Studies have revealed that difficulties arise during the injection of suspension grouts into soil due to their rheological behavior and selective filtration attributed to physicochemical characteristics.  Concepts from the fields of cement chemistry, colloid chemistry, rheology, and transport processes are being synthesized to better understand and interrelate the early age microstructure of grout to its injectability and deposition in the interparticle pore space.  Injection experiments include laboratory tests that are bench-scale and full-scale and results are used to quantitatively assess influential characteristics of both the wet grout during the permeation process and the wet grout deposited within the soil pores.

Consideration of cementitious suspensions must include the time dependent hydration process and development of the various products.  Hydration will also affect such factors as the rheological behavior of the material, bleed or sedimentation of the particles from suspension prior to initial hardening, and set time. Shown in Figure 1 on the left-hand side are the initial materials before cement comes in contact with water, and on the right-hand side are the basic products from hydration.

                                                                   Figure 1

The morphology of various hydration products has been documented by environmental scanning electron microscopy (ESEM) and linked to rheological characteristics of the suspension.  The early formation of products is shown schematically in Figure 2.

                                                      Figure 2

As the hydration process continues, the viscosity of a grout will increase and it will require a larger gradient for the grout to effectively permeate soil.