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Abstract Various in situ and laboratory tests that have been used to study the behavior and engineering characteristics of granular carbonate sediments are described and evaluated. Based on success or failure of these different test procedures (in terms of foundation performance) in situ and laboratory tests are recommended to make future geotechnical investigations in these soils more cost effective while meetin8 the technical demands of designing foundations in a material that is not well understood. Such standardization schemes will lead to significant improvements in soil characterization procedures and ultimately pave the way for improved foundation design methods. It is hoped that this will lead to development of rational geotechnical investigation programs rather than the arbitrary selection of tests and test procedures which may not always be appropriate. Introduction On a global basis, use of in situ and laboratory tests for foundation design in a siliceous environment has more or less been standardized over the last 30 years and more. For geotechnical investigations in granular carbonate deposits, no such standard exists and in situ and laboratory tests applicable to siliceous soils are often utilized in an attempt to describe the behavior andengineering characteristics of carbonate sediments. The resulting foundation design has had, in many cases, severe economic impact on a project, mainly from remedial work that has been necessary to improve foundation performance (de Matos and de Mello, 1982; Dutt et al., 1985; King and Lodge, 1988). In this paper, commonly used in situ tests are described and it is shown how some of these tests have been used (successfully and unsuccessfully) to select pile design parameters in granular carbonate soils. It is shown that, in general, in situ tests have had limited success and that there is a shift in emphasis toward more meaningful laboratory tests. This change in emphasis stems from a growing erception that in situ tests do not provide reliable data in nonhomogeneous. partially cemented, granular carbonate aeposits: Also contributing to this negative sentiment is the high cost to benefit ratio associated with most in situ test procedures. Successes and failures of various laboratory tests that have been tried to develop meaningful definition of soil conditions are described. Index for grain crushability, once thought of as the most important parameter affecting soil-pile behavior, is shown to have minimal impact, and the significance of photomicrographs of thin sections and soil compressibility is demonstrated. Finally, both in situ and laboratory tests are identified which show promise for describing material behavior and rovide reasonable material properties for Foundation design. In Situ Testing In the early days of geotechnical site investigations in carbonate deposits (in the seventies), testing of carbonate soils was limited to a suite of index tests such as grain size analysis, specific gravity, carbonate content, and Atterberg limits, and a few drained triaxial compression tests. As it became increasingly evident that results from these conventional laboratory tests on carbonate soil samples were inadequate for predicting in situ soil structure interaction, there was a widespread support and recognition in the industry for in situ testing. The following paragraphs describe some of the important in situ tests that have been used in attempts to improve foundation design practice in carbonate soils.
- Asia > Middle East > Saudi Arabia (1.00)
- Asia > Middle East > Yemen (0.94)
- Africa > Sudan (0.94)
- (5 more...)
- Geology > Geological Subdiscipline > Geomechanics (0.94)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (0.88)
- Materials > Chemicals (1.00)
- Health & Medicine > Diagnostic Medicine > Lab Test (1.00)
Abstract On-bottom stability of subsea pipelines has been the focus of substantial research in recent years with particular emphasis on the topic of pipe-soil interaction. Numerous models have been developed to predict the pipe-soil interaction behavior under combined vertical and horizontal loading scenarios. The Verley and Sotberg energy based soil resistance model for silica sand is among these models. The model is recommended by Det Norske Veritas (DNV) and widely accepted and used by subsea pipeline design industry to model the pipe-soil interaction on silica sand soils. Calcareous sand soils are found in many of the world's offshore hydrocarbon development regions including offshore of Western Australia. The engineering characteristics of the calcareous sand are different from those of the typical silica sand soils. As such, Verley and Sotberg parameters for silica sand soils are not suitable for calcareous sand soils. This paper presents a calibration of the Verley and Sotberg silica sand soil resistance model for calcareous sand soil conditions using the results of a set of centrifuge tests of a pipe model on calcareous sand soil.
- North America > United States (1.00)
- Oceania > Australia > Western Australia (0.49)
Electrochemical Cementation of Calcareous Sand For Offshore Foundations
Shang, J.Q. (Department of Civil and Environmental Engineering, University of Western Ontario) | Mohamedelhassan, E. (Department of Civil and Environmental Engineering, University of Western Ontario) | Ismail, M.A. (Centre for Offshore Foundation Systems, University of Western Australia) | Randolph, M.F. (Centre for Offshore Foundation Systems, University of Western Australia)
ABSTRACT A laboratory floor experimental study was conducted on the electrochemical cementation of calcareous sand for offshore foundations. A caisson, 200 mm in diameter and 400 mm long, was embedded in a calcareous sand under seawater. The calcareous sand and seawater used in the study were recovered from the coast of Western Australia. Twelve electrodes, made of perforated steel pipes of 14 mm in diameter and 450 mm long, were installed around the caisson. The hollow electrodes were filled with soluble CaCl2 granules as the cementation agent, which were forced into the calcareous sand by an applied intermittent electric current. A dc voltage of 8 volts with current intermittence and polarity reversal was applied over a period of 7 days. A control test with identical configuration to that of the electrochemical treatment test was also set up to provide baseline data. The results of the treatment were assessed by a pullout resistance test. After the pullout test, the caisson was pushed back into the soil sample and the treatment was repeated to simulate post-failure recovery. X-ray diffraction analysis, X-ray fluorescence analysis and electron microscopy imaging for soil particles and chemical analyses for soil pore fluid were conducted on control and treated soil samples. The results showed that the pullout resistance of the foundation model increased by 140% prior to failure and 255% post-failure after the electrochemical treatment, as compared with that of the control test. The cementation generated by the electrochemical treatment was evidenced by the attachment of cemented soil to the electrodes and caisson. The cementation effects were further evidenced from the mineralogical and chemical analyses, which indicated formation of new calcite and calcium iron chlorate minerals. In addition, XRF analysis showed significant increase of iron oxide (Fe2O3) an amorphous compound known as a cementation agent in soils.
