JP2013147882A - Calibration method and device for measuring saturation of ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a calibration method and a device which enable a high-precision measurement to be achieved in measuring saturation of the ground on the basis of specific resistance of sand ground with air injected thereinto.SOLUTION: A calibration method obtains a relation between saturation and specific resistance by: filling a sample of the ground G in a container 2 which can be sealed and has two conducting electrodes 7 arranged with a distance in between as well as detection electrodes 8a to 8e separately arranged in the distance between the two conductive electrodes 7; bringing the sample of the ground G to have saturation of 100% by filling water in the container 2 through a water supply pipe 5 while deaerating the container 2 through a suction pipe 6; sequentially reducing the saturation by draining water from the container 2 through the water supply pipe 5; detecting voltages between the detection electrodes 8a to 8e, at respective saturation, by voltage detection means 11 with an electric current applied to the conducting electrodes 7 by conducting means 10; and calculating the specific resistance of the sample of the ground G by calculation means 12 on the basis of the electric current as well as the voltages.

Description

  The present invention relates to a calibration method and apparatus for measuring soil saturation, and more specifically, in measuring soil saturation based on the resistivity of sandy soil injected with air to prevent liquefaction. The present invention relates to a calibration method and apparatus for ground saturation that enables highly accurate measurement.

  Conventionally, in order to prevent liquefaction of sandy ground saturated with water, water in which air bubbles are mixed into sandy ground or by directly injecting air into sandy ground saturated with water It has been proposed to reduce the degree of saturation of sandy ground by mixing a large number of bubbles. Under the present circumstances, the method of measuring the saturation degree of a ground based on the specific resistance of the sandy ground which inject | poured air is proposed (for example, refer patent document 1).

  When carrying out this method for measuring the degree of saturation of the ground, it is necessary to obtain in advance the relationship between the degree of saturation and the specific resistance of the sandy ground on which construction is to be performed. If the relationship between the two is not accurately grasped, the precise state cannot be grasped even if the specific resistance of the ground is measured and the saturation of the ground is calculated based on the specific resistance. Therefore, in order to improve the measurement accuracy of the saturation level of the ground, a calibration method and apparatus capable of acquiring the relationship between the saturation level of the sandy ground and the specific resistance in advance more accurately are required.

JP 2009-121066 A

  An object of the present invention is to measure the degree of saturation of the ground, which enables high-precision measurement in measuring the degree of saturation of the ground based on the specific resistance of sandy ground injected with air to prevent liquefaction. It is to provide a calibration method and apparatus.

  In order to achieve the above object, the calibration method for soil saturation measurement according to the present invention is based on the specific resistance detected between the electrodes installed in the ground and the saturation of the sandy soil injected with air. A calibration method for measuring the degree of saturation of the ground used for measurement, comprising two current-carrying electrodes spaced apart, and a plurality of detection electrodes spaced between the current-carrying electrodes, By filling the inside of the container that can be sealed with a ground sample collected from the sandy ground to be measured and filling the inside of the container with water while degassing the inside, After the saturation level of the ground sample inside the container is set to 100%, water is discharged from the inside of the container in order to decrease the saturation level of the ground sample inside the container. A current is passed between them, a voltage is detected between the detection electrodes, and a specific resistance of the ground sample is calculated based on the current and the voltage. It is characterized by acquiring a relationship.

  The calibration device for measuring the degree of saturation of the ground according to the present invention includes a sealable container filled with a ground sample collected from a sandy ground to be measured, and a suction attached to the container and connected to a vacuum pump. A pipe, a water supply pipe attached to the container and connected to a water supply source, a drain pipe for discharging the water inside the container to the outside, and two energizations arranged at intervals inside the container An electrode, a plurality of detection electrodes arranged at intervals between the energization electrodes in the container, an energization means for passing a current between the energization electrodes, and a voltage for detecting a voltage between the detection electrodes It comprises a detecting means, and an arithmetic unit that calculates the specific resistance of the ground sample based on the current and voltage, and calculates the relationship between the saturation degree of the ground sample and the specific resistance.

