Ground Improvement

Location: Long Beach, CA

Project Partner: Long Beach Unified School District

Challenge: Installation of cement deep soil mixing with tight tolerances and within project schedule

Overview: To limit the anticipated total and differential settlement due to structural loads and liquefaction potential below two new proposed classroom buildings M & N, Division of State Architects (DSA) designed a Cement Deep Soil Mixing (CDSM) program. Although designed by DSA, Condon-Johnson was required to conduct additional soil investigation and trial batch testing on retrieved soil samples to confirm that DSA’s design would meet the performance criteria. Additional scopes included spoils export, demolition of existing buildings and earthwork.

Results: Condon-Johnson conducted analysis and submitted the results. Condon-Johnson intended on installing the soil mixing with triple axis augers, however, the owner’s geotechnical engineer did not agree with the grid pattern and the double axis mixing with intermittent single axis columns were installed. Condon-Johnson installed 1,490 double axis panels (3 foot diameter) and 66 single axis columns (3 foot diamater) to treatment depths of 32.5 feet below working grade. The dense soil required each location to be pre-drilled full depth. The project was completed within schedule.