# I-BIM Applied in Railway Geometric Inspection Activity: Diagnostic and Alert
## 4 Railway Inspection Activity
### Rail Inspection Metodologies  
Distinct test processes can be considered in inspection work. The nondestructive testing (NDT) methods are used as preventive measures against track geometric failures and possible derailment [40]. The nondestructive evaluation (NDE) techniques can also be applied, namely, to visual detection, ultrasonic inspection or acoustic emission inspection [31]. The horizontal track geometry value can be obtained using a track geometry recording system positioned in a service vehicle.  
Figure 8: Measurement of the twist railway parameter [9].  
Figure 7: Measurement of the longitudinal level (**a**) and alignment (**b**) parameters [9].  
A visual inspection or walking inspection can be applied as a first action before the use of NDT or NDE methods. The manual basic inspection is utilized to detect rail defects in track elements, materials, installed equipment and drainage systems. After this, an ultrasound instrument can be used, providing greater precision and control over the geometric defects identified on the rail track. Advanced and complex equipment can also be considered, namely, an electromagnetic inspection device, laser measurement, prospecting radars for ballast and sub-ballast inspection and ultrasonic techniques [37].  
A manual inspection can be supported with the use of trolley KRAB equipment (Figure 9a) containing two measure rollers allowing one to verify the gauge, alignment, cant and twist dimension [41]. The LaserRail device (Figure 9b) allows for monitoring the rail wear with high precision, by reading the profile, and providing data concerning the material loss of the rail head [42]. The Iris 320 equipment is a railway inspection vehicle that offers digitized measurement systems, networking, information technology and flexible facilities to execute data production, resulting from the fusion of innovation and railway maintenance [43]. In the present case, the provided inspection data were collected using the EM120 track car [25].  
Inspectors and work crews can use a rail inspection car to move to and from the repair work or inspection sites and carry the inspection equipment on board, including probes and transducers mounted underneath the carriages (Figure 9c). The inspection vehicle allows the testing of various parameters of track geometry without obstructing normal railroad operations. The mobile track inspection systems, easily mounted on passenger or freight trains, use a variety of sensors, measuring devices and data management software [44]. Based on the inspection data, the necessary diagnoses are then performed. The analysis of the inspection record allows engineers to prevent eventual failures and establish an adequate maintenance plan for the railway infrastructure, ensuring the safe operation of rail trains [45].  
The inspection activity in railway tracks considers anomalies, in order to guarantee good structural integrity, safety and longevity. Structural Health Monitoring (SHM) has emerged as a critical tool for early damage detection and preventive maintenance. In addition, the adoption of digital twin technology, considering dynamic loads, enables continuous, data-driven monitoring and predictive analytics [46]. SHM plays a crucial role in assessing structural conditions and predicting failures to maintain structural integrity. Vibration-based condition monitoring employs non-destructive, in situ sensing and analysis of system dynamics across time, frequency or modal domains. This method detects changes indicative of damage or deterioration [47].