JP2019128272A - Estimation method of tensioning force of tendon in ground anchor - Google Patents

Abstract

To provide a method which can estimate a tensioning force working to a tendon of a ground anchor more easily in a spot where the ground anchor is provided.SOLUTION: A method estimating a tensioning force working to a tendon of a ground anchor having the tendon fastened by a fixing member located on a compression plate arranged to a pressed body with a condition that the end is projected includes: (1) a step measuring residual stress of the fixing member fastening the tendon to the compression plate; and (2) a step calculating the tensioning force corresponding to the measured residual stress on the basis of a calibration curve obtained previously indicating a correlation relationship between the residual stress and the tensioning force.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for estimating a tension force of a tension material in a ground anchor that has already been constructed.

  Ground anchors are widely used as a technique for preventing landslides and collapse on slopes such as mountain slopes. The ground anchor is a system that stabilizes the ground using tension as tension of a tendon located between an anchor body embedded in the ground and a pressure receiver located on the ground surface.

  FIG. 1 schematically shows the ground anchor in a sectional view. One end portion 12 of the tendon 10 is coupled to an anchor body 14 formed in the ground by, for example, grout, and the other end portion 16 projects from the ground surface 18. A pressure receiving body 20 and a bearing plate 22 are provided on the ground surface 18, and the tendon 10 protrudes outward through them.

  When installing a ground anchor, the tension member 10 is fixed by a fixing member 24 (for example, a nut) located on the bearing plate 22 in a state of being pulled by a tension means (for example, jack), that is, in a state of tension applied. Has been. As a result, the ground is stabilized by the tension acting on the tendon 10 between the pressure receiving body 20 and the anchor body 14. As shown in the figure, the end portion 26 of the tension member 10 is held in a state of being exposed from the fixing member 24 in order to sufficiently retain the acting tension force.

  After the construction of the ground anchor, the adhesion of the end portion of the tendon 10 to the fixing member 24 causes corrosion of the tendon and the fixing member to the surrounding environment, vibration of the ground, and surrounding environment with the passage of time. As a result, there is a possibility that the tensioning state of the tendon changes and the tension during construction is not always maintained. Therefore, even after construction, the soundness of the ground anchor, specifically, a change in tension state such as loosening or over-tensioning or breaking in the tension member 10, a change in adhesion state in the fixing member 24, deterioration due to corrosion of the tension member 10, etc. It is necessary to properly manage the function of the ground anchor by appropriately grasping the occurrence of damage and damage.

  Heretofore, visual inspections for visually confirming the state of exposed portions of the tendon 10 on the ground, the pressure bearing plate, etc., and lift-off tests to evaluate the tense force of the tendon 10 by pulling the tendon 10 have been conducted. .

  Since visual inspection only confirms the occurrence of rusting of the tendon 10 and floating of the bearing plate 22, the tension of the tendon 10 directly linked to the function of the ground anchor can not be properly evaluated. In addition, it is not possible to evaluate the deterioration of the fixing state of the fixing member 24 and the deterioration and damage of the tension material 10 and the anchor body 14 in the ground.

  In the lift-off test, center hole type jacks and small / lightweight jacks are used, so it is necessary to install such equipment and take measures to prevent falling. For this reason, it takes a lot of time to measure the tension of the tension members of a large number of ground anchors that are enforced on the slope, and the amount of work is enormous. In addition, due to the nature of the ground and aging, when the lift is turned off, the anchor body 14 may come off, and the tension member 10 may break.

  In consideration of such problems, as a method for nondestructively evaluating the ground anchor health, Patent Document 1 and Patent Document 2 propose to evaluate the ground anchor health based on the vibration frequency. ing. Although these techniques can be evaluated with sufficient accuracy at the laboratory level, it cannot be said that they have been evaluated with sufficient accuracy in field measurements, and further improvements have been desired.

