Ch 10. Soils and Subsidence

A. Soil ClassificationB. Engineering Properties of Soil C. Settlement, Consolidation, Subsidence

Weathering forms Soils

Chemical Weathering in Soils

Oxidation: 4FeSiO3 + O2 + H2O FeO(OH) + 4SiO2

Hydration: CaSO4 + 2H2O CaSO4·2H2O

Hydrolysis

Expansive Soils (clay rich) Platelets of clay Negatively charged surfaces

Adsorb water . Causing expansion

SoilHorizons

(Illuvial zone)

K Carbonate precipitation and grain coating

R Bedrock (typically with some illuviated clay in fractures)

(Eluvial zone)

Tropical Soils

Oxisols (Laterites) form in humid tropical climates

Iron and Aluminum oxides

Clays (Kaolinite, Gibbsite, Geothite)

Formation of Aluminum Ore

Arid Soils

Upward movement of soil water transports salts into shallow soil

Soil Orders Soil Taxonomy Classification System Table 10.3

US Soils

Engineering Classification of Soils Based on:

grainsize and plasticity (i.e., clay content)

USCS (ASTM D-2487)

Galveston Bay Subsidence

Houston and coastal areas subsiding sue to pumping

Land Subsidence

Subsidence related to pumping

Reduced pressure increases weight supported by soil skeleton

Water is expelled and land subsides

Interferometer Satellite

imagery used to detect subsidence on a mm scale