About Retaining Wall Material Estimation
A **Retaining Wall Calculator** estimates the quantity of segmental retaining wall (SRW) blocks and the volume of drainage gravel required to build a straight wall of a specified length and height. It accounts for the required embedded portion of the wall.
Key Formulas Used
$$\text{Blocks Needed} = \frac{\text{Wall Area (Exposed + Embedded)}}{\text{Block Face Area}} \times (1 + \text{Waste})$$ $$\text{Gravel Volume (yd}^3) = \frac{\text{Length} \times \text{Exposed Height} \times \text{Gravel Width}}{27} \times (1 + \text{Waste})$$ The Block Face Area is the total area covered by one block (length x height). Gravel volume is calculated for the area directly behind the wall.
Construction Best Practices
Foundation & Embedment
- **Base Layer:** The first course of blocks must be placed on a level, compacted trench base (usually compacted gravel or concrete).
- **Embedment:** For walls under 4 feet, embed the first course (about 6 inches) below grade for stability. Taller walls require deeper embedment.
- **Batter:** Most SRW systems require a slight backward lean (batter) to resist soil pressure.
Drainage and Safety
- **Gravel Layer:** A 1-foot wide layer of clean drainage rock (#57 stone) behind the wall is essential to prevent hydrostatic pressure buildup.
- **Drain Pipe:** A perforated drain pipe should be placed at the base of the gravel layer to collect and divert water.
- **Geogrid:** Walls over 4 feet tall require horizontal layers of **geogrid** (reinforcement fabric) laid into the soil to maintain structural integrity.
Trenching & Base Preparation
Trench Width
- Wall Block Depth + Gravel Width + 6 inches working room.
Base Requirement
- A compacted base (road base or gravel) 6 inches deep and slightly wider than the block is mandatory for leveling and support.
Installation Time Estimate (DIY)
Low Wall (< 2ft)
1-2 Weekends
Focus on leveling base
Medium Wall (2-4ft)
3-5 Weekends
Involves heavy lifting and backfilling
Tall Wall (> 4ft)
Professional Project
Requires structural engineering and permits