  Patent Document 3 discloses a method for evaluating the soundness of a ground anchor based on vibration characteristics obtained by hitting the ground anchor from the outside. This method includes a database construction step, a soundness evaluation formula model. Includes the construction process and the soundness evaluation process. When the soundness level is evaluated by this method, the tension can be estimated with high accuracy, but it is not always easy to perform these steps.

Japanese Patent Laid-Open No. 2001-074706 JP 2003-121278 A JP, 2017-194275, A

  Therefore, it is desirable to provide a method that can more easily estimate the tension acting on the tendon of the ground anchor at the site where the ground anchor is installed.

  The inventors conducted various studies on a method capable of estimating the tension acting on the tendon of the ground anchor more simply, and as a result, the residual stress acting on the fixing member of the ground anchor and the tension acting on the tendon Therefore, there is a correlation with the tension force, and when the correlation is used, the residual stress acting on the fixing member is measured, and the tensile force acting on the tension member using the tension is measured. It has been found that the force can be easily estimated, and the present invention has been completed.

Therefore, the present invention provides the tension force acting on the tension member in the ground anchor having the tension member fastened with the end portion protruding by the fixing member positioned on the bearing plate provided on the pressure receiving body. Provide a way to estimate. This method
(1) a step of measuring the residual stress of the fixing member that fastens the tension member to the bearing plate; and (2) a residual measured based on a calibration curve obtained in advance showing a correlation between the residual stress and the tension force. And determining a tension corresponding to the stress.

The "calibration curve" used in the method of the present invention can be obtained as follows:
(A) Preparation of ground anchor model The ground anchor for which the tension force is actually measured is normally in a state after being already applied on a slope or the like, and this is applied based on a predetermined specification. Therefore, the ground anchor in the field is installed using predetermined elements (that is, a predetermined anchor body, a pressure receiving body, a predetermined bearing plate, a fixing member, and a tension member). A ground anchor is similarly constructed using the same elements as those constituting the ground anchor, and this is used as a ground anchor model.

  Therefore, in the ground anchor model, the end of the ground anchor is measured by the elements constituting the ground anchor whose tension is to be measured, that is, the pressure receiving body, the support plate provided thereon, and the fixing member provided thereon. The tendon is attached to the pressure receiving body in a projecting state. Specifically, the ground anchor shown in FIG. 1 in a state where the ground 30 does not exist is prepared as a ground anchor model. As long as a tensile force can be applied to the tendon 10, the anchor body 14 may or may not be provided at the end portion 12 of the tendon 10 as illustrated.

(B) Acquisition of calibration curve using ground anchor model Next, using the above-described model, for example, a tensile force tester is used to apply a predetermined tensile force x1 (hence, tension force x1) to the tension material. Then, measure the residual stress y1 on the side surface of the fixing member, which is measured at that time. Then, different tensile force x2 (hence, tension force x2) is applied to the tension member, and the residual stress y2 on the side surface of the fixing member measured at that time is measured. The different tensile forces to be applied are at least two different, preferably three or more different, for example, four different tensile forces, and the respective residual stresses are measured. The number of different tensile forces is not particularly limited as long as it is two or more. Basically, the greater the number, the better the estimation accuracy of the tension.

  In this way, the relationship between the applied tensile force (x) and the measured residual stress (y) is plotted on, for example, xy coordinates, a graph is drawn, and this is obtained in advance as a correlation. In another embodiment, instead of a graph, it is possible to obtain correlation as an equation representing the relationship between x and y, particularly in the form of an approximation. In obtaining the mathematical expression, for example, various mathematical methods, use of various functions, and use of the least square method may be used. In this specification, a graph, a mathematical expression or the like indicating the correlation between the tensile force and the residual stress, which is obtained in advance in this manner, is referred to as a "calibration curve".

Based on the calibration curve thus obtained, the tension on the ground anchor already constructed on site is estimated as follows:
At the site where the ground anchor for which the tension force is to be estimated is installed, the residual stress on the side surface of the fixing member from which the tension material protrudes is measured (that is, the above step (1) is performed), and then obtained in advance. Based on the calibration curve, that is, the correlation between the residual stress and the tensile force, the tensile force acting on the tendon corresponding to the measured residual stress is obtained, and this is used to determine the tensile force acting on the tendon. Obtained as an estimated value (ie, carry out step (2) above).

