A contractor recently started shoring a four-story mixed-use building on Mission Avenue, just a few blocks from the Oceanside Pier. The excavation depth hit 18 feet, and the adjacent street had to stay open to traffic. That is where active and passive anchor design became the deciding factor. Active anchors, post-tensioned against a reaction wall, held the soldier pile system in place before any soil was removed. Passive anchors, essentially grouted untensioned bars, took over once the passive wedge developed behind the wall. For that project, the team ran a placa de carga on the anchor bond zone to confirm the grout-to-soil bond stress met the 150 psi assumed in the LRFD design. The combination of both anchor types saved the schedule and kept the sidewalk crack-free.
In loose sands below the water table, post-grouting can increase anchor bond capacity by 60 percent compared to a straight shaft tremie grout.
Method and coverage
Regional considerations
California Building Code (CBC) 2022, based on IBC 2021, explicitly requires that permanent anchors in Seismic Design Category D, which covers all of Oceanside, be designed for the anchor load combinations that include overstrength factor (Ω₀). That means the steel tendon must resist 1.7 times the nominal seismic load without yielding. The other risk we see locally is the high groundwater table. If the anchor bond zone is installed below the water table, the tremie grout must be placed using a positive displacement pump with a tremie pipe that reaches the bottom of the hole. Otherwise, the grout dilutes and the bond strength drops by half. We avoid that by performing a permeabilidad de campo test in each anchor hole before grouting, so the team can adjust the water-cement ratio from 0.45 to 0.40 if the permeability exceeds 10⁻² cm/s.
Standards that apply
FHWA-NHI-10-047 (Geotechnical Engineering Circular No. 7, Anchor Design), PTI DC35.1-14 (Post-Tensioning Institute, Recommendations for Prestressed Rock and Soil Anchors), ASTM D5767-18 (Standard Test Method for Determining the Performance of a Post-Tensioned Anchor System), CBC 2022 / IBC 2021 Chapter 18 (Soils and Foundations, Seismic Design Category D)
Complementary services
Active Anchor Design (Post-Tensioned)
For excavations requiring immediate load transfer, we design post-tensioned anchors locked off at 80% of the tendon's ultimate strength. We specify the bond zone length, grout mix, and corrosion protection per PTI DC35.1. Each anchor is proof-tested to 133% of the design load using a calibrated hydraulic jack and load cell, with creep monitored for 10 minutes.
Passive Anchor Design (Untensioned Bars)
Permanent tiebacks or soil nails that rely on the soil's passive resistance are our go-to solution for retaining walls where headroom is limited. We calculate the pullout capacity using the effective stress method with the friction angle from triaxial tests. The bars are grouted in a 6-inch diameter hole and checked for long-term creep under sustained load.
Anchor Pullout Verification and Monitoring
After installation, we perform verification tests on 5% of the anchors (minimum one per 1,000 square feet of wall) following ASTM D5767. Load is applied in cycles up to 150% of the design load, and the total creep displacement is recorded. For permanent anchors, we install a vibrating-wire load cell on the anchor head and monitor it monthly for the first year.
Typical parameters
Top questions
When should I choose active anchors over passive anchors for my Oceanside project?
Active anchors are best when you need immediate support during excavation, such as in a top-down shoring system where the wall must hold the soil before the floor slabs are cast. Passive anchors work well for permanent retaining walls or slopes where the ground can deform slightly and develop the passive wedge. In Oceanside's sandy soils, active anchors are usually preferred for temporary shoring because they lock the wall in place before any movement starts.
What is the typical bond stress you use for anchor design in Oceanside's sandy soils?
For clean silty sands (SP-SM) with SPT N-values between 10 and 30, we use a grout-to-soil bond stress of 100 to 130 psi for straight-shaft grouted anchors. If we post-grout the bond zone, that value can increase to 160 to 190 psi. The final design value is always confirmed by a field pullout test on the first production anchor.
How much does an anchor design and testing program cost in Oceanside?
For a typical project with 20 to 40 anchors, the design, proof testing, and monitoring program ranges between US$990 and US$4,010, depending on the anchor depth, corrosion protection class, and number of verification tests. Permanent anchors with double corrosion protection and long-term load cells are at the higher end of that range.
Does the high groundwater table in Oceanside affect the anchor grouting procedure?
Yes, significantly. When the bond zone is below the water table, tremie grouting must be done with a positive displacement pump and a tremie pipe that reaches the bottom of the hole. The water-cement ratio is reduced from 0.45 to 0.40 to prevent dilution, and the grout is placed at a rate that keeps the tremie pipe submerged. We always perform a permeability test in the anchor hole before grouting to confirm the formation is tight enough to avoid excessive grout loss.