Variation Of Pore Water Pressure Research Articles

Simulation and Evaluation of the Pore Water Pressure Variations with Groundwater Levels Variations at the Depths

Simulation and Evaluation of the Pore water pressure (P) variations with the Depths, which did carefully by the Viet Nam Standard “TCVN 4197:2012”; “TCVN 8723:2012” and “TCVN: 8721: 2012. Research results presented particularly for Permeability Coefficient (χ) obtained 1.00E-08; whereas the minimum value has only shown 2.00E-09 at 0.5 kg/cm2 and 8.0 kg/cm2 at 24.3m depths. On the other hand, the pore coefficient (ε) variations decreased gradually as the increasing depths; whereas the minimum value obtained 0.685 at 27.3m depth. Moreover, standards viscosity (B) and Compaction density (ζ) increased gradually as the depths increased gradually. From the analysis, simulation of the Pore water pressure with depths was calculated particularly with remarkable results, which as done by the Plaxis 3D software, so results presented in 360 kN/m2 at 4.0m and minimum value of 20 kN/m2 at 38.0m depth. In conclusion, research results can be applied and credited affections to the construction deformation. Moreover, research results can be used as useful references for engineers of Civil, Geology, researchers, and scientists in the future.

Cavity expansions in partially drained soils and a comparison to CPT results

Cylindrical and spherical cavity expansions in soils are of interest, especially when interpreting cone penetration tests (CPTs) and pressuremeter tests (PMTs). Here the cavity expansion problem is solved semi-analytically, considering partial drainage of the soil, when the cavity wall velocity is constant. The solutions may assist with the interpretation of CPTs and PMTs when partially drained conditions prevail in the surrounding soils. The solution procedure involves writing the governing partial differential equations in dimensionless form. The modified Cam-clay constitutive model is adopted for the soil to demonstrate the solution procedure, due to its wide familiarity, although other models could be used by making simple modifications. The variables in the partial differential equations are functions of a dimensionless time, T, and a dimensionless radial coordinate, H. T depends on cavity radius, the time after expansion began and a coefficient of consolidation. The equations are solved for when T is fixed, simultaneously as an initial value problem, as the partial differential equations become ordinary differential equations. Important features captured by the analyses include pore water pressure variations with soil volume changes, as well as the differential of the pore water pressure satisfying the no-flow cavity wall boundary condition. Results for a cavity expansion reveal that initially, when T and the cavity are small, drained conditions prevail. As T and the cavity become larger the soil becomes partially drained and eventually undrained. T is analogous to the dimensionless cone penetration velocity used in CPT studies. Normalised cavity wall pressures vary with T similar to that of normalised cone penetration resistances, demonstrated using experimental data. Plots of the normalised cavity wall pressures against the state parameter show that the two key fitting constants are heavily influenced by partial drainage. A similar dependence must exist when plotting a normalised cone penetration resistance against the state parameter when partially drained conditions prevail. The practical ramifications of not dealing with this partial drainage may be huge, especially when assessing liquefaction susceptibility through estimations of the state parameter using correlations developed for when drained conditions prevail. Significant underestimations of state parameter, liquefaction susceptibility and post-liquefaction strengths may result.

Experimental and computational analysis of thermal consolidation of prefabricated vertical drains using solar energy

This investigation was conducted on reconstituted clay with prefabricated vertical drains to assess the performance of solar energy-based thermal consolidation. Variations in temperature, excess pore water pressure and surface settlement under ambient temperatures and solar heating conditions were observed by two loading methods, multistage loading and vacuum preloading. A theoretical calculation of the coupling impact of multistage loading and solar heating was performed. And the economic cost was analyzed for practical engineering application. It was found that solar heating contributes to sinusoidal variations in soil pore water pressure and settlement rate, with the former rising during the day and dissipating at night and the latter increasing at night and decreasing during the day. The cost of foundation treatment increases by 5.66% when using solar heating method, but it will be close to the cost of traditional vacuum preloading as time costs rise.

The importance of permeability in modelling soil-atmosphere interaction

Soil-atmosphere interaction has been attracting increasing interest as the seasonal variation of pore water pressures (pwp) has been linked to a variety of geotechnical problems (e.g. slope stability and serviceability, foundation subsidence or swelling, desiccation cracking etc.) or has been identified as part of the solution of geotechnical problems (e.g. in sustainable urban drainage systems). Prediction of how the pwp will change within soils of low permeability under the combined effect of evapotranspiration and precipitation requires adequate knowledge of the soil permeability and how it varies spatially (e.g with depth) and temporally (e.g. with suction or degree of saturation, void ratio or due to the opening and closing of desiccation cracks). Nonetheless, in-situ measurements of permeability that satisfy both the spatial and temporal variation are difficult. In order to clarify the importance of variable permeability in predicting pwp variations under atmospheric loads, a series of one- and two-dimensional finite element analyses was performed, where the permeability model and the variation of permeability were parametrically studied. The results demonstrated that the variation of permeability, as well as the model employed in the analysis, e.g. allowing or not for desiccation cracking, influenced the values of suction calculated as well as the pwp profile with depth, highlighting the importance of estimating the spatial and temporal variation of permeability with some level of confidence.

