JPH03226627A - Apparatus for observing ground subsidence - Google Patents

Abstract

PURPOSE:To achieve a simplification of an observing hole by a method wherein an installation weight fixed at one end of a wire is set on the bottom of the observing hole and a relatively light weight for tensioning the wire is fixed at the other end of the wire while being suspended. CONSTITUTION:An installation weight 14 is fixed at one end of a wire 13 to be set on the bottom of an observing hole 1 and a weight 15 for tensioning the wire and lighter than the weight 14 is fixed at the other end thereof 13. As a layer contracts to ground surface 9 from a basement 8, the ground surface 9 lowers to the basement 8 relatively and a pulley 12 set on the ground surface 9 lowers. Therefore, a distance to the pulley 12 from the weight 14 decreases and hence, the weight 15 lowers by a value of decrease to the ground surface 9 relatively. As a result, a distance to a magnetostrictive type range finder 18 set on the ground surface 9 from a magnet 16 mounted on the weight 15 decreases and the distance is measured with the range finer 18. A difference is calculated with a computer 22 between a distance data measured and an initial distance data to determine a subsidence of the ground surface 9.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a ground subsidence observation device used to monitor the state of ground subsidence. The present invention relates to a ground subsidence observation device for measuring the amount of contraction of land.

(Prior Art) Ground subsidence is generally thought to occur as a result of contraction of the strata between the ground surface and the foundation due to a drop in groundwater pressure as a result of pumping up groundwater. Therefore, in order to prevent ground subsidence, it is necessary to monitor the shrinkage of the strata between the ground surface and the foundation and the groundwater level.

In order to observe such ground subsidence, conventionally,
As shown in Figure 3, a double-pipe observation well consisting of an inner pipe 31 and an outer pipe 32 was installed, and the amount of ground subsidence was measured from the time the inner pipe 31 was removed. . A case tube 33 is fixed to the lower end of the inner tube 31, and the case tube 33 is fixed to a base plate 34. Further, the outer tube 32 has an intermediate portion fixed to a stratum 37 between the base 34 and the ground surface 36 by cement 35, and descends as the stratum 37 contracts. The lower end of the outer tube 32 is fitted into a case tube 33 fixed to a base plate 34 and is supported in a slidable manner.

A pen 38 or the like is attached to the upper end of the inner tube 31. On the other hand, a frame 39 is fixedly installed on the ground surface 36,
A recording paper roll 40 is supported on the frame 39. In this way, the pen 38 fixed to the inner tube 31 and the ground surface 3
The relative displacement amount of the distance between 6 and 6 is recorded on the recording paper roll 4o.

In addition, a strainer 42 consisting of a large number of small holes is formed in the outer pipe 32 at a portion where there is a sand layer or gravel layer 41 through which groundwater flows, so that groundwater flows into the inner side of the outer pipe 32. A float 43 is floated on the water surface inside the outer tube 32. That float 43
A wire 45 having a weight 44 attached to one end is connected to the wire 45 . The weight 44 is supported in a suspended state via a pulley 46 installed on the ground surface 36, and the wire 45 is held in a tensioned state. The rotation angle of the pulley 46 is then recorded on the recording paper roll 47.

In such a ground subsidence observation device, when the stratum 37 above the base 34 contracts and the ground surface 36 descends relative to the base 34, the frame 39 fixedly installed on the ground surface 36 descends. , the recording paper roll 40 supported on the frame 39 also descends. On the other hand, inner pipe 3
1 is only fixed at its lower end to the base 34 and is separated from the outer pipe 32 or the stratum 37, so even if the stratum 37 contracts, the inner pipe 31 is not affected. When 37 is contracted, the inner tube 31
will protrude further from the ground surface 36. Then, the pen 38 attached to the upper end of the inner tube 31 rises relative to the ground surface 36.

In this way, the amount of contraction of the stratum 37, that is, the amount of subsidence of the ground surface 36, is recorded on the recording paper roll 4o.

Further, when the water pressure of the groundwater fluctuates, the water surface position within the outer pipe 32 changes with the fluctuation of the water pressure. and,
The float 43 moves up and down as the water level changes, and the pulley 46 is rotated by the wire 45 kept under tension.

Therefore, changes in the groundwater level are recorded on the recording paper roll 47.

In this way, this ground subsidence observation device observes the amount of ground subsidence and the fluctuations in the groundwater level that are closely related to the ground subsidence.

