Karst development area tunnel face gushing advanced grouting effect detection method

Abstract

The invention discloses a karst development area tunnel face water burst advanced grouting effect detection method, which comprises the following steps of S1, detecting electromagnetic reflection data of a rock mass in front of a tunnel face by adopting a geological radar method before advanced grouting, speculating distribution characteristics of a karst cave and a corrosion zone according to a radar detection result, and making an advanced grouting scheme on the basis of the distribution characteristics; s2, after grouting is completed, geological radar retesting is carried out at the same or similar positions detected by the geological radar for the first time, and radar acquisition parameters and processing parameters are the same as those detected in the previous time; and S3, by comparing the changes of the radar profile abnormal region in the aspects of amplitude, frequency and phase in two times, evaluating the advanced grouting effect. According to the invention, the geological radar detection method is adopted to detect the completeness of the rock mass in front of the tunnel before and after advanced grouting and the change condition of underground water, so that the tunnel advanced grouting effect is evaluated. The method is fast and accurate, and guidance can be provided for optimization of an advanced grouting scheme and follow-up tunnel construction.

Description

Technical Field

[0001] The present invention relates to the field of tunnel advance geological prediction and advance grouting effect detection, and in particular to a geological radar detection method for evaluating the advance grouting effect by observing the changes in electromagnetic anomaly characteristics of rock masses before and after the advance grouting. Background Art

[0002] When constructing tunnels in karst-developed areas, it is easy to encounter water seepage at the tunnel face. During construction, the water body is often blocked by pre-grouting in the rock mass in front of and around the tunnel face, which can avoid a larger amount of water seepage disasters in the subsequent construction process. Therefore, understanding the distribution characteristics of the karst caves and karst zones in front of the tunnel face in advance, and then carrying out targeted grouting in the karst-developed areas, can greatly shorten the grouting cycle and reduce the grouting cost. The main methods for tunnel advance detection are seismic reflection wave method, transient electromagnetic method and geological radar method. The seismic reflection wave method has low detection efficiency and insufficient detection resolution for small caves. The transient electromagnetic method has a detection blind spot within 15m near the tunnel face, so it is not suitable for rapid detection of the karst zone near the tunnel face. The geological radar method uses a single-point measurement method to collect electromagnetic information of the rock mass directly in front of the antenna, with high detection efficiency. In addition, the tunnel is in a shutdown state when water is gushing, and the large metal body (such as a trolley) in front of the tunnel face can be moved away from the tunnel face to reduce electromagnetic interference. Therefore, this method is very suitable for tunnel geological advance prediction when small-volume water is gushing from the local rock mass of the tunnel face. Summary of the invention

[0003] The purpose of the present invention is to provide a method for detecting the effect of water gushing advance grouting at a tunnel face in a karst development area.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] A method for detecting the effect of water gushing advance grouting at a tunnel face in a karst development area comprises the following steps:

[0006] S1. Before advance grouting, the electromagnetic reflection data of the rock mass in front of the tunnel face is detected by geological radar method. The collected data is processed by initial zeroing, horizontal background signal removal, signal gain, bandpass filtering, etc. to obtain a high signal-to-noise ratio electromagnetic reflection wave profile, which is used to infer the distribution characteristics of caves and dissolution zones;

[0007] S2. Develop an advance grouting plan based on the geological radar detection results. After the grouting is completed, conduct a geological radar re-survey at the same or similar location as the initial geological radar detection. The radar acquisition parameters and processing parameters are the same as the previous detection.

[0008] S3. Compare the changes in amplitude, frequency and phase of the abnormal area of ​​the radar profiles before and after to evaluate the effect of advance grouting.

[0009] Furthermore, the geological radar refers to the SIR4000 geological radar equipped with a 100MHz shielded antenna.

[0010] Furthermore, the first arrival zeroing refers to cutting off the data above the first arrival wave of the radar profile.

[0011] Furthermore, the horizontal background signal removal refers to removing horizontal strong amplitude multiple reflection signals within a time window of less than 50ns.

[0012] Furthermore, the signal gain refers to a 7-point exponential gain, and the gain values ​​are set to -10, 21, 39, 50, 56, 61, and 64 from shallow to deep.

[0013] Furthermore, the bandpass filtering only retains the electromagnetic reflection signal in the range of 25 MHz-125 MHz.

[0014] Furthermore, the radar acquisition parameters refer to that the radar detection mode is set to the point measurement mode, the number of superpositions is 64 times, the time window is 650ns, and the IIR filter frequency band is 25MHz-300MHz.

[0015] Furthermore, the changes in amplitude, frequency and phase of the abnormal area of ​​the radar profile refer to that the cave or dissolution zone usually corresponds to the radar electromagnetic anomaly characteristics of strong reflection amplitude, low frequency, phase axis interruption or hyperbolic shape;

[0016] After advance grouting, if the amplitude of the abnormal area is significantly reduced, the frequency becomes higher, the continuity of the event axis becomes better and no bending characteristics are shown, it indicates that the advance grouting effect is good.

[0017] The beneficial effects of the present invention are:

[0018] The present invention uses the geological radar method with the same acquisition and data processing parameters to detect the integrity of the rock mass in front of the heading face and the changes in groundwater before and after grouting, and then evaluates the effect of advance grouting, which can provide a reference for the optimization of advance grouting and subsequent tunnel excavation plans. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of geological radar detection results before advanced grouting;

[0020] Figure 2 This is a schematic diagram of the geological radar detection results after advance grouting. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific implementation modes.

