Acoustic emission (AE) technique that is capable of diagnosing the failure process of stressed materials has rarely reported its application to sandy soils subjected to triaxial compression. In this paper, drained triaxial compression tests incorporating with a high-performance AE measurement system were conducted for dry sands with different confining stresses and initial relative densities. Generally, an increased confining stress or initial relative density generates more acoustic emissions, while there also exist exceptions due to different failure patterns. A good resemblance between stress–strain and AE hit rate–strain relations was observed, and power functions between the mechanical parameters and AE hit rate were well established regardless of different confining stresses and initial relative densities. Besides, the behavioral state of yield and peak during compression could be also evaluated by AE hit rate, compared with conventional stress–strain determination. Particularly, the peak AE hit rate is found not always synchronous to but fluctuating at around the peak stress depending on different failure patterns, which might provide beneficial insights into the incipient failure of sands. The present good consistencies suggest that AE characteristics could be used as alternative parameters to evaluate and even predict the mechanical behavior of dry sands.
Liquefaction-induced ground deformation is a major cause of structural damage during earthquakes. However, a better understanding of seismic liquefaction is needed to improve earthquake hazard analyses and mitigate structural damage. In this paper, a dynamic triaxial test apparatus was employed to investigate the fluidic characteristics of post-liquefaction sand. The specimens were vibrated to the point of liquefaction by dynamic loading, and then the liquefied sand was further sheared by triaxial compression in an undrained manner. It was found that a non-Newtonian fluid model can accurately describe the shear stress and the shear strain rate of post-liquefaction sand during undrained triaxial compression. The apparent viscosity, a major parameter in a constitutive model of a non-Newtonian fluid, decreases with an increase in the shear strain rate. 相似文献
A new type of insoluble potassium ore, newly found in North China, consists of microcline, dolomite, and pyroclastic particles of silty to clayey grade, falling into potassic dolomitic mudstone in petrological no-menclature. The geological surveys and explorations of the deposit by the Tianjin Bureau of Geological Survey evidenced that the main bodies of the potas-sium deposit elongated up to 1600 m with an average thickness about 85 m, and the concentration of potas-sium as K2O was around 1… 相似文献
Particle breakage is a common occurrence in granular systems when the external stress exceeds the individual particle strength.A large number of experimental evidences suggested that particle breakage may significantly influence the soil behavior.In the case of pile foundations,the subsoil below the pile tip experiences considerable high stress and consequently prone to break.Due to the lack of sufficient understanding on particle breakage mechanism,there is currently no consentaneous theoretical background for particle breakage analysis during the pile penetration process.This study aims to clarify the location of particle breakage and its evolving characteristics with the aid of acoustic emission(AE)source location method.The spatial distribution of AE hypocenters is interpreted to be associated with the mechanism of particle breakage.Results showed that the AE sources were not uniformly distributed,but concentrated within certain zones below the pile tip.This AE concentration zone was pushed downward with the advancing pile tip,and its distance from the real time pile tip position decreased after certain depth of pile penetration.The location of particle breakage interpreted from AE source location was verified with posttest excavations and the insights on the particle breakage evolution zone were further discussed. 相似文献
Because of the low-gravity on the Moon and Mars, landslides there have characteristics that are very different from those observed in a conventional gravity environment. These include highly marked dynamic characteristics, evidence of fierce movement at high speed and on a large scale. One of the key problems in extra-planetary exploration is understanding the behavior of granular material flows under the influence of low gravity. A drop-tower testing system situated in Beijing has been developed and used to investigate granular flow in a microgravity environment. A set of granular flow tests was performed in both normal and microgravity environments, during which the configurations of sand flows were captured by the monitoring system. Preliminary results provide fundamental information for the future exploration of planetary landscapes. 相似文献
Soil flow and induced air blasts are of great harm to humanity, and historically they have caused a lot of damage to infrastructure.
However, these phenomena cannot be described by traditional analog modeling methods that limit their use in disaster prevention
efforts. Computational fluid dynamics (CFD) is an applied technique commonly used in a range of fields including the chemical
industry, and aircraft and automobile manufacturing, but little is reported on the use of this method to simulate flowing
soil in geotechnical engineering applications. The CFD method can effectively make up for the deficiency of normal calculation
methods in the analysis of soil flow and air blasts. This paper uses the FLUENT (version 6.3) CFD calculation software to
simulate the processes of soil flow and induced air blast changes during soil flow with an Eulerian air–soil two-phase model
included in a standard k-ε turbulence model. Velocity vectors of air blasts at different times during soil flow are obtained, and the characteristics
of turbulent flow can be found based on the velocity vectors. The numerical simulation techniques adopted in this paper captured
precise configurations of soil flow. The results show that the CFD method is especially suitable for simulating the process
of soil flow; hazard assessments can be implemented, and the performance of structures involved with disaster prevention can
be improved based on the numerical simulation of changing air blasts. 相似文献