JPH1082669A - Apparatus for simultaneously measuring water pressure and strain in gap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a simultaneous measuring apparatus by which a water staying layer and a strain only in a part required for a measurement can be measured by using one set of devices provided with protective pipes composed of short pipes and by which a water pressure and a stratum strain can be measured precisely without being subjected to an influence of the torsional stress and the reaction force of a pipe column. SOLUTION: A pipe body 2 of a protective pipe 1 is composed of a short pipe having a total length of about 100cm, and a bottom plate 3 and a lid body 4 are screwed to it. A water-pressure measuring chamber 5 is partitioned by an inside partition material 6 inside the pipe body 2, and a plurality of water introduction holes 7 are formed in the pipe body 2 so as to communicate with the water-pressure measuring chamber 5. A hairlike filter part 8 is formed on the outer circumferential face of the pipe body 2 so as to be positioned around the water introduction holes 7. A water pressure sensor 9 is installed inside the water-pressure measuring chamber 5. A plurality of strain gages 10A, 10A,... are arranged and installed at the outer circumferential face 2B of the protective pipe 1 so as to be separated in the axial direction and the circumferential direction, and the water pressure sensor 9 and the strain gages are connected to an automatic measuring device 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention analyzes phenomena such as landslides, landslides, and liquefaction of the ground to predict or prevent the occurrence thereof, and measures pore water pressure of an aquifer to prevent the occurrence. TECHNICAL FIELD The present invention relates to a pore water pressure / strain simultaneous measurement device for simultaneously measuring strains of an object.

[0002]

2. Description of the Related Art Conventionally, as means for measuring the water pressure of groundwater, first, a long protective tube having a full length strained is inserted into a borehole, and a water level gauge is provided in the protective tube. The second is the Casagrande type water level measurement method, in which the water pressure is estimated by measuring the water level. Insert a piezometer or pore water pressure gauge according to the water layer remaining in the protective tube,
Pore water pressure measuring device with upper and lower sides sealed with bentonite sealing material. Third, a long protective tube with a strainer processed to its entire length is inserted into the borehole, and each of a plurality of water layers A water pressure sensor covered with a mesh-shaped protection filter in a protective tube corresponding to the position of the water pressure sensor is arranged, and an upper and lower water pressure sensor is cut off from the outside by an annular sealing material above and below each water pressure sensor. It has been known. Further, the applicant of the present application has disclosed in Japanese Patent Application No. 5-320944,
A plurality of water pressure measurement chambers are defined in the protection pipe inserted into the borehole, and a water pressure sensor is disposed in each of the water pressure measurement chambers, and a water guide hole that connects each water pressure measurement chamber to the borehole is formed in the protection pipe. At the same time, a multilayer pore water pressure measuring device having a configuration in which a strain measuring pipe is provided on the outer peripheral surface of a protective tube is proposed.

[0003]

By the way, among the above-mentioned prior arts, the first Casagrande type water level measuring method is as follows.
When the ground is heterogeneous and there are multiple aquifers, it can measure only the groundwater level synthesized by water leakage, and accurately measure the pore water pressure of each aquifer to estimate the water pressure from the measured water level There is a drawback that you can not. In addition, a pore water pressure measuring device in which a boring hole is formed for each second aquifer and a protective tube is inserted requires a large amount of cost to form a plurality of boring holes, and a pore water pressure gauge is required. There is a drawback in that the risk of failure is high because the cable is inserted bare, and there is a drawback that the sealing material cannot cope with fluctuations in the ground, water leaks in the borehole, and accurate measurement cannot be performed.

[0004] A third method of disposing a water pressure sensor covered with a mesh-shaped protective filter is to insert a long protective tube having a length of about the entire length into a boring hole. There is a disadvantage that the measurement value is affected by the torsional stress and reaction force of the column portion, and accurate measurement cannot be performed. The problems common to the above-mentioned conventional technologies are that, because a long protective tube is used, a deep boring hole must be formed, and high measurement accuracy is required due to the effect of an increase in the weight of the protective tube itself. That is what you cannot get.

The pore water pressure is related to the landslide phenomenon. However, since the strain gauge for detecting the landslide is integrated with a long protective tube, the depth of the boring hole is long. As a matter of fact, there is a problem that the installation work requires a lot of expense and the preparation for the measurement is troublesome.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks and problems of the prior art, and is directed to a set of devices having a protective tube formed of a short pipe and a water-reservoir layer and a stratum distortion only in a portion required for measurement. Simultaneous pore water pressure and strain measurement device that can measure and accurately measure water pressure and strain of the formation without being affected by torsion stress and reaction force of the tube column because strain gauges with narrow distance between strain gauges are provided. The purpose is to provide.

