Keynote Lecture: Challenges in the Design of Jet Grouted Structures-Paper

Paper

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The paper examines how uncertainty in jet-grouted columns should be addressed in design. Unlike idealized cylindrical, homogeneous elements, columns vary in diameter, position and strength because their properties depend on execution and interactions with the surrounding soil. The authors compare Eurocode 7-style deterministic or semi-probabilistic design, using characteristic values and partial factors, with fully probabilistic analysis based on measured distributions and Monte Carlo simulation.<br /><br />Two applications are considered. For massive jet-grouted bottom plugs, the main checks are uplift and structural cracking from bending. Analyses indicate that, for realistic soil–plug shear interaction, bending can govern; neglecting this interaction can make design excessively conservative. Once the plug’s static stability is established, seepage through untreated gaps depends on column diameter and inclination variability. The authors therefore recommend probabilistic assessment of water inflow, rather than assuming a perfectly continuous plug.<br /><br />For vertically loaded isolated columns, the study evaluates bearing capacity and load transfer. Because jet-grouted material has limited strength, a column can reach structural failure before fully mobilizing its potential geotechnical resistance. This creates an optimum effective length: extending the column beyond it provides little benefit. Greater variability in column geometry and strength can substantially reduce this length and capacity.<br /><br />The paper concludes that probabilistic analysis is particularly valuable where random defects directly control performance, such as seepage through bottom plugs. Simpler deterministic methods can be appropriate for overall plug stability and isolated-column design, but only if partial factors reflect soil heterogeneity and the reliability of the data. In all cases, variability in geometry and material strength must be recognized rather than ignored.

Keywords

jet grouting

uncertainty

probabilistic analysis

Eurocode 7

Monte Carlo simulation

bottom plug

bearing capacity

seepage

partial factors

soil heterogeneity