Soil is a mixture of sand, gravel, silts, clay, water and other materials. The more unstable the soil, the greater the chance of a cave-in. Use a protective system, such as shoring or a shield. Shoring is made of timber, mechanical or hydraulic systems that support the sides of an excavation. A shield, also called a trench box, protects workers if there is a cave-in.
Trench boxes are a good system for laying pipe.
See Figure 4. Figure 4 Sloping is digging at an angle as shown in Figure 5. For each foot deep, the soil is dug a foot and a half back from the edge of the trench. Benching is another method of digging that is like making stairs into the excavation. Sloping and benching are not used often because there is usually not enough space.