Effect of overburden pressure and degree of saturation on compressibility characteristics

Abstract

The settlement of a structure founded on clay comprises of immediate and consolidation settlements. In the case of clays, consolidation settlement is more than immediate settlement. The parameters influencing consolidation settlement of a normally loaded clay layer are degree of saturation (S%), void ratio (e) of soil prior to excavation, amount of overburden (σ_o) removed, amount of rebound and intensity of loading (σ) upon building superstructure. This paper presents the effect of the above parameters on compressibility characteristics of a clay. The different steps undertaken for footing construction were simulated in the laboratory. Remoulded clay samples were prepared from oven-dry fraction passing 425 μm sieve. The density of the samples was kept constant at 13 kN/m³. Degree of saturation was varied at 25%, 50%, 75% and 100%. The surcharge on the samples (overburden in the case of field clay layer) was varied as 25 kPa, 50 kPa and 100 kPa. Compressibility characteristics such as initial compression under the applied surcharge (overburden), rebound upon removal of surcharge and recompression were studied through one-dimensional consolidation tests. The rate and amount of initial compression, rebound, e-σ and e-log σ curves, compression index (C_c), coefficient of compressibility (a_v) and coefficient of volume compressibility (m_v) were studied.

Keywords:

• overburden pressure
• degree of saturation
• initial compression
• rebound
• recompression
• consolidation settlement