Pressure Dissipation Research Articles

Mathematical characterization of pile–soil interface boundary for consolidation analysis of soil around permeable pipe pile

A permeable pipe pile is proposed to accelerate the dissipation of excess pore-water pressure through drainage holes around the pile circumference into the pile’s cavity. This investigation generalizes the permeable pile–soil interface as an impeded boundary, based on which a mathematical model for soil consolidation around the permeable pile is derived. Subsequently, the influence of opening pattern, drainage hole-to-pipe pile radius ratio, and opening ratio on the consolidation efficiency is numerically investigated. A total of 240 numerical cases with different drainage hole-to-pipe pile radius ratios, opening ratios, and hydraulic conductivity ratios are calculated to determine the permeable pile–soil interface parameter using back-analysis, and an approximate expression for interface parameter is obtained. Comparing against experimentally measured excess pore-water pressure dissipation, the proposed technique with impeded drainage boundary can provide good evaluations for drainage characteristics at the permeable pile–soil interface and consolidation behavior of the surrounding soil. It is found that the spatial distribution pattern of drainage holes has negligible influence on the consolidation efficiency. Increasing the opening ratio (with constant opening size) or reducing the drainage hole-to-pipe pile radius ratio (with constant opening ratio) can both accelerate the consolidation efficiency.

Thermal Consolidation Theory

This study presents an analytical formulation to predict the generation and dissipation of thermal pore pressures and volumetric strains in low permeability soils. The developed relations facilitate mimicking the transient nature of the thermal loads applied to energy geostructures overcoming the commonly adopted assumptions of fully drained or undrained conditions. This theoretical model relies on coupling Darcy’s law with relations predicting the thermal volumetric strains in soils. The developed relations were validated against experimental results under different conditions (e.g., heating rates, confining stresses, and stress states), showing good agreement between the predicted and the experimental results. The developed relations were then used to explain why the maximum thermal pore pressures at the bottom of the tested specimens were observed before the specimen temperature reaches its maximum. Finally, a sensitivity analysis was performed to identify the significance of various parameters to the thermal consolidation process.

Application of Constant Rate of Strain Tests in Consolidation Analysis of the Band-Shaped Prefabricated Vertical Drains for Vietnam Clays: The Validation Analysis

Band-shaped prefabricated vertical drains in the combination of surcharge preloading have been widely applied in the soft ground improvement cases in Vietnam to eliminate the post-construction settlement of the ground. However, the method of the settlement prediction has remained incorrect on the comparison between the field and calculation. A new procedure for consolidation analysis is proposed to determine the ground settlement more accurately in the routine design of the soft ground improvement. Two case studies are presented to study the ground performance under consolidation with surcharge preloading. The consolidation analysis of the soft ground deposits with the application of the constant rate of strain (CRS) consolidation tests is performed. In addition to that, the input parameters as the coefficient of consolidation and compression indices of the soft ground are characterized based on the CRS tests under the strain rate of 0.02%/min. on undisturbed soil samples that are taken at the two sites by stationary piston sampler. On the comparison of calculated and field monitored data of surface settlement, layered settlement, dissipation of the excess pore water pressure, and undrained strength gain, this analysis is also to confirm the appropriate strain rate for CRS tests, which are utilized in the determination of consolidation parameters.

Characteristic parameters and process maps for fully-filled twin-screw extruder elements

The shape and form of twin-screw extruder elements determine the physical conditions under which the material is processed. In this work, we investigated the pressure build-up, power consumption, dissipation and distributive mixing behavior of fully filled extruder elements via Smoothed Particle Hydrodynamics simulations, covering a wide range of conveying, kneading and mixing elements used in the ZSE12, ZSE18 and ZSE27 pharma extrusion equipment series. As a result, a comprehensive parameter catalogue of characteristic values was computed. These parameters allow studying the pressure build-up, power consumption and mixing behavior for all elements under various operating conditions. Additionally, we show novel process maps which support optimizing the length of a process zone. Properly used, the catalogue can assist a rational selection of screw elements during process design and transfer.

