Value Of Hydraulic Gradient Research Articles

MoS2@Hydrochar nanocomposites with cost-effective fluid turbulent eddies induced piezoelectric catalytic peroxymonosulfate utilization efficiency for water polluted dye degradation

Piezoelectric materials can induce strain due to the fluid turbulent force produced during fluid shaking, which may be used to activate peroxymonosulfate (PMS). In this study, the effective interfacial interaction of few-odd-numbered layered MoS2 nanosheets and hydrochar (HC) nanocomposites as the piezoelectric material was used in a hydrodynamics energy-driven piezoelectric catalytic PMS activation process (piezo-PMS activation process) for Eriochrome Black T dye degradation. The results showed that Black T dye was efficiently degraded with an efficiency of 99.23 % within 15 min and a pseudo-first-order rate constant of 3.10 min−1 in the MoS2@HC-(6.5:3.5)/PMS/Shaking system. To clearly see the influence of hydraulic gradient (G) value, the hydrodynamics energy-driven piezo-PMS activation process for Black T dye degradation was performed at different shaking frequencies. The results indicated an optimal G value of (14.106 s−1) for Black T dye degradation. Notably, the MoS2@HC-(6.5:3.5)/ PMS/Shaking system produced the lowest EE/O value (34.05 kWhm−3 order−1), resulting in energy savings over 127 times of HC and 9 times of MoS2. Furthermore, piezoelectrochemical measurements of MoS2@HC-(6.5:3.5) indicated that these superior performances primarily resulted from the synergistic effects of MoS2 and HC. This led to a stronger piezoelectric response with effective piezo-generated charge separation, which in turn improved the efficiency of producing reactive species. Combining the scavenger test, FT-IR, and zeta potential analysis, we determined that •OH and SO4•− played a major role, while O2•− and 1O2 played a secondary role in Black T dye degradation. The steady-state concentrations of [•OH]ss, and [SO4•−]ss were 14.52 × 10−14 M and 20.00 × 10−14 M, respectively in the fluid turbulent force driven piezo-PMS activation process. Furthermore, a plausible degradation pathway of Black T dye was proposed based on the assessment of carbon number reduction, the mean oxidation number of organic carbon (MOC) and the predicted TOC/color index.

Novel MoS2-based heterojunction as an efficient and magnetically retrievable piezo-photocatalyst for diclofenac sodium degradation

It is a challenging and meaningful task to design a piezo-photocatalyst with excellent performance under mild mechanical stirring conditions rather than ultrasonic irradiation. Herein, a hydraulic-driven piezo-photocatalytic process was proposed, using MoS2-based heterojunction as catalysts for diclofenac sodium (DCF) degradation. A magnetically retrievable MoS2/TiO2/Fe3O4 composite was designed and successfully prepared by a facile one-step solvothermal process. Among various heterojunction composites and pure MoS2, the ternary composite MoS2/TiO2/Fe3O4 exhibited the strongest piezo-photocatalysis capability, with a DCF degradation efficiency of 99.6% and a pseudo-first-order rate constant of 0.733 min−1. Additionally, the degradation efficiency of DCF was still up to 85.2% in 6 min after 5 cycles by MoS2/TiO2/Fe3O4. The ternary composite can be easily collected and separated using a magnet. There was an optimum hydraulic gradient value (0.45 s–1) for DCF degradation. •OH played a major role in DCF degradation during the hydraulic-driven piezo-photocatalytic process. A satisfactory DCF degradation was found in the actual water media. The results verify the existence of a synergetic effect between piezo and photocatalytic processes. Thereupon, the hydraulic-driven piezo-photocatalysis can be an efficient, sustainable, and energy-saving process for water treatment.

Multi-scale variations of subglacial hydro-mechanical conditions at Kongsvegen glacier, Svalbard

