Deep cement mixing solution for underpinning existing construction

The refurbishment, the increase of the capacity of urban buildings and transport infrastructure is an important stake of the sustainable development. The related challenges are on one hand, to renew and densify urban area without using new land resources and on the other hand, to maintain and strengthen the existing transport networks without interruption of service. However, foundation techniques that are essential to maintain and strengthen these structures are often expensive and/or incompatible with the available space: This usually leads to the destruction and replacement of the existing structure – to the detriment of the sustainable development goals.For this reason, a low invasive technology was developed several years ago, based on deep cement mixing columns built with small diameter drilling machines. This configuration allows to build up to 800mm diameter columns, from vertical to sub-horizontal position, inside existing buildings, under low headroom or confined space conditions, and/or underpinning existing structures (railway ballast, road subgrade, slabs or shallow foundations). Through various case histories and examples, this paper shows the range of application of this deep mixing technique and its advantages compared to jet grouting columns of modest diameter.