One-Dimensional Consolidation Analysis of Saturated Soft Clay Based on Water Content Variation

The degree of consolidation is an important parameter to evaluate the stability and consolidation effect of soft soil foundation. The degree of consolidation calculated by deformation often overestimates the actual degree of consolidation of soil, resulting in a large post construction settlement. To accurately reflect the actual consolidation degree of soil, based on Terzaghi’s consolidation theory, this paper considers that the deformation amount to soil is equal to the volume of water discharged from the soil pores, and theoretically deduces the calculation method of soil consolidation degree with water content. The one-dimensional consolidation test was carried out by improving the test instrument. The results show that the degree of consolidation calculated by water content is smaller than that calculated by deformation in the same time. The pore pressure is calculated by inversion of the consolidation coefficient, which is close to the value of the pore pressure monitored by the test. It is found that there is a linear relationship between pore ratio and pore pressure (u). When the pressure is large, the e-lgu curve is approximately linear, and its slope can be used as an indicator to evaluate the difficulty of pore pressure dissipation. The research results have a certain theoretical value for revealing the consolidation change and development of soft clay.

3D Numerical Analyses of Column-Supported Embankments: Failure Heights, Failure Modes, and Deformations

Design of column-supported embankments (CSE) requires the evaluation of global stability using the conventional limit equilibrium method (LEM). Yet, for CSEs using unreinforced concrete columns and load transferring geogrids, the failure mechanisms and corresponding soil-structure interactions are not well understood. There is increasing evidence pointing to large bending moments in columns and failure of columns in flexure, as opposed to a failure by shear as assumed in limit equilibrium analyses. In response to these design uncertainties, the failure height, failure mode, and deformations of eight column-supported embankment scenarios were investigated using three-dimensional (3D) numerical analyses. For the same embankment scenarios at failure height, factors of safety (FS) were then calculated using the two-dimensional (2D) LEM for investigating its applicability in evaluating global stability of CSEs. The 3D numerical analyses examined CSE stability for the limiting conditions at undrained end-of-construction and after long-term dissipation of excess pore water pressures. The numerical model included representations of flexural tensile failure in the concrete columns and tensile failure in the geosynthetic reinforcement. Scenarios consisted of a base case with typical concrete column design, five single-parameter variations using base case conditions, and two multiparameter variations using base case conditions. The undrained condition was the most critical, and two failure modes were found: (1) multisurface shearing in the embankment coupled with bending failure of columns and near-circular shear failure in the clay, and (2) multisurface shearing in the embankment coupled with bending failure of columns and shearing in the upper portion of the soft foundation clay. Both failure modes were accompanied by a rupture of the geosynthetic when included in the load transfer platform. Soil-column interactions were complex, and many columns failed in bending at lower embankment heights than those that produced collapse. The factors of safety calculated using the LEM were overstated. This is because the LEM assumes failure by shear, which has limited applicability for examining the complex mechanisms by which CSEs fail. The practical implication is that the LEM should not be used for evaluating global stability of this system type and, by extension, other system types in which soil-structure interactions result in failures controlled by mechanisms other than shear.

Influences on Liquefaction-Induced Damage of Pore Water Seepage into an Unsaturated Surface Layer

