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Deformational Characteristics of Soils at Small to Intermediate Strains from Cyclic Tests

File Language:
English


Details

  • Creators:
  • Corporate Creators:
    University of Texas at Austin. Center for Transportation Research
  • Corporate Contributors:
  • Subject/TRT Terms:
  • Publication/ Report Number:
    FHWA/TX-92+ll77-3
  • Resource Type:
    Tech Report
  • Geographical Coverage:
    United States
  • Edition:
    Interim Report
  • Corporate Publisher:
    Texas. Department of Transportation
  • Abstract:
    The deformational characteristics of various soils at small (.00001 to .001%) to intermediate (.001 to .1%) shearing strains using resonant column and torsional shear (RCTS) equipment were investigated. Soils 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 .001%. To accomplish this task, the motion monitoring system in the torsional shear test was modified with a micro-proximitor system; shear modulus was then measured at strains as small as .00001% and hysteretic damping ratio was measured at strains as small as .006%. The elastic zone, where the stress-strain relation is independent of loading cycles and strain amplitude, was also 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) were investigated. Resonant column (RC) and torsional shear (TS) tests were performed in a sequential series on the same specimen. A cyclic threshold strain was defined for dry sand where the deformational characteristics are independent of loading cycles. The cyclic threshold strain was about 4 to 10 times greater than the elastic threshold strain. At strains above the cyclic threshold, shear modulus increases and damping ratio decreases with increasing number of loading cycles. Moduli and damping ratios of dry sand are independent of loading frequency, and values obtained from both RC and TS tests are identical, provided the number of loading cycles is considered in the comparison. A cyclic threshold strain was also defined for cohesive soil. Above the cyclic threshold strain, the modulus of cohesive soil decreases with increasing number of cycles, while damping ratio is almost independent of number of load cycles. Moduli and damping ratios of cohesive soil obtained by the RC test are higher than those from the TS test because of the frequency effect. Shear modulus of cohesive soil increases linearly as a function of the logarithm of loading frequency while damping ratio of cohesive soil remains constant below about 2 Hz. 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 RCTS tests agree well in synthetic specimens as well as compacted subgrade soils.
  • Format:
    PDF
  • Funding:
    Rsch. Study 2/3/10-8-88/0-1177
  • Collection(s):
  • Main Document Checksum:
    urn:sha-512:b27486aadfbda3e27ac4b47ffa18a1cd7a700b3d8210ba37bd340a87ba600ab24eb136657f086d98ae75e012599a55354b3aff5922d671621236b94a281c9c9b
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  • File Type:
    Filetype[PDF - 6.46 MB ]
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