The TRD Method: Slag-Cement Materials for In Situ Mixed Vertical Barriers

The conventional slurry trench method of construction to form low-permeability vertical barriers of soil-bentonite (SB), cement-bentonite (CB) and slag-CB have been widely used. More recently, in situ mixing methods to construct vertical barriers, such as deep mixing method (DMM) and the Trench Remixing and Deep wall method (TRD) have found increased usage. For the first TRD project in the United States, the method has been used for construction of test cells and is under consideration for the construction of a soil mixed barrier wall to prevent the intrusion of salt water into fresh ground water aquifers at the Alamitos Gap in southern California. To fully investigate the technology and its suitability for the application under consideration, laboratory and field studies (including construction and evaluation of two test cells) were conducted. This paper presents the results of various material formulations upon properties such as hydraulic conductivity and unconfined compressive strength. Laboratory studies demonstrated that mixtures of site soils containing saline pore water and blends of clay-water slurry, slag and Portland cement could be developed having measured values of hydraulic conductivity less than 1 x 10^–7 cm/s and being resistant to long-term degradation in the presence of the saline ground water.