Ground movement prediction method and ground movement prediction system

Abstract

To provide a ground deformation prediction method capable of suppressing occurrence of a deformation of a ground surface or the like by predicting a ground deformation after applying a load on the ground.SOLUTION: A method for predicting a ground deformation which occurs when a steel pipe is propelled includes: step S1 of arranging a detection device on a ground surface in an advance direction of the steel pipe; a step of vibrating the ground between a tip end of the steel pipe and the detection device; step S2 of measuring an elastic wave speed by the detection device when a vibration is generated; step S4 of obtaining an elastic wave speed ratio when comparing the elastic wave speed measured when the vibration is generated during excavating the ground with an elastic wave speed before the excavation; and step S7 of predicting the ground deformation after the measurement based on the elastic wave speed ratio.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and system for predicting ground deformation that occurs when element pipes are excavated. [Background technology]

[0002] There is a known tunnel construction method in which an outer shell with multiple parallel element pipes is installed first, as disclosed in Patent Document 1. In this construction method, by excavating the tunnel cross section in sections, it is possible to minimize subsidence of the ground surface even with very low earth cover, and so it is applied to construction work such as crossing under railway tracks.

[0003] On the other hand, when the load of excavating the ground to build a tunnel is applied, stress release occurs, which can cause deformation of the surrounding ground and the ground surface.In addition, when the load of injecting an improvement agent into the ground is applied, deformation such as heaving of the ground surface can occur.

[0004] In railways, track subsidence can disrupt train operations, so track measurements are taken in real time during excavation work, and track maintenance is carried out if problematic subsidence occurs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-68549 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-168087 Summary of the Invention [Problem to be solved by the invention]

[0006] However, with track measurements, measures can only be taken after track displacement has occurred. Therefore, in the event that track displacement that suddenly affects train operations is discovered, personnel must be constantly on hand to carry out emergency track maintenance, which tends to be more expensive than normal tunnel construction.

[0007] On the other hand, as disclosed in Patent Document 2, the ground conditions ahead of the tunnel face can be investigated using sound waves, radio waves, elastic waves, etc. to determine the current geological structure and the presence or absence of obstacles, but this does not allow for prediction of ground movement as excavation proceeds.

[0008] Therefore, the present invention aims to provide a method and system for predicting ground movement that can prevent deformation of the ground surface by predicting ground movement after a load is applied to the ground. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the method for predicting ground movement of the present invention is a method for predicting ground movement that occurs when an element pipe is excavated, and is characterized by comprising the steps of installing a detection device on the ground surface in the direction of travel of the element pipe, vibrating the ground between the tip of the element pipe and the detection device, measuring the elastic wave velocity at the time of excitation using the detection device, calculating the elastic wave velocity ratio by comparing the elastic wave velocity measured at the time of excitation during ground excavation with the elastic wave velocity before excavation, and predicting ground movement after the time of measurement from the elastic wave velocity ratio.

[0010] Here, the application of vibration can be performed by exciting the vicinity of the tip from inside the element pipe. Also, the prediction of ground deformation can be a predicted value of the elastic wave velocity ratio after the measurement, and the configuration can include a step of considering measures to suppress ground deformation when the predicted value falls below a predetermined threshold.

[0011] Furthermore, the invention of the ground movement prediction system is a ground movement prediction system for predicting ground movement after applying a load to the ground, characterized in that it comprises a measurement unit that measures elastic wave velocity when the ground is vibrated, a velocity ratio calculation unit that calculates an elastic wave velocity ratio by comparing the elastic wave velocity during loading measured by the measurement unit with the elastic wave velocity before loading, and a prediction unit that predicts the elastic wave velocity ratio after the measurement. Here, the system can also be configured to comprise a determination unit that determines the degree of influence of the ground movement based on the prediction result by the prediction unit. [Effects of the Invention]

[0012] The ground movement prediction method of the present invention, configured as described above, measures the elastic wave velocity at the time of excitation using a detector installed on the ground surface in the direction of travel of the element pipe that excavates the ground, and calculates the elastic wave velocity ratio by comparing the elastic wave velocity measured during excavation with the elastic wave velocity before excavation. Ground movement after the measurement is then predicted from this elastic wave velocity ratio.

