Each new road begins with soil and rock construction
Nature does not always provide the ideal ground conditions – whether for civil engineering or structural engineering projects. Quite often, the existing soil requires preliminary treatment to improve its bearing capacity. In other places, massive rock formations need to be levelled. What methods are used for laying the foundations?
Since the soil is frequently loose and insufficiently cohesive, earthworks are required before the base course, binder course and surface course can be laid. Compaction is the most important process in earthworks. The purpose of compaction is to reduce the volume of soil filled with air and water. This gives the soil the desired properties: it becomes more resistant to the stresses imposed by traffic and climate.
Dynamic compaction with vibrating or oscillating rollers has proved particularly effective in earthworks, as it compacts the soil through the combination of vibrations from the roller drum and the weight of the roller.
Cohesive soils are best compacted using compactors with padfoot roller drums and high amplitudes, while non-cohesive soils are more effectively compacted with smooth roller drums and lower amplitudes. The ground is then ready to be paved - provided that it does not still contain too much moisture. In that case, it must additionally be stabilized.
Extremely cohesive and wet soils are not suitable for compaction by rollers. In such cases, the existing soil needs to be stabilized first to improve its bearing capacity and prepare it as a suitable base for the upper pavement structure.
Stabilization ensures that the water is durably bound in the soil. This is achieved by mixing a lime or cement binder into the soil. Particularly when stabilizing the soil with cement, the base becomes more resistant to traffic loads, ingress of water and frost in the long term. Soil requiring stabilization is frequently boggy and can only be driven over by powerful vehicles with all-wheel drive. For this reason, soil stabilizers have large studded tyres, high traction and a powerful travel drive system. Their mixing rotors mix the previously spread binder into the soil to depths of up to 56 cm in a single pass. This reduces the water content and makes the soil friable for perfect subsequent compaction by vibratory compactors.
When driving roads through rocky terrain, cold milling machines or surface miners are used to prepare the ground for road construction - or to cut the route, as the professionals would say.
Blasting is common when routing roads on bases of limestone, slate, granite or other rock. This causes vibrations, noise and dust. If blasting is prevented by nearby buildings, industrial plants or railway sidings, the routes are produced by cutting through the rock. This eco-friendly method extracts the rock without vibrations.
Even as the carbide cutters on the cutting drum continue to cut, the crushed stone is loaded onto trucks by a pivotable discharge belt . Due to the uniform grain size, it can be reused as filler without further processing. The road can now be paved without difficulty on the accurately profiled surface.