Various studies have examined soil liquefaction and the resultant structure damage. The 1995 Southern Hyogo Prefecture Earthquake, a near-field earthquake, caused significant damage when the ground was liquified due to the rapidly increased pore water pressure in several cycles of major motions. Therefore, the effect of pore water movement during earthquakes has been assumed to be limited, and liquefaction has mainly been evaluated in undrained conditions. Additionally, the ground and building settlement or inclination caused by liquefaction are deemed to result from pore water drainage after earthquakes. Meanwhile, in the 2011 Tohoku Earthquake, off the Pacific Coast, a subduction-zone earthquake, long-duration motions were observed for over 300 s with frequent aftershocks. Long-duration motions with frequent aftershocks are also anticipated in a future Nankai Trough Earthquake. The effect of pore water movement not only after but during an earthquake should be considered in cases where pore water pressure gradually increases in long-duration motion. The movement of pore water during and after an earthquake typically results in simultaneous dissipation and buildup of water pressure, as well as volumetric changes associated with settlement and lateral spreading. Such effects must reasonably be considered in liquefaction evaluation and building damage prediction. This research focuses on pore water seepage into the unsaturated surface layer caused by the movement of pore water. Seepage experiments were performed based on parameters such as height of test ground, ground surface permeability, and liquefaction duration. In the tests, water pressure when the saturated ground below the groundwater level is fully liquified was applied to the bottom of the specimen representing an unsaturated surface layer. Seepage behaviors into the unsaturated surface layer were then evaluated based on the experiment data. The results show that the water level rises due to pore water seepage from the liquefied ground into the unsaturated surface layer right above the liquefied ground. For this reason, a ground shallower than the original groundwater level can be liquified.

Peak-shift Optimization Model and Pricing Strategies of Power Trading System in Bay Area

Zhu, W.; Gu, H.J.; Zhou, H.F.; Nie, Y.Q.; Peng, C.Y., and Xu, D.L., 2020. Peak-shift optimization model and pricing strategies of power trading system in bay area. In: Al-Tarawneh, O. and Megahed, A. (eds.), Recent Developments of Port, Marine, and Ocean Engineering. Journal of Coastal Research, Special Issue No. 110, pp. 34–37. Coconut Creek (Florida), ISSN 0749-0208.The rapid economic development in coastal areas is inseparable from the support of the power trading system. It also poses increasing demands for the power, which results in obvious peaks and troughs in daily power consumption, and causing distribution pressure and power dissipation of the transmission network. Based on the power trading model in Daya Bay area, this paper explores the peak shift optimization model in this coastal area, and establishes a new power trading model to eliminate the impact of power grid monopoly on electricity prices. The results show that the orderly power use in the bilateral trading model can effectively alleviate peak problems in the power trading system; pricing of power system cannot use market bidding, and it must be conducive to the development of high-voltage or ultra-high-voltage power, and also optimized investment by grid companies. The research findings provide a theoretical basis for the realization of power trading between supply and marketing parties.

Effect of tamping interval on consolidation of dredged slurry using vacuum preloading combined with dynamic consolidation

The effect of combining vacuum preloading and low-energy dynamic consolidation is predominantly controlled by the tamping interval time. It is, therefore, imperative to identify a suitable parameter and optimise the tamping interval time. In this study, the effect of the tamping interval time on the consolidation of slurries was investigated by conducting laboratory model tests. Consequently, various tamping interval times were obtained by controlling the dissipation of pore water pressure at different levels of 20%, 40%, 60%, 80%, and 100% to determine the optimal interval time. In terms of surface settlement variation, dissipation of pore water pressure, and distributions of the water content and shear strength variation profile, it was shown that a rubber soil state was reached at a dissipation rate of 20% pore water pressure. When the tamping interval time was set to a dissipation rate of 80% pore water pressure, the consolidation effect was optimal.

Numerical prediction of settlement due to the Pohang earthquake

On 15 November 2017, an earthquake with a magnitude of 5.4 caused geotechnical damage over a wide area of Pohang, South Korea. In this study, the UBCSAND constitutive effective stress model is calibrated by cyclic direct simple shear (CDSS) tests conducted on a type of sand from liquefied paddy fields at Pohang under confining stresses of 100 and 200 kPa. The calibrated UBCSAND model is then used to assess the liquefaction and calculate the ground settlement based on standard penetration test (SPT) data near the epicenter of the Pohang earthquake. The liquefaction characteristics from the UBCSAND model matched those from laboratory tests. According to the numerical results, liquefaction mostly occurred within the uppermost 10 m, and ground surface settlement from excess pore water pressure dissipation varied from 3.86 to 10.95 cm. These settlements were higher than the surface displacement estimated by satellite image analysis with interferometric synthetic aperture radar (InSAR) and lower than the ground subsidence observed solely by visiting the sites.

