JP4196279B2 - Estimated amount of spring water and tunnel excavation method - Google Patents

Description

  The present invention relates to a method for estimating a spring water amount and a hydraulic conductivity when excavating a tunnel in a springy ground, and a tunnel excavation method using the method.

  When excavating a tunnel in a spring ground, it may be advantageous in terms of construction to drain a large amount of spring water to lower the groundwater level, but in recent years the groundwater level has been artificially reduced from the viewpoint of protecting the natural environment. Therefore, it is not preferable to reduce the temperature of the water, and it is desired to suppress the drainage of spring water as much as possible. Therefore, as shown in Patent Document 1, for example, as a method for excavating a tunnel with a large cross section in a springy ground, first a pilot hole with a small diameter is first excavated and the water stop is improved around it, A construction method has been proposed that reduces the amount of drainage and suppresses the decrease in groundwater level by expanding the water stop improvement range and constructing a main tunnel.

In order to make an appropriate water stop improvement for the natural ground in the above case, it is necessary to accurately grasp the hydraulic state of the natural ground beforehand, and therefore, for example, disclosed in Patent Document 2 It is normal to conduct such a permeability test in advance to understand the spring water volume and permeability coefficient of the natural ground.
JP 2002-201890 A JP-A-6-294116

  By the way, in the tunnel excavation method as shown in Patent Document 1, in order to improve the water stop appropriately for the entire periphery of the pilot hole, a water permeability test is performed in advance over the widest possible range of the water stop improvement. Although it is preferable to perform, as shown in Patent Document 2, the conventional water permeability test is based on drilling a deep borehole from the ground surface and pumping water from the borehole. It is not practical to perform such a water permeability test at a large number of locations over a wide range in advance because it requires a great deal of labor and cost.

In view of the above circumstances, the present invention is an effective and appropriate estimation method that can easily estimate the amount of spring water in a natural mountain without using a full-scale permeability test, and estimates the amount of spring water and the permeability coefficient during excavation by such a method. The purpose of this study is to provide an effective and appropriate tunnel excavation method that can make the best water stop improvement.

  The invention of claim 1 is a method for estimating the amount of spring water in the middle of the tunnel excavation machine while excavating the tunnel in the spring ground with a sealed tunnel excavator, Measure the time required to drain the spring water in the tunnel excavator and reduce the water level in the gap by a certain amount and the amount of drainage, and measure the time required for the water level to recover after the drainage is stopped. The amount of spring water per unit time is estimated based on the above.

In the invention of claim 2 , in order to construct a tunnel in a springy ground, first of all, by carrying out a lining with a segment while excavating a closed type tunnel excavator, it has a smaller cross section than the main tunnel to be constructed. The pilot mine is penetrated in the cross section of the main tunnel, and then the water is improved from the inside of the pilot mine to the spring ground in the outside of the pilot mine. Improving the water-resistant ground to a water-stopped ground, and then excavating the ring-shaped ground between the improved water-stopped ground and the pilot mine with a tunnel machine while dismantling and removing the pilot mine segment. In the tunnel excavation method that constructs the main tunnel by lining, the tunnel excavator is used to excavate the pilot mine while excavating the spring water in the gap around the tunnel excavator. In addition to measuring the time required to reduce the water level in the gap by a certain amount and the amount of drainage, and measuring the time required for the water level to recover after stopping the drainage and the water level change between them, On the basis of this, it is characterized by estimating the amount of spring water per unit time and the permeability coefficient of surrounding ground, and improving the water stoppage for the spring ground outside the pilot mine based on the estimated values.

According to the method for estimating the amount of spring water of the present invention, the amount of spring water can be simplified by carrying out a simple water permeability test in the middle of excavating with a tunnel excavator and assuming the surrounding void as a test section in a normal water permeability test. Therefore, hydraulic data at a desired point can be obtained without requiring any labor and cost.

  According to the tunnel excavation method of the present invention, when excavating the pilot mine, the amount of spring water and the hydraulic conductivity are estimated at each point by the above estimation method, and the obtained data is reflected in the water stop improvement process for the outside of the pilot mine. By doing so, it becomes possible to carry out optimal water stop improvement in accordance with the actual conditions of natural ground.

