Internal stability of a grout is critical in determining whether a grouting job is successful or not. A highly stable grout would be able to permeate through formations/fractures without losing any significant percentage of its solids fraction to filtration. Having an unstable grout would result in non-uniform distribution of the cement along the grouted distance, with a higher concentration of cement near the injection point (above the design value based on the grout concentration) and a much weaker cementation at the end of the grouted zone. Formations grouted with unstable grouts end up with non-uniformly enhanced properties and increase the local heterogeneity. Due to the many problems associated with unstable grout use, it is undesirable in most cement grouting operations (RosquoΓ«t et al. 2003, Naudts et al. 2004, Tan et al. 2004, Bremen 1997). This Thesis presents a comprehensive study on internal stability of a micro-fine cement (UltraFine) and its impact on grouted sand through an experimental investigation. The hydration and particle size distribution of the Ultrafine cement is determined through a physio-chemical characterization to help understand the observed behavior during stability tests. Grouts with a wide range of w/c ratios are then tested using the traditional internal stability characterization methods (Column Bleed Test and API Filter press test). These tests are index tests and do not represent the state of the grout during its application in the field, among other limitation. Additionally, image analysis is used to better understand grout stability and the movement of solids within a standing column. The digital analysis approach allows for characterization of the bleed test beyond measuring the height of free standing water on top by accounting for the change in grout concentration with depth. A new testing procedure (Dynamic Stability Test) is developed to investigate the impact of continuous shearing on the internal stability of the grouts. All the current methods for determining the stability of a grout are performed under static condition. However, for its first few hours after mixing in the field, the grout is never under static. The new method measures the change in the rheology of a grout using Physica MCR 301 rheometer (Anton Paar, Graz, Austria). The rheological measurements are performed under different shearing conditions between measurements to evaluate impact of shearing/flow on internal stability of the grouts and the results showed that grouts are more stable when continuously sheared, implying that the static tests can underestimate internal stability of grouts. Last, a new Grout Filtration Test is proposed in this study that is a modification of the filter press to better model the grout performance in the field. Two testing procedures and analysis methods (Simplified field and Laboratory) are presented to quantify the internal stability of grouts. Results from the current and newly proposed testing are used to better understand the internal stability of the grout and identify the most efficient way to measure grout internal stabilityCivil, Architectural, and Environmental Engineerin
