executes the stability evaluating step S202.

As shown in FIG. 8, in step S801, a variable N indicating the optimum number of drain holes 5 is set to “0 (zero)”. In step S802, the evaluation result obtained in stability evaluation step S202 is acquired. In step S803, it is determined whether or not the acquired evaluation result is an evaluation that the face 2 has an unstable period.

If it is determined in step S803 that the face 2 is not unstable for a certain period, the process proceeds to step S804. When it is determined in step S803 that there is a period during which the face 2 becomes unstable, the process proceeds to step S805.

In step S805, "1" is added to the variable N. In step S806, the stability of the face 2 when N drain holes 5 have been drilled is evaluated. Specifically, the groundwater pressure P of the spring zone when N drain holes 5 are drilled is predicted by the same method as the method of predicting the groundwater pressure P of the spring zone in the stability evaluation step S202. It is determined whether the predicted groundwater pressure P in the spring zone exceeds the stable water pressure Ps.

FIG. 6 also shows the prediction results of the groundwater pressure P in the spring zone when one drain hole 5 is drilled and when two drain holes 5 are drilled. FIG. 6 shows an example in which drilling of the drain hole 5 is completed at time T4. In the example shown in FIG. 6, when the number of drain holes 5 is one, there is a period in which the predicted groundwater pressure P in the spring zone exceeds the stable water pressure Ps, while the number of drain holes 5 is two. In this case, the predicted groundwater pressure P in the spring zone does not exceed the stable water pressure Ps. That is, the microcomputer 30 evaluates that there is a period in which the face 2 becomes unstable when the number of the drain holes 5 is one, and when the number of the drain holes 5 is 2, the face 2 Evaluates as stable.

After the stability of the face 2 is evaluated in step S806, the process returns to step S803.

In step S804, the optimum number of drain holes 5 is determined to be N. In the example shown in FIG. 6, the microcomputer 30 determines that the optimum number of drain holes 5 is two. Note that determining that the optimum number of drainage holes 5 is 0 is synonymous with determining that no countermeasure work is required.

With the above, the countermeasure engineering specification determining step S203 is completed.

In the above tunnel excavation method, the number of drainage holes 5 as the specification of the countermeasure work for the spring zone 3 is determined based on the stability of the cutting face 2 evaluated by the face stability evaluation method. Therefore, the necessity of the water drainage holes 5 can be appropriately determined, and the number of the water drainage holes 5 can be appropriately determined. Therefore, it is possible to prevent the cutting face 2 from being broken and suppress an increase in cost.

<Digging step>
Next, the digging step S204 of the tunnel digging method will be described with reference to FIG. In the digging step S204, the drainage holes 5 of the number determined in the countermeasure construction specification deciding step S203 are drilled, and the countermeasure work for draining groundwater from the spring zone 3 through the drainage holes 5 is performed, and the tunnel 1 is dug To do. By performing the countermeasure work for the spring zone 3 and the excavation of the tunnel 1 in parallel, the construction period of the tunnel 1 can be shortened while preventing the destruction of the face 2.

When the microcomputer 30 determines that the optimum number of drainage holes 5 is 0 in the countermeasure construction specification determination step S203, the drainage holes 5 are not drilled and only the tunnel 1 is dug. Be seen.

<Re-information acquisition step>
Next, the re-information acquisition step S205 of the tunnel excavation method will be described with reference to FIG. The re-information acquisition step S205 is performed to determine the effect of the countermeasure work by re-measuring the groundwater pressure in the spring zone 3 and the flow rate of groundwater flowing out from the spring zone 3.

As shown in FIG. 9, in the re-information acquisition step S205, the second boring hole 7 is drilled from the vicinity of the face 2 in the tunneling direction of the tunnel 1, and the groundwater in the spring zone 3 is utilized by using the second boring hole 7. Get information. The procedure for drilling the second boring hole 7 and the procedure for acquiring the groundwater information are substantially the same as the drilling procedure for the first boring hole 6 and the procedure for acquiring the groundwater information, and therefore description thereof is omitted here.

The second boring hole 7 is drilled after the tunnel 1 is dug. Therefore, the drilling start point of the second boring hole 7 can be closer to the spring zone 3 than the drilling start point of the first boring hole 6, and the drilling length of the second boring hole 7 can be set to the first boring hole. It can be shorter than the drilling length of 6. Therefore, the pressure and flow rate of groundwater flowing from the spring zone 3 into the second boring hole 7 can be measured more accurately. This makes it possible to more accurately determine the effect of the countermeasure work and more reliably prevent the face 2 from being broken when excavating the ground near the spring zone 3.

