JP3552594B2 - Measurement method of water saturation in tunnel excavation - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for measuring water saturation in excavation of a tunnel for a storage tank in a bedrock or the like.
[0002]
[Prior art]
As a facility for storing liquefied petroleum gas such as LPG, a water-sealed storage tank in rock is known. This type of storage tank in rock is used to create a natural or artificial water flow that flows from the outside to the inside of the tank body that stores liquefied petroleum gas. Have secured.
[0003]
In such a water-sealed storage tank in rock, it is difficult to re-saturate the rock once it is in an unsaturated state even at the time of construction, so it is necessary to construct while maintaining the saturated state.
[0004]
However, conventionally, it has not been possible to directly measure the water saturation of the bedrock.For example, in places where there is a high permeability zone on the site where Since the water level is below the critical groundwater level and the possibility of water unsaturated condition is very high, it was prevented to become unsaturated by detecting such locations by drilling.
[0005]
In other words, if there is a high permeability zone, the bedrock will be in an unsaturated state even at the time of construction. Then, it is presumed that the water will be in an unsaturated state, and measures have been taken by grouting or the like.
[0006]
However, such a conventional method for estimating the water saturation has the following technical problems.
[0007]
[Problems to be solved by the invention]
In other words, it is quite difficult to find a high water permeability zone by drilling during construction of the tunnel, and in addition to the conventional method of measuring water saturation, after storing oil gas etc. in the tank body tunnel and starting operation , Could not monitor the water seal.
[0008]
By the way, such a measurement of the water saturation at the time of excavation of a tunnel has an advantage that when it is carried out at the time of excavation of a normal mountain tunnel, a place where a large amount of spring water is generated can be known in advance. In the method of estimating the water saturation, the main purpose is to estimate the water content of the rock mass rather than the water saturation, and it has been difficult to accurately estimate the water saturation.
[0009]
The present invention has been made in view of such a conventional problem, and an object thereof is to estimate the water saturation relatively accurately by measuring over time at the time of tunnel construction. Another object of the present invention is to provide a method for measuring a water saturation, which can easily monitor a water seal state in a storage tank in a bedrock both during construction and operation.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method of measuring the water saturation of rock mass around an excavation cross section when excavating a tunnel , wherein the tunnel is a tank body for storing a liquefied gas such as LPG and LNG. A water ring tunnel for a storage tank in a rock mass, which is provided at a predetermined interval on an upper side of the tunnel and creates a water flow flowing from the outside to the inside of the tank body tunnel, wherein the water ring tunnel is excavated. In accordance with the progress of the excavation, a plurality of specific resistance measurement electrodes are sequentially installed on a measurement line along the tunnel axis direction of the water seal tunnel, and the specific resistance on the measurement line is measured through the electrode, A method for estimating the water saturation of rock in the lower part of the water seal tunnel based on the measured specific resistance, wherein the water saturation of the rock includes during construction of the tank body tunnel, Even after storage of the liquefied gas in the tank body tunnel, and so estimated that based on the specific resistance measured through the electrode installed in the water seal tunnel.
According to the water saturation measurement method configured as described above, the water resistance tunnel for estimating the water saturation of the rock is installed along with the excavation of the water seal tunnel, thereby constructing the water seal tunnel. It is possible to control the moisture saturation at the time of the construction, and to prevent the rock mass from becoming unsaturated during construction.
In this case, in the normal measurement of the specific resistance, when the measurement depth becomes deep, the measurement line must be secured long, but in the present invention, the inside of the water seal tunnel installed at a position of about several tens of meters above the tank body tunnel. Since the electrodes are installed on the tank and the rock saturation of the tank body tunnel is estimated, a long survey line is not required as in the case of estimating the rock saturation of the tank body tunnel from the electrodes installed on the ground surface. A sufficiently high-precision estimation is possible only by the length of the sealed tunnel.
In addition, even after storing liquefied petroleum gas in the tank body tunnel, the water saturation of the bedrock is estimated based on the specific resistance measured through the electrodes installed in the water ring tunnel, so the liquefied The water seal state can be monitored even in the service state where the petroleum gas is stored.
In the present invention, when excavating the tank body tunnel, a plurality of specific resistance measurement electrodes are installed on the excavated cross section, and the specific resistance on the excavated cross section is measured via the electrode, and the measured resistance is measured. Based on the specific resistance, it is possible to estimate the water saturation of the rock at the outer peripheral portion of the tank body tunnel.