  In addition, as described above, a relationship between two types of values that are correlated using a model is obtained in advance as a calibration curve, and in actual measurement, the other value corresponding to the measured value is estimated from one measured value. As such, which is often performed, the contents can be easily understood by those skilled in the art from the description “determine based on a standard curve”.

  The tension force estimating method of the present invention can be used for a ground anchor in which a tension material is fixed in a state where the end portion protrudes outward from the end surface of the fixing member. Thus, for example, the fixing member is used for a nut type ground anchor (for example, used for SEEE method, OPS anchor, EGS method, NM method, CFRP method, STAR method etc.), wedge or wedge / nut combined type ground anchor The present invention can be applied to ground anchors of all types of commonly used methods such as those used for the SSL method, VSL method, SHS method, KTB method, Super Flowtech method, EHD method, SuperMC method, etc.

  The method of measuring the residual stress on the side of the fixing member may be carried out by any suitable known method, but it needs to be able to be measured nondestructively. For example, a method of measurement using X-rays, magnetism, light may be used.

  A particularly preferred measurement method is the X-ray diffraction stress measurement method utilizing the X-ray diffraction phenomenon. In this measurement method, X-rays are irradiated to a predetermined location on the side surface of the fixing member, and diffracted X-rays are detected to estimate residual stress. This method of measuring the lattice spacing on the metal surface of the fixing member depending on the residual stress using X-ray diffraction is known per se. An apparatus for measuring residual stress using this method is commercially available from Pulstec Industrial Co., Ltd. as a residual stress X-ray measuring apparatus (product name: μ-X360). Such an apparatus can measure the residual stress inherent in metal, ceramic, etc. using X-rays in a nondestructive manner, is small and lightweight, and can measure at high speed and high accuracy. Therefore, since the residual stress of the fixing member can be measured even at the site where the ground anchor is installed, it is suitable for use in the method of the present invention.

  In the method of the present invention, when measuring the residual stress of the fixing member of the ground anchor in the field, the oxide film or the like existing on the surface of the fixing member may adversely affect the measurement. In order to suppress this, it is preferable to electropolish the X-ray irradiated portion of the fixing member prior to measurement, if necessary.

  By the method of the present invention, the tension acting on the tendon of the ground anchor that has already been installed can be easily estimated on site.

It is sectional drawing which shows typically the structure of a ground anchor, and the element which comprises it. It is a graph as a calibration curve which shows correlation with residual stress and tension, and therefore tension, obtained using a nut type ground anchor model. It is a graph as a calibration curve which shows correlation with residual stress and tension, and therefore tension, obtained using a wedge type ground anchor model. The detail of the element which comprises a nut type ground anchor model is shown typically. The detail of the element which comprises a wedge-shaped ground anchor model is shown typically.

  In the method of the present invention, it is necessary to prepare a calibration curve in advance. For this purpose, a ground anchor model is prepared as described above, which is composed of substantially the same elements as those of the ground anchor in the field having the tendon to be measured for tension.

  Next, a predetermined tensile force is applied to the tendon of the ground anchor model using a tensile force tester, and the residual stress generated in the fixing member at that time is measured. Furthermore, different tensile forces are applied, and the residual stress that occurs in the fixing member at that time is measured.

  More specifically, using the same elements as the on-site ground anchor shown in FIG. 1, using a tensile force tester on a ground anchor model composed of a pressure receiver, a support plate, a fixing member and a tendon attached thereto, Apply tension (x) to the tendon. That is, in FIG. 1, while the pressure receiving member is fixed, a tensile force is applied to the tendon (that is, the tendon is pulled downward in FIG. 1), and residuals generated on the side of the fixing member corresponding to the tensile force applied at that time. Measure the stress (y). In this manner, various (at least two different) tensile forces are applied, and the residual stress at that time is measured. Based on these measurement results, a calibration curve indicating the correlation between tensile force (and hence tension) and residual stress is obtained as a graph, for example.