According to the above embodiment, the following operational effects are exhibited.

In the face stability evaluation method according to the present embodiment, the stability of the face 2 is evaluated based on the acquired groundwater information, distance information, and ground strength information. Therefore, the stability evaluation changes according to the acquired groundwater information, distance information, and ground strength information. Therefore, the stability of the face 2 can be evaluated more accurately.

In the face stability evaluation method, the groundwater pressure P of the spring zone after a predetermined period has been predicted based on the acquired groundwater information, and the stability of the face 2 is predicted based on the predicted groundwater pressure P of the spring zone. Evaluate. Therefore, the stability evaluation changes according to the predicted value of the groundwater pressure P in the spring zone after the elapse of a predetermined period. Therefore, the stability of the face 2 can be evaluated more accurately in advance.

In the face stability evaluation method, the distance L between the face 2 and the spring zone 3 after a lapse of a predetermined period is predicted based on the acquired distance information and the excavation speed Vt of the tunnel 1, and the predicted distance is calculated. The stability of the face 2 is evaluated based on L, the predicted groundwater pressure P of the spring zone, and the acquired ground strength information. Therefore, the stability evaluation changes according to the predicted value of the distance L and the groundwater pressure P of the spring zone after the lapse of a predetermined period. Therefore, the stability of the face 2 can be evaluated more accurately in advance.

In the face stability evaluation method, the first boring hole 6 is drilled in the direction of excavation of the tunnel 1, and the groundwater pressure P in the spring zone and the groundwater flowing out from the spring zone 3 are utilized by using the first boring hole 6. The flow rate Q of is acquired. Therefore, the groundwater in the spring zone 3 flows into the first boring hole 6, and the groundwater pressure P and the flow rate Q of the acquired spring zone change according to the state of the spring zone 3. Therefore, information on groundwater in the spring zone 3 can be acquired accurately, and the stability of the face 2 can be evaluated more accurately.

In the tunnel excavation method according to the present embodiment, the number of drainage holes 5 as a specification of countermeasure work for the spring zone 3 is determined based on the stability of the face 2 evaluated by the face stability evaluation method. Therefore, the necessity of the water drainage holes 5 can be appropriately determined, and the number of the water drainage holes 5 can be appropriately determined. Therefore, it is possible to prevent the cutting face 2 from being broken and suppress an increase in cost.

Further, in the tunnel excavation method, after the determined countermeasure work is performed and the tunnel 1 is excavated, the second boring hole 7 is bored in the excavation direction of the tunnel 1 and the spring zone is utilized by using the second boring hole 7. Get groundwater information of 3. Therefore, the drilling start point of the second boring hole 7 can be closer to the spring zone 3 than the drilling start point of the first boring hole 6, and the drilling length of the second boring hole 7 can be set to the first boring hole. It can be shorter than the drilling length of 6. Therefore, the pressure and flow rate of groundwater flowing from the spring zone 3 into the second boring hole 7 can be measured more accurately. As a result, the effect of the countermeasure work can be determined more accurately and the tunnel 1 can be dug forward, and the destruction of the face 2 can be prevented more reliably.

Although the embodiment of the present invention has been described above, the above embodiment merely shows a part of the application example of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

Even after the stability of the face 2 is evaluated, the groundwater pressure P and the flow rate Q of the spring zone may be continuously acquired using the first boring hole 6, and in this case, the predicted groundwater of the spring zone may be acquired. It is preferable to confirm whether the pressure P and the flow rate Q match the acquired groundwater pressure P and the flow rate Q of the spring zone. If the predicted groundwater pressure P and flow rate Q of the spring zone do not match the acquired groundwater pressure P and flow rate Q of the spring zone, re-predict the groundwater pressure P and flow rate Q of the spring zone and It is preferable to reassess the stability.

In the above embodiment, the stability of the face 2 is evaluated by predicting both the groundwater pressure P and the distance L in the spring zone after time T3, but one of the groundwater pressure P and the distance L in the spring zone is evaluated. It may be a form of predicting only. In this case, the groundwater pressure P or the distance L of the spring zone at the acquired time T3 may be used as the other of the groundwater pressure P or the distance L of the spring zone.

