Method for estimating amount of gap in sheath of existing PC structure and grout re-filling method

Abstract

To provide a method with which measurement of an amount of a gap in a sheath can be accurately performed with simpler equipment on site, and operation to fill grout into a gap part in the sheath can be efficiently performed while minimizing unnecessary consumption of a grout material.SOLUTION: A method includes: mortising a hole part reaching a gap part in a sheath from a surface of an existing PC structure; reducing a pressure in the gap part in the sheath and measuring the pressure in a stationary state with a vacuum gauge; when the pressure enters the stationary state, causing the gap part in the sheath and gas capacity measurement means to communicate with each other and measuring the gas capacity in the gap part in the sheath as the amount of a gap in the sheath; calculating a correction coefficient for the pressure in the stationary state by using a formula for correction coefficient calculation obtained by calibration in advance; and correcting a measured value of the amount of the gap in the sheath by using the correction coefficient.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for estimating the volume of voids that are not filled with grout within the sheath of an existing PC structure, and a method for refilling the voids with grout. [Background technology]

[0002] In post-tensioned prestressed concrete structures (PC structures), the PC steel is inserted into the sheath, then tensioned and grout is injected, but the grout used in structures built in the 1980s allowed bleeding, so there are cases where voids have formed inside the sheath near the ends of the grout girders. If water containing antifreeze gets into the areas where the grout is insufficiently filled, the PC steel may corrode and break, ultimately reducing the load-bearing capacity of the structure.

[0003] In the areas where grout has not been filled, holes are drilled from the concrete surface to the voids in the sheath, and grout is re-injected through these holes. In this case, it is desirable to determine the amount of voids in the unfilled areas before construction in order to determine the amount of grout required. If the amount of voids is not adequately determined, there may be a shortage of material, which may force the injection work to be stopped midway, making construction impossible or causing delays in the construction period. In addition, excess material may be generated, making the process uneconomical.

[0004] Known techniques for measuring the amount of voids in a sheath include a method in which a predetermined amount of gas is allowed to flow at a predetermined pressure into or out of a hole in an existing PC structure or into a void in the sheath, and the amount of voids (volume) in the sheath is measured based on the time variation of the pressure ratio obtained by dividing the measured pressure by the predetermined pressure (Patent Document 1); A method in which gas is made to flow into or out of the void in the sheath at a predetermined pressure, and the amount of void (volume) in the sheath is calculated based on the time fluctuation of the measured pressure in the low pressure range where the measured pressure starts to increase after the gas flow starts (Patent Document 2); A method of flowing a fluid into the void in the sheath, measuring the flow rate and pressure, measuring the flow time and pressure fluctuations, and calculating the void volume (volume) in the sheath based on these data (Patent Document 3). One known method (Patent Document 4) is to connect a reduced pressure container to a gap in a sheath via an on-off valve, measure the pressure and temperature in the reduced pressure container and the pressure and temperature of the air connecting the reduced pressure container to the gap in the sheath before and after the on-off valve is opened, and determine the amount of gap (volume) in the sheath based on this data. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-150734 A (Patent No. 4959541) [Patent Document 2] JP 2012-127970 A (Patent No. 5286427) [Patent Document 3] JP 2018-169239 A (Patent No. 6810422) [Patent Document 4] JP 2018-003464 A (Patent No. 5997864) Summary of the Invention [Problem to be solved by the invention]

[0006] However, all of the above-mentioned known techniques estimate void volume by measuring pressure fluctuations together with time information, so measurements are performed in a complicated environment with on-site instruments such as a personal computer, a data logger, a temperature sensor, a pressure gauge, a vacuum gauge, etc. Furthermore, the above-mentioned known techniques estimate void volume through analytical studies of measurements continuously obtained by instruments, so there is a time limit for obtaining void volume measurement results on-site.

[0007] In consideration of the above circumstances, the present invention aims to provide a method for estimating the void volume in the sheath of an existing PC structure and a method for refilling grout, which can accurately estimate the void volume in the sheath on-site using simpler equipment and can efficiently fill the voids in the sheath with grout while minimizing wasteful consumption of grout material. [Means for solving the problem]

[0008] In order to solve such problems, the method for estimating the void volume in the sheath of an existing PC structure according to the present invention is a method for estimating the volume of the void portion in the sheath of an existing PC structure as the void volume, A hole is drilled from the surface of the existing PC structure to the gap in the sheath, The pressure in the cavity in the sheath is reduced, and the steady-state pressure is measured with a vacuum gauge; When the steady state is reached, the gap in the sheath is communicated with a gas volume measuring means to measure the gas volume in the gap in the sheath as the gap volume in the sheath; A correction factor is used to correct the measurement of the amount of void space within the sheath.

