Medway Viaduct Refurbishment

Friday 30 April 2010

Medway Viaduct Refurbishment

The Challenge
The Highways Agency needed a solution to ensure the future life of the Medway viaduct and solve their need for a high capacity crossing. The solution from the CS  (Costain, Skanska, Mowlem) joint venture sounded straight forward enough; build a new viaduct alongside the old one, divert traffic onto that, refurbish the old and then use the new viaduct for traffic from coastal ports such as Dover and the old one for traffic from London, doubling the original capacity. Given the concerns over potential chloride attack from road salt penetration into the deck of the old viaduct a detailed survey covering the entire 1km was required to evaluate the extent of the damage. A huge task in itself covering a deck area of almost 30,000m² was undertaken by the materials testing division of Soil Mechanics.

Solution
The process adopted by Soil Mechanics include nondestructive investigation, visual inspections, material sampling and laboratory testing to identify the areas suffering chloride attack and in need of repair. Once the tarmac surface had been stripped by the main contractor, well over 100,000 'half cell' potential readings were taken to survey the entire viaduct deck.

The investigation provided the following advantages:-

• Survey results enabled the areas of high chloride content to be delineated
• Four commercial laboratories carried out 8000 tests to determine the precise levels of chloride
• Visual and sampling inspection of the joints and the bridge under neck
• 'Cover survey' enabled damage to existing buried reinforcement to be avoided during repair work

Results
The depth of service provided by Soil Mechanics, working alongside the main contractors for some four months resulted in valuable information that enabled a timely completion of the repair work on the old viaduct.

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