JPH036484A - Ground serveying method - Google Patents

Abstract

PURPOSE:To accurately determine a crack by correcting the data obtained by an NaI detector on the basis of Bi/K calculated by a Ge detector to calculate more accurate Bi/K distribution and further together using an underground radar method. CONSTITUTION:A wide range of many measuring points are measured within a short time while an NaI detector is moved and the intensities of gamma-rays corresponding to the gamma-ray energies inherent to Bi-214 and K-40 are calculated to calculate a Bi/K ratio and the positioning of a point having a high Bi/K ratio is performed. Subsequently, the absolute value of the intensity of gamma-rays at the specified high Bi/K position is measured by a Ge detector high in the resolving power of gamma-ray energy and having good linearity. Then, the energy correction of Bi or K is performed from the data of the NaI detector on the basis of the Bi/K ratio calculated by the Ge detector and more accurate Bi/K distribution is calculated. Further, the relation between the outline structure of a shallow underground stratum read from the fault image of the ground due to an underground radar method and the high Bi/K position and a geological mechanism generating radon are investigated and, by synthesizing these results, the position of a crack can be determined accurately.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to large-scale underground excavation work such as underground space.

The present invention relates to a method for accurately and easily conducting ground investigation (particularly fault detection) required in tunnel construction, nuclear power related facility construction, etc.

[Conventional technology]

Conventionally, the most commonly used methods for investigating underground strata are the outcrop observation method, the elastic wave exploration method, and the poling method.

In the outcrop observation method, faults are identified based on the fault topography (triangular terminal surface) and the continuity of the geology of the outcrop, but this method cannot be used at all if there is no outcrop and the topography cannot be determined. The elastic wave exploration method has a good track record as a physical exploration method, but its detection accuracy is affected by the presence and amount of groundwater. Although the polling method is the most reliable method, it has problems in terms of polling position selection and cost, so it is usually adopted as a final confirmation method.

Geological surveys using natural radioactivity have also made great progress, but one method that has attracted attention is the method of determining the location of the second crack by utilizing the phenomenon in which radon from deep layers rises to the surface through faults and cracks. Bismuth-2, a daughter nuclide
A method has been realized in which the ratio of the photoelectric peak count rates of No. 14 and Kali-40 is used as an index. For example, Journal of Japan Society of Agricultural and Civil Engineers, Vol. 54, No. 2 (February 1986 issue), P139-14
4 describes a method for determining this Bi/K ratio using a NaI detector.

On the other hand, Article 9, Article 1 of the Construction Technology Evaluation Regulations pertaining to the applicant's application
In Kengihyo No. 85303, the method uses reflected waves of electromagnetic pulses radiated into the ground by a portable underground radar as a method for detecting cavities under the paved road surface or directly under the sprayed surface of mortar etc. without destroying the structure. A method was proposed to easily detect cavities in shallow layers by measuring the reflected waveform from the paved road surface, analyzing the reflected waveform, and projecting it as an image on a CRT.

[Problem that the invention seeks to solve]

Although the method using natural radioactivity described above provides useful guidance for crack exploration, ZI4134 halo or B
In order to more accurately determine the strata from the i/K halo, there is still a problem with reliability with this method alone, and it cannot be denied that the accuracy is inferior if only a NaI detector is used as a detector. Furthermore, although the method described in Kengihyo No. 85303 is effective in detecting cavities in shallow areas, it is still problematic when used alone for ground investigation.

Therefore, the object of the present invention is to develop a simple and accurate ground investigation system capable of conducting ground investigation with high precision, exceeding the level of these conventional techniques.

[Structure of the invention]

The ground investigation method according to the present invention includes NaI along the survey line on the ground surface.
Measure the gamma ray intensity while moving the detector, and one of these!
+413i and γ corresponding to the unique γ-ray energy of “K”
a step of determining the line intensity and detecting the position of a point where the B i /K ratio is high;
The step of re-watering the γ-ray intensity at the position where the /K ratio is high, and the step of adjusting the measured value of the former NaI detector based on the Bi/K ratio determined by the latter Ge detector, and adjusting the Bi /K ratio distribution analysis using natural radioactivity, and ground investigation to understand the general underground structure of the shallow layer from cross-sectional images using underground radar method. It is characterized by determining the position.

In other words, the present invention combines ground investigation using natural radioactivity and ground investigation using electromagnetic waves, and in particular, the former natural radioactivity investigation requires a short measurement time.
After performing a general survey using the aI detector, we further narrowed down the investigation range based on the information obtained, and in the narrowed range, we determined the absolute value of 1 intensity using the Ge detector, and the B value determined using this Ge detector. Based on i/K, we corrected the data obtained with the previous NaI detector and found a more accurate distribution of i/K over the entire survey range.

Furthermore, we determined the general structure of the shallow underground through ground investigation using electromagnetic waves, and determined the radon eruption location (high W of Bi/K).
The unique feature is that the location of the crack is determined by considering the relationship between the two and the geological mechanism by which radon is generated.

[Details of the invention]

NaI detectors (NaI (TI) detectors activated with a trace amount of thallium), which are known as radiation measuring instruments, are generally characterized by high detection efficiency for gamma rays, easy handling, and short measurement time. However, it is inferior to Ge detectors using Ge semiconductors in terms of energy resolution and linearity, and the amount of emitted light changes depending on the natural count rate at 40K and temperature changes, and in particular, count rate dependence affects the measurement accuracy of Bi/K distribution. make a big impact.

On the other hand, high-purity germanium detectors have high energy resolution and good linearity, making spectrum analysis easy and the results obtained highly reliable.