Abstract. The flow of glaciers is largely controlled by changes at the ice–bed interface, where basal slip and sediment deformation drive basal glacier motion. Determining subglacial conditions and their responses to hydraulic forcing remains challenging due to the difficulty of accessing the glacier bed. Here, we monitor the interplay between surface runoff and hydro-mechanical conditions at the base of the Kongsvegen glacier in Svalbard. From July 2021 to August 2022, we measured both subglacial water pressure and till strength. Additionally, we derived median values of subglacial hydraulic gradient and radius of channelized subglacial drainage system from seismic power, recorded at the glacier surface. To characterize the variations in the subglacial conditions caused by changes in surface runoff, we investigate the variations of the following hydro-mechanical properties: measured water pressure, measured sediment ploughing forces, and derived hydraulic gradient and radius, over seasonal, multi-day, and diurnal timescales. We discuss our results in light of existing theories of subglacial hydrology and till mechanics to describe subglacial conditions. We find that during the short, low-melt-rate season in 2021, the subglacial drainage system evolved at equilibrium with runoff, increasing its capacity as the melt season progressed. In contrast, during the long and high-melt-rate season in 2022, the subglacial drainage system evolved transiently to respond to the abrupt and large water supply. We suggest that in the latter configuration, the drainage capacity of the preferential drainage axis was exceeded, promoting the expansion of hydraulically connected regions and local weakening of ice–bed coupling and, hence, enhanced sliding.

A probabilistic approach to levee reliability based on sliding, backward erosion and overflowing mechanisms: Application to an inspired Canadian case study

AbstractImproving protection against fluvial floods requires a better estimation of levee failure. We developed an assessment method of levee failure probabilities for sliding, backward erosion, and overflowing each represented by fragility curves. We tested two approaches to aggregate those fragility curves into a global fragility curve respectively using: an enveloping curve and Monte‐Carlo simulations. We implemented this approach to earthen levee reliability for several flood return periods to the Bow River in Calgary, Canada. We used limit equilibrium method to estimate the safety factor of the levee segment and Monte‐Carlo simulations to estimate sliding probabilities. We used Terzaghi's critical hydraulic gradient to estimate backward erosion failure probabilities. The estimation of overflowing probabilities required expert judgment. We discussed how the choice of the hydraulic gradient area and the consideration of a steady state or transient model impact backward erosion failure probabilities. The results showed for our study case that, even though the transient model is a closer representation of reality, the levee saturation parameter has little impact on hydraulic gradient values, by extension, on sliding and backward erosion failure probabilities. The Monte‐Carlo aggregated fragility curve is more realistic than the envelop curve of the failure mechanisms for an equivalent computation time.

Sand modification with a saponite clay suspension as a waste of the diamond mining industry

The results of the laboratory water permeability tests of a sand modified by a saponite clay fraction from the diamond mining industry waste are presented. The filtration of clay suspension through a landfill ground bed as a method of the additive enrichment is approved. The experimental apparatus consisted of the triaxial test chambers and semi-automatic devices for water and suspension supplying. The chambers excluded a sidewall leakage in the samples and provided required values of the vertical and horizontal stresses when measuring permeability. The samples of an alluvial fine sand and a sand mixed with 3 and 5 % a chalk and a dolomite were investigated. After preliminary saturation the rate of distilled water flow through the samples were determined at four values of hydraulic gradient. Then the filtration of a suspension containing up to 0.58-0.63 % clay particles was conducted. After that, the pore disks at the top of samples were washed by circulating water flow. At the last step of experiments the velocity of water flow was measured again at four values of hydraulic gradient. The experiments indicated that the modification of the sand by clogging the pores by the saponite clay fraction from a suspension flow is possible if a sand comprises the additives causing the aggregation of clay particles. The hydraulic conductivity of a sand with 3 % chalk decreased by 15-31 times, with 5 % - by 15-39 times at different values of relative compaction. The effect of a dolomite addition was not significant, the hydraulic conductivity decreased by a maximum of 14.3 times. To achieve the maximum depth of clogging, it is recommended to filtrate the suspension through a loose sand at a hydraulic gradient that provides a flow rate more than 3.5 m/day, after that, the sand layer should be compacted.

Preliminary investigation of saline water intrusion (SWI) and submarine groundwater discharge (SGD) along the south-eastern coast of Andhra Pradesh, India, using groundwater dynamics, sea surface temperature and field water quality anomalies.

