Effects of Tar on CPT and Shear Wave Velocity Correlations for the LA Metro Purple Line (D-Line)

Taki Chrysovergis, Anne Lemnitzer, Lisa M. Star, Joseph Rodriguez, Youssef Hashash, Namasivayam Sathialingam, Edward Cording, Thomas D. O'Rourke

Research output: Contribution to journalConference articlepeer-review


The Los Angeles (LA) Metro Purple Line (D-Line) Extension project requires the design and construction of deep station excavations and tunnels for rail transit from downtown to west LA. The tunnel alignment for Reach 2 of the Westside Purple Line Extension 1 construction transects naturally-occurring tar-infused soils, which have been known to cause challenging construction conditions in southern California, as well as many other locations around the world. Two stations in similar geology but located within and outside tar soils were compared. The soil investigations of the tunnels and station excavations consisted of subsurface exploration including deep soil borings, Cone Penetration Testing (CPT), seismic velocity measurements, pressuremeter testing, and gas measurements, among others. The results of CPT and shear-wave velocity testing provide extensive data in tar soils unique to Southern California and an opportunity to increase our understanding of four-phase soil materials and the effects of tar on soil behavior interpretation and engineering properties. CPT correlations for conventional (non-tar-infused) soils were found to be inadequate for tar soils in the Los Angeles basin. The CPT based Soil Behavior Type Index (SBTn) determined in tar soils suggested the presence of much finer-grained material than determined from laboratory testing and field observations. Additionally, the presence of tar soils amplified the difference between CPT correlations for shear wave velocity (Vs) and direct Vs seismic CPT measurements.

Original languageEnglish (US)
Pages (from-to)204-214
Number of pages11
JournalGeotechnical Special Publication
Issue numberGSP 343
StatePublished - 2023
Event2023 Geo-Congress: Sustainable Infrastructure Solutions from the Ground Up - Geotechnical Systems from Pore-Scale to City-Scale - Los Angeles, United States
Duration: Mar 26 2023Mar 29 2023

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Architecture
  • Building and Construction
  • Geotechnical Engineering and Engineering Geology


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