[0013] In this way, not only can the current state of the ground be investigated, but ground deformation after load is applied to the ground can also be predicted from the elastic wave velocity ratio. This makes it possible to prevent problematic track displacement and other deformations of the ground surface by reviewing construction conditions in advance.

[0014] The invention of the ground movement prediction system also includes a velocity ratio calculation unit that calculates the elastic wave velocity ratio by comparing the elastic wave velocity under load measured by a measurement unit that measures the elastic wave velocity when the ground is vibrated with the elastic wave velocity before loading, and a prediction unit that predicts the elastic wave velocity ratio after the time of measurement.

[0015] For example, if it becomes possible to look at the prediction results from the prediction unit and predict in advance that significant ground movements will occur, it will be possible to consider and implement measures at an early stage to prevent deformation of the ground surface and other such phenomena. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a flowchart illustrating a processing flow of a method for predicting ground movement according to the present embodiment. [Figure 2] FIG. 1 is an explanatory diagram illustrating loads applied to the ground that may cause ground deformation. [Figure 3] FIG. 2 is an explanatory diagram illustrating the configuration of a detection device. [Figure 4] FIG. 1 is an explanatory diagram showing an overview of the jacking method for digging a steel pipe into the ground and the measurement of elastic wave velocity. [Figure 5] 1 is an explanatory diagram showing an overview of a ground movement prediction system according to an embodiment of the present invention; [Figure 6] FIG. 1 is an explanatory diagram showing an outline and results of a drop floor experiment. [Figure 7] FIG. 10 is an explanatory diagram showing assumptions for deriving a mathematical formula for setting a threshold value of an elastic wave velocity ratio. [Figure 8] FIG. 10 is an explanatory diagram comparing the experimental results of the drop floor experiment with the elastic wave velocity ratio calculated from a mathematical formula. [Figure 9] FIG. 1 is an explanatory diagram showing an outline of a verification experiment. [Figure 10] FIG. 1 is an explanatory diagram showing a schematic diagram of the progression of a landslide in a verification experiment. [Figure 11] FIG. 1 is an explanatory diagram showing the relationship between landslides, ground surface subsidence, and elastic wave velocity ratio in a verification experiment. [Figure 12] 10 is a flowchart illustrating the processing flow of the ground movement prediction system of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a flowchart illustrating the processing flow of the method for predicting ground movement according to this embodiment, while Fig. 2 is an explanatory diagram illustrating loads applied to the ground that may cause ground movement.

[0018] As mentioned above, there is a known method for constructing a tunnel in which an outer shell with multiple parallel element pipes is installed first. Figure 2 shows an example of such a tunnel construction method in which the tunnel crosses under a railway track R on which trains run. This tunnel construction method is applied when the allowable amount of settlement on the ground surface formed by embankments or the like is extremely small.

[0019] For example, when constructing a tunnel with a generally rectangular cross section, a plurality of steel pipes 1, which are element pipes, are excavated first at a position that will become the outer shell of the tunnel. These steel pipes 1 are, for example, square steel pipes formed with a generally rectangular cross section, and by lining up and excavating a plurality of steel pipes 1, the ceiling, walls, and floor of the tunnel are constructed first.

[0020] When the steel pipe 1 is excavated, the ground is excavated to a cross-sectional area equivalent to the cross section of the steel pipe 1. This excavation is carried out carefully by manual excavation, auger excavation, cutter face excavation, etc., but it places a load on the ground which has some effect on the ground. In short, excavating the ground can cause loosening, which can cause the ground surface to collapse.

[0021] Furthermore, as shown on the right side of Figure 2, reinforcing the ground by injecting improvers such as cement milk or chemical solutions into the ground can also be an act that places a load on the ground that has some effect on the ground. In other words, when an improver is injected into the ground, it can cause cracks at the injection site, causing expansion and uplifting of the ground surface.

[0022] In the following, we will explain the act of applying a load to the ground by using the example of element pipe excavation work, in which the ground is excavated in front of the tip 11 of the steel pipe 1 and the steel pipe 1 is advanced toward the excavated cavity.

[0023] In the method for predicting ground movement of this embodiment, a detection device 2 is installed on the ground surface at least in the direction of travel of the steel pipe 1. The detection device 2 is a device that measures elastic waves such as P waves (longitudinal waves) and S waves (transverse waves) that propagate through the ground.

