Section 1902 requires that a geotechnical investigation be performed for buildings above certain size thresholds and for buildings in areas with known soil hazards. The investigation must be conducted by a professional engineer licensed in soil mechanics or geotechnical engineering. The investigation includes soil boring and sampling at depths sufficient to identify all soil layers that could affect foundation performance. Boring depths typically extend to 20-50 feet depending on foundation type and soil conditions. Laboratory testing of soil samples includes particle size analysis, Atterberg limits (plasticity tests), bearing capacity tests, permeability tests, and corrosion potential evaluation. The engineer determines bearing capacity through bearing capacity formulas incorporating soil properties, foundation depth, and shape factors. Settlement analysis estimates the magnitude of downward movement expected at the foundation level. Liquefaction analysis is required in areas of high seismic risk to determine if ground shaking could cause loss of strength in saturated sand. Slope stability analysis is required for sites with steep slopes or where fill will be placed at angle greater than 1 on 2 (50 percent slope). The investigation report must clearly state the allowable bearing pressure, safe depth for foundations, seasonal variations affecting construction, groundwater conditions, and recommendations for construction sequencing and precautions. The report becomes the basis for foundation design and permits the structural engineer to design adequate foundations.