3D effects of soil-atmosphere interaction on infrastructure slope stability

It has long been established that pore water pressure (pwp) variations affect the stability and serviceability of slopes. Pwp variations may be due to consolidation/swelling processes within soils of low permeability or may be due to seasonal evapotranspiration and precipitation processes. The simultaneous study of such phenomena and of hydro-mechanical coupling in sloping ground requires use of advancednumerical methods. Often, infrastructure slopes are considered in plane strain (two-dimensional) conditions for simplicity and to date this is the case for most numerical analyses considering soil-atmosphere interaction. However, this approach makes it impossible to study the longitudinal extent of a possible slip surface forming following vegetation removal. Three-dimensional, fully-coupled numerical analyses of acut slope were performed herein to study the effect of vegetation clearance on stability and explore numerically ways of implementing effective vegetation management.

Analysis of spatiotemporal variations of excess pore water pressure during mechanized tunneling using genetic programming

Analysis of spatiotemporal variations of excess pore water pressure during mechanized tunneling using genetic programming

Measurement of Physical Parameters for Transient Seepage Assessment of Levees

Abstract An embankment was instrumented and monitored as part of a multiyear project to assess appropriate pore-water pressure distributions and soil water retention curves for use as initial conditions in transient seepage analyses. The increased use of unsaturated soil mechanics and transient seepage has led to the need for practical methods of assigning accurate properties and initial conditions in these types of analyses. Monitoring results were validated against published pore-water pressure measurements collected from multiple embankment studies. The collected distributions showed nonlinear behavior in near-surface embankment soils due to infiltration and evapotranspiration processes. Seasonal variations in pore-water pressure and the soil moisture deficit were shown to correlate at the monitoring site. The seasonal response of the embankments exhibited a large variation in pressures between summer and winter. Assessment of flood occurrence showed the distribution of pore pressures during flood loading was typically near −10 kPa at a depth of 2 m at the onset of the flood. Laboratory soil water retention testing of undisturbed samples collected from the embankment showed that when compared with field measurements, they overestimated the field response for the considered initial water content and dry density values. Also, comparisons between hydrostatic pore pressures above the phreatic surface showed that at soil moisture deficits greater than 20 mm, the difference between the measured and hydrostatic pore pressures greatly increased. The laboratory and monitoring results were used to provide practical methods of assigning representative pore-water pressure distributions and material properties necessary for performing transient seepage analyses. These results will aid in more accurate transient seepage analyses of flood control embankments.

Three-dimensional reliability analysis of unsaturated soil slope considering permeability rotated anisotropy random fields

The spatial variability is an inherent characteristic of soils. In addition to isotropic and transversely anisotropic soils, rotated anisotropic soils can also be observed in nature owing to deposition and weathering. Recent studies revealed that the spatially variable soil strength parameters can significantly affect rotated anisotropically deposited soil slope stability. However, the influence of spatial variability of saturated water permeability (ks) on this type of slope stability has been not fully understood, especially for the three-dimensional (3D) slope analysis. This paper aims to investigate unsaturated soil slope reliability with 3D ks rotated anisotropy random fields under rainfall infiltration. Due to the low efficiency of the covariance matric decomposition method (CMD) in simulating large-scale 3D rotated anisotropy random fields, a modified CMD method is proposed to save the computational cost. Moreover, comparisons between 2D and 3D random finite element analyses are also discussed. The results indicate the modified CMD method can markedly improve computational efficiency by more than 3.3 times compared with the CMD method. Only applying variations of pore water pressure (PWP) of a section or groundwater table (GWT) cannot sufficiently account for the uncertainty of slope stability. The cross-dip slope, where the dip direction of the slope is perpendicular to the dip direction of strata, has a larger reliability index (1.3−3.0 times) than the dip slope and reverse slope at the same soil bedding plane orientation. The most unfavorable soil bedding plane orientation for the cross-dip slope and the dip/reverse slope is 0° (horizontally deposited) and 30° (slightly larger than slope angle), respectively. It is attributed to the relatively low ks along these two orientations being more likely to form the aquiclude, affecting overall variations of PWP, leading to a larger standard deviation of the factor of safety and a lower reliability index. Furthermore, the reliability of cross-dip slope can only be studied in 3D, while the dip slope and reverse slope reliability can be studied with 2D analysis to decrease computational burden when the slope length does not exceed 50 m.

