CN111736227B - Method for determining spatial positions of two underground parallel metal pipelines - Google Patents

Method for determining spatial positions of two underground parallel metal pipelines Download PDF

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CN111736227B
CN111736227B CN202010628466.1A CN202010628466A CN111736227B CN 111736227 B CN111736227 B CN 111736227B CN 202010628466 A CN202010628466 A CN 202010628466A CN 111736227 B CN111736227 B CN 111736227B
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pipeline
magnetic field
field component
curve
metal
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CN111736227A (en
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赵明堂
刘康
熊建华
王小章
黄晓航
李志强
詹秉烨
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Mcc Wukan Engineering Consulting Hubei Co ltd
MCC Wukan Engineering Technology Co Ltd
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Wuhan Surveying Geotechnical Research Institute Co Ltd of MCC
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/083—Controlled source electromagnetic [CSEM] surveying
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/083—Controlled source electromagnetic [CSEM] surveying
    • G01V2003/085—Receivers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/083—Controlled source electromagnetic [CSEM] surveying
    • G01V2003/086—Processing

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Abstract

The invention provides a method for determining the spatial position of two underground parallel metal pipelines. The method specifically comprises the steps of preliminarily judging the position of the pipeline, arranging measuring points to measure the horizontal magnetic field component, the vertical magnetic field component and the change rate of the pipeline, comparing the measured values with a theoretical curve of a single metal pipeline, and combining the semipolar chord length of the horizontal magnetic field component
Figure DDA0003582984930000011
All in one
Figure DDA0003582984930000012
Judging whether the number of underground metal pipelines is two or not according to the relation between the chord lengths; then actually measuring the horizontal magnetic field component again, calculating and finding out the maximum value of the difference between the actually measured horizontal magnetic field components of two adjacent measuring points, and solving the abnormal maximum value generated by the target pipeline according to the determined maximum value position
Figure DDA0003582984930000013
Finally utilize
Figure DDA0003582984930000014
And
Figure DDA0003582984930000015
the depth and the planar position of the parallel lines are jointly determined. The judging method is simple and accurate, and solves the problem that the pipe depth and plane position relation of two underground parallel metal pipelines cannot be determined in the existing underground pipeline detection process.

Description

Method for determining spatial positions of underground two parallel metal pipelines
Technical Field
The invention belongs to a method for detecting an underground metal pipe, in particular to a method for detecting an underground metal pipe by using a half-extreme chord length
Figure GDA0003595325240000011
Is composed of
Figure GDA0003595325240000012
And determining the spatial position of the underground parallel steel pipeline by combining the chord lengths.
Background introduction
Underground pipelines are an important infrastructure of cities. In recent years, with the development of urban construction, traffic systems, energy systems, communications, information networks and the like are vigorously developed, such as railways, subways, light rails, power supply, heat supply, gas supply and the like, all projects are implemented without leaving the important hidden infrastructure of underground pipelines, due to various reasons, the pipeline data are not complete, some projects are inconsistent with the current situation, and the authority of various pipelines belongs to different departments, and the management of pipelines is not sufficiently emphasized, so that the management difficulty of the pipelines is increased, in the project construction, accidents such as water cut, power cut, communication interruption and the like are caused by the fact that the pipelines are not dug at different positions, great inconvenience is brought to the lives of people, meanwhile, corrosion and leakage accidents on the pipelines are caused by the parallel interference of urban vehicles and electric power and radio parallel pipelines, such as cable ditches, thermal pipelines and tap water pipelines, and the accidents are avoided, finding out the position and the trend of the underground pipeline becomes an indispensable prerequisite for engineering construction, and has important significance for promoting the harmonious development of urban construction
The prior art mainly adopts electromagnetic detection and electromagnetic detection aiming at the detection of a deeply buried metal pipeline. Among them, the electromagnetic method for detecting underground metal pipelines is usually to excite the underground pipelines with good conductivity and observe the response (including the response of underground medium and the interaction between the pipelines and the surrounding medium) on the ground. And then analyzing the electromagnetic anomalies to achieve the purpose of detecting the underground pipeline. The preconditions must satisfy the following physical models: (1) the surrounding medium and the pipeline have obvious electrical difference; (2) the pipeline length is far greater than its buried depth, and generally must be 5-6 times greater than the buried depth.
The electromagnetic wave method for detecting underground pipelines is that a transmitter is arranged on the ground, the transmitter directly charges the underground pipelines with alternating current or supplies the underground pipelines with a transmitting coil (T), and an alternating magnetic field generated by the pipelines charged with the alternating current is called a primary field; the transmitting coil also generates a primary field around it, which excites the underground pipeline to generate an induced current (i.e., a secondary current), and the alternating magnetic field generated by the secondary alternating current is called a secondary field. The primary field generated by the pipeline or the secondary field generated by induction is received by a receiver at a certain distance away from the transmitting coil, and the purpose of detecting the underground pipeline is achieved by analyzing the form rule of the received field.
The detection methods can only detect the position of a single pipeline, and the condition that a plurality of metal pipelines coexist underground is the most common in the underground pipeline detection process. Because the buried depth and the distance of each metal pipeline are different, a plurality of electromagnetic abnormal curves can be combined in the detection process by using an electromagnetic method. How to identify these anomalies and reduce their multi-solution, and finally determine the occurrence space of the tested target metal pipeline is the most troublesome problem facing pipeline explorers.
Disclosure of Invention
The invention provides a method for analyzing an abnormal curve of a parallel pipeline by using a horizontal magnetic field component gradient method and a method for analyzing the abnormal curve by using the abnormal curve of the parallel pipeline by using the horizontal magnetic field component gradient method aiming at the detection problem of the existing two concurrent metal pipelines
Figure GDA0003595325240000021
And
Figure GDA0003595325240000022
the method can judge whether the underground metal pipelines are single or parallel, carry out electromagnetic excitation on the underground metal pipelines in different excitation modes, receive an electromagnetic field curve generated by the metal pipelines on the ground, and determine the spatial positions of the two underground parallel metal pipelines according to the electromagnetic excitation curve
Figure GDA0003595325240000023
And
Figure GDA0003595325240000024
the buried depth and the plane position of the pipeline can be calculated according to the position, and the problem that the buried depth and the plane position of two underground parallel metal pipelines cannot be determined in the existing underground pipeline detection process can be solved.
