JP4929039B2 - Ground survey method - Google Patents

Description

  The present invention relates to a ground survey method. More specifically, the present invention relates to a ground investigation method suitable for use in evaluating the possibility of occurrence of ground depression.

  It is generally considered that the subsidence of the ground is caused by collapse of artificial cavities such as cavities left behind in mines such as coal mines and cavities left after tunnel excavation. In particular, as shown in FIG. 10A, when a tunnel 101 such as a road, a railway, or a waterway is constructed, the ground 102 may be excavated with a cross section larger than the actual cross section of the tunnel 101. In some cases, the gap 103 between the outer peripheral surface of the constructed tunnel 101 and the inner peripheral surface of the excavated ground cavity is not backfilled, leaving a gap 103 in the vicinity of the outside of the tunnel 101. Then, as shown in FIG. 10B, it is considered that the ground 102 collapses due to the collapse of the gap 103 left on the back surface of the tunnel 101, that is, the artificial cavity. In addition, it is thought that there are cases where ground depression occurs due to a sudden drop in the ground surface, and there are cases where ground depression occurs due to the gradual rise of the cavity with repeated collapse. (Non-Patent Document 1).

Kawamoto: Geophysical exploration, Vol.58, No.6, pp.589-597, 2005, regarding ground subsidence disaster and underground cavern survey.

  However, the present inventors are investigating the mechanism of the occurrence of ground subsidence, and the ground subsidence is limited to a case where an artificially formed cavity is generated in advance in the ground. It is not a thing, but a pipe-like hole (also called a water channel) is present or formed in the ground, and the soil is drawn into the flow of water in this pipe-shaped hole, that is, the water channel becomes a path for transporting the soil. It was discovered that this may occur due to the formation of a new cavity near the ground surface.

  Specifically, as shown in FIG. 11, rainwater 105 that has fallen on the ground surface 104 passes through the weak point of the ground 102 that has been subjected to shearing or tension, and penetrates into the ground 102 while selectively flowing (see FIG. )), A water channel 107 having a hole in the form of a pipe is formed in the rainwater infiltration path 106 at a weak point of the ground 102, and the earth and sand of the ground 102 is drawn into and transported by the water flow in the water channel 107. A cavity 108 is formed at a location close to the ground surface 104 (FIG. 11B). And it discovered that there existed a mechanism that the depression of the ground 102 generate | occur | produced by the cavity 108 newly formed in this way.

  In addition, as described above, conventionally, it has been thought that the depression of the ground occurs due to the collapse of the cavity that is artificially formed and pre-existing in the ground. Measures have been taken to find and fill the cavities below the surface. For this reason, the conventional ground survey for evaluating the possibility of ground subsidence is aimed at discovering the cavities themselves already formed in the ground. The abnormal region appearing in the obtained result is estimated as a cavity. Therefore, the conventional ground survey does not detect that there is a situation in which earth and sand can be transported and a state in which a cavity can be formed occurs in the ground. Therefore, in the conventional concept of ground subsidence occurrence mechanism and ground investigation based on it, ground subsidence is caused by the mechanism that the ground is depressed by newly forming a cavity by transporting the earth and sand in the ground by the flow of water in the water path. Cannot be detected before the cavity is formed.

  As described above, it is assumed that the ground depression occurs as a conventional mechanism only when a cavity exists in the ground in advance, and in order to fill the cavity in order to prevent the ground depression caused by this mechanism, It is not sufficient to prevent the occurrence of ground subsidence by using only the discovery of formed cavities as the purpose of ground investigation.

  Therefore, the present invention is based on the function of the water channel in the ground in order to prevent the occurrence of ground subsidence due to the mechanism that the ground sinks due to the formation of cavities accompanying the flow of earth and sand by the function of the water channel in the ground. It is an object of the present invention to provide a ground survey method capable of determining whether or not there exists a situation in which sediment flow can occur.

In order to achieve this object, the ground survey method according to claim 1 is performed by repeating the step of infiltrating the liquid from the ground surface into the ground and the step of performing the three-dimensional electrical exploration of the ground once or twice or more, By detecting the location where the liquid penetrates deeper than the distribution of the penetration of the liquid into the ground, the danger location of the ground depression before the formation of the cavity is specified.