[0007]

Means for Solving the Problems The means of the present invention constituted to solve the above-mentioned problem comprises a bottomed tubular body having an upper lid, and is suspended in a boring hole via a suspension cable. A water pressure measuring chamber defined between the protective tube, the upper lid by an internal partition member provided in the protective tube, and a pipe wall of the protective tube, and communicating the water pressure measuring chamber with the boring hole. A water guide hole, a hair filter portion provided around the water guide hole and provided on the outer peripheral surface of the protective tube, and disposed in the water pressure measurement chamber, and the hair filter portion is provided through the water guide hole through the water guide hole. A water pressure sensor for detecting the water pressure of groundwater infiltrating into the water pressure measurement chamber; a strain gauge comprising a plurality of strain gauges disposed on an outer peripheral surface of the protective tube in an axial direction and a circumferential direction; Automatic measurement that simultaneously measures detection signals from sensors Consisting of.

[0008] By forming the protective tube so as to be connected in a chain shape, it is possible to measure the multi-layer pore water pressure and strain.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawing, reference numeral 1 denotes a protective tube inserted into a boring hole A formed in the ground. Reference numeral 2 denotes a pipe main body constituting the protective tube 1. The pipe main body 2 is a short pipe made of vinyl chloride having a total length of about 100 cm, and female screw portions 2A, 2A are formed on inner circumferential surfaces at both ends in the axial direction. It is. 3 is the pipe body 2
A bottom plate made of vinyl chloride screwed to the lower end of the tube body 4
Shows a lid screwed to the upper end side, and a signal line insertion hole 4A is formed in the lid 4 in the axial direction. Reference numeral 5 denotes a water pressure measurement chamber defined in the pipe main body 2. The water pressure measurement chamber 5 is fitted with an internal partition member 6 made of a vinyl chloride disc in the pipe main body 2 so as to face the lid 4. Is formed.

.. Indicate a plurality of water introduction holes for introducing groundwater into the water pressure measuring chamber 5. Are formed through holes having a diameter of 2 to 5 mm, and are formed in the pipe main body 2 so as to be spaced apart in the axial direction and the circumferential direction. Reference numeral 8 denotes a bristle filter portion provided around the water guide holes 7, 7,... And provided on the outer peripheral surface 2B of the protective tube 1 in a substantially band shape. The hairy filter portion 8 has a length of about 4 mm and a thickness of about 1 mm.
It consists of a 2 denier capillary pile implanted by means of electrodeposition.

Reference numeral 9 denotes a water inlet 7 from the hairy filter portion 8;
7 shows a water pressure sensor for measuring the water pressure of the groundwater entering the water pressure measurement chamber 5 through the water pressure measurement chamber 5, and the water pressure sensor 9 is located in the water pressure measurement chamber 5 and attached to the lid 4. And
The signal line 9A is inserted into the signal line insertion hole 4A and extends to the ground side. The space between the signal line 9A and the signal line insertion hole 4A is sealed gas-liquid-tight by filling a sealant.

Further, reference numeral 10 denotes a strain gauge for detecting strain in the formation, and the strain gauge 10 includes a plurality of strain gauges 10A, 1A.
0A,... Each strain gauge 10A
In the prior art, at least 50 cm had to be provided at a distance from the conventional technology.
Are attached to the outer circumferential surface 2B of the strain gauge at an interval of about 10 cm in the axial direction and at about 90 degrees in the circumferential direction.
A signal line 10 </ b> B extends to the ground along the protection tube 1.

In the figure, reference numeral 11 denotes an automatic measuring instrument installed on the ground. The automatic measuring instrument 11 has a built-in timer and a battery so that simultaneous measurement can be performed at a preset time.
A water pressure sensor 9 via a signal line 9A and a signal line 10B;
It is connected to each strain gauge 10A. Reference numeral 12 denotes a suspending means for suspending the protective tube 1 in the borehole A. The suspending means 12 is connected to the support plate 12A so that the upper end is adjustable in length and the lower end is a cover. 4 and a pair of suspension wires 12B, 12B. Reference numeral 13 denotes a suspension hook attached to the lower surface of the bottom plate 3, and another protection tube 1 is suspended from the suspension hook 13 via a suspension wire 14.

The apparatus for simultaneously measuring pore water pressure and strain according to the present embodiment has the above-described configuration. Next, the installation procedure will be described. First, a boring hole A is formed in the ground from the ground surface, and the depth at which the aquifer is located is measured. The depth at which the protective tube 1 is inserted is set so that the water pressure measurement chamber 5 is located in the aquifer, and the soil is backfilled to a required depth to form a backfill portion B. Next, the protection tube 1 is inserted into the boring hole A, and after adjusting the insertion depth, the surroundings are filled with medium-sized sand to a position below the bristle filter portion 8 to form a sand filling portion C. Then, an annular water-impervious seal portion D is provided above and below the bristle filter portion 8. The annular water-impervious seal portion D is composed of a stretchable synthetic resin annular bag attached to the outer peripheral surface of the protective tube 1 and a foamable synthetic resin filled in the annular bag.
By expanding the expandable synthetic resin agent, the gap between the boring hole A and the protective tube 1 is closed in close contact with the hole wall.

