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25% of A10 hit by sulphide attack

INVESTIGATIONS CONTINUED this week into the heave that has left up to 25% of the new carriageways on the 7.5km A10 Wadesmill bypass buckled, cracked and ridged.

Sulphate attack on the lime stabilised capping layer below the full depth flexible road construction is still seen as the most likely cause (NCE 26 February).

If so, main design and build JV contractor Fitzpatrick Lafarge and its consultant URS will have to explain how the battery of chemical tests demanded by the Highways Agency failed to detect the presence of dangerous levels of sulphates or sulphides in the soil stabilised.

Late last year the Agency further improved the test methods for sulphate and sulphide by including a direct test for sulphide content in its specification. Earlier forms of sulphate and sulphide tests were known to be labour intensive and more prone to human error.

This week when NCE visited the bypass, the road surface was scarred by extensive trial pits and core holes as well as the random patterns of heave effects.

Determining exactly how much of the road will have to be repaired is the most important next step. At one time it was hoped to open the £25M bypass eight months ahead of schedule. Now it seems unlikely that the August opening deadlines will be met.

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