  According to the present invention, the inside of the container that can be sealed is filled with a ground sample collected from the sandy ground to be measured, and then filled with water while degassing the inside of the container. The saturation degree of the ground sample can be easily made 100%, and then the saturation degree of the ground sample can be easily lowered by sequentially discharging water from the inside of the container. And in each saturation degree, an electric current is sent between the two energization electrodes arranged at intervals in the interior of the container, and a voltage is generated between the plurality of detection electrodes arranged at intervals between these energization electrodes. The actual sandy soil saturation and resistivity are obtained by calculating the resistivity of the ground sample based on this current and voltage and obtaining the relationship between the saturation and resistivity of the ground sample. It is possible to easily obtain data that approximates the relationship. Therefore, when measuring the saturation of sandy soil injected with air based on the specific resistance detected between the electrodes installed in the ground, the relationship between the saturation and the specific resistance of the ground sample obtained by the present invention By using this, it becomes possible to measure the saturation degree of the actual ground with high accuracy.

  For example, a container is installed in a state where the plurality of detection electrodes are arranged side by side, and a voltage is detected between the detection electrodes. As a result, even when the saturation level of the ground sample inside the container is lowered, the variation in the saturation level inside the container is reduced, which is advantageous for accurately detecting the voltage at each saturation level. .

  Three or more detection electrodes are arranged, a plurality of combinations of two detection electrodes are selected from among the detection electrodes, a voltage is detected between each selected combination of the two detection electrodes, and the detected voltages Based on the above, it is also possible to determine a voltage for calculating the specific resistance. This is advantageous for accurately detecting the voltage at each saturation level.

  The detection electrode has, for example, an annular shape along the inner peripheral surface of the container. This increases the voltage detection area, which is advantageous for accurately detecting the voltage. In addition, when the ground sample is filled into the container, the detection electrode does not get in the way and can be filled smoothly.

1 is an overall schematic diagram of a calibration apparatus according to the present invention. It is AA sectional drawing of FIG. It is BB sectional drawing of FIG. It is explanatory drawing which illustrates the process which makes the saturation degree of the ground sample inside a container 100%. It is a graph which shows the relationship between the saturation of the ground sample acquired by this invention, and specific resistance. It is a graph which shows the relationship between the saturation degree of the sandy ground computed based on the data of FIG. 5, and a specific resistance change rate.

  Hereinafter, a calibration method and apparatus for soil saturation measurement according to the present invention will be described based on the embodiments shown in the drawings.

  As illustrated in FIGS. 1 to 3, the calibration device 1 of the present invention includes a container 2 filled with a ground sample G collected from a sandy ground to be measured, and a suction pipe 6 attached to one end of the container 2. And a water supply / drainage pipe 5 attached to the other end of the container 2. The container 2 has the cylindrical part 3 which has the flange part 4a in both ends, and the detachable cover part 4b attached so that each flange part 4a may be covered.

  The suction pipe 6 has an open / close valve 6a and is detachably connected to the vacuum pump. The water supply / drainage pipe 5 has an open / close valve 5a and is detachably connected to a water supply source. The container 2 can be sealed by closing the open / close valves 5a and 6a.

  At both ends inside the container 2, the energization electrodes 7 are disposed, and a plurality of detection electrodes 8 a to 8 e are disposed with a gap between the two energization electrodes 7. That is, the energizing electrode 7 and the detection electrodes 8a to 8e are arranged with a space in the cylinder axis direction of the cylindrical portion 3.

  The energization electrode 7 and the detection electrodes 8a to 8e can adopt various shapes, but in this embodiment, the energization electrode 7 has a disk shape, and the detection electrodes 8a to 8e extend along the inner peripheral surface of the cylindrical portion 3. It has a circular shape.

  Although the size of the cylindrical part 3 is not specifically limited, For example, an internal diameter is about 10 cm-20 cm, and length is about 30-60 cm. The outer diameters of the energizing electrode 7 and the detection electrodes 8 a to 8 e are substantially the same as the inner diameter of the cylindrical portion 3.

  The number of the detection electrodes 8a to 8e is plural and is not particularly limited, but is preferably 3 or more, and is appropriately determined within a range of, for example, about 3 to 10. The interval between the adjacent detection electrodes 8a to 8e is, for example, about 5 cm to 10 cm, and can be arranged at equal intervals or unequal intervals. The intervals between the adjacent energizing electrode 7 and the detection electrode 8a, and the interval between the energizing electrode 7 and the detection electrode 8e are the same as described above.

  The suction tube 6 is fixed to one end of the container 2 through the lid portion 4 b on one end side of the container 2 and the energizing electrode 7. The water supply / drainage pipe 5 is fixed to the other end of the container 2 through the lid portion 4 b on the other end side of the container 2 and the energizing electrode 7. In this embodiment, although the water supply / drainage pipe 5 which functions as a water supply pipe and a drainage pipe is provided, a water supply pipe and a drainage pipe can also be provided separately.