  Therefore, according to this ground survey method, since the three-dimensional electrical exploration of the ground is performed while infiltrating the liquid into the ground, the liquid is highly permeable, such as a water channel, and the soil is transported by the flow of the liquid. The situation that can be performed is detected as a location where the liquid penetrates and protrudes compared to the penetration distribution of the liquid into the ground.

According to the ground survey method of the present invention, for example, a situation where the liquid has high permeability such as a water channel and the earth and sand can be transported by the flow of the liquid protrudes compared with the liquid penetration distribution into the ground, and the liquid is deeper. It is possible to detect the area as it penetrates toward the ground, and the ground sinks due to the mechanism that the ground sinks due to the formation of new cavities when the soil in the ground is transported by the flow of water in the water path Can be detected and prevented before the cavity is formed.

  Hereinafter, the configuration of the present invention will be described in detail based on the best mode shown in the drawings.

FIG. 1 to FIG. 9 show an example of an embodiment of the ground investigation method of the present invention. In this ground investigation method, the step of infiltrating the liquid 9 from the ground surface 7 into the ground 6 and the step of conducting the three-dimensional electric exploration of the ground 6 are repeated once or twice, and the liquid 9 into the ground 6 is obtained. By detecting a portion that protrudes in comparison with the permeation distribution of the liquid 9 and permeates the liquid 9 toward the deep portion, the dangerous portion of the ground collapse before the formation of the cavity is specified.

  FIG. 1 shows a flowchart of an example of an embodiment of the ground investigation method of the present invention. In the present embodiment, description will be given according to the flowchart shown in FIG. In executing the ground survey method of the present invention, first, an electrode for performing the three-dimensional electrical exploration in the process of S3 is developed on the ground surface of the survey target area (S1).

  In the present invention, a plurality of electrodes 1-1, 1-2, 1-3,... (Hereinafter simply referred to as electrodes 1) are spread on the ground surface 7. The point where the electrode 1 is installed is called a measuring point. Therefore, since the electrode 1 is also a measuring point, it is described as the electrode 1 or the measuring point 1 as appropriate.

  In the present invention, in order to perform a three-dimensional electrical exploration of the ground, there are no restrictions on the number, arrangement, or mutual spacing of the measuring points 1 developed on the ground surface 7, and the area and shape of the survey area 13 are required. It is set as appropriate considering the accuracy of the survey results. Specifically, for example, it is conceivable that about 60 to 300 measuring points are arranged with the vertical and horizontal alignments arranged at equal intervals, and the mutual interval is set to about 10 cm to 2 m. In this embodiment, as shown in FIG. 2, a total of 60 measurement points 1 are arranged in 5 × 12 rows at 1 m intervals with the vertical and horizontal arrangements aligned.

  The electrode 1 is, for example, a stainless steel electrode and is inserted from the ground surface 7 to a depth of, for example, 30 to 40 cm. The thickness of the electrode 1 is about 15 mm, for example.

  In addition, this invention is applicable if it is the ground which has the permeability | transmittance of the liquid from the ground surface 7 in the ground at least.

  Next, a liquid is infiltrated into the ground from the ground surface 7 of the investigation target area 13 (S2).

  The liquid to be infiltrated into the ground may be any liquid that can change the specific resistance of the ground when infiltrated into the ground. Specifically, for example, rainwater, river water, tap water, etc., or these A liquid whose electroconductivity is increased by mixing an electrolyte substance into the liquid is used. In addition, when conducting three-dimensional electrical exploration, a liquid with higher electrical conductivity or higher electrical conductivity is used in order to facilitate the determination of the ground condition because the degree of change in the specific resistance of the ground is increased. It is desirable.

  As a method of infiltrating the liquid into the ground, for example, a method of utilizing the infiltration of rainwater into the ground due to rain, and as shown in FIG. 3, the liquid 9 is artificially investigated using a water truck 8 or the like. It is conceivable that the method is to spread over the entire 13 ground surfaces 7 to penetrate into the ground. Note that these two methods may be used in combination.

  The total amount of the liquid 9 that permeates into the ground and the speed at which the liquid 9 permeates into the ground are the third order in the process of S3 when there is a water channel in the ground and water flows in the water channel. According to the original electric exploration, the presence of the water channel is appropriately adjusted to a level where the penetration speed of the liquid 9 is faster than the surrounding ground.