[0009] The correction coefficient is calculated by preparing a plurality of pseudo sheaths having different known void volumes, measuring the volume of each of the pseudo sheaths for each of a plurality of set pressures using the gas volume measuring means, A calibration is performed in advance to obtain a formula for calculating the correction coefficient, which approximates the relationship between the pressure of the volume of the pseudo sheath and the value obtained by dividing the value of the known void volume of the pseudo sheath by the measured value for each pressure, using the least squares method, and the correction coefficient is calculated from the pressure that has reached the steady state using the formula for calculating the correction coefficient obtained by the calibration.

[0010] The gas volume measuring means may have a cylinder whose interior is capable of communicating with the void in the sheath, and a plug that moves inside the cylinder so as to vary the volume of the space inside the cylinder in response to changes in the pressure inside the cylinder, and may be configured so that the amount of movement of the plug indicates the measurement result of the gas volume of the void in the sheath of the existing PC structure or the void in the pseudo sheath.

[0011] Furthermore, the grout refilling method of the present invention involves refilling the voids in the sheath of the existing PC structure with an amount of grout corresponding to the void volume in the sheath obtained by the method described in any one of claims 1 to 3.

[0012] According to the present invention, before measuring the void volume in the sheath of the existing PC structure, a formula for calculating the correction coefficient is prepared by calibration, a correction coefficient for the pressure in the steady state is calculated using this formula, and the measured value of the void volume in the sheath is corrected using this correction coefficient. Here, the preparation of the formula for calculating the correction coefficient by calibration can be performed at a location other than the measurement site as long as there is equipment used to measure the void volume in the sheath of the existing PC structure, and once the formula for calculating the correction coefficient is prepared, it can be used universally as long as the same equipment is used. Therefore, at the measurement site, the correction coefficient calculated for the pressure in the steady state is obtained from the formula, and the measurement result of the void volume in the sheath is corrected using the correction coefficient, and an estimated value of the void volume in the sheath can be obtained, eliminating errors caused by the airtightness of the system from the void in the sheath to the gas volume measuring means, the variation in the accuracy of the gas volume measuring means, the deformation of the above system, and the like. This enables the amount of voids in the sheath to be estimated accurately on-site, and enables the work of filling the voids in the sheath with grout to be carried out efficiently while minimizing wasteful consumption of grout material. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram for explaining a method for measuring the amount of void in a sheath 3 according to this embodiment. [Diagram 2] 2 is a diagram showing a state in which a gap 10 in a sheath 3 and a cylinder 11 are in communication with each other in the measurement method of FIG. 1. FIG. [Diagram 3] 11 is a graph showing the relationship between the measured value and the true value of the void volume in the sheath 3. [Figure 4] FIG. 13 is a diagram showing a specific example of calibration. [Diagram 5] 13 is a diagram showing a method for calculating the gas volume in the pseudo sheath A0 from the amount of movement of the plug 11b. FIG. [Figure 6] This is a graph showing the relationship between pressure, the measured gas volume of the pseudo sheath, and the value (correction coefficient α) obtained by dividing the known void volume of the pseudo sheath by the measured gas volume of the pseudo sheath, for each pseudo sheath (A0-A4) with different known void volumes. [Figure 7] FIG. 13 is a diagram showing the addition of a cylinder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Next, an embodiment of the present invention will be described in detail with reference to the drawings.

[0015] FIG. 1 is a diagram for explaining a method for measuring the amount of void in the sheath 3 in this embodiment. In the figure, 1 denotes an existing PC structure, and a sheath 3 into which PC steel members 2 are inserted is disposed within the existing PC structure 1. Grout 4 is filled within the sheath 3 to prevent the PC steel members 2 from coming into contact with air and water and protect the PC steel members 2 from corrosion. If there is an unfilled portion 10 of grout 4 within the sheath 3 (hereinafter referred to as a "void portion"), this portion of the PC steel members 2 will come into contact with air and water and become susceptible to corrosion. Therefore, an amount of grout equivalent to the volume of the void portion 10 within the sheath 3 is reinjected into the void portion 10 to eliminate the void portion 10. This embodiment relates to a method for estimating the void volume, which is the volume of the void portion 10 within the sheath 3.

[0016] In estimating the volume of the void in the sheath 3, a hole 12 is first provided from the surface of the existing PC structure 1 to the void 10 in the sheath 3, and a connection cap 5 attached to one end of a first hose 6a is connected to the hole 12. A vacuum gauge 7 capable of measuring the pressure of the system from the void 10 in the sheath 3 to the vacuum pump 9 is connected to the first hose 6a. The other end of the first hose 6a is connected to either the system of the vacuum pump 9 or the system of the cylinder 11, which is a gas volume measuring means, via a three-way switching valve 8, which can be freely switched between them. The vacuum pump 9 is connected to one of the switching paths 8a of the three-way switching valve 8 via a second hose 6b. The cylinder 11 is connected to the other switching path 8b of the three-way switching valve 8 via a third hose 6c. The cylinder 11 includes a cylindrical cylinder body 11a having an internal space communicating with the third hose 6c, and a stopper 11b that moves so as to vary the volume of the internal space in response to changes in air pressure in the internal space of the cylinder body 11a. The three-way switching valve 8 is a valve that can manually switch whether the vacuum pump 9 or the cylinder 11 is connected to the gap 10 in the sheath 3 via the first hose 6a.

