In April 2004, I was working on a tunneling project in NYC, we estimated the slurry wall cost at $145/SF (3' thick x 64'deep (average depth); key-in to rock was $830/LF
Mean High Water was about 6' below grade; soil consisted of a deep layer of fill over a layer of organics over a thin sand layer (5' to 10')> It was mainly fill.
It depends on the stratigraphy. If you have borings, you should be able to come up with a reasonable estimate for means and methods. Use the RS Means estimating books to come up with ballpark costs and production rates.
You may need to go out-of-house to get the opinion of engineers who have worked on slurry jobs in similar conditions.
Finally, you can show some representative borings to slurry wall contractors to get their opinion on a ballpark or baseline cost in advance of a formal bid solicitation.
Typical means and methods include crane-mounted clamshell, long-reach excavator or hydromill, depending on the soil and groundwater conditions. Some equipment can key into bedrock. However, on one job I was involved with, the contractor used a crane-mounted chisel to create the key. Significant costs can also include site preparation (include installation of concrete guide walls), batch plant for slurry, and handling/transport of excavated materials.
