Injection experiments ranging in length from bench-scale to field-scale are used to quantitatively assess the degree of improvement in the engineering properties of improved soil.  The properties of most concern are permeability, strength, and stiffness.  One of the fundamental challenges in research is to link the microstructure and macrostructure of the material system before and after soil modification.

                                                                     Figure 1

Illustrated in Figure 1 is a one dimensional injection system that is typically used in laboratory experiments.  A column filled with soil is permeated by grout via applied pressure gradients.  The grouted soil can be allowed to harden within the column and then be subsequently removed for determining the effective improvement in the engineering properties of the grouted mass.

Improvement in the engineering properties of modified soil is determined by assessing the deformation of the material for a given loading condition and ultimately, the maximum load that the modified soil is capable of carrying.  The ability of a fluid to permeate the modified soil is also of primary interest and this property is quantified by permeability testing.  Strength, stiffness, and permeability are properties of a grouted soil and are indicative of the structure of the modified soil on both macroscopic and microscopic scales.