Further Thoughts on Maximum Pressures for Rock Grouting and Lugeon WPT-Paper

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The article argues that maximum rock-grouting pressures should not be set by conventional rules of thumb, such as 1 psi/ft or 1 bar/m, without considering site-specific conditions. These conservative limits may reduce risk but can also prevent grout from entering fine fissures, increase the number of holes required, and raise project costs.<br /><br />Instead, pressure should be selected through an engineered, stage-by-stage assessment of rock type and condition, grout properties, flow, and observed pressure–volume behaviour. Because subsurface conditions vary and are not fully known in advance, the author recommends real-time monitoring and control by an experienced grouting engineer, with safety and equipment limits in place. Possible approaches include increasing pressure until signs of hydro-jacking occur, subject to a stage-volume limit, or applying the GIN method. Field trials are useful, but their parameters should not be treated as universally applicable to the entire project.<br /><br />The article also questions the common practice of using the grouting pressure as the maximum pressure for Lugeon water pressure tests (WPT). Since water and grout behave differently, and the final hydraulic conditions may differ from the conditions during construction, WPT pressures should be evaluated separately based on anticipated hydraulic conditions.<br /><br />Three case examples illustrate how pressure–volume and flow data can help distinguish actual hydraulic opening from pressure changes caused by variations in grout flow. The author concludes that grouting should be treated as a fully engineered process, guided by continuous interpretation of field data rather than unsupported rules of thumb.

Keywords

rock grouting

grouting pressure

site-specific conditions

pressure-volume behavior

hydro-jacking

GIN method

Lugeon water pressure test

field monitoring

grout flow

engineered grouting process