We’ve mentioned that preparations for the Rochester Bridge Refurbishment have been going on behind the scenes for some time, but not all of the preparations have been hidden.
In autumn 2016 – and for some time after – you may remember the investigations on Rochester Esplanade. The work was only scheduled to take a few weeks, but hoarding stayed up in one area for considerably longer, because of the discovery of the castle water gate, but we digress. The reason for bringing this up now is because these were geotechnical investigations to help us prepare for the refurbishment.
The works, which were detailed in another article, were conducted to make sure we had the most accurate information possible about the geological make-up of the Esplanade before drawing up designs for the refurbishment: despite our extensive collection of archives we have very little historical information about the Rochester river wall’s profile (shape) or foundations. We knew the Esplanade was built in its current form when the Victorian bridge was created, but otherwise the records are fairly limited – the bridge itself being considered more noteworthy at the time. This meant we had to find out the information for ourselves.
Comprising bore holes (long, narrow holes about 8m deep, providing a core of material to be analysed) and trial pits (shallow, wide pits), the investigations resulted in confirmation of our belief that the fill behind the river wall is a mixture of soil and the remains of the medieval bridge, an early example of recycling! The bore holes went down to the bedrock, and confirmed this is chalk. This is the same bedrock which Rochester Castle is built on, with the River Medway following (or creating) the contours within the chalk.
We needed this information because the material used in the foundations of the Esplanade could have a significant impact on our refurbishment works, which include improvements to the underground drainage system and a redesign of the public area by the river – more on those later.