Relevance Of Project
Deep cutoff wall mostly through sand formations, including cementation
• Use of Soil Bentonite Technique
• Low permeability of the Backfill
• High gradient
The city of San Antonio Water Board desired to construct a dam and reservoir for water impoundment. The design included a deep soil bentonite cutoff wall to stop seepage under the future dam through pervious sand layer. HB Zachry was awarded the contract and selected Inquip Associates, Inc. for the construction of the soil bentonite cutoff wall. Approximately 2,000 linear feet of soil bentonite cutoff was constructed to a maximum depth of 115 feet.
Note: The project was subsequently interrupted as a result of funding issues.
Principal Client Issues
Depth of the soil bentonite cutoffand the presence of very hard cemented sand/sandstone layers throughout the depth of the cutoff.
Inquip mobilized on site a powerful long reach excavator, (Koehring 1266) for the excavation of the upper 75 feet of trench. Specialized mechanical clamshells, attached to a 100 tons crawler crane, were used to deepen the trench. Heavy chisels were utilized as necessary to break the cemented formations.
The soil bentonite backfill, with a hydraulic conductivity of k £ 1×10-7 cm/sec, was mixed adjacent to the trench using a low ground pressure bulldozer.