  First, an embodiment of the tunnel excavation method of the present invention will be described with reference to FIG.

“Drilling process of pilot mine”
When constructing the tunnel 100 having a large cross section with respect to the spring ground, first the pilot mine 101 is excavated as shown in FIG. The pilot mine 101 may be sufficiently smaller in diameter than the main tunnel 100 to be finally constructed. For example, when the diameter of the main tunnel 100 is about 13 m, the diameter of the pilot mine 101 may be about 5 m. The excavation position of the pilot mine 101 is approximately the center position of the cross section of the main tunnel 100.

  The pilot mine 101 is excavated by excavating a sealed tunnel excavator 102 that can stop water itself, for example, a sealed TBM, or a sealed shield excavator. At the same time, the hole wall is covered with the segment 103 to ensure the water stoppage of the entire pilot mine 101. Of course, in the construction, as in the case of normal tunnel excavation, each material and equipment such as the segment 103 is transported from the starting side wellhead to the face, and the slip is carried backward toward the starting side wellhead. .

"Water stop improvement process"
After penetrating the pilot mine 101, as shown in (b), by injecting a water-stopping material from the inside to the surrounding natural ground, the natural ground outside the planned excavation section of the main tunnel 100 ( The cross-hatched area) is improved to the water-stopping ground 104 to ensure the water-stopping. The operation may be performed by causing the appropriate water stop improvement device 105 to enter the pilot pit 101 from the starting side of the pit and making improvements gradually by a predetermined length in the axial direction of the pilot pit 101. It should be noted that transportation of materials and equipment required for water stop improvement may be carried out from either the start side or the arrival side or from both sides. After starting excavation, it is better to start from the front (arrival side) wellhead.

"Excavation process of the main tunnel"
When the water stop improvement is completed by a certain distance from the starting-side wellhead, the main tunnel 100 is started to be excavated. That is, as shown in (c), the open-type full-section tunnel excavator 106 equipped with an annular cutter is started from the start-side pit, and the segment 103 of the pilot pit 101 is dismantled and removed to improve the water stoppage. The main tunnel 100 is formed in a form in which the pilot pit 101 is expanded (reamed) by excavating an annular ground between the water-stopping ground 104 and the pilot mine 101 with a tunnel excavator 106 having a full cross section. The main tunnel 100 is constructed by excavating and lining the entire area with the segment 107 while excavating the entire cross-section tunnel excavator 106.

  At this time, the segment 107 covering the main tunnel 100 may be conveyed from the starting side wellhead to the face as usual, and the gap may be carried from the face to the starting side wellhead. Further, the dismantling and removal of the segment 103 in the pilot mine 101 is performed by disposing an appropriate dismantling device (not shown in the figure). What is necessary is just to convey the segment 103 forward by the suitable conveying apparatus provided in the pilot well 101, and to carry out from the arrival side wellhead.

  According to the above construction method, the preliminary excavation of the small-diameter pilot mine 101 can be efficiently carried out while ensuring the water-stopping property by the normal hermetic tunnel excavator 102, and at that time, a large amount of spring water is used. There is no need to drain. In addition, since the water stop is improved from the inside to the surrounding ground after penetrating the pilot mine 101, it is possible to supply sufficient materials and equipment for the water stop improvement work. Can also be done efficiently. And while performing the above-mentioned water stop improvement, the excavation of the main tunnel 100 is performed in parallel from the rear, and the surrounding natural ground has already been improved to the water stop natural ground 104 when excavating the main tunnel 100. Since the water-stopping property is naturally secured, the excavation of the main tunnel 100 is sufficient with the open-type full-section tunnel excavator 106, and the spring water is naturally suppressed, so a large amount of groundwater is drained. There is no need to do.