[0017] Next, a method for estimating the amount of void space in the sheath 3 will be described. First, the state of the three-way switching valve 8 is set so that the system of the vacuum pump 9 is communicated with the gap 10 in the sheath 3 via the first hose 6a and the second hose 6b, and then the vacuum pump 9 is operated to start depressurizing the gap 10 in the sheath 3. Here, since the vacuum gauge 7 is connected to the first hose 6a between the three-way switching valve 8 and the connection cap 5, the pressure of the gap 10 in the sheath 3 is measured in real time by the vacuum gauge 7. The pressure of the gap 10 in the sheath 3 is gradually reduced by the evacuation by the vacuum pump 9, and the pressure measured by the vacuum gauge 7 becomes approximately stable and steady state as the exhaust speed of air from the gap 10 in the sheath 3 to the three-way switching valve 8 balances with the leakage speed of air from the atmosphere to the gap 10 in the sheath 3 to the three-way switching valve 8. At this time, as shown in FIG. 2, the three-way switching valve 8 is switched so that the cylinder 11 is communicated with the gap 10 in the sheath 3 via the first hose 6a and the third hose 6c. When the system of the void 10 in the sheath 3 and the cylinder 11 is connected, the plug 11b of the cylinder 11 moves an amount corresponding to the void volume of the void 10 in the sheath 3, and by artificially reading the amount of movement of this plug 11b, a measurement value of the void volume, which is the gas volume of the void 10 in the sheath 3, can be obtained.

[0018] However, in reality, the measured value of the void volume in the sheath 3 obtained as described above includes errors due to the degree of sealing of the system between the gap 10 in the sheath 3 and the cylinder 11, the friction of the plug 11b in the cylinder 11, the deformation of each hose 6a, 6b, 6c, etc., as shown in the graph of FIG. 3. In the graph of FIG. 3, the horizontal axis indicates the measured value of the void volume in the sheath 3, the vertical axis indicates the true value of the void volume, and the area between the two dashed lines indicates an area in which the error of the measured value of the void volume from the true value is within 10%. Therefore, it is desirable to correct the measured value of the void volume in the sheath 3 to eliminate the above-mentioned error. For this correction, a method is adopted in which a calculation formula for calculating a correction coefficient is created in advance by calibration, and when measuring the void volume in the sheath 3, a correction coefficient for the pressure in the steady state is calculated using the calculation formula for calculating the correction coefficient, and the measured value of the void volume in the sheath 3 is corrected using this correction coefficient.

[0019] Calibration is performed by preparing multiple pseudo sheaths with different known void volumes, measuring the volume of each pseudo sheath using a gas volume measuring means for multiple set pressures, and deriving a calculation formula for calculating a correction coefficient that approximates a linear equation using the least squares method to the relationship between the pressure of the pseudo sheath volume and the value obtained by dividing the value of the known void volume of the pseudo sheath by the measured value for each pressure.

[0020] (Specific example of calibration) Fig. 4 shows a specific example of calibration. As a plurality of pseudo sheaths A with different known void volumes, for example, a plurality of pseudo sheaths A0, A1, A2, A3, and A4 with known void volumes (liters) of 0.66, 1.98, 3.3, 4.62, and 6.6 are prepared. One end of each of the pseudo sheaths A0, A1, A2, A3, and A4 is provided with a connection valve 13 to which a connection cap 5 can be connected, and a separate valve capable of controlling the flow of air between the inside and outside of the sheath is attached to the other end, and the degree of airtightness is set by opening and closing this valve during decompression.

[0021] First, the connection cap 5 attached to one end of the first hose 6a is connected to the connection valve 13 of one of the pseudo sheaths (let's call it pseudo sheath A0), and the vacuum pump 9 is operated to start decompression while the three-way switching valve 8 is switched so that the vacuum pump 9 communicates with the pseudo sheath A0 via the first hose 6a and the second hose 6b. When the pressure measured by the vacuum gauge 7 drops to a set value, the three-way switching valve 8 is switched so that the cylinder 11 communicates with the pseudo sheath A0 via the first hose 6a and the third hose 6c. This causes the stopper 11b to move within the cylinder 11, and the amount of movement of this stopper 11b is read, and the gas volume within the pseudo sheath A0 is calculated from the amount of movement that was read.