However, this method requires a high-capacity multichannel analyzer and requires a large amount of data analysis, which is time-consuming. Therefore, by moving this to a long total survey line, B 1-214. K
It is not practical to measure the entire −40 distribution.

The present invention combines the advantages and disadvantages of the NaI detector with the disadvantages and advantages of the Ge detector, and further incorporates an underground radar method to perform accurate ground investigation.

FIG. 1 shows the equipment arrangement of the ground investigation system according to the present invention. As shown, the NaI and Ge detectors are connected to a multichannel analyzer. This multi-channel analyzer can use a commercially available 2, for example, 4096 channel, 50 old 1z Wilkinson type ADC (for example, product name E-560MC^), and has a radiation counting function, including manual input of 4096 channel data. It has a data recording function. A
The MT is a data recorder that uses audio cassette tape to record data from the multichannel analyzer in the field.

On the other hand, the equipment on the radar side corresponds to that described in Kengihyo No. 85303, which includes a radio wave emitting device (antenna section), a radio wave control/display device (main body control section), and an AM
It consists of T (signal recording section). The radio wave emitting device (antenna section) consists of a pulse controller, a transmitter, a receiver, a transmission/reception switch, an antenna, and a distance detector.1 Radio waves are transmitted by the pulse controller, transmitter, and transmit/receive by signals from the main body control section. It is transmitted from the antenna via a switching device.

If an underground cavity exists, the reflected waves generated on the surface of the cave are converted into signals by the receiver via the antenna, and then transferred to the main control unit. The radio wave control/display device (main body control section) consists of an operation section, a control processing section, and an output display section.
Control of the signal sent to the antenna section, A of the received signal
/D conversion, display on CRT, data transfer to AMT and analysis equipment, etc. An image of the reflected waves (ground plane image) is displayed on the CRT, and the image is temporarily recorded in a semiconductor memory. Further, the relative dielectric constant, apparent depth, and travel distance are displayed on the CRT, and the position and depth of the cavity can be displayed numerically using the cursor device on the operation section. The analysis device consists of a computer, CRT, disk drive, and printer, and has functions such as data analysis of self-thermal radioactivity, analysis of reflected waves, output of these analysis results, and data recording.The analysis results can be printed. be outed.

FIG. 2 shows the investigation and analysis flow of ground investigation according to the present invention. As shown in the figure, a measuring line is first set, and a rough measurement is performed while moving the NaI detector along this measuring line. Here, the gamma ray intensity from 0 to 3000 KeV is measured on the measuring line, and the gamma ray intensity corresponding to the specific gamma ray energy of x+aBi and 40 is determined, and the Bi/K ratio is calculated.

Locate a point with a high B i / K ratio. Next, use a Ge detector to find the absolute value of the γ-ray intensity at the position where the Bi/K value is higher than the overall value.Ge
The detector has high energy resolution, but the time for one measurement is N
It requires nearly 10 times as much as the aI detector. According to the present invention, a large number of measurement points over a wide range are measured in a short time using a NaI detector having a short measurement time, and only the specified narrow high Bi/K position is measured using a Ge detector. Then, based on the Bi/K obtained with the Ge detector, energy correction of Bi and K is performed from the data of the NaI detector to obtain a more accurate i/K distribution. On the other hand, we investigated the relationship between the general structure of the shallow underground as determined from cross-sectional images of the ground using underground radar methods and the radon eruption location (high Bi/K level K), as well as the geological mechanism by which radon occurs. The crack location is determined based on the results.

The upper part of Figure 3 shows the Bi/K ratio distribution (upper part of the figure) obtained by implementing the method of the present invention, and the lower part shows the results of actual ground investigation using a survey pit. From the figure, it can be seen that according to the method of the present invention, tomographic analysis can be performed accurately.

〔effect〕

According to the present invention, there is an underground radar method that can easily and responsively investigate the presence or absence of underground cavities, and the direction and size of cracks, which are difficult to decipher with this underground radar method, can be determined by measuring natural radioactivity. This natural radioactivity measurement can also be carried out in a short time and accurately using a combination of a NaI detector and a Ge detector, so it can be used as a ground investigation system for large-scale underground excavation work, tunnel construction, nuclear power related facility construction work, etc. can make a contribution.

[Brief explanation of the drawing]

FIG. 1 is a layout system diagram of ground investigation equipment for carrying out the method of the present invention, FIG. 2 is a ground investigation/analysis flow diagram of the method of the present invention, and FIG. 3 is a diagram showing the results of an embodiment of the method of the present invention.

Claims (2)

[Claims] (1) Measure the γ-ray intensity while moving the NaI detector along the survey line on the earth's surface, and among these, ^2^1^4Bi and ^4
A step of determining the γ-ray intensity corresponding to the specific γ-ray energy of ^0K and detecting the position of the point where the Bi/K ratio is high, and using a Ge detector to detect the γ-ray intensity at the position where the Bi/K ratio is high. A step of re-calculating the intensity, and a step of correcting the measured value of the former NaI detector based on the Bi/K ratio determined by the latter Ge detector and analyzing the distribution of the Bi/K ratio on the survey line. Ground investigation using natural radioactivity; and
A ground investigation method in which a ground investigation is carried out to understand the rough underground structure of shallow layers from cross-sectional images taken using underground radar, and the location of cracks is determined from the results of both investigations. (2) Claim 1: The ground investigation to understand the general underground structure of shallow layers from cross-sectional images obtained by underground radar method is carried out by the method described in Construction Technology Review No. 85303 pursuant to Article 9, Paragraph 1 of the Construction Technology Evaluation Regulations. Ground investigation method described in.