{"id":19858,"date":"2025-12-25T14:04:32","date_gmt":"2025-12-25T13:04:32","guid":{"rendered":"https:\/\/www.darda.de\/?page_id=19858"},"modified":"2025-12-25T14:04:32","modified_gmt":"2025-12-25T13:04:32","slug":"sprayed-wall","status":"publish","type":"page","link":"https:\/\/www.darda.de\/en\/knowledge\/sprayed-wall","title":{"rendered":"Sprayed wall"},"content":{"rendered":"
\n

A sprayed wall is an applied shotcrete lining that secures and lines terrain, excavation pits, or cavities on a short-term to permanent basis. It is created by applying shotcrete to rock, soil, or existing structural elements and combines load-bearing action, surface protection, and the leveling of irregularities. For deconstruction, adjustments, and openings in sprayed walls, practical day-to-day work often uses concrete pulverizers<\/strong> as well as hydraulic rock and concrete splitters<\/a>, especially in sensitive environments such as tunnel heading<\/strong>, existing structures, and confined inner-city settings.<\/p>\n

Definition: What is meant by a sprayed wall<\/h2>\n

A sprayed wall is a structural safeguard in the form of a thin-walled shotcrete shell. It is applied to the prepared substrate in layers using the wet-mix or dry-mix spraying method. Typical tasks include primary support in tunnel construction<\/strong>, temporary bracing of excavation pits<\/strong> and slopes, protection against weathering and spalling, and the leveling of uneven rock and concrete surfaces. Depending on the project, the sprayed wall serves as a temporary support until the final lining or as a permanent load-bearing lining. Reinforcement (steel mesh, lattice girder beams), steel or plastic fibres<\/em>, and anchors complement the load-bearing action. The required bond tensile strength and layer thickness result from geology, loading, and the planned service life.<\/p>\n

Structure, materials, and layer thicknesses<\/h2>\n

A sprayed wall consists of shotcrete with coordinated aggregate, cement, water, and, if necessary, admixtures (e.g., accelerators) and additions (e.g., steel fibres). The layer is applied to a load-bearing, cleaned, roughened substrate. Typical nominal thicknesses\u2014depending on the stabilization objective\u2014range from about 50 to 300 mm, and more for multilayer application. The layer is often coupled with lattice girder beams, mesh reinforcement, and anchors to safely transfer bending moments, shear forces, and membrane stresses into the ground. So-called rebound (rebounding material) must be minimized and properly removed. Substrate preparation includes removing loose components, knocking off overhangs, and exposing joints. In practice, hydraulic tools can be used for compact material removal; for adjustments, touch-ups, or local thickenings, precise, low-vibration methods such as concrete pulverizers<\/strong> or\u2014if underlying rock must be separated\u2014hydraulic wedge splitters<\/strong> are considered.<\/p>\n

Manufacturing methods: wet-mix and dry-mix spraying<\/h2>\n

In the dry-mix process, dry components are conveyed to the nozzle and mixed with water only at the nozzle. The wet-mix process conveys a premixed suspension. Selection criteria include component geometry, layer thickness, accessibility, desired surface quality, and environmental requirements. Important parameters are spray nozzle stand-off distance, angle of incidence, reinforcement position, temperature, and moisture. Smooth, even nozzle guidance reduces voids and ensures high density. Controlled layer build-up<\/em> is crucial, particularly overhead and on steep faces. The accelerator is dosed to steer setting behavior, early strength, and rebound without impairing adhesion and durability.<\/p>\n

Fields of application: tunnel construction, excavation pits, slope protection, and existing buildings<\/h2>\n

Sprayed walls stabilize the tunnel face and crown in rock breakout and tunnel construction<\/strong>, secure excavation pits<\/strong> in inner-city areas, protect slopes from erosion, and serve in concrete demolition and special demolition<\/strong> as temporary protection or separation layers. In existing structures, they help level irregular substrates or take up interim loads. For subsequent adjustments\u2014such as service routes, shafts, or drainage\u2014openings are often produced selectively<\/em>. For this, concrete pulverizers<\/strong> with finely controllable force are suitable to remove layers without large-scale vibration. If the rock behind a sprayed wall needs to be opened with minimal induced stress, hydraulic wedge splitters<\/strong> are a proven tool, especially where vibration or noise limits must be observed (special demolition<\/strong>).<\/p>\n

Deconstruction, openings, and finishing on sprayed walls<\/h2>\n

During construction or later refurbishment, recesses, niches, and adjustments are often required. The aim is a controlled, material-conserving intervention that maintains bond and load-bearing action in adjacent areas. In practice, the following steps have proven effective:<\/p>\n