udrained

udrained is not a standard term in professional geotechnical literature and is usually a misspelling of undrained. In geotechnical engineering, undrained describes a drainage condition in which pore water cannot escape from a soil during the time scale of interest, typically due to rapid loading or low permeability. Under undrained conditions, pore water pressure tends to rise while total volume changes are constrained, causing a reduction in effective stress and a change in strength and deformation behavior.

Commonly, soils are analyzed under drained or undrained assumptions. In saturated fine-grained soils like clays, rapid loading such as impact or short-term loading can produce an undrained response. The undrained shear strength cu characterizes resistance to shear under undrained conditions and is often determined with laboratory tests such as the unconsolidated-undrained (UU) test or the consolidated-undrained (CU) test. In the field, undrained behavior is inferred from pore pressure measurements and field tests like CPTu, which can indicate undrained strength characteristics.

Design implications: Under undrained conditions, the soil may experience higher pore pressures, reduced effective stress, greater settlement, or potential for sudden failure after loading. It contrasts with drained behavior where pore pressures dissipate and effective stress governs strength gradually. The term udrained is not standard; use undrained in formal writing.