Evolution of soil cement mixes using an observational approach

Abstract

Soil Cement mixes and parameters used for mechanical mixing and injection, and the evolution of these mix designs and mixing parameters, are typically developed using a combination of previous project test results, a series of early trials for a new application, a theoretical mix design including injection parameters, followed by commencement of mixing on site. An observational approach meaning iterations/cycles of theory and the early practical results, would then lead to continuous adjustment of the site installation parameters, to meet the project requirements. Deep mixing techniques such as Cutter Soil Mixing (CSM), and mixing by excavator base machine known by varying names including Mass Soil Mixing (MSM) or Insitu Mass Stabilisation (IMS), has been observed over a number of years to achieve very successful and efficient ground improvement. Designers acting for clients, typically start with quite stringent requirements and expectations that ground improvement by soil mixing should end up with certain material properties, as if insitu mixing were equally as controllable as the batching of concrete. The challenge for us as specialist contractor, is to convince client-side designers that insitu mixing is not done in factory conditions, and will be more variable compared to concrete manufactured in a batch plant. The target parameters and boundary limits then need to be set, and QA/QC verification carried out during construction to indicate the outcome. The idea of ground improvement is to provide an economical solution to a ground engineering problem, at a lower cost than conventional deep foundation structural installations such as piling, diaphragm walls, and the like. In turn the most economic solution is also likely to be the most environmentally sustainable one. The various concepts and measures of environmental issues, sustainability, emissions targets and the like, typically fall under the same umbrella of economics i.e. low cost is also likely to be most sustainable. Chasing environmental targets which are not the most economic, are unlikely to be sustainable. The most economic approach is based on merit, and for soil mixing the basic concepts such as minimizing binder content, minimize work done, etc. to solve the ground improvement problem. By observation of early performance, the site installation can be progressively adjusted to arrive at the most economical and there for most sustainable outcome.