Modified Standard Penetration Test for Drilled Shaft Design in Weak Fine-Grained Rocks

Timothy D. Stark, Ahmed K. Baghdady, Abdolreza Osouli, Heather Shoup, Michael A. Short

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

Standard penetration tests (SPTs) have been used to estimate strength parameters of soils and weak rocks when it is difficult to obtain high-quality samples for laboratory shear testing. SPTs require 45 cm (18 in.) of split-spoon sampler penetration to determine the blowcounts per 0.3 m (1 ft), which is difficult to impossible to obtain in weak rock, that is, intermediate geomaterials. As a result, a modified SPT is presented here for sampler penetrations less than 45 cm (18 in.) in weak rocks. This new procedure is termed the modified standard penetration test (MSPT) and uses the penetration rate, not the sum of penetration blowcounts per 0.3 m, to estimate the unconfined compressive strength for the design of drilled shafts in weak fine-grained rocks. The penetration rate is the inverse of the linear slope of the penetration depth versus blowcount relationship. With this new test and interpretation procedure, 45 cm (18 in.) of sampler penetration is no longer required to estimate the unconfined compressive strength of weak rocks. An empirical correlation between MSPT penetration rate and laboratory-measured unconfined compressive strength is presented here for weak Illinois shale. This correlation could be used to estimate the unconfined compressive strength for the design of drilled shafts in weak rocks.

Original languageEnglish (US)
Title of host publicationTransportation Research Record
PublisherSAGE Publishing
Pages176-185
Number of pages10
Edition2
DOIs
StatePublished - Feb 2022

Publication series

NameTransportation Research Record
Number2
Volume2676
ISSN (Print)0361-1981
ISSN (Electronic)2169-4052

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Mechanical Engineering

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