A method for advanced geological prediction of tunnels

Abstract

The present invention discloses a method for advanced geological prediction of a tunnel, and relates to the technical field of advanced geological prediction of a tunnel, and comprises the following steps: selecting an observation system according to the completeness of the rock mass of the face; arranging boreholes according to different observation systems; designing excitation points according to the number of boreholes; exciting the excitation points multiple times to obtain multiple groups of elastic wave data to draw a wave velocity-depth curve, and processing the wave velocity-depth curve data through the processing software of the TGS host to obtain a longitudinal wave velocity curve, and continuously correcting the initial wave velocity model according to the longitudinal wave velocity curve; finally, obtaining the comprehensive velocity of the surrounding rock in front of the face according to the wave velocity empirical correction formula, so as to improve the accuracy of the advanced prediction. The present invention can improve the accuracy of TGS advanced geological prediction and obtain a more accurate prediction result.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel advanced geological prediction, in particular to a tunnel advanced geological prediction method. Background Art

[0002] During the construction of underground projects and tunnels, adverse geological problems such as large deformation of surrounding rocks, landslides, water and mud inrush often occur, bringing serious safety hazards to engineering construction. As an important part of the engineering construction process, advanced geological prediction technology is of great significance for analyzing and inferring the geological structural conditions in front of the face, timely discovering abnormal conditions, predicting the location, shape and scale of adverse geological bodies in front of the face, and ensuring the safety, quality and progress of the project.

[0003] At present, TGS technology is widely used. TGS technology is a method based on recording seismic wave signals of different polarized reflected seismic waves to predict geological conditions such as adverse geology or lithology change zones in front of and around the tunnel face. However, TGP technology adopts a one-dimensional observation method, and only zero offset data is obtained. Zero offset data is theoretically unable to determine the velocity distribution of the surrounding rock in front of the tunnel face. In particular, in the offset image processing, it is necessary to manually set the surrounding rock wave velocity parameters. This practice lacks objectivity. When the seismic wave velocity values ​​selected in the prediction velocity model are inconsistent, the shape, position, and size presented in the corresponding image show large differences, and the corresponding predicted adverse geological properties, positions, and scales will also be different. Due to the inability to accurately determine the surrounding rock wave velocity, the structural positioning is inaccurate, which will lead to large deviations in the predicted position in complex structural areas, and there is a lack of basis for the classification of surrounding rock engineering.

[0004] Therefore, the greater the error between the selected seismic wave velocity value and the actual surrounding rock wave velocity value, the less reliable the prediction result. As the prediction distance increases, the unreliability of the prediction result will continue to accumulate, and the final prediction result will be incomparable with the actual result. Therefore, in the prediction interpretation, only by selecting accurate prediction wave velocity can reliable advanced geological prediction be achieved; and the closer the selected prediction wave velocity is to the actual surrounding rock wave velocity (the average value of the wave velocity in the prediction mileage section), the better the prediction effect; on the contrary, the greater the error of the prediction wave velocity, the lower the prediction accuracy, and the worse the reference of the prediction result. Summary of the invention

[0005] The purpose of the present invention is to provide a method for advanced geological prediction of a tunnel to improve the accuracy of geological prediction.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A method for advanced geological prediction of a tunnel comprises the following steps:

[0008] S1: Select the observation system according to the integrity of the rock mass at the tunnel face;

[0009] S2: Arrange drilling holes according to different observation systems;

[0010] S3: designing excitation points according to the number of drill holes, wherein the multiple excitation points have an excitation sequence;

[0011] S4: a detector string is placed in the borehole, the detector string includes at least three detectors, one end of the detector string is connected to the host, an SGD-SHC hammer source synchronization system is used, an excitation trigger is provided on the side of the hammer head of the sledgehammer, the excitation trigger uses an SGD-SAH accelerometer, the excitation trigger is connected to the TGS host in a wired or wireless manner, and the host receives the elastic wave signal through the detector string;

[0012] S5: After one excitation is completed, the detector string is moved out of the borehole, and the excitation point is struck again to obtain a new round of elastic wave signals; the moving distance of the detector string is n×L, where n is the number of detectors and L is the distance between two adjacent detectors. The detector string is moved until the distance between the probe of the detector closest to the TGS host and the orifice of the borehole is less than L, at which time the data collection work is completed;