Intensive anthropogenic activities along the coastal plains of Andhra Pradesh (such as urbanisation, agriculture and aquaculture) rely extensively on coastal fresh groundwater resources that are pumped at unsustainable rates causing groundwater decline and water quality problems due to saline water intrusion. Hydrogeological studies are imperative to implement groundwater conservation strategies in coastal Andhra Pradesh, which is experiencing a severe freshwater shortage due to overexploitation and saline water intrusion as well as clean water loss through the aquifer system close to the coastal plains. An attempt is made in this study to demarcate the submarine groundwater discharge (SGD) and saline water intrusion (SWI) zones adopting a three-tier validation system, i.e. groundwater dynamic, LANDSAT resultant sea surface temperature (SST) variance and site-specific water characteristics along the southeast coast of Andhra Pradesh, India. A total of 234 water samples (139 porewater, 31 groundwater and 64 seawater samples) were evaluated along ~ 450km southeast coastline of Andhra Pradesh. In situ porewater physio-chemical parameters, i.e. EC, TDS, pH, DO, temperature, and salinity, at every 1km except non-accessible areas and groundwater for every 5km were analysed and used for identification of SGD zones in the study area. The hydraulic gradient values vary from - 11 to 250m in post-monsoon and - 14 to 250m in pre-monsoon. And sea surface temperature anomaly for 2017, 2018 and 2019 varies between 21-39°C, 15-34°C and 20-39°C. Three districts out of the four districts studied (Krishna, Guntur and Nellore) were shown to be prone to SWI, whereas Prakasam district was susceptible for SGD. For the first time, this kind of preliminary study was carried out in the coastal Andhra Pradesh region, and it will serve as a basis for the meticulous analysis of the fresh and saline water mixing zones/process as well as to develop and manage the groundwater resources along the water-stressed coastal plains of Andhra Pradesh, India.

The use of scaling parameters and the impact of non-uniqueness in the simulation of a large-scale solute transport experiment conducted in discrete fractures

There are few studies analyzing tracer experiments conducted in rock fractures at large scales (>50 m) and fewer still which have succeeded in simulating experimental data without the use of parameters which increase/decrease with increasing scale of observation (i.e. scaling or effective parameters). To explore the use of effective parameters at large scales, a numerical model is used to examine the results of a divergent tracer experiment conducted in sparsely fractured rock where five observation points ranged over distances from 30 to 125 m. The experiment was conducted in what was first interpreted as a single horizontal fracture, traceable using geological and hydraulic evidence over that range in distance. Initial simulations were conducted using measured values of porosity, fracture aperture, and regional hydraulic gradient but were not successful in matching the field data at all measured locations. Multiple fits of equal quality at each observation point however were obtained with models using effective parameters (such as increasing porosity with scale) to represent heterogeneity. Additional fits were achieved by physically representing the same heterogeneity with different conceptual models, such as added horizontal and vertical fractures. This illustrates the non-uniqueness that arises in the interpretation of a divergent tracer experiment with multiple observation well distances. Using the models, predictions at distances beyond the measured domain were then generated. These showed that the choice of conceptual model significantly impacted simulated arrival times and concentrations at distances of only 75–175 m larger than the experimental scale. In particular, predictions made with effective parameters provided estimates that were less conservative (i.e. under predicting concentrations) than those made by directly adding heterogeneity to the numerical model.

Random finite element analysis of backward erosion piping

Backward erosion piping (BEP) is a type of internal erosion that threatens the integrity of dams and levees. BEP has been shown to be highly sensitive to spatial variations in soil properties; however, there are presently no assessment methods that permit incorporating spatial variation in soil properties into BEP analysis. The Random Finite Element Method (RFEM) is a numerical approach for incorporating spatially variable properties into finite element analysis. In this study, an RFEM approach to simulating BEP was developed to assess pipe progression through variable soils. The soil hydraulic conductivity and critical hydraulic gradient for pipe progression were treated as log-normal random variables. Analyses were conducted for a range of hydraulic conductivity and critical gradient random fields with varied spatial correlation lengths, distribution parameters, and field correlations. Results indicate that the probability of failure increases with increasing spatial correlation length. Additionally, increased variance in soil permeability was shown to increase the probability of failure for large correlation lengths and decrease the probability of failure for short correlation lengths. Regardless of correlation length, increasing values of the mean critical hydraulic gradient led to decreased failure probabilities, and increasing values of critical hydraulic gradient variance led to increased failure probabilities.