In order to solve the problems of the prior art, the invention provides a method for determining the spatial positions of two underground parallel metal pipelines, which is characterized by comprising the following steps:
a method for determining the spatial position of two parallel metal pipelines underground, which is characterized by comprising the following steps:
(1) utilizing the position of the metal pipeline exposed out of the ground, exciting the known metal pipeline by using a charging method or an induction method, receiving the horizontal magnetic field component of the measured target metal pipeline by using a receiver of a pipeline detector within a certain range, and primarily judging the plane position of the metal pipeline;
(2) arranging a survey line on the ground at the site in a direction perpendicular to the metal pipeline, exciting the metal pipeline at the position of the metal pipeline determined in step (1) with a pipeline probe transmitter, and measuring a horizontal magnetic field component H generated from the metal pipeline along the survey line with a pipeline probe receiverx 1And a perpendicular magnetic field component H1 ZAnd drawing the actual horizontal magnetic field component H according to the primary measurement result1 XCurve and vertical magnetic field component H1 ZA curve; according to the horizontal magnetic field component H of the actual measurement pipeline1 XBy the formula Δ Hx 1＝H1 x(i+1)-H1 xiCalculating the horizontal magnetic field component H of adjacent i points1 Xi and i +1 point horizontal magnetic field component H1 XHorizontal magnetic field component difference Δ H between i +1 x 1I.e. the horizontal magnetic field component H1 XRate of change H in horizontal direction1 XXAnd plotting the rate of change H1 XXThe curve of (c);
(3) measuring the field actual measurement horizontal magnetic field component H obtained in the step (2)1 XCurved, perpendicular magnetic field component H1 ZCurve and H1 XRate of change in horizontal direction H1 XXCurve and theoretical horizontal magnetic field component H of single metal pipelineXCurved, perpendicular magnetic field component HZCurve and HXRate of change in horizontal direction HXXComparing the curves, and comparing the results or actually measuring the horizontal magnetic field component H according to the curves1 XHalf-pole chord length in curve
Figure GDA0003595325240000031
All in one
Figure GDA0003595325240000032
Judging whether one or two pipelines are based on the relation between the chord lengths or the combination of the chord lengths and the two pipelines;
(4) when two underground metal pipelines are judged, any one of a T displacement method, an isolation excitation method and an offset induction method is selected for carrying out electromagnetic excitation on the metal pipelines, and the horizontal magnetic field component generated by the underground two parallel metal pipelines on the ground is measured on the original measuring line in the step (2) again
Figure GDA0003595325240000033
And according to the formula Δ H11 x＝H11 x(i+1)-H11 xiCalculating the horizontal magnetic field component H of the (i + 1) th measuring point11 x(i+1)And i measuring point horizontal magnetic field component H11 xiDifference Δ Hx 11And finding out Δ Hx 11Maximum value of
Figure GDA0003595325240000034
(5) Maximum value of difference between horizontal magnetic field components determined in step (4)
Figure GDA0003595325240000035
Finding a maximum value
Figure GDA0003595325240000036
Corresponding horizontal magnetic field component
Figure GDA0003595325240000037
Maximum value of
Figure GDA0003595325240000038
By the formula
Figure GDA0003595325240000039
Determining apparent maximum of abnormality generated by target pipeline
Figure GDA00035953252400000310
(6) Generating abnormal maximum value according to the target pipeline calculated in the step (5)
Figure GDA0003595325240000041
Determination on the horizontal magnetic field component curve
Figure GDA0003595325240000042
And
Figure GDA0003595325240000043
the buried depth h of the pipeline is calculated by using a formula (I):
Figure GDA0003595325240000044
in formula (I): h is the apparent buried depth of the pipeline, b is
Figure GDA0003595325240000045
And
Figure GDA0003595325240000046
a corresponding ground level distance;
(7) and further determining the plane position of the pipeline, namely the position corresponding to the length of the half-extreme point moving towards the maximum value direction by h, as the horizontal position of the center of the metal pipeline.
The further technical scheme of the invention is as follows: the specific judgment process of the number of pipelines in the step (3) is as follows:when in use
Figure GDA0003595325240000047
Determining that the underground is two pipelines; when the horizontal magnetic field component H is actually measured on site1 XCurve and vertical magnetic field component H1 ZCurve and single metal pipeline theoretical horizontal magnetic field component HXCurve and vertical magnetic field component HZIf the shapes of the curves are completely different, judging that the two metal pipelines are formed; when the horizontal magnetic field component H is actually measured on site1 XCurve and vertical magnetic field component H1 ZCurve and single metal pipeline theoretical horizontal magnetic field component HXCurve and vertical magnetic field component HZSimilar curve form, actually measured H on site1 XRate of change in horizontal direction H 1 XXCurve and single metal pipeline theory HXRate of change in horizontal direction H1 xxThe curve has an obvious slope variation range, and if an inflection point exists, the underground part of the curve is judged to be two metal pipelines; when the horizontal magnetic field component H is actually measured on site1 XCurve and vertical magnetic field component H1 ZCurve and single metal pipeline theoretical horizontal magnetic field component HXCurve and vertical magnetic field component HZSimilar curve form, H1 xxIf the curve has no inflection point, the underground is judged to be a pipeline.
The further technical scheme of the invention is as follows: the T displacement method in the step (4) is that the receiver R is placed right above the detected point or the exposed point of the target pipeline, the transmitter T is moved in a proper distance and perpendicular to the direction of the pipeline, and the position of the metal pipeline is judged and accurately positioned according to the strength change of the signal received by the receiver; the isolation induction method is characterized in that a section with sparser pipelines is selected to induce or charge a target pipeline so as to reduce side influence, so that signals of the target pipeline are highlighted on the section with high pipeline density, and positioning and depth setting are realized; the deviation induction method is based on the principle that the primary field of a magnetic dipole does not uniformly change along with the change of a theta angle, the contrast of a secondary field between a target pipeline and a side pipeline is increased, signals of the target pipeline are highlighted, and therefore the purpose of distinguishing and tracking the target pipeline is achieved, wherein the theta angle is an included angle between a transmitting coil axis and a vector r.
The further technical scheme of the invention is as follows: when the position of the underground metal pipeline is preliminarily judged by utilizing the position of the metal pipeline exposed out of the ground in the step (1), the part of the metal pipeline exposed out of the ground comprises a fire hydrant, a water meter, a pipeline manhole, a valve, a lifting or entering equipment connecting point or the underground pipeline exposed out due to construction excavation.