  A lead wire 9 a is connected to each energizing electrode 7 via a connector 9 that communicates the inside and outside of the container 2, and each lead wire 9 a is connected to energizing means 10. The energizing means 10 energizes the energizing electrode 7 by passing a current between them.

  A lead wire 9 a is connected to each of the detection electrodes 8 a to 8 e via a connector 9 that communicates the inside and the outside of the container 2, and each lead wire 9 a is connected to the voltage detection means 11. The voltage detection means 11 detects the voltage between the detection electrodes 8a to 8e.

  The energizing means 10 and the voltage detecting means 11 are connected to a computing device 12 such as a personal computer through a lead wire 9a. The arithmetic device 12 receives the current (current value) passed by the energization means 10 and the voltage (voltage value) detected by the voltage detection means 11. Further, the arithmetic device 12 is configured to receive the saturation of the ground sample G inside the container 2.

The specific resistance ρt of the ground is expressed by the following formula (1) (archy formula) using the relationship between the porosity B and the saturation degree Sw when the specific resistance ρw of the groundwater is small.
ρt = A · (B) ^-m · (Sw) ^-n · ρw (1)

  A, m, and n are values determined empirically, and are generally m = 1.3-3, n = 2, and A = 0.6-1.5.

When air is injected into the ground and the groundwater is replaced with air, if the porosity B and the specific resistance ρw of the groundwater do not change, the saturation level of the ground changes from Sw1 to Sw2. If the specific resistance of the ground is ρt1, ρt2, it is expressed by the following equation (2).
(Ρt2 / ρt1) = (Sw2 / Sw1) ⁻ⁿ (2)

When the degree of saturation of the sandy ground that is in a fully saturated state deeper than the groundwater level is changed by injecting air, since Sw1 = 1 in the equation (2), it is expressed by the following equation (3).
Sw2 = (ρt2 / ρt1) ^{(−1 / n)} (3)

  Therefore, in the present invention, the specific resistance ρt1 when the saturation degree Sw of the ground sample G is 100% (= 1) is measured, and the specific resistance ρt2 is calculated at each saturation degree Sw2 by sequentially changing the saturation degree Sw2. To do. Then, the obtained data is plotted on a graph to calculate the n value of equation (3). Thereby, the n value of the ground sample G, that is, the sandy ground from which the ground sample G is collected is grasped.

  The procedure for acquiring the relationship between the saturation of the ground sample G and the specific resistance by the calibration method of the present invention will be described below.

  First, the lid portion 4 b is removed from the one flange portion 4 a and the one energizing electrode 7 is removed from the cylindrical portion 3. Next, the ground portion G collected from the sandy ground to be measured is filled into the cylindrical portion 3. Then, while arrange | positioning one energizing electrode 7 in the predetermined position of the cylindrical part 3, the cover part 4b is fixed to one flange part 4a. Thereby, the inside of the sealable container 2 in which two energizing electrodes 7 arranged at intervals and a plurality of detection electrodes 8a to 8e arranged at intervals between these energizing electrodes 7 are provided, Fill with ground sample G.

  Next, as illustrated in FIG. 4, the air a inside the container 2 is discharged by a vacuum pump through the suction pipe 6 with the open / close valve 6 a opened. At the same time, water W is filled from the water supply source into the container through the water supply / drain pipe 5 with the open / close valve 5a opened. Water W fills the inside of the container 2, and excess water W is discharged through the suction pipe 6. Thereby, the saturation degree of the ground sample G inside the container 2 is made 100%. As the water W to be filled in the container 2, groundwater flowing through the sandy ground from which the ground sample G is collected is used, or water having a specific resistance close to that of the groundwater is used.

  After the saturation is set to 100%, the opening and closing valves 5a and 5b are closed, and the inside of the container 2 is sealed. Here, a current is passed between the energizing electrodes 7, and a voltage is detected between two detection electrodes selected from the detection electrodes 8a to 8e. The specific resistance of the ground sample G is calculated based on the current passed by the energizing means 10 and the voltage detected between the two selected detection electrodes. The saturation level (100%) of the ground sample G at this time is input to the arithmetic unit 12.

