Deformational Characteristics of Soils at Small to Intermediate Strains fromCyclic Tests

摘要

The deformational characteristics of various soils at small to intermediateshearing strains using resonant column and torsional shear (RCTS) equipment were investigated. Soil tested include dry sand, undisturbed silts and clays, and compacted clay subgrades. In addition, metal specimens have been developed to investigate system compliance of RCTS equipment which resulted in damping ratios of soils measured at frequencies above 1 Hz being corrected for equipment compliance. A key aspect of this work was to measure accurate stress-strain hysteresis loops at shearing strains below 10(exp -3) percent. To accomplish this task, the motion monitoring system in the torsional shear test was modified with a micro-proximitor system, and shear modulus was measured at strains as small as 10(exp -5) percent and hysteretic damping ratio was measured at strains as small as 6 x 10(exp -5) percent. The elastic zone, where the stress-strain relation is independent of loading cycles and strain amplitude, was verified. Hysteretic damping was found even in this elastic zone. The effects of loading frequency and number of loading cycles on deformational characteristics (modulus and damping) are investigated. Resonant column (RC) and torsional shear (TS) tests were performed in a sequential series on the same specimen. A cyclic threshold strain was also defined for dry sand where the deformational characteristics are independent of loading cycles. A cyclic threshold strain was also defined for cohesive soil. Synthetic specimens were developed and calibrated with independent tests. With known stiffness specimens, the compliance problem in resilient modulus M(sub R) equipment was detected and modifications of equipment were undertaken. After calibrating the equipment, moduli obtained from both M(sub R) and and RCTS tests agree well on synthetic specimens as well as compacted subgrade soils.