The further technical scheme of the invention is as follows: the charging method in the step (1) is that one end of an alternating current power supply of a pipeline detector transmitter with a certain frequency is connected to the exposed part of the pipeline, the other end of the alternating current power supply is connected with a grounding electrode far away from the connection point, namely single-end charging is carried out, or two ends of the alternating current power supply are respectively connected to two exposed points far away from the same target pipeline, namely double-end charging is carried out, at the moment, a current loop is formed between the metal pipeline and the ground or between the metal pipeline and the power supply, and an alternating magnetic field is generated around the pipeline; the induction method in the step (1) is to use a pipeline detector transmitter to generate a primary alternating magnetic dipole field on the ground, if a metal pipeline exists underground, the size and the direction of the magnetic flux of a primary field passing through the underground metal pipeline are continuously changed, an induced current is generated in the metal pipeline according to an electromagnetic induction law, the size of the induced current is in direct proportion to the change rate of the magnetic flux, the frequency of the induced current is the same as that of the primary field, and a receiver is used for observing and researching a secondary field generated by the induced current on the ground to achieve the purpose of detecting the underground metal pipeline.
The preferred technical scheme of the invention is as follows: in the step (2), when the survey line is arranged, the distance between the initial position of the survey point and the center of the pipeline is 2-3 times of the estimated burial depth of the metal pipeline, the total length of the survey line is 4-6 times of the estimated burial depth of the metal pipeline, and the distance between the survey points is 0.05-0.2 m.
The preferred technical scheme of the invention is as follows: the excitation mode in the step (4) is selected according to the exposure condition and the distribution characteristics of the metal pipeline and the applicability field repeated test comparison determination of various excitation modes, and the target pipeline is gradually detected from the known state to the unknown state, wherein if the distance between pipelines is small, an offset induction method is not selected; the T-shift method is chosen for applications where the target line must have a dew point or a known point and where the receiver experiences little side interference.
The invention aims at the electromagnetic field abnormity generated by two parallel steel pipes in the underground pipeline detection process, deduces the electromagnetic field abnormity curve generated by two or more underground steel pipes by using the existing electromagnetic field theory, and the calculation shows that the abnormity superposition between the central lines of the two steel pipes is serious, and the abnormity on the outer sides of the two pipelines is greatly disturbed less or even basically zero. Therefore, different excitation modes are selected according to the actual situation on site to carry out electromagnetic excitation on the underground metal pipeline, the electromagnetic field curve generated by the metal pipeline is received on the ground, and H is selected xAnd (4) carrying out analysis and inversion calculation on the half of the curve with smaller interference to obtain the buried depth and the horizontal position of the underground metal pipeline.
The invention utilizes the change rate curve H of the horizontal magnetic field component in the horizontal directionxxHalf pole chord length combined with horizontal magnetic field component
Figure GDA0003595325240000061
Is composed of
Figure GDA0003595325240000062
The relation between the chord lengths judges whether the underground metal pipelines are one or two; when two magnetic field components are judged, the horizontal magnetic field components are actually measured according to the site
Figure GDA0003595325240000063
And calculate to find
Figure GDA0003595325240000064
The i +1 th measuring point and the i measuring point
Figure GDA0003595325240000065
Difference Δ Hx 1Maximum value Δ H ofx 1＝H1 x(i+1)-H1 xiDetermined Δ Hx 1The maximum value position of the target pipeline is obtained to obtain the maximum value of the abnormality generated in the target pipeline
Figure GDA0003595325240000066
Determination on the horizontal magnetic field component curve
Figure GDA0003595325240000067
And
Figure GDA0003595325240000068
and the utilization should be
Figure GDA0003595325240000069
And
Figure GDA00035953252400000610
Figure GDA00035953252400000611
calculating the buried depth and the plane position of the pipeline according to the corresponding ground horizontal distance; the invention can analyze the abnormal curve of the parallel pipeline by a horizontal magnetic field component gradient method and utilize
Figure GDA00035953252400000612
And
Figure GDA00035953252400000613
the depth and the plane position of the parallel pipelines are jointly determined, the judgment method is simple and accurate, and the problem that the relation between the pipe depth and the plane position of two underground parallel metal pipelines cannot be determined in the existing underground pipeline detection process is solved.
Drawings
FIG. 1 is a magnetic field generated by current in an infinite straight wire;
FIG. 2 is a schematic diagram of magnetic field component calculation;
FIG. 3 is a graph of the electromagnetic response of current in a single subsurface horizontal pipeline;
FIG. 4 shows H at different distances a under the same current conditions such as the buried depths of two metal linesXHz magnetic field component curve and HXRate of change H in horizontal directionXXA graph;
FIG. 5 is a graph of the magnetic field components of two underground parallel pipelines at h ═ a;
FIG. 6 is a graph of the magnetic field components of two underground parallel pipelines when a is 1.5 h;
fig. 7 is a graph of the buried pipeline variation of 80% and 50% of the extreme chord length calculated under the conditions of different distances a between the current i and the current i of 1 m;
FIG. 8 is a schematic diagram of the pipeline in the example;
FIG. 9 shows the first measured horizontal magnetic field component H in the example1 XCurve and H1 XRate of change in horizontal direction H1 XXA graph;
FIG. 10 shows the optimized horizontal magnetic field component excited by the offset induction method in the embodiment
Figure GDA0003595325240000071
And
Figure GDA0003595325240000072
rate of change in horizontal direction H11 XXA graph;
fig. 11 is a graph of the theoretically calculated horizontal magnetic field component and the rate of change in the horizontal direction in the example.
Detailed Description
The invention is further illustrated by the following figures and examples. The following claims presented in the drawings are specific to embodiments of the invention and are not intended to limit the scope of the claimed invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The magnetic field generated by a single pipeline in the present invention is derived as follows: the current direction at a certain moment in the pipeline is shown in figure 1, and according to the biot-shafahr law, the magnetic field generated by the current element at a certain point P in space is as follows:
Figure GDA0003595325240000081
in the formula: dB represents the micro magnetic flux generated by the current element at the point P;
I0represents the current intensity;
dl represents the length of the current element;
r represents the length from the current element to the point P;
theta represents an included angle between the direction of the current element and the vector from the current element to the point P;
μ represents a magnetic permeability;
w represents the ac circular frequency.
