This thesis is concerned with the mass compressibility of fractured chalk and its influence on the settlement of shallow foundations. A review of the literature reveals nineteen case records of load-settlement behaviour from relatively small diameter « 1m) plate loading tests but only six welldocumented case records of the behaviour of shallow foundations on chalk. The plate loading tests indicate that highly fractured near-surface chalk undergoes yield at relatively low stresses (200 - 400kPa) resulting in a significant reduction in stiffness. This behaviour contrasts with that observed in other rock types with similar discontinuity patterns. For chalk it has only been observed in one case record for a full-scale foundation. Little is understood about the mechanisms causing yield. At the time of starting this research, based largely upon the experience ..gained from in-situ loading tests carried out at Mundford, Norfolk (Ward et aI., 1968), it was known that factors such as fracture spacing and aperture played an important role in controlling the load-settlement behaviour of shallow foundations. Little attention was paid to the large variation in intact properties displayed by the chalk. In this research nine 1.8m diameter plate loading tests have been carried out by the author on chalks with different intact mechanical properties and similar discontinuity patterns. These data are used to evaluate other in-situ tests (such as SPT, surface-wave geophysics and visual assessment) as means of providing parameters for the prediction of foundation settlement. The results of this research indicate that fractured near-surface chalk undergoes yield within the range of stresses likely to be imposed by shallow foundations and that the pre-yield stiffness of the rock mass is controlled to a large extent by the looseness of the fracture-block system, which in tum appears to be associated with the intact mechanical properties of the rock. The post yield-stiffness of the rock mass is generally about one tenth of the pre-yield stiffness and is relatively insensitive to the rock material properties.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:359742 |
| Date | January 1993 |
| Creators | Matthews, Marcus Charles |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://epubs.surrey.ac.uk/773029/ |
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