In this paper, a simple expression to predict the average diameter of columns created with single, double and triple fluid jet grouting is proposed considering both the energy of the eroding jet and the resistance of the soil. The injection system (single, double or triple) and the composition of the injected fluids are taken into account on the basis of theoretical analysis of the turbulent diffusion of submerged jets. Instead of separately considering the energy of the air jet shrouding the eroding fluid, a simple parameter is introduced which represents the beneficial effect of air in reducing the energetic dissipation on the jet external surface. In this way, a new expression of the specific kinetic energy of the jet at any distance from the nozzle is proposed, which is a relevant step forward if compared with that at the nozzle or at the pump previously proposed, as it takes into account both the system characteristics and the composition of the eroding jet (either grout or water). In the expression proposed to predict the diameter of jet grouting columns, soil resistance is considered by way of the results of the standard penetration test and cone penetration test, in terms of N_SPT and q_c respectively. The expression has been calibrated on a number of experimental data, and in most cases proved its efficiency in predicting columns' diameter with a scatter of less than ±20%. The field trials results highlight that jet grouting is more effective in coarse-grained soils, as clearly shown by an efficiency parameter proposed by the authors. Design charts are drawn to quickly estimate the average diameter D_a for different soils, injection systems and input energies.

An overall analysis of single-fluid jet grouting is presented. Current concepts and design rules are first reviewed and compared. Alternative approaches to the analysis of single-fluid jet grouting are proposed and implemented with experimental data and observations taken from recent and well-documented case histories. In-situ observations and measurements as well as laboratory tests are presented, indicating the influence of both treatment parameters and original soil properties on treatment effects. On the basis of the experimental evidence, the mechanical phenomena induced by jet grouting are discussed.

Deformation characteristics at strains less than about 0·001% in compacted well-graded sandy gravel were evaluated by measuring vertical and horizontal strains locally in very small amplitude cyclic tests on square prismatic specimens. The very small strain Young's modulus E&up0; exhibits strong inherent anisotropy and stress-state-induced anisotropy. The very small strain Poisson's ratio v&up0;vh is a function of stress ratio. Effects of ageing on the values of E&up0;v and v&up0;vh are discussed. On a évalué les caractéristiques de déformation d'un gravier sableux compacté et à granulomé trie continue à des contraintes inférieures à 0,001 p. 100 environ, en mesurant les contraintes verticales et horizontales locales dans des essais cycliques à très faible amplitude réalisés sur des éprouvettes prismatiques carrées. Le module de Young pour très faibles contraintes E0 met en évidence une forte anisotropie inhérente et une anisotropie provoquée par l'état de contrainte. Le coefficient de Poisson pour très faibles contraintes v&up0;vh est une fonction du rapport de contrainte. L'article examine les effets du vieillissement sur les valeurs de E&up0;v, et v&up0;vh.

A methodology for cost-effective design of jet grouted water-sealing bottom plugs is presented in this paper. These massive barriers, made of partially overlapping jet grouted columns, are required to ensure temporary waterproofing to excavation areas and adequate uplift resistance against water loads. Therefore, the proposed calculation procedure simultaneously focuses on the structural performance and continuity of the plug. The design may be optimized by considering the possibility of reducing column length, performing injections only in the lower part of the plug, and leaving the upper part of the plug untreated. The reduction in column length may then result in a very slender slab, and a structural check has to be performed to avoid tension fracturing or overall structural collapse. Additionally, in spite of strict controls, jet grouted columns are never perfectly cylindrical or exactly aligned along their prescribed position, and thus the plug may present imperfections. Statistical evaluatio...