KR101432069B1 - Apparatus and methode for measuring in-situ stress of rock using overcoring - Google Patents

Abstract

The present invention relates to initial stress measuring means capable of accurately measuring rock bed initial stress with improved means and methods applied to be capable of measuring a multi-axis strain with accuracy. The present invention provides initial stress measuring means including a piston unit (200) having a rod portion (220) that is inserted into one side of a drilling hole and is in contact with an end portion side and a body that is formed to extend to the other side of the rod portion; a body portion (100) having an accommodating portion (120) where a body of the piston unit is inserted into an inner circumferential side and a plurality of strain gauges (300) that are arranged in a circumferential direction and are oriented to have at least three angles with respect to a central axis; a cable (130) that extends to the other side of the body portion and outputs strain gauge detection signals to the outside; a first sealing unit (110) that has the shape of a ring which is formed to protrude in an outer circumferential direction on the other side of the body portion and has a radius corresponding to an inner circumference of the drilling hole; and a second sealing unit (210) that has the shape of a ring which is formed to protrude in an outer circumferential direction on one side of the body of the piston unit and allows a curing material to be injected between the second sealing unit and the first sealing unit. Accordingly, accurate fixing with respect to the drilling hole is possible and the strain with respect to multiple directions can be accurately measured.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an initial stress measurement method using an overcorling method,

More particularly, the present invention relates to an initial stress measuring means capable of accurately measuring an initial stress of a rock by applying an improved means and a method so as to measure an accurate strain to multiple axes, And a method of measuring the initial stress of the rock.

In general, when various tunnels are constructed such as underground tunnels or mine tunnels, the ground, soil, and rock condition are preliminarily investigated using various measuring devices before construction, and based on this, the design, construction schedule And then worked on these data.

However, since the stresses and excavation structures obtained based on the data obtained from the results of the limited ground, rock excavation, and soil tests show considerable differences from the values estimated at the design stage and the actual measured values at the construction site, Unexpected large-scale safety accidents, such as the collapse of some grounds due to the stresses caused by the motion of the faulty rocks and the ground, which surrounds the tunnel around the tunnel, or the complete cement curing tunnel, There was always a concern to occur.

Initial stress refers to the unstressed stresses present in the rock before excavation, which is disturbed and redistributed by excavation and other processes. Accurate measurement of the initial stress is very important to predict these variables and to evaluate the stability against redistributed stresses. Typical methods of measuring the initial stress can be classified into hydraulic fracturing method, stress solution method, and stress compensation method.

Registered Patent No. 10-0765973 proposes a conventional underground stress measurement method.

A conventional stress measurement method is a method of monitoring a change in horizontal or vertical stress after a predetermined amount of pressure is applied in a state in which a stress meter is inserted into a tunnel such as a tunnel to closely contact the inner surface of the hole. .

However, in this case, not only is it possible to measure stress in either one direction or a limited direction, but also there is a problem that the accuracy as an initial stress measurement is poor. Particularly, there is a problem in that it is necessary to continuously correct the data because the change of the stress is measured in a state in which the hydraulic pressure is externally applied and closely contacted.

This is because the degree of deviation between actual stress and data varies depending on the proficiency of the measurer, so that it is not only a problem that the accurate amount of displacement can not be detected, but also influences the post management of the tunnel construction or completion of the construction depending on the error, And in serious cases there was a risk of an unexpected large safety accident, such as a collapse of some ground or an entire tunnel collapse.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide an initial stress measuring means which can verify the stability of construction by precisely and specifically measuring and analyzing the value of the side- And an object of the present invention is to provide a method of measuring an initial stress of a used rock mass.

The present invention is characterized in that it comprises a rod part (220) inserted into one side of a drill hole and contacting with an end side, a piston part (200) composed of a body extended to the other side of the rod part, (100) comprising a plurality of strain gauges (300) arranged in a circumferential direction with respect to a central axis of the strain gauges (120) and having a direction at three or more angles with respect to a central axis, A first sealing part 110 having a ring shape protruding in the outer circumferential direction of the other side of the body part and having a radius corresponding to the inner circumference of the excavating hole, And a second sealing part (210) formed in a ring shape protruding from the first sealing part and allowing a space between the first sealing part and the second sealing part to be injected with a hardened material, Provided. Therefore, accurate fixation to the excavation hole is possible and accurate strain measurement can be made for multiple directions.

