JPH06137905A - Method and apparatus for measuring land subsidence - Google Patents

Abstract

PURPOSE:To provide method and apparatus for measuring land subsidence suitable for automatic measurement in which multilayer measurement can be made through one boring hole with no restriction on the depth and accurate measurement can be made even if the boring hole is bent. CONSTITUTION:A plurality of pressure converters 12 are fixed longitudinally at positions, corresponding to underground measuring points, to a telescopic tubular member 10 which is then inserted into a hole 18 bored in the land to be measured. Each pressure converter 12 is secured sequentially at an underground measuring point through a corresponding securing block 14 such that no slip takes place between the pressure converter 12 and the wall face of the boring hole 18. The tubular member 10 is then filled with water thus forming a water column 22. Each pressure converter measures variation of hydraulic pressure with time and the amount of land subsidence is determined basing on the variation of hydraulic pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground subsidence measuring method and apparatus capable of measuring the subsidence amount of each layer of the ground by using a single boring hole. More specifically, a plurality of pressure transducers are attached to a tubular member that can be expanded and contracted in the longitudinal direction, the pressure transducers are inserted into a boring hole, and each pressure transducer is fixed at a position corresponding to an underground measurement point. The present invention relates to a technique for determining the amount of ground subsidence from the hydraulic pressure measured by a pressure transducer, which is filled with liquid. INDUSTRIAL APPLICABILITY The present invention can be used for measuring various types of ground subsidence due to various causes, but is particularly useful for measuring ground subsidence over a depth of several tens of meters underground.

[0002]

2. Description of the Related Art Ground subsidence includes, for example, ground subsidence caused by pumping up groundwater, extraction of natural gas, mining of petroleum, etc. Subsidence due to the normalization of. The aspect of the settlement, such as the extent and extent of the settlement, changes intricately depending on the cause of these settlements and the conditions of the strata in the ground. Therefore, in order to investigate the behavior of ground subsidence, it is necessary to obtain the amount and speed of subsidence for each layer within the ground to be measured.

The following method has been used to measure the amount of ground subsidence for each layer. First, on the measurement ground, boring to reach the measurement stratum (measurement point) and boring to reach the fixed point are performed. If there are multiple measurement strata, drill as many as that number. Then, the lower end of the rod having a length protruding from the bottom of the boring hole to the ground is joined to the sinking plate, and the rod is inserted into the boring hole to embed the sinking plate in the hole bottom. This is performed for each boring hole, and the same position of the exposed portion of each rod on the ground is marked in advance.
When the ground subsidence occurs, the corresponding rod subsides according to the subsidence amount of each layer. Therefore, the relative subsidence amount at each layer position can be obtained from the displacement amount of the mark attached to the rod. If the rod installed so as to reach the fixed point is used as a reference, the absolute subsidence amount in each measurement layer can be obtained.

[0004]

However, in the above measuring method, since it is necessary to excavate the boring hole by the number of measurement layers of the ground, the measurement range is expanded or the number of measurement layers is increased so as to perform more detailed measurement. Then, it is necessary to drill more boring holes, and it takes time to prepare for the measurement, and the cost increases.

Further, when it is attempted to measure the subsidence in a deep stratum, the boring hole is often bent due to the slip of the ground, etc., and the rod is also bent accordingly.
The rod will not reliably transmit the amount of displacement due to compaction or subsidence to the ground part, making accurate measurement difficult. Therefore, the conventional method has a limit in measurement depth. Further, since the amount of ground subsidence is measured by mechanical displacement, it is difficult to automate the measurement, especially when a large subsidence occurs or when the measurement is performed for a long period of time, and it has to be done manually.

The object of the present invention is to perform multi-layer measurement at one location with one boring hole, and there is no particular limitation on the measurement depth, and accurate measurement can be performed even if the boring hole is curved, and automatic measurement is possible. An object of the present invention is to provide a suitable ground subsidence measuring method and apparatus.