Experimental study of one-dimensional nonlinear consolidation of an aquitard under multistage loading

• Design of experimental instrument for simulating consolidation of aquifer system. • Monitor the parameters of aquitard and characterize their nonlinear distribution. • Conduct multistage loading to simulate complex and realistic loading conditions. • Reverse pore water pressure fluctuations occur in the thicker aquitard. • Calculate the curves of pore water pressure base on different hydraulic conductivities. Aquifer heterogeneity is critical for predicting processes involved in the dissipation of pore water pressure, consolidation, and rebound. The consolidation and rebound of aquifer systems should consider the spatiotemporal variation in the hydraulic and mechanical parameters of the aquifer and aquitard. In this study, a series of laboratory experiments was conducted to characterize the consolidation and rebound of the aquifer system and estimate the hydraulic conductivity of the aquitard. The experimental results revealed that under multistage loading, the compression in the upper part of the aquitard tended to decrease, while the compression in the lower part of the aquitard tended to increase. In addition, the variation in hydraulic conductivity and deformation of the aquitard were closely related and reasonably matched at each stage. Moreover, a one-dimensional consolidation model was developed to simulate the variation in pore water pressure and compare it with the experimental pore water pressure. Reverse pore water pressure fluctuations occurred within a part of the aquitard away from the drainage boundary. Compared to the theoretical curves, the experimental curves of the pore water pressure calculated from the initial and asymptotic hydraulic conductivities exhibited delayed and advanced effects. These findings can help elucidate the characteristics of consolidation and rebound of aquifer systems and the spatiotemporal variation in hydraulic conductivity.

Simulation and Evaluation of the Pore Water Pressure Variations with Groundwater Levels Variations at the Depths

Simulation and Evaluation of the Pore water pressure (P) variations with the Depths, which did carefully by the Viet Nam Standard “TCVN 4197:2012”; “TCVN 8723:2012” and “TCVN: 8721: 2012. Research results presented particularly for Permeability Coefficient (χ) obtained 1.00E-08; whereas the minimum value has only shown 2.00E-09 at 0.5 kg/cm2 and 8.0 kg/cm2 at 24.3m depths. On the other hand, the pore coefficient (ε) variations decreased gradually as the increasing depths; whereas the minimum value obtained 0.685 at 27.3m depth. Moreover, standards viscosity (B) and Compaction density (ζ) increased gradually as the depths increased gradually. From the analysis, simulation of the Pore water pressure with depths was calculated particularly with remarkable results, which as done by the Plaxis 3D software, so results presented in 360 kN/m2 at 4.0m and minimum value of 20 kN/m2 at 38.0m depth. In conclusion, research results can be applied and credited affections to the construction deformation. Moreover, research results can be used as useful references for engineers of Civil, Geology, researchers, and scientists in the future.

Analysis of Mechanical Performance of Double-Arch Biological Channel in the Operation Period considering the Effect of Fluid-Solid Coupling

In order to solve the problem that highway development needs to cross environmentally protected areas, which results in the cutting off of wildlife habitats and fragmentation of the biosphere, on-road biological passages are established in many places. This paper carries out a numerical analysis of the biased load, caused by the backfill of the biological channel, the environment, and the seepage problem of the backfill under rainfall conditions. By comparing the pore water pressure’s test data in backfill with the modeling result data, the influence law of biased pressure load on open hole lining during running period, and the law of water pressure change are derived. The analysis shows that: (1) the backfill soil has a restraining effect on the double-arch tunnel, and the side arch ring’s deformation of the backfill decreases with the increase of the height of the backfill; when backfilling on both sides is flush with the top of the cave and continuing to backfill at the cave’s top, the arch ring near the higher mountain deforms greater because of the mountain’s pressure. (2) The internal force of the channel and the temperature are closely relevant, and the value is gradually stable without the influence of construction or other causes. (3) Pore water pressure variation correlates with seasons: the water pressure is lower in winter and higher in summer. After the pore water is saturated, the monitoring data does not change with the increase of rainfall.