And a reinforcing sealing portion 111 formed on the body portion and spaced apart from the first sealing portion.

The strain gauges 300 are preferably composed of twelve strain gages 300 and are arranged at different angles in the longitudinal and circumferential directions of the central axis.

The body of the piston unit can inject the hardened material into the space between the outlet 231 and the excavation hole through the outflow channel 230 while applying pressure to the other side of the receiving unit.

Further comprising at least two connecting means (400) connected to the other side of the body portion,

Preferably, the connecting means is provided with an indicator 420 so that the circumferential placement of the strain gauges relative to the direction of gravity during insertion into the excavator can be maintained.

According to another aspect of the present invention, there is provided a method of measuring an initial stress using the initial stress measuring means, comprising the steps of: forming an outer hole formed by punching an outer hole with a first depth (? 1) A step of filling the hardened material into the receiving portion, a step of coupling the piston to the receiving portion, a step of inserting the stress measuring means in the circumferential fixed state into the inner hole, A step of injecting a hardening material inside the receiving part into a space between the body and the inner space by the pressure provided on the rod part, a step of hardening the hardened material and fixing the body part to the inner cavity, A step of overcorrection in which a strain due to stress release is detected from strain gauges while a tertiary bulging portion is formed with an inner diameter of the core block, A pressure measuring step in which the strain is detected from the strain gauges as pressure is applied, a calculation step in which the core elastic modulus and Poisson's ratio are calculated through the strain at the pressure measuring step, and the elastic modulus and Poisson's ratio at the over- And calculating a lateral pressure coefficient as a horizontal normal stress and a magnitude and direction of the calculated main stress. The excavation hole is pushed through the outer hole and the inner hole in two steps, and the core is subjected to the excavation for the separation process of the core, so that two types of strain measurements can be easily performed.

The diameter of the outer hole is 130 mm, the diameter of the inner hole is 38 mm, and the diameter of the core is 107 mm.

It is preferable that the outer hole and the inner hole are pivoted so as to be upwardly inclined from 0 DEG to 1 DEG or less in the horizontal direction with respect to gravity.

The strain, the elastic modulus and the Poisson's ratio at the time of stress release can be measured by performing the two processes according to the stress release and the pressing of the mined core by the initial stress measurement means and the initial stress side method according to the present invention, This makes it possible to calculate the maximum, minimum horizontal stress, vertical stress and lateral pressure coefficient accurately. Therefore, it is possible to design and construct the excavation process appropriately for the situation, and the reliability of the construction can be remarkably improved.

Particularly, by applying the triaxial strain cell, it is possible to perform accurate measurement in multiple directions, and by inserting the body part, the piston part, and the rod part of the present invention, it is possible to insert and fix the accurate depth of field, .

1 is a plan view showing an initial stress measuring means according to a preferred embodiment of the present invention;
Fig. 2 is a view showing a state in which connecting means are connected to the initial stress measuring means of Fig. 1; Fig.
3 is a flowchart showing an initial stress measurement method according to the concept of the present invention;
4 is a diagram for visualizing the process of Fig. 3; Fig.
5 is a flowchart specifically showing an installation step of the stress measuring means in the initial stress measuring method of the present invention.
6 is a view showing a configuration for pressure measurement in the initial stress measurement method of the present invention.
7 is a graph showing strain data at the time of stress release according to an initial stress measuring means and an initial stress measuring method therefor according to an embodiment of the present invention.
8 is a graph showing strain data at the time of pressure measurement according to the initial stress measuring means and the initial stress measuring method therefor in the embodiment of the present invention.

Hereinafter, the initial stress measuring means according to the present invention and the initial stress measuring method using the same will be described in detail with reference to the accompanying drawings.

1 is a view showing an initial stress measuring means according to a preferred embodiment of the present invention.

