CS26A - Concurrent Session 26A: Deep Foundations Institute - Guidelines for Selecting Cutoff Wall Systems

Over the past five decades, the industry has developed innovative systems, equipment, tools, and materials that provide designers, contractors, and owners with a variety of solutions for seepage cutoff and environmental containment. Many practical, technical, operational, and logistical factors must be evaluated to select the appropriate cutoff wall and barrier system.

This presentation will overview Deep Foundation Institute’s Guidelines for Selecting Cutoff Wall Systems (www.dfi.org, 2021). The document provides fundamental background information and a selection process for identifying appropriate methods for constructing vertical cutoff walls and seepage barriers to reduce water flow through embankments, dams, levees, and deep excavations.

Three broad categories of cutoff and barrier methods are presented:
• Excavated cutoff systems where in-situ embankment and/or foundation materials are excavated and fully replaced with engineered backfill material. These can be constructed using a series of individual elements (rectangular, circular, or a combination of the two) or continuous trenches.
• In situ techniques where existing materials are improved in place, either through addition of stabilizing agents and binders (deep mixing, jet grouting, and grouting), or ground freezing.
• Driven sheet pile cutoff walls.

The presentation will overview the structure of the document including overviews relevant terminology, basic cutoff and barrier applications, a procedure and criteria for selection, details of cutoff methods (relevant evolution of method, general construction process, typical sizes, depths, widths, or shapes of walls, materials used, special considerations, and performance expectations).

The document emphasizes that the cutoff wall designer should consider three important components when generating a design: 1) the construction risk factors (risk registry or risk profile) and concerns of the owner; 2) the material properties and nature and variability of subsurface soils and rock, groundwater flows, aquifer characteristics, and site geology; and 3) constructability, site logistic requirements, and the full cost-benefit considerations for the different systems. It is particularly recommended to involve experienced construction personnel to assist with the selection process by providing detailed construction and economic analyses of the project conditions, which in turn can influence the type of wall selected and the cutoff wall design. Additional resources and references are listed.