  By the way, in order to perform the optimum water stop improvement from the inside of the pilot mine 101 to the ground outside of the pilot mine 101 in the above construction method, it is necessary to grasp the actual hydraulic state of the natural ground over a wide range. In the middle of excavating the pilot mine 101, the amount of spring water and hydraulic conductivity at each position of the surrounding ground are estimated along the way, and the obtained hydraulic data is reflected in the subsequent water stop improvement process. The water is improved.

  Therefore, in the tunnel machine 102 for excavating the pilot mine 101, a drain pipe 109 is connected to the bulkhead 108 as shown in FIG. Water or drilling mud can be drained into the tunnel machine 102 through the drain pipe 109, and a water level meter 110 for detecting the water level there is communicated with the outside near the top of the bulkhead 108. Is provided. The drain pipe 109 is provided with a flow meter 111 and a valve 112. In addition, it is better to store the drained spring water and drilling mud in a drainage tank and finally condense it into the natural ground. The water level meter 110 may be provided with a water pressure meter 113 for measuring the water pressure as required.

"Estimation of spring water"
In order to estimate the amount of spring water, the tunnel excavator 102 is stopped at that point, and the valve 112 attached to the drain pipe 109 is opened to drain the spring water flowing into the void around the tunnel excavator 102. While draining from the pipe 109, the water level is monitored by the water level meter 110, and as shown in FIG. 3, the time t required for the water level decrease amount δ to become a constant value (for example, 5 cm) and the drainage amount Q therebetween are determined as the water meter 111. Measure with Thereafter, when the valve 112 is closed and drainage is stopped, the water level naturally recovers, so the time T required for the water level to recover is also measured. Based on these measured values t, Q, T, the amount of spring water A per unit time can be estimated as follows.

The amount of drainage Q until the water level lowering amount δ reaches a constant value, the time t required for it, the time T required for the water level to recover, the amount of spring water A per unit time from the natural ground, and the volume of the void in which the water level lowering amount δ is generated Between V,
V = Q−A × t
A = V / T
Therefore, the amount of spring water A to be estimated from now on is not related to the volume V of the air gap where the water level is lowered. A = Q / (T + t)
Can be obtained as

As shown in FIG. 3, in the case of the tunnel machine 102 having a diameter of 5 m and a total length of 10 m, when the surplus amount is 10 cm, and the water level drop amount δ is set to 5 cm, such a water level drop is caused. The volume V of the generated void is about 200 liters, that is, V = (2 × 1 × 0.05) + (0.1 × 0.05 × 10 × 2)
= 0.2 m ³ = 200 liters, and the time required for such water level lowering and water level recovery is only a few minutes to several tens of minutes. Therefore, the above estimation of the spring water amount (and the estimation of the hydraulic conductivity shown below) ) Can be performed, for example, by using the excavation stoppage (usually 2 to 3 times a day) that is set periodically for the replacement of workers, which may delay the entire process. Absent.

"Estimation of hydraulic conductivity"
The permeability coefficient is estimated according to the well-known field permeability test (unsteady water level recovery method). In the in-situ permeability test, a strainer part into which groundwater flows into the borehole is set as a test section, the water level in the test section is artificially lowered, and the water level recovery status is momentarily measured. Measure and plot the relationship between the groundwater level recovery (water level difference S between the measured water level and the equilibrium water level) and the elapsed time t in the graph shown in FIG. 4 to obtain the slope m of the initial straight line portion. The hydraulic conductivity k is calculated.
k = 0.66 × d ² × log ( ² L / D) × m / L
Where k: hydraulic conductivity (cm / sec)
m: slope of the initial straight line part of the graph
m = log (S1 / S2) / (t2-t1)
S1: Water level difference at time t1,
S2: Water level difference at time t2
d: Inner diameter of measurement pipe (cm)
D: Diameter of test section (cm)
L: Length of test section (cm)

The above-described permeability coefficient estimation method is to obtain the permeability coefficient from the graph of FIG. 4 and the above formula, assuming that the void around the tunnel excavator 102 is a test section in the above-mentioned field permeability test.