[0022] A main water delivery tunnel passes through a karst-developed area. When excavating to pile number K4+410, water suddenly gushed out of two boreholes about 80 cm away from the bottom plate on the left side of the face during drilling. The measured pressure at the gushing point is 0.6Mpa. After continuous pumping for 10 days, the water pressure and flow rate have not decreased, and the groundwater recharge is strong. It is planned to carry out grouting and plugging treatment on the rock mass in front of the face and the surrounding rock near the face. The blasting construction can only be continued after the seepage channel is completely cut off. The method of the present invention is used to detect the grouting effect.

[0023] The present invention provides a method for detecting the effect of water gushing advance grouting at a tunnel face in a karst development area, comprising the following steps:

[0024] S1. Before detection, move large metal objects such as trolleys and excavators away from the tunnel face to reduce electromagnetic interference during radar detection. Connect the 100MHz shielded antenna to the SIR4000 geological radar host through a cable. Set the radar detection mode to point measurement mode in the SIR4000 host. The center of the antenna is about 1.5m away from the tunnel floor. Detect point by point from left to right, with 64 superpositions and a time window of 650ns. Use IIR filtering to retain only electromagnetic signals with a frequency range of 25MHz-300MHz. For each radar waveform collected, the antenna moves to the right once, and the moving distance does not exceed 10cm. During detection, the total number of electromagnetic waves collected on the tunnel face is required to be no less than 60. The collected data is processed by initial zeroing, removal of horizontal background signals in the range of 0-50ns, 7-point exponential gain, bandpass filtering, etc., to obtain a high signal-to-noise ratio electromagnetic reflection wave profile, which is used to infer the distribution characteristics of caves and dissolution zones;

[0025] The 7-point exponential gain values ​​in S1 are -10, 21, 39, 50, 56, 61, and 64 from shallow to deep, and FIR filtering is selected for bandpass filtering, with a filter frequency band of 25MHz-125MHz.

[0026] S2. Develop an advance grouting plan based on the geological radar detection results. After the grouting is completed, conduct a geological radar re-survey at the same or similar location as the initial geological radar detection. The radar acquisition parameters and processing parameters are the same as the previous detection.

[0027] S3. Compare the changes in amplitude, frequency and phase of the abnormal area of ​​the radar profile before and after. Figure 1 As shown in the figure, the geological radar detection results before the advance grouting show that the reflected wave amplitude of the section with pile numbers K4+408~K4+400 is strong, the frequency is low, the continuity of the phase axis is poor, and there is a slight curvature in some parts, indicating that this section has developed dissolution, poor rock integrity, and rich groundwater; there is a low-frequency strong reflection signal slightly to the left of the middle of the tunnel face in the section with pile numbers K4+400~K4+380, and this section may develop a water-bearing dissolution channel. Figure 2As shown in the figure, after grouting, the amplitude of the abnormal area is significantly reduced, the frequency becomes higher, the continuity of the event axis is improved and no bending characteristics are shown. Only in the section of pile number K4+406~K4+404 near the middle of the tunnel face, there are a small number of areas with slightly stronger reflection waves, indicating that the advance grouting effect is good.

[0028] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for detecting the effect of advance grouting of water inflow at a tunnel face in a karst development area, characterized by: It includes the following steps: S1. Before advance grouting, the electromagnetic reflection data of the rock mass in front of the tunnel face is detected by geological radar method. The collected data is processed by initial zeroing, horizontal background signal removal, signal gain, and bandpass filtering to obtain a high signal-to-noise ratio electromagnetic reflection wave profile, which is used to infer the distribution characteristics of the cave and dissolution zone; S2. Develop an advance grouting plan based on the geological radar detection results. After the grouting is completed, conduct a geological radar re-survey at the same or similar location as the initial geological radar detection. The radar acquisition parameters and processing parameters are the same as the previous detection. S3. Compare the changes in amplitude, frequency and phase of the abnormal area of ​​the radar profiles before and after to evaluate the effect of advance grouting.

2. The method for detecting the effect of water inrush advance grouting at the tunnel face in a karst development area according to claim 1 is characterized by: The geological radar mentioned above refers to the SIR4000 geological radar equipped with a 100MHz shielded antenna.

3. The method for detecting the effect of water inrush advance grouting at a tunnel face in a karst development area according to claim 1 is characterized in that: The first arrival zeroing refers to cutting off the data above the first arrival wave of the radar profile.

4. The method for detecting the effect of water inrush advance grouting at a tunnel face in a karst development area according to claim 1 is characterized in that: The horizontal background signal removal refers to removing horizontal strong amplitude multiple reflection signals within a time window less than 50ns.

5. The method for detecting the effect of water inrush advance grouting at the tunnel face in a karst development area according to claim 1 is characterized by: The signal gain refers to a 7-point exponential gain, and the gain values ​​are set to -10, 21, 39, 50, 56, 61, and 64 from shallow to deep.

6. The method for detecting the effect of water inrush advance grouting at a tunnel face in a karst development area according to claim 1, characterized in that: The band-pass filtering only retains the electromagnetic reflection signal in the range of 25 MHz-125 MHz.

7. The method for detecting the effect of water inrush advance grouting at a tunnel face in a karst development area according to claim 1 is characterized by: The radar acquisition parameters refer to that the radar detection mode is set to point measurement mode, the number of superpositions is 64 times, the time window is 650ns, and the IIR filter frequency band is 25MHz-300MHz.

8. The method for detecting the effect of water inrush advance grouting at a tunnel face in a karst development area according to claim 1 is characterized by: The changes in amplitude, frequency and phase of the abnormal area of ​​the radar profile refer to the fact that the cave or dissolution zone usually corresponds to the radar electromagnetic anomaly characteristics of strong reflection amplitude, low frequency, phase axis interruption or hyperbolic shape; After the advance grouting, if the amplitude of the abnormal area is significantly reduced, the frequency becomes higher, the continuity of the event axis becomes better and no bending characteristics are shown, it indicates that the advance grouting effect is good.

Images