Proceedings of the 34th Annual Conference on Deep Foundations, 2009, Kansas City, MO, USA, (DFI)
Impact of Clay on Early Jet Grouting Strength
Debra F. Laefer, Daire O’Neill and Cian O’Mahony, University College Dublin
"Jet grouting is a ground improvement technique that has become widely adopted over the past three decades, yet relatively little data has been published about performance characteristics of mixes under adverse conditions, such as the inclusion of clay lenses. This paper presents an experimental investigation on the impact of clay on the strength of jet grouting. A total of 150 grout samples were subjected to 0-10% levels of Kaolinite and Bentonite inclusion. While the Bentonite was introduced as a pre-hydrated slurry, the Kaolinite was mixed in two ways: in a pulverized condition and as large chunks. Sample strength and stiffness were measured at multiple dates within the first 28 days. With 10% clay inclusion all samples exhibited significant strength and stiffness losses. With some, substantial losses began with as little as 4% clay. Even a 1% clay inclusion tended to decrease strength and stiffness between one-quarter and onethird
of the control sample. Depending upon clay type and inclusion method, results differed significantly with respect to strength and stiffness development and
failure mechanism. Petrographic analysis is used to provide further insights as to apparently divergent behaviors."