  For example, if the current I flows and the detected voltage V, the resistance value R = V / I. And in the case of the distance L between the detection electrodes which detected the voltage and the cross-sectional area S of the ground sample G existing between the detection electrodes, the specific resistance is calculated as ρt = R × S / L. Therefore, the arithmetic unit 12 includes the distance L between the detection electrodes 8a to 8e and the cross-sectional area S of the ground sample G existing between the detection electrodes 8a to 8e (that is, the inside of the cylindrical portion 3 of the container 2). (Cross-sectional area) is entered.

  Next, as shown in FIG. 4, the container 2 is arranged so that the water supply / drainage pipe 5 is positioned downward, the opening / closing valve 5a is opened, and an appropriate amount of water W is discharged from the inside of the container 2 through the water supply / drainage pipe 5; Close. After the saturation degree of the ground sample G is lowered, a current is passed between the energizing electrodes 7, and the voltage is detected between the two detection electrodes selected from the detection electrodes 8a to 8e. Based on the current passed by the energizing means 10 and the voltage detected between the detection electrodes, the arithmetic device 12 calculates the specific resistance of the ground sample G. Further, the degree of saturation of the ground sample G is calculated based on the amount of water W discharged from the inside of the container 2 at this time, and this degree of saturation is input to the arithmetic unit 12.

  Similarly, an appropriate amount of water W is sequentially discharged from the inside of the container 2 to reduce the saturation of the ground sample G inside the container 2, and at each saturation, a current is passed between the conducting electrodes 7, The voltage is detected between two detection electrodes selected from the detection electrodes 8a to 8e, and the specific resistance of the ground sample G is calculated based on the current and the voltage. Further, the saturation level of the ground sample G at that time is input to the arithmetic unit 12. The amount of water W discharged each time from the inside of the container 2 can be determined as appropriate.

  The specific resistance of the ground sample G calculated by the above procedure and the saturation data of the ground sample G are processed by the arithmetic unit 12 and plotted on a graph as illustrated in FIG. get. FIG. 5 shows the relationship between the specific resistance and the saturation degree for two types of ground samples G (sample 1 and sample 2). According to this graph, the n value in equation (3) is approximately 1.

Therefore, the equation (3) becomes Sw2 = (ρt2 / ρt1) ⁻¹ , and by detecting the specific resistances ρt1 and ρt2 between the electrodes installed in the sandy ground, the ratio is obtained by injecting air into the ground. The saturation degree Sw2 of the sandy ground when the resistance ρt2 is reached can be grasped.

  The relationship between the specific resistance change rate (rate of change of ρt2 with respect to ρt1) and the saturation degree as illustrated in FIG. 6 for the ground sample G, that is, the sandy ground, may be acquired from the data acquired according to the present invention. it can. FIG. 6 shows the relationship between the resistivity change rate and the saturation degree of the ground sample G (sandy ground) when the n value of the expression (3) is 1 and 2.

  As described above, according to the present invention, after the ground sample G is filled into the sealable container 2, the ground sample G inside the container 2 is filled by filling the water W while degassing the inside of the container 2. Can be easily set to 100%. Thereafter, by sequentially discharging the water W from the inside of the container 2, the degree of saturation of the ground sample G can be easily reduced.

  In addition, by calculating the specific resistance of the ground sample G at each saturation level using the above method and obtaining the relationship between the saturation level of the ground sample and the specific resistance, the saturation level of the actual sandy ground and Data approximate to the relationship with the specific resistance can be easily obtained. Therefore, when measuring the saturation of sandy soil injected with air based on the specific resistance detected between the electrodes installed in the ground, the relationship between the saturation and the specific resistance of the ground sample obtained by the present invention By using this, it becomes possible to measure the saturation degree of the actual ground with high accuracy.

  When detecting a voltage between the detection electrodes 8a to 8e, it is preferable that the container 2 is laid down and the detection electrodes 8a to 8e are arranged side by side as illustrated in FIG. When the saturation level of the ground sample G is lowered, the saturation level of the ground sample G existing between the detection electrodes varies depending on the vertical position of the selected detection electrodes 8a to 8e when the container 2 is erected. However, by arranging the detection electrodes 8a to 8e side by side, the variation in the saturation of the ground sample G existing between the detection electrodes is reduced regardless of the selected detection electrodes 8a to 8e. This is advantageous for accurately detecting the voltage.

