Analysis of Common Stop Criteria in Rock Grouting-Paper

Paper

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The paper examines common stop criteria used to control rock grouting, where real-time decisions largely rely on grout pressure and flow rate. Stop criteria help achieve the required improvement in fractured rock while limiting excessive grout injection, fracture widening, or hydraulic jacking. The authors describe four approaches: Apparent Lugeon, Grouting Intensity Number (GIN), Transient Pressure Analysis (TPA), and Real Time Grouting Control (RTGC). They explain the information each can provide about grout uptake, fracture saturation, pressure response, and grout spread, without ranking the methods.<br /><br />The approaches are compared using real-time data from one grouting operation. Under the GIN method, the target intensity of 40 bar·l/m was reached, although the target curve was nearly attained before the final injection step. RTGC analysis estimated that the required grout spread had been reached after about 15 minutes; little additional spread occurred during the last two steps, suggesting diminishing returns and possibly the opening of new fissures or cavities. TPA showed rising residual pressure, consistent with increasing fracture saturation, while changes in pressure-drop gradients suggested that fissures or cavities may have opened and subsequently closed. Apparent Lugeon analysis also indicated reduced benefits from continuing at a later stage.<br /><br />Overall, the different analyses broadly suggested that grouting could have been stopped earlier, saving approximately 5–10 minutes according to the RTGC assessment. The authors conclude that stop criteria are valuable for guiding grouting and identifying likely process outcomes in real time. However, they cannot by themselves determine whether more grout holes are needed or confirm that the final foundation permeability target has been achieved.

Keywords

rock grouting

stop criteria

grout pressure

flow rate

fractured rock

Grouting Intensity Number

Transient Pressure Analysis

Real Time Grouting Control

Apparent Lugeon

hydraulic jacking