Execution of Diaphragm and Cut-Off-Walls in rock – applications, performance and limits-Paper

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The paper examines the use of trench cutters to construct diaphragm walls and deep groundwater cut-off walls in rock. Rock excavation is often the most difficult and costly part of the work, and performance depends on more than unconfined compressive strength (UCS). Weathering, discontinuities and bedding orientation, abrasiveness, equipment and tooling choices, and operator experience can all significantly affect cutting rates.<br /><br />Trench cutters use counter-rotating wheels to break up ground, which is mixed with slurry and pumped to the surface for cleaning. Wheel and tooth configurations should match ground conditions: standard wheels suit soils and weaker rock, round-shank chisel wheels are more effective in stronger rock, and roller-bit wheels may be needed for rock above roughly 120 MPa. Maintaining and replacing worn teeth is essential to productivity.<br /><br />Drawing on more than 100 projects, the authors developed a performance-estimation chart based on UCS. They emphasize that it is only a guide: incomplete ground data and interacting site variables prevent reliable guarantees. Detailed geological information and experienced judgment are needed to select equipment and estimate costs.<br /><br />The Clearwater Lake Dam project illustrates these challenges. Its cut-off wall passed through karstic dolomite with UCS values from about 20 to over 220 MPa, including solution features and weathered joints. Using multiple cutters, adaptable tooling, precise steering and verification methods, the contractor achieved cutting rates of approximately 1–6 m³ per hour, depending on local conditions.<br /><br />The paper concludes that better characterization of rock mass conditions—not UCS alone—would improve performance estimates, equipment selection and cost control.

Keywords

trench cutters

diaphragm walls

groundwater cut-off walls

rock excavation

unconfined compressive strength

weathering

abrasiveness

wheel and tooth configurations

karstic dolomite

Clearwater Lake Dam