[0024] 3 is an explanatory diagram showing an example of the detection device 2. This detection device 2 is provided with a sensor 21 at the tip for measuring elastic waves propagating through the ground when the tip 11 of the steel pipe 1 excavating the ground is vibrated by hitting it with a hammer or the like.

[0025] The sensor 21 is formed by a piezoelectric element or the like. Piezoelectric elements have directionality, so that P waves or S waves are recorded depending on the incident direction. In this embodiment, the orientation of the piezoelectric element is adjusted so that P waves, which arrive quickly and are not easily absorbed by the steel pipe 1, can be measured.

[0026] The sensor 21 is attached to the tip of the main body 22 formed of a double pipe or the like, and is placed inside the ground. For example, the outer pipe of the main body 22 is inserted from the ballast on the ground surface beside the track R toward the ground, and after the outer pipe is buried to a predetermined depth, the inner pipe with the sensor 21 attached to the tip is inserted into the outer pipe, thereby placing the sensor 21 at a desired depth in the ground without damaging it.

[0027] In addition to the sensor 21, the detection device 2 is equipped with a GPS receiver 23 for acquiring three-dimensional position coordinates, a transceiver (not shown) for transmitting and receiving various data, and a battery 24 for operating these devices.

[0028] Figure 4 is an explanatory diagram showing an overview of the jacking method for driving a steel pipe 1 into the ground and the measurement of elastic wave velocity. As shown in this figure, the tip 11 of the steel pipe 1 driven into the ground, such as an embankment, is excited to vibrate the surrounding ground, and the pressure waveform of the elastic waves generated by this is measured by a detection device 2.

[0029] In short, the ground between the tip 11 of the steel pipe 1 and the detection device 2 is vibrated and converted into a voltage waveform by a piezoelectric element of a sensor 21 installed near the ground surface. In construction using the jacking method, excavation is carried out, for example, by digging about 20 to 30 cm of the ground and jacking the steel pipe 1, with one cycle consisting of this, and waveforms are recorded multiple times during each excavation cycle.

[0030] In detail, as shown on the left side of Figure 4, at the beginning of the excavation cycle after the completion of the previous cycle's thrust, vibrations are excited from inside the steel pipe 1 near the tip 11 in the pre-excavation state where the tip 11 is in close contact with the ground. This excitation causes the detector 2 to measure the elastic wave velocity V before excavation.

[0031] Next, as shown on the right side of Figure 4, the elastic wave velocity V' during excavation is measured by exciting vibrations near the tip 11 from inside the steel pipe 1 while the ground ahead of the tip 11 of the steel pipe 1 is being excavated. The elastic wave velocity V' measured at this time is affected by loosening of the ground that has occurred in the ground between the tip 11 of the steel pipe 1 and the detection device 2, and therefore a different value is measured, such as being lower than the elastic wave velocity V before excavation. Measurement of the elastic wave velocity V' during excavation is performed, for example, two to three times in one excavation cycle.

[0032] In the method for predicting ground movement in this embodiment, the elastic wave velocity ratio (V' / V) obtained by comparing the elastic wave velocity V' measured during excavation of the ground with the elastic wave velocity V before excavation is used to capture changes in elastic wave velocity, thereby detecting signs of ground movement due to loosening of the ground, etc.

[0033] Fig. 5 is an explanatory diagram showing an overview of the ground movement prediction system of this embodiment. The ground movement prediction system of this embodiment includes a measurement unit that measures the elastic wave velocity when the ground is vibrated, a velocity ratio calculation unit that calculates the elastic wave velocity ratio by comparing the elastic wave velocity during excavation measured by the measurement unit with the elastic wave velocity before excavation, a prediction unit that predicts the elastic wave velocity ratio after the measurement, and a determination unit that determines the degree of influence of ground movement based on the prediction result by the prediction unit.

[0034] The measurement unit corresponds to a detection device 2 that is installed on the ground surface in the direction of travel of the steel pipe 1. Multiple detection devices 2 can be installed on a plane, not just in the direction of travel of the steel pipe 1. The measurement data measured by the detection device 2 is transmitted wirelessly in real time to a terminal 3 such as a tablet. The terminal 3 may be a personal computer (PC), a laptop computer, a smartphone, etc.

