In the previous article, we explored in detail the common types of diseases in tunnel secondary linings, such as cracks, leakage, spalling, and voids, along with an in-depth analysis of their causes. Understanding these "symptoms" is the first step. However, to ensure the long-term health and safety of a tunnel, a set of scientific and reliable "diagnostic" methods is essential. This article follows the previous one, systematically introducing several widely used inspection techniques for tunnel secondary lining diseases in the industry, helping you understand how engineers perform precise "health checks" on tunnels, bringing hidden defects to light.

1. Visual Inspection

Visual inspection is the most fundamental method for detecting diseases in tunnel secondary linings. It involves the visual observation of surface defects such as cracks, water leakage, and spalling on the secondary lining, recording their location, size, shape, and other information. Visual inspection can quickly identify some obvious defects but may fail to detect some hidden issues.

2. Ground Penetrating Radar (GPR) Inspection

Ground Penetrating Radar inspection is a method based on the principle of electromagnetic wave reflection. The GPR transmits high-frequency electromagnetic waves, which generate reflected waves when encountering interfaces between different materials. By receiving these reflected waves and analyzing parameters such as propagation time, amplitude, and frequency, the internal structure of the tunnel secondary lining can be inferred. GPR inspection offers advantages such as speed, being non-destructive, and high resolution, enabling the detection of internal defects like cracks, voids, and delamination within the secondary lining.

3. Ultrasonic Testing

Ultrasonic testing is a method that utilizes the propagation characteristics of ultrasonic waves in concrete. When ultrasonic waves travel through concrete, parameters such as their velocity, amplitude, and frequency are influenced by the internal structure of the concrete. By transmitting and receiving ultrasonic waves and analyzing changes in these parameters, the strength and defects of the concrete can be inferred. Ultrasonic testing can detect internal defects such as cracks, voids, and honeycombed areas in the tunnel secondary lining. However, the accuracy of the results can be affected by factors like the presence of reinforcing steel within the concrete.

4. Infrared Thermography Inspection

Infrared thermography inspection is a method based on detecting the surface temperature distribution of an object. When defects such as cracks or water leakage are present on the surface, the temperature distribution changes. Using an infrared thermography camera, the surface temperature distribution can be detected, thereby inferring the location and extent of the defects. Infrared thermography inspection offers advantages such as speed, non-contact operation, and intuitive results. However, the accuracy of the inspection can be influenced by environmental factors like ambient temperature and humidity.

5. Core Drilling and Sampling

Core drilling and sampling is a method involving the extraction of concrete core samples from the tunnel secondary lining for inspection. This method allows for direct observation of the internal structure and quality of the concrete, such as its strength, density, and cracks. The results from core sampling are accurate and reliable. However, it is a destructive testing method that causes some damage to the tunnel secondary lining structure.

To Wrap Up

In summary, from traditional visual inspection to modern non-destructive testing technologies like Ground Penetrating Radar, Ultrasonic Testing, and Infrared Thermography, and further to the accurate but destructive Core Drilling, each inspection method has its unique advantages and suitable applications. In practical engineering, it is often necessary to "combine multiple methods" based on the specific situation, integrating various techniques to conduct a comprehensive and accurate assessment of the health condition of the tunnel secondary lining. Precise inspection is the prerequisite for effective treatment, providing the crucial scientific basis for subsequent maintenance and strengthening work.

Identifying the diseases is only the first step. How to "apply the right remedy" for repair and strengthening is the key to ensuring the safety of the tunnel structure. In the next article, we will move into the core part: we will detail the Treatment Methods for Diseases in Tunnel Secondary Linings for different types of defects.