Design and optimization of multiple wells layout for electricity generation in a multi-fracture enhanced geothermal system

The major challenge in Enhanced Geothermal System is to circulate the injected fluid in most part of the reservoir. One solution to this problem is to create artificial fractures in the reservoir and optimally position multiple injection wells and multiple production wells. The wells layout plays a crucial role and requires investigation. This is the ultimate goal of this paper in order to extract a sufficient amount of energy and allow the fluid to reach a larger volume in the heterogeneous reservoir. The results show that a combination of three injection wells with two production wells provides the best performance. With this well layout, the output electrical power drops from 10.40 to 9.40 MW to 6.84–4.53 MW increasing the injection fluid flow rate in 0.075–0.125 m3/s range because higher the volume flow rate, greater the water losses. The average production temperature after a 40-year period is 164.8 °C and reduced by 3.1%, which is acceptable. The injected fluid temperature and the hydraulic gradient have a low influence on the production temperature evolution and the heat extraction ratio change. Hydraulic gradient influence on the production temperature is noticeable for a hydraulic gradient value greater than 10 mm/m.

The impact of aquifer stratification on saltwater intrusion characteristics. Comprehensive laboratory and numerical study

AbstractLaboratory experiments and numerical simulations were utilized in this study to assess the impact of aquifer stratification on saltwater intrusion. Three homogeneous and six layered aquifers were investigated. Image processing algorithms facilitated the precise calculation of saltwater wedge toe length, width of the mixing zone, and angle of intrusion. It was concluded that the length of intrusion in stratified aquifers is predominantly a function of permeability contrast, total aquifer transmissivity and the number of heterogeneous layers, being positively correlated to all three. When a lower permeability layer overlays or underlays more permeable zones its mixing zone widens, while it becomes thinner for the higher permeability strata. The change in the width of the mixing zone (WMZ) is positively correlated to permeability contrast, while it applies to all strata irrespectively of their relative vertical position in the aquifer. Variations in the applied hydraulic head causes the transient widening of WMZ. These peak WMZ values are larger during saltwater retreat and are negatively correlated to the layer's permeability and distance from the aquifer's bottom. Moreover, steeper angles of intrusion are observed in cases where low permeability layers overlay more permeable strata, and milder ones in the inverse aquifer setups. The presence of a low permeability upper layer results in the confinement of the saltwater wedge in the lower part of the stratified aquifer. This occurs until a critical hydraulic head difference is applied to the system. This hydraulic gradient value was found to be a function of layer width and permeability contrast alike.

Experimental study on seepage characteristics and water inrush of filled karst structure in tunnel

Taking Qiyueshan Tunnel as the engineering background, the three-dimensional model test system of tunnel water inrush and mud gushing was independently developed to study the structural instability characteristics and seepage laws of karst conduit fillings with different permeability coefficients. Then, the instability process of the filling, the evolution of water pressure, and the characteristics of the hydraulic gradient were analyzed. It is concluded that the fillings with different permeability coefficients show different instability characteristics, and the failure types of karst conduit filling are divided into sand inrush, water inrush, and mud inrush according to the instability characteristics of the filling. The pore water pressure at each measuring point in the filling material tends to decrease gradually along the direction of the confined water seepage. As the pressure of the confined water increases, the pore water pressure value of each measuring point increases gradually. And the higher the content of clay in the filling material is, the higher the maximum confined water pressure that the filling can bear when the filling material is unstable. The average hydraulic gradient in the filling increases with the increase of confined water pressure. The adjacent hydraulic gradient value increases with the increase of confined water pressure.

Optimum layout of weep holes in concrete irrigation canals to control uplift pressure and hydraulic gradient

In this study, the effect of weep holes on controlling uplift pressure and hydraulic gradient under concrete canals was investigated in different groundwater levels. For this purpose, three weep holes were embedded in different locations and combinations on the bottom and the sidewall of a laboratory canal. The amounts of seepage discharge were measured from these weep holes in single and combined modes. The corresponding values of seepage discharge, uplift pressure, and exit hydraulic gradient were calculated through simulation with the Seep/W model. The comparison of the observed and the simulated seepage values was indicative of the model’s high accuracy with a mean error of 6.23%. The results showed that uplift pressure values in the single modes of weep holes in three different groundwater levels are similar. Uplift pressure in the binary combinations had a significant reduction compared to the single modes (an average of 73%). The maximum exit hydraulic gradient occurred at the weep hole located at the corner of the canal bottom. In general, the binary combinations of the weep holes were the best choice in terms of the minimum uplift pressure and the suitable exit hydraulic gradient.