[0035] The velocity ratio calculation unit, prediction unit, and judgment unit of the ground movement prediction system of this embodiment can be configured as part of terminal 3, or can be configured in combination with a computer installed in an office or the like separately from terminal 3.

[0036] While the steel pipe 1 is being excavated, the detection device 2 measures elastic waves when the tip 11 vibrates, and the terminal 3 calculates and monitors the elastic wave velocity ratio in real time based on the measurement data. Furthermore, the terminal 3 predicts how much further excavation will increase the likelihood of the ground surface collapsing.

[0037] In short, it will be possible to predict future ground deformation before track displacement occurs on Track R. To achieve this, it is necessary to clarify what physical quantities should be used to detect signs of ground deformation and what threshold values ​​should be set for the physical quantities to determine the signs.

[0038] Therefore, we first conducted a floor drop experiment simulating the excavation of a square steel pipe to determine the threshold value, and then verified the validity of the threshold value through an excavation experiment using an actual square steel pipe. Figure 6 is an explanatory diagram showing the outline and results of the floor drop experiment.

[0039] The drop-floor experiment involves constructing a model ground in a soil tank as shown on the right side of Figure 6, and lowering part of the bottom of the soil tank (the drop-floor) to reproduce the loosening of the surrounding ground caused by tunnel excavation. Here, a drop-floor experiment was carried out simulating the excavation of a square steel pipe, and the velocity of elastic waves passing through the loosened area directly above the drop-floor was measured.

[0040] The graph on the left side of Figure 6 shows the results of the floor drop experiment. The horizontal axis of this graph represents the drop distance (mm) of the floor drop, and the vertical axis represents the elastic wave velocity ratio (V' / V), which is the ratio of the elastic wave velocity V before drop to the elastic wave velocity V' during drop.

[0041] The results of this experiment showed that the elastic wave velocity ratio decreases as the drop in the floor (increased drop) and converges to a constant value when it reaches the drop of approximately 1 mm at which the soil in the loosened area begins to collapse. These experimental results show that it may be possible to detect signs of ground movement by checking whether the elastic wave velocity ratio falls below a certain threshold. It also became clear that this threshold for the elastic wave velocity ratio changes depending on the soil cover (1D is the excavation width (see Figure 7)).

[0042] Therefore, we investigated how to set the threshold value according to the excavation width and soil cover. This investigation was carried out by verifying the results of the drop-bed experiment using a simple model. Figure 7 is a diagram to explain the assumptions of the simple model.

[0043] As shown on the right side of Figure 7, just above the drop floor, we simply assume that there are only loosened areas and areas that maintain the initial stress state, and the elastic wave velocity in each area is v p1 ,v p2 In other words, the elastic wave velocity in the loosened region is v p1 The elastic wave velocity outside the loosened region is v p2 Let's say.

[0044] Then, assuming that the propagation path connecting the excitation point, which is the apex of the descending floor, and the receiver on the ground that measures the elastic wave velocity is a straight line, the elastic wave velocities V and V' before and after descent can be expressed by the following equation based on the relationship with the travel time (the time it takes for the elastic wave to arrive): V=v p2 (1) V'=(v p1 v p2 H) / (v p2 h+(Hh)v p1 ) (2) where V is the elastic wave velocity before descent, V' is the elastic wave velocity after descent, H is the soil cover, h is the height of the loosening, and v p1 is the elastic wave velocity in the relaxation region, v p2 denotes the elastic wave velocity outside the relaxed region.

[0045] From the above equations (1) and (2), the elastic wave velocity ratio V' / V before and after the drop is given by the following equation: V' / V=(v p1 H) / (v p2 h+(Hh)v p1 ) (3) where v p1 / v p2 Regarding v, we will organize the possible values ​​based on previous knowledge. Assuming that the changes in density and Poisson's ratio are secondary and can be ignored, v p1 / v p2 is proportional to the 1 / 2 power of the deformation coefficient of the ground. v p1 / v p2 =(E1 / E2) 1 / 2 (4) Here, E1 is the deformation coefficient of the ground within the loosened area, and E2 is the deformation coefficient of the ground outside the loosened area.

[0046] Furthermore, based on the dependence of the deformation modulus on the confining pressure, the relationship between the deformation modulus E and the confining pressure σ can be expressed as the following equation (5). E=A·σ n (5) Here, E is the deformation coefficient of the ground, σ is the confining pressure, A and n are coefficients, and the value of n is generally set to 0.5, but approaches 1 as the fine particle content increases.