(Problem to be Solved by the Invention) However, in the case of such a ground subsidence observation device, it is necessary to fix the case pipe 33 at the lower end of the inner pipe 31 to the base 34. Therefore, it is necessary to dig a deep hole with a diameter sufficiently larger than that of the outer pipe 32, install the case pipe 33 on the base 34, and harden the surrounding area with cement or the like. Such construction would be extremely large-scale, and construction costs would increase significantly.

Moreover, similar construction work is required when such ground subsidence observation equipment is removed. Therefore, it is extremely difficult to change the observation location.

It has been considered to use a stainless steel wire instead of the inner tube 31 as described above, but in that case as well, the lower end of the wire would have to be fixed to the bottom of the observation hole, which would cause the same problem. Ta.

Furthermore, fluctuations in the groundwater level can reach several 20 meters. Therefore, when measuring groundwater level fluctuations using the float 43 as described above, it is necessary to allow the vertical movement of the wire tensioning weight 44 in the air.
In addition to installing the pulley 46 at a high position, the diameter of the upper end of the outer tube 32 is increased as shown in the figure, or a deep hole is dug where no water can enter, and the weight 44 is placed in the hole. It is necessary to be able to go up and down.

The present invention has been made in view of these problems, and its purpose is to provide a ground subsidence observation device that can be easily installed by simply digging a small-diameter hole.

(Means for Solving the Problems) In order to achieve this object, in the present invention, weights of different weights are attached to both ends of a lightweight, low-stretch, and highly flexible wire, and one relatively A heavy installation weight is installed at the bottom of the observation hole, and the other relatively light weight for tensioning the wire is supported in a suspended state via a bobber installed on the ground surface, and the wire is suspended between the wire and the ground surface. The relative displacement amount is measured by a displacement meter. As the displacement meter, for example, a magnetostrictive distance meter is used, which is installed on the ground surface and detects the distance to a magnet attached to a wire tensioning weight.

Furthermore, in order to observe changes in the groundwater level, a pore water pressure gauge is used that is suspended and supported at a certain depth in an observation hole.

(Function) With this configuration, a relatively heavy installation weight attached to one end of the wire can be lowered into the observation hole,
When the other end of the wire is wrapped around a pulley, the installation weight descends to the bottom of the observation hole and is installed at the bottom, while a relatively light weight for tensioning the wire is attached to the other end. keeps the wire taut. and,
In this state, when the strata between the bottom of the observation hole and the ground surface contract and the ground surface descends, the boob descends with the ground surface, causing the ground surface to be displaced relative to the wire. Therefore, by detecting the amount of displacement, it is possible to determine the amount of contraction of the strata, that is, the amount of subsidence of the ground.

Additionally, if a water pressure gauge is installed at a certain depth in the observation hole, changes in water pressure at that position can be known. The water pressure is proportional to the depth from the water surface to that point. Therefore, the groundwater level can be determined from the water pressure.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

In the drawings, FIG. 1 is a longitudinal sectional view showing one embodiment of the ground subsidence observation device according to the present invention, and FIG. 2 is a configuration diagram showing the observation system.

As is clear from FIG. 1, in the case of this ground subsidence observation device, two observation holes 1.1 are provided adjacent to each other. The outer periphery of each observation hole 1 is formed by a protective vibe 2,
Its lower end is a strainer 3 consisting of a large number of small holes. One observation hole 1 penetrates the surface alluvial clay layer 4 and sand layer 5 and reaches the upper surface of the diluvial clay layer 6 below. The other observation hole 1 further penetrates the diluvial clay layer 6 and sand gravel layer 7 and reaches the upper surface of the base 8. In this way, groundwater flowing through the sand layer 5 and the gravel layer 7 flows into each observation hole 1.degree. 1 separately.

A pair of stands 11 and 11 are erected on the ground surface 9. Each stand 11 has a pair of pulleys 12.
, 12 are rotatably supported. One of the pulleys 12 is positioned above the observation hole l. A wire 13 made of aramid fiber, which is lightweight, has low elongation, and is highly flexible, is passed over these boots 912.12.

A relatively heavy installation weight 14 is attached to one end of the wire 13. The weight 14 is installed at the bottom of the observation hole 1. Further, the other end of the wire 13 has the wire 1
A wire tensioning weight 15, which is heavier than the weight 3 and lighter than the installation weight 14, is attached. This weight 15 is
When installation mold #i14 is located at the bottom of observation hole 1,
It is supported in a suspended state above the ground surface 9.

A magnet 16 is attached to the wire tensioning weight 15. The magnet 16 is moved up and down while being guided along a guide 17 provided on the stand 11. A magnetostrictive distance meter 18 is installed below the guide 17 to detect the distance between the guide 17 and the magnet 16. In this way, the amount of relative displacement of the distance between the wire tensioning weight 15 and the ground surface 9 is measured.

