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Road and bridge pile-based acoustic tube often has problems and related operational specifications when burying
Acoustic tubes used in road and bridge pile testing are prone to various issues when buried underground. These problems can significantly affect the accuracy of the test results and even lead to costly rework or unreliable data. Here's a detailed breakdown of common issues and operational guidelines:
1. **Common Problems During Burial**
- The bottom of the pile is a high-risk area for defects. Poor construction practices can cause the acoustic tube to bend inward, reducing the spacing between tubes. This misalignment affects the parallel alignment of transducers, leading to abnormal ultrasonic pulse velocity, reduced amplitude, and irregular sound velocity curves.
- If the acoustic tubes are not securely fastened or the spacing between bindings is too wide, they may tilt or bend due to concrete pressure during pouring. This changes the distance between tubes, making it difficult to accurately assess the pile integrity. In severe cases, only core sampling or other reliable methods can be used, which delays construction.
- Excessively long steel casings can trap air inside, forcing the acoustic signal to travel through air layers instead of water. This causes serious signal distortion, affecting the evaluation of the pile’s structural integrity.
- It is often assumed that the transducer is centered within the acoustic tube. However, if the tube is large, the transducer can move freely inside, increasing the delay in the coupling water layer and affecting the propagation time of the sound wave. This leads to greater inaccuracies in the test results.
2. **Operational Specifications for Proper Installation**
- **Embedding Depth**: The acoustic tube should extend to the bottom of the pile, with the top end protruding 300–500 mm above the pile surface. All tubes on the same pile should have the same exposed height.
- **Sealing Requirements**: The bottom of the tube must be sealed with a blind cover or steel plate to prevent grout leakage. After installation, the top of the tube should be covered or plugged to avoid foreign objects falling in during concrete pouring, which could block the tube.
- **Fixing Standards**: Acoustic tubes can be directly welded or tied to the inner side of the reinforcing cage. Fixing points should be no more than 2 meters apart, with extra attention given to the bottom and joints. For piles without reinforcement cages, steel brackets can be used. To keep the tubes parallel, triangular steel frames can be spot-welded between them.
- **Joint Specifications**: When placing the steel cage, care must be taken to prevent twisting. The acoustic tube is usually installed along with the steel cage. The lower section is fixed to the first part of the cage, while the rest is temporarily secured. When connecting sections, the upper part of the tube should align and plug into the lower one. Joints can use reverse-threaded sleeves with soft rubber seals or welded steel sleeves. The joint must be strong enough to prevent bending or disconnection, especially under high hydrostatic pressure. The inner wall of the joint should be smooth, free from weld slag or burrs, to allow the transducer to move freely. If cutting is necessary, use a cutting machine and polish the edges to remove any roughness. Avoid using electric welding, as molten material can damage the tube.
- **Water Filling Guidelines**: Each section of the acoustic tube should be filled with clean water as a coupling medium. Avoid using river water, especially during flood season, as it may contain impurities that could clog the tube. Before pouring concrete, check the water level in the tube and refill if necessary.
- **Testing Procedures**: Testing can begin after the pile has cured for at least 14 days. Before testing, chisel the pile head to the design elevation. Use a 20 cm-long, 32 mm-diameter steel bar to tap the tube and check its smoothness, then fill it with clean water.
Zhangzhou Lianyu Steel Pipe Co., Ltd.
Phone: 15231769003 | 0317-2012503
Website: http://news.chinawj.com.cn
Editor: Hardware Business Network Information Center
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