JP2010230106A - Pipeline for fault - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pipeline crossing a fault with a means for improving earthquake resistance performance of the same in a relatively short term of construction work and at a low cost. <P>SOLUTION: A pipe formed with a buckling mode shape in a case where compressive force in a pipe axis direction acts is used as a structure for absorbing fault displacement. The pipe with the buckling mode shape is used in the pipeline in combination with straight pipes. During ground deformation, in the pipeline, only the buckling mode part absorbs extension (compression) deformation and therefore almost no force acts on the straight pipe parts. The problem is solved by the pipeline for a fault made of a steel pipe in which the buckling mode part and the straight pipe parts are connected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pipeline used for various uses such as water supply, gas, and electric power, and more particularly to a pipeline capable of absorbing fault displacement.

  There are thousands of active faults in Japan, and many pipelines cross these active faults. Some of these active faults have displacements exceeding a few meters, and if the main pipeline is affected by a fault displacement of several meters at the time of the earthquake, the pipeline may break and the entire area may be drained. For this reason, the main pipelines that cross the fault are required to have high seismic performance that does not cause cracks against fault displacement.

  The general seismic design for buried pipes is generally designed to increase the proof strength by increasing or reinforcing the standard pipe thickness and to withstand the pipe body itself. It is impossible to add sufficient rigidity to the pipe line to withstand the ground deformation.

Therefore, there are the following construction examples in the seismic design of faults in pipelines such as water supply.
a Method to absorb fault displacement by arranging bellows-type telescopic flexible tubes continuously on the fault plane
b Method of digging a tunnel larger than the fault displacement in the section where the fault is displaced and absorbing the displacement in space
c Method of disabling the effect of faults by using piping in the expected fault displacement section as ground piping

  The method of continuously arranging bellows-type telescopic flexible pipes to absorb fault displacement is applied when the pipe line is laid below the board surface at a large depth, and the fault plane and fault displacement are already known. it can. For this reason, it is difficult to use this method because a fault plane cannot be accurately assumed in a pipeline buried with a relatively shallow cover.

  In the method of absorbing fault displacement using ground pipes and tunnels, the pipeline is in space at the time of fault displacement and is not affected by the ground, so the pipeline is not damaged, but all sections where the fault plane is assumed are all Is very expensive. For this reason, it is desirable to develop a structure that absorbs the ground deformation by deforming the pipeline itself following the ground deformation without using a special construction method.

  It is an object of the present invention to provide a means for improving the seismic performance of a pipeline that crosses a fault with a relatively short construction period and low cost.

  The present invention provides a pipeline that solves the above-mentioned problems. When a pipeline that crosses a fault is subjected to a fault displacement caused by an earthquake, the fault displacement is achieved by adopting a structure that can absorb the displacement by the pipeline itself. The cracks from the pipeline at the time are suppressed, and water outage etc. at the time of disaster can be prevented.

The present invention uses a tube having a buckling waveform when a compressive force in the tube axis direction is applied as a structure that absorbs fault displacement. This buckled corrugated pipe is used in a pipe line in combination with a straight pipe, and exhibits the following effects.
a At the time of ground deformation, only the buckling waveform portion of the pipe stretches (compresses) and absorbs the deformation, so almost no force acts on the straight pipe.
b In the deformation of the tube, the buckling waveform part is more than the same pipe thickness as the straight pipe, so even if the buckling waveform part is fully extended, the deformation does not concentrate and moves to the next buckling waveform part. Moreover, since it is more than the same pipe thickness as a straight pipe, even if it extends fully, it has sufficient pipe thickness with respect to earth pressure.
c Arbitrary permissible bending angles can be set according to fault displacement by increasing the number of peaks (number of buckling waveforms) to 2 and 3 peaks.
d By installing a manhole tube at the end of the main pipe alignment, it is possible to enter the tube after a fault displacement and check for damage.

  The pipe of the present invention has a large force to withstand a fault displacement, and even if a fault displacement occurs, the risk of breakage and water leakage can be greatly reduced compared to conventional pipes. Moreover, the cost is low.

It is sectional drawing which shows the pipe line which embed | buried the buckling waveform steel pipe which has a buckling waveform part of this invention. It is a figure explaining a buckling waveform. It is a side view which shows the buckling state of the straight pipe by fault displacement. It is a side view which shows the deformation | transformation by the fault displacement of the steel pipe whose buckling waveform part is a mountain. It is a side view which shows the deformation | transformation by the fault displacement of a steel pipe with two buckling waveform parts. It is a side view which shows the deformation | transformation by the fault displacement of a steel pipe with three buckling waveform parts.