[0022] The method for calculating the gas volume in the pseudo sheath A0 from the movement of the plug 11b is as follows: As shown in Fig. 5, when the inner diameter of the cylinder 11 is d (mm) and the movement of the plug 11b is L (mm), the gas volume V in the pseudo sheath A0 is obtained by the following formula. V = π × d 2 ÷4×L×1000

[0023] The measurement of the gas volume in the pseudo sheath A0 is repeated in the same manner by changing the pressure setting value. In this example, the pressure (MPa) setting value is switched to -0.095, -0.09, -0.08, -0.07, and -0.06 in sequence, and the gas volume V in the pseudo sheath A0 is calculated for each pressure setting value. The gas volume V is similarly calculated for each pressure setting value for the other pseudo sheaths (A1-A4). Furthermore, the vacuum gauge will show 0 (zero) at atmospheric pressure, and will show a negative value (minus) for pressures lower than atmospheric pressure.

[0024] 6 is a graph showing the relationship between pressure (MPa) and the value (correction coefficient α) obtained by dividing the known void volume of each pseudo sheath (A0-A4) by the measured gas volume of the pseudo sheath. According to the graph, the relationship between pressure (MPa) and correction coefficient α can be approximated to a linear equation using, for example, the least squares method, and this approximation equation is used as the calculation equation for calculating the correction coefficient.

[0025] When measuring the void volume within the sheath 3 of an existing PC structure 1, a correction coefficient for the steady-state pressure is calculated using a formula for calculating the correction coefficient, and the correction coefficient is multiplied by the measured value of the void volume within the sheath 3 to obtain a corrected result for the measured value of the void volume within the sheath 3.

[0026] This makes it possible to obtain the volume of void space within the sheath 3 with errors caused as much as possible by the degree of airtightness of the system from the void space 10 within the sheath 3 to the cylinder 11, which is the gas volume measuring means, friction of the plug 11b in the cylinder 11, deformation of the hoses 6a, 6b, 6c, etc., eliminated. Furthermore, by filling the void 10 in the sheath 3 of the existing PC structure 1 with an amount of grout 4 corresponding to the amount of void in the sheath 3 obtained in this manner, it is possible to significantly reduce the amount of grout 4 that is wasted, and to prevent the injection work from having to be interrupted midway due to a lack of material, making the work impossible, and also to increase the efficiency of the work of refilling the grout 4.

[0027] In addition, when the variation range of the gas volume in the void portion of the sheath 3 and the pseudo sheath A is large, it is possible to measure the void volume with a large variation range simply by adding an additional cylinder 11' as shown in Figure 7. [Explanation of symbols]

[0028] 1 Existing PC structure 2 PC steel material 3 Sheath 4. Grouting 6a First Hose 6b Second Hose 6c Third Hose 7 Vacuum gauge 8 Three-way switching valve 9. Vacuum Pump 10. Void in sheath 11 Cylinder 11b Stopper A Pseudo sheath

Claims

1. This is a method to estimate the volume of voids in the sheath of an existing PC structure as the void volume. A hole is drilled from the surface of the existing PC structure to the gap in the sheath, The pressure in the cavity in the sheath is reduced, and the steady-state pressure is measured with a vacuum gauge; When the steady state is reached, the gap in the sheath is communicated with a gas volume measuring means to measure the gas volume in the gap in the sheath as the gap volume in the sheath; Correcting the measurement of the amount of void in the sheath using a correction factor A method for estimating the amount of voids within the sheath of existing PC structures.

2. The correction coefficient is Prepare multiple pseudo sheaths with different known void volumes, measuring the volume of each of the pseudo sheaths for each of a plurality of set pressures using the gas volume measuring means; Calibration is performed in advance to obtain a formula for calculating a correction coefficient that approximates a relationship between the pressure of the volume of the pseudo sheath and a value obtained by dividing the value of the known void volume of the pseudo sheath by a measured value for each pressure, using a least squares method, to a linear equation; The correction coefficient is calculated from the pressure in the steady state using a calculation formula for calculating the correction coefficient obtained by the calibration. A method for estimating the amount of voids in the sheath of an existing PC structure as described in claim 1.

3. The gas volume measuring means has a cylinder whose inside can communicate with the void in the sheath, and a plug that moves inside the cylinder so as to vary the volume of the space inside the cylinder in response to a change in the pressure inside the cylinder, and is configured so that the amount of movement of the plug indicates the measurement result of the gas volume of the void in the sheath of the existing PC structure or the void in the pseudo sheath. A method for estimating the amount of voids in the sheath of an existing PC structure as described in claim 2.

4. A grout refilling method, comprising refilling the voids in the sheath of the existing PC structure with an amount of grout corresponding to the amount of voids in the sheath obtained by the method according to any one of claims 1 to 3.

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