The material of the acoustic tube is selected with the highest sound transmittance

The choice of acoustic tube material is based on the greater sound transmittance
< r> >
>< >. The selection of acoustic tube
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> Acoustic Measurement The selection of pipe materials is based on the principles of greater sound transmittance, ease of installation and lower cost.
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> The acoustic pulse is emitted from the transmitting transducer, reaches the interface between the water and the acoustic pipe wall through the coupled water, and then passes through the pipe wall to the interface between the acoustic pipe wall and the concrete, passing through The concrete then needs to pass through two interfaces of another acoustic tube to reach the receiving transducer.
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> Therefore, the acoustic tube forms < r>< > interfaces, and the sound energy transmission coefficient of each interface can be calculated as follows:
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> ( < r>< >) In the formula: < r>< >The sound energy transmission coefficient of a certain interface
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> < r>< >The acoustic impedance rate of the medium on both sides of the interface< r>()
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> The total sound transmission coefficient of the < r>< > interface between the transmitting and receiving transducers is
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> (< r>< >) currently commonly used The pipes include steel pipes, steel corrugated pipes, and plastic pipes.
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> The advantage of steel pipe is that it is easy to install. It can be welded to the steel frame by electric welding, which can replace part of the steel bar section. Moreover, the steel pipe has high stiffness. After embedding, its parallelism and straightness can be basically maintained. Currently, many large-diameter cast-in-place piles use steel as the acoustic tube. However, the price of steel pipes is more expensive:
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> Steel corrugated pipes are a better material for acoustic detection pipes. They have thin pipe walls, less steel and are impermeable, pressure resistant, high strength, It has good flexibility and other characteristics, and is usually used to reserve holes for post-tensioning in prestressed structures: when used as acoustic tubes. It can be tied directly to the steel frame soil, and the joints can be connected with one size larger corrugated socket. Because the bellows is very light, it is very easy to operate, but care must be taken to keep its axis straight during installation.
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> Plastic pipes have a low acoustic impedance and have a large sound transmittance when used as acoustic detection tubes. They can usually be used in smaller cast-in-place piles. They should be used with caution in large cast-in-place piles. < r>< >Because large-diameter piles need to be filled with a large amount of concrete, the heat of hydration of the cement is not easy to dissipate: since the thermal expansion coefficient of plastic is very different from that of concrete, the plastic pipe will shrink radially and longitudinally due to the temperature drop after the concrete solidifies, which causes It may be partially separated from the concrete and cause air or water gaps, and more strongly reflective interfaces will be added to the sound path, which may easily lead to misjudgment.
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> The diameter of the acoustic tube is usually larger than the diameter of the radial transducer < r>< >. The common specification is the inner diameter < r>< >. The wall thickness of the pipe has little impact on the sound transmission. Therefore, in principle, there is no limit on the thickness of the pipe wall. However, from the perspective of saving steel, as long as the pipe wall can withstand the lateral pressure of newly poured concrete, the thinner it will be. More provinces.
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>< >, the number and arrangement of buried acoustic tubes
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> Arrangement of buried acoustic tubes The number and layout of the pile cross-section should take into account the control area of the inspection. Usually there is an arrangement as shown in the figure < r>< >. The shaded area in the figure is the detection control area.
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> Generally, when the pile diameter is smaller than < r>.~< >, two piles with a diameter of < r>~.< > are arranged along the diameter. When the pile diameter is < r>~.< >, the < r>< > roots are arranged in equal shape When the diameter of the side triangular pile is larger than < r>.< >, arrange the roots of < r>< > in a square shape.
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