JPH0454484A - Ground investigating method - Google Patents

Abstract

PURPOSE:To improve the measurement accuracy of mean density and increase a measurable distance by moving a gamma-ray source and a transmission type gamma-ray detector, which are inserted into investigation holes digged in the ground almost in parallel, along the investigation holes. CONSTITUTION:The nearly parallel investigation holes 1 and 4 where the gamma-ray source and gamma-ray detector are inserted respectively are digged in the ground A at a specific distance. Further, an insert tube 3 where the gamma-ray source 2 is put atop is inserted into the investigation hole 1 and the probe 5 equipped with the transmission type gamma-ray detector 6 is inserted into the investigation hole 4. The gamma-ray source 2 in the investigation hole 1 and the gamma-ray detector 6 in the investigation hole 4 are moved up along the investigation holes 1 and 4 respectively and the gamma rays from the gamma-ray source 2 are detected by the gamma-ray detector 6 to measure the density of the ground, thereby investigating the ground state between the investigation holes 1 and 4.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a ground investigation method for investigating the conditions within the ground or rock, and in particular, the method of investigating the ground by measuring the density of the ground using the gamma ray transmission method. This field relates to a ground investigation method that can estimate conditions over a wide range with high precision.

[Conventional technology]

As a ground investigation method using a radioisotope (RI), a method using a scattering type (reflection type) gamma ray densitometer is conventionally known. This reflection type gamma ray densitometer detects gamma rays that have been scattered once, and the directionality of the injection state can be determined by installing a collimator, but the measurable range is at most a radius of 5 to 10 cm. be. Furthermore, since the measured value is dependent on the density distribution within the measurement range, it cannot be said to represent the average density, and therefore accurate measurement cannot be performed.

[Problem that the invention seeks to solve]

In this way, conventional measurement methods using reflective measuring instruments have a narrow measurement range of 5 to 10 holes, so it is necessary to drill a large number of test holes at narrow intervals in order to obtain accurate ground conditions. Moreover, the number of measurements increases accordingly, which requires a great deal of effort and time, and furthermore, the accuracy is essentially low.

The present invention was made with the aim of improving such conventional technology, and by applying a transmission gamma ray densitometer, the average density within a narrow directivity range is measured, improving measurement accuracy and increasing the measurable distance. The aim is to

That is, an object of the present invention is to provide a ground investigation method that measures the density of the ground using the gamma ray transmission method, thereby estimating the ground condition with high precision and over a wide range, and that improves the drawbacks of the above-mentioned known techniques. It is in.

[Means for solving problems]

In order to achieve the above-mentioned object, according to the present invention, an investigation hole for inserting a T-ray source and an investigation hole for inserting a gamma-ray detector are excavated almost parallel to each other in the ground, and a T-ray source is inserted into each of these investigation holes. Insert the source and gamma ray detector, and
source and /′! Alternatively, the ground condition between the investigation holes is investigated by detecting the γ-rays from the T-ray source with the γ-ray detector while moving the γ-ray detector along the investigation hole.

Hereinafter, the present invention will be explained in detail using the accompanying drawings.

FIG. 1 shows a sectional view of a device for explaining the ground investigation method according to the present invention. As shown in Figure 1, there is a T in ground A.
Survey holes 1.4 for inserting a radiation source and a gamma ray detector, respectively, are drilled approximately parallel to each other at positions separated by a predetermined distance. Further, an insertion tube 3 containing a gamma ray source 2 at its tip is inserted into the investigation hole 1, and a probe 5 is inserted into the investigation hole 4.

The probe 5 houses a gamma ray detector 6, a high-voltage power supply 7 that supplies power to it, and a preamplifier 8 that amplifies the output signal of the detector 6, and is inserted into the investigation hole 4 by a cable 9 with a signal line attached. It is inserted by hanging. 10 is a counter that counts the gamma ray detection signal sent via the signal line.