[0013] S6: Record the elastic wave starting point of each excitation point, record the time t0 when the elastic wave is received by the detector string, and draw a time-depth curve;

[0014] S7: Calculate the elastic wave travel distance ΔL of each data according to the position coordinates of the excitation point and the position coordinates of the detector string. , and obtain the comprehensive wave velocity of the rock mass at this distance ,After obtaining the wave velocities of all the collected data, the wave velocity-depth curve can be obtained by inversion;

[0015] S8: The velocity-depth curve data is processed by the processing software in the TGS host to obtain the longitudinal wave velocity curve, and the initial velocity model is continuously corrected according to the longitudinal wave velocity curve; finally, the comprehensive velocity of the surrounding rock in front of the tunnel face is obtained according to the velocity empirical correction formula, and the velocity empirical correction formula is: , is the comprehensive velocity of the surrounding rock in front of the tunnel face, β is the correction factor for the corresponding geology, h is the location of known adverse geology obtained after combining the excavation verification data, The location of adverse geological anomalies predicted by the TGS host. is the predicted P-wave velocity in the initial velocity model;

[0016] S9: Based on the comprehensive velocity of the surrounding rock in front of the tunnel face, the processing software in the TGS host generates a corresponding map, which is interpreted to accurately predict the geological conditions in front of and around the tunnel construction.

[0017] Furthermore, the observation system in S1 includes a tunnel face layout observation system and a side wall observation system.

[0018] Furthermore, the number of boreholes in the side wall observation system is 2, 1 borehole on each of the left and right sides; the tunnel face arrangement observation system includes two situations: 1 borehole and 3 boreholes.

[0019] Furthermore, for the case where there is one borehole in the tunnel face arrangement observation system, the longest secant line of the tunnel face contour line passing through the borehole position is drawn after calculation, and the two intersection points of the secant line and the tunnel face contour line are the first excitation point and the second excitation point.

[0020] Furthermore, for the case where there are three boreholes in the observation system of the tunnel face arrangement, the circumcenter of the triangle formed by the lines connecting the positions of the three boreholes is first calculated, and the circumcenter is the first excitation point. After calculation, the longest secant line on the tunnel face contour line passing through the first excitation point is drawn, and the two intersection points at both ends of the secant line and the tunnel face contour line are the second excitation point and the third excitation point.

[0021] Furthermore, the detector string placed in the borehole in S4 is tightly coupled to the borehole wall of the borehole, which is no more than 50 cm.

[0022] The beneficial effects of the present invention are:

[0023] 1) Improve the accuracy of TGS advanced geological forecast and obtain more accurate forecast results.

[0024] 2) By deploying multiple artificial seismic sources on the tunnel face to stimulate seismic waves, the seismic waves propagate toward the front of the tunnel excavation and its surroundings, and generate reflected waves when encountering geological anomalies. These waves are received by multiple geophones arranged on the surface of the tunnel face, so that the geological information of the rock mass in front of the tunnel face can be obtained more accurately, and the geological conditions in front of the tunnel construction and its surroundings can be accurately predicted in advance.

[0025] 3) By continuously moving the detection string, reflection information from different locations can be received, enriching the data volume and thus improving the forecast accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A flow chart of a method for advanced geological prediction of a tunnel according to the present invention;

[0027] Figure 2 The selection of the excitation point when drilling a hole in the tunnel face arrangement observation system of the present invention;

[0028] Figure 3 It is a schematic diagram of data collection when one hole is drilled in the tunnel face arrangement observation system of the present invention;

[0029] Figure 4 The selection of the excitation points when three holes are drilled in the tunnel face arrangement observation system in the present invention;

[0030] In the figure, 1-drilling hole, 2-first excitation point, 3-second excitation point, 4-third excitation point, 5-detector. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0032] See also Figure 1-Figure 4 , the present invention provides a technical solution:

[0033] When selecting the observation system, if the rock mass at the face is in the range of relatively broken to intact, select the face observation system; if the rock mass at the face is in the range of extremely broken to broken, select the side wall observation system.

[0034] The location of the drill hole is determined according to the design drawings. The general size of the drill hole is 50mm. In the tunnel face observation system, the drill hole is arranged in the middle of the tunnel face as much as possible, and the height is 1m from the ground; in the side wall observation system, the drill hole is 5-15m away from the tunnel face, and the height of the drill hole is preferably 1m from the ground.

