Marine Pile Load Testing in Carbonate Rocks
Authors: Settgast Robert H. 
Published: October 2008

A marine pile load test program was undertaken to test the performance and installation methods for both driven and grouted piles supported in carbonate rocks. which underlie much of the nearshore waters of the southern Arabian Gulf. Forty-two-inch (1.07m) openend steel pipe piles, driven 2 to 6.5m into bedrock with variable degrees of pilot drilling, were tested in bending, compression, and tension. A single grouted insert pile was tested in tension.

Test loading was conducted from a preassembled reaction frame supported on driven sleeve piles anchored to grouted insert piles. The installation of this frame, as well as the test piles, enabled the contractor to gage driving behavior, predrill requirements, and hammer performance; and to refine the installation techniques for grouted insert piles.

Although stratigraphic variations and the 450tonne reaction limitation dictated some generalization in test interpretation, the program added confidence to pile design and permitted the acceptance of minimum design penetrations.

In this paper, the stratigraphy, installation methods, driving behavior, and testing procedures are discussed along with the test results.

INTRODUCTION

Testing was conducted in September 1978 for an NGL loading jetty, sited in the nearshore waters of the southern Arabian Gulf. The pile-supported structures include an unloading platform 1,700m from shore near the -13m isobath, a shore-connected trestle, and breasting and mooring dolphins (Figure 1). The platform and trestle will be supported on 30- to 42-inch (0.76 to 1.07m) open-end driven pipe piles with 0.5 to 1.5 inches (13 to 38mm) walls. Grouted insert piles were planned where substantial uplift loads are expected, such as for the mooring dolphins.

Although the carbonate rocks encountered while investigating this site were consistent with the local stratigraphic data, the test borings and construction experience had disclosed significant variations in their engineering and construction properties. This factor, combined with the inherent limitations in developing reliable pile strength parameters in carbonate rocks was the prime basis for initiating the test program.

Testing was performed at two locations. At Location No. 1 near the platform position in 12.5m of water, a driven pile (TFI) was tested in bending, compression, and tension; and a grouted insert pile was tested in tension. At Location No.2, near the trestle midpoint in 6m of water, a driven pile (TP2) was tested at two penetrations.

The axial load test data are summarized in Table 1. Driving data, and corresponding stratagraphy, are summarized on Figure 3. The load deflection relationships for all tests are illustrated on Figures 4 through 9. The equipment and procedures used for the test program are shown on the accompanying photos (Figures 11 through 16).

SEAFLOOR STRATIGRAPHY AND LITHOLOGY

The seafloor is mantled by a sand overburden ranging in thickness from 2m at the -6m isobath 700m offshore at Test Location No.2, to 6m at the -12.5m isobath 1,700m offshore at Test Location No.1 (Figure 2). The overburden is comprised mainly of loose bioclastic sands with random units of weak cementation and a weakly cemented mantle (cap rock) up to 0.3m thick.