JP4900615B2 - Ground failure / collapse prediction method - Google Patents

Description

  The present invention relates to a technique for predicting the occurrence of ground destruction and collapse phenomena.

  To avoid dangers due to slopes due to embankments, cuts, etc., or ground destruction or collapse (landslides, rock collapses, slope failures, rock falls, etc.) in areas where stratification is expected to be unstable due to weathering, etc. Therefore, it is important to accurately grasp whether or not a precursory phenomenon leading to ground destruction or collapse has occurred before actual ground destruction or collapse occurs. Conventionally, in such ground failure / collapse prediction, attempts have been made to grasp the precursors of ground failure / collapse by observing minute electrical changes in the ground.

  Of these, for example, the method of measuring the displacement and strain of the ground on unstable slopes and trying to predict collapse is suitable for predicting landslides with slow fluctuations, but rock collapse is very small. Since collapse occurs instantaneously due to displacement and strain, it is extremely difficult to predict the collapse by measuring the displacement and strain of the ground.

  In addition, AE (Acoustic Emission), which is an acoustic signal generated when the ground is destroyed, is originally used for prediction of fatigue failure of metallic materials because AE has been used for prediction of uniform materials. Although it is effective for fracture prediction, its applicability to natural and composite materials such as the ground is low. In addition, since AE measures a considerable high-frequency component in ground vibration, propagation attenuation of vibration in the ground is very large, and measurement in a wide range is impossible. Therefore, AE is effective for measuring the just point where the fracture / collapse position is estimated with high accuracy, but it is difficult to estimate the fracture / collapse position in the ground at present. Moreover, if the destruction / collapse position can be estimated, effective countermeasures can be taken. Therefore, taking into account the risk of disaster occurrence, it is wise to take countermeasures in advance rather than predicting destruction / collapse. . For this reason, it can be said that the development of a technique that can estimate the position and scale of the ground is expected.

  In addition, the VAN method developed in Greece, which measures the potential change of the ground and uses it for earthquake prediction, takes advantage of the characteristics that electromagnetic waves with low attenuation in the ground are advantageous for measurement over a wide area, Attempts have been made to identify location and scale. Therefore, it is suggested that it is possible to identify the position and scale of ground collapse by observing small potential changes in the ground.

  On the other hand, since it is difficult to measure the absolute potential by observing the ground potential, the difference (potential difference) from the common cathode (reference electrode) placed at a certain point is observed. The self-potential method (SP method, a kind of electrical exploration), which is an investigation method used for heat source exploration in deep underground metal deposits and geothermal areas, similarly measures a wide range of ground potential distribution based on the reference electrode, The underground state is grasped from the distribution shape.

As a method of removing noise due to external factors such as rainfall from observation values in ground potential observation, electrodes are placed far from the target point or at different conditions, and this line is used as a noise line to remove noise. Attempts have been made (see, for example, Patent Document 1 below), however, in the potential observation of the ground, it is necessary to place a common cathode as described above. For example, an electrode is installed at a distance of several km from the observation target area. It is currently difficult to do in practice. On the other hand, there may be a method to remove the noise specific to each observation point from the data of multiple different observation points, but it is not guaranteed that the individual external factors received at each point are the same. Therefore, this method is also not realistic.
Japanese Patent No. 3803470

  The present invention has been made in view of the above-described problems, and its technical problem is to remove potential changes due to external factors from ground potential difference data in order to improve the reliability of ground fracture / collapse prediction. An object of the present invention is to provide a method for accurately grasping a potential change due to an internal factor.

  As a means for effectively solving the above technical problem, the ground fracture / collapse prediction method according to the present invention measures a potential difference with a plurality of measurement lines connecting electrodes installed on the ground, The potential share is obtained by dividing the potential difference data by the sum of the potential difference data from each survey line, and the change in the potential share is evaluated as a precursor change due to internal factors related to ground destruction and collapse. Is.

  In the above configuration, preferably, each survey line is connected to a plurality of electrodes installed on the ground, which are expected to be unstable or unstable, with an electrode installed on the ground in the stable region as a common cathode. .