  For example, even if there is a water channel because the total amount of the liquid 9 is small or the speed at which the liquid 9 is permeated is low, the amount of the liquid 9 supplied to the water channel is only small or the liquid in the water channel. Since there is no difference between the permeation rate of 9 and the permeation rate of the liquid 9 in the surrounding ground, it is considered that the presence of the water channel cannot be detected as a location where the progress of the permeation of the liquid 9 protrudes compared to the surroundings. In some cases, the amount of the liquid 9 is increased or the speed at which the liquid 9 is permeated is increased. On the other hand, since the speed at which the liquid 9 is permeated is high, the liquid 9 rapidly permeates all over the ground regardless of whether or not the water path exists, and the permeation speed of the liquid 9 in the water path and the surrounding ground. Since there is no difference between the permeation speed of the liquid 9, the liquid 9 is permeated when it is considered that the progress of the permeation of the liquid 9 cannot be detected as a location where the progress of the permeation of the liquid 9 protrudes from the periphery. Reduce the speed.

  In addition, since the average penetration speed of the liquid 9 into the ground in the investigation target area 13 varies depending on, for example, the hydraulic conductivity of the ground, the viscosity of the liquid 9, and the like, it should be adjusted as appropriate while actually performing the three-dimensional electric exploration. May be.

  In addition, when using rainwater due to rain, the amount of liquid 9 that permeates into the ground and the speed of permeation cannot be artificially adjusted, so that it is possible to expect precipitation of rain that meets the conditions. Apply the ground survey method, or apply the ground survey method of the present invention by spraying the liquid 9 using a water truck 8 or the like when the amount of the liquid 9 is not enough only by rain water due to rainfall. .

  Next, the state of penetration of the liquid into the ground is measured using a three-dimensional electrical exploration method (S3).

  In the ground survey method of the present invention, when there is a water channel in the ground of the survey target area 13, the water channel is detected as a location where the liquid 9 penetrates by projecting compared to the permeation distribution of the liquid 9 in the ground. The purpose is to do.

  Here, even if the liquid 9 protrudes in a short time compared with the surrounding ground in the water path and the liquid 9 penetrates, the penetration of the liquid 9 progresses in the surrounding ground with the passage of time, and the liquid 9 penetrates in the water path. It is thought to catch up. That is, even if the penetration of the liquid 9 temporarily protrudes in the water path as compared to the surrounding ground, it is considered that the liquid 9 is buried in the surrounding ground with the passage of time.

  Therefore, in order to detect the location where the liquid 9 protrudes and penetrates compared to the surrounding ground, the measurement of the penetration state of the liquid 9 into the ground using the three-dimensional electric exploration method is continuously performed at short time intervals. There is a need. For example, when the predicted fluid permeation speed of the water channel is about 10-2 cm / second, that is, 0.6 cm / min, measurement at intervals of several minutes is sufficient. Moreover, when the penetration rate is about 10-0 cm / second, that is, 60 cm / min, it is preferable to perform measurement at intervals shorter than 1 minute.

  Here, the conventional apparatus which performs the electrical survey of the ground by the three-dimensional electrical exploration method requires a great deal of time for one measurement, and cannot be measured at intervals of several minutes. Therefore, in the present invention, in order to apply the present invention, the penetration state of the liquid 9 into the ground using an original ground surveying apparatus capable of performing electrical survey of the ground using the three-dimensional electrical survey method in a short time. Measure.

  FIG. 4 shows a functional block diagram of a ground investigation device for conducting a three-dimensional electrical exploration of the ground according to the ground investigation method of the present invention. This ground survey device is composed of a control device 10, a transmission device 11, and a reception device 20.

  The control device 10 is, for example, a computer having a central processing unit 33 and controls operations of the transmission device 11 and the reception device 20.

  The transmitter 11 supplies current to one current electrode 1 a and current far electrode 2 selected from the measuring points 1.

  The transmission device 11 includes a terminal 11a and a terminal 11b, and can supply a current between these terminals at a constant period to adjust a current value and a transmission frequency of the current. A generator 5 is connected to the transmission device 11, and the transmission device 11 operates by receiving power supply from the generator 5.

