Ajax sits on the South Slope of the Oak Ridges Moraine, where the overburden shifts from dense sandy silt till to the glaciolacustrine deposits of the old Lake Iroquois plain. The water table sits high across much of the town, often within 3 meters of grade in the southern sections near the 401. This means any anchored retaining system here has to solve for two things at once: low effective stress during construction and aggressive corrosion potential from the silty groundwater. We size the unbonded length to reach past the Rankine failure wedge, then verify the fixed anchor length using the effective stress method with residual strength parameters from direct shear tests on the local Halton Till.
A properly designed ground anchor in Ajax doesn't just hold a wall back — it transfers load deep into competent till below the seasonal groundwater fluctuation zone.
Process and scope
Local ground factors
The hollow-stem auger rig arrives on site with the tendon pre-greased and the centralizers spaced at 2 meters on center. In Ajax, the real challenge starts when the auger hits cobbles within the till — you hear it before you feel it. The driller has to retract and switch to a rock roller bit if the obstruction won't clear, which changes the borehole diameter and forces a recalculation of the grout-to-ground bond stress. We keep a geotechnical engineer on standby during drilling because a single boulder can shift the anchor location by half a meter, and that changes the entire load distribution on the waler beam. Before any tensioning begins, we correlate the grout take with the expected theoretical volume — a sudden loss of grout into a sand lens means the bond zone might be compromised and a grouting program may be needed to seal the annulus before the anchor can be accepted.
Reference standards
NBCC 2020 Division B Part 4, CSA A23.3-19 Annex D: Anchorage, ASTM D3689-22: Anchor Testing Procedure, PTI DC-35.1-14: Recommendations for Prestressed Rock and Soil Anchors
Other technical services
Permanent tieback anchor design
Full design package for soldier pile and lagging walls, including tendon selection, bond length calculation in Ajax till, corrosion protection specification, and staged stressing sequence compatible with the excavation schedule.
Proof testing and lift-off supervision
On-site supervision of cyclic proof testing per ASTM D3689, including dial gauge monitoring, creep rate interpretation, and lock-off load verification. We provide the stamped test report within 24 hours of completion.
Typical parameters
Questions and answers
What does anchor design and testing cost for a typical Ajax retaining wall project?
For a standard scope covering design calculations for 2 to 3 anchor rows plus on-site proof testing supervision, the fee range is CA$1,230 to CA$5,660. The spread depends on whether we are doing a simple single-row temporary anchor or a multi-row permanent system with full corrosion protection and long-term monitoring requirements.
How do you determine the bond length in the till we have in Ajax?
We start with a lab direct shear test on an undisturbed Shelby tube sample of the Halton Till to get the drained residual friction angle. Then we apply the effective stress method — the bond stress is a function of the vertical effective stress at mid-bond depth, reduced by a factor of safety of 2.0 for permanent anchors. We verify the assumption with at least one sacrificial anchor tested to failure on site.
Is double corrosion protection mandatory for permanent anchors in Ajax?
It depends on the soil resistivity profile. We run a Wenner four-pin resistivity test down to the anchor bond zone depth. If readings are above 5,000 ohm-cm, Class I protection is often sufficient. Below that, or if the resistivity varies by more than 50% across the borehole, we specify Class II double encapsulation. The Ajax waterfront area near Duffins Creek almost always requires Class II due to the saline groundwater influence.
What testing do you require before accepting an anchor?
Every anchor undergoes a cyclic proof test per ASTM D3689: we load in increments to 133% of the design load, hold, and measure creep. The acceptance criterion is less than 2 millimeters of movement per log cycle of time during the hold period. Production anchors that fail the creep test get replaced or re-grouted and re-tested. We also do lift-off checks on 10% of the anchors after lock-off to confirm the residual load hasn't decayed.