Taking the pipeline detection of Shenzhen Yayuan overpass as an example, this paper discusses the comprehensive application of various geophysical methods in pipeline detection.
Methods and techniques for detection in areas with complex distribution and large interference.
Underground pipeline; Pipeline detector; Geological radar.
O introduction
With the rapid development of urban construction, the contradiction of the lack of information of the original urban underground pipelines is becoming more and more prominent. Therefore, we found that
With the construction and development of cities, the task of underground pipelines and the determination of their distribution, buried depth and direction have also attracted the attention of the Ministry of Urban Construction.
In a sense, the degree of modernization of a city is also reflected in the buried pipelines.
Therefore, in terms of quantity, the more developed the city, the more underground projects there are. In recent years, the detection of underground pipelines at home and abroad,
Great improvements have been made in both technology and methods, especially in equipment.
Intuitive, accurate and portable are the three advantages of this kind of instrument, but only one instrument can detect underground.
The task of pipelines is very arduous, especially underground pipelines with complex distribution, deep burial and mixed metal pipelines and non-metal pipelines.
This is especially true in the case of many interference sources. Various methods and testing instruments must be adopted to solve the problem comprehensively. This paper needs
Taking the underground pipeline detection results of Shenzhen Yayuan overpass site as an example, combined with the pipeline detection produced by Reddy company in Britain,
Measuring instruments: Canadian pulseEKKOw ground penetrating radar and DDW- 1 multifunctional electromagnetic measuring instrument manufactured by our school.
Will, the detection technology of underground pipelines; And solve the complicated problems of urban underground pipeline distribution and drainage by comprehensive geophysical exploration methods.
In this paper, the interference problem is discussed in order to provide some practical experience for pipeline detection in complex areas.
1 Geological and geophysical survey in the work area
The exploration task in Shenzhen Yayuan overpass site is to find out all kinds of pipelines laid underground. These pipes usually
Due to shallow burial depth, the strata involved in this survey are mainly artificial fill and Quaternary Holocene alluvium (Q4).
Fill includes asphalt pavement, cement pavement, macadam subgrade, construction waste and sundries, generally 0.2~0.4m, which are divided into
Quaternary alluvium (Q4) is mainly composed of black muddy clay and yellowish brown clay.
Soil, the surface layer contains plant roots, locally contains a small amount of gravel and timely gravel, and has different degrees of consolidation, with a thickness of. . 2~3.Zm。
Buried pipelines mainly include cables and upper and lower drainage pipes, which are good conductors of metal cables and pipelines.
Electric body; For non-metallic pipes, such as some rainwater pipes, sewage pipes and some cement pipes, the outer side
Although the shell is a high-resistance body, it is a good conductor when it is filled with water, and a high-resistance body when it is not filled with water or not.
There are obvious electrical differences between these pipelines and topsoil. However, due to the staggered old and new pipelines in the area, the distribution is complex.
Miscellaneous, there must be electrical interference between pipelines, and the work area is located in downtown areas, traffic and cement pavement reinforcement.
Nets, iron fences, iron billboards in roads, high-voltage wires beside sidewalks, iron sundries in surface backfill,
All this hindered the exploration. In this complex area, exploration must rely on the cooperation of various geophysical methods.
Eliminate interference, identify and distinguish various underground pipelines. To this end, we adopted the electromagnetic wave reflection method and
Diffraction method, electromagnetic induction method, connection method (charging method).
2 detection methods and techniques
According to the design of Shenzhen Urban Construction and Development Office, the underground pipeline detection work is mainly arranged at Dongmen Road and Jinwen Middle Road.
Jinwen South Road and Sungang Road. There are two intersections, which are one of the traffic arteries in Shenzhen.
Except Jinwen South Road, all other sections are asphalt pavements. The survey work is based on the known pipeline outcrop, from
Starting from the section where the pile position is under construction, the abnormal section is tracked and located. The instruments used for detection are British.
RD-400 pipeline detector produced by Reddy company, pulseEKKOw geological radar produced by Canada and our school.
Self-made DDW- 1 multifunctional electromagnetic measuring instrument.
RD-400 underground pipeline instrument consists of a receiver and a transmitter. The receiver can be used alone. Without pipes,
Outcrop is usually detected by induction method. At this time, the transmitter emits an electromagnetic wave of skHz or 33kHz, which satisfies the following requirements.
After reaching the underground metal pipeline, the metal pipeline will produce induced current and induced electromagnetic field. When a receiver (dual coil antenna) is connected,
After receiving the electromagnetic field, the electronic circuit in the receiver monitors the electromagnetic field signal and sends it to the detection target.