The buckled corrugated steel pipe used in the pipe line of the present invention makes it easy to absorb compressive deformation due to fault displacement by giving in advance an initial deformation similar to the corrugation generated by causing local buckling of a straight pipe. Therefore, it is necessary that the buckled waveform portion can be deformed without breaking according to the fault displacement, and mild steel (SS400) or the like is preferable in this respect. Here, the mild steel has a carbon content of 0.13 to 0.20% and a tensile strength of 330 to 430 N / mm ² .

  The pipe diameter and plate thickness of the steel pipe are determined depending on the application and the like, but the pipe diameter is about 600A to 3000A in terms of the diameter (nominal diameter). The plate thickness is a tube thickness that can withstand constant loads (earth pressure, automobile load), and is usually about 6.0 to 20.0 mm.

  Moreover, it resists tensile deformation due to fault displacement with the rigidity of a straight pipe used in connection with the buckled corrugated steel pipe of the present invention. By the way, in the bellows type telescopic flexible tube, both the tension and the compression are absorbed by the bellows part.

  The buckling waveform is a parameter study using FEM with compression local buckling wavelength (L = 1.72√ (r · t), r: tube radius, t: tube thickness) and peak height (n times the plate thickness) as parameters. To be determined.

  Since the maximum amount of displacement that can be absorbed by one buckling waveform portion is the buckling wavelength, the number of peaks of the buckling waveform portion is determined from the buckling wavelength and the fault displacement assumed at the installation site. For example, when a steel pipe having a plate thickness of 9.0 mm and a diameter of 600 A is provided with a buckling wavelength portion having a buckling wavelength of 270 mm, a minimum of about 12 mountains are required for a portion where a 3 m fault displacement is predicted. Since the displacement of many fault displacement locations is predicted to be about 1 m to 5 m, the number of peaks of the buckling waveform portion is set to about 1 m to 5 m / buckling wavelength.

  The interval between the buckling waveform portions needs to be determined by analysis in consideration of the fault displacement and the fault angle, and usually about 0.5 to 2D (D: pipe outer diameter) is appropriate. Since the buckling corrugated portion and the straight pipe portion are integrally formed, welding is desirable.

    The buckling corrugated steel pipe used in the present invention can be manufactured, for example, by forming a buckling corrugated mold in advance and forming a buckling corrugated portion by applying water pressure to the steel pipe from the inside according to the mold. .

In the present invention, when a new construction is performed, excavation is performed in the same manner as a normal buried pipe and a fault pipe is laid. In the case of replacement of the existing installation, the existing pipe in the section affected by the fault crossing is removed and a fault pipe is installed.
In addition, when the embedding depth is deep and the fractured part of the fault can be specified, the laying range can be made a very short section.

FIG. 1 shows a state in which a buckled corrugated steel pipe which is an embodiment of the pipe line of the present invention is embedded.
The buckling waveform portion of this steel pipe has a buckling wavelength d and a peak height e shown in FIG. This buckling waveform was obtained from the optimal buckling wavelength and tube thickness by performing a parameter study using FEM with the local buckling wavelength and plate thickness as parameters. A buckling waveform portion having a peak height (e) of 4 t (36 mm) and a buckling wavelength (d) of 270 mm was formed on a 9.0 mm steel pipe. This buckling waveform portion was expanded in a mountain shape around the entire circumference in the circumferential direction of the tube, and the plate thickness was the same as that of the straight tube portion.

As shown in FIG. 1, three buckling corrugated portions were provided with a 1D (600 mm) straight pipe interposed therebetween.
If the pipe line is only a straight pipe, if a fault displacement occurs, it will buckle as shown in FIG.

However, when a fault displacement is applied to the buckled corrugated tube, deformation (bending) is concentrated on the tube as shown in FIG. 4, and the buckled corrugated tube absorbs the deformation.
By increasing the number of buckling corrugated pipes to two, as shown in FIG. 5, when the deformation of the first mountain proceeds and contacts the inner surface of the tube, the deformation moves to the second mountain and further deforms.

  If the buckling corrugated pipe is further increased to three peaks and a larger displacement is applied, the deformation exceeds the allowable value of the buckling corrugated pipe as shown in FIG. It corresponds. Further, since the allowable bending angle can be changed depending on the installation interval of mountains, a fault conduit that can cope with any fault displacement can be laid according to the number of mountains and the installation interval of mountains.

  The pipe of the present invention can be widely used in a fault portion because it is resistant to fault displacement and is not easily destroyed.

a Straight pipe
b Fault plane
c Buckling corrugated tube
d Buckling wavelength
e Mountain height

Claims (2)

  Fault pipe made of steel pipe with buckling corrugated part and straight pipe part connected   2. The fault conduit according to claim 1, wherein the straight pipe portion is made of a steel pipe having a diameter and a pipe length substantially equal to each other.

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