The magnetic field of the long wire corresponding to the above formula dB integral is:
Figure GDA0003595325240000082
the geometrical relationship shows that:
l＝rcos(π-θ)＝-rcosθ
r0＝rsin(π-θ)＝rsinθ
l＝-r0ctgθ
Figure GDA0003595325240000083
in the formula: dl represents the length of the current element;
l represents the current length;
r represents the length from the current element to the point P;
r0representing the vertical distance from the point P to the current element;
theta represents an included angle between the direction of the current element and the vector from the current element to the point P;
substituting the transformation relation into a formula (c) to obtain:
Figure GDA0003595325240000084
when A is1→-∞、A2→ infinity time θ1＝0、θ2Pi (bar)The length of the part is 5-6 times greater than the buried depth of the pipeline). The magnetic field generated by the current in the infinite straight wire is thus:
Figure GDA0003595325240000091
for non-magnetic media, μ is approximately equal to μ in vacuum0(vacuum permeability), since the magnitude of the magnetic field is measured in our actual work, for convenience, the formula is rewritten as follows:
Figure GDA0003595325240000092
If the center buried depth of the charging pipeline is H, the coordinate of any observation point on the ground is x, and when the measuring line is vertical to the trend of the pipeline along the axial direction, the horizontal magnetic field component H observed on the groundxAnd the vertical component Hz are respectively expressed as follows, and the schematic diagram is shown in fig. 2.
Figure GDA0003595325240000093
Figure GDA0003595325240000094
Figure GDA0003595325240000095
Figure GDA0003595325240000096
In the formula: hpRepresenting the magnetic field at observation point p; the unit is Henry
HxRepresents H at observation point ppA horizontal component of (a);
Hzrepresents H at observation point ppPerpendicular component of；
Alpha represents the included angle formed by the connecting line of the center of the tube and the point p and the normal of the ground;
Figure GDA0003595325240000097
representing the magnetic field component received when the receiving coil face is at a 45 ° angle to the ground;
it can be seen from the formula that the magnetic coil generated in space by the current in the long pipeline is a group of concentric circles taking the pipeline as the center on the section perpendicular to the pipeline trend, and the theoretical section curve of each parameter is shown in fig. 3: from the formula (c), (b), (c), and (c) and the theoretical curve thereof, it can be seen that:
(1) directly above the pipeline, i.e. X is 0, HZ＝0,
Figure GDA0003595325240000098
α is 0; i.e. indicating that the horizontal component of the magnetic field generated by the current in the pipeline is maximum and the vertical component is zero, directly above the pipeline. These features can be used to measure and determine the horizontal position of the underground utility.
(2) In that
Figure GDA0003595325240000101
Where x is h (half-pole chord length)
Figure GDA0003595325240000102
)，
Figure GDA0003595325240000103
α＝45°、
Figure GDA0003595325240000104
The above equations show that at x ═ h on the line, the horizontal component of the magnetic field produced by the line current is equal to the vertical component of the magnetic field and that the vertical component is now at its maximum, being the horizontal component
Figure GDA0003595325240000105
Half of (a) measured by the 45 ° angle method
Figure GDA0003595325240000106
(3) When the temperature is higher than the set temperature
Figure GDA0003595325240000107
Hour (80% maximum chord length
Figure GDA0003595325240000108
) To obtain
Figure GDA0003595325240000109
Namely when
Figure GDA00035953252400001010
When the horizontal component of the magnetic field is equal to 80% of its maximum value; therefore, can be used
Figure GDA00035953252400001011
To determine the planar position and burial depth of the pipeline.
(4) In the range of X → - ∞ or X → + ∞ HX＝0，H Z0. I.e. the magnetic field measured when the vertical line runs far away is the normal field.
(5) To pair
Figure GDA00035953252400001012
Obtaining the change rate H of the horizontal magnetic field component in the horizontal direction by taking the first derivative of xXXCurve
Figure GDA00035953252400001013
When in use
Figure GDA00035953252400001014
When H is presentXXAnd obtaining a maximum value.
The derivation process of the invention is as follows:
(1) the horizontal magnetic field component H generated by the underground single parallel metal pipeline on the ground is deduced based on the basic principle of detecting the underground pipeline by an electromagnetic wave method, namely the electromagnetic induction lawXThe forward calculation formula of (c) and a vertical magnetic field component HZIs performingThe computational formula is two:
Figure GDA00035953252400001015
Figure GDA00035953252400001016
the formula is.
I represents the current magnitude on the pipeline; h is the central buried depth of the pipeline;
x is the horizontal distance on the ground from the centre of the pipeline in a direction perpendicular to the pipeline
(2) According to the formula in the step (1), the formula II and the horizontal magnetic field component H XPerpendicular magnetic field component HZDeriving, for scalar superposition, the horizontal magnetic field components generated at the surface by two or more pipelines
Figure GDA0003595325240000117
And a perpendicular magnetic field component
Figure GDA0003595325240000118
The forward calculation formula three and the formula fourth, and the superposition magnetic fields of the horizontal parallel pipelines with different quantities are calculated according to the formula third and the formula fourth, wherein the formula third and the formula fourth are as follows:
Figure GDA0003595325240000111
Figure GDA0003595325240000112
formula three and formula fourth:
n represents the number of pipelines;
Figure GDA0003595325240000113
Iithe current on the ith parallel pipeline is largeSmall;
aithe horizontal distance between the center line of the ith parallel pipeline and the center line of the pipeline with the i being 0; wherein (a)0＝0)；hiThe center burial depth of the ith pipeline;
(3) horizontal magnetic field components generated on the ground for two or more pipelines in the step (2)
Figure GDA0003595325240000119
The change rate H of the horizontal direction is obtainedXXThen, obtaining:
Figure GDA0003595325240000114
(4) calculating horizontal magnetic field components of the two parallel metal pipelines at different distances a under the condition that the currents such as the burial depths of the two metal pipelines are constant according to the formula three and the formula four in the step (2)
Figure GDA0003595325240000115
And a perpendicular magnetic field component
Figure GDA0003595325240000116
Calculating H under different distances a of the two parallel metal pipelines under the condition that the current such as the buried depth of the two metal pipelines is constant according to the formula in the step (3)XIs in the horizontal direction of XXAnd drawing H under the current conditions of equal burial depth and the like and different distances a of the two metal pipelinesXHz magnetic field component curve and HXRate of change H in horizontal directionXXThe curves are shown in fig. 4 and are plotted separately for the magnetic field component plots for a depth of burial h with a spacing a equal to its depth of burial h and a spacing a equal to 1.5 times the depth of burial h, as detailed in fig. 5(h ═ a) and fig. 6(a ═ 1.5 h); when the distance a between the two pipelines is less than or equal to the buried depth H, H is found through the curvex、HzThe general characteristics of the abnormal curve are similar to those of a single pipeline and are a single peak value, so that the two pipelines are judged to be one by the detection scheme, but H isxxThe curve has a distinct point between the two tubesThe slope variation range of the system has two inflection points which can be used for judging that two pipelines are underground; when the distance a between two pipelines is greater than the buried depth H, the other Hx、HzThe general characteristics of the abnormal curve are completely different from those of a single pipeline, and the underground of the abnormal curve can be directly judged to be two pipelines; half-pole chord length combined with horizontal magnetic field component
Figure GDA0003595325240000121
All in one
Figure GDA0003595325240000122
The relationship between the chord lengths is determined, the pipeline buried depths corresponding to the 80% extreme chord length and the 50% extreme chord length calculated when the current i is 1A with the distance a between the two pipeline buried depths h and 1m are calculated as shown in table 1, and a variation curve is drawn (as shown in fig. 7):
Figure GDA0003595325240000123
From the above data, it can be seen that the q of the two pipelines at different spacings0.8Are all made of
Figure GDA0003595325240000124
Therefore, is at
Figure GDA0003595325240000125
Two pipelines are determined underground.
