DYWI® Drill Hollow Bar System
Borehole grout, whilst beneficial, is not the primary basis for ensuring durability of the soil nail over its design life.
Corrosion protection for hollow bar soil nails is achieved through:
Sacrificial Corrosion Protection
1. Sacrificial Corrosion Allowance;
This technique calculates the loss of steel over the proposed design life of the soil nail or micro pile based on the total surface area of the bar. The residual strength of the bar is then calculated based on the remaining cross sectional area of steel, this can then be assessed against the required working load of the bar. The quantity of steel loss is based on research in accordance with TRL 380, EN14199, CIRIA C637. Corrosion rates are determined by the aggressive levels of the soil in accordance with the values outlined in the standards. In most cases, highly aggressive ground conditions don’t occur naturally and are only present in locations formerly used for industrial processes which have contaminated the soil.
Galvanizing / Sheradizing
2. Supplementary Galvanizing;
in accordance with EN1461 hot dipped galvanizing will provide an additional 5-15 years lifespan, depending on aggressive of the soil, for buried installations. This method when applied to the top bar, located at the soil / air interface ,the most corrosive area, provides a practical basis for increasing lifespans but minimises additional cost. Corrosion in the deeper parts of the borehole is less prevalent due to the lack of oxygen. A fully galvanized system can be adopted if the project specification requires it.
3. Duplex Coatings; comprises an additional Epoxy Powder coating (80-90 μm) over the hot dipped galvanizing. Although the coating can be damage during rotary percussive installation the remaining Epoxy Coating will provide an additional protective benefit especially in the valleys between the threads, where the Epoxy coating generally remains intact. Loss of Epoxy at the crest of the thread is common, but this part of the bar tends to have a greater wall thickness forming the thread ridge and has greater resistance to corrosion. Any visible damage to the Epoxy coating can be repaired with a twopack Epoxy paint “touch-up” kit.