tienpohjaa

Tienpohja, or road foundation, refers to the lower load-bearing layer of a road structure. It is formed from the compacted natural soil or from stabilized fill, and it serves to distribute traffic loads to the underlying ground, while providing stability and resistance to frost and moisture effects. The tienpohja acts as the foundation for the upper layers of the road, and its properties influence the overall bearing capacity, settlement, and durability of the pavement.

Materials and methods vary with local conditions. In many cases tienpohja consists of compacted natural soil that meets specified density and strength requirements. If the native soil is unstable or weak, stabilization with binders such as cement or lime, or reinforcement with geosynthetics, may be employed to improve stiffness and bearing capacity. Drainage considerations are also important, as excess moisture weakens the subgrade; drainage layers or geosynthetic drainage elements may be used to manage pore water.

Design and testing practices aim to ensure adequate bearing capacity, frost protection, and long-term performance. Common evaluation methods include soil compaction tests and bearing capacity assessments, such as the CBR or Proctor tests, to verify that the tienpohja meets project specifications. Quality control during construction emphasizes proper moisture conditioning, compaction sequencing, and protection from disturbance during nearby work.

Maintenance of tienpohja focuses on preventing excessive settlements and moisture-related deterioration. Drainage improvements, re-compaction, or stabilization treatments may be employed if performance issues arise. In Finnish civil engineering, tienpohja is viewed as a crucial element of the tien alusrakenne, forming the foundation on which durable, safe, and rideable roads are built.