Cement-Bentonite Cutoff Wall (CB)
8.5 SMA Limited Curtai
n Wall
Miami, Florida
Project Features:
- Cement-Bentonite Slurry Wall
- 12,155 Linear Feet. 760,000 Square Feet. Maximum of 80-feet deep
- Target Average Permeability of 9 x 10-6 cm/s
- Target Average Unconfined Compression Strength 10 psi
Background:
Levee L-357W cutoff wall was constructed by the US Army Corp of Engineers and separates the 8.5 Square Mile Area (SMA) from the Florida Everglades with the purpose of flood mitigation. The 8.5 SMA located in southern Miami-Dade County approximately 13 miles northwest of Homestead, FL, and consists residential homes and smaller agricultural operations experience flooding.
Project Objectives:
In order to control groundwater flows from Everglades National Park into the 8.5 SMA, GSI constructed a ~2.3-mile long Cement-Bentonite (CB) cutoff wall along the center of the existing levee with depths up to 80 feet below the existing ground surface reaching the soils under the porous limestone layer.
Description of Work:
The cutoff wall measured 12,155 feet in length and consisted of 725,000 vertical square feet (vsf) of cement-bentonite (CB) slurry wall. The cutoff wall depth ranged from 58 feet to 80 feet below ground surface, and keyed in a minimum of three feet into the underlying Tamiami sand layer. Due to the hard limestone material, pre-trenching and blasting was necessary.
The CB cutoff wall was installed using a Komatsu PC1250 excavator and GSI’s custom long-reach boom and stick. The self-hardening Cement Bentonite slurry was pumped into the trench during excavation to maintain stability and serve as the final backfill. The cement-bentonite grout was mixed onsite in GSI’s custom-made batch plant and pumped to trench.
At the completion of each cut, bucket samples (visual verification of Tamiami sand) and depth measurements were done to ensure proper tie in. Additionally, samples were collected and tested per specifications for permeability with a target of 9×10-6 cm/sec and an unconfined compression strength of 10 psi.
While keeping commitment to safety, GSI worked through the extreme heat conditions of south Florida and around significant lightning shut-down events, without incident.
