R. G. Robinson has suggested an approach for studying the beginning of secondary consolidation. Secondary compression is defined as any extra compression other than primary compression . The primary consolidation occurs due to the dissipation of excess pore water pressure. Terzaghi's one-dimensional consolidation theory  has been used widely to analyze the time-compression data but is valid only in the primary consolidation phase. Non-linear stress-strain curves, time-dependent loading, impeded drainage, stratified soils multi-dimensional flow, large strains, effective stress-dependent (void ratio dependent) hydraulic conductivities, anisotropy, and other such effects are included and can lead to a response that deviates widely from that predicted using Terzaghi's theory. Remaining effects may loosely be termed initial and secondary. Secondary effects are then defined as all effects except these classified as initial and primary .
Research Scholar, Central Soil and Materials, Research Station, Hauz Khas, New Delhi,
Professor and Head of Civil and Environmental Engineering Department, Delhi College of Engineering, Delhi University, Near Rohini, Delhi,
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