A common feature of civil engineering design is the “french drain,” a trench intended to intercept and collect groundwater and transfer it laterally to a sump. The environmental marketplace has created a larger demand for these drains for the purpose of the collection of contaminated groundwater. Traditional construction methods that use trench boxes or shoring, sometimes in combination with dewatering systems, present a number of problems, particularly if the trenches have depths in excess of about five meters.
The Bio-Polymer Slurry Drain (BP Drain) has provided a new method for constructing deep drains that eliminates shoring and dewatering. It does not require a wide excavation, reducing spoil disposal and does not require trench entry by workers, improving safety.
The system uses basic slurry trench technology but, instead of bentonite clay slurry, a guar-gum based slurry is used to maintain the open trench. Once the trench is dug to full depth, it is backfilled with a pervious material such as gravel. Wells can be inserted, pipe laterals can be placed and filter fabric inserted, all under slurry. When the trench is filled, the slurry is chemically and biologically “broken”, allowing the slot to collect water.
This paper reviews the current practice as illustrated by these case studies: a collection trench for oil, another for a chemical containment, and a drain constructed inside a slurry wall at a landfill site. The authors believe that this methodology will be subject to wide application once all of its features and advantages are fully realized.