Pore Water Pressure Distribution Research Articles

State-of-the-Art Review on Determining One-Dimensional Consolidation Parameters Based on Compression and Distribution of Pore Water Pressure: Coefficient of Consolidation (cv), End of Primary (EOP) Consolidation

State-of-the-Art Review on Determining One-Dimensional Consolidation Parameters Based on Compression and Distribution of Pore Water Pressure: Coefficient of Consolidation (cv), End of Primary (EOP) Consolidation

Hydrogeological characterization of low permeability medium for conceptualization of a mine site in Eastern Turkey

The mining site in Eastern Anatolia of Turkey were encounter a significant risk of slope instability within the operational area. One of the processes that govern slope stability is the pore water pressure distribution. The conceptualization and characterization of porous media serve as fundamental prerequisites for the implementation of numerical methods aimed at predicting pore water distribution. This study aims to characterize the hydrogeological properties of water bearing rocks in the active mining site in Eastern Anatolia of Turkey. A total of 21 wells and drill holes were drilled in the study area to conduct in-situ tests, monitoring, and sampling. The large diameter wells drilled in surrounding the carbonate rocks were to determine the groundwater flow and boundary conditions and also wells tapped metasediments and diorite unit for hydraulic testing. The lugeon tests and installation of vibrating wire piezometers were carried out at small diameter drill holes to obtain localized hydraulic conductivity of metasediments and diorite at different depths and monitoring pore water pressure distribution along some critical cross-sections. The results obtained from these tests are used for developing hydrogeological conceptual model for groundwater flow. The results of in-situ tests show that the metasediment and diorite units act as a single hydrostratigraphic unit. The metasediments and diorite have high total porosity and low specific yield indicating that the pore water is retained by electrostatic forces in the medium and it resists flow due to low hydraulic conductivity. The vertical variation in hydraulic conductivity values indicates that the medium is highly heterogeneous.

Effect of near-surface heterogeneities on the pore-water pressure distribution and slope stability

Effect of near-surface heterogeneities on the pore-water pressure distribution and slope stability

Study of hydrothermal processes in ice-layers subgrade under constant temperature and dynamic loading

The presence of ice-layers in the subgrade soils makes the hydrothermal state of road subgrade built in island permafrost regions more susceptible to external environmental influences. In order to deepen the study of the ice-layers subgrade, a hydrothermal study of subgrade under constant temperature and dynamic loading was carried out. It was found that dynamic loading can change the temperature, moisture and pore water pressure distribution. Under dynamic loading, the hydrothermal and pore water pressure state of the soil in the upper part of the ice layer changed significantly at the beginning of the test. The application of dynamic loads alters the spatial distribution of pore water pressure in the soil, resulting in pressure differences between different areas, which affects the migration of moisture and ultimately leads to the formation of areas with higher moisture content in the area below the load. However, the reduction in soil temperature will weaken the effect of the load, therefore, the temperature of the soil should be controlled for frozen subgrade with ice-layers to prevent the accumulation of moisture in the soil.

Seismic behavior of irregular underground structures in saturated sand

Sand liquefaction is one of the leading causes of severe earthquake damage. In this study, shaking table tests were carried out to investigate the dynamic interaction between the saturated sand and the irregular subway stations. In this test, a method for the preparation of a liquefiable foundation based on a flexible sensing chain combined with water sedimentation was proposed. Typical test results were interpreted, including the development and spatial distribution of pore pressure, surface subsidence, acceleration, deformation, and dynamic earth pressure. Results show that the spatial distribution of excess pore water pressure is changed by the irregular underground structure, and the liquefiable soil below the bottom plate of the structure can be divided into I, II, and III areas based on the degree of liquefication. The surface subsidence is significantly related to Arias intensity and is concentrated within the range of 5 %–95 % of the intensity. The structural floating is synchronized with the liquefaction of the saturated sand, and the uneven floating and inclination of the underground structure are remarkable, anti-flotation design of underground structures should take into account differences in section forms. During the liquefaction of saturated sand, the foundation soil has conspicuous lateral deformation, especially in the deep soil layer. The shape of the dynamic earth pressure increments turns from triangular to linear, when the foundation soil changes from non-liquefied to liquefied. Compared with the limiting values of the elastic inter-story drift ratio, the maximum inter-story drift ratio of the structure is smaller. The tensile strain responses on the columns, particularly in the lower layer, are more prominent than those at the slabs and side walls.