Response. Using this response, we can locate the target, measure the depth and track the target successively. When the pipeline is exposed to the inspection position.
At first, the electromagnetic wave emitted by the transmitter can be directly sent to the pipeline (metal) through the signal clip, and the receiver can receive this.
Signal, location and continuous tracking. This method is called connection method (or charging method). Because of the signal, the connection method is very strong, so
The detection precision and accuracy are better than that of induction method. Underground power lines and communication lines are usually smaller in diameter, when they
When there is a certain buried depth, the induced electromagnetic field is very weak, so it can be detected by connection. In order to measure it more accurately,
Determine the direction and buried depth of the pipeline to avoid the interference of traffic and road metal objects, and require the receiver to walk with the pipeline as much as possible when detecting.
Vertical (the strongest signal can be obtained at this time), and the transmitter should be as parallel as possible to the pipeline and placed above the pipeline as much as possible.
PulseEKKOIV geological radar is mainly composed of a pair of antennas. When that transmit antenna transmits high-frequency electromagnetic pulse to the ground,
The receiving antenna can receive reflected or diffracted echoes from underground targets. Because of the detection of underground pipelines and surrounding areas
There are obvious electrical differences (mainly differences in conductivity and dielectric constant) in the surrounding media, so what is emitted by the transmitting antenna?
When the high-frequency electromagnetic wave propagates to the underground pipeline, it will form a strong reflection or diffraction echo, which will be received by the receiving antenna.
After the echo, the signal is transmitted to the console through the optical cable. After data collection, recording and processing, radar images are displayed on the screen.
On the screen or printed. Through the recognition and interpretation of radar images, the buried depth and location of underground pipelines are determined. This kind of exploration
The center frequency of the antenna used in the measurement is100 MH; The peak working voltage of the transmitter is 4o0V, and the sampling time window is 256ns (which can be
Ensure that the detection depth reaches GM); The sampling interval in time domain is 0. The sampling interval (trajectory distance) in 0.sns space domain is 0. zm； low
The number of direct piles is128; The antenna distance is 0.6m According to the general trend of underground pipelines, the work is carried out by the reverse profile method.
When wiring, the direction of the survey line should be perpendicular to the direction of the pipeline to be tested as much as possible. In order to avoid rollover during measurement.
The interference of metal objects on the surface must keep the antenna plate in good contact with the ground, so that the antenna can be well coupled with the underground medium.
When the radar detects the pipeline, it can cooperate with other instruments to track and verify each other.
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DDW- 1 Multi-function electromagnetic measuring instrument consists of transmitting coil and receiving coil, which is mainly used in places with pipeline outcrops.
Long-distance tracking When detecting, the transmitter charges the target, that is, the signal current is directly connected to the pipeline, and the pipeline is generated.
Magnetic field generation. When the receiving coil receives the magnetic field signal, it generates a current on the coil (the maximum value can be obtained at the target).
Current), the maximum value can be found by the pointer swing on the receiver instrument. According to this maximum value, the detection target can be located.
The instrument can conveniently track the pipeline continuously.
The cooperation of the above three instruments has achieved good results in the detection of underground pipelines in Yayuan overpass site.
Detection effect, especially for complex pipeline trends (such as crossing, overlapping, tee, etc. ), has been given a more accurate positioning, which
Compared with the actual mining in the future, these results have little error.
3 Interpretation and analysis of test results
In this exploration, * * * totally identified underground water supply pipelines 12, 6 power lines and 9 communication lines.
Some pipelines were inspected to correct their errors and make them consistent with the actual trend of pipelines. See table 1 and figure 1 for the test results.
Because this detection work is carried out in downtown areas where vehicles come and go, there is great interference, and because underground pipelines cross each other.
And the distribution of underground electromagnetic field is very complex, which brings great difficulties to the detection and identification of pipelines.
Do not have all kinds of advanced instruments and equipment, methods and technologies, as well as rich field work experience and strong interpretation and judgment ability.
Force, this exploration task is really difficult to complete. Figs. 2 and 3 are geological radar images on complex sections, in which fig. 2 is at 5.sm.
And 7.gm reflect two pipelines; Figure 3 reflects several pipelines (see figure 1 for radar survey line layout).
There is a pipeline with the most complicated distribution at Yayuan intersection. There are valves on both sides of the pipeline and a tee in the middle. The pipe is from one side.
After the valve comes out, it passes through another pipeline (Figure 4). The pipeline elbow passes through Pier 52 (see Figure 1), and there are
Binding pile foundation reinforcement cage. How to determine the position of the tee in this complicated situation? How to judge a pipe and b pipe (figure