Abstract
Chalk putties are common in Southern England, occurring naturally and as a result of earthworks in intact Chalk. The ease and readiness with which intact Chalk breaks down into putty makes establishing a good geotechnical profile of the material necessary.A review of literature indicates that previous laboratory studies on chalk putties are limited, and that testing of the material has proven difficult using standard procedures. This study initially quantifies index parameters such as Atterberg limits, thixotropy and particle size distribution before considering susceptibility to age-related strength gains and shear strength-strain dependency so that subsequent shear test data can be normalised.
Contrary to literature, age-related strength gains were found to be minor, whilst shear strength-strain dependencies were found to be significant. Large strain tests in ring shear apparatus (following recommended test procedures) found non linearity in the drained shear failure envelopes, with effective friction angles (Ø') increasing with strain. This non linearity is explained by sample grading evolution.
Using these findings the study develops new preparation and testing methodologies to create ‘identical soils’ of known stress history. Testing in a computer governed stress path cell (using ‘Triax’ software) found that chalk putty behaves as a contractive material, ‘wet’ of its critical state, exhibiting failure by liquefaction for mean effective stresses (p') lower than 200kPa. Pre and post yield permeability values in the range 2.5-13 x 10-9m/s were recorded with state parameters indicating a constant reduction in sample void ratio during shear tests conducted at a pre shear p' of between 0 and 400kPa.
| Date of Award | Aug 2013 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Paul David Julian Watson (Supervisor), Steve Mitchell (Supervisor) & Dave Giles (Supervisor) |