- Europe (1.00)
- North America > Canada (0.68)
- Oceania > Australia > Western Australia (0.49)
- Reservoir Description and Dynamics > Formation Evaluation & Management (0.87)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Platform design (0.61)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Installation equipment and techniques (0.61)
Abstract To enable optimal design of shallow foundations, anchors and pipelines, it is common practice to test seabed samples at the anticipated consolidation stresses. The direct simple shear (DSS) apparatus has proved to be a favoured means by which the response of a calcareous sediments can be characterised Previously unpublished DSS data for a fine-grained calcareous sediment, presented herein, has helped reinforce the theory that some calcareous sediments exhibit cyclic resilience at low consolidation stress levels that are disproportionately high when compared to the cyclic resilience shown when tested under elevated consolidation stress levels. When analysing DSS test results, a direct proportionality between cyclic strength and consolidation stress has traditionally been adopted. Data presented in this paper helps confirm and extend the relevance of previous work that suggested that the cyclic resilience of certain (in that case, coarse-grained) sediments more closely reflects their behaviour under monotonic loading, with the strength being related to the consolidation stress by a power function, i.e. square-root. Up to now, some difficulty has been experienced obtaining reliable and repeatable test results at low consolidation stress levels that conform with the theoretical expectations. It is suggested in this paper that the reason may be associated with previously unnoticed preferential slip at the platen interfaces in the DSS apparatus Simple modifications to the apparatus have been implemented successfully to minimise this effect and allow more reliable definition of the cyclic resilience of these sediments at low consolidation stress levels It is considered that the information contained with the paper may prove especially useful to designers of shallow foundations in calcareous sediments. INTRODUCTION The direct simple shear (DSS) apparatus (eg. Airey & Wood, 1987) has become a favoured method to establish the undrained cyclic strength of uncemented seabed sediments, which often forms the primary basis for the design of offshore shallow foundations, anchors and pipelines, including seismic liquefaction studies. In their state of the art presentation of the laboratory testing of calcareous soils, Carter et al. (2000) reproduce convenient design charts for calcareous sand and silts that represented a reasonable average of DSS data from many offshore projects. Charts like these suggest that cyclic strength is directly proportional to the consolidation stress Airey and Fahey (1991) used this assumption when summarising the cyclic strength of silty sand from the North West Shelf in Australia Finnie et al. (1999) presented data from DSS tests performed on calcareous sand from an offshore project in the Philippines and modified the assumption of direct proportionality to consolidation stress, indicating that cyclic resilience tended to reflect the monotonic strength. This concept was originally suggested by Andersen et al (1994) for non-calcareous soils. The term cyclic resilience (rather than strength) was used to define the resistance a sediment has to accumulating strain under particular cyclic load levels, given that the sediments tested were always able to sustain the demanded load, without collapsing This paper presents some data from DSS and triaxial tests performed on calcareous silt, sand and clay sized soils recovered from the seabed in the in the Timor Sea, supported by data from the Malampaya development in the Philippines
- Asia > Philippines (0.56)
- Oceania > Australia > Western Australia > North West Shelf (0.25)
- Asia > Philippines > Palawan > South China Sea > West Philippine Sea > Northwest Palawan Basin > Block SC 38 > Malampaya Field (0.99)
- Asia > Philippines > Palawan > South China Sea > Quezon > Northwest Palawan Basin > Block SC 38 > Malampaya Field (0.99)
- Asia > Philippines > Palawan > Palawan > West Philippine Sea > Northwest Palawan Basin > Block SC 38 > Malampaya Field (0.99)
- (5 more...)
Consideration For On-bottom Stability of Unburied Pipelines Using Force-resultant Models
Tian, Yinghui (Centre for Offshore Foundation Systems, the University of Western Australia) | Cassidy, Mark J. (Centre for Offshore Foundation Systems, the University of Western Australia) | Youssef, Bassem S. (Centre for Offshore Foundation Systems, the University of Western Australia)
ABSTRACT The modeling of pipe-soil interaction in current industry practice is still based on Coulomb friction models and passive resistance. Analysis of the ultimate resistance capacity of the on-bottom pipeline subjected to wave and current loading is taken as the criterion for on-bottom stability design. This approach is widely used in industry and considerable experience has been accumulated. However, a sounder theoretical basis and more thorough understanding of the pipe-soil mechanism are still required. This paper presents some consideration and discussion regarding the analysis of unburied pipeline stability using force-resultant models, which are becoming increasingly popular in offshore engineering. Their use in pipeline analysis offer the advantages of a sounder theoretical basis, numerical efficiency and straight-forward incorporation into structural finite element programs. The aim of this paper is to illustrate some important issues of pipeline on-bottom stability and highlight alternate results using the integrated force-resultant modeling approach. It is hoped that these analysis results will provide offshore pipeline designers with additional insight into this complex wave-structure-soil interaction problem.