  A current synchronized with a reference signal (which is a cosine wave) having an arbitrary frequency is amplified from a transmission device 11 by a power amplifier (power amplifier) and an insulation transformer 11c and transmitted between the terminal 11a and the terminal 11b. This reference signal is controlled by the central processing unit 33 of the control device 10. The terminal 11a is electrically connected to one current electrode 1a selected from the measuring points 1 via the receiving device 20, and the terminal 11b is connected to the current far electrode 2. The current value can be adjusted within a range of 1 mA to 400 mA, for example, and is appropriately selected according to measurement conditions and the like. However, the adjustable range is not limited to this, and a current less than 1 mA or more than 400 mA may be supplied.

  Moreover, in order to detect the location where the liquid 9 protrudes and penetrates compared to the surrounding ground, it is necessary to perform the three-dimensional electrical exploration of the ground in a short time as described above. Therefore, the transmitter 11 supplies a sine wave current between the current electrode 1a and the current far electrode 2 at a high transmission frequency. Specifically, for example, the transmission device 11 supplies a sine wave current at a transmission frequency in the range of 128 Hz to 5120 Hz. Although the optimal transmission frequency is selected based on the predicted fluid penetration rate, the higher the penetration rate, the greater the rate at which the specific resistance of the ground changes. It is preferable to measure with.

  The receiving device 20 switches the current electrode 1a of the measuring point 1 that supplies the sine wave current of the transmitting device 11, and also detects a potential signal between the potential electrode 1b of the measuring point 1 and the potential far electrode 3 (specifically, Is for receiving a potential difference) at the same time. Here, the potential electrode 1b is the electrode 1 installed at all the measurement points except the measurement point that works as the current electrode 1a.

  For example, when the total number of measurement points is 60, any one measurement point 1 is switched as the current electrode 1a, and potential signals generated in the ground due to the current flowing from the current electrode 1a are all the signals except the current electrode 1a. Simultaneously received as a potential signal at station 1 (59 points). The potential signal is measured as a potential difference between each electrode 1 and the potential far electrode 3.

  The receiving device 20 includes an electrode switching unit 21, a complex phase detection unit 22, and a sampling unit 23. Note that a battery 4 is connected to the receiving device 20, and the receiving device 20 operates by receiving power supplied from the battery 4.

  The electrode switching unit 21 of the receiving device 20 connects a lead wire that leads to one current electrode 1 a selected from the plurality of measuring points 1 to the terminal 11 a of the transmitting device 11. Normally, all the measuring points 1 are disconnected from the terminal 11a of the transmitter 11 and are electrically connected to the plurality of potential effective value integrating circuits 31 of the complex phase detector 22, respectively. The one measuring point 1 selected as 1a is disconnected from the potential effective value integration circuit 31 and is connected to the terminal 11a of the transmitter 11.

  The electrode switching unit 21 of the receiving device 20 includes a current detection circuit 24, a current switch circuit 25, a potential switch circuit 34, and an amplification and filter circuit 29.

  The current detection circuit 24 detects the current flowing from the current electrode 1a to the ground by the isolation amplifier 24a as a voltage value generated by the resistor 24b. The current detection circuit 24 is connected between the terminal 11 a of the transmission device 11 and the current switch circuit 25.

  The current switch circuit 25 controls connection and disconnection of the conductive wire leading to the current electrode 1 a of the measuring point 1.

  As shown in FIG. 5, the current switch circuit 25 includes a main line 27 connected to the electrode 1, a branch line 28 that connects the terminal 11 a of the transmission device 11 and each main line 27, and a middle part of each branch line 28. Provided with current relays 26-1, 26-2, 26-3,... (Hereinafter simply referred to as current relay 26 as appropriate). In the present embodiment, there are 60 main lines 27 corresponding to the number of measuring points 1 and 60 current relays 26.

  The potential switch circuit 34 controls the connection and disconnection of the conductive wires leading to all the measuring point 1 electrodes.

  As shown in FIG. 4, the potential switch circuit 34 includes a main line 27 connected to each electrode of the measuring point 1 and potential relays 35-1, 35-2, 35 provided in the middle of each main line 27. -3,... (Hereinafter simply referred to as potential relay 35 as appropriate). In this embodiment, 60 main lines 27 and 60 potential relays 35 are provided corresponding to the number of measuring points 1.

