Soil Inclusions in Jet Grout Columns-Article

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The study examines soil inclusions in large-diameter jet-grout columns constructed during a ground-improvement trial at Tuttle Creek Dam, Kansas. The trial was part of seismic-stabilization planning and tested columns in alluvial soils ranging from a cohesive clay-and-silt blanket to layers of sand and gravel.<br /><br />After construction, the site was dewatered and columns were excavated to about 35 ft (10.7 m). Several triple-fluid columns were cut open for inspection. Although the columns appeared satisfactory externally and core samples did not reveal the problem, sectioning showed substantial untreated soil inclusions—estimated at 40–50% or more of some column interiors. The inclusions included clay, silt, and intact sand, sometimes with natural bedding still visible. In contrast, inspected soil-mix columns were comparatively homogeneous.<br /><br />The authors identify two likely mechanisms. First, cohesive, relatively dry fine-grained soils can resist erosion and may not be broken down sufficiently by the jets. Second, large columns may develop unstable roofs during excavation. Material falling from the roof can sink through the uncured grout and escape the jets’ mixing action. The location and soil properties of some inclusions suggest that both cohesive blocks and sand masses moved downward within the slurry.<br /><br />The findings caution that jet grouting—particularly for large-diameter columns—does not necessarily create a uniform, impermeable mass. Conventional coring and spoil-return observations may not fully represent conditions inside completed columns. The authors recommend project-specific field trials that include excavation and sectioning of trial columns; permeability testing may also be appropriate where seepage control is the primary objective. The study notes that the results do not establish whether the same inclusion problem occurs in smaller columns or with other jet-grouting systems.

Keywords

jet grouting

soil inclusions

large-diameter columns

Tuttle Creek Dam

ground improvement

seismic stabilization

alluvial soils

triple-fluid columns

column excavation

permeability testing