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ABSTRACT Model pile tests have been conducted in samples of calcareous sand, derived from both on and off shore sources in Australia. Samples 1.2 m diameter by 1.8 m high were formed and saturated in a large calibration chamber, modified to allow three piles to be driven into each sample. The silty fines created unique problems in sample formation and in creating a realistic test environment. Results of initial pull testing are discussed and compared with the CPT test. INTRODUCTION Carbonate soils found in Bass Strait, a major hydrocarbon producing region off the southeast coast of Australia, generally provide relatively poor support for driven piles [1]. Drilled and grouted piles [2] which provide extremely high skin frictions, upwards of 400 kPa, are now the preferred solution, but are datively expensive. In an effort to improve the cost effectiveness of grouted pile foundations, Esso Australia Ltd. conducted an extensive experimental program in 1987 and 1988 which included tests of 100 mm and 150 mm driven piles and grouted piles in a modified laboratory calibration chamber at Monash University, Melbourne. The tests were performed in three incremented carbonate soils that ranged in grain size from a medium sand to a sandy silt. This paper presents descriptions of test equipment, procedures, and results of driven pile and cone electrometer tests performed in two of these soils, designated A and C. These were medium and silky sands, respectively. Results obtained in the sandy silt are reported in a companion paper[3]. Soil A was recovered References and illustrations at end of pare by dredging from a site in Bass Strait, while Soil C was derived from an on-shorn Tertiary deposit in South Australia. In respect of their compressibility and fines content, these soils differ notably from the clean silica sands normally used in calibration chamber studies, introducing severe problems in handling and sample formation, as well as causing notable differences in pile behavior. THE CALIBRATION CHAMBER AND ACCESSORIES The Monash University calibration chamber was developed from the design of a small chamber described by Holden [4], and was constructed solely for the purpose of calibrating friction cone electrometers in sand. It consists essentially of a large triaxial sample of sand, 1.2 m diameter and 1.8 m high, enclosed in rubber membranes and compressed by a lateral water jacket and a base piston (Fig. 1). The exterior cell wall is of cavity consummation to permit the imposition of Ko lateral constraint, and the base piston acts through a water cushion for the measurement of vertical stress. An overhead reaction frame provides restraint to hold the cell together, and also mounts the driving equipment for a standard cone electrometer on the sample axis. Further details are given by Chapman [5], Bellotti et al. [6] and others. |