  Normally, the main line 27 leading to the first measuring point 1 electrode is connected to the first potential relay 35-1, and the main line 27 leading to the second measuring point 1 electrode is connected to the second potential relay 35-2. Similarly, the main line 27 leading to the electrode of the third station 1 is connected to the third potential relay 35-3, and further the main line 27 leading to the electrode of the 60th station 1 is connected to the 60th potential relay 35-. Connected to each 60.

  Here, each current relay 26 is normally in a disconnected state, and is selectively operated. Each potential relay 35 is normally in a conductive state and is selectively cut off. For example, when all the current relays 26 are in a disconnected state and the first measuring point 1 is made to conduct to the terminal 11a as the current electrode 1a, it is provided on the branch line 28 connected to the first main line 27. The current relay 26-1 is turned on. At the same time, the potential relay 35-1 connected to the first main line 27 is disconnected (the state shown in FIG. 4). That is, when one of the current relay 26 and the potential relay 35 on the same main line 27 is in a conductive state, the other is always in a disconnected state. When the second measuring point 1 is connected to the terminal 11a as the current electrode 1a, the current relay 26-1 provided on the branch line 28 connected to the first main line 27 is disconnected and The potential relay 35-1 connected to the first main line 27 is turned on, the current relay 26-2 provided on the branch line 28 connected to the second main line 27 is turned on, and The potential relay 35-2 connected to the second main line 27 is disconnected. The same applies to the case where the third to 60th measuring points 1 are connected to the terminal 11a as the current electrode 1a.

  Switching operation between disconnection and connection of each current relay 26 and each potential relay 35 is controlled by a central processing unit 33 of the control device 10.

  The amplification and filter circuit 29 selects and amplifies one of the amplification levels 0, 20, and 40 dB (0, 10, 100 times) with respect to the potential signal received at each electrode installed at the measuring point 1. At the same time, the level of the commercial frequency band (50 to 60 Hz) that becomes noise in the filter circuit (high-pass filter) is reduced to -6 dB (1/2 times). In addition, the phase shift by this filter circuit hardly arises.

  The complex phase detector 22 includes a set of current effective value integration circuits 30 connected to the current detection circuit 24 and 60 sets of potential effective value integration circuits 31 connected to the amplification and filter circuits 29, respectively. With.

  The current effective value integration circuit 30 performs the same type of processing as the Fourier transform normally performed by a computer on the digitized waveform data in this analog system, and is converted into a voltage value by the current detection circuit 24. The effective value of the current signal is detected.

  The 60 sets of potential effective value integration circuits 31 detect the effective value of the received potential signal as a potential difference between each electrode of the measuring point 1 and the potential far electrode 3 in the same manner as described above. .

  FIG. 6 shows a configuration diagram of the effective value integration circuit 31 for potential. The configuration of the current effective value integration circuit 30 is the same. The input signal (current signal or potential signal) is subjected to gain control using a reference signal transmitted from the central processing unit 33 of the control device 10 corresponding to the set frequency, that is, a cosine wave and a sine wave. That is, the input signal is branched and input to the cos wave gain control circuit 41a and the sine wave gain control circuit 41b. Of these two reference signals, the cosine wave is synchronized with the transmission current. Next, the output signals whose gains are controlled by the control circuits 41a and 41b are input to the cos integration circuit 42a and the sin integration circuit 42b, respectively, and stored as integral values (cos conversion component and sin conversion component) for T seconds. In these integral values, only the signal wave having the same frequency as the transmission frequency increases with time, and the signal value or noise of other frequencies becomes zero due to mathematical orthogonality.

  The sampling unit 23 includes an A / D converter 32.

  The A / D converter 32 receives signals from one set of current effective value integration circuits 30 and 60 sets of effective value integration circuits 31 for potentials, and inputs to each of the cos integration circuit 42a and the sin integration circuit 42b. The accumulated integral values (that is, the cos conversion component and the sin conversion component) are sequentially scanned and converted into digital data and output.

  The digital data output from the A / D converter 32 is input to the central processing unit 33 of the control device 10.