A method to convert stand-alone OH fluorescence images into OH mole fraction

Due to the accessibility of the planar laser-induced fluorescence technique, images of OH fluorescence intensity are often used to study the structure of turbulent flames. However, there are differences between the measured OH fluorescence intensity and the actual OH mole fraction. These are often neglected because accurate conversion from fluorescence to mole fraction requires the combined knowledge of all major species mole fractions and temperature, which was rarely achieved in 2-D. Here, a new method to convert images of OH fluorescence intensity into OH mole fraction is proposed. This model relies only on inexpensive 1-D laminar flame calculations and does not require information on major species or temperature. The primary assumption behind the applicability of this model is the local approximation of multi-dimensional flames with 1-D counterflow flames. The method utilizes the fact that both OH mole fraction and OH fluorescence intensity profiles are self-similar with pressure and scalar dissipation rate. Only two empirical constants need to be calibrated using 1-D laminar flame calculations. The model was validated using computed 2-D axisymmetric laminar flames and 3-D turbulent flames computed with LES. The accuracy of the conversion model was estimated to about 8% (for Reynolds number up to Re =66,800), which includes errors due to the 3-D effects that are not included in this method relying on 2-D images. As a proof of concept, the conversion model was finally applied to one single-shot image of OH fluorescence intensity measured with OH-PLIF for syngas at P=4bar and Re =16,700, demonstrating potential applications of this new method. The method was tested for hydrogen, syngas and methane fuels but, for brevity, only syngas results are reported in detail.

Partially drained cyclic behaviour of granular fill material in triaxial condition

The dynamic responses of granular materials subjected to cyclic loading under partially drained condition were seldom investigated, though the partially drained condition is commonly existing for the granular materials that locate nearby the drainage boundaries. Besides, the prevalent studies mainly focus on the liquefaction behaviour of granular materials under high stress levels. In this study, a granular fill material was chosen as testing material. A series of partially drained cyclic triaxial tests was conducted with low level of cyclic loading and high cycle number that are commonly experienced in the geostructures of transportation projects. Note that the cyclic triaxial test under partially drained condition is a model test rather than an element test since the distribution of excess pore water pressure is not homogeneous inside the specimen. The test results show that cyclic loading induces the reconstruction effect on the microstructure of the specimen, thereby changing the trend between permeability and void ratio. Under partially drained condition, the granular fill material normally experiences a sudden decrease of stiffness and a quick increase in deformation during the first cycles of loading, followed by gradually decreasing excess pore water pressure and stabilizing deformation. Importantly, the deformation response of the material can be contributed by two items: (a) that caused by densification effect of applied cyclic loading and (b) that due to the dissipation of excess pore water pressure. Two linear relationships were established to correlate the deformations with excess pore water pressure and applied cyclic loading.

Comparison of undrained behaviors of granular media using fluid-coupled discrete element method and constant volume method

The fluid-coupled discrete element method (DEM) and the constant volume method as two types of discrete modeling methods for fundamental study of undrained responses of granular materials, have been discussed by many researchers. The fluid-coupled DEM, which couples the motions of discrete particles with pore fluid movements, is theoretically robust although it requires a large amount of computation time. As a substitution for the complex fluid-coupled DEM, the constant volume method simulates an undrained condition for a saturated granular material by simply preserving the total volume of a granular assembly without considering interactions between fluids and particles; hence, the validity of its results is questionable. In this paper, the undrained behaviors of granular assemblies simulated using the aforementioned two methods are compared. Based on a comparison of both macroscopic and microscopic responses given by the two methods, it is demonstrated that the constant volume method may reasonably simulate the responses of a loose saturated granular material with very coarse grains, which has a high permeability, and thus a rapid pore pressure equalization. However, it is ineffective in simulating the responses of a loose material with fine components due to its failure to capture the process of a slow dissipation of the excess pore pressure among the individual pores. With regard to the dense material adopted, similar behaviors at the early and intermediate shearing stages given by the two methods are displayed.

