Which method is used to measure the thickness of pavement after it has been placed?

The method involving core samples or non-destructive testing is the most reliable choice for measuring the thickness of pavement after installation. Core sampling involves extracting a cylindrical section of the pavement to directly measure the thickness at that particular location. This method allows for checking the actual thickness of the pavement against specifications, providing an accurate assessment.

Non-destructive testing methods, such as ground-penetrating radar, can also determine pavement thickness without removing any material. These methods offer the advantage of surveying large areas quickly and safely, which can help identify variations in thickness throughout the pavement structure.

As for the other methods mentioned, visual inspection may give a general idea of pavement condition but does not provide a precise measure of thickness. Measuring with a measuring tape is impractical for completed pavements due to access issues and the potential for error. Using a level gauge is not suitable for measuring thickness as it is designed to assess levels rather than dimensions. Thus, the combination of core sampling and non-destructive methods is essential for accurate pavement thickness measurement.