REDUCING NEGATIVE FRICTION WITH BITUMEN SLIP LAYERS-CLOSURE

The authors reply to questions raised by discussers regarding the low level of permissible downdrag, the choice of the foundation for the Moerdijk site, the availability of better calculation methods for negative friction on piles, and the use of thinner layers of pen-grade bitumen for slip layers. The low value of the permissible negative skin friction was chosen in view of the limitation in the attainable bearing capacity in the sandy loam foundation stratum, the many uncertainities regarding the soil condition for the given heterogeneous structure of the foundation stratum, the loading conditions and the assumptions made for calculating the reduced negative skin friction from the settlement, and slip layer properties. Apart from the obvious effect of slip layer thickness on remaining frictional force, it is emphasized that the use of thin layers will present problems in the long run, when granular soil will penetrate into the slip layer and thus reduce its effect considerably. Comments are made on the choice of type of bitumen, and on the need for a comprehensive study of the negative skin friction to be expected and a cost comparison before it is decided to apply the slip layer system. Points considered in the Moerdijk site application are listed. It is shown that for the foundation in the sandy-loam stratum a reduction of the negative skin friction to a negligible value is a necessity when one needs piles with a safe bearing capacity of 60 ft. - 75 ft.

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  • Accession Number: 00134652
  • Record Type: Publication
  • Report/Paper Numbers: SCE #10764
  • Files: TRIS
  • Created Date: Jun 23 1976 12:00AM