  The cosine transform component and sin transform component transferred to the control device 10 are normalized by the integration time T, and the amplitude and phase difference are calculated by computer processing according to the following steps. First, the signal is expressed by Equation 1.

Here, A: signal, R: amplitude, φ: phase, ω: angular frequency, t: time.

  The conversion of Expression 2 is performed as the cosine wave gain control, and the conversion of Expression 3 is performed as the sine wave gain control.

  By dividing Equation 2 and Equation 3 by the integration time T, the cos conversion component becomes as shown in Equation 4, and the sin conversion component becomes as shown in Equation 5.

  Therefore, the amplitude R is as shown in Equation 6, and the phase difference φ is as shown in Equation 7.

  Further, the central processing unit 33 sends reference signals to the transmission device 11 and the reception device 20. That is, the transmitter 11 transmits a current synchronized with this signal to the ground. In the current value and potential value effective value integration circuits 30 and 31 of the receiving device 20, cosine conversion synchronized with this signal and sin conversion processing in which the phase is shifted by 90 degrees are performed on the input signal. Further, the central processing unit 33 controls the operation of the current relay 26 that is the transmission relay of the electrode switching unit 21 and the potential relay 35 that is the reception relay.

  Next, a method for electrical exploration of the ground using this ground survey device will be described.

  This device is dedicated to exploration based on the bipolar method. Electrodes are installed at measurement point intervals corresponding to the scale and depth of the object to be searched and at measurement point positions in the investigation area, and are connected to the connection terminals of each electrode and the receiving device. For example, when it is predicted that a 1 m-scale exploration target is at a depth of about 5 m, it is necessary that the interval between the measurement points is within 1 m and the measurement line length is 25 m or more. In addition, the far electrode for current 2 and the far electrode for potential 3 are installed at two points separated from each other in the opposite direction from the investigation area (more than 5 times the long side in the case of a rectangle). Connect with. For example, as shown in FIG. 2, when the survey area is 24 m × 4 m, it is necessary to install a far electrode at a point 100 m or more away from the center position.

  Next, in the measurement by the bipolar method, the potential is measured at all electrodes (59 points) except for the current electrode 1a with respect to an arbitrary current electrode 1a. Therefore, when the total number of measurement points is 60, the number of combinations of all measurement data is 60 × 59 = 3540. Here, in the case of measuring the change in specific resistance accompanying the movement of fluid in the ground, the apparent specific resistance obtained by multiplying the obtained amplitude by a coefficient determined by the electrode arrangement is necessary information. If a non-polarized electrode is used as a measuring point, it is possible to perform the electric exploration IP method for measuring the charging effect of the ground with this apparatus, and in this case, information on the phase difference is also required.

  Therefore, according to the ground survey device configured as described above, the electrode arrangement is limited to the bipolar method, and the electrode switching operation is limited to only the current electrode by incorporating the receiving circuits for all the measuring points, so that the electronic circuit Can be greatly simplified. Thereby, it becomes possible to perform an electrical survey of the ground in a short time.

  That is, it is only necessary to perform a switching operation for bringing only one arbitrary measurement point into a conductive state from all the measurement point electrodes, and only the integration values in the cos integration circuit 42a and the sin integration circuit 42b of each reception channel are transferred to the control device 10. Therefore, since the waveform data is not digitized, a wide dynamic range is not necessary. Therefore, the receiving electrode switching operation and the amplification degree switching operation are not required, and the measurement time can be greatly shortened.

As a specific example, the measurement time is compared with the case where an electric exploration is performed using a conventional ground electric exploration device according to the following conditions. An example of the conventional device is an electric exploration device described in Japanese Patent Application No. 2004-372116. This device is designed to transfer the digitized received waveform itself and perform a Fourier transform process etc. in the control device to obtain the amplitude and phase difference.
i) Exploration method: Quadrupole method
ii) Number of received channels: 4
iii) Number of measurement points: 60 positions
iv) Transmission frequency: 2.5 Hz (that is, the transmission cycle is 0.4 seconds)
v) Transmission time: 4 seconds (however, 10 waves)
vi) Transfer time to controller: 20 seconds

  Assuming the above conditions, if the potential of 1200 electrode combinations is measured with 4 stacking times, {4 seconds (transmission time) × 4 (stacking number) +20 seconds (transfer time)} × 1200 (number of combinations) ÷ 4 (Number of channels) = 10800 seconds = 3 hours.