If the metal pipeline is a single metal pipeline, the metal pipeline can be excited by a charging method or an induction method at a place with a dew point, and the metal pipeline is excited by the induction method under the condition of the known dew point; the two pipelines are electromagnetically excited by selecting any one of a T displacement method, an isolation excitation method and a deviation induction method, wherein the T displacement method is characterized in that a receiver R is arranged right above an ascertained point or an exposed point of a target pipeline, a transmitter T is moved in a direction perpendicular to the pipeline in a proper distance, the position of a metal pipeline is judged and accurately positioned according to the strength change of a signal received by the receiver, and the application condition of the T displacement method is as follows: the target line must have a dew point or a detected point at which the receiver experiences little side interference; the isolation induction method is to select a section with sparser pipelines to induce or charge a target pipeline so as to reduce side influence, thereby highlighting signals of the target pipeline in the section with high pipeline density and realizing positioning and depth setting; the offset induction method is based on the principle that the primary field of a magnetic dipole does not change uniformly with the change of an angle theta (the angle theta is the included angle between the axis of a transmitting coil and the radius r), so that the contrast of the secondary field between a target pipeline and a side pipeline is increased, the signal of the target pipeline is highlighted, and the purpose of distinguishing and tracking the target pipeline is achieved. The selection of the excitation mode is determined according to the exposure condition and the distribution characteristics of the metal pipeline and the applicability field trial and error comparison of various excitation modes, and the target pipeline is gradually detected from known to unknown.
(4) By using
Figure GDA0003595325240000131
And
Figure GDA0003595325240000132
joint determination of depth and plane position of parallel pipelines
Arranging a measuring line in the direction vertical to the metal pipeline on the ground on site, and measuring the horizontal magnetic field component H generated by the metal pipeline along the measuring linex 1Using the horizontal magnetic field component curve Hx 1X and H corresponding to the maximum horizontal gradient of (1)xThe apparent maximum value of the target pipeline can be obtained
Figure GDA0003595325240000133
In theoretical calculation, when the underground is a single pipeline, H is calculatedxxIs located at the maximum value of
Figure GDA0003595325240000134
At this time
Figure GDA0003595325240000135
At the placeFind out the position with the maximum slope in the profile curve, i.e. find out
Figure GDA0003595325240000136
Position of, by
Figure GDA0003595325240000137
The apparent maximum value of the abnormality generated in the target pipeline can be obtained
Figure GDA0003595325240000138
If it is a single pipeline
Figure GDA0003595325240000139
Is equal to
Figure GDA00035953252400001310
If two or more lines are provided
Figure GDA00035953252400001311
Definitely less than two-pipe synthetic anomaly
Figure GDA00035953252400001312
Recording horizontal magnetic field components in detail during field work
Figure GDA00035953252400001313
Difference DeltaH between the i +1 th point and the i pointx 1(ΔHx 1＝H1 x(i+1)-H1 xi) Finding out Δ Hx 1Maximum value corresponds to
Figure GDA00035953252400001314
The horizontal position is combined with the semiextreme method to obtain the buried depth of the pipeline, and the horizontal position of the pipeline is further determined, namely
Figure GDA0003595325240000141
In the formula: h is1Apparent burial depth of the pipeline, b1Is composed of
Figure GDA0003595325240000142
And
Figure GDA0003595325240000143
the corresponding ground horizontal distance (the distance between the half-extreme point and the maximum slope point on the measuring line, which can be measured on the spot, is known.)
The visual burial depth h of the pipeline can be obtained by utilizing the formula1The pipeline center is located at the half-extreme point and moves towards the direction of the maximum value h1The position of (a). The horizontal position and the buried depth of another pipeline can be obtained by a line pressing method or field separation processing on the section curve.
When data acquisition is carried out in field work, attention needs to be paid to
Figure GDA0003595325240000144
The local measuring points with large abnormal change are encrypted so as to extract the horizontal magnetic field component indoors
Figure GDA0003595325240000145
Difference DeltaH between the i +1 th point and the i pointx 1Maximum value of (Δ H)x 1＝H1 x(i+1)-H1 xi). The method is very effective for detecting and analyzing the close-distance parallel pipelines, and can play an important role in the detection work of the underground pipelines if being matched with a flexible excitation mode, so that a plurality of difficult problems are solved, which is proved in the actual work.