The present invention basically includes a stress measuring means 10 inserted into a hole of a rock, comprising: a piston portion 200 which is in contact with one end of a hole; a piston portion 200 in which the piston portion 200 is inserted, A body part 100 having a plurality of strain gauges 300 and a cable 130 extending to the other side of the body part 100 and transmitting a measured strain signal from the strain gauge 300 .

The stress measuring means 10 according to the concept of the present invention basically explains a case where the stress applied to the rock is measured at the construction stage inside the tunnel, but it can be applied to the ground having various physical properties, The present invention can be applied to the measurement of the stress in the oblique direction with respect to the pressure or gravity provided in the direction.

The stress measuring means 10 is basically inserted into a rock as in the initial stress measuring method described later. After measuring the release stress, the stress measuring means 10 is separated from the drilled rock and is used for compression test, Step measurement test.

The piston part 200 includes a rod part 220 which is inserted into an inner cavity to be described later and which is brought into contact with an end part of the excavated end to provide a predetermined pressure to the other side and a rod part 220 extending from the rod part 220 to the other side, Shaped body (not shown) inserted into the body 100.

The body portion 100 is disposed adjacent to the rock mass through a hardening material that is in direct contact with the rock mass or interposed therebetween so that the pressure of the rock mass can be measured substantially from the strain gage 300, Of the strain gauge 300 on the side where the strain gauge 300 is disposed corresponds to the inner hole of the hole into which the stress measuring means 10 is inserted.

The body part 100 includes a receiving part 120 which is a predetermined receiving space so that the body of the piston part 200 can be inserted into the inner side of the receiving part 120, And functions to discharge the cured material by the movement of the piston portion 200, more precisely to the other side of the piston portion 200, by the rod portion 220 which comes into contact with the end portion of the inner side and provides the pressure, The inner diameter of the receiving portion 120 may substantially correspond to the outer diameter of the body of the piston portion 200.

More specifically, the piston 200 has a ring-shaped second sealing portion 210 protruding toward the outer circumference, and the second sealing portion 210 is preferably formed of Can be made in a size and shape to the extent that it is in close contact with the inner wall of the inner cavity.

The first sealing part 110 and the second sealing part 210 may be provided on the other side of the body part 100 to correspond to the second sealing part 210. The first sealing part 110 and the second sealing part 210, Provides a function of sealing so that when the curing material is discharged into a space therebetween, the curing material is densely structured to some extent while preventing the consumption of the curing material to one side or the other side.

For this, the first and second sealing portions 110 and 210 are preferably formed in a plurality of ring shapes, but are not limited thereto. Here, sealing does not mean that the flow of the fluid is completely prevented.

In addition, the accommodating portion 120 preferably substantially corresponds to the inner wall of the inner cavity, and the body of the piston portion 200 is formed in a straight shape smaller than the inner wall of the accommodating portion 120, May be formed through the interior of the piston portion 200. [ Accordingly, the piston 200 may include an outflow channel 230 formed on the inner circumferential side of the accommodating portion 120 and an outflow portion 231 adjacent to one side of the body and being an end of the outflow channel 230 .

In addition, since the cable 130 extends to the other side of the body 100, it is preferable that the reinforcing sealing portion 111 is additionally formed to be spaced apart from the first sealing portion 110 in order to improve the sealing property .

The stress measuring means 10 according to the present invention measures a pressure or a strain which is inserted in a horizontal direction substantially in a tunnel or standing-up soil and formed in a vertical direction. In order to measure strain in various directions, a plurality of strain gauges 300 may be arranged in the circumferential direction of the body 100.

The strain gauges 300 have predetermined directionality and measure the strain. In the present invention, twelve strain gauges 300 can be used basically, but the present invention is not limited thereto. Here, it should be noted that the arrangement of the strain gages 300 is directed to the direction of the strain measurement rather than the configuration thereof.

In the present invention, the stress measuring means 10 as a whole is formed in a columnar shape, and a predetermined central axis may exist because the drilling hole to be described later is formed in a cylindrical shape. The orientation of the strain gage 300 may be understood to be about the central axis.

