The three main protection methods against cave-ins are:

1. Sloping and Benching Systems: This method involves cutting the trench walls at an angle away from the excavation, forming a sloped or stepped (benched) shape. The angle and design depend on the soil type, with more loose soils requiring wider slopes to prevent collapse.
2. Shoring Systems: This involves installing supports such as hydraulic pistons, steel plates, or wooden beams against the trench walls to hold back soil and prevent cave-ins. Shoring braces the trench walls temporarily during excavation work.
3. Trench Shields or Trench Boxes: These are strong protective metal boxes placed inside the trench to create a safe zone for workers. The shield does not prevent the walls from collapsing but protects workers within the box from soil falling on them.

These methods are selected based on soil conditions, trench depth, and other factors to ensure worker safety during excavation.