  Next, the residual stress at a predetermined location on the side surface of the fixing member of the ground anchor that has been installed is actually measured on site to obtain a measurement value (y3). Based on the calibration curve obtained as described above, a tensile force corresponding to the measured value (y3), that is, a tension force x3 is obtained. This tension force x3 corresponds to the estimated value of the tension force acting on the tension material in the ground anchor at the site.

(Correlation of nut type ground anchor)
For a nut-type ground anchor model in which the anchoring member is in the form of a nut, as a result of the residual stress measured on the side of the anchoring member when various tensions are applied to the tendon as described above, The correlation with the residual stress is shown in the graph of FIG.

The ground anchor model used for this measurement was constructed using the following elements.
A SEEE anchor (multi-PC steel strand φ33.3 mm 7 × φ11.1) was used as a tension material for the model ground anchor. A nut (S45C) was used as a fixing member, and a ground anchor in the field was reproduced in combination with a bearing plate (SS material length 280 mm × width 280 mm, thickness 36 mm). The ground anchor at the site has a pressure receiving body on the ground surface. However, in this model, the tensile force acting on the tension material is all transmitted to the fixing member, so that the pressure receiving body is omitted. The details of the elements constituting this anchor model are schematically shown in FIG.

In this measurement, three different tensile forces (100 kN, 200 kN, and 400 kN) were applied to the tendon, and the residual stress was measured at four different locations on the fixing member (total height h (see FIG. 1): 45 mm). Specifically, the following points were measured:
(A) A location 5 mm away from the boundary surface between the bearing plate and the fixing member (in FIG. 1, the end surface of the fixing member contacting the bearing plate, ie, the lower end) (that is, 11.1% of the total height of the fixing member from the boundary surface) Position away)
(B) A location 10 mm away from the boundary surface between the bearing plate and the fixing member (that is, a position away from the boundary surface by 22.2% of the total height of the fixing member).
(C) A location 15 mm away from the boundary surface between the bearing plate and the fixing member (that is, a position away from the boundary surface by 33.3% of the total height of the fixing member)
(D) A location 20 mm away from the boundary surface between the pressure bearing plate and the fixing member (that is, a position 44.4% of the total height of the fixing member away from the boundary surface).

  In the present specification, the “total height (h)” means a distance between both end faces of the fixing member, and more specifically, an end face of the fixing member and an end part of the tension member that are in contact with the bearing plate. Means the distance between the end surface of the fixing member, which protrudes outward.

  As apparent from the graph of FIG. 2, the residual stress acting on the fixing member increases as the applied tensile force increases, regardless of the measurement at any location, that is, between the tensile force and the residual stress. It turns out that there is a correlation. Instead of the graph, for example, the correlation may be expressed by an equation y = fn (x) (where fn represents a function) using an appropriate approximation method based on the obtained result.

  Regarding the measurement location, measurement at a location 20 mm away from the boundary surface (a location where the distance from the boundary surface to the measurement location is about 44% of the total height of the fixing member), that is, measurement at a location far from the boundary surface is closer to the boundary surface. Although the sensitivity is slightly inferior to the measurement at the point, it can be determined that there is no problem in practical use. Considering these, in the case of a nut-type ground anchor, it is preferable to measure at a location where the distance from the boundary surface to the measurement location is about 5% to about 40% of the total height of the fixing member, and the distance from the boundary surface to the measurement location. It is more preferable to measure at about 10% to about 35% of the total height of the fixing member, for example 10% to 30%, particularly 10% to 25%. In the case of a nut type ground anchor, the total height (h) of the fixing member is usually about 35 mm to 60 mm. Therefore, the above-mentioned ratio based on the result of using the fixing member having a total height of 45 mm is based on the nut type fixing member. It is estimated that the same applies to ground anchors.