  The present invention seeks to detect the precursors of destruction phenomena (rock collapse, landslide, rock fall, slope failure, etc.) by minute electrical changes in the ground, and in this type of technique, rainfall, snowfall, temperature, Unless changes in potential due to meteorological changes such as humidity and external factors such as freezing and thawing of water in the ground are not removed, potential changes due to ground destruction / collapse (internal factors) cannot be accurately evaluated. . This is because the potential change caused by the destruction of the ground is very small, only a few mV to several hundred mV, while the potential change during the rain is large, so the ground breaks down during the rain. In this case, the potential change caused by it is buried in the potential change caused by rainfall, and the pattern of potential change due to internal factors is also a pattern that changes with a substantially constant gradient over a long period of time or changes periodically. This is because there are various patterns such as a pattern that changes and a pattern that changes abruptly, so it is impossible to grasp a precursor phenomenon such as a microfracture of the ground only by the measured potential difference data.

  Also, even in laboratory experiments using ground samples, the ground samples are inherently affected by many electromagnetic waves generated from devices that use electricity as a power source, such as electric trains that pass nearby, electrical equipment in factories and homes, etc. A change in potential due to external factors unrelated to the destruction of the film is also observed.

  However, since the external factors as described above are equally affected by individual points (measurements) in the observation target region, the influence is included as a multiplication in the potential difference data measured at each survey line. . Therefore, the present invention pays attention to this point, calculates the potential sharing rate by canceling the external factor by dividing the individual potential difference data by the sum of the potential difference data from each survey line, and uses it as a change index of the internal factor. It captures.

  According to the ground fracture / collapse prediction method according to the present invention, potential fluctuations due to external factors are removed from a plurality of measured potential difference data, and only the potential sharing rate due to the precursory phenomenon of ground fracture / collapse is extracted. Therefore, the prediction accuracy of ground destruction / collapse can be improved.

  Hereinafter, a ground fracture / collapse prediction method according to the present invention will be described with reference to the drawings. First, FIG. 1 is an explanatory diagram schematically showing a preferred embodiment of the ground fracture / collapse prediction method according to the present invention together with an example of a planar arrangement of electrodes, and FIG. 2 schematically shows an example of a vertical arrangement of electrodes. It is explanatory drawing.

In FIG. 1, the upper side is the upper part of the ground slope, and the lower side is the lower part of the ground slope. Reference numeral G1 is a stable region, G2 is expected to be unstable or unstable where landslides indicated by thick arrows are likely to occur. A region (hereinafter referred to as an unstable region). In this embodiment, the electrode ER ₀ is embedded at an arbitrary position in the stable region G1, and the electrodes ER ₁ to ER _n are embedded at a plurality of points in the unstable region G2, and the electrode ER ₀ is a multi-channel voltage. Connected in parallel to the cathode input terminals 11 _{1 to} 11 _n of the measuring instrument (for example, data logger) 1, and the electrodes ER _{1 to} ER _n are connected to the anode input terminals 12 _{1 to} 12 _n of the voltage measuring instrument 1, respectively. is doing.

The electrodes ER _{1 to} ER _n embedded in the unstable region G2 form a plurality of measurement lines using one electrode ER ₀ embedded in the stable region G1 as a common cathode. The potential difference between each of the electrodes ER _{1 to} ER _n on the side and the electrode ER ₀ on the cathode side is measured and recorded at a constant sampling period (for example, 10 seconds).

In FIG. 2, reference symbol GWL is a groundwater level, and reference symbol SF is a surface on which a landslide is likely to occur (hereinafter referred to as a slip surface), and corresponds to a boundary surface between the stable region G1 and the unstable region G2. 2 is a boring hole for embedding the electrodes P _1U , P _1L , P _2U , and P _2L . Of these, the upper electrodes P _1U and P _2U are located in the unstable region G2 above the slip surface SF, and the lower electrodes P _1L and P _2L are located in the stable region G1 below the slip surface SF. Yes. The electrodes P _1U , P _2U , P _1L , and P _2L were installed below the groundwater level GWL in order to eliminate the influence of rain.