[0035] The empirical correction formula for wave speed is , is the comprehensive velocity of the surrounding rock in front of the face, β is the correction factor for the corresponding geology, β in granite is 1.3~1.5; β in sandstone is 1.15~1.35; β in shale is 1.0~1.2, h is the location of known adverse geology obtained after combining excavation verification data, The location of adverse geological anomalies predicted by the host. is the predicted P-wave velocity in the initial velocity model;

[0036] Embodiment 1:

[0037] like Figure 1-Figure 3, in order to select the observation system for the tunnel face arrangement, the situation of 1 borehole is described. According to the design requirements, a borehole 1 with a depth of 30m is arranged at a height of 1m above the ground in the middle of the tunnel face. According to the coordinates of the tunnel face contour line and the coordinates of the borehole position, the longest secant of the tunnel face contour line passing through the advance borehole position is calculated, and the coordinates of the intersection of the secant line and the contour line are calculated. The tunnel face is marked with red paint by measuring means.

[0038] Insert a detector string suitable for horizontal drilling into the borehole 1 until the bottom of the hole and couple it; adopt the SGD-SHC hammer source synchronization system, set an excitation trigger on the side of the hammer head of the sledgehammer, and the excitation trigger adopts the SGD-SAH accelerometer; connect the detector string and the host, and connect the excitation trigger and the TGS host.

[0039] Use a sledgehammer to hit the first excitation point 2, and observe the waveform characteristics through the TGS host screen. If the waveform characteristics are normal, save the data; if the waveform characteristics are abnormal, re-tap the first excitation point 2 until the waveform is normal and save the data. Use a sledgehammer to hit the second excitation point 3, and observe the waveform characteristics through the TGS host screen. If the waveform characteristics are normal, save the data; if the waveform characteristics are abnormal, re-tap the second excitation point 3 until the waveform is normal and save the data.

[0040] Release the coupling state between the detector string and the borehole wall, move the detector string outward, and move the distance n×L. After moving into place, continue to couple the detector string with the borehole wall. Then repeat the data collection of the first excitation point 2 and the second excitation point 3, and repeat this step until the distance between the detector 7 closest to the TGS host and the borehole 1 mouth is less than L, and the data collection is completed. By moving the detector string, reflection information at different positions can be received, enriching the data volume, thereby improving the prediction accuracy

[0041] Data processing is performed to record the pick-up elastic wave signal starting time t0, and according to the excitation point of each waveform collected and the detector distance ΔL, according to , and obtain the comprehensive wave velocity of the rock mass at this distance After all data analysis is completed, the velocity-depth curve can be obtained through inversion.

[0042] The velocity-depth curve data is processed by the processing software of the TGS host to obtain the P-wave velocity curve. In this process, the clutter is filtered out and the P-wave is separated to obtain a separate P-wave velocity curve. The initial velocity model is continuously corrected according to the P-wave velocity curve, and the P-wave velocity within 8 to 10 m in front of the tunnel face in the forecast results is selected as the initial velocity model.

[0043] Then, the empirical formula of wave velocity is used to obtain the comprehensive velocity of the surrounding rock in front of the tunnel face, and finally a corresponding map can be formed through TGS processing software. By interpreting the map, accurate advance prediction of the geological conditions in front of and around the tunnel construction can be made, thereby guiding the tunnel excavation construction and completing the advance prediction work.

[0044] Embodiment 2:

[0045] like Figure 4 As shown in the figure, the selection of the excitation point is explained by selecting the observation system for the tunnel face and arranging three boreholes. First, the circumcenter of the triangle formed by the three borehole positions is calculated. The distance between this point and the three boreholes is equal, and this point is set as the first excitation point 2. The longest secant line on the tunnel face contour line passing through the first excitation point 2 is calculated. The two intersection points of the two ends of the secant line and the tunnel face contour line are the second excitation point 3 and the third excitation point 4.

[0046] Insert the detector string suitable for horizontal drilling into the borehole 1 until the bottom of the hole and couple it; firmly tie the excitation trigger to the side of the sledgehammer with electrical tape; connect the detector string and the TGS host, and connect the excitation trigger and the host.