  Next, using the same elements as the above ground anchor model, the residual stress at a predetermined location (for example, a location 10 mm away from the boundary surface) of the fixing member of the ground anchor that has already been constructed in the field is measured, and this measured value is obtained. It is assumed that y3 = 60 MPa. The tensile force (x3) corresponding to the measured residual stress (60 MPa) based on the calibration curve as the broken curve in the graph of FIG. As indicated by the broken arrows, it can be estimated to be about 260 kN.

(Correlation of wedge-shaped ground anchors)
For a wedge-shaped ground anchor model in which the anchoring member is in the form of a wedge, as a result of the residual stresses measured on the flanks of the anchoring member when various tensions are applied to the tendon as described above, The correlation with the residual stress is shown in the graph of FIG.

The ground anchor model used for this measurement was a VSL anchor ER type (multi-PC steel strand 7 × φ12.7) capable of load adjustment as a tension material of the model ground anchor constructed using the following elements. . A ring nut (S45C) was used as a fixing member, and a ground anchor in the field was reproduced in combination with a bearing plate (SS material length 275 mm × width 275 mm thickness 40 mm) and an anchor head (S45C). The ground anchor at the site has a pressure receiving body on the ground surface. However, in this model, the tensile force acting on the tension material is all transmitted to the fixing member, so that the pressure receiving body is omitted. Details of the elements constituting this anchor model are schematically shown in FIG.

  As in the case of the nut-type ground anchor, it can be seen that as the applied tensile force increases, the residual stress acting on the fixing member increases, that is, there is a correlation between the tensile force and the residual stress. Instead of the graph, the correlation may be expressed by an equation using an appropriate approximation method from the obtained result. Also in this ground anchor, the height of the fixing member was 80 mm.

In this measurement, five different tensile forces (100 kN, 200 kN, 400 kN, 600 kN, and 800 kN) were applied to the tension material, and the residual stress was measured at four different locations on the fixing member (total height: 50 mm). Specifically, the following points were measured:
(A) A location 5 mm away from the boundary surface between the bearing plate and the fixing member (that is, a position away from the boundary surface by 6.25% of the total height of the fixing member)
(B) A location 10 mm away from the boundary surface between the bearing plate and the fixing member (that is, a position 12.5% away from the boundary surface of the total height of the fixing member).
(C) A location 15 mm away from the boundary surface between the bearing plate and the fixing member (that is, a position away from the boundary surface by 18.75% of the total height of the fixing member)
(D) A location that is 20 mm away from the boundary surface between the bearing plate and the fixing member (that is, a location that is 25% of the total height of the fixing member from the boundary surface).

  As is clear from FIG. 3, it was found that there is a correlation at any of the measurement points. However, when the correlation is measured at a location 10 mm from the boundary surface (ie, a position 12.5% away from the total height of the fixing member) and at a location 15 mm (ie, the total height of the fixing member from the boundary surface). 18. When measuring at a position 75% away) When measuring at a location 20 mm away from the boundary surface (ie, at a location 25% away from the total height of the fixing member) and a location closer to the boundary surface It can be determined that the sensitivity is better than in the case of measurement at a position 5 mm away from the interface.

  Therefore, even in the case of a wedge type ground anchor, it is preferable to measure at a location where the distance from the boundary surface to the measurement location is about 5% to about 30% of the total height of the fixing member, and the distance from the boundary surface to the measurement location is fixed. It is more preferable to measure at about 10% to about 35% of the total height of the member, especially about 10% to 30%, for example about 10% to about 25%, especially about 10% to 20%. In the case of a wedge-shaped ground anchor, since the total height (h) of the fixing member is usually about 50 mm to 100 mm, the above ratio based on the result of using a fixing member with a total height of 80 mm uses a wedge-shaped fixing member It is estimated that the same applies to ground anchors.

  Next, using the same elements as the above-mentioned wedge-shaped ground anchor model, measure the residual stress at a predetermined location (for example, a location 10 mm away from the boundary surface) of the fixing member of the ground anchor already installed in the field. The value is y4 = 150 MPa. The tensile force (x4) corresponding to the residual stress (150 MPa) measured based on the calibration curve as a broken line curve of the graph of FIG. 2 in consideration of the measurement point of the fixing member is the downward direction in the graph of FIG. As indicated by the dashed arrow, it can be estimated to be about 770 kN.