The strain gauges 300 are arranged in the circumferential direction of the body 100, and each of the strain gauges 300 forms a predetermined angle with respect to the central axis to measure the multi-directional rock strain to calculate the initial stress. In a preferred embodiment, Direction may be defined as 45 degrees, 90 degrees, and 135 degrees, respectively. The angle with respect to the axial direction means an angle in the longitudinal direction, and an angle with respect to the central axis in the circumferential direction may also be defined. Accordingly, the twelve strain gauges 300 are arranged as angles with respect to different radii or lengths of the central axes, and data having different meanings are transmitted. The angles of the center axis are defined as 45 series, 90 series and 135 series, respectively. Here, it can be predicted that strain strain gauges 300 of 90 series with respect to the axial direction have the largest strain, and this will be explained separately as specific data in this regard.

Due to the multi-directionality of the strain gauge 300 of the present invention, the circumferential disposition upon insertion into the drill hole has a significant effect on the results. That is, when the stress measuring means 10 is rotated in the inserted state, an interpretation of a completely different meaning can not be obtained. Therefore, it is possible to cause a problem of poor construction as described in the related art.

2 is a diagram showing an initial stress measurement stage according to a further concept of the present invention.

One or more connecting means 400 may be coupled to the other end side of the body part 100 for insertion of the stress measuring means 10 and the correct insertion in the circumferential direction of the stress measuring means 10, The connection means 400 may include an instruction unit 420. [

The indicator 420 preferably indicates the direction of gravity, and may specifically indicate the upper or lower portion of the stress measuring means 10. The indicating part 420 enables the accurate measurement of the circumferential position of the stress measuring means 10 when the connecting means 400 are connected to each other. Also, the indicator 420 may be disposed at a position where the stress measuring means 10 is coupled to the connecting means 400.

The indication unit 420 may be a variety of display means such as a predetermined projection or engraving. In some cases, the indication unit itself may be formed as a stopper, a hole or a groove in a predetermined coupling means, have.

The anchor part 410 may further include an anchor part 410 connecting the connecting parts 400 to each other so that the connecting parts 400 can be coupled while aligning the positions of the indicating parts 420.

The connecting means 400 is formed in a hollow shape so that the cable 130 can be guided while being inserted into the inner circumferential side and guided out to the outside. As will be described later, in the overcoring process, It is preferable to be coupled to the stress measuring means 10 by a force in one direction so as to be able to be detached from the test piece 10, and to be released by force in the other direction.

Hereinafter, the initial stress measurement method by the initial stress measuring means described above will be described.

3 is a flowchart showing an initial stress measurement method according to the concept of the present invention.

In the concept of the present invention, a method of measuring the stress due to release in the osteotomy through the stress measuring means 10 is presented.

In order to achieve this, first, an outer hole is formed by firstly pouring a predetermined bit and a drilling device to a predetermined depth to form an outer hole (S110), and then the inner hole having a diameter smaller than that of the outer hole is secondarily pushed (S120).

The inner cavity can be formed with a diameter and a depth into which the stress measuring means 10 can be inserted, the diameter of the inner cavity substantially corresponding to the overall outer diameter of the stress measuring means 10, The length of the rod portion 220 of the first embodiment.

After the inner hole is formed, the stress measurement means 10 is sequentially installed from the load unit 220 (S200), and then the third stage of bending (S130) is performed. . ≪ / RTI >

That is, the stress measuring means 10 inserted in the inner hole is pushed back to the periphery of the rock around the rock by means of a bit having a large diameter, thereby releasing the pressure applied to the stress measuring means 10 in the surrounding rock mass, It is possible to calculate the release stress.

In this manner, the overcoring strain measurement S140 is performed at the same time as the third pushing step S130, and the strain detected from the plurality of strain gages 300 is transmitted to the external data calculating means City).

The above procedure was described as a method of measuring the release stress as a primary stress measurement process. In addition, the stress measuring means 10 formed in the third pivoting after the third pivoting and the rock surrounding it are used as the core for the pressure measurement (S300), as described below.

FIG. 4 is a diagram for explaining the above-described initial stress measurement method visually.

As described above, the concept of the present invention is that the release stress is measured through the first to third pumping processes. In this case, the depth of the first punched hole 1010 is determined by the depth required for measurement.

