A study of strength gain of driven piles

Abstract

Piles can be classified into three categories depending on the amount of soil displaced during installation: (i) Large volume displacement piles: (ii) Small volume displacement piles and: (iii) Replacement piles. Installation of piles can disturb the soil surrounding the pile and have an effect on the surrounding area by two different ways: (i) Due to variation of the material properties of the soil surrounding the pile and: (ii) Due to changes in the pore water pressure in the soil surrounding the pile. Magnitude of these variations is highest in large volume displacement piles compared with small volume displacement piles and replacement piles due to the high disturbance in the surrounding area caused by large volume of soil displaced. Moreover. the pore pressure generated during installation process might be dissipated with time depending on the permeability of the surrounding soils and the structure of the soil disturbed due to driving may also be recovered with time. The recovering of the soil structure with time and the equalization of pore pressure with time is termed, "Tixotropic Recover". Time taken for the recovery to complete depends on the amount of disturbance caused by the pile installation process and the properties of the surrounding soil. Due to the strength regaining of the soil surrounding the pile as a result or rixotropic recovery, the ultimate carrying capacity of the pile will vary with time. If the ultimate carrying capacity of the pile is increased due to tixotropic recovery it is termed 'setup' whereas if it's decreased it is termed 'relaxation'.