[0047] Use a sledgehammer to hit the first excitation point 2, and observe the waveform characteristics through the TGS host screen. If the waveform characteristics are normal, save the data; if the waveform characteristics are abnormal, re-tap the first excitation point 2 until the waveform is normal and the data is saved. Use a sledgehammer to hit the second excitation point 3, and observe the waveform characteristics through the TGS host screen. If the waveform characteristics are normal, save the data; if the waveform characteristics are abnormal, re-tap the second excitation point 3 until the waveform is normal and the data is saved; use a sledgehammer to hit the third excitation point 4, and observe the waveform characteristics through the TGS host screen. If the waveform characteristics are normal, save the data; if the waveform characteristics are abnormal, re-tap the second excitation point 4 until the waveform is normal and the data is saved. The remaining steps are the same as Example 1.

[0048] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for advanced geological prediction of a tunnel, characterized by: The following steps are involved: S1: Select the observation system according to the integrity of the rock mass at the tunnel face; S2: Arrange drilling holes according to different observation systems; S3: designing excitation points according to the number of drill holes, wherein the multiple excitation points have an excitation sequence; S4: a detector string is placed in the borehole, the detector string includes at least three detectors, one end of the detector string is connected to the TGS host, and the SGD-SHC hammer source synchronization system is used. The excitation points are hit in sequence by a sledgehammer, and an excitation trigger is provided on the side of the hammer head of the sledgehammer. The excitation trigger adopts an SGD-SAH accelerometer, and the excitation trigger is connected to the TGS host by wire or wirelessly. The TGS host receives the elastic wave signal through the detector string; S5: After one excitation is completed, the detector string is moved out of the borehole, and the excitation point is struck again to obtain a new round of elastic wave signals; the moving distance of the detector string is n×L, where n is the number of detectors and L is the distance between two adjacent detectors. The detector string is moved until the distance between the probe of the detector closest to the TGS host and the orifice of the borehole is less than L, at which time the data collection work is completed; S6: Record the starting point of the elastic wave at each excitation point and the time when the elastic wave is received by the detector string , and draw the time-depth curve; S7: Calculate the elastic wave travel distance ΔL of each data according to the excitation point position coordinates and the detector string position coordinates. , and obtain the comprehensive wave velocity of the rock mass at this distance ,After obtaining the wave velocities of all the collected data, the wave velocity-depth curve can be obtained by inversion; S8: The velocity-depth curve data is processed by the processing software in the TGS host to obtain the longitudinal wave velocity curve, and the initial velocity model is continuously corrected according to the longitudinal wave velocity curve; finally, the comprehensive velocity of the surrounding rock in front of the tunnel face is obtained according to the velocity empirical correction formula, and the velocity empirical correction formula is: , is the comprehensive velocity of the surrounding rock in front of the tunnel face, β is the correction factor for the corresponding geology, h is the location of known adverse geology obtained after combining the excavation verification data, The location of adverse geological anomalies predicted by the TGS host. is the predicted P-wave velocity in the initial velocity model; S9: Based on the comprehensive velocity of the surrounding rock in front of the tunnel face, the processing software in the TGS host generates a corresponding map, which is interpreted to accurately predict the geological conditions in front of and around the tunnel construction.

2. The method for advanced tunnel geological prediction according to claim 1, characterized in that: The observation system in S1 includes a tunnel face arrangement observation system and a side wall observation system.

3. The method for advanced tunnel geological prediction according to claim 2, characterized in that: The number of boreholes in the side wall observation system is 2, 1 borehole on each of the left and right sides; the tunnel face arrangement observation system includes two situations: 1 borehole and 3 boreholes.

4. The method for advanced tunnel geological prediction according to claim 3 is characterized in that: For the case of one borehole in the tunnel face arrangement observation system, the longest secant line of the tunnel face contour line passing through the borehole position is drawn after calculation, and the two intersection points of the secant line and the tunnel face contour line are the first excitation point and the second excitation point.

5. The method for advanced tunnel geological prediction according to claim 3 is characterized in that: For the case where there are three boreholes in the observation system of the tunnel face arrangement, the circumcenter of the triangle formed by the lines connecting the positions of the three boreholes is first calculated, and the circumcenter is the first excitation point. After calculation, the longest secant line on the tunnel face contour line passing through the first excitation point is drawn, and the two intersection points at both ends of the secant line and the tunnel face contour line are the second excitation point and the third excitation point.

6. The method for advanced tunnel geological prediction according to claim 1, characterized in that: The detector string placed in the borehole in S4 is tightly coupled to the borehole wall of the borehole, with a distance of no more than 50 cm.

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