Project Description:
The purpose of this project was to construct a Soil-Bentonite (SB) cut-off wall for the Ramona Municipal Water District as part of the San Vicente WRP Pond 1 Rehabilitation Project located in Ramona, California. Geo-Solutions Inc. (GSI) successfully completed the work as a subcontractor to Pacific HydroTech Corporation of Perris, California. GSI conducted a bench scale mix design and value engineering with regards to various installation methods, ultimately providing a single pass (continuous) trenching option that best fit the challenging site characteristics. Pacific Hydrotech prepared the work platform by degrading the existing embankment while GSI furnished supervision, labor, materials, equipment and supplies necessary to construct the low permeability barrier.
GSI used our Geo-Trencher to complete the installation which entailed in-situ trenching with fresh water and dry bentonite. Bentonite powder was added to a shallow pre-trench and distributed throughout the depth of the wall using the trencher chain or “blade”. GSI collected frequent quality control samples for evaluation and testing.
The in-situ mixed cutoff wall was installed from the prepared work platform through overburden, coarse alluvial and weathered bed rock until competent bedrock (granite) was encountered. This continuous operation where in-situ soils were mixed vertically along the alignment used an assortment of cutting teeth to achieve an 18-inch wide wall through the center of the embankment.
Single-Pass Trencher Soil Bentonite Cutoff Wall:
| Soil-Bentonite Cutoff Wall Parameters | ||
| Length | 700 | LF |
| Depth (maximum) | 23 | FT |
| Depth (minimum) | 13 | FT |
| Bid Quantity | 13,755 | SF |
| Width | >12 | IN |
| Permeability | < 5.0 x 10-7 | cm/sec |
Project Challenges
- Following degrade, GSI only had approximately 14 feet of work platform to utilize for trenching operations. The ability to operate the Geo-Trench with a narrow footprint greatly benefited GSI throughout the installation process.
- Refusal conditions encountered when trenching to the top of bed rock (granite) proved difficult on the equipment. Increased wear and repairs were required throughout construction in order to ensure a tight seal at the base of the wall.