Experimental and Numerical Investigation of Rock Failure Process under Hydromechanical Coupling Action

Abstract In order to study the initiation mechanism of rocks under hydromechanical coupling, hydromechanical coupling triaxial tests and acoustic emission tests were carried out on basalt in the Xiluodu hydropower station dam site area in southwestern China. The test results indicate that the basalt displays typical hard brittle behavior, and its peak strength increases as confining pressure rises. Conversely, the peak strength decreases gradually as the initial water pressure increases, which leads to decreased hardness. Meanwhile, tensile failure is the main crack initiation mode under hydromechanical coupling action. During the stable crack growth stage, tensile failure is predominant, complemented by shear failure, with failures mainly occurring in the rock middle position. Contrary to this, during the unstable stage, the rock failure is mainly due to shear failure. The critical pore water pressure failure criterion of rock crack initiation under hydromechanical coupling conditions is derived based on the test results and introduced into the numerical simulation. The hydromechanical coupling failure process and pore water pressure distribution law of basalt are analyzed, and the rationality of the critical pore water pressure failure criterion is verified. These findings are significant for understanding the rock failure process under hydromechanical coupling action and provide a valuable reference for future research.

Coupling dynamic response of saturated soil with anisotropic thermal conductivity under fractional order thermoelastic theory.

In this paper, a two-dimensional (2D) thermo-hydro-mechanical dynamic (THMD) coupling analysis in the presence of a half-space medium is studied using Ezzat's fractional order generalized theory of thermoelasticity. Using normal mode analysis (NMA), the influence of the anisotropy of the thermal conduction coefficient, fractional derivatives, and frequency on the THMD response of anisotropy, fully saturated, and poroelastic subgrade is then analyzed with a time-harmonic load including mechanical load and thermal source subjected to the surface. The general relationships among the dimensionless physical variables such as the vertical displacement, excess pore water pressure, vertical stress, and temperature distribution are graphically illustrated. The NMA method does not require the integration and inverse transformation, increases the decoupling speed, and eliminates the limitation of numerical inverse transformation. The obtained results can guide the geotechnical engineering construction according to different values of load frequency, fractional order coefficient, and anisotropy of thermal conduction coefficient. This improves the subgrade stability and enriches the theoretical studies on thermo-hydro-mechanical coupling.

Analytical study of steady state seepage in a circular tunnel considering the outer boundary of the grouting ring as a non-constant head boundary

The influence of groundwater seepage on tunnel is not negligible, so it is very important to calculate the distribution of pore water pressure and the seepage volume accurately. The current analytical studies of seepage field in tunnels with grouting ring assume the head outside the grouting ring to be constant, which is accurate when there is a large difference between the permeability of the grouting ring and the soil body, but less accurate when there is a small difference in permeability. Accordingly, this paper combines a new conformal transformation method and the separated variable method to overcome the current problem of not being able to obtain an analytical solution after assuming the head at the outer boundary of the grouting circle as a non-constant head. And according to the obtained analytical solution and the existing analytical solutions and numerical simulation results for comparison, comparison results show that: when 1 ≤ kr/kg ≤ 100, the absolute value of the maximum relative error between the calculation results of the external pore water pressure of the grouting circle of the CVM solution and those of the numerical solution is more than 1.5 times of that of the analytical solution of this paper, and the maximum value is nearly 3 times of that of the analytical solution of this paper. Therefore, the analytical solution obtained in this paper by assuming that the outer boundary of the grout ring is a non-constant head is more accurate and has some applicability in the case where the permeability of the soil and the grout ring do not differ much. Finally, extensive parametric analyses of the permeability and thickness of the grouting ring and the depth of the tunnel are also performed to demonstrate the capability of the proposed analytical solution. In addition, the proposed analytical solution is much less computationally demanding compared to numerical software, but the accuracy is comparable.

