Towards a more rational approach for the design of cement-bentonite grouts

Abstract

Cement-bentonite grouts are commonly used to seal boreholes containing different types of geotechnical instrumentation. The function and type of instrumentation and the surrounding ground conditions dictate the desired engineering properties of the grout, including strength, stiffness and permeability. Cement-bentonite grouts have been little studied, and there is not much guidance from which to determine the proportion of constituents (cement/bentonite and water) to obtain particular engineering properties in the final grout. This makes it desirable to try to mix or test grouts in the laboratory prior to deployment on site, but it can be difficult to know where to start. Further difficulties arise from the tendency to mix cement-bentonite grouts in small batches on site, where the water chemistry, the type and form of bentonite, and mixing apparatus may vary. The paper presents a brief summary of current understanding, and then looks at range of existing grout mixes and their engineering properties to propose an interaction diagram to try to suggest possible mixing and final set properties of grouts based on the proportion of constituents used (cement, bentonite and water). The diagram has some limitations, not least a lack of quantitative data to support some aspects, but the authors hope that it could form a rational basis that can be further developed.

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ORCID for Tristan Rees-White: orcid.org/0000-0001-9009-8432

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