Subgrade, the prepared earth surface on which a pavement or the ballast of a railroad track is placed or upon which the foundation of a structure is built. A subgrade’s performance generally depends on three interrelated characteristics:

• Load Bearing Capacity
  • Degree of compaction
  • Moisture content
  • Type of soils
• Moisture Content
  • Surface Drainage
  • Ground water elevation
  • Infiltration / Pavement porosity
• Shrinkage/ Swelling
  • Soils with excessive fine particles
  • High moisture content

Roads that were built on poor subgrade might lead to failed/damaged roads. Typical road failures are;

• Crocodile Cracking
  • Crocodile cracking is the appearance of a distinctive pattern of small cracks in the surface of asphalt pavement. These cracks first appear in a lengthwise, parallel fashion, but they are eventually connected horizontally by stress cracks. This process of crack formation creates small, rectangular- shaped patterns that resemble the hide of a crocodile, hence the name.

• Depression
  • A depression in an asphalt surface is developed by poor sub-bases or companions over time. Depressions have a lower elevation than the asphalt surface which will cause the area to hold water for longer. Water buildup can cause further issues like raveling or potholes

• Rutting
  • Surface depression in the wheelpath. Pavement uplift (shearing) may occur along the sides of the rut. Ruts are particularly evident after a rainfall when they are filled with water.