What it measures
A single-direction tensile load is applied to an installed anchor or rock bolt and the load–displacement behaviour is recorded. It answers one question: does this anchor, in this ground, carry the force the calculation has assigned to it? The bond between grout and ground, the drill diameter and the placement of the bar are assumed in the design; the test measures the result.
Why it is done
| Reason | What is learned |
|---|---|
| Workmanship | That drilling, grouting and bar placement were carried out as specified |
| Capacity | That the anchor carries the required load for its design failure mode — pull-out, cone failure in rock or concrete, steel failure |
| Design verification | Whether the ground–grout bond matches the value used in the calculation; anchor length corrected if not |
The test alone is not enough: the anchor bar's certificates (European Technical Assessment where applicable, material certificates, corrosion protection) go into the file together with the test records.
Who asks for it
- The specification. Clauses referring to EN 1537 for ground anchors and EN 14490 for soil nails give the number of tests and the test load — see the eight clauses in Reading a rockfall barrier specification: ETAG 027 to EAD 340059 and Anchored high-tensile mesh: how slope stabilization works (EAD 230025).
- The consultant or the client, as an independent check before acceptance.
- The contractor, to document its own workmanship. On every anchored line we install we propose sampling tests even where the specification is silent.
How it is done
A hydraulic jack and a load cell are seated on the anchor head; displacement is read with a dial gauge or transducer. The load is applied in the stages given in the specification, held for the stated time at each stage, and permanent and elastic displacement are separated. The result is delivered as a load–displacement graph and a signed record. The acceptance criterion — test load and admissible displacement — comes from the specification; it is not improvised on site.
The record becomes part of the line's acceptance file; later inspections compare the anchor head with it. The service is independent of the system: we test anchors and bolts of any manufacturer, on our own lines and on others'.
Questions on this topic
How many anchors are tested?
The number and the test load come from the specification — typically one test per stated number of anchors under EN 1537 or EN 14490. Where the specification is silent we propose a sampling programme.
Does the test damage the anchor?
No. The test load and the displacement limit are chosen so that a sound anchor stays within its elastic range; only an anchor that fails the criterion is rejected and replaced.
Sources
- EN 1537, Execution of special geotechnical work — Ground anchors.
- EN 14490, Execution of special geotechnical work — Soil nailing.