The method of the invention is further proved by combining a specific example, the embodiment aims at a Hunan lake steel male and underground pipeline excavation project, the pipeline distribution of the project is shown in figure 8, two groups of parallel production water feeding pipes, namely AB, CD, EF and GH, are distributed, the pipe diameters of the AB, CD, EF and GH are 300mm, the buried depths of the AB and CD are equal to each other and are 1.40m, the distance between the two pipes is 1.20m, the buried depths of the EF and GH are equal to each other and are 1.10m, and the distance between the two pipes is 0.70 m. The buried depth h of the two groups of water pipes is larger than the distance L between the two groups of water pipes. According to the induction principle, if the AB water pipe is to be tracked, the AB water pipe is tracked The AB signal is sensed most strongly directly above it, but the secondary field generated is also large as the CD is closer to AB. In this case, the measured AB position must be shifted toward the CD, and the positioning and depth fixing requirements cannot be met. If the excitation mode is not proper, the two water pipes are in the abnormal curve H of the magnetic fieldxThe upper is shown as having only one peak, as is the anomaly of the other three water tubes. Therefore we first compare q0.8And one half q0.5In a size relationship or use
Figure GDA0003595325240000151
The positioning and depth fixing method judges whether the abnormality is a single-tube abnormality or a double-tube abnormality. When we determine that two water pipes are underground, the deviation induction method is adopted, so that the CD signal relative to the AB signal becomes very weak, and the requirement of accurate positioning is met, and the same is true for positioning and depth setting of other three water pipes. The specific implementation steps are as follows:
(1) utilizing the part of the underground metal pipeline which is generally exposed out of the ground, such as a fire hydrant, a water meter, a pipeline inspection well, a valve, a connecting point of lifting or entering equipment or exposing the underground pipeline due to construction excavation, exciting the known metal pipeline by using a charging method or an induction method, receiving the horizontal magnetic field component of the measured target metal pipeline by using a receiver of a pipeline detector within a certain range to approximate the plane position of the pipeline, and initially judging that the plane position of the pipeline in the area is positioned at the ABCD and EFGH positions in the graph 7; the charging method comprises the following steps: one end of an alternating current power supply of a pipeline detector transmitter with a certain frequency is connected to an exposed part of a pipeline, the other end of the alternating current power supply is connected with a grounding electrode far away from a connection point, namely single-end charging is carried out, or two ends of the alternating current power supply are respectively connected to two exposed points of the same target pipeline, namely double-end charging is carried out, at the moment, a current loop is formed between a metal pipeline and the ground or between the metal pipeline and the power supply, and an alternating magnetic field is generated around the pipeline; the induction method is to use the transmitter of the pipeline detector to generate a primary alternating magnetic dipole field on the ground, and if the underground metal pipeline exists, the magnitude and direction of the primary magnetic flux passing through the underground metal pipeline are changed constantly. According to the law of electromagnetic induction, an induced current is generated in the metal pipeline, the magnitude of the induced current is proportional to the change rate of the magnetic flux, and the frequency of the induced current is the same as that of the primary field. The purpose of detecting the underground metal pipeline can be achieved by observing and researching a secondary field generated by the induced current on the ground by using a receiver;
(2) Arranging a measuring line ab along the direction vertical to the routing of the ABCD metal pipeline, placing the measuring line ab on the ground by using a long measuring tape, wherein the distance from the initial position of the measuring point to the center of the pipeline is about 2-3 times of the predicted buried depth of the metal pipeline, the total length of the measuring line is 4-6 times of the predicted buried depth of the metal pipeline, sensing and exciting the pipeline above the ABCD metal pipeline by using a pipeline detector transmitter, measuring and recording the horizontal component H of the magnetic field at the position of each measuring point from the point a on the ground at the interval of 0.1mx 1And drawing the actual horizontal magnetic field component H according to the measurement result1 XA curve; horizontal magnetic field component H through the actual measured pipeline1 XUsing Δ Hx 1＝H1 x(i+1)-H1 xiThe change rate H of the horizontal direction is obtained1 XXAnd plotting the rate of change H1 XXCurve of (d), measured horizontal magnetic field component H thereof1 XCurve and H1 XRate of change in horizontal direction H1 XXThe curves are shown in FIG. 8; the maximum position of the horizontal magnetic field component is roughly measured on a measuring line before measurement, the sensitivity of a pipeline detector receiver is adjusted at the position to enable the displayed numerical value to be 100, the measuring sensitivity of the measuring line is set, and the sensitivity of the pipeline detector receiver is kept consistent in the measuring process;
(3) measuring the field actual measurement horizontal magnetic field component H obtained in the step (2)1 XCurve and H 1 XRate of change H in horizontal direction1 XXCurve (fig. 9) and theoretical horizontal magnetic field component H of single metal pipelineXCurved, perpendicular magnetic field component HZCurve and HXRate of change in horizontal direction HXXComparing the curves (FIG. 3), and comparing the results or actually measuring the horizontal magnetic field component H according to the curves1 XHalf-pole chord length in curve
Figure GDA0003595325240000161
Figure GDA0003595325240000162
All in one
Figure GDA0003595325240000163
Judging whether one or two pipelines are based on the relation between the chord lengths or the combination of the chord lengths and the two pipelines; as can be seen by comparing FIG. 8 with FIG. 3, it measures the horizontal magnetic field component H1 XThe overall characteristics of the curve are similar to those of a single pipeline, and the curve is a single peak and only has a maximum value, but H1 XXThe curve has an obvious slope variation range between two pipes and two inflection points, and can be used for judging that two pipelines are underground; q can be obtained from the measured data table and the magnetic field curve0.8＝2.0m，
Figure GDA0003595325240000164
Confirming that two metal pipelines are underground; the measured data are shown in table 2:
TABLE 2 actual measurement data of magnetic field of AB and CD metal pipeline (normalization treatment)
Figure GDA0003595325240000165
Figure GDA0003595325240000171
According to the measured data and the formula delta H'x＝H′x(i+1)-H′xiCalculating a horizontal magnetic field component H 'of the (i + 1) th measuring point'x(i+1)And i measures the horizontal magnetic field component H'xiDifference Δ Hx', and find out Δ HxMaximum of
Figure GDA0003595325240000172
Finding a maximum value
Figure GDA0003595325240000173
Corresponding horizontal magnetic field component H 1 XMaximum value of
Figure GDA0003595325240000174
By the formula
Figure GDA0003595325240000175
Determining the maximum value of the abnormality of the target pipeline
Figure GDA0003595325240000176
And determining on the horizontal magnetic field component curve
Figure GDA0003595325240000177
And
Figure GDA0003595325240000178
position of (a), q0.75The buried depth h of the pipeline is 1.49m by formula (i), wherein b is 1.14m
Figure GDA0003595325240000179
And q is0.751.14 difference:
Figure GDA00035953252400001710
in formula (I): h is the apparent buried depth of the pipeline, b is
Figure GDA00035953252400001711
And
Figure GDA00035953252400001712
a corresponding ground level distance;
the error between the 1.40m buried depth obtained by the method and the actual excavation buried depth is 0.09m, the detection standard requirement is met, and the plane error is 0.3 m.
