Grondlast

Grondlast is the load transmitted to a foundation or structure by the soil. It covers the vertical load from the soil mass itself and any additional loads placed on the ground surface, such as buildings, equipment, or traffic. In geotechnical engineering, grondlast is considered in terms of vertical stresses in the soil and, for structures that retain soil, horizontal earth pressures.

Vertical ground load arises from the weight of soil above a point. The total vertical stress at depth z is approximately sigma_v = gamma z, where gamma is the unit weight of the soil. Typical soil unit weights range from about 15 to 20 kN/m^3, depending on density and moisture. Saturation and pore pressure affect the effective stress acting on foundations; the effective vertical stress is sigma_v' = sigma_v - u, where u is the pore-water pressure.

In retaining structures, the soil also exerts horizontal grondlast. This lateral earth pressure depends on soil properties, wall movement, and backfill conditions. It is commonly estimated with earth-pressure theories (such as Rankine or Coulomb) using an at-rest, active, or passive coefficient. The horizontal stress is often expressed as sigma_h = K sigma_v, with K determined by the soil friction angle, backfill state, and wall behavior.

Several factors influence grondlast, including soil type (clay, silt, sand, rock), moisture content, density, depth, drainage, and the presence of water tables or surcharge loads on the surface. In design practice, grondlast is combined with other loads to ensure foundation safety and serviceability, following relevant codes and guidelines.