Then, the electrode ER ₀ embedded in the stable region G1 is used as a common cathode, and connected in parallel to the cathode input terminals 21 _{1 to} 21 ₄ of the multi-channel voltage measuring device (for example, data logger) 2, and the electrodes P _1U and P _1L are connected. , P _2U , P _2L are connected to the anode input terminals 22 _{1 to} 22 ₄ of the voltage measuring instrument 2, respectively.

Here, the potential difference measured on a certain line is Ps _i , of which Pt _{i is} the potential change due to internal factors such as the destruction of the ground, Pn _{i is the} unknown unknown noise due to the electrode state, etc. Assuming that the change in potential due to external factors such as change is Pc, the inventors' research has revealed that the following equation is established.
Ps _i ≒ (Pt _i + Pn _i ) × Pc

Further, the sum (or sum) of potential differences measured on each survey line (between electrodes ER ₀ and ER ₁ , between electrodes ER ₀ and ER ₂ , between electrodes ER ₀ and ER ₃ , and so on) is ΣPs, Of the potential difference measured on each line, let Pt be the potential change due to internal factors, and Pn be the unknown unknown noise caused by the state of the individual electrodes.
ΣPs ≒ Σ (Pt + Pn) × Pc
Therefore, by dividing the individual potential difference Psi by ΣPs, the potential sharing ratio Ri in which the potential change Pc due to an external factor is canceled can be obtained individually as in the following equation.
R _i = Ps _i / ΣPs = (Pt _i + Pn _i ) × Pc / Σ (Pt + Pn) × Pc
= (Pt _i + Pn _i ) / Σ (Pt + Pn)

  That is, the potential sharing ratio Ri is the one in which the potential change Pc due to external factors such as weather changes has been removed, and the potential at the place where the ground collapse / destruction changes changes prior to the displacement, so the destruction of the ground It can be used as an index for grasping changes in internal factors caused by phenomena. Further, since the sum ΣPs of potential differences is data in which the influence of external factors on the observation target region is emphasized, it can be used as an index representing the difference in the degree of external factors. In addition, as a result of analyzing various potential difference data observed by the inventors in the field, it was found that the change in potential difference is sensitive to the presence or absence of precipitation, but is not proportional to precipitation.

  Note that ΣPs is the sum of the measured values at two or more locations, and does not necessarily have to be the sum of the measured values at each survey line in the observation target area. At least two locations installed at locations subject to the same external factors ( It is possible to calculate if there is a set of observation data, and calculate the ratio of potential difference with internal change in the moving clot, in the immovable clot, or in the area across the immovable clot and the moving clot. The phenomenon can be grasped.

  If two electrodes have the same electrode installation status, shape, material, etc., and are considered to be ideal situations subject to the same external factors, the potential sharing rate at each electrode will share the potential equally. So it becomes 0.5. Similarly, in the case of 4 places, it is 0.25. Therefore, when an electric potential change due to an internal factor due to ground destruction or the like is observed at the electrode position, the electric potential sharing rate at that point changes to the positive side or the negative side. Therefore, it is effective to pay attention to the change of the potential sharing rate in order to grasp the precursory phenomenon accompanying the destruction of the ground.

  In addition, since it is difficult to determine the potential difference generated due to the breakdown in the present situation, the amount of change is various, and the polarity of the change can be both positive and negative.

Next, FIG. 3 is explanatory drawing which shows the laboratory test implemented in order to verify the destruction and collapse prediction method of the ground which concerns on this invention. In this test, a specimen TP made of cylindrical rock is installed between a pair of pressers 101, 101 facing each other in the vertical direction in the uniaxial compression tester 100, and electrodes ER ₁₁ , ER are placed at both upper and lower ends of the specimen TP. ₁₂ , and the pressers 101 and 101 and the electrodes ER ₁₁ and ER ₁₂ were electrically insulated from each other by an insulator 102. Further, one electrode _{ER 11,} the sampling period is connected to the anode input terminal ₃₂ 1, 32 ₂ in the data logger 3 0.1 second, the other electrode _{ER 12} includes a cathode input terminal 31 ₁ in the data logger 3 connected to the anode input terminal 32 _3, in the course of up to cathode input terminals ₃₁ 2, 31 ₃ is grounded, is destroyed by gradually adding a compressive load specimens TP between pressure members 101 and 101, the upper electrode ER ₁₁ and the potential difference P _U −P _L generated between the lower electrode ER ₁₂ and input to the ch 1, the potential difference P _U −G generated between the upper electrode ER ₁₁ and the ground GND and input to the ch 2, and the lower electrode ER ₁₂ A change in the potential difference P _L -G generated between the ground GND and input to ch3 was measured.