Further, the soil excavated in the borehole A is backfilled, and an upper backfill portion E is provided above the annular water-impervious seal portion D.
Is formed, and mortar, concrete, or the like is cast on the upper end side of the boring hole A to form the closed portion F. When forming the closing portion F, the signal line 9A of the water pressure sensor 9 and the signal line 10B of the strain gauge 10A are led out to the outside and connected to the automatic measuring instrument 11.

Thus, the water pressure measuring chamber 5 defined in the protective tube 1 is in a state of being located in the water-retaining layer, and is in a state of being shut off from other water-retaining layers by a pair of upper and lower annular water-impervious seal portions D. I do. Thereby, the water pressure sensor 9 in the water pressure measurement chamber 5
Can measure only the pore water pressure of groundwater flowing from a communicating aquifer.

When groundwater flows into the water pressure measuring chamber 5, the pile constituting the hairy filter section 8 is bent by water pressure, and the pile near the water introduction hole 7 covers the water introduction hole 7 in an arch shape. It prevents fine soil particles mixed in the groundwater from entering the water pressure measurement chamber 5.

As described above, according to the measuring apparatus of the present embodiment, the pore water pressure of the aquifer due to the groundwater can be measured. A plurality of strain gauges 10A, 1
Since 0A,... Are arranged at intervals of about 10 cm in the axial direction, distortion of the stratum can be accurately measured. Since the automatic measuring device 11 can simultaneously measure the strain of the stratum and the pore water pressure at a predetermined time, the causal relationship between them can be scientifically examined.

Further, the suspension hook 1 is attached to the bottom plate 3 of the protection tube 1.
Since a plurality of protective tubes 1, 1,... Can be connected in a chain (see FIG. 2), the water pressure in the multilayer gap can also be measured. In this case, the signal line 9A of the water pressure sensor 9 located below may be formed by forming a line insertion hole in the bottom plate 3 and the internal partition member 6 of the protection tube 1 located above and leading out to the ground.

In this embodiment, a short pipe made of vinyl chloride is used for the pipe main body 2 constituting the protection pipe 1. However, a metal pipe may be used.

[0021]

The present invention has the following advantages because it is constructed as described above. (1) The protection tube is constituted by a short tube, and a water pressure sensor is disposed in a water pressure measurement chamber defined inside the protection tube, and a plurality of strain sensors constituting a strain gauge are provided on the outer peripheral surface with the conventional technology. In comparison, the arrangement at close intervals makes it possible to accurately measure the water pressure and the strain of the formation without being affected by the twisting of the protective tube. (2) Since the signals detected by the water pressure sensor and the strain gauge can be periodically measured at a predetermined time by an automatic measuring device, the causal relationship between the change of the water pressure and the strain of the formation can be known and measured. Work efficiency can be improved. (3) By connecting a plurality of protection tubes in a chain, the pore water pressure of a plurality of aquifers can be accurately measured, and the efficiency of the measurement operation can be improved. Further, since it is sufficient to drill the boring hole to a required depth, the drilling cost can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a pore water pressure / strain measuring device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state in which a plurality of pore water pressure / strain measuring devices are connected.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Protective tube 4 Lid 5 Water pressure measuring chamber 6 Internal partitioning material 7 Water guide hole 8 Hairy filter part 9 Water pressure sensor 10 Strain gauge 10A Strain gauge 11 Automatic measuring device 13 Hanging hook A Boring hole

Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location G01L 1/22 E21B 47/00 7/00 G01B 7/18 G G01V 9/02

Claims (2)

[Claims] 1. A protective tube comprising a bottomed tubular body having an upper lid and suspended in a boring hole via a suspension cable, and an inner partition member provided in the protective tube between the protective lid and the upper lid. A defined water pressure measurement chamber, a water guide hole formed in the pipe wall of the protection tube, and communicating the water pressure measurement chamber with the boring hole, and a water supply hole provided around the water guide hole and provided on an outer peripheral surface of the protection tube. A hair filter section, a water pressure sensor disposed in the water pressure measurement chamber, and detecting a pressure of groundwater entering the water pressure measurement chamber from the hair filter section through the water introduction hole, and an outer periphery of the protection tube. A strain gauge comprising a plurality of strain gauges disposed on the surface at a distance in the axial direction and the circumferential direction, and a pore water pressure / pressure gauge comprising an automatic measuring device for simultaneously measuring detection signals from the strain gauge and a water pressure sensor. Simultaneous strain measurement device. 2. The apparatus for simultaneous measurement of pore water pressure and strain according to claim 1, wherein the protective tube is configured to be connected in a chain.