HS2 Grim's Ditch

The site contains part of Grim’s Ditch, an Iron Age boundary ditch forming part of a larger monument extending beyond the site boundary. A section of the ditch to the south-west of the reburial area is scheduled, with other scheduled and undesignated sections located throughout Buckinghamshire. The area preserved beneath the embankment is not designated, as its archaeological significance was not known prior to the HS2 works. In addition to Grim’s Ditch, the site contained archaeology of variable density dating from the Late Iron Age to the post-medieval period. Elements of a Roman landscape were identified to the west of the ditch, while settlement remains to the north included industrial features such as furnaces and corn-drying ovens.

Two open-area excavations were undertaken. One area of around 9,000m was preserved in situ, while recording in a second, larger area containing Grim’s Ditch was limited to strip, map and sampling to assess condition and significance. Following this, archaeology here was reburied beneath Terram geotextile and soil while a long-term reburial solution was developed for both areas. Preservation beneath a 4 m-high engineered embankment, rather than excavation, was in accordance with HS2’s Heritage Memorandum, which states that the nominated undertaker will seek to reduce harm to the historic environment where reasonably practicable.

ALIGN undertook a settlement assessment and designed the reburial solution, demonstrating that archaeological deposits would experience less than 10mm of compression, with overall settlement predicted to be less than 35mm. A protective starter layer and construction control measures were implemented to ensure even settlement and prevent damage from construction plant. As a result, 25,000m² of archaeological remains have been preserved in situ, involving more than 50,000m² of geotextiles beneath 25,000m² of hardcore.

The embankment will reduce long-term maintenance and the risk of accidental damage. The preservation area was fenced and signed prior to construction, with access tightly controlled. No topsoil stripping or removal of temporary reburial material was required, ensuring the archaeology remained undisturbed. Historic England and Buckinghamshire Council were closely engaged throughout, and the reburial is intended to be permanent.

If you want to learn more about our work on the only scheduled monument excavated as part of HS2, you can visit the interactive StoryMap here!