Analytical solution for consolidation of saturated viscoelastic soils around tunnels with general Voigt model

This paper presents a novel analytical solution for the consolidation behavior of viscoelastic saturated soft soil subjected to large-scale ground loading. The rheological properties of clay are described using the general Voigt model. Based on the Terzaghi-Rendulic theory, the governing equations for the dissipation of excess pore water pressure in the surrounding soil mass of a tunnel are established under the first and second boundary conditions. The governing equations are solved using the complex variable method. The obtained solutions are verified by reducing them to the forms of three traditional rheological models, demonstrating the reliability of the proposed approach. Finally, based on the established solutions, the dissipation characteristics of excess pore water pressure around the tunnel are analyzed. The case results indicate that the soil permeability coefficient (k), the independent Newtonian viscosity coefficient (K0) and Hooke’s spring modulus (E0) in the general Voigt model have significant influences on the dissipation of excess pore water pressure and the degree of consolidation. A larger k, K0, and E0 lead to faster dissipation and consolidation development, while a greater tunnel buried depth (b) results in slower consolidation process. The influence of k on excess pore water pressure dissipation is more significant than that of K0 and E0. For the first boundary type, consolidation is instantaneous when k > 0.1 m/d. For the second type, when k < 0.0001 m/d, excess pore pressure remains unchanged within 100 d. The permeability condition of the tunnel has a considerable impact on the distribution of excess pore water pressure in the soil layer directly above the crown. When the tunnel is fully permeable, the effects of k, K0, and E0 on the dissipation of excess pore water pressure are more pronounced in the early stage, with almost complete dissipation of excess pore pressure above the tunnel before 100 d. However, when the tunnel is completely impermeable, their effects are more prominent in the later stage, and by 100 d, the maximum excess pore pressure within the depth range is 25 % of the initial.

Investigation on the pore water pressure in steel bridge deck pavement under the coupling effect of water and vehicle load

The water damage is a severe problem existing steel bridge deck pavement (SBDP) and still has not been fully studied. To investigate the pore water pressure of SBDP under the coupling effect of water and vehicle load, some typical permeability characterization parameters are selected firstly. Then, the water permeability simulation model under the most unfavorable vehicle load is established. Next, the spatial distribution of pore water pressure in different area of SBDP is analyzed and compared. Lastly, the process of water flow and pore water pressure changes are discussed. Results show that the simulation results are consistent with the characteristics of water permeability phenomenon during practical vehicle travel. The process of water flow and pore water pressure changes is corresponding to the pumping phenomenon in the engineering practice. This positive and negative cycle of pore water pressure could lead to spalling between asphalt and aggregate, which would accelerate the appearance and development of SBDP distress. This paper clarifies the permeability characteristics and pore water pressure change in SBDP. The findings are important for the design, construction and maintenance of SBDP to mitigate or avoid water damage.

Study of the Influence of Damage Structures in Coal Seam Floors on the Damage of Small Hidden Faults

In order to study the catastrophe law of small hidden faults along the floors of deep quarries under the coupled conditions of high stress and strong seepage, this paper proposes a concept of damage structure that can replace the overall performance of a population of tiny fracture swarms within a non-homogeneous rock mass. Numerical simulation software is used to simulate and analyze the influence of damage structure on the evolution of surrounding rock, regarding its plastic zones, shear stress, and displacement, and the pore water pressure distribution in small hidden faults along coal seam floors. This study shows that under the influence of damage structure, the shear stress of the rock above the fault shows “N”-type change, the displacement of the surrounding area shows “S”-type change, and the shear stress of the rock below the fault and the pore water pressure above the fault show “M”-type change. The damage structure changes the performance of the coal seam floor’s water barrier by reducing the strength of the rock surrounding the fault, blocking the release rate of the shear stress of the surrounding rock, weakening the support pressure of the fault, reducing the degree of expansion of the surrounding rocks and shifting the direction of concentration of the pore water pressure. The results of this study can provide a reference for technology for water damage prevention and control of coal seam floors containing small hidden faults, under the influence of non-homogeneous rock bodies.

