There will be full pedestrian access to the Castle and Lighthouse during the eight week project.
It was announced in December 2025 that essential work was needed on Castle Bridge, at a cost of more than £6million.
Contractors Geomarine will start work today (15 June) on the bridge's historic granite piers, which date back to the 1800s.
It will involve drilling into the rubble core of the piers and injecting cement grout to solidify that material.
The piers will be kept as part of the like-for-like replacement of the bridge.
People can still walk across the main bridge and the approach bridge to Castle Cornet throughout this period of work.
Project Manager Joe Armstrong said:
"These preparatory works are an important first stage of the Castle Bridge reconstruction. They are necessary to ensure the existing granite piers can be utilised as part of the new structure.
"We have carefully planned these works so that people can continue to access Castle Cornet and the Breakwater, providing they follow the safety signage and any temporary arrangements in place."
No-one can walk underneath the bridge because of the risk of falling material, given how old the structure is and its deteriorating quality.
The main construction works are due to begin in September and will take approximately nine months to complete.
The bridge will close while that happens, so the existing 95-metre concrete deck can be demolished and replaced with a new structure.
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