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Correlation of In Situ Test Data with Shear Strength for Deep Foundation Design.
  • Published Date:
    2016-06-16
  • Language:
    English
Filetype[PDF-909.96 KB]


Details:
  • Publication/ Report Number:
    019-13-803
  • Resource Type:
  • Geographical Coverage:
  • NTL Classification:
    NTL-ENERGY AND ENVIRONMENT-Environment Impacts
  • Format:
  • Abstract:
    The project addresses drilled shaft foundation design for Nevada, especially for the population center of Las Vegas Valley. Specifically, we address overconservatism due to challenges in characterizing deformability and strength of dense, hard-to-sample sediments such as gravel, sand and mixed materials; and carbonate-cemented sediments of all types (which are identified as caliche when cementation is heavy). Sampling is a problem for these materials because of disturbance during collection (in cases of low-cohesion sediment or weak, brittle cement) or high costs of coring (caliche). Blow counts (N) from a standard penetration test (SPT; ASTM D1586) are not informative in caliche once the sampler meets refusal. Direct, in situ measurements of stiffness and shear strength (shear stress at failure),particularly using the pressuremeter test (PMT), can help reduce overconservatism in design. However, these would not be so effective in very stiff sediments and especially caliche. And questions have arisen as to representativeness / interpretation of results of such a localized test in our strongly heterogeneous sediments . Further, considerations for time and dollars limit use of in situ tests of strength / stiffness. Thus, foundation designers must make best use of those relevant datasets that are easiest and most economical to capture. To accompany PMT and laboratory strength / stiffness tests conducted on some readily sampled soils, correlations might be developed that relate shear strength or stiffness with readily measured in situ parameters. For weaker soils, the correlation is logically with cone penetration resistance ; however, the cone penetration test is rarely viable in southern Nevada because of the soils’ intermittent zones of high stiffness, particularly due to cementation. The next logical choice for correlations is N. This approach is widely used. In one of many examples, Coduto et al. (2011) present correlations of N with the angle of internal friction of uncemented coarsegrained soils and with the undrained shear strength (su) of fine-grained soils. For stronger materials for which the SPT meets refusal, shear wave velocity (VS) might be a valuable indicator. VS information might also improve robustness of correlations to shear strength in weaker soil types.

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