[0007]

A method for measuring ground subsidence according to the present invention is as follows. First, a plurality of pressure transducers are attached to a tubular member that can expand and contract in the longitudinal direction. Next, the tubular member is inserted into the boring hole excavated in the ground, and each pressure transducer is fixed to the wall of the boring hole corresponding to the underground measurement point so as not to slip. Then, the tubular member is filled with the liquid, and the hydraulic pressure is measured with time by each pressure transducer. Thus, the amount of ground subsidence is measured from the change in hydraulic pressure. During measurement, if the liquid contained in the tubular member is brought into an overflow state, the liquid surface position can be kept constant.

As a measuring device used for carrying out this measuring method, a tubular member which is capable of expanding and contracting in the longitudinal direction, has large deformation resistance in the diametrical direction and exhibits liquid tightness, and a pressure conversion device arranged in the longitudinal direction of the tubular member are dispersed. And a fixing means for fixing the pressure converter to the borehole wall.

[0009]

Each of the pressure transducers detects the pressure of the liquid column from the liquid surface to the position where the pressure transducer is installed. Since the depth can be calculated from the density of the liquid filling the inside of the tubular member and the pressure of the liquid, the depth from the liquid surface to the pressure converter can be obtained from the liquid pressure measured by each pressure converter. By the way, since each pressure transducer is fixed to the wall of the borehole, when the subsidence occurs locally in the ground, the position of the pressure transducer also changes accordingly. The distance between the upper and lower pressure transducers can be derived by calculation from the difference between the hydraulic pressure measurements by the pressure transducers. Therefore, when the hydraulic pressure is measured with each pressure converter over time, the position of each pressure converter can be determined over time, and thus the amount of consolidation settlement over time for each layer can be determined. Then, the sum of the consolidation settlement amounts for each layer indicates the total settlement amount.

Since the ground consolidation settlement amount is obtained from the difference in hydraulic pressure, the change in the position of the liquid surface affects only the measurement of the uppermost layer, and the change is offset in the measurement of other depths, so the influence is affected. Do not give. If you want to measure the displacement of the pressure transducer at the uppermost position, you can set the liquid in the overflow state so that the position of the liquid surface can be kept constant at all times. The amount of can also be measured.

[0011]

EXAMPLE FIG. 1 is an explanatory view showing an example of the ground subsidence measuring method according to the present invention. The ground subsidence measuring device used for this purpose comprises a tubular member 10, a plurality of pressure transducers 12, and a fixed block 14 provided near each pressure transducer 12. The tubular member 10 is stretchable in the longitudinal direction,
It has a large deformation resistance in the diametrical direction, is open at the top and is closed at the bottom, and is made of a watertight material. The tubular member 10 may be made of a material such as rubber that can be expanded or contracted, or the material itself is not easily expanded or contracted but may be structurally accordion-shaped and expandable. As the pressure converter 12, for example, a highly sensitive crystal oscillation type pressure gauge is preferable. This is because the oscillation frequency changes according to the applied pressure, and a minute pressure difference can be detected as a digital amount.
A required number of such pressure transducers 12 are attached in the longitudinal direction of the tubular member 10 at positions corresponding to the underground measurement points. At this time, each pressure transducer 12 is provided so as to be able to accurately detect the internal pressure of the tubular member 10, for example, exposed from the outside of the tubular member 10 to the inside surface. A lead wire 16 is connected to each pressure transducer 12. The fixed block 14 is for fixing the pressure converter 12 to the wall of the bore hole. This may be, for example, a structure that mechanically deforms so as to spread at a predetermined position by using a spring or the like.

This ground subsidence measuring device is inserted into the boring hole 18 excavated in the measurement ground. Each pressure transducer 1
2 are fixed in order by the corresponding fixing block 14 so as not to cause slippage with the wall surface of the boring hole 18 at the underground measurement point. The lead wire 16 connected to each pressure transducer 12 is drawn out from the boring hole 18 to the surface of the earth. Then, the hole filling material 20 is supplied to the gap between the tubular member 10 and the wall surface of the boring hole 18 and fixed to the ground, so that the ground subsidence measuring device can follow the movement of the ground. The hole filling material 20 integrates the surrounding ground and the ground subsidence measuring device, and for example, cement milk or the like is used. The tubular member 10 is filled with water to form a water column 22. Lead wire 1 pulled out from the boring hole 18
6 is wired to the automatic measurement recording device 24.