The gamma ray source 2 in the investigation hole 1 and the gamma ray detector 6 in the investigation hole 4 described above are each moved from below to above (or may be moved from above to below) along the investigation hole 1.4.

The same goes for the following. ), the density of the ground is measured by detecting the γ-rays from the γ-ray source 2 with the γ-ray detector 6, and
Investigate the ground conditions between.

In addition, as shown in the fourth diagram, the present invention is directed to the insertion tube 3 of the investigation hole 1.
A plurality of γ-ray sources 2,2...2 are installed in the axial inspection hole 4.
γ-ray detectors 6 are arranged, and only the γ-ray detectors 6 are moved from the bottom to the top along the investigation hole 4 to each T-ray source 2.2.
By detecting the γ-rays from 2 while moving with one γ-ray detector 6, it is also possible to measure the density of each ground level and investigate the ground condition between the investigation holes 1.4.

Of course, although not shown, in the opposite case, one gamma ray source 2 and a plurality of gamma ray detectors 6 are provided in the investigation hole 1.
The ground condition may be investigated in the same manner as described above by moving only the γ-ray source 2 from below to above along the investigation hole 1.

Furthermore, in the present invention, as shown in the third figure, a plurality of gamma ray detectors 6 are inserted around the investigation hole 1, into which the gamma ray source 2 is inserted, at a predetermined distance from this position (in the circumferential direction). For example, as shown in the figure, six investigation holes 4.4...4 are drilled almost parallel to investigation hole 1, and these investigation holes 1 and 4 are filled with γ-rays, respectively. One source 2 and one gamma ray detector 6 are inserted, and these gamma ray sources 2 and gamma ray detectors 6 are inserted.
The T-rays from the γ-ray source 2 are detected by moving the ray detector 6 along the investigation hole 1 and the ray detector 6 along the investigation hole 1.4, respectively, as shown in the first figure. Detector 6.
By detecting at 6...6, γ centered on investigation hole 1
It is also possible to investigate the ground conditions between the line detectors 6, 6, and 6. In addition, in FIG. 3, a plurality of either rWA sources 2 or gamma ray detectors 6 are inserted into one investigation hole 1 or 4, and one of the other is inserted into each, and the ground condition is determined in the same manner as in FIG. You can also investigate.

Further, in FIG. 3, the investigation holes 4 are arranged so as to form a regular hexagon on the circumference with the investigation hole l as the center, but the invention is not limited to this example, and other regular polygons may be used. .

Further, the distance from the investigation hole 4 to the investigation hole 1 and the intervals between the investigation holes 4 do not necessarily need to be the same. However, investigation hole 4
The advantage of arranging them in a regular polygon makes it easier to analyze planar ground density changes, and by arranging them symmetrically with the survey hole l as the center, it becomes easier to analyze cross-sectional ground density changes. There is.

In the present invention, it is necessary that the investigation holes into which the γ-ray source 2 and the T-ray detector are inserted are installed as parallel as possible. The reason for this is that detection of the T-line is inversely proportional to the square of the distance, so when the distance changes, the effect of the change in distance is greater than that of the change in the soil layer, making accurate analysis difficult.

Furthermore, for the same reason, it is desirable that the T-ray source and T-ray detector within the investigation hole be moved so that they both maintain approximately the same depth.

This can be accomplished by measuring both from the bottom of the hole at the same speed (for example lfl+/min) or by measuring and pulling them every 0.5 m.

The present invention described above can be used not only for soil investigation of natural ground but also for confirming the effect of improved ground.

For example, in Figure 3, after measuring the ground before injection, injecting chemical solution or cement grout through the investigation hole, and then measuring the improved ground again through the investigation hole1; then, the increase in density in each soil layer β can be continuously observed. Can be measured accurately.

Furthermore, it goes without saying that the investigation hole in the present invention does not have to be provided vertically, but may be provided obliquely or horizontally.