Shear strength and failure mechanism of needle-punched geosynthetic clay liner

The internal shear strength of a geosynthetic clay liner (GCL) within composite liner systems is crucial for the stability of landfills and should be carefully considered in the design. To explore the shear strength and failure mechanism of the extensively used needle-punched GCL, a series of displacement-controlled direct shear tests with five normal stress levels (250–1000 kPa) and eight displacement rates (1–200 mm/min) were conducted. The shear stress to horizontal displacement relationships exhibit well-defined peak shear strengths and significant post-peak strength reductions. The monitoring results of the thickness change indicate that the degree of volumetric contraction is related to the reorientation of fibers and dissipation of pore water pressure. Furthermore, the peak and residual shear strengths both depend on the displacement rate because of the rate-dependent tensile stiffness of needle-punched fibers and shear strength of the soil/geosynthetic interface. Through additional tests and lateral comparison, it was discovered that the shear behavior of sodium bentonite, degree of hydration, and pore water pressures all affect the shear mechanisms of the NP GCL. In particular, the failure mode transfers from fiber pullout to fiber rupture with the increase in water content as the hydrated bentonite particles facilitate the stretching of needle-punched fibers.

Liquefaction resistance of fibre-reinforced silty sands under cyclic loading

Whether the so-called double porosity in soils with a loose and natural packing state is a concept with real-world implications is a fundamental yet controversial question in the study of cyclic undrained shear behaviour of fibre-reinforced silty sands. An attempt is made here to clarify the question by means of particle-level modelling combined with 41 undrained cyclic triaxial shear tests. The study shows that the initial Random Loose Packing changes to Random Close Packing and then Close Packing with silt content increments. The transition from random to close packing occurs at a threshold silt content which is relatively lower in coarser sands. For sands with <40% silt content, the rate of pore pressure growth with loading-unloading cycles increase with silt content increment. Reverse trend applies to silty sands with >40% silt content. Irrespective of fine content, fibres tend to sit deep into the silt pellets and encrust the macro-pore spaces. Generally, increasing fibre content leads to an increase in the average number of contacts per particle, dilation and easier dissipation of excess pore water pressure, a decrease in contact forces and improved liquefaction resistance. For sands with >40% silt content, effectiveness of fibre reinforcement diminishes with increasing sand median size.

CFD-Based Framework for Analysis of Soil–Pipeline Interaction in Reconsolidating Liquefied Sand

Submarine buried pipelines interact with shallow soil layers that are often loose and prone to fluidization/liquefaction. Such occurrence is a possible consequence of pore pressure build-up induced by hydrodynamic loading, earthquakes, and/or structural vibrations. When liquefaction is triggered in sand, the soil tends to behave as a viscous solid–fluid mixture of negligible shear strength, possibly unable to constrain pipeline movements. Therefore, pipelines may experience excessive displacement, for instance, in the form of vertical flotation or sinking. To date, there are no well-established methods to predict pipe displacement in the event of liquefaction. To fill such a gap, this work proposes a computational fluid dynamics (CFD) framework enriched with soil mechanics principles. It is shown that the interaction between pipe and liquefied sand can be successfully analyzed via one-phase Bingham fluid modeling of the soil. Postliquefaction enhancement of rheological properties, viscosity, and yield stress can also be accounted for by linking soil–pipe CFD simulations to a separate analysis of the pore pressure dissipation. The proposed approach is thoroughly validated against the results of small-scale pipe flotation and pipe dragging tests from the literature.

Controlling the Permeability of Sandy Soil Using Different Local Waste Materials

Advanced developed technologies associated with people demands have caused production and expansion of different local wastes where the process of managing such waste becomes a real need for controlling the pollution risk. One of the procedures for recycling can be made through using local wastes in permeability control for sandy soil since the soil permeability plays a crucial function on the water drainage, pore water pressure buildup and dissipation, and ground movement for saturated sand during and after earthquake occurrences. In addition, any economical mixture should maintain hydraulic constraints for practice use. In this study, a laboratory experiment was prepared to perform tests for estimating the water movements and permeability in a pure sand column and treated sandy soil with different locally waste materials including plastic, glass, rubber, and aluminum. In addition, a numerical investigation including finite element method has been adopted to verify the experimental procedure. It was shown that the permeability could be controlled to different rates using these local wastes.

Spatiotemporal Variations of Mesoscale Eddies in the Southeast Indian Ocean

AbstractStrong eddy activities exist in the Leeuwin Current (LC) and the South Indian Countercurrent (SICC) systems. Through a detailed investigation based on satellite observations, we find a cyclonic preference for eddies with more frequent genesis, longer lifespan, smaller size and stronger intensity in both systems. The evolutions of amplitudes, radii and total vorticities of eddies can be classified as the generation, stable, and decay stages; however, those of the EKE and relative vorticities lack the stable stage, due to planetary vorticity changes related to the meridional deflections, as eddies drift westward. Eddy properties exhibit significant seasonal and interannual variations. In the LC system, more and stronger eddies tend to be generated in winter and in La Niña years; while in the SICC system, eddy properties generally reach their peaks in spring and in years when the negative Southern Annular Mode (SAM) occurs. And eddy intensities in the SICC system are also modulated by ENSO with about a one‐year phase lag. Through instability analysis, we find that baroclinic instability is the most dominant contributor to the development of eddies. By contrast, barotropic instability mainly acts to dampen eddies. Advection of EKE makes almost no net contribution when spatially averaged, although it is locally significant. Pressure work and dissipation may be nonnegligible EKE sinks in the LC system. The EKE variations in these two systems have close connections through the westward‐propagating baroclinic instability anomalies, which may explain the phase lags between these two systems.

Consolidation effects on monotonic and cyclic capacity of plate anchors in sand

This study investigated the change in monotonic and cyclic capacity of a plate anchor across different degrees of consolidation in dense sand. To quantify the effect of consolidation on anchor capacity, a framework is introduced and validated using centrifuge model anchor test data. The centrifuge tests considered a rectangular plate loaded at varying rates in dense sand, under both monotonic and irregular cyclic conditions, at a fixed embedment depth and with a horizontal load inclination (at the seabed). In order to vary from drained to undrained conditions, the sand was saturated using both water and a viscous pore fluid with viscosity approximately 700 times higher than water. The anchor's ultimate monotonic capacity in dense sand increased by up to 173% as the consolidation response evolved from drained to undrained with generation of dilation-induced suction. This increase in capacity across the consolidation regime can be adequately quantified using the proposed framework; however, uncertainty arises in achieving the theoretical undrained capacity. Both drained and undrained irregular cyclic loading resulted in anchor capacity increases of up to 33%, attributed to soil volume changes associated with cyclic densification under drained cyclic loading and excess pore pressure dissipation under undrained cyclic loading.

A multilateral analysis of slope failure due to liquefaction-induced lateral deformation using shaking table tests

Liquefaction-induced lateral displacement can cause substantial deformations and trigger failure in the saturated sandy slopes. This study elaborates on the results of a shaking table experiment performed on a saturated sandy slope model. A transparent Plexiglass container was used to allow visualization of the time-dependent ground displacements at different grid points. Using colored sand grid along with the video-tracking analysis technique provided an excellent opportunity for instant monitoring of the model deformation in both the time and space domains. Furthermore, the pore pressure buildup and dissipation in the soil medium and acceleration time histories of the model were recorded and analyzed. Detailed and comprehensive analyses of the high-resolution recorded data streams resulted in the determination of the onset of liquefaction and the induced subsidence, acceleration response, deformation behavior, and shear strain progress through time and depth at different slope sections. It was also found that the shear strain rate was different in the on-slope and free field locations, and its value was proportional to the liquefaction duration. It was also observed that the variation of the shear strain rate at different depths in the free field led to a localized sliding event.