Ch 10 Soils and Subsidence A Soil Classification

Ch 10. Soils and Subsidence A. Soil Classification B. Engineering Properties of Soil C. Settlement, Consolidation, Subsidence

Weathering forms Soils

Chemical Weathering in Soils Hydrolysis Oxidation: 4 Fe. Si. O 3 + O 2 + H 2 O Fe. O(OH) + 4 Si. O 2 Hydration: Ca. SO 4 + 2 H 2 O Ca. SO 4· 2 H 2 O

Expansive Soils (clay rich) n n Platelets of clay Negatively charged surfaces n Adsorb water. n Causing expansion

Soil Horizons (Eluvial zone) (Illuvial zone) K Carbonate precipitation and grain coating R Bedrock (typically with some illuviated clay in fractures)

Tropical Soils n n n Oxisols (Laterites) form in humid tropical climates Iron and Aluminum oxides Clays (Kaolinite, Gibbsite, Geothite)

Formation of Aluminum Ore

Arid Soils n 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 n Based on: n n grainsize and plasticity (i. e. , clay content)

USCS (ASTM D-2487)

Galveston Bay Subsidence n Houston and coastal areas subsiding sue to pumping

Land Subsidence n n n Subsidence related to pumping Reduced pressure increases weight supported by soil skeleton Water is expelled and land subsides

n n Interferometer Satellite imagery used to detect subsidence on a mm scale