Soil conditions and areas of application
The foundation and success of every construction project depends on proper compaction. On one hand, the correct compaction increases the durability and load-bearing capacity. On the other hand, it protects against damage caused by water and frost.
What is soil?
Each type of soil consists of air (gas), water and solid mass. Grain shape, grain size and water content determine the soil type. The soil types, considered here, are divided into "granular soils", "cohesive soils" and "mixed-grained soils".
Granular soil (Fig. 1)
Granular soils consist of coarse grains, e.g. rock debris, stones, gravel, or coarse-grained sands. They are characterized by larger air voids and high water permeability, resulting in this type of soil slightly drying out. Therefore, granular soil types are generally frost-proof and less weather-sensitive. Another characteristic of this type of soil is its high load-bearing capacity and durability due to a dense collection of the individual grain sizes after compaction.
Cohesive soil (Fig. 2)
Cohesive soils consist of fine grains and have a high water content. Examples of this type of soil are silt and clay. Due to the high water content, these soils are sensitive to frost and weather. With heavy rain, the ground wells up. The water lies like a shroud around the individual grains and prevents friction. The compaction ability is thus significantly lower. To compact this type of soil, the contained water must reach the surface by kneading or tamping for it to dry.
Mixed-grained soils (Fig. 3)
Mixed-grained soils consist proportionally of granular and cohesive grains of different sizes. The compaction ratio of the soil depends on the percentage of fine and coarse grains.
Rough edged grain shapes (Fig. 4)
Shapes with rough edges are harder to compact, but highly resilient and have a high load-bearing capacity. To give an example: gravel and crushed stone have rough edges and angular grain shapes. Together with crushed stone, a gravel-crushed stone mixture results.
Round grain shapes (Fig. 5)
Round grain shapes are easier to compact but have a lower load-bearing capacity. An example would be a mixture of gravel and sand.
How does compaction work?
The vibration of the machine causes the material to vibrate. This results in a repositioning of the grains. This process reduces air voids in the material to a minimum. A dense, homogeneous substrate is created.
The application chart was created to assist you in finding the right machine. The chart takes factors into consideration such as machine weight, dumping height, and number of passes in relation to the different soil types. In addition, it provides a guideline for the maximum compaction depth of a machine. The compaction depth varies for different soil types.
>> Click here for application chart
Verdichtungstechnik im Erdbau und Verkehrswegebau
Prof. Dr.-Ing. Dr. Ing. E. h. Rudolf Floss