Underground structures require routine inspections and maintenance processes for their optimal use In particular, the practical inspection of tunnels commonly relies on human-based methods that entail inherent limitations The applications of laser technology are rapidly expanding, with decreased cost and increased accuracy This study attempted to investigate the feasibility of applying laser scanning technology to the management of infra-structures A trial model of a laser-based tunnel scanning system was developed to facilitate an automated tunnel inspection process The trial model scanner scans a tunnel in the time-of-flight manner, and delivers the scanned data in ASCII files containing x, y and z coordinates In addition, this paper proposed an algorithm to extract the information for tunnel management from the data set acquired from the trial model The proposed algorithm extracts installations on the liner and the physically damaged parts of a tunnel liner using the geometric and radiometric features of the scanning data The algorithm was tested and evaluated by using the scanned data set from an operating railway tunnel and a concrete box with various diameters of pipes attached on one wall of the box Due to the mechanical and laser sensor limitations, the developed trial model is limited with respect to the identification of cracks and installations; cracks and installations having a gap or width of less than 5 mm are not detected well This limitation, however, will be overcome by upgrading the scanning system and through increased density of the point cloud (A) Reprinted with permission from Elsevier

Feature extraction of a concrete tunnel liner from 3D laser scanning data

Concrete crack detection and quantification using deep learning and structured light

Elastic wave-based non-destructive test (NDT) methods are effective for detecting flaws in concrete structures. With the recent developments in computing hardware and software, imaging techniques have become very popular in NDT applications. However the application of elastic wave-based imaging methods for concrete structures is severely limited by the physical coupling between sensors and concrete surface, which reduces testing efficiency. In this report, the air-coupled sensing technique is proposed as a solution to improve the efficiency of elastic wave-based test methods for concrete structures. Theoretical analyses are first conducted to study the propagation of leaky Rayleigh waves in fluid-solid half spaces. Closed-form solutions of the Green’s function are derived for pressure and displacement in both the fluid and solid. This analysis provides theoretical background necessary for practical air-coupled sensing of leaky Rayleigh waves in concrete. The theory is also extended to underwater NDT applications. Two applications of air-coupled sensing are considered. One is air-coupled leaky surface wave sensing in concrete. A laboratory study and field tests demonstrate that air-coupled sensors are very effective for sensing leaky surface waves in concrete. The sensitivity and accuracy of air-coupled sensors are comparable to contact sensors. Aircoupled sensors are suitable replacement for contact sensors in SASW and MASW tests and moreover help improve test efficiency. In addition, the contact-less nature of aircoupled sensing enables the study of the effect of defects on wave attenuation. The experimental results show leaky Rayleigh waves are sensitive to the existence of cracks in concrete when waves propagate across cracks; the crack positions are clearly located in a 2-D scanning test image. The second application is air-coupled impact-echo. Two reinforced concrete slabs containing different types of defects were inspected using an air-coupled impact test testing scheme. 2-D scanning impact-echo tests were conducted over the slab containing voids and delaminations. The 2-D scanning image clearly shows the location of embedded defects, and their depths are also determined. Air-coupled impact-echo is also applied to examine the grouting condition of embedded ducts. The poorly-grouted and ungrouted sections are identified within the metal duct.

Non-Contact NDT of Concrete Structures Using Air -Coupled Sensors

An experimental study of the effect of local contact loss on the earth pressure distribution on existing tunnel linings

Manufacturing processes such as casting, rolling, forging, extrusion, material removal processes, etc are some of the common techniques used today in manufacturing industries However, these proce

Advances in applications of Non-Destructive Testing (NDT): A review

Concrete tunnel linings, whether pre-cast or cast in place, are designed to distribute external soil pressures as uniformly as possible through the tunnel shell. To this effect, the contact between the lining and the surrounding soil is usually assured by grouting the annular space between. Any voiding in the grout at this interface negates the purpose of the grout. This paper describes the use of non-destructive testing to examine the efficiency of tunnel lining grouting programmes, with particular emphasis on results obtained by the impulse response and impulse radar methods. The rail, water supply and sewer tunnels discussed in this article vary in diameter between 1 and 5 m, and emphasis is placed on the rapid results obtained by these methods.

Claus Germann Petersen

Papers

Rapid and economical evaluation of concrete tunnel linings with impulse response and impulse radar non-destructive methods