The construction of Berths 57/58 at the Port of Oakland required the stabilization of a cut slope under a proposed container wharf extending 2,400 ft. The cut slope was constructed to transition soil backlands to the design dredge depth for a maximum slope height of 65 ft.
Soil conditions encountered on the project consisted of surface fill, bay mud and young bay deposits described as soft, weak and/or susceptible to seismically induced liquefaction and lateral spreading. This condition posed a potential threat to the stability of the proposed wharf structures during and after major earthquakes. A DSM buttress system was proposed to provide shoreline stabilization and control lateral spreading.
The soil-cement buttress consisted of a rectangular grid of Deep Soil Mixing (DSM) walls formed using 3ft. diameter columns spaced 2 ft. on center. In the shallow bay mud area, the grid consisted of two longitudinal walls parallel to the shoreline spaced 31 ft. apart and a series of transverse walls perpendicular to the shoreline spaced 12 ft. apart. In the deep bay mud area, the width of the DSM grid was inreased by extending the transverse walls in the direction of the shoreline slope. When the width of the DSM grid was greater than 68.5 ft., a third longiudinal wall was added. The maximum treatment depth in the deep bay mud area was 88ft.
Over 60,000 cubic yards of DSM ground stabilization was constructed over a period of five months. Triple-shaft DSM equipment with a real-time monitoring system was used for ground stabilization.
Test specimens for unconfined compressive strength were retrieved by a triple barrel coring system. Test results exceeded the acceptance criteria of an average of 150 psi at 28 days.
Two DSM rigs improving ground
for Berths 57/5/