According to the water saturation measurement method configured as described above, a plurality of electrodes for measuring specific resistance are installed on the excavation section of the tank body tunnel, and the water saturation on the excavation section is estimated. The accuracy of management of the degree of unsaturation in the vicinity is improved.
As the specific resistance measurement electrode, a quadrupole electrode including a pair of current electrodes and a pair of voltage electrodes can be used.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a basic configuration of measurement of a method for measuring water saturation in tunnel excavation according to the present invention.
[0012]
The measurement method shown in the figure is a measurement example applied to a normal tunnel 1. When measuring the water saturation of the rock mass on the outer peripheral side of the excavation section 2 during excavation of the tunnel 1, the measurement method shown in the figure is used. As described above, a plurality of specific resistance measurement electrodes 20 are provided along the circumferential direction of the excavation section 2.
[0013]
In the example shown in FIG. 1, a total of four sets of measurement electrodes 20 are installed on the same excavation section 2 at predetermined intervals, and the measurement electrodes 20 are connected to the terminal box 3 via lead wires. , And the terminal box 3 is connected to a specific resistance measuring device 4.
[0014]
As shown in FIG. 2, the specific resistance measuring electrode 20 of the present embodiment has a structure of a set of four poles, and a pair of current electrodes C ₁ and C ₂ installed at equal intervals. It has a pair of voltage electrodes P ₁ and P ₂ .
[0015]
Then, a pair of current electrodes C ₁ and C ₂ are arranged on both sides, and voltage electrodes P ₁ and P ₂ are arranged between the current electrodes C ₁ and C ₂ .
[0016]
In the arrangement direction blades of the current and voltage electrodes C ₁ , C ₂ , P ₁ , and P ₂ , in the case of the present embodiment, along the circumferential direction of the excavation section 2, the C ₁ , C ₂ , P ₁ , and P ₂ Although they are arranged in this order, they may be arranged in the order of C ₁ , C ₂ , P ₁ , P _{2 in} the tunnel axis direction with the excavation section 2 as the center.
[0017]
If the specific resistance measurement electrode 20 is placed, by connecting sequentially the resistivity measuring device 4 between the electrodes 20, by energizing the current and voltage electrodes _{C 1, C 2, P 1} , between P _2, bedrock Is measured.
[0018]
In this measurement, as shown in FIG. 2, when a DC current I flows between the pair of current electrodes C ₁ and C ₂ , a voltage V appearing between the pair of voltage electrodes P ₁ and P ₂ is measured.
[0019]
When the voltage V and the current I are obtained, they are calculated by the specific resistance ρ = 2πaV / I. Here, a is an arrangement interval of the current and voltage electrodes C ₁ , C ₂ , P ₁ , and P ₂ .
[0020]
As shown in FIG. 3, the resistivity ρ of the bedrock depends on the moisture saturation of the bedrock, so if the resistivity ρ of the bedrock is known, the moisture saturation of the bedrock can be estimated from the value. .
[0021]
In this case, the specific resistance ρ of the bedrock is affected by the rocks and the like, and the electric resistance of the groundwater also varies depending on its components. It is desirable to prepare a calibration curve of specific resistance with respect to saturation.
[0022]
As described above, when the tunnel 1 is excavated while estimating the water saturation of the rock based on the specific resistance ρ of the rock, the amount of water saturation of the rock at the outer peripheral portion of the excavation section 2 becomes, for example, a large amount. Since the location of spring generation is known in advance, spring countermeasures can be formulated at an early stage.
[0023]
4 to 8 show one embodiment of a method of measuring the moisture saturation in tunnel excavation according to the present invention. In the embodiments shown in these figures, the present invention relates to the excavation of a tunnel for a storage tank in a bedrock. Is applied.
[0024]
The storage tank in the bedrock has a tank main body tunnel 10 and a water seal tunnel 12 as shown in FIG.
[0025]
The tank main body tunnel 10 stores liquefied petroleum gas such as LPG and LNG therein. The water seal tunnel 12 is smaller in diameter than the main body tunnel 12, has almost the same length as the tank main body tunnel 10, is located coaxially about several tens of meters above, and extends from the inside to the outside. It has a plurality of drilled holes 14. A plurality of the boring holes 14 are arranged at predetermined intervals along the tunnel axis direction of the water seal tunnel 12, and the tip side is inclined downward.