Further, a pore water pressure gauge 19 is installed inside the observation hole 1. The water pressure gauge 19 outputs a signal according to the water pressure at that time, and is suspended and supported by a double sheathed cable 20 at a certain depth that is submerged even when the groundwater level is lowest. There is.

As shown in FIG. 2, the output signals of the magnetostrictive distance meter 18 and the pore water pressure gauge 19 are both guided to a data logger 21 and input as digital signals to a personal computer 22 installed near the observation hole 1. It is becoming more and more common.

In the computer 22, the data is recorded in a secondary storage device 23 such as a hard disk. The data is then retrieved via a public telephone line 25 in response to a command from a personal computer 24 installed at a remote location. In addition, by making the remote computer 24 issue a measurement start command to the computer 22 near the observation hole 1, the public telephone line 2
It is also possible to obtain instant measurement data through 5.

Next, the operation of the ground subsidence observation device configured as described above will be explained.

When attempting to monitor the ground subsidence situation, an observation hole 1.1 is formed at an appropriate observation location by polling or the like.

Since a protective pipe is usually inserted into the hole during polling, if a pipe with a strainer 3 formed at the lower end is used as the pipe, the hole can be used as the observation hole 1 as it is.

When the observation holes 1.1 reach the sand layer 5 and the gravel layer 7, the groundwater flowing through each layer 5.7 flows into the observation holes 1.1. The water surface within each observation hole 1.1 has a height corresponding to the water pressure of groundwater flowing from those layers 5.7.

The installation weight 14 attached to one end of the wire 13 is suspended from the upper end of the observation hole 1.1 formed in this way. It lands on the upper surface of the clay layer 6 or the base 8. A wire tensioning weight 15 attached to the other end of the wire 13 is supported in a suspended state via a pulley 12.12. At this time, since the wire tensioning mold #115 is lighter than the installation weight 14, the wire tensioning mold #115 is lighter than the installation weight 14.
4 will not float up from the bottom of the observation hole 1, and since the weight 15 for tensioning the wire is heavier than the wire 13, the wire 13 will be kept under tension by the weight 15. .

Furthermore, a pore water pressure gauge 19 attached to one end of the double-sheathed cable 20 is inserted into the observation hole 1.1 and is suspended.The water pressure gauge 19 measures the groundwater level in the observation hole 1. so that it is held at a constant depth position so that it does not move even when the depth changes. The depth is such that it will not be exposed even when the groundwater level is at its lowest, but it is preferable that it be as shallow as possible.

After arranging each piece of equipment in this way, the elevation of the observation location is determined by leveling. Further, a magnetostrictive distance meter 18 installed on the ground surface 10 measures the distance from the distance meter 18 to the magnet 16 attached to the wire tensioning weight 15. Then, the distance data is transferred to the computer 2.
The water pressure data at that time detected by the water pressure gauge 19 is also stored in the secondary storage device 23 of No. 2. These data become the initial values of the ground subsidence observation device.

In this state, when the water pressure of the groundwater flowing through the sand layer 5 changes, the water surface position in one observation hole 1 into which the groundwater flows changes. Moreover, when the water pressure of the groundwater flowing through the gravel layer 7 changes, the water surface position in the other observation hole 1 changes. When the water surface position changes in this way, the distance from the pore water pressure gauge 19 held at a constant depth position in the observation hole 1 to the water surface changes. The distance is the water pressure gauge 19
proportional to the water pressure at the installation location. Therefore, the current water surface position can be determined from the water pressure measured by the water pressure gauge 19. Furthermore, changes in the groundwater level can be measured based on the difference between the water pressure at that time and the initial water pressure. Such operations are performed by computer 22.

In this way, fluctuations in the level of groundwater flowing through each layer 5.7 are observed. In this case, if the water pressure gauge 19 is installed at a shallow position, the fluctuations in the water pressure measured by the water pressure gauge 19 will increase, allowing highly accurate observation.

Also, when the strata between the foundation 8 and the surface 9 shrink,
The ground surface 9 descends relative to the base 8, and the pulleys 12, 12 installed on the ground surface 9 descend. Therefore, the distance from the installation weight 14 to the pulley 12 is reduced, and the wire tensioning weight 15 is lowered relative to the ground surface 9 by the distance. As a result, the distance from the magnet 16 attached to the wire tensioning weight 15 to the magnetostrictive distance meter 18 installed on the ground surface 9 is reduced, and the distance is measured by the distance meter 18. Then, by calculating the difference between the measured distance data and the initial distance data, the amount of subsidence of the ground surface 9 is determined. The calculation is performed by computer 22.