Further, in the above embodiment, the pressure of groundwater in the spring zone 3 and the flow rate of groundwater flowing out from the spring zone 3 are measured using the first boring hole 6, but only one of the pressure and the flow rate is measured. Alternatively, the first boring hole 6 may be used for the acquisition. In this case, the other of the pressure and the flow rate may be measured using a boring hole drilled separately from the first boring hole 6.

Further, in the above-described embodiment, the stable hydraulic pressure Ps is calculated by regarding the unexcavated ground UEG as a lump of soil, but the individual element method (Distinct Element) which is an analysis method that can evaluate the rock collapse phenomenon in consideration of fluid flow. The stable water pressure Ps may be calculated using Method: DEM). In this case, the stable water pressure Ps can be calculated based on the breaking water pressure that causes the collapse of the cutting face 2 due to hydraulic fracturing, and the stability of the cutting face 2 can be evaluated more accurately.

Further, in the above-described embodiment, the relationship between the flow rate Q and the water level H (or groundwater pressure) can take into consideration the theoretical analysis that can consider the arrangement of the drain holes around the tunnel, the shape of the spring zone, and the surrounding geological structure. It can be calculated using the Manning's formula and the permeation flow analysis method by the finite element method (FEM), and more accurate evaluation is possible.

Further, in the above embodiment, the relationship between the flow rate Q and the water level H shown in FIG. 7 is calculated based on the measured pressure Pm and the flow rate Qm, but the roughness coefficient RC on the inner peripheral surface of the intake pipe 20 is If it is known in advance, the relationship between the flow rate Q and the water level H may be calculated using the known roughness coefficient RC and the Manning formula.

Further, in the above-described embodiment, the resistance coefficient as the ground strength is acquired when the first boring hole 6 is drilled, but it may be acquired separately from the drilling of the first boring hole 6. For example, the side wall of the tunnel 1 may be excavated to collect a sample, and the resistance coefficient, the uniaxial compressive strength or the triaxial compressive strength as the ground strength may be acquired using the collected sample. Moreover, assuming that the rock mass strength is almost constant over the whole rock mass, the ground surface is excavated and a sample is sampled. Using the sampled sample, the resistance coefficient as the rock mass strength, uniaxial compressive strength or Axial compressive strength may be obtained. Further, it is also possible to use those used as indexes corresponding to the uniaxial compressive strength and the triaxial compressive strength.

Further, in the above embodiment, the excavation speed Vt of the tunnel 1 is set to a constant value. However, when it is known in advance that the excavation speed Vt of the tunnel 1 is not constant, the known excavation speed Vt is used. It is sufficient to predict the distance L.

1... Tunnel 2... Face 3... Spring zone 5... Drainage hole 6... First boring hole 7... Second boring hole C... Resistance coefficient (ground strength information)
P... Groundwater pressure in the spring zone (groundwater information)
Q: Flow rate (groundwater information)
L: Distance between face and spring

Claims (6)

A face stability evaluation method for evaluating face stability during tunnel excavation,
Information acquisition step of acquiring groundwater information of a spring zone in front of the face, distance information between the face and the spring zone, and ground strength information.
A face stability evaluation method, comprising: a stability evaluation step of evaluating the stability of the face based on the groundwater information, the distance information, and the ground strength information acquired in the information acquisition step. In the stability evaluation step, the state of the spring zone after a lapse of a predetermined period is predicted based on the groundwater information acquired in the information acquisition step, and the face is predicted based on the predicted state of the spring zone. Evaluate the stability of
The face stability evaluation method according to claim 1. In the stability evaluation step, based on the distance information acquired in the information acquisition step, and the excavation speed of the tunnel, the distance between the face and the spring zone after the predetermined period of time is predicted. Evaluating the stability of the face based on the predicted distance, the predicted state of the spring zone, and the rock mass intensity information acquired in the information acquisition step,
The face stability evaluation method according to claim 2. In the information acquisition step, the first boring hole is drilled in the tunneling direction, and the pressure of groundwater in the spring zone or the flow rate of groundwater flowing out of the spring zone is utilized by using the first borehole. get,
The face stability evaluation method according to any one of claims 1 to 3. A tunnel digging method for digging a tunnel,
The specification of the countermeasure work for the spring zone is determined based on the stability of the face evaluated by the face stability evaluation method according to any one of claims 1 to 4.
Tunnel digging method. After performing the determined countermeasure work and excavating the tunnel, the second boring hole is drilled in the tunnel advancing direction, and the groundwater information of the spring zone is obtained by using the second boring hole.
The tunnel excavation method according to claim 5.

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