Active and Passive Anchor Design for Kamloops Terrain

An active anchor is prestressed to a specified lock-off load—typically 60 to 80 percent of the design working load—immediately after the grout reaches adequate strength. This pre-compresses the soil mass and minimizes lateral movement before excavation proceeds deeper. A passive anchor, by contrast, is not prestressed; it only develops resistance as the soil mass deforms and the tendon elongates, usually requiring 5 to 15 millimeters of movement to mobilize the full design load. In Kamloops glacial till, we often combine both: active anchors near the top of a cut to protect adjacent infrastructure, and passive anchors lower in the excavation where some deformation is tolerable.

For a typical project involving 10 to 25 tieback anchors with full design, load testing, and stamped engineering deliverables, the fee generally falls between CA$1,360 and CA$4,670 depending on the number of anchor types, the complexity of the ground profile, and the required number of proof tests. A single anchor type with uniform soil conditions occupies the lower end of this range; hybrid active-passive systems with rock sockets and extended creep testing move toward the upper end.

We log every core run from the geotechnical investigation and assign a rock mass rating. For fractured andesite typical of the Kamloops Group, we calculate the grout-to-rock bond using the empirical relationship between unconfined compressive strength and bond stress from the CFEM, then apply a reduction factor for joint spacing and infill condition. A sacrificial test anchor is always installed to validate the design before production drilling begins. If the test anchor's load-displacement curve shows excessive creep beyond 2 millimeters per log cycle, we increase the bonded length or switch to a post-grouting technique to improve the interface strength.