JPH03252538A - Nondestructive stress estimating method for buried piping system - Google Patents

Abstract

PURPOSE:To estimate a stress value or strain value without requiring large-scale construction by performing small local digging within the range of earthquake displacement and analyzing the stress deformation of a buried part piping model according to the result of stress measurement. CONSTITUTION:The small local digging is carried out within the range of the influence of the earthquake sinking, landslide, etc., of the buried piping system and a stress measuring instrument which uses X rays, a magnetostriction method, an acousto-elastic method, etc., measures the current bending stress of the exposed buried piping without destruction. Consequently, the piping need not be cut. The stress of the buried piping is estimated by a stress deformation analyzing method according to the measurement result by using a signal processing method. Namely, stress measurement data on the buried piping which is measured as an absolute value and a set piping analytic model are inputted to the processing means and computer simulation is carried out so that the stress measured value equals a stress value found by the analysis. Thus, the found sinking quantity is used as an input conditions and stress values at other points in the ground displacement area are calculated as estimated values according to the condition.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a non-destructive method for removing exposed piping parts by performing small local excavations when ground subsidence or landslides occur in a buried piping system. The present invention relates to a non-destructive stress estimation method for buried piping systems that estimates stress values generated in buried piping in areas of ground displacement through stress measurements.

[Prior art] In the case of buried piping systems, when localized ground subsidence such as road subsidence or landslides occurs, there has been a desire to quantitatively evaluate stress or strain values in the piping system due to these effects. It was happening more.

FIG. 8 is a diagram showing an example of piping displacement in a buried piping system,
The figure shows a situation in which the pipeline was initially buried underground at a certain depth, but the ground subsequently subsided, and this subsidence caused the pipe to become displaced. Furthermore, the two-dot chain line of the pipeline shows the state before displacement at the time of burial, and the solid line shows the state after displacement due to ground subsidence. Generally, the amount of ground displacement d1 and the amount of piping displacement d2 due to this subsidence are also unknown. Conventionally, in order to measure the stress or strain value that occurs in the ground displacement part of a buried piping system as shown in Figure 8, a fairly long extension of the buried pipe is excavated and many parts of the exposed piping part are strained. Install a strain sensor such as a gauge and adjust the initial value of the strain measuring device to zero.

Next, a part of the piping is cut and the stress is released, and the difference between the measured strain values before and after the cutting is used for quantitative evaluation as the strain value that the piping system has been subjected to.

[Problems to be Solved by the Invention] The conventional method for measuring stress or strain values of buried piping systems as described above requires large-scale construction work such as excavating a fairly long section of the buried piping path and cutting the pipe. There was a problem.

In addition, with this method, it is not only difficult to identify the location where the maximum stress occurs, but although it is possible to evaluate the relative value of the stress state of the piping system before and after cutting the pipe, it is difficult to evaluate the absolute value. There was a problem.

The present invention has been made to solve such problems, and it is possible to calculate the stress or strain value of a buried piping system in a ground displacement area without requiring construction work such as large-scale excavation of the buried piping path and cutting of the pipe. The purpose of this study is to obtain a non-destructive stress estimation method for buried piping systems.

[Means for Solving the Problems] A non-destructive stress estimation method for a buried piping system according to the present invention, when a buried piping system in which a pipeline is buried underground is subjected to ground displacement, calculates the effect of the ground displacement. A small local excavation is carried out within the area, and a non-destructive stress measurement means is used to measure the stress in the exposed piping part by the small excavation using a non-destructive measurement method. A stress deformation analysis of the buried part piping model in the displacement area is performed, the amount of ground displacement that yields a stress analysis result that matches the stress measurement value is calculated, and the buried part in the ground displacement area is calculated based on the calculated amount of ground displacement. It is equipped with a signal processing means for estimating the stress value or strain value occurring in the piping.

[Function] In the present invention, when a buried piping system in which a pipeline is buried underground is subject to ground displacement, a small local excavation is performed within the range of the influence of the ground displacement, and the small excavation causes the exposed area to be removed. The stress in the pipe section is measured by a non-destructive stress measuring means (for example, a non-destructive stress measuring device using X-ray, magnetostrictive method, or acousto-elastic method), and the stress in the piping section is measured by a signal processing means (for example, a digital computer, a microcomputer). Perform stress deformation analysis of the buried piping model in the ground displacement area based on the stress measurement results obtained from the non-destructive stress measurement means, calculate the amount of ground displacement that will give a stress analysis result that matches the stress measurement value, and calculate the amount of ground displacement. The stress value or strain value occurring in the buried pipe in the ground displacement area is estimated based on the ground displacement amount determined.

[Example] The present invention aims to quantitatively evaluate the effects of ground subsidence, landslides, etc. on a buried piping system using a non-destructive stress estimation method for the buried piping system.

First, the outline of the non-destructive stress estimation method according to the present invention will be explained below.

(1) First, within the influence of the ground quality of the buried piping system,
One or more localized small excavations are made and stress measurements are made on the exposed piping.

This stress measurement is performed using a stress measurement device that can non-destructively measure the current bending stress of the exposed buried pipe. For example,
Stress measuring device using wire, stress measuring device using magnetostrictive method,
The measurement may be performed using any stress measuring device using the acousto-elastic method. This non-destructive method of stress measurement eliminates the need to cut pipes, unlike conventional strain gauge measuring instruments.

(2) Next, based on the stress measurement results of the exposed piping performed in section (1), stress estimation of the buried piping is performed using a stress deformation analysis method. This method eliminates the need for large-scale excavation of underground pipes and cutting of pipes, as required in the past.

An example of a non-destructive stress measuring device and an example of a stress deformation analysis method based on the stress measurement results will be described in detail below.

In this example, as an example of a device for non-destructively measuring the bending stress of the exposed piping part after performing a small local excavation,
The case of a magnetostrictive stress measuring device will be described.

In addition to X-rays and ultrasonic waves, methods using magnetostrictive sensors are available as methods for non-destructively measuring stress and residual stress in steel materials, steel structures, etc. As a method for measuring the stress of a magnetizable cylindrical material such as a round bar or a vibrator using this magnetostrictive sensor, there is a magnetostrictive stress measurement method disclosed in the previously filed Japanese Patent Application No. 153822/1982.

In the magnetostrictive stress measurement method, when a load is applied to a magnetic material, anisotropy occurs in the magnetic permeability, and the permeability in the direction of the load increases, while the permeability in the direction perpendicular to the load direction decreases. A magnetostrictive sensor with an excitation coil and a detection coil (
This method measures the direction and magnitude of principal stress by detecting it with a magnetic anisotropy sensor (also called a magnetic anisotropy sensor).

According to this measurement method, the measurement time at the - point is 10~100
■It takes only seconds and is extremely convenient to handle.

However, since conventional magnetostrictive stress measurement methods are generally performed by bringing a magnetostrictive sensor into contact with a surface to be measured, the magnetic resistance at the contact surface varies greatly depending on the state of the surface to be measured. Therefore, there was a drawback that the measurement error became large.

Therefore, the idea of measuring in a non-contact state, that is, with the magnetostrictive sensor a certain distance away from the surface to be measured, has come up, but in this case, the magnetostrictive sensitivity decreases, so the settings of the magnetostrictive sensor must be adjusted. There was another problem that required some very delicate adjustments.

The invention of the earlier application solves the problems in the non-contact measurement and develops a device that can perform magnetostrictive stress measurement on cylindrical materials such as magnetizable round bars and knobs in a non-contact manner. We have provided a method that uses a measuring device to measure the stress distribution in the circumferential direction of a cylindrical material with higher accuracy than before.