FIG. 4 is a diagram showing the test results. In FIG. 4, R _U and R _L are potential sharing ratios obtained by dividing the potential difference data P _U -G and P _L -G by their sums, that is, obtained as follows.
R _U = P _U −G / Σ (P _U −G + P _L −G)
R _L = P _L −G / Σ (P _U −G + P _L −G)

When the compressive load on the specimen TP is increased, the specimen TP will eventually be destroyed at the time indicated by the broken line in FIG. 4, but before that (time 0:35 to 0:42) So it can be seen that the potential distribution ratio is 0.5 reversed relationship of R _L which was a R _U and negative values were positive value as a reference, has collapsed balance before. This change is considered to be due to a potential change accompanying the start of microfracture of the internal tissue of the specimen TP.

Next, FIG. 5 is a plan view of an electrode showing an embodiment in which the ground fracture / collapse prediction method according to the present invention is used for observation at a tunnel excavation site, and FIG. 6 is a sectional view taken along line VI-VI in FIG. is there. 5 and 6, reference numeral TN is a tunnel to be excavated, reference numeral G3 is a region made of a foundation made of peridotite, etc., G4 is a region that is likely to become unstable due to excavation of tunnel TN, clay, sand, It consists of unconsolidated sediments such as cliffs. In this embodiment, an electrode ER ₂₀ located outside the range of influence of loosening due to tunnel excavation is buried and connected to the input terminal on the cathode side of a data logger (not shown), and directly above the tunnel TN in the excavation direction. Electrodes ER _{21 to} ER ₂₈ were respectively embedded so as to be arranged in a direction perpendicular to each other and connected to the input terminal on the anode side of the data logger.

7 shows potential measurement data of the electrodes ER ₂₁ to ER ₂₃ having the electrode ER ₂₀ at the tunnel excavation site shown in FIGS. 5 and 6 as a common cathode, and the potential sharing rate calculated based on the measurement data over time. It is a diagram which shows the relationship between a change and rainfall. In this case, in the potential measurement data of the electrodes ER _{21 to} ER ₂₃ , the influence appears as a change to the negative side at the time of rain, but the change due to the rain is almost canceled at the lower potential sharing rate. As indicated by the oval in the figure, it can be seen that the potential change due to the influence of tunnel excavation, which is an internal factor, is emphasized.

8 is calculated based on the sum of the potential measurement data of the electrodes ER ₂₁ to ER ₂₈ having the electrode ER ₂₀ as the common cathode at the tunnel excavation site shown in FIGS. 5 and 6 and each potential measurement data. It is a diagram which shows a time-dependent change of the electric potential sharing rate of each electrode. In this case, the sum of the potential differences (ΣER _{21 to} ER ₂₈ ) is exaggerated by the influence of rainfall, but it can be seen that the influence of the rain is almost cancelled on the potential sharing rate at each electrode.

Next, FIG. 9 is a plan view of electrodes showing an embodiment in which the ground fracture / collapse prediction method according to the present invention is used for landslide observation. In FIG. 9, reference numeral G5 is a stable area of a natural ground, G6 (range surrounded by a thick line) is a landslide area which is an unstable area, A is a river, and B is a road. In this embodiment, an electrode ER ₃₀ is embedded in the stable region G5, and this is connected to the input terminal on the cathode side of a data logger (not shown). A plurality of electrodes ER ₃₁ , ER ₃₂ , ER ₃₆ A plurality of electrodes ER _{33 to} ER ₃₅ were embedded in the ground G6 and connected to the input terminal on the anode side of the data logger. P ₃₁ and P ₃₂ are pipe strain gauges that detect a landslide in the depth direction from a change in the electrical resistance of the metal wire.

