Foundations
In this next section, we will briefly deal with problems which may arise from the ground which will support the paving Project. These problems are often underestimated but in fact may be the cause of subsidence or irregularities which can negatively affect the outcome of the project. Obviously for large-scale projects advice must be sought from a geologist before starting any architectural work, so here we will mention some points which may be useful for designers but which do not in any way replace the need for a Slue), of the terrain where the paving shall be laid.
Any terrain consists of a natural agglomerate of mineral and organic particles of different forms, sizes and structures. The Soil for the foundation should be identified and classified according to Its grain size as it can affect the mechanical behavior of the ground itself Here is the system of classification of soil based on grain size as used in Germany.
MATERIAL |
Grain Size |
Stones |
larger than 60 mm |
Gravel |
between 2-60 mm |
Sand |
between 0.06-2 mm |
Silt |
between 0.002 - 0.06 mm |
Clay |
less than 0.002 mm |
Another classification consists of the distinction between cohesive and uncohesive ground. The terms uncohesive or loose are applied to soils made up of masses of granules without a binding substance (without water). Cohesive soils are those which exhibit resistance to traction due to the capillary tension of the water.
It is important to know the average values of the angle of internal attrition which depends on the grain size and type, and increases with the size of the grains; the reaction of the ground to compression; the elasticity, which is the return to normal once a load has been removed; freeze-thaw behavior - the tendency to increase in volume due to freezing of pore water - a characteristic which can lead to serious problems of stability on the paving above, especially in very cold climates. We will not dwell on the loads and structures the foundation ground can withstand apart from these brief notes but please refer to the bibliography for further information about soil mechanics. We will only summarize ground/soil as good, mediocre and poor, based on their intrinsic ability to bear the foundations, bedding mortar and the paving in porphyry. In general terms rocky, or compact grave or sand and dry clay are considered good ground, clayey sandy and wet clay are considered mediocre, and sandy, marshy or areas with high organic content are considered poor. Clayey soils tend to expand on being made wet and contract on drying.
The Foundation
The foundation is made of an incompressible layer (with minimal give when road is applied) between the foundation ground and the bedding mortar of the paving. It is very important that the foundation is formed in the most appropriate way for the consistency and characteristics of the ground.
Another fundamental element is that it said at a suitable height and inclination for the paved surface. If the foundation layer is too high it can affect the correct choice of thickness for the paving elements and thus alter the resistance Coefficient of the paving (e.g. cubes which are too thin).
