Subgrade Preparation

The suitability of existing subgrade for paving depends on its characteristics, such as plasticity, stickiness, capillarity (the ability of water to rise through pores from the groundwater level), water absorption, and permeability, among others.

Sandy subgrades that filter water are more suitable for paving, while clayey subgrades, which do not absorb moisture, are less suitable.

If the subgrade is not suitable for paving, the issue can be resolved by removing the unsuitable soil and replacing it with appropriate material suitable for paving, which will then form the road surface.

In Latvia, the following types of subgrades can be found:

Sandy Subgrades: These are not plastic or sticky, and they retain minimal amounts of water. They have high water permeability and very low capillarity.
Dusty Sandy Subgrades: These are also non-plastic and non-sticky. Their capillarity ranges from 0.3 to 0.6 meters. In a dry state, they are non-cohesive. When saturated with water, these subgrades lose stability and become fluid. Dusty sandy subgrades are unsuitable for areas exposed to water.
Clayey Sandy Subgrades: Similar to sandy subgrades, these are not plastic or sticky but have a greater particle cohesion due to the presence of clay particles. They are good materials for subgrade construction and can be used in both wet and dry conditions.
Light Clayey Sands: These exhibit slight plasticity and stickiness. Their water permeability is satisfactory, with capillarity ranging from 0.5 to 0.8 meters. They are non-cohesive and dusty in a dry state, and prone to crumbling when wet. They can be used for subgrade construction if measures are taken to prevent erosion and saturation.
Sandy Clay Subgrades: These are plastic and sticky, making them most commonly used for subgrade construction. Their water permeability is minimal, and their capillarity ranges from 1.0 to 1.3 meters. In a dry state, sandy clay subgrades are cohesive.
Heavy Sandy Clay Subgrades: These are plastic and sticky but have very poor water permeability. Their capillarity ranges from 1.5 to 2.0 meters. They can be used for subgrade construction if constructive measures are taken for rapid water drainage.
Dusty Sandy Clay Subgrades: These have very poor water permeability and do not absorb water. When wet, they lose stability and turn into a flowing mass. Under adverse hydrological conditions, these subgrades are unsuitable for subgrade construction.
Clay Subgrades: These are highly plastic, sticky, and impermeable to water. Their capillarity ranges from 1.5 to 2 meters. They are very cohesive in a dry state but difficult to work with. When wet, they retain water for long periods, so they are not recommended for wet areas. They must be thoroughly compacted.

When designing site landscaping, it is essential to understand the presence and characteristics of surface water on the property, as this will affect the type of surface, its use, and consequently its lifespan. When planning the layout, decisions need to be made regarding vehicle access to the building, the location of the main driveway, and the positioning of smaller paths. Ideally, the vehicle should enter the garage with a slight incline. Surfaces in front of the house should be sloped downward to prevent surface water from accumulating around the foundation, ensuring that it drains away from the building.

In some cases, drainage systems must be implemented to manage groundwater or lower its level. Installing a drainage system involves significant costs, but a well-drained pathway will have a longer lifespan. Drainage construction reduces the hydrostatic pressure zone within the groundwater-saturated soil layer. The simplest method is to dig an open drainage trench. Under the influence of hydrostatic pressure differences, groundwater will filter through the soil and flow into the drainage trench. The effectiveness of drainage depends on the soil type and the rate of water inflow.