Expertise
Across the globe, many dams are reaching the end of their original design lives. Built decades ago, they were designed to standards that did not anticipate today’s knowledge of seismic loading, durability or climate resilience. Yet these structures remain vital for water supply, hydropower and community safety.
The challenge is clear: how do we strengthen ageing dams without rebuilding them entirely? Drawing on more than 75 years of heritage, SMEC combines global expertise with local insight to modernise assets in ways that are practical, resilient and sustainable. This reflects our commitment to engineering positive change — delivering solutions that extend asset life while safeguarding communities.
Why Head Block Design Matters
One proven way to stabilise dams is through post‑tensioned anchors, which apply restoring force directly into the structure. But when very large anchors are installed — sometimes with up to 91 strands — the forces involved are immense. Concrete that has been in place for decades was not designed to absorb such concentrated stresses, and without careful design, cracking or crushing can occur.
Typical post-tensioned anchor assembly showing how forces are transferred into existing dam-concrete
Head blocks are the critical interface between modern anchors and ageing concrete. They spread forces across a larger footprint, protecting the original structure. Choosing the right type of head block is therefore central to both safety and constructability.
Two Main Approaches
SMEC’s study compared two contemporary head block types:
- Stress beam head blocks: Reinforced beams cast above the dam crest to distribute anchor forces. Well suited to spreading very high anchor loads, particularly where anchor spacing and crest access allow.
- Cylindrical precast head blocks: Prefabricated units recessed into the dam crest, providing a compact and less intrusive anchorage solution. Ideal where minimising crest obstructions is critical, with performance governed by concrete condition and anchor layout.
Each option has advantages depending on dam geometry, concrete condition and operational needs. Stress beams are straightforward to build above the surface, while cylindrical blocks are less intrusive and often easier to maintain.
Applying Advanced Analysis
To provide clear guidance, SMEC undertook a parametric study using advanced finite element analysis (FEA). By varying concrete strength, anchor spacing and proximity to the upstream face, the study produced practical design charts that simplify complexity and support early‑stage decisions.
Principal compressive stresses long section – stress beam head block – 3.0 m spacing
These charts help answer key questions:
- What anchor spacing is safe for a given concrete strength?
- How close can anchors be placed to the upstream face?
- Which head block type is better suited to the dam’s condition?
Practical Outcomes
The findings show how modern analysis tools can validate designs, reduce risk and support more resilient upgrade strategies. By turning detailed modelling into practical guidance, SMEC equips dam owners and regulators with evidence‑based recommendations that inform feasibility and concept design.
SMEC continues to advance dam safety and resilience through innovative design and analysis. If you’d like to explore how these insights can support your projects, connect with our team to learn more about applying these approaches to real-world challenges.
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