Validity of the Method of Fragments for Seepage Analysis in Circular Cofferdams

The method of fragments (MoF) is a simple solution method for confined seepage problems. MoF based seepage solutions have been proposed and validated in the literature on cofferdams analyzed in the 2D Cartesian plane (i.e., double-walled cofferdams). More recently, this method has been extended by the authors for determining the flow rate and exit hydraulic gradient for axisymmetric cases (circular cofferdams). The accuracy of the MoF solutions for circular cofferdams relies on the assumption that the equipotential surface along the cofferdam perimeter at the tip of the cut-off wall is vertical. Therefore, in the first part of the paper, the validity of this assumption and the effect of any deviation on the seepage solutions for circular cofferdams were studied. For that, series of circular cofferdam geometries were studied using numerical simulations, and then the seepage solutions (flow rate and exit hydraulic gradient values) obtained were compared with corresponding MoF solutions. It shows that the MoF solutions are conservative in all the cases and also the error is limited to 10% for most of the cases. In the second part of the paper, an attempt is made to simplify the MoF solutions, further developing expressions for the form factors of the two fragments and the exit hydraulic gradient without relying on the graphical solutions proposed by the authors. The equations presented herein enable the MoF to be implemented in spreadsheet and hence be used as an effective tool for parametric studies.

Simple solutions for square and rectangular cofferdam seepage problems

Cofferdams are widely used temporary structures at construction sites. Two of the main parameters required in designing a cofferdam are the flow rate and exit hydraulic gradient at the bottom of the excavation. Commonly, these two parameters are evaluated by using two-dimensional (2D) ground water flow models. However, when the flow pattern is three-dimensional (3D), such as flow into the square or rectangular cofferdams, predictions by the 2D models underestimate the flow rate and exit gradients considerably. Therefore, it is necessary to incorporate the 3D flow effect through a correction factor. It is shown that treating a square cofferdam as a circular one of the same width or treating a rectangular cofferdam as a 2D double-walled cofferdam significantly underestimates the flow rate. In this study, simple expressions are developed and validated for accurately estimating the flow rate and exit hydraulic gradient values of square and rectangular cofferdams, based on hundreds of finite element simulations in both 2D and 3D. It is suggested that the expressions given in the Canadian foundation engineering manual be improved.

Calculation of pressure loss and critical velocity for slurry flows with additive agents in vertical polyethylene pipelines

The method of determination of parameters of hydrotransport of solid polydisperse materials in vertical pipelines is offered. The reasons of discrepancy between estimated and observed data when using A. Smoldyrev’s method for calculation of hydraulic gradient and critical velocity in vertical steel pipelines are analysed. Particularly non-applicability of Velicanov principle to hydrotransport of solid materials in vertical pipelines is proved and contribution of particles fall velocity to the value of complementary hydraulic gradient in vertical pipelines is estimated. Suggested formulas for calculation of hydraulic gradient and critical velocity in vertical pipelines are multipurpose because they may be used for calculation of hydrotransport parameters in steel and polymeric vertical pipelines with using of friction reducing agents and without it. The method for parameters calculation of solid materials hydrotransport in vertical polymeric pipelines is first offered. Elaborated formulas ensure also increasing of accuracy of calculations.

Discussion of “Experimental study on the hydraulic conductivity of calcareous sand in South China Sea”

ABSTRACTHydraulic conductivity of the granular soils depends on many factors including the soil density and the particle size distribution. For internally unstable soils, the hydraulic conductivity could be changed beyond a critical value of hydraulic gradient. This discussion calls attention to the effect of the internal stability on the hydraulic conductivity, where the internal stability of the soils is assessed and the critical hydraulic gradient is computed using some theoretical methods, and such calculations could be used to plan the experimental tests.

A hydraulic gradient model of paste-like crude tailings backfill slurry transported by a pipeline system

A hydraulic gradient model, which can be used to compute the hydraulic gradient of paste-like crude tailings backfill slurry (PTBS) transported by a pipeline system in a mine, was constructed based on rheological model derivation, numerical simulation, and regression analysis. It was proven, by a Bingham rheological model analysis of the PTBS, that the hydraulic gradient of the PTBS is inversely proportional to the pipe diameter and proportional to the average flow velocity. It was also clarified that the hydraulic gradient value depends primarily on the rheological parameters of the PTBS if the pipe diameter and flow velocity are adjustable. Consequently, rheological parameters of the PTBS in different slurry mass fractions were obtained through 3D simulation with FLUENT. The slurry pipeline transportation process and the relationship between rheological parameters and slurry mass fraction were regressed by MATLAB mathematical software. Finally, a hydraulic gradient model describing a variation rule of the hydraulic gradient of the PTBS to pipe diameter, flow velocity, and slurry mass fraction was constructed. A comparable study between the calculation result and site date indicates that the model has enough accuracy to satisfy the requirement of backfill system design with an average deviation of 8 %.