[Effect]

In the method of the present invention described above, a γ-ray transmission type densitometer is arranged. In such a density meter, the detector detects only the T-rays that have passed through the ground among the T-rays emitted from the γ-ray source 2, so the measurement range is 11! It is a narrow range sandwiched between the dashed-dotted line A-A' in FIG. 1 and the dashed-dotted line BB' in FIG.

Therefore, the measured value in the present invention indicates the average density of the ground within the range AA' in Figure 1 and BB' in Figure 2 surrounded by the dashed-dotted line, and furthermore, the direction of the measurement range is Because of its good properties (small spread), measurement accuracy is greatly improved compared to conventionally used scattering type RI instruments.

Furthermore, assuming that the distance between the γ-ray source 2 and the detector 6 is 50 cm, if 100 μCj of cobalt-60 is used for the γ-ray source 2 and a GM tube is used for the detector 6, the ground can be measured with the necessary accuracy in about 10 minutes. If a gamma ray source 2 with a density of 10 mC1 is used, the required accuracy can be measured in about 1 minute.

Next, the measurement procedure of the present invention shown in FIG. 3 will be explained. γ
If 10 mC1 is used as the radiation source 2 and the distance between the gamma ray source 2 and the detector 6 is set to 501, it is possible to measure with the required accuracy in a measurement time of about 1 minute. First, the counting rate of each detector 6 is recorded at the bottom for a predetermined period of time (1 minute in this example), and then the measurement is repeated while raising the gamma ray source 2 and detector 6 by a predetermined length, or the measurement is continuously performed. It was pulled up at a speed of 1 meter per minute while measuring the distance. In this way, based on this data, it is possible to know the mode of ground density changes, the distribution of ground density, changes in soil layers, their positional relationships, and their three-dimensional relationships. Ground conditions can be estimated with high accuracy.

〔Effect of the invention〕

As explained in detail above, the present invention provides investigation holes in the ground in parallel to each other, and inserts a T-ray into one of the holes and a T-ray detector into another hole. Measure the density of the ground while pulling up, and measure the density between the guard holes.
1 of these density distributions! ! Since the measurement is performed using a transmission type T-line densitometer, the measurement range is wide (up to a distance of approximately 1 m), the number of investigation holes can be reduced, and the directional distribution can be ascertained. Furthermore, since the obtained measurement value is the average density within the measurement range, there is also the advantage that the ground condition or improvement condition can be estimated with high accuracy. In addition, the improvement state can be estimated with high accuracy from the distribution state of the density difference between the investigation holes before and after the improvement.

3...insertion tube, 6...T-ray detector, 8...Preamplifier, lO...Counter.

5... Probe, 7...High voltage power supply, 9... Cable,

Claims (3)

[Claims] (1) A survey hole for inserting a gamma-ray source into the ground and a survey hole for inserting a gamma-ray detector are excavated almost parallel to each other, and a gamma-ray source and a gamma-ray detector are respectively inserted into these survey holes. Investigate the ground conditions between the investigation holes by detecting γ-rays from the γ-ray source with the γ-ray detector while moving the γ-ray source and/or γ-ray detector inside the investigation hole. A ground investigation method characterized by: (2) In the ground investigation method according to claim 1, γ
Centering around the research hole into which the radiation source is inserted, multiple research holes into which the gamma-ray detectors are inserted are drilled approximately parallel to the research hole for the gamma-ray source, and each gamma-ray source is inserted into each of these research holes. and a gamma ray detector, and detecting gamma rays from the gamma ray source with the gamma ray detector while moving the gamma ray source and/or the gamma ray detector in these investigation holes along the hole. A ground investigation method characterized by investigating the ground conditions between the gamma ray source investigation hole and the gamma ray detector investigation hole. (3) In the ground investigation method according to claim 1 or 2, a plurality of either a gamma ray source or a gamma ray detector and one gamma ray detector are inserted into each investigation hole, and the A ground investigation method characterized by investigating the ground condition between investigation holes by detecting γ-rays from a γ-ray source with a γ-ray detector while moving the other one along the investigation hole.