Residual soils of piedmont and Blue Ridge
GF Sowers, TL Richardson - Transportation Research Record, 1983 - trid.trb.org
GF Sowers, TL Richardson
Transportation Research Record, 1983•trid.trb.orgThe Piedmont and Blue Ridge form a band of crystalline rocks that extend from New Jersey
southwest into Alabama. They are deeply and irregularly weathered into residual soils
without appreciable transportation. The residual soils retain the mineral segregation, mineral
alignment, and structural defects of the parent rocks. These are reflected in
nonhomogeneous and anisotropic engineering properties. The soils inherit large residual
stresses from the tectonically disturbed rock that are not related to overburden weight. They …
southwest into Alabama. They are deeply and irregularly weathered into residual soils
without appreciable transportation. The residual soils retain the mineral segregation, mineral
alignment, and structural defects of the parent rocks. These are reflected in
nonhomogeneous and anisotropic engineering properties. The soils inherit large residual
stresses from the tectonically disturbed rock that are not related to overburden weight. They …
The Piedmont and Blue Ridge form a band of crystalline rocks that extend from New Jersey southwest into Alabama. They are deeply and irregularly weathered into residual soils without appreciable transportation. The residual soils retain the mineral segregation, mineral alignment, and structural defects of the parent rocks. These are reflected in nonhomogeneous and anisotropic engineering properties. The soils inherit large residual stresses from the tectonically disturbed rock that are not related to overburden weight. They are stronger than their high void ratios imply. However, they exhibit localized surfaces of weakness that are responsible for excavation cave-ins and landslides despite average strengths that indicate stability. Settlements due to imposed loads can be significant and nonuniform, particularly when the void ratios exceed 1.5. Settlements computed from ordinary consolidation theory usually exceed those observed, probably because of unknown residual stresses and pseudopreconsolidation. Initial settlements are large because the upper strata are partly saturated, hydrodynamic settlement is rapid, and secondary compression is often large because of the large mica content. The deeper horizons of residual soil (partly weathered rock) when loosened by ripping or blasting produce angular gravelly silty sands that are dense, strong, incompressible, and slow to drain when compacted. The more completely weathered residual soils produce sandy silts and silty sands. Their density and incompressibility vary inversely with their mica content. The usual soil classification systems (ASTM-Unified or AASHTO) are poor indexes to residual soil behavior. Instead, void ratio and defect characterization in undisturbed soil and mica content and compacted density in embankment materials are more reliable.(Author)
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