Site characterization and foundation design in sands.

摘要

A major concern in soil characterization is whether the soil is tested in its natural physical and chemical environment. In particular, where cohesionless soils are encountered, reliable soil characterization is difficult using conventional sampling and laboratory testing, due to unavoidable disturbance and difficulties associated with sampling. Consideration is therefore directed to alternative methods of in situ testing.; Much of the existing research work on sand is based on ideal uncemented low to medium compressible sand. Hence, engineering design based on these studies may not always be valid for all sands. A comprehensive procedure to identify and to evaluate 'unusual' sands has not yet been established. The effect of cementation on the strength-deformation behavior of sands is often ignored since cementation usually improves the shear strength. However, neglecting cementation can result in an overly conservative design of shallow and deep foundations as well as slopes and retaining walls. The stress history and age of the deposit are among the important factors which control the deformation characteristics of the soil. A reliable procedure for determining horizontal in situ stress has also not yet been established for cohesionless soils.; Few attempts have been made to estimate the ultimate bearing capacity of shallow footings directly from CPT data. The ultimate bearing capacity of shallow footings on sand is often overpredicted using correlations based on test results from calibration chamber tests performed on uncemented unaged sands while some natural sands are lightly cemented. Most of the methods for the prediction of settlement of footings on sand have been based on the conventional elastic formula. An equivalent soil modulus is frequently estimated based on in-situ testing measurements using empirical correlations.; The objective of this research has been to identify new ways to evaluate cohesionless soils, based on seismic techniques, such as the Seismic CPT. The research has focused on the identification of unusual sands, such as, highly compressible and/or cemented sands, and the quantification of their compressibility, stiffness, level of cementation, and in-situ stress and stress history. Relationships and methods have also been developed to evaluate the bearing capacity, and settlement of shallow footings on sand.