For example, when the interval between 7.8 m and 8.4 m is the measurement interval, the first depth (l 1) of the outer hole 1010 is formed to be 7.8 m, and the inner hole 1020 is formed at a portion of the outer hole 1010 And is formed in a second depth l2 corresponding to 0.6 m.

Accordingly, FIG. 4A shows a process of forming the outer hole 1010, which is the first step, and FIG. 10B shows a process of forming the inner hole 1020.

The diameter of the outer hole 1010 may be determined to be, for example, 130 mm. At this time, the excavation is performed by a cylindrical excavation means. As described later, the outer hole 1010 and the third excavation portion 1030 are the same and can be made of the same equipment. The thickness of the excavation means is 11.5 mm . That is, the excavating means can be set to an outer diameter of 130 mm and an inner diameter of 107 mm.

On the other hand, in the concept of the present invention, in order to measure the release stress, insertion is required in a state in which the bottom surface of the stress measuring means 10 is maintained substantially on the horizontal plane.

However, in consideration of the inserting process, it is necessary to request a slight upward upward inclination and an upward angle of more than 0 DEG and less than 1 DEG is preferably formed. Due to this upward angle, water and foreign substances are discharged when perforating and inserting the equipment, so that smooth entry is possible. If it is excessively large, a measurement error may occur due to the characteristics of the stress measuring means of the present invention.

4C shows a step of inserting the stress measuring means 10 so as to correspond to the inner circumferential side of the inner cavity 1020 through the outer hole 1010 after the formation of the inner cavity 1020 is completed.

In the case of the inner cavity 1020, it is formed to correspond to the outer periphery of the stress measuring means 10, and in the description of the present invention, it can be formed by an excavating means having an outer diameter of 38 mm.

In this case, since insertion into a predetermined depth is required, insertion through a plurality of connection means 400 is required, and the connection means 400 can be accurately connected to each other by the anchor portion 410 As described above. At this time, the directing part 420 is formed on the opposite side of the connecting means 400, so that the arrangement of the strain gauges 300 for multi-directional measurement can be effectively maintained in the inserting process.

4 (d) shows a state in which the insertion of the stress measuring means 10 is completed. At this time, in the state where the end of the rod portion 220 is in contact with one end of the inner hole 1020, The body of the piston unit 200 connected to the rod unit 220 is moved to the other side and the pressure is applied to the cured material in the receiving unit 120 during the process. The piston 200 is moved to the other side and the hardened material is discharged to the outflow portion 231 through the inside of the outflow channel 230 to cover the piston portion 200 mainly, .

When the hardened material is hardened, the stress measuring means 10 can be fixed at the correct position of the inner cavity 1020, so that the position and the contact portion at the time of the pushing by the third- do.

At this time, the connecting means 400 is drawn out to the other side, and the cable 130 transmits a signal to the outside.

When the insertion and fixing of the stress measuring means 10 is completed, the third bending is performed. The third bending is preferably made to correspond to the radius of the bushing 1010 for simplicity of the process and the equipment.

FIG. 4D shows a process of measuring the release stress by the third-order leak portion 1030. At this time, there is a difficult problem in continuous measurement, and preferably, the third leaked portion 1030 is pushed at intervals of 50 mm, and the release strain is detected step by step.

When the third pivoting is completed, the stress measuring means 10 and the core of the surrounding rock mass can be separated from each other, and the core is subjected to a separate pressure strain measurement step S300.

5 is a flowchart specifically showing the step S200 of installing the stress measuring means in the above-described release stress measuring method.

1, a hardening material is injected (S210) into the receiving portion 120 of the body portion 100 when the body portion 100 and the piston portion 200 are separated from each other, do. In this case, it is preferable that the cured material is made of epoxy in consideration of curability and adhesion with the rock and stress measuring means 10, but it is not limited thereto.

After the filling of the hardened material is completed, the body of the piston 200 is partially inserted into the receiving part 120 of the body part 100 and inserted into the inner cavity 1020 (S230).

At this time, the connection (S260) between the stress measuring means 10 and the connecting means 400 and the connecting means 400 can be performed as described above, and the accurate measurement of the circumferential direction of the stress measuring means 10 An instruction unit 420 may be formed. At this time, it is preferable that the instruction unit 420 is formed at the same position in the circumferential direction on the both end sides of the connection unit 400.