Slope susceptibility map for preventive measures against rainfall-induced slope failure

Rainfall-induced slope failures frequently occurs in many urban areas around the world especially due to the impact of the global warming. Some slope failures result in casualties that have negative impacts on urban sustainability. The slope failures are normally observed near slope surface within the unsaturated zone above the groundwater table. Hence, it is important to incorporate the unsaturated soil mechanics principles in analysing the slope stability during rainfall. This study focuses predominantly on the regional stability analyses of residual soils within the Jurong Formation and Bukit Timah Granite in Singapore. The objective of the study is to develop slope susceptibility map as part of preventive measures against extreme rainfall conditions. The slope susceptibility map was evaluated using 2-D numerical analyses of slopes with historical failure. The recently developed sustainable retaining structure system, GeoBarrier System (GBS) is investigated to understand its suitability as a preventive measure for critical slopes with high risk as identified from the slope susceptibility map. Using Transient Rainfall Infiltration (TRIGRS) and Grid-Based Regional Slope Stability Analysis (Scoops3D), the pore-water pressure distributions and factors of safety (FS) within each zone are determined. The results from slope susceptibility maps and 2-D numerical analyses are consistent. Moreover, the incorporation of GeoBarrier System on the critical slope is demonstrated to be an effective slope stabilization measure based on the numerical simulations of two-dimensional analyses.

Upper-bound optimized solution of unsaturated soil slope stability under steady and unsteady flows

The increasing frequency of extreme weather events is leading to a rise in unsaturated soil slope instability near the earth's surface year by year. Establishing the method for analyzing slope stability under complicated hydrological conditions is imperative. This study proposes an approach that combines finite element (FE) seepage analysis with upper-bound limit analysis to evaluate the stability of unsaturated soil slopes. Two kinematically failure mechanisms are constructed based on the spatial discretization technique via point by point including the rotational and rotational-translational combinational failure modes, which can adapt to the complex pore water pressure distribution and varying soil unit weight. Additionally, a novel optimized solution scheme that integrates dichotomy and meta-heuristic optimization approaches is adopted to determine the factor of safety (FoS) and critical slip surface of slopes. The effectiveness and practicality of this method are validated by comparing with the published examples of slope stability evaluation under horizontal and inclined water table. Moreover, the variation of failure mode during the rainfall infiltration is illustrated by a case study of the slope under heavy rainfall. The methodological framework presented in this study can provide a basis for evaluating the stability of saturated–unsaturated soil slopes with 2D seepage conditions.

Model tests on penetration and seepage behaviors of a scaled suction caisson in sand

This study presents a new type of the offshore mooring foundation named as a scaled suction caisson (SSC), of which concept is inspired from the kinetic function of the scaled skin of snakes. When the SSC penetrates into the soil, the penetration resistance effectively decreases due to decreasing the friction force between the soil and sidewall. However, the bearing capacity increases due to increasing the friction force between the soil and sidewall when the SSC is subjected to pull load. A series of the suction-assisted installation model tests are carried out to investigate the penetration and seepage behaviors of the scaled suction caisson in sand. The result indicates that penetration resistance of the SSC increases with decreasing the aspect ratio H1/D1 of the scale structure. For example, when the aspect ratio H1/D1 equals 10, the penetration resistance decreases by 3.1% compared with the traditional suction caisson. And as the aspect ratio H1/D1 decreases from 10 to 5, the penetration resistance increases by 9.9%. In spite of these cases, it shows that reasonable selection of H1/D1 is helpful or not an obstacle to penetration. Furthermore, it is found that the height of the soil plug effectively decreases by the intermittent suction-assisted installation. The formula of calculating the penetration resistance of the SSC during suction-assisted installation is presented in terms of the excess pore water pressure distribution inside and outside the sidewall. The calculation results agree well with the model test results, indicating that the proposed formula of calculating the penetration resistance is reliable.

