Chapter 19 of the International Building Code establishes requirements for soil investigation, foundation design, construction, and inspection. A geotechnical investigation by a licensed professional engineer is required for most buildings to determine soil bearing capacity, settlement potential, groundwater conditions, and construction hazards. The investigation establishes the allowable bearing pressure, which is the maximum downward pressure the foundation can exert on soil without causing unacceptable settlement or failure. Allowable bearing pressures for common soil types range from 1,500 pounds per square foot for silt and clay to 4,000 pounds per square foot or higher for compacted gravel and sand. Settlement is the downward movement of the foundation due to soil compression, which can cause structural damage if uneven. Differential settlement (different settlement at different locations) can cause more damage than uniform settlement. Foundation design must establish depth below grade sufficient to place footings below frost depth (typically 2-4 feet depending on climate) to prevent frost heave. Foundations must be protected from water infiltration and frost action through proper drainage and waterproofing. Shallow foundations including footings and slabs can be used for many buildings and are designed per bearing capacity requirements. Deep foundations including piles and drilled shafts are used where soil bearing capacity is inadequate or settlement control is critical. Pile installation requires quality assurance testing including load tests to verify bearing capacity. Retaining walls must be designed to resist lateral soil pressure with appropriate factors of safety against sliding and overturning.