Sonic Logging Tube (SLT) - Introduction

1. Definition & Purpose (定义与用途)

Sonic Logging Tubes, commonly known as Acoustic Tube or Pile Testing Tubes, are a pre-installed cross-hole testing system used primarily for integrity evaluation of deep foundation elements, such as bored piles, drilled shafts, barrettes, and diaphragm walls.

Their primary purpose is to provide a reliable access channel for ultrasonic probes to assess the concrete's quality, integrity, and the presence of defects like voids, soil inclusions, necking, or segregation within the foundation element.

2. Key Components & Working Principle (关键组件与工作原理)

Components:
  Tubes: Typically made of steel (galvanized or black) or PVC, with a standard diameter of 50-60mm. They are connected by threaded couplings or welded sleeves.
  Couplers: Used to join individual tube sections, ensuring a smooth internal bore and water-tightness.
  Bottom Cap/Plug: Seals the bottom of the tube to prevent concrete and slurry from entering.
  Top Cap: Protects the tube from debris and damage before and after pouring.
  Working Principle: The system consists of at least two or more tubes installed in parallel, forming a "testing profile." After the concrete has gained sufficient strength, the tubes are filled with water as a coupling medium. An ultrasonic probe (transmitter) is lowered into one tube, and a receiver probe is lowered into an adjacent tube at the same depth.
 The transmitter emits ultrasonic pulses, which travel through the water, the tube wall, the concrete between the tubes, and into the receiver tube. The received signal's travel time (wave velocity) and amplitude (energy attenuation) are analyzed.
  High-quality, homogeneous concrete results in fast wave velocity and high amplitude.
  Defects (e.g., voids, inclusions) disrupt the sound path, causing slower wave velocity and a significant drop in amplitude, which is clearly identifiable on the data plot.

3. Types & Layouts (类型与布局)

Layouts:
  2-Tube Layout: For single cross-hole profile. Limited defect localization.
  3-Tube Layout: Forms three profiles (A-B, B-C, C-A), allowing for better defect localization in the pile cross-section.
  4-Tube Layout (or more): Provides comprehensive coverage and highly accurate 3D imaging of the entire pile shaft, ideal for large-diameter piles.

4. Key Advantages (主要优势)

High Accuracy & Detail: Provides a detailed and accurate assessment of the entire pile length and cross-section.
  Early Defect Detection: Allows for the identification of potential issues before superstructure construction, mitigating future risks and costs.
  Quantitative Data: Provides objective, measurable data on concrete quality.
  Deep Application: Suitable for very deep foundations where other methods (like low-strain integrity testing) are ineffective.
  Permanent Record: Creates a permanent record of the pile's as-built condition.

5. Installation Procedure (安装流程简介)

1. Fabrication: Tubes are assembled into cages corresponding to the rebar cage.
 2. Fixing: Tubes are firmly fastened to the reinforcement cage at regular intervals using straps or wires to prevent displacement during concrete pouring.
 3. Alignment: Tubes must be installed parallel to each other and vertical.
 4. Sealing: Bottom caps are secured, and top caps are placed after the cage is positioned.
 5. Concreting: Concrete is poured. The tubes remain in the structure permanently.
 6. Testing: Conducted typically 7-28 days after concreting, once the concrete has cured.

6. Important Considerations (重要注意事项)

Water-tightness: The entire tube system must be perfectly sealed. Any leakage can render the test invalid.
  Parallelism: Tubes must be parallel for accurate data interpretation.
  Flushing: Before testing, tubes must be flushed clean and filled with clean water to ensure proper acoustic coupling.

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简洁版本 (For a quick overview):

Sonic Logging Tubes are a non-destructive testing (NDT) system used to check the quality of concrete in deep foundations like piles. Several tubes are built into the foundation. After pouring concrete, technicians send sound waves between these water-filled tubes. By analyzing how the sound travels, they can create a detailed "health map" of the concrete and find any hidden defects, ensuring the foundation is safe and sound.