In this way, with a pair of observation devices, the diluvial clay layer 6
The amount of contraction of the upper strata and the amount of contraction of the strata between the base 8 and the ground surface 9 are observed. Therefore, the amount of subsidence of each of the alluvial clay layer 4 and the diluvial clay layer 6 can be determined.

During this period, the amount of ground subsidence is on the order of several tens of centimeters at most, so the wire tensioning weight 15 only needs to be allowed to descend by that amount.
Therefore, the stand 11 may be low and can be easily installed.

Furthermore, by using a lightweight wire 13, the weight 15 for tensioning the wire can be made lightweight. This makes it easier to handle,
Furthermore, since the elongation of the wire 13 is suppressed, high precision can be achieved.

The subsidence of the foundation 8 itself or the error of this ground subsidence observation device is determined by leveling conducted periodically, and the measured data is corrected as appropriate based on the data.

In this way, according to this ground subsidence observation device, observation hole 1
It only needs to have a diameter that allows the installation weight 14 to be suspended, and therefore, it can be easily formed by polling, which is commonly performed in construction work. Moreover, since the shape may be arbitrary, an existing well can also be used as the observation hole 1.

Then, the installation weight 14 is lowered to the bottom of the observation hole 1,
Since it is only necessary to suspend and support the pore water pressure gauge 19 at a certain depth position in the observation hole 1, its installation and removal are extremely easy. Therefore, it can be constructed at extremely low cost.

Furthermore, by using the magnetostrictive distance meter 18 and the pore water pressure gauge 19, the measured data is extracted as an electrical signal and digitized, so that it can be easily processed by the computer 22, so that it can be easily processed at a remote location. It also becomes possible to obtain instant measurement data.

In the above embodiment, the amount of relative displacement of the ground surface 9 with respect to the wire 13 is detected by the position of the wire tensioning weight 15 attached to the end of the wire 13, but it is similar to the conventional one. Then, a pen or the like is attached to an appropriate position on the wire 13 between the installation weight 14 and the pulley 12, and a recording paper roll is placed on the ground surface 9 to record the amount of relative displacement between them. It is also possible to use a conventional float to measure the groundwater level. Doing so will make it difficult to extract the measurement data as an electrical signal, but
The effect of easy formation can be obtained.

(Effects of the Invention) As is clear from the above description, according to the present invention, the installation weight attached to one end of the wire is lowered and installed at the bottom of the observation hole, and the other end of the wire is compared. The ground subsidence observation device can be installed by simply attaching a light wire tensioning weight and supporting the weight in a suspended state, so there is no need to fix the inner pipe, etc. to the bottom of the observation hole by construction as in the past. disappears. Moreover, the observation hole only needs to be large enough to allow the installation weight to be suspended, and therefore the observation hole can be a simple poling hole or the like. Moreover, an existing well etc. can also be used as an observation hole. Furthermore, its removal becomes easy.

In this way, an inexpensive ground subsidence observation device can be obtained.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the ground subsidence observation device according to the present invention, FIG. 2 is a configuration diagram showing an example of an observation system using the ground subsidence observation device, and FIG. 3 is a conventional ground subsidence observation device. FIG. 2 is a vertical cross-sectional view showing a typical example of a subsidence observation device. 1... Observation hole 3... Strainer 8... Base 9... Ground surface 11... Stand 12... Pulley 13... Wire 14... Weight for installation
15... Weight for wire tension 16... Magnet 18.
... Magnetostrictive distance meter (displacement meter) 19... Pore water pressure meter

Claims (3)

[Claims] (1) A lightweight, highly flexible wire with low elongation, a relatively heavy installation weight attached to one end of the wire and installed at the bottom of the observation hole, and a relatively heavy installation weight attached to the other end of the wire. , a wire tensioning weight that is lighter than the installation weight and supported in a suspended state via a pulley installed on the ground surface; and a displacement meter that measures the amount of relative displacement between the wire and the ground surface. A ground subsidence observation device equipped with the following. (2) A magnet is attached to the wire tensioning weight, and the displacement meter is a magnetostrictive distance meter that is installed on the ground surface and generates a signal according to the distance to the magnet. The ground subsidence observation device described. (3) The ground subsidence observation device according to claim 1 or 2, wherein a pore water pressure gauge that generates a signal according to the water pressure at that time is suspended and supported at a certain depth position of the observation hole.