Posted: Friday 15th September 2017
Following the specialist surveys of the void under the road at High Street Green, Hemel Hempstead, repair work is due to begin on Tuesday 19 September.
The surveys confirmed that the void stretches six metres along the length of the road, and is around eight metres deep. It also highlighted that there was a small extension to the void on one side of the road and so we decided to undertake a second investigation to make sure that we were certain of the full extents of the void.
What have these tests told us?
- We know the approximate size and shape of the void – it’s around 5 to 6m across in each direction and around 7.5m deep with a total volume of at least 75 m3
- We know that there is disturbed ground around the void, as you might expect, but no more voids under the road nearby
- We’ve found no evidence that it is connected with historic works (such as chalk mining or clay extraction)
- The void was formed by water dissolving the chalk although we can’t tell whether that water came from a leaking pipe or was natural ground water
- The void probably formed over a number of years before it collapsed to form the hole in the road surface
The first step will be to safely enlarge the hole in the road using a special long-reach excavator to enable engineers to get a clearer look at the void.
Assuming that nothing unexpected is found which didn’t show up on the geotechnical surveys the void will then be partially filled with concrete, to just below sewer level, so that the water company can start repairs.
It is hope that all repairs will be completed and the road reopened before the end of November 2017 but this estimate is dependent on the weather and the complexity of the repair work required.
We apologise for the inconvenience caused and would like to thank residents and road users for their patience.