[0047] Then, rearranging equations (3) to (5), we get equation (6). V' / V=((σ1 / σ2) n / 2 H) / (h+(Hh)(σ1 / σ2) n / 2 ) (6) Here, σ1 denotes the soil stress within the loosened region, and σ2 denotes the soil stress outside the loosened region.

[0048] The stress ratio σ1 / σ2 was measured in Terzaghi's experiment, and the soil stress ratio for a 4D soil cover is approximately 10% to 25%. Also, a method has been proposed to determine the loosening height h in more detail based on the ground conditions, but the loosening area when the earth pressure acting on the drop floor is constant is roughly 1D. Therefore, by setting the stress ratio σ1 / σ2 as a and substituting this into equation (6), we obtain the following equation (7). V' / V=(a n / 2 H) / (D+(HD)an / 2 ) (However, when H < D, then H = D) (7) Here, a is the soil stress ratio and ranges from 0.10 to 0.25, and D represents the excavation width.

[0049] Regarding this equation (7), the results of comparing the elastic wave velocity ratio V' / V with the experimental results of the drop table test are shown in Fig. 8. In the calculation using equation (7), since the soil sample used was silica sand, n = 0.5 was used, and for a, the results with a minimum of 0.10 and a maximum of 0.25 were shown. On the other hand, regarding the drop table test results (● plots), as described above, the values at a settlement of 1 mm were shown assuming that the excavation face becomes unstable. From this figure, it became clear that the drop table test results distribute with a similar tendency in the range where a of the formulated equation (7) is from 0.10 to 0.25.

[0050] From the above, it is inferred that equation (7) represents the lower limit value of the elastic wave velocity ratio for ensuring the stability of the excavation face, and it was found that the experimental results of the drop table test can be used as a method for calculating the threshold value when evaluating the stability of the excavation face. Note that the variable n in the equation can also be obtained from a triaxial compression test, but simply setting it to 0.5 will result in a value on the safe side.

[0051] Similarly, regarding the soil stress ratio a, setting it to 0.25 will result in a value on the safe side, so the following equation can be derived. V' / V=(0.25 1 / 4 H) / (h+(H - h)0.25 1 / 4 ) (However, when H < D, then H = D) (8) Based on the above, in this embodiment, the threshold value of the elastic wave velocity ratio is set by inputting the excavation width D and the overburden H into equation (8).

[0052] Subsequently, a verification experiment of the ground movement prediction method using the threshold value was conducted using an actual square steel pipe. Fig. 9 is an explanatory diagram showing the outline of the verification experiment. The square steel pipe used was a steel pipe with a square cross-section having a width of 1 m and a height of 1 m, and the overburden was set to 0.5 m.

[0053] Then, manual excavation was performed from the cutting edge of the square steel pipe buried in the ground, and the elastic wave velocity between the square steel pipe and the ground surface was measured sequentially. Figure 10 is an explanatory diagram that shows a schematic diagram of the progression of the landslide in the verification experiment.

[0054] In other words, as the excavation length increases, the collapse of the top of the excavation progresses, and the behavior was reproduced until the ground surface finally collapses. Meanwhile, when the threshold value of the elastic wave velocity ratio was calculated in advance, by substituting the conditions of this case (cover H = 0.5 m, excavation width D = 1 m) into equation (8), the threshold value of the elastic wave velocity ratio V' / V was obtained as 0.71.

[0055] Figure 11 is an explanatory diagram showing the relationship between landslides, ground surface subsidence, and elastic wave velocity ratio in the verification experiment. As can be seen from this diagram, the elastic wave velocity ratio before and after excavation behaved in a manner linked to the results of measuring ground surface subsidence using a high-sensitivity laser displacement meter. Furthermore, ground collapse began to be observed in the excavation cycle immediately after it fell below the threshold value (0.71), and ground surface subsidence also increased significantly in a short period of time. This confirmed that by measuring elastic waves in real time, it is possible to detect the onset of landslides immediately before they begin.

