ABSTRACT

As part of a comprehensive research project on the behavior of piles in calcareous sands, three series of complementary experiments were undertaken: laboratory tests with 3 cm OD piles installed in remolded calcareous sands, model tests with 7 cm 00 piles installed on two sites of calcareous formation, and full-scale tests with 30 cm OD piles installed in a Shelly sand formation. The instrumented piles were driven or drilled and grouted and then subjected to static pullout tests. This paper describes the experimental conditions of the tests and gives the results obtained. The skin friction of drilled and grouted piles is much higher than that of driven piles in the same formations. A thorough understanding of the geotechnical characteristics of carbonate formations, particularly their compressibility and cementation, is indispensable for the designing of piles.

INTRODUCTION

Calcareous sands, which are accumulations of sand-size pieces of carbonate materials, have very different characteristics depending on their origin. Biogenic calcareous sand grains (Shelly, coralline or algal debris) are often very angular and are characterized by the presence of in trap article voids. Such sands tend to crush under stress more readily than ferruginous sands. Calcareous sands may be found in cemented and incremented states.

Calcareous sands entail difficult ties for selecting, designing and installing platform foundations. The skin friction of driven piles is known to be very low and always difficult to estimate. As a result, all laboratory and field tests generally show that grouted piles in calcareous sands offer much better bearing capacity than driven piles of the same size, but data on this are still limited. For this purpose, the "Association de Recherche en GEotechnique MArine" (ARGEMA) has undertaken three series of complementary experiments:

  • laboratory tests with 3 cm OD piles (called "lab tests") installed in remolded calcareous sands;

  • in situ tests with 7 cm OD piles (called "model tests") installed at Quiou and Pisiou, two sites of calcareous sands in western France ;

  • in situ tests with 30 cm OD piles (called "full-scale tests") installed in a shelly sand at Plouasne in Brittany (western France).

The instrumented piles were driven or drilled and grouted and then subjected to static pullout tests. This paper describes the experimental conditions of the tests and gives the results obtained.

1. EXPERIMENTAL CONDITIONS

This section successively describes the experiments performed: lab tests, model tests, full-scale tests.

1.1. Lab Tests

Lab tests were performed with 2 to 3 cm OD piles installed in remolded sands.

1.1.1. Sands

Three calcareous sands were used: sands Cl, C2 and C3. Sand Cl is a coarse shelly and taken from the English Channel. Sands C2 and C3 are coralline and shelly ands taken from quarries at Quiou in Brittany and Pisiou in Touraine.

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