An example will be described with specific numerical values. When the diameter of the tunnel excavator (corresponding to the diameter D of the test section) is 5 m and the length (corresponding to the length L of the test section) is 10 m, It is assumed that it took 10 minutes to recover the water level after the water level was lowered by 5 cm. The inner diameter d of the measurement pipe is assumed to be 224 cm, corresponding to the diameter of a cylinder in which the water level rises by 5 cm, assuming that the volume V of the air gap corresponding to the water level lowering amount is 200 liters. Since the equilibrium water level cannot be measured, it is assumed that the hydrostatic pressure from the groundwater surface in the geological profile at the time of design is 50 m from the groundwater surface. The hydrostatic pressure can be measured by the water pressure gauge 113 if the water level is lowered when the excavation is stopped, and then waits until the water level recovers, becomes full, and becomes a steady water pressure. In this case, each value in the above equation is
S1 = 5000 (cm)
S2 = 4995 (cm)
t1 = 0
t2 = 600 (sec)
m = log (5000/4995) / (t2-t1) = 7.24 × 10 ⁻⁷
d = 224 (cm)
D = 500 (cm)
L = 1000 (cm)
Therefore, from now on, the hydraulic conductivity k is k = 0.66 × 224 ² × log (2 × 1000/500) × 7.24 × 10 ⁻⁷ / 1000
= 1.4 × 10 ⁻⁵
As required.

  Note that the permeability coefficient and the amount of spring water have a relationship as shown in FIG. 5 with the depth (or hydrostatic pressure at that point) as a parameter, so such a graph is created in advance based on osmotic flow analysis. Then, the other can be roughly estimated by obtaining either the amount of spring water or the permeability coefficient as described above, and both estimated values can be verified.

  As described above, according to the present invention, the spring water is temporarily drained from the gap around the tunnel machine 102 while the pilot mine 101 is being excavated, and the water level is slightly lowered and condensed. Only by measuring the amount of drainage and time during that period, the amount of spring water and the hydraulic conductivity can be easily estimated without the need for labor and expense. Then, by reflecting the data in the subsequent water stop improvement process, the optimum water stop material can be selected, the injection amount of the water stop material can be increased or decreased, etc. If there is a section where there is almost no spring water, it is possible to omit the water stop improvement there, and rational and efficient construction is possible.

It is a figure which shows one Embodiment of the tunnel excavation method of this invention. It is a figure which shows an example of the tunnel excavation machine for performing the spring amount estimation method of this invention. It is a figure for demonstrating the estimation method of the amount of springs in the amount of springs estimation method of the present invention. It is a figure for demonstrating the estimation method of a hydraulic conductivity similarly . Same is a diagram showing the relationship between the groundwater discharge and permeability.

Explanation of symbols

100 Main tunnel 101 Pilot pit 102 Tunnel digging machine 109 Drain pipe 110 Water level gauge

Claims (2)

  A method for estimating the amount of spring water in a natural tunnel while excavating a tunnel in a spring ground with a closed tunnel tunnel machine. Measure the time and amount of drainage required to drain water into the excavator and reduce the water level in the gap by a certain amount, and measure the time required for the water level to recover after the drainage is stopped. A method for estimating the amount of spring water, characterized by estimating the amount of spring water. In order to build a tunnel in the spring ground, first of all, a pilot tunnel with a smaller cross section than the main tunnel to be constructed is constructed by lining up with a segment while excavating a closed tunnel excavator. By penetrating within the cross section, and then improving the water stoppage from the inside of the pilot mine to the springland outside the pilot mine, After that, the pilot mine segment was dismantled and removed, and the ring-shaped ground between the improved water-stopping ground and the pilot mine was excavated with a tunnel excavator and laid. In the tunnel excavation method to construct the tunnel,
While excavating the pilot mine, the spring water that is springing up in the gap around the tunnel excavator is drained into the tunnel excavator and the time and amount of drainage required to reduce the water level in the gap by a certain amount are measured. By measuring the time it takes for the water level to recover after the drainage stop and the change in the water level during that time, based on those measurements, estimate the amount of spring water per unit time and the permeability coefficient of the surrounding ground,
A tunnel excavation method characterized by the improvement of water stoppage for the spring ground outside the pilot mine based on the estimated values.

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