Dewatering drains along roadways

1. Bored subsurface horizontal drain
2. They use a drill rig to drill horizontally to the required length, slide in the perforated pipe, and pull out any temporary casing or HSA. Sometimes they leave in some permanent casing.
3. Yes
4. Depends on how far back from the face of the slope you need to lower the groundwater. The geotechnical engineer or engineering geologist would run a slope stability analysis and see how lowering the groundwater table will increase the stability of the slope, changing the groundwater table's location vertically and laterally from the face of the slope. At a certain point, the safety factor will be adequate, indicating how far the drains need to be installed.