When the insertion of the stress measuring means 10 into the inner cavity 1020 is completed, the hardening substance S240 is injected into the space between the inner cavity 1020 and the stress measuring means 10 due to the pressure applied to the rod portion 220 S250), and the cured material is hardened (S250) with a lapse of a predetermined period of time, and the close fixation is completed. This curing process can be controlled by the temperature, composition or environment of the material, but it can be considered that the curing is completed between about 12 hours and 24 hours when it is made of epoxy.

6 shows a configuration for pressure measurement of an initial stress measurement method according to a further concept of the present invention.

As described above, when the core is separated from the excavation site by the third excavation part 1030, it is inserted into the chamber part 20 with the stress measuring means 10 coupled to the inner circumferential side.

The chamber 20 may have a substantially cylindrical shape with an inner diameter corresponding to the outer diameter of the core, and the outer diameter of the core may be 107 mm according to the embodiment. However, the present invention is not limited thereto .

At this time, the chamber part 20 forms a hydraulic oil path therein, and is supplied with the hydraulic pressure of the pressure supply part 500 through the hydraulic line 510 to provide the pressure in the inner circumferential direction of the core block 1100 .

When the stress is measured by the stress measuring means 10 while pressure is applied again as opposed to the release stress measurement, the modulus of elasticity of the core and the Poisson's ratio can be calculated.

When the calculation of the strain due to stress release, the elastic modulus of the rock core and the Poisson's ratio are completed, the magnitude and direction of the principal stress can be analyzed, and the stress in the horizontal and vertical directions and the calculation of the lateral pressure coefficient Lt; / RTI > The Poisson's ratio means the ratio of the shrinkage ratio to the elongation, and the lateral pressure coefficient means the ratio of the horizontal stress to the vertical stress in any part of the ground based on the Poisson's ratio.

7 is a graph showing strain data at the time of stress release according to the initial stress measuring means and the initial stress measuring method therefor in the embodiment of the present invention.

As shown in the drawing, it is confirmed that the expansion deviations of 90 series perpendicular to the central axis are larger than that of the 45 series and 135 series.

At this time, it can be seen that the degree of increase and decrease of strain is relatively large in the case where the increase of the strain rate is reversed in the interval of 10 cm to 20 cm of the cavity 1020 and in the case of the interval thereafter. This indicates the influence of the other end portion farther from the portion where the strain gauge 300 is disposed in the initial section of the inner cavity 1020. It is preferable that the analysis of this section is excluded when calculating the data.

8 is a graph showing strain data at the time of pressure measurement according to the initial stress measuring means and the initial stress measuring method therefor in the embodiment of the present invention. The embodiment of the present invention shows a result of performing a biaxial compression test, in which pressurization by the chamber part 20 is performed.

The pressing of the present invention shows the strain when a biaxial compressive force is applied to a core having a length of 50 mm and a diameter of 107 mm and is increased in units of 2.5 MPa up to 15 MPa.

In the same way, it is confirmed that the strain of the 90 strain strain gages 300 is the largest. Unlike the case of the interference due to the pivoting process of the third strain relief portion 1030, the strain is shown as a first straight line.

The calculated elastic modulus is 12.6 GPa and Poisson 's ratio is 0.218.

The calculation results of the initial stress based on the above data are shown in the following table.

division Primary stress (MPa) Direction (°) Slope (°) The maximum principal stress (σ1) 2.6 054 24 Intermediate principal stress (σ2) 2.4 228 65 Minimum principal stress (σ3) 1.3 320 03

Maximum horizontal stress (MPa) Minimum horizontal stress (MPa) Vertical stress (MPa) Side pressure coefficient (Ko) 1.97 1.74 1.02 1.82

Here, the lateral pressure coefficient is expressed by the following equation.

The strain, elastic modulus and Poisson's ratio at stress release can be measured by performing two processes according to the concept of the present invention according to the initial stress measurement means and the initial stress side method according to the stress release and the pressing on the mined core And it is possible to calculate the maximum, minimum horizontal stress, vertical stress and lateral pressure coefficient accurately. Therefore, it is possible to design and construct the excavation process appropriately for the situation, and the reliability of the construction can be remarkably improved.