FIG. 1 is a diagram explaining the magnetostrictive stress measurement method according to the previous application, and FIG. Stress - σ
indicates that it is working. In addition, the same figure (b) shows the cylindrical material 1.
While maintaining a lift-off (gap) perpendicular to the central axis of the cylinder and a certain distance from the outer circumferential surface, move the magnetostrictive sensor 2 clockwise from the top point of the cylindrical material 1, that is, the 0'' angular position. This figure shows a method of continuously measuring magnetostrictive signals detected by the magnetostrictive sensor 2 at each angular position between 0'' and 380° by making one rotation along the circumferential direction.

FIG. 2 is a diagram for explaining the SIN approximation method using the magnetostrictive stress measurement method shown in FIG. ,
Since the maximum tensile stress occurs at an angle of 0'' (i.e. directly above the cylindrical material 1) and the maximum compressive stress occurs at an angle of 180@ (i.e. directly below the cylindrical material 1), the stress distribution is SI
The distribution approximates the Nθ curve.

FIG. 2(b) shows the actual value of stress measured by the strain gauge and the approximate value of SINθ when a load of -20 kg/- is applied to the cylindrical material. From this figure, the actual stress distribution and SI
It can be seen that it is quite similar to the Nθ curve.

Therefore, by preparing in advance a calibration curve in which this SINθ approximate value corresponds to stress values actually measured using a strain gauge or the like, the absolute value of bending stress can be measured by the magnetostrictive stress measurement method.

This concludes the explanation of the magnetostrictive stress measuring method, and next the magnetostrictive stress measuring device will be explained.

FIG. 3 is a block diagram of a magnetostrictive stress measuring device as an example of a device for measuring bending stress of a pipe in an exposed piping section according to the present invention. In the figure, IO is a traveling unit, which includes a magnetic anisotropic sensor 1 and a traveling trolley 12. The magnetic anisotropy sensor 11 is a sensor for detecting magnetic anisotropy in the circumferential direction of a pipe material in a non-contact manner, and includes, for example, an excitation coil and a detection coil that are perpendicular to each other, and a constant excitation current is passed through the excitation coil. The magnetic anisotropy caused by the action of stress is detected as a voltage signal obtained from a detection coil. The traveling trolley 1z is a traveling mechanism that travels, for example, on rails and/or gears provided on the outer periphery of the tube, and moves the magnetic anisotropy sensor 11 in the circumferential direction of the tube to perform measurements. 13 is a magnetostriction measuring section, and magnetic anisotropy sensor 1
A constant current is supplied to the excitation coil of sensor 11, and at the same time
This is a magnetostriction measurement unit that amplifies the detection signal obtained from the detection coil and outputs it as a voltage signal proportional to magnetic anisotropy. Reference numeral 14 denotes a motor driver which supplies a driving signal to the traveling trolley 12 to cause it to travel, and returns an encoder signal as position information as a result of the traveling. 15 is an A/D converter, 16 is an interface such as R8232C, I7
is a personal computer (hereinafter referred to as a personal computer),
18 is a data display section using a CRT or liquid crystal.

The operation shown in FIG. 3 will be explained. To measure the stress in the circumferential direction of a tube, for example, a rail or/and gear (not shown) is attached to the outer peripheral surface of the tube on a plane perpendicular to the central axis of the tube, and a holder is placed on the rail or/and gear. The traveling device section 10 is installed so that it can travel. Next, the personal computer 17 gives a traveling command for one rotation to the motor driver 14 via the interface 16, and the motor driver 14 causes the traveling device 10 on the rail or/and gear to travel one rotation along the tube circumference. During this traveling, the magnetic anisotropy sensor 11 (
Each detection signal detected by the sensor 11 at each angular position between 09° and 360° on the outer circumferential surface of the tube shown in FIG. The signal is amplified and outputted by the A/D converter 15, and the output is quantized by the A/D converter 15 and supplied to the personal computer 17. The personal computer 17 converts the measured values from the magnetostrictive measurement unit 13 for each angle indicating the direction on the outer circumference of the tube material of the magnetic anisotropy sensor 11 and/or the stress measurement data obtained by approximating the measured values by a SIN approximation curve into graphic or numerical form. Depending on the display format, the data display section 8 displays the data, and if necessary, outputs a hard copy using a printer (not shown).

