Shotcrete is pneumatically applied concrete. It is a low slump concrete that is blown onto the receiving surface after mixing with compressed air. The concrete has a relatively low water/cement ratio, high cement content, and typically small aggregate not exceeding pea gravel size. High compressive strengths in excess of 5,000 psi are commonly attained. The sticky nature of shotcrete allows it to be placed on vertical and even overhead surfaces without the need for formwork. With good quality control a wall surface can be built out to an 8 inch thickness or more in a single pass.
Schnabel Foundation Company uses shotcrete to build temporary and permanent facings for our soil nail retention walls. A temporary shotcrete layer of 4 to 6 inches is applied directly to the excavated ground surface, often prior to soil nail installation. If the wall is to be a permanent structure (as opposed to temporary excavation support) an additional 6 to12 inches of reinforced shotcrete will be applied after the soil nails are installed. The surface of the permanent facing can have a finish that varies from gun finished, to finish toweled, similar to a formed concrete wall. The facing can also be sculpted and stained to produce a finish which resembles a bedrock outcrop.
Shotcrete with similar thicknesses and finishes is placed on tiedback soldier beam walls to make a permanent wall facing. The shotcrete is attached to the soldier beam system with shear connectors if the wall is to be free standing. If the application is for a basement wall, which will have floor slabs to support the walls, the soldier beams are not attached to the shotcrete. In this case, the soldier beams and wood lagging are merely temporary excavation support and a back form for the new shotcrete basement wall.