(5) Exciting the AB or CD metal pipeline by using a deviation induction method, so that the magnetic field induction signal of the target pipeline is enhanced relative to the side interference signal, and measuring the underground two pipelines on the original measuring line in the step (2) againHorizontal magnetic field component generated on ground by parallel metal pipelines
Figure GDA0003595325240000181
Horizontal magnetic field component through the actual measured pipeline
Figure GDA0003595325240000182
The change rate H of the horizontal direction is obtained11 XXAnd drawing the horizontal magnetic field component
Figure GDA0003595325240000183
And rate of change H11 XXThe measured data after the off-normal induction method optimized excitation are shown in table 3:
TABLE 3 measured magnetic field data of AB and CD metal pipelines (after normalization process) after excitation optimization by off-normal induction method
Figure GDA0003595325240000184
Figure GDA0003595325240000191
According to the formula Δ H11 x＝H11 x(i+1)-H11 xiCalculating the horizontal magnetic field component H of the (i + 1) th measuring point 11 x(i+1)And i measuring point horizontal magnetic field component H11 xiDifference Δ Hx 11And finding out Δ Hx 11Maximum value of
Figure GDA0003595325240000192
Finding a maximum value
Figure GDA0003595325240000193
Corresponding horizontal magnetic field component
Figure GDA0003595325240000194
Maximum value of
Figure GDA0003595325240000195
By the formula
Figure GDA0003595325240000196
Determining the maximum value of the abnormality of the target pipeline
Figure GDA0003595325240000197
And is determined on the horizontal magnetic field component curve
Figure GDA0003595325240000198
And
Figure GDA0003595325240000199
the buried depth h of the pipeline is 1.44m and the plane error is 0.16m by using a formula I, and the determined buried depth and plane position error completely meet the requirement of detection specifications.
Meanwhile, the inventor calculates q according to the data and the calculation method in the step (4) and the step (5)0.8And
Figure GDA00035953252400001910
the results of (A) are compared and the comparison results are shown in Table 4:
table 4 shows the calculated contrast for different positioning depth-fixing methods
Figure GDA00035953252400001911
Figure GDA0003595325240000201
As can be seen from the data calculated in Table 3, taken alone
Figure GDA0003595325240000202
Chord length method and
Figure GDA0003595325240000203
the error of the plane position calculated by the chord length method is 0.6m and does not meet the specification requirement, but the method is used in the invention
Figure GDA0003595325240000204
And
Figure GDA0003595325240000205
the plane error of the calculation result of the combination method is 0.3m, and the method is optimized and excited by adopting deviation induction
Figure GDA0003595325240000206
And
Figure GDA0003595325240000207
the plane error of the calculation result of the combination method is 0.16m, the depth and the plane position both meet the detection precision requirements of urban underground pipeline detection technical regulation (CJJ 61-94) and underground pipeline electromagnetic detection regulation (YB/T9027-94) of Ministry of construction, and the deviation induction is adopted to optimize the excited plane
Figure GDA0003595325240000208
And
Figure GDA0003595325240000209
the error of the combination method is smaller, and the measuring result is more accurate.
Meanwhile, the inventor calculates the horizontal magnetic field components of different measuring points in the embodiment and the change rate thereof in the horizontal direction by adopting a theoretical calculation mode, which is specifically shown in table 5, and draws a curve (shown in fig. 11) according to the calculation data;
table 5 shows the theoretical calculation data of the magnetic field of AB and CD metal pipelines
Figure GDA00035953252400002010
Figure GDA0003595325240000211
The comparison between the calculated theoretical data and the theoretical data curve and the actually measured data curve shows that the actually measured horizontal magnetic field component and the change rate thereof in the horizontal direction are basically similar to the theoretically calculated data curve.

Claims (7)

1. A method for determining the spatial position of two parallel metal pipelines underground, characterized in that the method comprises the following steps:
(1) utilizing the position of the metal pipeline exposed out of the ground, exciting the known metal pipeline by using a charging method or an induction method, receiving the horizontal magnetic field component of the measured target metal pipeline by using a receiver of a pipeline detector within a certain range, and primarily judging the plane position of the metal pipeline;
(2) arranging a survey line on the ground at the site in a direction perpendicular to the metal pipeline, exciting the metal pipeline at the position of the metal pipeline determined in step (1) with a pipeline probe transmitter, and measuring a horizontal magnetic field component H generated from the metal pipeline along the survey line with a pipeline probe receiver x 1And a perpendicular magnetic field component H1 ZAnd drawing the actual horizontal magnetic field component H according to the primary measurement result1 XCurve and vertical magnetic field component H1 ZA curve; according to the horizontal magnetic field component H of the actual measurement pipeline1 XBy the formula Δ Hx 1＝H1 x(i+1)-H1 xiCalculating the horizontal magnetic field component H of adjacent i points1 Xi and i +1 point horizontal magnetic field component H1 XHorizontal magnetic field component difference Δ H between i +1x 1I.e. the horizontal magnetic field component H1 XRate of change in horizontal direction H1 XXAnd plotting the rate of change H1 XXThe curve of (d);
(3) measuring the field actual measurement horizontal magnetic field component H obtained in the step (2)1 XCurved, perpendicular magnetic field component H1 ZCurve and H1 XRate of change in horizontal direction H1 XXCurve and theoretical horizontal magnetic field component of single metal pipelineHXCurved, perpendicular magnetic field component HZCurve and HXRate of change in horizontal direction HXXComparing the curves, and comparing the results or actually measuring the horizontal magnetic field component H according to the curves1 XHalf-pole chord length q in the curve0.5
Figure FDA0003582984910000011
Q being equal to0.8
Figure FDA0003582984910000012
Judging whether one or two pipelines are based on the relation between the chord lengths or the combination of the chord lengths and the two pipelines;
(4) when two underground metal pipelines are judged, any one of a T displacement method, an isolation excitation method and an offset induction method is selected for carrying out electromagnetic excitation on the metal pipelines, and the horizontal magnetic field component generated by the underground two parallel metal pipelines on the ground is measured on the original measuring line in the step (2) again
Figure FDA0003582984910000013
And according to the formula Δ H11 x＝H11 x(i+1)-H11 xiCalculating the horizontal magnetic field component H of the (i + 1) th measuring point11 x(i+1)And i measuring point horizontal magnetic field component H11 xiDifference Δ Hx 11And finding out Δ Hx 11Maximum value of
Figure FDA0003582984910000021
(5) Maximum value of difference between horizontal magnetic field components determined in step (4)
Figure FDA0003582984910000022
Finding a maximum value
Figure FDA0003582984910000023
Corresponding horizontal magnetic field component
Figure FDA0003582984910000024
Maximum value of
Figure FDA0003582984910000025
By the formula
Figure FDA0003582984910000026
Determining the maximum value of the abnormality of the target pipeline
Figure FDA0003582984910000027
(6) Generating abnormal maximum value according to the target pipeline calculated in the step (5)
Figure FDA0003582984910000028
Determining q on a horizontal magnetic field component curve0.5
Figure FDA0003582984910000029
And q is0.75
Figure FDA00035829849100000210
The buried depth h of the pipeline is calculated by using a formula (I):
Figure FDA00035829849100000211
in formula (I): h is the apparent buried depth of the pipeline, b is 75%
Figure FDA00035829849100000212
And 50 percent of
Figure FDA00035829849100000213
A corresponding ground level distance;
(7) and further determining the plane position of the pipeline, namely the position corresponding to the length of the half-extreme point moving towards the maximum value direction by h, as the horizontal position of the center of the metal pipeline.
