Cement-based grouting of rock foundations for new and existing dams
Time: Fri 2025-08-29 14.00
Location: F3 (Flodis), Lindstedtsvägen 26 & 28, Stockholm
Video link: https://kth-se.zoom.us/j/69019536392
Language: English
Subject area: Civil and Architectural Engineering, Soil and Rock Mechanics
Doctoral student: Suihan Zhang , Jord- och bergmekanik
Opponent: Docent Åsa Fransson, WSP
Supervisor: Professor Fredrik Johansson, Jord- och bergmekanik; Associ Liangchao Zou, Resurser, energi och infrastruktur, Vatten- och miljöteknik; Associate Professor Johan Funehag, Luleå University of Technology. Division: Mining and Geotechnical Engineering Department of Civil, Environmental and Natural Resources Engineering.
QC250711
Abstract
Grout curtains are usually constructed under dams as a barrier to prevent leakage from the reservoir, reduce uplift, and also prevent transport of fine material through the foundation. These grout curtains have mainly been designed by using an empirical design approach. However, the empirical approach has its limitations, such as lack of design over grout curtain thickness, long grouting time as a result of the stop criterion, and high grouting pressure which can cause unfavorable jacking.
To deal with these limitations, a theory-based design methodology for grout curtains under new dams has been developed. The grout curtain is treated as a structural component in the dam foundation. The geometry and location of the grout curtain is firstly designed with respect to three requirements: (i) the hydraulic conductivity reduction, (ii) prevention of erosion of fracture infillings and (iii) optimization of uplift reduction. Grouting work is then designed to obtain the designed geometry of the grout curtain. In the design of the grouting work, analytical calculations are implemented to determine the grouting pressure, grouting time and grout hole layout. The erosion process of fracture infilling materials was studied as a supplement to the requirement (ii). Coupled numerical analyses were performed to better understand the initiation of erosion of fracture infillings. The results showed that a previous equation derived by White under laminar flow can be suitable to estimate the incipient motion of fracture infilling materials.
For existing dams, remedial grouting is a measure to strengthen the deteriorated grout curtains under old dams. The major challenge of remedial grouting is the high pressure gradient in the previously grouted zones. High gradient leads to high water velocities, where the flowing water can erode the injected fresh grout in the rock fractures. Even if the fractures are sealed, a phenomenon called viscous fingering can occur, which destabilize the grout front and creates new leakage channels. Erosion of fresh cement-based grout and viscous fingering between water and grout were studied with experiments and numerical simulations. The experiments revealed that the existing criterion on grout erosion tends to be oversimplified. Viscous fingering was observed despite the theoretical prediction and the numerical simulations suggested it would not occur. This deviation was further discussed with respect to uncertainties in the experimental setup.
Strategies were suggested for remedial grouting practice using cement-based grout to minimize disturbance by flowing water: (i) utilize multiple pressure relief holes upstream of grout holes to reduce water-induced shear stress on the fresh grout; (ii) maintain sufficient pressure holding time to provide time for the grout to harden and prevent the displacement of the injected grout.