Fraser Heights Bridge – Comparison between PDA Tests and Pile Capacity Estimation Methods-Paper

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The Fraser Heights Bridge in Surrey, British Columbia, was built across an environmentally sensitive wetland using a top-down construction method. Driven steel pipe piles supported the bridge and allowed construction equipment to operate from the completed structure, avoiding access onto the wetland. Design and construction were complicated by a tight schedule, highly variable subsurface conditions, and limited geotechnical investigation.<br /><br />Soils ranged from shallow, dense glacial deposits in the west to deep sequences of loose sand, peat, soft silt and clay over till-like material in the east. More than 40 Pile Driving Analyzer (PDA) tests were conducted on 12% of the piles, with capacities interpreted using CAPWAP and compared with estimates from design-code methods.<br /><br />PDA results showed substantial variation in pile resistance. In till-like soils, shaft resistance was typically 25–75 kPa, while equivalent plugged-pile toe resistance was generally 6,000–12,000 kPa, with some much lower values. Back-calculated shaft and toe parameters (Beta and Nt) were often below code recommendations for dense sand or gravel. Code ranges for weaker soils more closely matched the observed results, and SPT-based toe-capacity estimates were also substantially higher than PDA-indicated capacities.<br /><br />Installation challenges included boulders, buried timber, pile damage, and inconsistent plugging. Sixteen piles—about 14%—were obstructed or damaged and required replacement or remedial measures. Actual pile lengths averaged 7.5% longer than design lengths, with one pile 67% longer. Some piles also gained significant capacity over time, demonstrating setup effects.<br /><br />The project shows that standard capacity assumptions may overestimate resistance in till-like soils and that difficult, variable sites can make capacity verification challenging. The authors recommend preconstruction pile testing to assess drivability, validate capacity-estimation methods, and characterize setup, helping reduce unexpected construction problems.

Keywords

Fraser Heights Bridge

Surrey British Columbia

top-down construction

wetland bridge construction

driven steel pipe piles

PDA testing

CAPWAP analysis

variable subsurface conditions

pile driving resistance

pile capacity verification