  On the other hand, the conditions of the ground investigation device used in the present invention are as follows.

i) Exploration method: Bipolar method
ii) Number of measurement points: 60 positions
iii) Transmission frequency: 1000 Hz (that is, the transmission cycle is 0.001 second)
iv) Transmission time: 0.01 seconds (however, 10 waves)
v) Transfer time to controller: 1 second

  As for the transfer time to the control device, in the case of the conventional device, if the number of data per waveform in the digital data of one transmission waveform and four reception waveforms is 512, the number of data to be transferred is 512 × 5 = In contrast to 2560, in the case of the apparatus used in the present invention, 60 sets of potential integration values and 1 set of current integration values, and the number of data to be transferred is 61 × 2 = 122. It is set based on 20: 1.

  Assuming the above conditions, when the potentials of the total number of combinations 60 × 59 = 3540 by the bipolar method are measured with 4 stacking times, {0.01 seconds (transmission time) × 4 (stacking number) +1 second ( Transfer time)} × 60 (transmission location) ≈60 seconds = 1 minute measurement time. That is, substantially only the transfer time to the control device is required. Since this apparatus is three times the number of data acquisitions in calculation, theoretically, the high speed performance of 180 × 3 = 540 times that of the conventional apparatus can be achieved.

  Next, the ground state is evaluated using the result of the three-dimensional electrical exploration obtained in the process of S3 (S4), and it is determined whether or not to end the measurement based on the state of liquid penetration into the ground. (S5).

  In the process of S2, the liquid 9 is sprayed on the ground surface 7 of the investigation target area 13 and penetrates into the ground. Then, when there is a water channel in the ground, the penetration speed of the liquid 9 becomes faster in the water channel than in the surrounding ground, so that the transport of the earth and sand in the ground from the result of the three-dimensional electric exploration in the processing of S3. The presence / absence of a water path as a route is determined.

  That is, as shown in FIG. 7, when the water channel 14 is present in the ground 6, the liquid 9 sprayed on the ground surface 7 is in the water channel 14 at a speed higher than the permeation rate in the surrounding ground 6. Flow. Accordingly, the liquid 9 in the water channel 14, the liquid 9 that flows in the water channel 14 and wets the wall of the water channel 14, or the liquid 9 that gradually permeates into the ground 6 from the wall of the water channel 14. Since it protrudes and penetrates from the liquid 9 penetrating into the surrounding ground 6 as a broken line (denoted by a reference numeral 16 in FIG. 7B), the transport route of earth and sand in the ground from the result of the three-dimensional electric exploration of the processing of S3. The presence or absence of a water path is determined.

  Specifically, as shown in FIG. 8, when the water channel 14 exists in the deep part of the ground 6, when the liquid 9 is sprayed on the ground surface 7, the influence of the water channel 14 near the ground surface 7. The liquid 9 permeates into the ground 6 gradually and uniformly over the entire survey target area 13 without receiving. And as the spraying of the liquid 9 is repeated or it continues to rain, the penetration of the liquid 9 proceeds toward the deep part of the ground 6.

  For example, as shown in FIG. 8 (B), in the first measurement after the first spraying of the liquid 9 or when a slight time has passed since the start of rainfall, the permeation distribution of the sprayed liquid or the rainwater 9 is the ground surface. 7 is a shallow range (infiltration front 17a in FIG. 8B), and the result obtained by the electric exploration of the ground 6 also shows that the liquid 9 penetrates into the shallow range from the ground surface 7. Then, as the number of sprays of the liquid 9 is increased or as the rainfall continues, the result of the electrical survey of the ground 6 that is sequentially performed shows that the liquid 9 gradually permeates toward the deep part of the ground 6 ( Penetration fronts 17b and 17c in FIG. 8B).

  When the penetration front 17d of the liquid 9 into the ground 6 reaches the end of the water channel 14 existing in the ground 6, the permeability of the liquid 9 is higher in the water channel 14 than in the surrounding ground 6. Therefore, the liquid 9 permeates through the water channel 14 faster than the average permeation distribution of the liquid 9 in the surrounding ground 6. Therefore, the result obtained by the electric exploration of the ground 6 also shows a state in which the liquid 9 is infiltrated by protruding from the penetration front 17 d of the liquid 9.