FIG. 10 shows the potential sharing rate calculated based on the potential measurement data of the electrodes ER ₃₁ to ER ₃₆ having the electrode ER ₃₀ shown in FIG. 9 as a common cathode, and the strain measurement of the pipe strain gauges P ₃₁ and P ₃₂ . It is a diagram which shows the relationship between the time-dependent change of data, and the amount of rainfall and snow cover. According to FIG. 10, it can be seen that a change appears in the potential sharing ratio prior to the change in strain data (occurrence of landslide deformation) after snow and rain.

FIG. 11 shows the potential sharing ratio calculated based on the potential measurement data of the electrode ER ₃₁ installed in the stable region G5 and the electrode ER ₃₃ installed in the landslide G6, with the electrode ER ₃₀ shown in FIG. 9 as a common cathode. FIG. 6 is a diagram showing a change with time of strain measurement data of borehole pipe strain gauges P ₃₁ and P ₃₂ installed adjacent to the electrodes ER ₃₁ and ER ₃₃ . According to FIG. 11, it can be seen that the potential sharing ratio between the landslide area G6 and the stable area G5 is reversed prior to the change of the distortion data (occurrence of landslide deformation).

Figure 12 is a common cathode electrode _{ER 30} shown in FIG. 9, the stable region electrode _ER 31 installed in G5, _{ER 32} potential measurement data potential share rate calculated on the basis of the, adjacent to the electrode _{ER 31} is a diagram showing changes with time of the strain measurement data bowling downhole pipe strain gauge P ₃₂ which is installed in. According to FIG. 12, it can be seen that there is almost no variation in the potential sharing ratio between the electrodes ER ₃₁ and ER ₃₂ installed in the stable region G5.

It is explanatory drawing which shows schematically preferable embodiment of the fracture | rupture / collapse | decay prediction method of the ground which concerns on this invention with the example of plane arrangement | positioning of an electrode. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram schematically showing a preferred embodiment of a ground fracture / collapse prediction method according to the present invention together with an example of vertical arrangement of electrodes. It is explanatory drawing which shows the laboratory test implemented in order to verify the destruction and collapse prediction method of the ground which concerns on this invention. It is a diagram which shows the result of a laboratory test. It is a plane arrangement view of electrodes showing an example in which the ground fracture / collapse prediction method according to the present invention is used for observation at a tunnel excavation site. It is VI-VI sectional drawing in FIG. FIG. 7 is a diagram showing potential measurement data at the tunnel excavation site in FIGS. 5 and 6 and a relationship between a temporal change in potential sharing ratio calculated based on the measurement data and rainfall. FIG. 7 is a diagram showing a change over time in the potential sharing rate of each electrode calculated based on the total sum of potential measurement data at the tunnel excavation site in FIGS. 5 and 6 and each potential measurement data. It is a plane arrangement view of electrodes showing an example in which the ground destruction / collapse prediction method according to the present invention is used for observation of a landslide. FIG. 10 is a diagram showing a relationship between a temporal change in potential share rate and strain measurement data individually calculated in the observation of the landslide area in FIG. 9, a rainfall amount, and a snowfall amount. FIG. 10 is a diagram showing a temporal change in potential sharing ratio calculated based on potential measurement values at two electrodes in a stable region and a landslide region in FIG. 9 and strain measurement data at a position adjacent to the electrodes. FIG. 10 is a diagram showing the change over time of the potential share calculated based on the measured potential values of the two electrodes in the stable region in FIG. 9 and the strain measurement data at a position adjacent to the electrodes.

Claims (2)

  Measure the potential difference with multiple survey lines connected between the electrodes installed on the ground, and divide the potential difference data for each survey line by the sum of the potential difference data from each survey line to obtain the potential share rate. A method for predicting ground failure / collapse, characterized in that changes are evaluated as precursory changes due to internal factors related to ground fracture / collapse.   Each survey line is characterized in that the electrodes installed on the ground in the stable region are connected as a common cathode and a plurality of electrodes installed on the ground that are expected to be unstable or unstable, respectively. The ground failure / collapse prediction method according to claim 1.

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