  Considering the results shown in FIGS. 2 and 3, it is not necessarily preferable that the residual stress measurement be performed near the boundary surface between the bearing plate and the fixing member, and a location far away from the boundary surface (boundary From the surface, for example, it is estimated that it is not so preferable to be carried out at a point separated by 50% or more of the total height of the fixing member. In consideration of this, in terms of sensitivity to residual stress, in a ground anchor using a fixing member having an overall height of about 35 mm to about 100 mm, it is generally performed at a location away from the boundary surface within a range of about 4 mm to about 22 mm. It can be determined that it is particularly preferable to carry out at a location separated by about 8 mm to about 18 mm from the interface. Therefore, it can be judged that it is practically preferable to carry out at an intermediate range between these ranges, for example, at a place away from the boundary surface within a range of about 10 mm to about 15 mm.

  In consideration of these, in the ground anchor, in a particularly preferable aspect, the distance from the boundary surface to the measurement location is preferably measured at a location where the distance from the boundary surface to the measurement location is about 10% to about 30% of the total height of the fixing member. It is more preferable to measure the residual stress at a position where the distance of the fixing member is about 10% to about 25% of the total height of the fixing member. For example, the distance from the boundary surface to the measuring position is about 20% of the total height of the fixing member. It is particularly preferable to measure at a point.

  The method of the present invention can estimate the tension force in a very simple manner as compared with the currently practiced method for measuring the tension force acting on the tension material of the ground anchor that has already been constructed.

DESCRIPTION OF SYMBOLS 10 Tensile material 12 End part 14 Anchor body 16 End part 18 Ground surface 20 Pressure receiving body 22 Supporting plate 24 Fixing member 26 End part 30 Ground

Claims (9)

A method for estimating the tension acting on a tendon in a ground anchor comprising a tendon fastened in a state in which the end projects from the fixing member by a fixing member located on a bearing plate provided on a pressure receiving body. ,
(1) a step of measuring the residual stress of the fixing member that fastens the tension member to the bearing plate; and (2) a residual measured based on a calibration curve obtained in advance showing a correlation between the residual stress and the tension force. A method for estimating tension according to claim 1, comprising the step of determining tension corresponding to stress. The calibration curve shows the correlation between residual stress and tension and
In the same anchor model as the ground anchor, a predetermined tension force is applied to the tension member using a tensile force tester, and the residual stress of the fixing member is measured at that time. The tension | tensile_strength estimation method of Claim 1 which obtains correlation with respect to the predetermined | prescribed tension | tensile_strength obtained and applied and the residual stress measured as this correlation.   The method according to claim 1 or 2, wherein the measurement of the residual stress is performed on the side of the fixing member using an X-ray diffraction stress measurement method using an X-ray diffraction phenomenon.   The side surface of the fixing member to which the X-ray diffraction stress measurement method is applied is a region that is 10% to 30% of the total height of the fixing member from the end surface of the fixing member that contacts the bearing plate. The tension estimation method described.   The side surface of the fixing member to which the X-ray diffraction stress measurement method is applied is a region that is 10% to 25% of the total height of the fixing member from the end surface of the fixing member in contact with the bearing plate. Tension estimation method described.   4. The method according to claim 3, further comprising: measuring a residual stress of the side surface of the fixing member in a region 4 mm to 22 mm away from the end surface of the fixing member contacting the bearing plate.   The method according to claim 6, wherein the residual stress of the side surface of the fixing member in a region 8 to 18 mm away from the end surface of the fixing member in contact with the bearing plate is measured.   The tension | tensile_strength estimation method in any one of Claims 1-7 with which a fixing member is an element which comprises a nut type ground anchor.   The tension force estimation method according to any one of claims 1 to 7, wherein the fixing member is an element constituting a wedge-shaped ground anchor or a combined wedge-nut-type ground anchor.