Tunnel 3D model and crack detection

Scenario: There is a 6m diameter and 8km long tunnel. The walls are covered by a mud layer, thickness no more than 2 inches.

Objective: Create a 3D model of the tunnel. Detect cracks on the tunnel walls and locate them on the 3D model.

Cleaning the mud layer is not feasible since the tunnel is 8km long. We plan on using a pickup car, with the devices necessary for this inspection. Which devices do you recommend? LIDARs, infrarred cameras, GRP? Which products to buy available on the market?

Maybe other options like drones perhaps?

Thank you!