Evaluation of the Performance of the Horizontal Drain in Drainage of the Infiltrated Water from Slope Soil under Rainfall Conditions

It is known that rainwater infiltration is crucial for rainfall-induced slope failure because the infiltrated water can significantly weaken the shear strength of unsaturated soil. Horizontal drains are commonly used to provide appropriate drainage for the rainwater that percolates out of a slope. However, the effects of the length and location of the subsoil pipe on the performance of horizontal drains have not been extensively investigated. In this paper, a parametric analysis by using a numerical model was adopted to investigate the distribution of pore-water pressure in a slope. The results reveal that an inclination angle of 10–15 degrees and strategic placement at the slope toe and mid-slope provide optimal drainage performance, as compared to the effect of pipe length. Multi-layers of horizontal drain (based on 10 m length) are recommended for slopes with a height of more than 15 m.

Experimental investigation on the efficiency of the phase change materials for enhancing the thermal performance of energy piles in sandy soils

The application of phase change materials (PCMs) is an efficient technique for enhancing the thermal properties of energy piles. In most previously applied studies, paraffin-based materials with low melting temperatures were implemented as PCM to improve energy piles in cold climate conditions. This study explored the efficiency of using lauric acid as a PCM in energy piles by performing small-scale physical model tests under warm climate conditions. Two concrete energy piles with the same diameter of 58 mm and length of 830 mm with PCM and without it were placed in the center of a tank filled with silica sand. The energy piles went through a series of heating tests with the loading temperature (corresponding to the initial temperature) of +10 to +40 °C. To analyze the effect of implementing lauric acid on temperature, and pore water pressure (PWP) distributions in sandy soil, digital thermometers and pore pressure transducers were used in different parts of the inlet side of the model. Results were compared between the two piles with and without PCM in dry and saturated media. The achieved results demonstrate that by adding 1.5% of lauric acid to the energy pile, temperature changes along the pile can be reduced up to 13% in the dry and 10% in the saturated condition. Also, the temperature changes in the soil media could be decreased by up to 5% in dry media. Additionally, the induced excess pore water pressure around the modified energy pile with lauric acid was about 2.14 times lower than the conventional pile. Besides the reduction in the temperature and PWP, the extracted power had an upward trend by increasing the thermal loading. The results revealed that due to the phase transition process, applying a small amount of lauric acid in the energy piles reduces the temperature fluctuations-related responses and could improve the thermal performance of the heat exchange system.

Analytical solution of electroosmotic-surcharge preloading coupled consolidation for unsaturated soil via Electric Prefabricated Vertical Drains (EVDs)

Electric prefabricated vertical drain made of new geosynthetic materials has the advantages of corrosion resistance, good water filtration, and unobstructed drainage. It has been used in unsaturated soils for embankment and slope stabilization as well as roadbed improvement. A theoretical model of the axisymmetric, free-strain consolidation for unsaturated soil under the coupled electrical-flow-mechanical fields considering radial-vertical flow is formulated, using the homogenization theory, method of separation of variables, and Bessel-Fourier series orthogonality. The relevant cases of saturated and unsaturated conditions are compared with the current analytical solution to examine the validity. The spatial and temporal distributions of excess pore-water and pore-air pressure are accurately reflected in the proposed solution, and its variation under electric fields is effectively displayed. The numerical calculations are also performed to investigate the effects of various important parameters, such as the single-layer unsaturated soil thickness, the effective voltage, and the radial water-to-electrical permeability ratio, on the excess pore-water pressure, excess pore-air pressure, and surface settlement. It is observed that the final negative pore-water pressure and the final settlement increase linearly as the effective voltage increases.