[0056] FIG. 12 is a flowchart illustrating the flow of processing in the ground movement prediction system of this embodiment. First, in step S21, in order to perform real-time measurement, monitoring, and prediction of ground movement using the ground movement prediction system, a threshold value α of the elastic wave velocity ratio V' / V is set according to the soil cover obtained from the above-mentioned drop-floor experiment.

[0057] Then, as the steel pipe 1 is excavated, the detection device 2, which serves as the measurement unit, measures the vibration of the ground, and the measurement data of the measured elastic wave velocity is wirelessly transmitted in real time and received by the terminal 3 (step S22).

[0058] Therefore, in step S23, the velocity ratio calculation unit of terminal 3 calculates the elastic wave velocity ratio V' / V by comparing the current elastic wave velocity V' during drilling received in real time with the elastic wave velocity V before drilling measured in advance.

[0059] Next, in step S24, the prediction unit of terminal 3 predicts the elastic wave velocity ratio beyond the current measurement time. For example, based on the elastic wave velocity ratio for one current excavation length, the change in the elastic wave velocity ratio when the excavation length is further increased is predicted using the experimental results of the verification experiment as described in Figure 11.

[0060] The elastic wave velocity ratio after the measurement time predicted by the prediction unit is compared with the threshold value α set in step S21 (step S25). In short, the judgment unit of terminal 3 compares the predicted elastic wave velocity ratio after the measurement time with the threshold value α to determine the influence of ground deformation. For example, it is confirmed to what length the excavation length must be increased before it falls below the threshold value α.

[0061] The prediction result by the prediction unit and the determination result by the determination unit are each displayed on the screen of the terminal 3. If the prediction value falls below the threshold value α, a warning is displayed on the screen of the terminal 3 (step S26).

[0062] The above is the processing flow of the ground movement prediction system of this embodiment. The processing flow of the ground movement prediction method of this embodiment, which incorporates the use of this ground movement prediction system, will now be explained with reference to the flowchart shown in Figure 1.

[0063] First, in step S1, in order to perform real-time measurements in the preparation stage for the construction of the jacking method for advancing the steel pipe 1, a detection device 2 is installed on the ground surface adjacent to the railway line R in the advancing direction of the steel pipe 1. Multiple detection devices 2 can be installed at intervals over a wide area in a plan view.

[0064] The measurement of elastic wave velocity by the detection device 2 in step S2 is carried out before and during excavation in each excavation cycle, each time vibration is generated by striking the tip 11 from inside the steel pipe 1 with a hammer or the like (see Figure 4). For example, measurement by the detection device 2 is carried out about three times in one excavation cycle.

[0065] The measurement data measured by the detection device 2 is transmitted in real time to a terminal 3 carried by a construction manager (step S3), as shown in Fig. 5. The measurement data transmitted in real time to the terminal 3 is used to monitor and predict ground deformation.

[0066] The velocity ratio calculation unit of the terminal 3 calculates the elastic wave velocity ratio in real time (step S4). In other words, the velocity ratio calculation unit calculates the ratio between the elastic wave velocity during excavation transmitted in real time and the elastic wave velocity before excavation, which is before the start of each excavation cycle.

[0067] This real-time monitoring is performed from the start of tunnel excavation (step S5) until construction is completed (YES in step S6). Then, in step S7, the predicted elastic wave velocity ratio is compared with the threshold value α set in the ground deformation prediction system before construction began.

[0068] If the determination by the determination unit in step S7 indicates that the elastic wave velocity ratio is equal to or greater than the threshold value α, the process proceeds to step S8, where it is examined whether ground deformation that would affect the track will occur if the current excavation is continued. If it is determined that there is little possibility of ground deformation occurring, the process proceeds to step S10, where construction management is carried out to continue tunnel excavation.

[0069] On the other hand, if the elastic wave velocity ratio falls below the threshold value α in step S7, or if it is determined in step S8 that ground movement will occur, the construction conditions are reviewed in step S9 to consider measures to suppress ground movement.

[0070] For example, construction conditions will be reviewed to consider measures such as shortening the excavation length per excavation cycle, injecting improvement agents into the ground to reinforce the ground, etc. In short, signs of track subsidence before it occurs can be detected by monitoring ground movements (loosening, collapse), and the construction method can be changed in advance to prevent track subsidence from occurring.

[0071] After reviewing the construction conditions in step S9 to confirm that no track displacement that would affect train operations will occur, tunnel excavation resumes (step S11), and real-time monitoring and predictions are continued until construction is completed.