Particularly, by applying the triaxial strain cell, it is possible to perform accurate measurement in multiple directions, and by inserting the body part, the piston part, and the rod part of the present invention, it is possible to insert and fix the accurate depth, .

In the foregoing, the present invention has been described in detail based on the embodiments and the accompanying drawings. However, the scope of the present invention is not limited by the above embodiments and drawings, and the scope of the present invention will be limited only by the content of the following claims.

10 ... stress measuring means 20 ... chamber portion
100: Body part 110: First sealing part
111 ... reinforced sealing portion 120 ... accommodating portion
130, 131 ... Cable 200 ... Piston part
210 ... second sealing portion 220 ... rod portion
230 ... outflow channel 231 ... outflow channel
250 ... sensor part 300 ... strain gauge
400 ... connection means 410 ... anchor portion
420 ... command unit 500 ... pressure supply unit
510 ... hydraulic line 1100 ... core block

Claims (8)

A piston unit 200 including a rod unit 220 inserted into one side of the excavation hole and contacting the end side, and a body extending from the other side of the rod unit;
A body part 100 comprising a plurality of strain gauges 300 arranged in a circumferential direction with respect to a receiving part 120 into which the body of the piston part is inserted to the inner periphery and having a direction at three or more angles with respect to the central axis;
A cable 130 extending to the other side of the body and outputting a detection signal of the strain gage to the outside;
A first sealing part 110 formed in a ring shape protruding in the outer circumferential direction of the other side of the body part and having a radius corresponding to the inner circumference of the excavating hole; And
And a second sealing part 210 formed in a ring shape protruding in a circumferential direction on one side of the body of the piston part and allowing a space between the first sealing part and the hardened material to be injected, Measuring means. The method according to claim 1,
And a reinforcing sealing part (111) formed on the body part and spaced apart from the first sealing part to one side. The method according to claim 1,
Wherein the strain gages (300) are composed of twelve strain gages (300) and are arranged at different angles in the longitudinal and circumferential directions of the central axis. The method according to claim 1,
The body of the piston portion includes:
And the hardened material is injected into the space between the outflow portion (231) and the excavated hole through the outflow passage (230) while applying pressure to the other side of the accommodating portion. The method according to claim 1,
And two or more connection means (400) connected to the other side of the body portion,
Characterized in that the connecting means comprises an indicator (420) so that the circumferential placement of the strain gauges relative to the direction of gravity during insertion into the drill hole can be maintained. 7. An initial stress measuring method using the initial stress measuring means according to any one of claims 1 to 5,
An outer hole forming step of forming an outer hole with a first depth (? 1);
Forming an inner hole having a radius smaller than a radius of the outer hole from the one end side of the outer hole by a second depth (? 2);
Filling a curing material in the receiving portion;
Coupling the piston portion to the receiving portion;
Inserting the stress measuring means in a fixed state in the circumferential direction;
Injecting a hardening material inside the receiving part into a space between the body and the inner space by the pressure provided to the rod part;
The hardened material is hardened and the body part is fixedly disposed in the hollow;
An overcooling step in which a strain due to stress release is detected from strain gauges while a tertiary bulging portion is formed from an outer circumferential side of the inner hole to an inner diameter corresponding to the outer circumferential hole;
A pressure measuring step in which strain is detected from the strain gauges while the core block due to the third bending is biaxially pressed in the chamber;
A calculation step of calculating a modulus of elasticity of the core and a Poisson's ratio through the strain at the pressure measuring step; And
And calculating a lateral pressure coefficient as a horizontal normal stress and a magnitude and direction of the principal stress calculated through the elastic modulus of the overcoring step, the elastic modulus of the calculation step, and the Poisson's ratio. The method according to claim 6,
The diameter of the outer hole is 130 mm,
The diameter of the inner hole is 38 mm,
Wherein the core has a diameter of 107 mm. The method according to claim 6,
Wherein the outer hole and the inner hole are pushed so as to be inclined upwards by more than 0 DEG and less than 1 DEG in the horizontal direction with respect to gravity.

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