Numerical investigation of solute migration and release from sediments driven by wave-induced accumulation of pore water pressure

Sediments with poor drainage conditions are prone to build-up of excess pore water pressure when exposed to dynamic wave loading. This results in accumulated seepage flow that may have a significant impact on migration of solutes in marine sediments. In this study, the complex interplay between solute transport and wave-induced seepage process is investigated through a pioneering approach that combines and synchronously solves the two-dimensional advection-dispersion equation governing nonreactive solute transport with the governing equations for wave-induced oscillatory and residual pore pressures. The simulated results have demonstrated that the accumulated seepage flow significantly contributes to the advective and dispersive fluxes of solute, where the advection leads to movement of the solute layer and the hydrodynamic dispersion primarily enlarges the thickness of solute layer. The distribution of residual pore water pressure along depth exhibits two patterns that are primarily influenced by the thickness of the seabed. When the seabed is thinner than 0.3 times the wavelength, the residual pore pressure increases monotonically with depth (Pattern I). In this situation, the solute always migrates upwards to the seabed surface. Otherwise, Pattern II depicts the distribution of residual pore pressure, where the peak value of residual pore pressure attains at a certain depth and may advance downwards with wave action time. In this case, the direction of solute migration in regions shallower than a certain depth (e.g., 0.6 times the thickness of sediment) may alternate over time but the solute can eventually be transported upwards to seabed surface. The parametric study shows that when the seabed thickness is 0.2–0.3 times the wavelength, accumulated seepage flow has less effect on solute migration, whereas decreasing relative density and shear modulus, as well as increasing soil permeability can enhance the effect of accumulated pore water pressure on solute migration.

Finite Element Analysis and Prediction of Rock Mass Permeability Based on a Two-Dimensional Plane Discrete Fracture Model

The safety of underground engineering projects is significantly influenced by groundwater. One of the key complexities is identifying the primary seepage paths within underground rock formations, understanding the patterns of seepage, and determining the effects of fracture parameters on the fluid movement inside the rock mass. To address these issues, a probabilistic model is constructed for random fractures using the finite element method, reflecting the random nature of fracture distributions in the real world. This model allows for an in-depth examination of the distribution of pore water pressure and Darcy velocity field, revealing the permeability trends in fractured rock masses. A variety of fracture models were devised to understand the relationship between factors such as fracture density, length, length power law, angle, dispersion coefficient, aperture, and power law, and how they affect the overall permeability of rock masses. The study suggests that, in the context of discrete fractured rock masses, there is a linear increase in permeability with an increase in fracture density and aperture. Moreover, fractures of greater length lead to increased permeability, with fractures aligned with the direction of water pressure having the most impact on seepage velocity. A thorough investigation of the factors that affect each fracture parameter was performed, and the permeability of each model was computed. From these findings, a series of predictive equations were suggested for estimating rock permeability based on fracture geometry parameters.

Analytical solutions for consolidation of stone column composite foundations considering time-dependent boundary and loading

In response to the existing consolidation theory for stone column composite foundations which cannot consider the time-dependent loading and the well resistance effect of stone columns under time-dependent boundaries, a consolidation model that can reflect these characteristics is developed in this study, and the corresponding analytical solutions are obtained under permeable top surface with permeable bottom surface (PTPB) and permeable top surface with impermeable bottom surface (PTIB), respectively. In addition, the reliability of the proposed solutions is verified by comparing them with existing analytical solutions. Extensive calculations are then performed by the proposed solutions to analyze the consolidation behaviors of stone column composite foundations under time-dependent boundaries, the results show that the interface parameters have a large effect on the distribution of excess pore water pressure (EPWP) along the depth; for projects with longer construction time, the permeability of the top and bottom surfaces of the composite foundation has a smaller effect on the average consolidation rate. Finally, the proposed solution is applied to the settlement calculation in an actual engineering project, and the theoretical results show a general agreement with the measured data by considering the influence of the interface parameters.