Monotonic Testing of a Model Pile Driven in a Calcareous Sandy Silt

Abstract

ABSTRACT A monotonic pull test was performed on a driven model pile in a large calibration chamber fried with incremented calcareous sandy silt, prepared as an analogue of material obtained in the vicinity of a new platform in Australia's Bass Strait. A cone electrometer test was performed prior to the installation of the pile. Strain gauges mounted along the pile enabled the evaluation of pile axial loads developed during the pile driving and pull test. INTRODUCTION Calcareous soils are found in many parts of the world where offshore platforms are built, for example Bass Strait and the North West Shelf of Australia, Arabian Gulf, Gulf of Mexico, Mediterranean Sea and the Brazilian Campos Basin. The carbonate formations occur in varying states of cementation, with classification ranging from well-graded sand to silty sand and sandy silt. There is, however, a lack of detailed information on pile behavior during driving and pull testing in the finer materials, and also on the geotechnical characteristics of such materials. As part of an investigation of the behavior of axially loaded driven piles and grouted piles in calcareous soils, a monotonic pull test was performed on an instrumented pile driven into a large calibration chamber filled with calcareous sandy silt. ?Ile soil, designated Soil B, is an analogue of material found in the vicinity of a new platform in Australia's Bass Strait, and was produced by grinding a medium calcareous sand, designated Soil A, dredged from another site in Bass Strait [1]. Descriptions of the cone electrometer, pile driving equipment, model pile, chamber and other associated equipment are given in [1]. This paper describes the characteristics of the test soils, the procedures that were developed to prepare the test sample, and the results of the cone penetration and model pile test that were performed in this soil PROTOTYPE AND ANALOGUE SOIL CHARACTERISTICS The in situ soil to be modeled in this investigation has a particle size distribution of a sandy silt. It is cemented, with typical in situ void ratios of 0.95 ± 0.05. Due to the unavailability of prototype soil to carry out model pile testing, an analogue material (Soil B) was produced by passing Soil A through a variable gap disc mill. Platey shells and elongated and coral fragments were broken down during the milling process. Grain size distribution curves for samples of the product were obtained during the process, and the gap between the discs was adjusted to compensate for disc wear when required. The particle size distribution curve of Soil B is shown in Fig. 1 and the specific gravity was found to be 2.73. It should be noted that the material is extremely fine and to the authors' knowledge, no other model pile tests have been conducted in such fine cohesion less material.