Soil characterization in and around a proposed waste disposal facility at Nuclear Fuel Complex, Hyderabad, India

Generation of site-specific hydrogeological parameters such as porosity, bulk density, hydraulic conductivity, pore water velocity, etc. are the pre-requisites to carry out studies on the low probability event of migration of radionuclides along with groundwater due to long-term leaching from a waste disposal site. In the present work, the hydrogeological parameters are estimated for soil samples collected from various locations in and around a proposed solid waste disposal site at the Nuclear Fuel Complex, Hyderabad, India. The groundwater velocity is estimated using Darcy’s law. The range of values for hydraulic conductivity, porosity, and bulk density are determined to be 16.24–76.90 m day−1 (average 48.12 m day−1), 0.42–0.53 (average 0.47), and 1.01–1.43 g cm−3 (average 1.24 g cm−3), respectively. Using the estimated values of hydraulic conductivity, porosity, and the average value of hydraulic gradient between various wells at the site, the average groundwater velocity has been estimated to be around 1.0 m day−1 which matches fairly well with the groundwater velocity estimated using radioactive tracer techniques. These site-specific results will be useful in the radiological impact assessment of a proposed near surface waste disposal facility at Nuclear Fuel Complex, Hyderabad, India.

DEFINITION OF CALCULATION DISTURBANCE FOR AUTOMATIC CONTROL SYSTEMS PRESSURE PUMPING STATIONS TRUNK OIL PIPELINES

The automatic control system (ACS) pressure pumping station must ensure testing of the estimated disturbance associated with the shutdown of the pump at the next pump station (PS), or start one pump at the previous PS [1,2]. Estimated disturbance occurs as the result of several processes: - the occurrence of the initial perturbation, education waves flow and pressure at the station, where there was a start-up or shutdown of the pump; - the spread of this disturbance through the pipeline section between the point of origin of the perturbation and the station where the ACS pressure and attenuation as we move, reducing the amplitude and rise time. The wave, which reached ACS stantsiis pressure is called the incoming wave; - the interaction of the incident wave with a pumping station. The regulatory system should have such a speed that it creates a pressure wave had the opposite sign of the slope of the front and not less than the rise time estimated disturbance. In this paper, the expression for determining the initial disturbance that occurs when the pump is turned off at an intermediate transfer station without the tank farm. Pressure pump performance approximated full second-order polynomial (all the coefficients are different from zero). To calculate the attenuation slope coefficient of wave front defined linearization of unsteady flow of fluid through the hydraulic gradient value of the derivative of consumption. To determine the minimum length of the decay is taken to be 50 km. The interaction of the incoming wave is formed with a pumping station to the station reflected pressure wave and flow, moving along the conduit in a direction opposite to the direction of motion of the oncoming wave. The relationship of the pressure waves and flow rate determined by the formula «Zhukovsky». The equation for determining the slope of the front of the reflected wave at a certain steepness of the wave front the pressure considering the nonlinearity of the discharge characteristics of the station. Calculations to determine the calculated perturbations for pipeline DN 500 - 1200 mm.

Variation of hydraulic gradient in nonlinear finite strain consolidation

In the research field of ground water, hydraulic gradient is studied for decades. In the consolidation field, hydraulic gradient is yet to be investigated as an important hydraulic variable. So, the variation of hydraulic gradient in nonlinear finite strain consolidation was focused on in this work. Based on lab tests, the nonlinear compressibility and nonlinear permeability of Ningbo soft clay were obtained. Then, a strongly nonlinear governing equation was derived and it was solved with the finite element method. Afterwards, the numerical analysis was performed and it was verified with the existing experiment for Hong Kong marine clay. It can be found that the variation of hydraulic gradient is closely related to the magnitude of external load and the depth in soils. It is interesting that the absolute value of hydraulic gradient (AVHG) increases rapidly first and then decreases gradually after reaching the maximum at different depths of soils. Furthermore, the changing curves of AVHG can be roughly divided into five phases. This five-phase model can be employed to study the migration of pore water during consolidation.