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Figure 15.11. Scope of EN 12716, Execution of... jet grouting

15.4.3 Deep mixing

Figure 15.12 summarizes the scope of EN 14679,19 which deals with the execution of deep mixing.

Deep mixing involves the mixing of in situ materials with a binder plus additives, if required. Mixing is achieved using mechanical tools to a minimum depth of 3m. The columns so formed can be used as load bearing elements, particularly where reinforcement is provided.

The standard provides a range of guidance on what needs to be considered as in design. It emphasizes the need to have a good knowledge of the variability of the ground, particularly any harder layers.

As the resultant column is a mixture of the natural soils and binding agent it is essential that a staged approach to design is adopted. This involves samples of natural soils being mixed in the laboratory to identify suitable design mixes that will achieve required strengths and other properties. Soils vary both vertically and horizontally across sites, making it all the more important that the in situ properties of the improved soil are similar to those of the laboratory samples. Higher strengths are commonly achieved in the laboratory and design mixes must taken this into account.

Two main processes are presented in EN 14679: dry and wet mixing. The main sections of the standard detail the factors that need to be considered in the design and construction of columns by deep mixing. Annex A provides useful information on the principles and practice of dry and wet mixing. This is further enhanced by Annex B, which discusses methods for: settlement reduction; improvement of stability; support of slopes; improvement of bearing capacity; confinement of wastes; containment structures; and reduction of vibrations.

EN 14679 was published by CEN in 2005 and is due for systematic review by TC 288 in 2010. A corrigendum was issued in 2006.

15.4.4 Deep vibration

Figure 15.13 summarizes the scope of EN 14731,20 which deals with the execution of deep vibration including densification of loose granular soils using vibrators and the provision of vibrated stone columns formed using dry top feed, wet bottom feed, and dry bottom feed.

Normative references ]

Terms and definitions

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