  That is, as shown in FIG. 9, the liquid 9 that has penetrated from the ground surface 7 penetrates the ground 6 faster than the penetration of the liquid 9 around the water channel 14 and in the surrounding ground 6, that is, protrudes from the surrounding penetration distribution. The aspect of doing this will be revealed by electric exploration. As a result of this electric exploration, the presence of the water path 14 in the ground 6 is detected, and it is determined that there is a risk of ground collapse as an evaluation of the state of the ground 6.

  Then, while conducting the electrical exploration of the ground 6 while penetrating the liquid 9 into the ground 6 and repeatedly evaluating the ground state based on the result, the liquid 9 is grounded to the originally planned depth as a process of S5. If it is determined that the measurement of the state of penetration of the liquid 9 is completed by penetrating into the inside (S5; Yes), the ground survey is terminated (S6).

  In addition, although the above-mentioned form is an example of the suitable form of this invention, it is not limited to this, A various deformation | transformation implementation is possible in the range which does not deviate from the summary of this invention. For example, the ground survey device according to the present embodiment is configured as a device that can handle up to 60 measurement points, but in principle, it can handle an infinite number of measurement points by sequentially adding 60-channel expansion devices. It is possible. For example, when three expansion devices are added, it is possible to measure up to 240 measurement points. In this case, the measurement time is four times that in the case of 60 channels of the present embodiment, that is, 1 minute × 240/60 = 4 minutes.

  Further, in the present embodiment, an example has been described on the assumption that the electrical exploration of the ground 6 while the liquid 9 is infiltrated into the ground 6 and the evaluation of the ground state based on the result are repeatedly performed. This is not sufficient, and it is sufficient as ground investigation because it is confirmed that the liquid 9 has penetrated to the initially planned exploration depth by the first electric exploration of the ground 6 or the presence of the water path is confirmed. If it is determined, it is not necessary to repeat the electrical exploration of the ground 6 and the evaluation of the ground state.

It is a flowchart explaining an example of embodiment of the ground investigation method of this invention. It is a figure explaining the expansion | deployment of the electrode of embodiment. It is a figure explaining dispersion | spreading of the liquid by the water truck of embodiment. It is a functional block diagram of the ground investigation apparatus of an embodiment. It is a functional block diagram of a switch circuit of the ground investigation device of an embodiment. It is a functional block diagram of the effective value integration circuit of the ground investigation device of an embodiment. It is a figure explaining the osmosis | permeation of the liquid in the water path in the ground. (A) is a figure which shows the water path which exists in the ground. (B) is a figure explaining the penetration | infiltration of the liquid centering on the water path in the ground. It is a figure explaining penetration | infiltration of the liquid in case a water path exists in the ground. (A) is a figure which shows the penetration | infiltration of the liquid which penetrates into the ground and the ground which exists in the ground. (B) is a figure explaining penetration of the liquid into the ground and penetration of the liquid into the water channel. It is a figure explaining the aspect which a liquid osmose | permeates along the water path in the ground. It is a figure explaining the ground depression occurrence mechanism considered conventionally. (A) is a figure explaining the state where the ground is excavated in a cross section larger than an actual tunnel cross section. (B) is a figure explaining that a ground depression occurs when the space | gap left on the tunnel back surface collapses. It is a figure explaining the penetration | infiltration of the liquid in a ground, and formation of a water channel and a cavity. (A) is a figure explaining the condition where the liquid permeates into the ground while selectively flowing through the weak points of the ground. (B) is a figure explaining the condition where a water path and a cavity are formed in the ground.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrode 11 Transmitter 25 Current switch circuit 26 Current relay 29 Amplification and filter circuit 31 Potential effective value integration circuit 34 Potential switch circuit 35 Potential relay

Claims (1)

The step of infiltrating the liquid from the ground surface into the ground and the step of performing the three-dimensional electric exploration of the ground are repeated once or twice or more, and protruded in comparison with the infiltration distribution of the liquid into the ground. A ground investigation method characterized by identifying a place of danger of subsidence before a cavity is formed by detecting a place where liquid penetrates deeper .