[0072] Next, the operation of the ground movement prediction method and ground movement prediction system of this embodiment will be described. The method for predicting ground movement of this embodiment, configured as described above, measures the elastic wave velocity when the tip 11 of the steel pipe 1 is vibrated from inside using a detection device 2 installed on the ground surface in the direction of travel of the steel pipe 1 that is excavating the ground (step S2).

[0073] Then, the elastic wave velocity ratio is calculated by comparing the elastic wave velocity measured during excavation with the elastic wave velocity before excavation (step S4). This elastic wave velocity ratio is used to predict ground deformation after the measurement.

[0074] In this way, not only can the current state of the ground be investigated, but the elastic wave velocity ratio can also be used to predict ground deformation after excavation loads the ground. This will allow for the prevention of problematic track displacement and other deformations of the ground surface by reviewing construction conditions in advance.

[0075] In the past, track maintenance was required every time problematic track displacement occurred, which required track maintenance personnel to be on standby and required excavation to be suspended.In contrast, if the ground movement prediction method and ground movement prediction system of this embodiment can detect signs of ground movement and review construction conditions in advance to avoid track displacement, it will be possible to shorten the construction period and reduce the number of personnel involved in excavation (cost reduction).

[0076] In addition, the ground movement prediction system of this embodiment is equipped with a velocity ratio calculation unit that calculates the elastic wave velocity ratio by comparing the elastic wave velocity during excavation measured by a measurement unit that measures the elastic wave velocity at the time of ground vibration with the elastic wave velocity before excavation, a prediction unit that predicts the elastic wave velocity ratio after the measurement, and a judgment unit that determines the degree of impact of ground movement based on the prediction result.

[0077] Therefore, when the prediction result falls below a predetermined threshold value α, the judgment unit can determine that the impact of ground movement is large, making it possible to consider and implement measures early on to prevent deformation of the ground surface and other problems from occurring.

[0078] The embodiments of the present invention have been described above in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes that do not deviate from the gist of the present invention are included in the present invention.

[0079] For example, in the above embodiment, a steel pipe 1 having a roughly rectangular cross section is used as the element pipe, but this is not limited to this, and the present invention can also be applied when tunneling through materials other than steel pipes or element pipes having cross-sectional shapes other than rectangular.

[0080] Furthermore, in the above embodiment, the load applied to the ground has been mainly explained as excavation of the ground, but the load is not limited to this and may be injection of an improvement agent into the ground, etc. When injecting the ground, problems such as uplift of the ground surface can arise, so when signs of ground movement are detected, the construction method will be modified, such as by changing the injection speed. [Explanation of symbols]

[0081] 1: Steel pipe (element pipe) 11: Tip 2:Detection device

Claims

1. A method for predicting ground deformation that occurs when an element pipe is excavated, comprising: a step of installing a detection device on the ground surface in the direction of travel of the element tube; vibrating the ground between the tip of the element pipe and the detection device; measuring, by the detection device, the velocity of the elastic wave generated by the vibration applied in the step when the vibration is excited; determining a ratio of the elastic wave velocity measured during excitation during excavation of the ground to the elastic wave velocity measured before excavation at the start of each excavation cycle; and calculating a predicted value of the elastic wave velocity ratio from the elastic wave velocity ratio in order to predict ground movement after the time of measurement.

2. 2. The method for predicting ground movement according to claim 1, wherein the vibration is applied by exciting the vicinity of the tip of the element pipe from inside the element pipe.

3. A method for predicting ground movement as described in claim 1 or 2, characterized in that it includes a step of considering measures to suppress ground movement when the predicted value falls below a predetermined threshold.

4. A ground movement prediction system that predicts ground movement after applying a load to the ground, a measuring unit that measures the elastic wave velocity when the ground is vibrated; a velocity ratio calculation unit that calculates an elastic wave velocity ratio by comparing the elastic wave velocity under load measured by the measurement unit with the elastic wave velocity before load; A ground movement prediction system comprising a prediction unit that predicts an elastic wave velocity ratio in order to predict ground movement after measurement.

5. The ground movement prediction system according to claim 4, further comprising a determination unit for determining the degree of influence of ground movement based on the prediction result by the prediction unit.

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