What is Stone or erosion control Pitching?
Stone pitching is a civil technique to prevent soil erosion by arranging stones or concrete blocks on slopes and surfaces and protecting infrastructure from damage caused by water flow. Consultants for civil design recommend stone pitching for soil erosion control as stone pitching protects soil slopes, embankments, and other ground surfaces from rain, runoff, wave action or wind.
Purpose and Application:
The primary purpose of stone pitching is to:
- Prevention: The stone pitching creates an armour and helps prevent soil loss due to flowing water or wind.
- Stabilisation: Pitching helps stabilise the earth and prevents landslides, slips, and slumps. Stone pitching is helpful in areas with heavy water flow.
- Reducing the flow: Pitching helps reduce the velocity and erosiveness of water flow, such as culvert inlets, culvert outlets, drain channels, and spillways.
- Protection: Erosion control pitching is a critical safeguard for riverbanks, canal linings, bridge abutments, culvert headwalls, and guide banks. Moreover, this process helps avoid scouring and undermining.
- Drainage: Pitching helps control the passage of water through the voids and prevents uplift pressure from accumulating behind the pitching.
Where do civil consultants recommend pitching?
Civil consultants recommend stone pitching in
- Canal and river banks
- Drainage channels
- Culverts, Inlets and Outlets
- Embankments
- Shorelines
- Spillways
- Landscaping and path construction
Design Considerations:
- Stones/Blocks: The stones must be hard, durable and dense. Pre-cast blocks are also an option in pitching. The slope angle, water force and protection level help decide the size and weight. Larger stones for steep slopes and higher flow velocity. Angular-shaped stones are better when compared with round ones because the interlocking is better. Civil consultants provide a well-graded mix of stones.
- Underlayment: The layer below the stone pitching is essential. The underlayment layer is either a granular filter or a non-woven geotextile fabric. The type of underlayment is based on the soil properties, site conditions and project requirements. Additionally, permeability is an essential criterion for the filter.
Stone Pitching and Rip-rap
While stone pitching is hand-placing stones to get organised, interlocking with aesthetic surface and structural integrity, the rip-rap is a machine dumping of angular stones. In rip-rap, the stones are large-sized and often loosely spread. Rip-rap is economical, less labour-intensive, and suitable for large areas. Though both prevent soil erosion, the choice is based on the scale, flow velocity, aesthetics and budget.
Conclusion
Consultants for civil design recommend the stone pitching for projects as per the project budget and requirements. So, they incorporate the design in civil tenders and GFC drawings for the project.