[0026]
Water is injected into the water seal tunnel 12 before the construction excavation of the tank body tunnel 10, and there is a head pressure difference between the water seal tunnel 12 and the tank body tunnel 10. The water flow 16 flows from the outside of the tunnel 10 toward the inside. By creating such a water flow 16, liquid tightness and air tightness during the construction of the tank body 10 and after the start of operation of the tank body 10 are secured.
[0028]
In the storage tank in the bedrock having such a configuration, a water seal tunnel 12 having a smaller sectional area than that of the tank main body tunnel 10 is usually constructed in advance. In the case of the present embodiment, as shown in FIG. 5, when the water sealing tunnel 12 is pre-constructed, along the tunnel axis of the water sealing tunnel 12 along the tunnel axis of the water sealing tunnel 12 as the excavation proceeds. A plurality of electrodes 20 for measuring the specific resistance having the same configuration as above are provided at predetermined intervals.
[0029]
In addition, the installation location of each electrode 20 may be installed so as to directly contact the ground immediately after excavation, or may be installed so as to come into contact with the surface after construction of the shotcrete.
[0030]
The side line 18 is set in a straight line along the tunnel axis of the water seal tunnel 12. For example, the side line 18 may be set in parallel with the left and right side surfaces of the water seal tunnel 12, or may be set in parallel. Can be set at one position on the bottom surface or the ceiling surface located on the same axis as the tunnel axis.
[0031]
Each of the electrodes 20 (the same applies to the electrodes 20a installed in the tank main body tunnel 10 to be described later) also has a four-pole, one-piece structure in the present embodiment, similarly to the above-described embodiment. Includes a pair of current electrodes C ₁ and C ₂ installed at equal intervals and a pair of voltage electrodes P ₁ and P ₂ .
[0032]
The relationship between the arrangement direction of the current and voltage electrodes C ₁ , C ₂ , P ₁ , P ₂ and the extension direction of the side line 18 may be such that the electrodes 20 may be arranged in the same direction as the side line 18, The arrangement direction of the electrodes 20 may be orthogonal.
[0033]
When the electrodes 20 are installed, the specific resistance measuring device 4 is connected between the electrodes 20 via the terminal box 3, and the specific resistance ρ of the rock is measured.
[0034]
As shown in FIG. 3, the resistivity ρ of the bedrock depends on the moisture saturation of the bedrock, so if the resistivity ρ of the bedrock is known, the moisture saturation of the bedrock can be estimated from the value. .
[0035]
In this way, when the excavation is performed while estimating the water saturation of the rock based on the resistivity ρ of the rock, it is possible to avoid the rock from becoming unsaturated when the water seal tunnel 12 is constructed. In addition, even when an unsaturated state is confirmed, it is possible to improve the accuracy of drill boring. If the accuracy of boring is improved, it is possible to accurately perform pre-out.
[0036]
The electrode 20 installed in the water seal tunnel 12 is installed as it is, and as shown in FIG. 6, after the completion of the water seal tunnel 12, water is injected into the water seal tunnel 12 to create a water flow 16. After the start of water sealing, the specific resistance ρ of the rock along the survey line 18 is measured. Then, based on the measured specific resistance ρ, the water saturation of the bedrock under the water seal tunnel 12 is estimated, and based on the water saturation, monitoring of the water seal state is continued.
[0037]
On the other hand, in the case of the present embodiment, water is injected into the water seal tunnel 12, and after the water seal is started, the water saturation of the bedrock excavating and forming the tank main body tunnel 10 is ensured. As shown in (1), excavation of the tank body tunnel 10 is performed.
[0038]
At this time, as the excavation of the tank main body tunnel 10 progresses, the electrode 20 installed in the water seal tunnel 12 and the electrode 20a substantially the same as those installed in the water seal tunnel 12 are installed, and the specific resistance ρ is measured. The water saturation of the rock mass is estimated based on the measured value.
[0039]
In this case, a plurality of electrodes 20a are provided at a predetermined interval along one cross section of the tank main body tunnel 10 on the excavation cross section. The installation location in this case is set on the side surface and the ceiling surface of the tank main body tunnel 10.
[0040]
As the excavation progresses, a plurality of electrodes 20a are similarly installed on the same excavation section at predetermined intervals in the tunnel axis direction, and the specific resistance ρ of the rock outside the side surface and the ceiling surface of the tank body tunnel 10 is increased. Is measured.
[0041]
Then, based on the measured specific resistance ρ, the water saturation of the bedrock outside the side surface and the ceiling surface of the tank body tunnel 10 is estimated, and if there is a non-saturated portion, a pre-grouting process is performed on the portion. .