The amount of ground subsidence is measured by each pressure transducer 12 in the water column 22.
Can be calculated by measuring the pressures P _{1 to} P _N (kgf / cm ² ). That is, since the water depth can be calculated from the water density and the water column pressure, the tubular member 10
Assuming that the density of water inside is 1, the water column pressure (10 × P ₁ to 10 × P _N ) measured by each pressure converter 12 is the depth of the water from the water surface to the corresponding pressure converter (H ₁ to H _N m). Therefore, the space between the pressure transducers (h ₁
To h _N m) _{is, h 1 = H 1 -H 2} = 10 × (P 1 -P 2) h 2 = H 2 -H 3 = 10 × (P 2 -P 3) ···· h N = It can be obtained by calculation of H _N = 10 × P _N. In this way, the layer thickness is determined by the difference between the water column pressures P _{1 to} P _N measured by each pressure converter 12. The amount of decrease over time in the thickness of each layer indicates the amount of consolidation settlement for each layer. Thus, a single boring hole can be used for one place to measure the subsidence amount of the ground.

When the depth becomes large, the boring hole often bends during measurement over a long period of time, but since the depth is measured by the water column pressure in this measuring method, only the vertical component is measured, and the boring hole is not bent. It can measure accurately without any influence. Therefore, there is basically no limit on the measurement depth.

The water level in the tubular member changes because the tubular member expands and contracts due to ground subsidence, but the water column pressure at each depth is to be measured under the common water level at the depth of each location of one tubular member. In addition, the amount of consolidation settlement of each layer can be obtained from the pressure difference. Therefore, changes in the water level at the head of the tubular member only affect the measurement of the uppermost layer h _N and not at other depth measurements, since they cancel out. Therefore, as long as it is intended to measure the consolidation settlement amount of each layer, the measurement value of the uppermost layer can be ignored, and the management of the water level becomes less important. When measuring the movement of the top layer, or when measuring the total subsidence from the ground surface to each layer, if the water is always in an overflow state, the water level can be easily and always kept constant. It is also possible to measure the total subsidence amount for each layer.

[0016]

EFFECTS OF THE INVENTION Since the present invention can measure the multi-layer subsidence with one boring hole per measurement point, it does not take much time to prepare for measurement and is economical. Further, since the pressure of the liquid is measured, even if the boring hole is bent, it is not affected by the bending, so that there is no particular limitation on the measurement depth and accurate measurement can be performed. Furthermore, since the measurement is performed by an electric signal, recording and calculation can be performed automatically without human intervention.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a ground subsidence measuring device according to the present invention.

[Explanation of reference numerals] 10 tubular member 12 pressure transducer 14 fixed block 18 boring hole

Claims (3)

[Claims] 1. A boring hole wall corresponding to an underground measurement point, in which a plurality of pressure transducers are attached to a tubular member which can be expanded and contracted in a longitudinal direction and are inserted into boreholes excavated in a measurement ground. A method for measuring ground subsidence, comprising: filling the inside of the tubular member with a liquid, fixing the liquid to a tubular member, measuring the hydraulic pressure with each pressure transducer over time, and determining the subsidence amount from the change. 2. The ground subsidence measuring method according to claim 1, wherein the liquid filling the inside of the tubular member is brought into an overflow state on the ground to maintain the liquid surface position constant. 3. A bottomed tubular member which is capable of expanding and contracting in the longitudinal direction, has large deformation resistance in the diametrical direction, and exhibits liquid tightness, and a plurality of pressure transducers distributed along the longitudinal direction of the tubular member. A ground subsidence measuring device comprising fixing means for fixing each of the pressure transducers to a borehole wall.