Based on the stress measurement data displayed on the data display section 18 of this measuring device or the hard copy data output by the printer, the next signal processing, which is non-destructive stress estimation processing for the extension piping system, can be performed.

Furthermore, in the above embodiment, an example of a magnetostrictive stress measuring device was shown as a device for non-destructively measuring the bending stress of the pipe acting on the exposed piping section, but the present invention is not limited to this. Any device that can measure stress in a non-destructive manner, such as a stress measuring device using a wire or a stress measuring device using an acousto-elastic method, may be used.

Using one of the stress measuring devices described above, stress measurements are performed at a required number of locations J of the buried piping section exposed by local manual excavation.

FIG. 7 is a diagram illustrating a state in which a small portion of a buried piping system is excavated and the stress of the exposed piping portion is measured. Measurements were taken at the measurement points of the exposed piping section indicated by the arrows in the same figure, and the stress measurement values σ and σ were measured.

]　　2 Obtain σ3...etc.

Next, a method for estimating the stress of the buried piping system based on the stress side results of the exposed piping section will be explained.

FIG. 4 is a flowchart of stress estimation processing for a buried piping system according to the present invention.

FIG. 5 is a diagram showing an example of an analytical model used for the pipe stress deformation analysis of FIG. 4.

FIG. 4 will be explained with reference to FIG. The stress estimation process according to the flowchart of FIG. 4 is performed using a signal processing means such as a digital computer or a microcomputer, for example. In step S1 in the same figure, stress measurement data regarding a desired position of the exposed piping section obtained from the stress measurement device is manually input to the signal processing means. This stress measurement data is measured as an absolute value. Next, in step S2, a piping analysis model is set, and this setting data is similarly input to the signal processing means.

Figure 5 is a diagram showing an example of this piping analysis model. In the figure, the pipeline is located at a depth of 1600 m below the ground surface.
+n+s, and a small area including a valve installed in the middle of the pipeline is excavated locally, and the stress value at the stress measurement point J1 is measured. In addition, as analysis conditions, for example, the pipe diameter x pipe thickness data is 200A pipe diameter 21B, 3φ x pipe thickness 5.8mm, and the ground displacement area length Ω is 5.
The distance between the m% stress measurement point J1 and the estimated maximum strain point is 350hm, and the amount of ground displacement is between 5cm and 5cm.
Data such as pitch up to a maximum of 40 cm is input to the signal processing means.

In step S3 of FIG. 4, a pipe stress deformation analysis is performed by using the buried part end plate as a nonlinear spring and giving a standard settlement amount to the buried part (for example, from 5 ann to 40 (7) for every 5 ann pitch). Generally, when a piping analysis model and the amount of ground subsidence are given, techniques for analyzing stress deformation of a piping system using a nonlinear finite element analysis program are already known. For example, the 44th Annual Academic Conference of the Japan Society of Civil Engineers (Vol. 1)
(Part), October 1989, “Deformation behavior of buried pipelines due to permanent displacement of the ground”, Japan, p. 1138-11.
89, Summaries of the 43rd Annual Academic Conference of the Society (Part 1), IO, 1986, “Dimensionless Representation of Nonlinear Behavior of Buried Pipelines,” picture book, etc., p. 1138-1139, etc. The technical details are disclosed.

