Application of the Ground-Freezing Method to Penetrate a Sequence of Water-Bearing and Dry Formations — Three Construction Cases

ABSTRACT Rupprecht, E., 1979. Application of the ground-freezing method to penetrate a sequence of water-bearing and dry formations — three construction cases. Eng. Geol., 13: 541–546. In large areas of the world adits to underground caverns, mineral deposits and other openings have to penetrate a sequence from surface to final depth of sweet-water-bearing ground, dry consolidated ground and salt-water-bearing ground. The pressure of the salt water is approximately equal to the full hydrostatic head to surface. Contamination of the upper sweet-water reservoir by the salt-water is to be avoided during construction work and also after completion. Three construction cases are presented using different methods as follows: Case 1: The top formation is penetrated using the ground-freezing method; the dry formation is penetrated conventionally; and the salt-water-bearing formation is penetrated using the ground-freezing method. Special problem: Drilling freeze holes from a station in the dry formation into the highpressure salt-water-bearing formation. Case 2: The entire sequence is penetrated using the ground-freezing method. Special problem: Abandonment of freeze holes to prevent salt-water migration from the lower aquifer to the sweet-water aquifer. Case 3: Freeze holes are drilled from surface and freeze pipes are set in the lower saltwater-bearing strata only; the top water-bearing formation is penetrated, using a dewatering system; the dry formation is penetrated conventionally; and the lower salt-water bearing formation is penetrated using the ground-freezing method. Special problem: Installation of freeze pipes and preabandonment.