Browsing by Author "Tsuha, Cristina de H. C."
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Item Advanced Laboratory Investigation of Axial Cyclic Loading in Silica Sands(2015) Tsuha, Cristina de H. C.; Jardine, Richard J.; Yang, Zhongxuan X.; Silva, M.; Rimoy, Siya P.This paper describes the global behaviour of and local stress conditions applying to highly instrumented cyclic laboratory model displacement pile tests conducted in a calibration chamber on medium dense Fontainebleau NE34 sand. The instrumentation provided measurements of the contact stresses on the jacked pile shaft and the local vertical, radial and circumferential stresses in the surrounding soil mass, in tests involving a range of cyclic load amplitudes. The patterns of effective stress developing on and around the pile shaft are described. The data obtained are interpreted by reference to cyclic soil element tests conducted on the same soil, as described in the parallel investigation by Aghakouchak et al (2015), reported in the same symposium. The calibration chamber experiments offer a comprehensive understanding of the cyclic degradation processes, and provide key information for improving the design of piled foundations under cyclic loading.Item Análisis De La Interacción Cíclica Arena-Pilote Bajo Cargas Axiales En Cámara De Calibración(2015) Silva, M.; Foray, P. Y.; Tsuha, Cristina de H. C.; Yang, Zhongxuan X.; Jardine, Richard J.; Rimoy, Siya P.El análisis de la distribución de tensiones a lo largo de un pilote modelo sometido a cargas axiales estáticas y cíclicas en una cámara de calibración es presentado. Una alta instrumentación permite estudiar en detalle las interacciones a nivel de la interfaz arena/pilote. Detallamos los mecanismos que controlan el mejoramiento o degradación en la capacidad de pilotes según la amplitud y tipo de cargas cíclicas aplicadas. Se introduce un nuevo diagrama de estabilidad cíclica.Item Behaviour of Displacement Piles in Sand under Cyclic Axial Loading(Elsevier, 2012) Tsuha, Cristina de H. C.; Foray, P. Y.; Jardine, R. J.; Yang, Zhongxuan X.; Silva, M.; Rimoy, Siya P.Field experiments have demonstrated that piles driven into sand can respond to axial cyclic loading in Stable, Unstable or Meta-Stable ways, depending on the combinations of mean and cyclic loads and the number of cycles. An understanding of the three styles of responses is provided by experiments involving a highly instrumented model displacement pile and an array of soil stress sensors installed in fine sand in a pressurised calibration chamber. The different patterns of effective stress developing on and around the shaft are reported, along with the results of static load tests that track the effects on shaft capacity. The interpretation links these observations to the sand's stress–strain behaviour. The interface-shear characteristics, the kinematic yielding, the local densification, the growth of a fractured interface-shear zone and the restrained dilatancy at the pile–soil interface are all found to be important. The model tests are shown to be compatible with the full-scale behaviour and to provide key information for improving the modelling and the design rules.Item Field and Model Investigations into the Influence of Age on Axial Capacity of Displacement Piles in Silica Sands(2015) Rimoy, Siya P.; Silva, M.; Jardine, Richard J.; Yang, Zhongxuan X.; Zhu, B. T.; Tsuha, Cristina de H. C.The axial capacities of piles driven in silica sands are known to grow over the months that follow installation, long after all driving-induced pore pressures have dissipated. However, there is uncertainty over the processes that govern the observed setup and how they may vary from case to case. This paper evaluates three hypotheses against evidence from updated field test databases and laboratory investigations with highly instrumented and pressurised model piles. Potential influential factors are considered including: pile and sand particle sizes, installation style, access to free water, test conditions and external stress change cycles. Laboratory local stress measurements support the hypothesis that moderation, over time, of the extreme stress distributions developed during installation is a key contributor to capacity growth, while field tests confirm the action of enhanced dilation near the shaft. However, field and laboratory piles show paradoxically different ageing trends. The paper proposes that the fractured but compacted sand shear zone that forms around pile shafts during installation leads to setup being far more significant with large field driven piles than in model tests.Item Local and Global Behaviour of Axial Cyclic Loaded Instrumented Model Displacement Piles in Sand(Society of Underwater Technology, 2012) Rimoy, Siya P.; Jardine, Richard J.; Tsuha, Cristina de H. C.; Yang, Zhongxuan X.This paper describes the first phase of an extensive campaign of axial cyclic loading tests performed on intensively instrumented displacement piles installed in large pressurised calibration chamber. The chamber was filled with medium dense silica sand that combined measurements of the effective stress paths developed along the pile shaft and within the sand mass at different distances from the shaft. The paper also outlines the evolution of the local interface effective stress paths during cyclic loading. Three different styles of cyclic response – stable, metastable and unstable – are identified and linked to the global degree of cyclic stability. Increases or decreases in shaft capacity induced by cycling can be related to the cyclic loading parameters and to the local mechanical behaviour of the pile-sand interface and the sand mass. The second phase of testing, which involves many more cyclic experiments, is currently underway.