Acepted paper 2 - Frost weathering of chalk.pdf (911.91 kB)
Frost weathering of chalk
The processes and factors that determine the heave and fracture of frost-susceptible bedrock exposed to temperature cycling above and below 0°C are little known but important to understanding of rock deformation, weathering and ground conditions. To investigate the early stages of heave, settlement and fracture of intact chalk, physical modelling experiments were performed on blocks of Saint Cyr Tuffeau and Totternhoe Clunch. Unidirectional (downward) freezing simulated seasonally frozen bedrock in non-permafrost regions, and bidirectional (upward from permafrost and downward from the surface) simulated an active layer above permafrost. Heave and settlement of the top of the blocks were monitored in relation to rock temperature and unfrozen water content. Heave and settlement showed complex behavior that varied with moisture content, freezing regime and time. Progressive heave of wet chalk during thaw periods (simulated summers) is attributed to microcracking in near-surface permafrost. Macrocracking was favoured near the rock top during unidirectional freezing and near the permafrost table during bidirectional freezing, producing extensive fracture networks. Four processes, operating singly or in combination, account for the heave and settlement behavior: (1) thermal expansion and contraction in dry chalk; (2) volumetric expansion of freezing water, causing bursts of heave; (3) ice segregation, causing sustained heave and rock fracture; and (4) freeze?thaw cycling, causing initial consolidation and settling of wet chalk during unidirectional freezing. The experimental data and field observations of chalk weathering profiles elucidate the nature and origin of chalk brecciation. Type 1 brecciation (angular or subangular rock fragments separated by unfilled fractures with matched sides) is attributed primarily to ice segregation. Type 2 brecciation (subangular to rounded lumps of rock—lithorelicts—set in a fine-grained matrix of the same, but softer and remoulded material) probably resulted from frost weathering and limited ground movement, particularly beneath the sides and bottoms of wet (now dry) valleys.
History
Publication status
- Published
File Version
- Accepted version
Journal
Engineering in Chalk: Proceedings of the Chalk 2018 ConferencePublisher
Ice PublishingExternal DOI
Event name
Engineering in Chalk 2018Event location
Imperial College, London, UKEvent type
conferenceEvent date
17th and 18th September 2018ISBN
9780727764072Department affiliated with
- Geography Publications
Full text available
- Yes
Peer reviewed?
- Yes
Editors
M Preene, J A Lawrence, R BuckleyLegacy Posted Date
2018-07-31First Open Access (FOA) Date
2018-08-31First Compliant Deposit (FCD) Date
2018-07-30Usage metrics
Categories
No categories selectedKeywords
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC