Dynamic Pore Research Articles

Wicking through complex interfaces at interlacing yarns

HypothesisWicking flow in the wale direction of knit fabrics is slowed by capillary pressure minima during the transition at yarn contacts. The characteristic pore structure of yarns leads to an unfavorable free energy evolution and is the cause of these minima. ExperimentsTime-resolved synchrotron tomographic microscopy is employed to study the evolution of water configuration during wicking flow in interlacing yarns. Dynamic pore network modeling is used based on the obtained image data and distributions of delay times for pore intrusion. Good agreement is observed by comparison to the experimental data. FindingsYarn-to-yarn transition is found to coincide with slow water advance in a thin interface zone at the yarn contact. The pore spaces of the two yarns merge within this interface zone and provide a transition path. A deep capillary pressure minimum occurs while water passes through the center of the interface zone, effectively delaying the wicking flow. A pore network model considering pore intrusion delay times is expanded to include inter-yarn wicking and reproduce the observed wicking dynamics.

Experimental Study on the Evolution of Dynamic Pore Pressure and Unidirectional and Bidirectional Vibrations of Phosphogypsum

Under seismic action, the stock of phosphogypsum (PG) affects the security risk significantly, so it is crucial to study the dynamic characteristics of PG. In this article, unidirectional and bidirectional vibration tests on typical PG in Yunnan under different consolidation-confining pressure and vibration conditions were carried out using a dynamic triaxial apparatus that can be used for bidirectional vibration. The results show that the pore pressure growth of PG under both unidirectional and bidirectional vibrations has obvious stages and can be fitted by the BiDoseResp function. The dynamic strength of PG does not increase monotonically with the increase in consolidation-confining pressure and dynamic stress under the same cyclic stress ratio (CSR) but varies under a specific critical condition. The dynamic strength of PG decreases significantly with the increase in CSR under unidirectional and bidirectional vibrations. The number of vibrations required for liquefaction by bidirectional vibrations is much larger than that by unidirectional vibrations under the same CSR conditions, and the specimens have significant softening characteristics after liquefaction by bidirectional vibrations. The study results can provide theoretical references for studying the dynamic stability of PG reservoirs under seismic action.

Modeling of a non-aqueous Li-O2 battery incorporating synergistic reaction mechanisms, microstructure, and species transport in the porous electrode

Li-O2 batteries are considered to be the next generation of new energy storage technology due to the extremely high theoretical energy density. The microstructure of the porous electrode takes an important role in the battery performance since the solid discharge product Li2O2 occupies the surface and void volume, increasing the transfer resistance. The product morphology and reaction mechanisms are affected by the electrode catalytic activity, electrolyte, and operating conditions. To systematically portray the microscopic processes in non-aqueous Li-O2 batteries, a model by coupling the above multiple factors is developed in this work. Unlike previous models where a single surface pathway or pore size distribution is considered alone, the present model focus on the interdependence of the reaction mechanisms and the electrode microstructure evolution, in which the reaction pathways are controlled by dynamic pore size. Moreover, the effective species transport relationship is modified, and the volume fraction and the corresponding active area of the products with different morphologies are calculated. The simulation results demonstrate the significant effects of microstructure on performance and explain the phenomenon of two discharge platforms, which comes from the tortuous variation of the electrode active area and are further influenced by current density and oxygen diffusion coefficient. This work is expected to guide the design of electrode structures and operating conditions for achieving improved performance.

The Co-Moving Velocity in Immiscible Two-Phase Flow in Porous Media

We present a continuum (i.e., an effective) description of immiscible two-phase flow in porous media characterized by two fields, the pressure and the saturation. Gradients in these two fields are the driving forces that move the immiscible fluids around. The fluids are characterized by two seepage velocity fields, one for each fluid. Following Hansen et al. (Transport in Porous Media, 125, 565 (2018)), we construct a two-way transformation between the velocity couple consisting of the seepage velocity of each fluid, to a velocity couple consisting of the average seepage velocity of both fluids and a new velocity parameter, the co-moving velocity. The co-moving velocity is related but not equal to velocity difference between the two immiscible fluids. The two-way mapping, the mass conservation equation and the constitutive equations for the average seepage velocity and the co-moving velocity form a closed set of equations that determine the flow. There is growing experimental, computational and theoretical evidence that constitutive equation for the average seepage velocity has the form of a power law in the pressure gradient over a wide range of capillary numbers. Through the transformation between the two velocity couples, this constitutive equation may be taken directly into account in the equations describing the flow of each fluid. This is, e.g., not possible using relative permeability theory. By reverse engineering relative permeability data from the literature, we construct the constitutive equation for the co-moving velocity. We also calculate the co-moving constitutive equation using a dynamic pore network model over a wide range of parameters, from where the flow is viscosity dominated to where the capillary and viscous forces compete. Both the relative permeability data from the literature and the dynamic pore network model give the same very simple functional form for the constitutive equation over the whole range of parameters.

Implications of Receiver Plane Uncertainty for the Static Stress Triggering Hypothesis

Static stress transfer from major earthquakes is commonly invoked as the primary mechanism for triggering aftershocks, but evaluating this mechanism depends on aftershock rupture plane orientations and hypocenter locations, which are often subject to significant observational uncertainty. We evaluate static stress change for an unusually large data set comprising hundreds to thousands of aftershocks following the 1997 Umbria-Marche, 2009 L’Aquila (Italy), and 2019 Ridgecrest (California) earthquake sequences. We compare failure stress resolved on aftershock focal mechanism planes and planes that are optimally oriented (OOPs) in the regional and earthquake perturbed stress field. Like previous studies, we find that failure stress resolved on OOPs overpredicts the percentage (>70%) of triggered aftershocks relative to that predicted from observed aftershock rupture planes (∼50%–65%) from focal mechanisms solutions, independent of how nodal plane ambiguity is resolved. Further, observed aftershock nodal planes appear statistically different from OOPs. Observed rupture planes, at least for larger magnitude events (M > 3), appear to align more closely with pre-existing tectonic structures. The inferred observational uncertainty associated with nodal plane ambiguity, plane orientation, and, to second order, hypocentral location yields a broad range of aftershocks potentially triggered by static stress changes, ranging from slightly better than random chance to nearly any aftershock promoted, particularly those further than 5 km from the causative fault. Dynamic stresses, afterslip, pore fluids, and other sources of unresolved small-scale heterogeneity in the post-mainshock stress field may also contribute appreciably to aftershock occurrence closer to the mainshock.

Failure Mechanism and Dynamic Response Characteristics of Loess Slopes Under the Effects of Earthquake and Groundwater

A large-scale shaking table test was conducted with simulated earthquakes and groundwater to study the dynamic response and instability mechanism of a loess slope with a saturated bottom. By examining the acceleration, dynamic pore water pressure, corresponding soil pressure and observed macroscopic failure behaviour of the slope under different shaking intensities, the dynamic responses of acceleration and pore water pressure of the loess slope were analysed. By comparing the time history curve of acceleration with the time history curves of pore water pressure and surrounding soil pressure, we found that the instability failure of the slope was first due to the continuous vibration that caused the local structure of the slope soil to be damaged, forming locally saturated soil and the rise in the groundwater table during shaking. Then, the saturated soil liquefied under the action of strong vibration, and the liquefied soil mass slid under the action of a high-intensity earthquake force. Finally, the acceleration and spectral characteristics of the pore water pressure changed sharply with a shift in the predominant frequency at the liquefied locations under a high shaking intensity. The significant changes in dynamic pore water pressure mainly occurred when the shaking components in the low-frequency bands below 1 Hz. This implied that the shift in the frequency mainly resulted from the damage in the structure of the loess slope after high-intensity shaking. These results help us better understand the triggering mechanism and failure mechanism of saturated loess slopes during the Minxian-Zhangxian earthquake.

Connecting dynamic pore filling mechanisms with equilibrium and out of equilibrium configurations of fluids in nanopores.

In the present study, using dynamic mean field theory complemented by grand canonical molecular dynamics simulations, we investigate the extent to which the density distributions encountered during the dynamics of capillary condensation are related to those distributions at equilibrium or metastable equilibrium in a system at fixed average density (canonical ensemble). We find that the states encountered can be categorized as out of equilibrium or quasi-equilibrium based on the magnitude of the driving force for mass transfer. More specifically, in open-ended slit pores, pore filling via double bridging is an out of equilibrium process, induced by the dynamics of the system, while pore filling by single bridge formation is connected to a series of configurations that are equilibrium configurations in the canonical ensemble and that cannot be observed experimentally by a standard adsorption process, corresponding to the grand canonical ensemble. Likewise, in closed cap slits, the formation of a liquid bridge near the pore opening and its subsequent growth while the initially detached meniscus from the capped end remains immobilized are out of equilibrium processes that occur at large driving forces. On the other hand, at small driving forces, there is a continuous acceleration of the detached meniscus from the capped end, which is associated with complete reversibility in the limit of an infinitesimally small driving force.

Prediction of dynamic pore water pressure for calcareous sand mixed with fine-grained soil under cyclic loading

To evaluate the effect of fine-grained soil (FS) on liquefaction resistance of calcareous sand (CS), a set of undrained cyclic triaxial experiments with stress-controlled method were conducted. The cyclic triaxial tests were performed with 1 Hz frequency at three effective confining pressure levels (100, 200, 300 kPa) and three cyclic stress ratio (CSR) levels (0.1, 0.2, 0.5). Test results demonstrated that pore water pressure (PWP) developing process of pure calcareous sand (PCS) and CS-FS mixtures present three stages along with the rate of PWP ratio (PWP to effective confining pressure). The PWP ratio ru of PCS first increased rapidly then grew slowly and finally kept constant. However, the ru of mixture increased slowly first, then grew sharply and finally became unchangeable. In addition, the terminal PWP ratio ruter of all specimens were less than 1.0 which suggests that PCS and CS-FS mixtures were liquefied partly in this study. Along with the PWP behavior, the modified logarithmic model and modified Seed model were proposed to predict PWP ratio development for PCS and CS-FS mixtures respectively. Test outcomes showed that terminal PWP ratio ruter has a positive relation with effective confining pressure and CSR, and the liquefaction degree was aggravated at high stress. Nevertheless, the cycle number to cause liquefaction has a negative relation with FS content or stress level. Besides, the ruter values decreased as increasing FS percentage from 0 to 50% which indicates that FS can improve the liquefaction resistance of CS-FS mixtures.

Dynamic pore network model to predict residual saturation and pressure drop in mist oleo-phobic filters

A dynamic pore network modelling (DPNM) framework is used to evaluate pressure drop and residual saturation in oleo-phobic nonwoven media in mist filters. The advanced fully-resolved VOF simulations along with μ-CT measurements are also carried out to substantiate the validity of the DPNM simulations. The results of the study show that PNM could be a beneficial and reliable tool for predicting oil saturation and pressure drop during early-stage design of oleo-phobic filters with nonwoven media. Given the considerably higher efficiency of PNM models compared to CFD-based techniques, some parametric studies were also conducted. Our findings suggest that, for a given set of operating conditions, efficiency/performance can be improved by appropriate choice of filters with optimized properties (fibre diameter, packing density, contact angle, etc.) for which the overall oil saturation and pressure drop in the filter attain minimum, may offer a self-cleaning mist filter. Finally, a correlation was developed for evaluating the performance of oleo-phobic media using the filter specifications and the data of steady state saturation and pressure drop found in open literature. The obtained correlation shows a good conformity with the experimental measurements with an average of 12.1% error for about 93% of data out of 68 data sets collected with a correlation coefficient of (R2) of 0.934.

Confocal Microscopy to Measure Three Modes of Fusion Pore Dynamics in Adrenal Chromaffin Cells.

Dynamic fusion pore opening and closure mediate exocytosis and endocytosis and determine their kinetics. Here, it is demonstrated in detail how confocal microscopy was used in combination with patch-clamp recording to detect three fusion modes in primary culture bovine adrenal chromaffin cells. The three fusion modes include 1) close-fusion (also called kiss-and-run), involving fusion pore opening and closure, 2) stay-fusion, involving fusion pore opening and maintaining the opened pore, and 3) shrink-fusion, involving shrinkage of the fusion-generated Ω-shape profile until it merges completely at the plasma membrane. To detect these fusion modes, the plasma membrane was labeled by overexpressing mNeonGreen attached with the PH domain of phospholipase C δ (PH-mNG), which binds to phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) at the cytosol-facing leaflet of the plasma membrane; vesicles were loaded with the fluorescent false neurotransmitter FFN511 to detect vesicular content release; and Atto 655 was included in the bath solution to detect fusion pore closure. These three fluorescent probes were imaged simultaneously at ~20-90 ms per frame in live chromaffin cells to detect fusion pore opening, content release, fusion pore closure, and fusing vesicle size changes. The analysis method is described to distinguish three fusion modes from these fluorescence measurements. The method described here can, in principle, apply to many secretory cells beyond chromaffin cells.

Coupling of pore network modelling and volume of fluid methods for multiphase flow in fractured media

Modelling multiphase flow in fractured media is a challenging multi-disciplinary problem which is of particular importance for the production of hydrocarbons from unconventional geological formations. At the pore-scale, this can be studied using pore network models that are computationally efficient due to the employment of pore-space geometrical simplifications. There are two distinctive approaches to pore network modelling: quasi-static and dynamic. However, only dynamic pore network models allow capturing the transient nature of the multiphase flow. Nevertheless, the dynamic models have a number of limitations including numerical oscillations and the inability of interface tracking in a particular network element. In order to overcome these drawbacks, a hybrid numerical method which combines the Hagen–Poiseuille analytical solution of the Navier–Stokes equations and the volume of fluid advection scheme is developed and validated. The proposed multiphase model is benchmarked against the conventional volume of fluid implementation for various drainage and imbibition cases using two-dimensional demo cases. Besides, three-dimensional simulations are also performed to ensure the applicability of the proposed model to real fractured media. The single pressure algorithm is employed while the capillary pressure drop is explicitly introduced as an additional term in the Hagen–Poiseuille equation. The conducted validation and following analysis show the applicability of the developed model for a wide range of Reynolds and capillary numbers and viscosity ratio. Thus, the new model can be used to investigate transient immiscible multiphase flow phenomena in fractures by pore network modelling.

The Candida albicans virulence factor candidalysin must self-assemble in solution to form membrane pores

Pathogenic Candida albicans is responsible for systemic infections resulting in high morbidity and mortality to vulnerable populations. This is in large part due to the diverse virulence factors C. albicans employs to invade and damage human cells. One of these, candidalysin (CL), was recently found to be required for infection. It was proposed that CL promotes infection by cell membrane disruption. However, the specific mechanism by which this occurs is unknown. Atomic force microscopy (AFM) imaging of supported lipid bilayers treated with CL revealed static and dynamic pore populations, suggesting that membrane disruption occurs through pore formation.

Enhanced thermal fingering in a shear-thinning fluid flow through porous media: Dynamic pore network modeling

Thermal-viscous fingering instability in porous media is a common phenomenon in nature as well as in many scientific problems and industrial applications. Despite the importance, however, thermal transport in flow of a non-Newtonian fluid in porous media and the resulting fingering has not been studied extensively, especially if the pore space is heterogeneous. In this paper, we propose a pore network model with full graphics processing unit-parallelized acceleration to simulate thermal transport in flow through three-dimensional unstructured pore networks at centimeter scale, containing millions of pores. A thermal Meter equation is proposed to model temperature- and shear stress-dependent rheology of the non-Newtonian fluids. After comparing the simulation results with an analytical solution for the location of the thermal front in a spatially uncorrelated pore network, thermal transport in flow of both Newtonian and non-Newtonian fluids is studied in the spatially uncorrelated and correlated pore networks over a range of injection flow rates. The simulations indicate that the injection flow rate, the shear-thinning rheology, and the morphological heterogeneity of the pore space all enhance thermal-viscous fingering instability in porous media, but with distinct patterns. In spatially correlated networks, the average temperature and apparent viscosity at the breakthrough point in flow of a shear-thinning fluid exhibit non-monotonic dependence on the injection flow rate. An analysis of the fractal dimension of thermal patterns at the breakthrough point supports the conclusion. The results highlight the importance of designing optimal flow conditions for application purposes.

Gasdermin D pores are dynamically regulated by local phosphoinositide circuitry

Gasdermin D forms large, ~21 nm diameter pores in the plasma membrane to drive the cell death program pyroptosis. These pores are thought to be permanently open, and the resultant osmotic imbalance is thought to be highly damaging. Yet some cells mitigate and survive pore formation, suggesting an undiscovered layer of regulation over the function of these pores. However, no methods exist to directly reveal these mechanistic details. Here, we combine optogenetic tools, live cell fluorescence biosensing, and electrophysiology to demonstrate that gasdermin pores display phosphoinositide-dependent dynamics. We quantify repeated and fast opening-closing of these pores on the tens of seconds timescale, visualize the dynamic pore geometry, and identify the signaling that controls dynamic pore activity. The identification of this circuit allows pharmacological tuning of pyroptosis and control of inflammatory cytokine release by living cells.

Dissolution and remobilization of NAPL in surfactant-enhanced aquifer remediation from microscopic scale simulations

In this paper, the dissolution and mobilization of non-aqueous phase liquid (NAPL) blobs in the Surfactant-Enhanced Aquifer Remediation (SEAR) process were upscaled using dynamic pore network modeling (PNM) of three-dimensional and unstructured networks. We considered corner flow and micro-flow mechanisms including snap-off and piston-like movement for two-phase flow. Moreover, NAPL entrapment and remobilization were evaluated using force analysis to develop the capillary desaturation curve (CDC) and predict the onset of remobilization. The corner diffusion mechanism was also applied in the modeling of interphase mass transfer to represent NAPL dissolution as the dominant mass transfer process. In addition, the effect of pore-scale heterogeneity on mass transfer rate coefficient and recovered residual NAPL was considered in the simulations. Sodium dodecyl sulfate (SDS) and Triton X-100 were used as the surfactant for the SEAR process. The results indicate that although surfactants enhance NAPL recovery during two-phase flow, surfactant-enhanced remediation of residual NAPL through dissolution is highly dependent on surfactant type. When SDS ─as a surfactant with high critical micelle concentration (CMC) and low micelle partition coefficient (Km)─ was injected into a NAPL contaminated site, the mass transfer rate coefficient decreased (due to considerable changes in interface chemical potentials) which leads to a significant reduction in NAPL recovery after the end of two-phase flow. In contrast, Triton X-100 (with low CMC and high Km) improved NAPL recovery, by enhancing solubility at surfactant concentrations greater than CMC which overcompensates the interphase mass transfer reduction.

Ultrastrong tough zirconia ceramics by defects‐engineering

AbstractWe report the preparation of a category of ultrastrong tough zirconia ceramics by engineering defects using an oscillatory pressure during pressure assisted sintering. The introduced oscillatory pressure enhances the dynamic grain rearrangement, plastic deformation, mass transportation, and pore removal, leading to the formation of pore‐free ceramics characterized by the rich coherent grain boundaries among individual mesocrystalline grains with intragranular quasi‐interfaces. As a proof of concept, the pressure required by oscillatory pressure sintering (OPS) for preparing fully dense 3Y‐TZP ceramics is significantly reduced, which is just ∼1/5 of that required by hot isostatic pressing. The OPS‐prepared 3Y‐TZP ceramics reached a record‐breaking high bending strength and fracture toughness, being up to 1.8 GPa and 16 MPa·m1/2, respectively. This success illustrates a universal principle of engineering defects for making breakthrough in exploring other ultrastrong tough ceramics.

Seismic Responses of a Large Unequal-span Underground Subway Station in Liquefiable Soil Using Shaking Table Test

ABSTRACT Sand liquefaction is considered to be one of the main causes of severe earthquake damage. The seismic response of large-scale underground structures is mainly controlled by the deformation of surrounding soils, and the large liquefaction-induced lateral displacement poses a serious threat to large underground structures. In this paper, a large-scale shaking table test is performed to simulate the dynamic interaction between liquefiable foundation, diaphragm wall and underground subway station. The results indicate that the interaction mode between soil and underground structure changes significantly with the different liquefaction states of surrounding soil. The underground structure improves the liquefaction resistance of adjacent lateral soils, but significantly reduces the liquefaction resistance of soils located directly below the structure. The development of dynamic pore pressure is related to the seismic intensity, and a significant dissipation of dynamic pore pressure usually occurs after the end of a strong seismic excitation. Moreover, the acceleration response law along the vertical direction has changed significantly within the buried depth of the underground structure. Specifically, the acceleration response of the lateral foundation is inhibited in the absence of liquefaction, but is enhanced in the complete liquefaction. In addition, the liquefaction states of model site also affect the spatial strain response of the underground structure.

Characterization of dynamic response of asphalt pavement in dry and saturated conditions using the full-scale accelerated loading test

Asphalt pavement exhibits different dynamic responses to vehicle loading in saturated conditions and in dry conditions. It is essential to directly conduct field full-scale tests to systematically investigate comprehensive influence of water on dynamic response of asphalt pavement. However, real vehicles which were often applied in field tests might result in a certain deviation in dynamic responses measured from each field loading test due to the inevitable influence of the driver’s subjective operation and the tread pattern on vehicle wheel. This study adopted the full-scale accelerated loading test system to comprehensively characterize dynamic response of asphalt pavement in both dry and saturated conditions based on the strict control of loading vehicle’s path. The results indicated that dynamic responses showed relatively larger magnitudes in saturated condition than those in dry condition. Strain and stress respectively showed slowly increasing and decreasing trends with the increase of vehicle load and speed correspondingly. Pore water pressure was apparently sensitive to vehicle speed compared with vehicle load. Pore water pressure generated by the front axle wheels showed obviously larger magnitudes than those produced by the rear axle wheels due to the change in thickness of surface runoff. The transverse distribution of pore water pressure obtained from both field tests and numerical simulation exhibited consistent variation trends. Decline degree of pore water pressure magnitudes was obtained at 86.1% for the two adjacent testing points with a distance of 100 mm under the vehicle wheel, which proved the great influence of the tread pattern of vehicle wheel on the transverse distribution of dynamic pore water pressure. A prediction model of positive pore water pressure that considered vehicle load and speed was proposed.

A New Method to Estimate Formation Pore Pressure in Fractured Areas of Shale Gas Reservoir

The matrix of shale gas reservoir has the characteristics of low porosity and ultra-low permeability, but also develop natural and hydraulic fractures. Many field operations observed that the formation pore pressure after hydraulic fracturing is higher than the original formation pore pressure. Drilling in the fractured areas of shale gas reservoir, including natural fractures and artificial fractures, always faces greater overflow risk. The pore pressure test after fracturing also shows that the test value is higher than the formation initial pore pressure. However the conventional formation pore pressure predicting methods are difficult to obtain the accurate pore pressure in the fractured areas of shale gas reservoir.In this paper, the causes of formation pore pressure changing and fracturing pressurization effect in the fractured zones of shale gas reservoir are analyzed. Based on the assumption of closed and constant volume material balance and the gas equation of state, the internal mechanism of the increase in pore pressure caused by fracturing operation in low-permeability shale gas formation is theoretically analyzed. A new method to predict pore pressure changing of shale gas reservoir during drilling and hydrofracturing operations is proposed. The pore connectivity of shale gas reservoir is poor, and the permeability is tens of nano-darcy. The permeability is usually between 0.01-0.20 millidarcy when natural fractures are developed. After fracturing, the permeability can be increased by 2-3 times. Based on the principle of effective stress, a pore pressure calculation model with the influence of permeability change is established by using logging data. Three influence terms are considered in the model: the first one is the overburden pressure term, the second one is the skeleton stress term, and the last one is the influence term of permeability change rate on local formation pore pressure. The proposed method shows simple principle, clear mechanism and easy to use in the field. Field applications show that this method could quickly and accurately predict dynamic formation pore pressure changing of shale gas reservoir. It offsets the shortcomings of traditional formation pore pressure calculation methods.

Deformation Behavior of Saturated Soft Clay under Cyclic Loading with Principal Stress Rotation

Under long-term traffic loading, the soil elements in subgrade are subjected to continuous principal stress rotation. In order to study the deformation properties of soft clays under traffic loading with principal stress rotation, a series of cyclic torsional shear tests were conducted on Wenzhou soft clays under different torsional cyclic stress ratios and degrees of principal stress rotation. The test results showed the stiffness softening of soil under long-term traffic loading. In addition, the principal stress rotation induced by traffic loading aggravated the deformation of clay samples and pore pressure accumulation. A modified dynamic pore pressure model was applied to consider the effect of principal stress rotation on undrained cumulative pore pressure, predicting the growth of cumulative pore pressure at different cycles. Considering loading cycles and the principal stress rotation, a modified Hardin–Drnevich (H-D) backbone curve model under traffic loading with principal stress rotation was proposed, and the predictive values of this model agreed well with the experimental values. Compared with the traditional H–D model, this model better reflects the cyclic deformation of soft clays under long-term traffic loading with principal stress rotation.