Supervised Personnel

Personnel supervising anchors (or anchorage reinforcements) must be thoroughly familiar with construction guidelines and the inspection process as recommended in PTI (1996) and AASHTO (1990). Unless otherwise specified in project documents, the selection of drilling methods and anchor construction equipment is at the contractor’s discretion. The supervisor must monitor and record any issues during installation. If problems arise, the supervisor should consult with the contractor on corrective measures. Any deviation from project specifications must be approved in writing by the design engineer prior to implementation. The supervisor should be able to evaluate the efficiency of proposed anchor installation methods based on site conditions.

Drilling Anchor Holes

Drilling methods for anchor holes are the contractor’s responsibility. Project concerns such as noise, vibration, hole arrangement, and potential damage to nearby structures must be considered. Failure to drill stable holes of specified dimensions and tolerances may require drilling method modification.

Anchor holes must be drilled at specified locations and tolerances indicated in approved drawings, including length, angle, and diameter. Over-drilling beyond design length for better cleaning is common. Anchors should not require tendon bending to connect components. The drilling angle relative to horizontal or vertical must be monitored at the start and during drilling.

Soil and rock types and ground conditions must be recorded during drilling. Unexpected conditions must be documented and sampled. Soil classification is necessary to identify collapse risk, which includes:

  • Non-cohesive soils below groundwater level

  • Highly fractured or weathered rock

  • Artesian pressure zones

Signs of collapse include:

  • Difficulty extracting drilling tools

  • Excessive soil volume with little drill progress

  • Abnormal large hole diameters

  • Ground settlement above the hole

  • Difficulty inserting tendons fully into the drilled hole

If excessive collapse occurs, drilling must stop and alternate methods like drilling fluids or casing should be used to stabilize the hole.

Drilling fluids or foam must comply with project specifications or design engineer approval. Bentonite slurry must not be used in uncased holes, as it weakens soil-grout bonding. Disposal of drilling fluids is the contractor’s responsibility.

Installing Tendons in Drilled Holes

After drilling, both cased and uncased holes must be cleaned thoroughly, removing cuttings and debris. Over-cleaning uncased holes in non-cohesive soils should be avoided to prevent wall collapse. Uncased holes should be inspected visually with mirrors and bright lights. If grout injection precedes tendon installation, hole depth must be measured to ensure full tendon insertion.

Tendon dimensions must be verified to meet minimum bond length requirements. Property restrictions may limit tendon length. Coatings, casings, and encapsulation layers must be undamaged; damaged protection must be repaired or the tendon rejected.

Tendon Installation

Just before installation, exposed steel surfaces must be inspected for corrosion. Loose rust and scale must be removed exposing pits or cavities. Steel deeply corroded must not be used. Light rusting is acceptable. Tendon bond lengths must be cleaned of foreign materials.

According to Sason (1992), colored photos illustrating corrosion degrees on tendons serve as effective inspection tools.

Centralizers must be installed at proper intervals to keep strands separated, ensuring grout fully covers each strand and preventing strand entanglement. Soil anchors drilled by hollow augers typically don’t require centralizers if grout fully fills the hole.

If hole collapse occurs during installation, the tendon must be withdrawn and the hole redrilled. Tendons must not be hammered or cut shorter than specified; reducing bonded length risks failing load tests.

Grouting Anchors

To minimize hole collapse, grout injection should occur before or immediately after tendon insertion. Open holes must be cleaned again if left open over 8 to 12 hours before grout or tendon placement (PTI, 1996). Injection equipment must enable continuous grout injection within one hour.

For cable tendons, strands must remain straight and untwisted until grout hardens.

Injection is done in one stage, filling both bonded and free lengths. Free length grout injection must be by gravity or low pressure. Grout is injected from the hole bottom upward to avoid air voids. The injection tube is withdrawn slowly while maintaining grout flow to keep the outlet submerged.

Injection Equipment

Injection pumps usually have pressure gauges, which must be calibrated and cleaned daily. Head loss is calculated based on hose length and height difference between gauge and grout outlet. Low slump grout or very long anchors may increase head loss.

Supervisors must measure and record grout volume injected. Excess grout consumption indicates leakage through hydraulic fractures or soil voids.

Hydraulic fracturing may occur with high injection pressures or shallow anchors under light overburden.

In soils prone to grout loss, special grout control devices (GCDs) using geotextile strips or folded steel tubes may be employed.

When using hollow augers, the auger must not be rotated backward when withdrawn through the bond length, to avoid mixing soil and grout, which reduces grout strength. A single backward rotation at the hole bottom may be allowed to free the bit.

Post-grouting is done by injecting grout at high pressure after initial grout sets. Tendons must be equipped for post-grouting before installation.

Anchor Installation

After grouting, anchors must be installed carefully to align tendon and maintain corrosion protection continuity. The grout sheath must overlap the free length without damage. The sheath may slide to cover free length firmly; grout sealing may not be necessary in such cases. The sheath must not be damaged by installation.

Bearing plates must be installed perpendicular to tendons without bending or twisting. Corrosion protection must not contact plates during stressing.

Wedges must be clean of rust to prevent slippage and ensure proper lock-off.

After load testing and lock-off, grout is injected into the sheath per project specs. Grout level and cover thickness must be checked and topped up if needed to ensure full sheath filling.