2. The method for determining the spatial position of two underground parallel metal pipelines according to claim 1, wherein the number of pipelines in the step (3) is determined as follows: when in use
Figure FDA00035829849100000214
Figure FDA00035829849100000215
Determining that the underground is two pipelines; when the horizontal magnetic field component H is actually measured on site1 XCurve and vertical magnetic field component H1 ZCurve and single metal pipeline theoretical horizontal magnetic field component H XCurve and vertical magnetic field component HZIf the shapes of the curves are completely different, judging that the two metal pipelines exist; when the horizontal magnetic field component H is actually measured on site1 XCurve and vertical magnetic field component H1 ZCurve and single metal pipeline theoretical horizontal magnetic field component HXCurve and vertical magnetic field component HZSimilar curve form, actually measured H on site1 XRate of change in horizontal direction H1 XXCurve and single metal pipeline theory HXRate of change in horizontal direction HxxThe curve has an obvious slope variation range, and if an inflection point exists, the underground part of the curve is judged to be two metal pipelines; when the horizontal magnetic field component H is actually measured on site1 XCurve and vertical magnetic field component H1 ZCurve and single metal pipeline theoretical horizontal magnetic field component HXCurve and vertical magnetic field component HZSimilar curve form, H1 xxIf the curve has no inflection point, the underground is judged to be a pipeline.
3. The method for determining the spatial position of two underground parallel metal pipelines according to claim 1, wherein: the T displacement method in the step (4) is that the receiver R is placed right above the detected point or the exposed point of the target pipeline, the transmitter T is moved in a proper distance and perpendicular to the direction of the pipeline, and the position of the metal pipeline is judged and accurately positioned according to the strength change of the signal received by the receiver; the isolation excitation method in the step (4) is to select a section with sparser pipelines to induce or charge the target pipeline so as to reduce side effects, so that signals of the target pipeline are highlighted on the section with high pipeline density, and positioning and depth fixing are realized; the deviation induction method is characterized in that the contrast of a secondary field between a target pipeline and a side pipeline is increased according to the principle that a primary field of a magnetic dipole does not change uniformly along with the change of an angle theta, the angle theta is an included angle between a transmitting coil axis and a vector r, and a signal of the target pipeline is highlighted, so that the aim of distinguishing and tracking the target pipeline is fulfilled.
4. The method for determining the spatial position of two underground parallel metal pipelines according to claim 1, wherein: when the position of the underground metal pipeline is preliminarily judged by utilizing the position of the metal pipeline exposed out of the ground in the step (1), the part of the metal pipeline exposed out of the ground comprises a fire hydrant, a water meter, a pipeline manhole, a valve, a connection point of a lifting or entering device, or the underground pipeline is exposed due to construction excavation.
5. The method for determining the spatial position of two underground parallel metal pipelines according to claim 1, wherein: the charging method in the step (1) is that one end of an alternating current power supply of a pipeline detector transmitter with a certain frequency is connected to the exposed part of the pipeline, the other end of the alternating current power supply is connected with a grounding electrode far away from the connection point, namely single-end charging is carried out, or two ends of the alternating current power supply are respectively connected to two exposed points far away from the same target pipeline, namely double-end charging is carried out, at the moment, a current loop is formed between the metal pipeline and the ground or between the metal pipeline and the power supply, and an alternating magnetic field is generated around the pipeline; the induction method in the step (1) is to use a pipeline detector transmitter to generate a primary alternating magnetic dipole field on the ground, if a metal pipeline exists underground, the size and the direction of the magnetic flux of a primary field passing through the underground metal pipeline are constantly changed, induction current is generated in the metal pipeline according to the electromagnetic induction law, the frequency is the same as that of the primary field, and a receiver is used on the ground to observe and research a secondary field generated by the induction current, so that the aim of detecting the underground metal pipeline can be achieved.
6. The method for determining the spatial position of two underground parallel metal pipelines according to claim 1, wherein: in the step (2), when the survey line is arranged, the distance between the initial position of the survey point and the center of the pipeline is 2-3 times of the estimated burial depth of the metal pipeline, the total length of the survey line is 4-6 times of the estimated burial depth of the metal pipeline, and the distance between the survey points is 0.05-0.2 m.
7. A method for determining the spatial position of two parallel metal pipelines underground according to claim 3, wherein: the excitation mode in the step (4) is selected according to the exposure condition and the distribution characteristics of the metal pipeline and the applicability field repeated test comparison determination of various excitation modes, and the target pipeline is gradually detected from the known state to the unknown state, wherein if the distance between pipelines is small, an offset induction method is not selected; the T-shift method is chosen for applications where the target line must have a dew point or a known point and where the receiver experiences little side interference.
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