  Two arbitrary detection electrodes can be selected from the plurality of detection electrodes 8a to 8e, and the voltage can be detected between the selected set of detection electrodes. It is preferable to detect between the detection electrodes. For example, three or more detection electrodes are arranged, a plurality of combinations of two detection electrodes are selected from among the detection electrodes, and a voltage is detected between each selected combination of the two detection electrodes, and these are detected. A voltage for calculating the specific resistance is determined based on the voltage. For example, in this embodiment, the detection electrodes 8a and 8b, 8a and 8c, 8a and 8d, 8a and 8e, 8b and 8c, 8b and 8d, 8b and 8e, 8c and 8d, 8c and 8e, 8d and 8e Sense voltage between. And let the average value which averaged the voltage detected by the combination of these 10 detection electrodes be a voltage for calculating a specific resistance. Alternatively, among the voltages detected by the combination of 10 detection electrodes, an average value obtained by averaging six voltages excluding upper two data having a large voltage value and two lower data having a small voltage value is a voltage for calculating a specific resistance. And

  In this way, by combining a plurality of combinations of two detection electrodes for detecting the voltage and determining the voltage for calculating the specific resistance based on the detected plurality of voltages, the positions of the detection electrodes 8a to 8e are determined. The variation in the detected voltage caused can be reduced. Therefore, it is advantageous to accurately detect the voltage at each saturation level of the ground sample G.

  Although the shape of the detection electrodes 8a to 8e is not particularly limited, it is preferable that the detection electrodes 8a to 8e have an annular shape along the inner peripheral surface of the cylindrical portion 3 as exemplified in the embodiment. As a result, since the voltage detection area is increased, it is possible to suppress variations in detection voltage caused by variations in the degree of saturation of the ground sample G inside the container 2, which is advantageous in accurately detecting the voltage. Become. Further, when the ground sample G is filled in the container 2, the detection electrodes 8a to 8e are easily filled without being obstructed, so that workability is improved.

DESCRIPTION OF SYMBOLS 1 Calibration apparatus 2 Container 3 Cylindrical part 4a Flange part 4b Cover part 5 Water supply / drainage pipe 5a Open / close valve 6 Suction pipe 6a Open / close valve 7 Current supply electrode 8a, 8b, 8c, 8d, 8e Detection electrode 9 Connector 9a Lead wire 10 Current supply means 11 Voltage detection means 12 Arithmetic unit G Ground sample W Water a Air

Claims (5)

A calibration method for measuring the degree of saturation of ground used for measuring the degree of saturation of sandy ground injected with air based on the specific resistance detected between electrodes installed in the ground,
The inside of a sealable container having two energizing electrodes arranged at intervals and a plurality of sensing electrodes arranged at intervals between these energizing electrodes was collected from the sandy ground to be measured. After filling the inside of the container with water with the ground sample filled, the inside of the container is filled with water, so that the degree of saturation of the ground sample inside the container becomes 100%, and then the inside of the container The water is discharged from the container to reduce the saturation of the ground sample inside the container, and at each saturation, a current is passed between the current-carrying electrodes, and then the voltage is detected between the detection electrodes, A calibration method for measuring the degree of saturation of the ground, wherein the relationship between the degree of saturation of the ground sample and the specific resistance is obtained by calculating the specific resistance of the ground sample based on the current and voltage.   The calibration method for measuring the degree of saturation of the ground according to claim 1, wherein a container is installed in a state where the plurality of detection electrodes are arranged side by side, and a voltage is detected between the detection electrodes.   Three or more detection electrodes are arranged, a plurality of combinations of two detection electrodes are selected from among the detection electrodes, a voltage is detected between each selected combination of the two detection electrodes, and the detected voltages The calibration method for measuring the degree of saturation of the ground according to claim 1, wherein a voltage for calculating the specific resistance is determined based on   The calibration method for measuring the degree of saturation of the ground according to claim 1, wherein the detection electrode has an annular shape along the inner peripheral surface of the container. A calibration device for measuring the degree of saturation of a ground used for measuring the degree of saturation of sandy ground injected with air based on the specific resistance detected between electrodes installed in the ground,
A sealable container filled with a ground sample collected from the sandy ground to be measured, a suction pipe attached to the container and connected to a vacuum pump, and attached to the container and connected to a water supply source A water supply pipe, a drain pipe for discharging water inside the container to the outside, two energizing electrodes arranged at an interval inside the container, and an interval between the energizing electrodes inside the container A plurality of detection electrodes arranged at intervals, energization means for passing current between the energization electrodes, voltage detection means for detecting voltage between the detection electrodes, and a ratio of ground samples based on the current and voltage A calibration device for measuring the degree of saturation of the ground, comprising: an arithmetic unit for calculating the resistance and calculating the relationship between the saturation of the ground sample and the specific resistance.

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