[0042]
Even when such a tank body tunnel 10 is excavated, the measurement of the specific resistance ρ by the electrode 20 installed in the water seal tunnel 12 is continuously performed, and further, as shown in FIG. Even after the tunnel 10 is completed and the liquefied petroleum gas is accommodated therein and the service is started, the measurement of the specific resistance ρ by the electrodes 20 installed in the water ring tunnel 12 is continuously performed, The moisture saturation of the rock is estimated based on the measured specific resistance ρ.
[0043]
In the water saturation measurement method for tunnel excavation configured as described above, since the specific resistance measurement electrode 20 is installed along with the excavation of the water seal tunnel 12, the water saturation during the construction of the water seal tunnel 12 is set. Degree management becomes possible.
[0044]
Further, in the present embodiment, a plurality of electrodes 20a for measuring specific resistance are installed on the excavated cross section of the tank main body tunnel 10, and the water saturation on the excavated cross section is estimated. Of the tank main body tunnel 10 can be performed while controlling the water saturation with high accuracy.
[0045]
Further, in the present embodiment, the moisture saturation of the bedrock is estimated based on the specific resistance ρ measured via the electrode 20 installed in the water ring tunnel 12 even after the liquefied petroleum gas is stored in the tank body tunnel 10. The water seal state can be monitored even in the service state where the liquefied petroleum gas is stored in the tank body tunnel 10.
[0046]
In the above embodiment, the case where the electrode 20 is installed in both the water seal tunnel 12 and the tank main body tunnel 10 is illustrated. However, in the measurement method of the present invention, even if the electrode 20 is installed only on the water seal tunnel 12 side, Water seal condition can be monitored.
[0048]
【The invention's effect】
As described above in detail in the examples, according to the method for measuring the water saturation in tunnel excavation according to the present invention, during the construction of the tunnel, it is possible to accurately estimate the water saturation, and in the storage tank in the bedrock In addition, the state of the water seal can be easily monitored both during construction and during operation.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of a method for measuring a water saturation in tunnel excavation according to the present invention.
FIG. 2 is an explanatory view of an arrangement state of electrodes when measuring a specific resistance of a rock in the present invention.
FIG. 3 is a graph showing a relationship between a specific resistance value and a water saturation.
FIG. 4 is an explanatory diagram showing an example of a storage tank in rock to which the method for measuring a water saturation according to the present invention is applied.
FIG. 5 is an explanatory view when a water sealing tunnel is constructed in the storage tank in the bedrock of FIG. 4;
FIG. 6 is an explanatory diagram when water sealing is started in the storage tank in the bedrock of FIG. 4;
FIG. 7 is an explanatory view when a tank main body tunnel is constructed after water sealing is started in the storage tank in the bedrock of FIG. 4;
8 is an explanatory view of the storage tank in the bedrock of FIG. 4 after the start of service.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Tank main body tunnel 12 Water sealing tunnel 14 Boring hole 16 Water flow 18 Measurement line 20 Electrode

Claims (3)

In the method of measuring the moisture saturation of the rock around the excavation cross section when excavating a tunnel,
The tunnel is provided at a predetermined interval above a tank body tunnel for storing a liquefied gas such as LPG , LNG, etc., and is used for a rock storage tank for creating a water flow flowing from the outside to the inside of the tank body tunnel. Water seal tunnel,
When excavating the water seal tunnel, with the progress of the excavation, a plurality of specific resistance measurement electrodes are sequentially installed on a measurement line along the tunnel axis direction of the water seal tunnel,
A method of measuring the specific resistance on the measurement line through the electrode, and estimating the water saturation of the rock in the lower part of the water seal tunnel based on the measured specific resistance,
Moisture saturation of the rock mass, including during the construction of the tank body tunnel, even after storing the liquefied gas in the tank body tunnel, the specific resistance measured via the electrode installed in the water ring tunnel A method for measuring moisture saturation in tunnel excavation, characterized in that the estimation is based on the following . When excavating the tank body tunnel, installing a plurality of specific resistance measurement electrodes on the excavation cross section,
  2. The method according to claim 1, further comprising: measuring a specific resistance on the excavated cross section through the electrode, and estimating a water saturation of rock in an outer peripheral portion of the tank body tunnel based on the measured specific resistance. Method for measuring water saturation in tunnel excavation in Japan. The method according to claim 1, wherein the specific resistance measurement electrode is a quadrupole electrode including a pair of current electrodes and a pair of voltage electrodes.

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