Using Crushed rock to build Driveways and Paths
To make a good surfacing material, they crushed should have a range of particle sizes from a fine dust up to a specified 3/8″ maximum particle size. With proper subgrade preparation and drainage, the crushed rock surface should remain stable for many years in all weather conditions.
A crushed rock surface combines the rustic feeling of a natural surface with a surface type that’s durable (but not concrete or asphalt). .
Selection of Crushed rock Material
Crushed rock isavailable in various stone types, colours, and particle sizes, but not all crushed rock are suitable for drives or raths. Tradeoffs may need to be made between the surface smoothness and erosion resistance, between colors and rock types, and between choice and availability.
The rock must be crushed into irregular and angular particles to allow interlocking into a tight matrix. The more angular the particles, the better. Rounded particles like pea gravel or decomposed granite never mechanically lock together.
The crushed rock must have adequate fines and some natural binders in order to cement the particles together after the fines are moistened, compacted, and allowed to dry. The fines, when laid to a depth of 4 to 5 inches, should bind to each other in a consolidated slab which is porous yet resistant to water falling on the surface.
Particle size should be 3/8″ minus. Fines from granite or other suitable hard stone works best. The ideal particle size distribution is one where there are enough small particles to completely fill the voids between the larger ones.
Colour
Crushed rock will have exactly the same colour as the rock from which they are crushed. The color should either match or complement the native stone and surroundings of the site, but colour is of secondary importance to the structural characteristics of the crushed rock, If the crushed rock surface needs to be patched in the future, the crushed rock added should be from the same rock source or the colours may not match..
Site Preparation
For Crushed rock Subgrade, slope, curves, and other components should be designed by engineers to the same standard as a paved surface. Special attention should be given to drainage to ensure all water is conveyed away from or underneath the surface. Concrete is recommended for areas where erosive flows are unavoidable.
Underlying soils need to be analyzed to determine soil suitability. Certain clays, organic soils, and high moisture soils require special preparation, such as placement of a geotextile. The fabric helps prevent fines from mixing with soft soils below and helps control damage from vegetation.
Construction
One method of placing the crushed rock involves excavation of a trench, and backfill with crushed rock material. Prior to placing the crushed rock a 5″ deep trench should be cut slightly wider than the desired width of the drive or path.
Underlying soils should be analyzed to determine the need for geotextiles. Certain clays, organic soils, and high moisture soils most likely will require placement of a non-degradable geotextile. The fabric will help prevent the crusher fines from mixing with the soft soils below. The geotextile is easilyhand laid using utility knives for cutting and wire staples for securing. If needed.
After the fabric is placed, the crushed rock are spread and smoothed with shovels, racke and other hand tools. Leveling bars may be used to smooth the surface to a 2% cross slope toward the downhill side for drainage or the surface may be crowned to drain to both sides of the drive or path. The crushed rock should be spread to a depth necessary to meet the desired compacted crushed rock thickness. (For example, spread 7″ to 8″ deep to get a 5″ compacted depth)
After initial smoothing and compacting, the edges are back-filled and dressed smooth. Finally, the trail surface is re-compacted with rollers or vibratory compactors. During the compaction process, the crushed rock should have some moisture to help “cement” the material when it dries, use a very fine mist type hose and spray the crushed rock sparingly. Using too much water will cause the crusher fines to become mushy or run off. The disturbed edges should be raked smooth and seeded.