In step S4 of FIG. 4, at the measurement position (hereinafter referred to as a node) where the stress measurement data was input in step S1, the stress measurement value and the stress value or strain value determined by the pipe stress deformation analysis in step S3 are equal. A computer simulation is performed using signal processing means to calculate the amount of settlement of other nodes of the buried piping system in the ground displacement area. In other words, based on the amount of settlement obtained by this simulation, the ground displacement j1 (input condition) is calculated inversely so that the stress analysis value analyzed at the node of the piping analysis model matches the actually measured stress measurement value. be. In step S5, the input condition is the amount of settlement determined so that the analytical value and the measured value of stress match in step S4, and the stress at other nodes of the buried piping system in the ground displacement area is calculated based on this amount of settlement. Calculate the value or distortion value as an estimated value. In step S6, step S
The external force of the entire piping system estimated in step 5 and the stress value or strain value of each node are output from the signal processing means via a recorder or a display.

FIG. 6 is a diagram showing the results of estimating the strain value of the buried piping system using the analytical model shown in FIG. 5.

This figure is a diagram obtained as a result of setting the amount of ground displacement from a minimum of 5 an to a maximum of 40 cm at every 5 cm pitch based on the analysis model and analysis conditions of FIG. 5.

According to the same figure, stress value σ-17kg/-1 (strain value ε-0.08%) was confirmed by measurement at stress measurement point J1 indicated by Δ mark, and in this case the piping indicated by circle mark The amount of settlement according to the analysis is 15 cm. Here, the input settlement amount d −
15001 and estimate the stress or strain value of the buried piping system using this analytical model, it is obtained at the position of maximum strain occurrence within the ground displacement area (the center of the ground displacement area shown in Figure 5). A maximum strain value ε-0.75% is obtained. This value is an estimated strain value in the analytical model, and in this way, stress values or strain values at other nodes can be calculated as estimated values.

[Effects of the Invention] As described above, according to the present invention, when a buried piping system in which a pipeline is buried underground is subjected to ground displacement, small local excavation can be performed within the influence of the ground displacement. Based on the amount of ground displacement calculated by performing stress deformation analysis of the buried pipe model in the ground displacement area based on the stress measurement results, Since the stress or strain value occurring in the buried piping in the ground displacement area is estimated, the stress state of the buried piping system can be estimated non-destructively and by partial manual excavation, and it is possible to determine whether safety measures are necessary or not. The effect of ranking is that preventive maintenance such as ranking can be easily performed.

[Brief explanation of drawings]

Figures 1 (a) and (b) are diagrams explaining the magnetostrictive stress measurement method according to the prior application, and Figures 2 (a) and (b) are diagrams explaining the SIN approximation method using the magnetostriction stress measurement method of Figure 1. 3 is a block diagram of a magnetostrictive stress measuring device as an example of a device for measuring the bending stress of a pipe in an exposed piping section according to the present invention, and FIG. 4 is a flowchart of stress estimation processing for a buried piping system according to the present invention. , Figure 5 is a diagram showing an example of the analytical model used for the piping stress deformation analysis in Figure 4, Figure 6 is a diagram showing the results of estimating the strain value of the buried piping system using the analytical model in Figure 5, FIG. 7 is a diagram illustrating a state in which a small portion of a buried piping system is excavated and the stress of the exposed piping portion is measured, and FIG. 8 is a diagram showing an example of piping displacement in the buried piping system. In the figure, 1 is a cylindrical material, 2 is a magnetostrictive sensor, IO is a traveling unit, 11 is a magnetic anisotropy sensor, 12 is a traveling trolley,
13 is a magnetostriction measuring section, 14 is a motor driver, 15 is A
/D converter, 1B is interface, 17 is personal computer,
18 is a data display section.

Claims (1)

[Claims] When a buried piping system with a pipeline buried underground experiences ground displacement, a small local excavation is performed within the area affected by the ground displacement, and stress in the exposed piping part due to the small excavation is non-destructively reduced. Measured by a stress measuring means, perform stress deformation analysis of the buried piping model in the ground displacement area based on the stress measurement results, calculate the amount of ground displacement for which a stress analysis result that matches the stress measurement value is obtained, and A non-destructive stress estimation method for a buried piping system, comprising estimating a stress value or a strain value occurring in the buried piping in the ground displacement area based on the ground displacement amount.