Tills and Other Glacially Associated Deposits

Typical gradings of some Scottish tills (after McGown, 1971). With kind permission of the Geological Society. 236 

Variation in some simple index properties with depth of the Upper Boulder Clay of Teesside, England (after Bell, 2002). 

The compressibility and consolidation of tills are determined principally by the clay content, as is the shear strength (Table 5.17). For example, the value of compressibility index tends to increase linearly with increasing clay content, whereas for tills of very low clay content (less than 2%), this index remains about constant (C = 0.01). The shear strength of till can range from 150 kPa to over 1.5 MPa. 

Fissures in till tend to be variable in character, spacing, orientation and areal extent, although they can have a preferred orientation. Opening up and softening along these fissures gives 

Note c = cohesion in kPa, r = residuai, u = undrained ip = angle of friction L = low sensitivity. 

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