Effect of concreting pressure on ground response caused by installation of diaphragm wall panels

The ground response during diaphragm wall panel installation is strongly affected by the support slurry pressure, and by the subsequent lateral pressures during the tremie placement and set-up of wet concrete. The support slurry pressure can be reliably assumed as hydrostatic within the excavated trench, whereas the lateral concreting pressure is much more complex due to the stiffening effect of wet concrete. This paper reviews the measurements of wet concrete pressures from a series of instrumented diaphragm wall panels which show that lateral pressures in the concrete slurry increase as the tremie displaces bentonite slurry and reach a maximum condition about 1 h after placement, while conditions over the longer term closely approximate the hydrostatic pressure of the bentonite-filled trench. The maximum increase of pressure varies at different heights of the same trench, and also varies for two separate panels in the same project, reflecting the varying velocity of concreting. Model tests of concreting pressure on formwork also demonstrate that the lateral pressure reduces from hydrostatic wet concrete pressure a few hours after casting. A time-dependent lateral concreting pressure model is developed to represent these measurements more realistically. This proposed model is implemented into a finite-element program to investigate its effects on the ground response due to the concreting process. Computed results from a reference case can capture the progressive variations of ground movement, earth and pore water pressure in the soil adjacent to the trench during and shortly after the concreting process, which is consistent with the reported measurements.

Post-failure process and kinematic behavior of two landslides: Case study and material point analyses

This paper presents a comprehensive and well-documented landslide case study involving detailed site investigation, field tests, seismic signal analyses, and advanced numerical analyses using the material point method (MPM) to investigate the post-failure process and kinematic behavior of two landslides. The slope failures were triggered by Typhoon Jangmi in September 2008 and had impacts on the downslope residential areas. The background information of two landslides, including geological and hydrological conditions obtained from the detailed site investigation and field tests, was first introduced. The MPM analyses were then conducted and validated by comparing measured and predicted results for the final landslide profiles and duration. The numerical results, including variations in deviatoric strain, volumetric strain, and excess pore water pressure with time, were further examined to determine the post-failure mechanism of the landslides. The effects of soil drainage conditions during landslides on the final landslide profile were also compared and discussed. This study demonstrated that MPM analyses could accurately predict the runout distance of both landslides. The numerical results indicate that the landslides occurred through a complex process of soil failure that involved the stages of shearing, translational movement, compression, and deposition. When the soil was subjected to different loading conditions in different stages, the corresponding post-failure mechanisms are also different. High positive excess porewater pressure could develop near the sliding surface and has a significant influence on landslide kinematics and final landslide profiles. Compared with undrained analysis, fully coupled analysis, which permitted porewater pressure dissipation during a landslide event, produced more accurate predictions of landslide kinematics.

New simplified transient method for determining the coefficient of permeability of unsaturated soil

The instantaneous profile (IP) method is widely used for determining the coefficient of permeability of unsaturated soils. IP method requires the measurement or control (i.e., zero flux) of flux at any one end of a soil profile. Besides, there are requirements of variations in volumetric water contents (VWCs) and pore-water pressures (PWPs) at various points from the above-mentioned one end of the soil profile to a particular point in which the unsaturated coefficient of permeability is derived. The measurement or control of flux at one end of the soil profile requires high accuracy which causes difficulty while performing tests in the laboratory and field. To overcome the difficulty of the IP method, this study proposes a new simplified transient method for determining the coefficient of permeability of the unsaturated soil. Variations in volumetric water contents and corresponding pore-water pressures at three points are required in the new simplified transient method. The intellectual advantage of this method as compared to the IP method is that there is no need to measure or control the flux at one end of the soil profile. Therefore, this new method is more practical and is expected to be widely used in both laboratory tests and field tests. The validity of the new simplified transient method is verified through numerical simulations considering a one-dimensional seepage for four different types of soils including coarse-grained soil, sand, clay, and silty sand with gravel. The applicability of the new simplified transient method is demonstrated by comparing the unsaturated coefficients of permeability of soils computed by the new simplified transient method and the IP method. Good agreements in comparisons prove that the new simplified transient method is effective for determining the unsaturated coefficient of permeability of soil regardless of soil types and hydraulic functions features.

Correlating groundwater level and shear strength: Kotkai Pakistan landslide as case study

Earth-fill dam failure and landsliding during heavy rainfall and flooding is a common problem observed all over the world. This paper examines and discusses the causes of landsliding due to rainfall and flooding. Climatic rainfall data are interconnected with rainfall precipitation and its effect on the increase in pore water pressure inside soil slopes. Various soil slopes with different geometries and material properties are analysed, and the variation in pore water pressure and the slope factors of safety (FSs) are calculated. Correlations between the groundwater level (GWL) and slope FS are developed in both seismic and non-seismic situations. Correlations between shear strength (τ), shear stress (σ) and FS are also developed. The Kotkai landslide in Pakistan is considered a case study for cross-checking the correctness of the developed correlations. These correlations can be applied to design a safe soil slope in intense flood and rainfall areas.

Experimental study on static characteristics of the Yellow River silt under (triaxial) consolidated undrained conditions

The siltation of reservoirs and rivers in the Yellow River Basin and the occurrence of flood disasters are mainly caused by silt transportation. The Yellow River silt being applied to practical production will help solve the problem of siltation in the Yellow River. In this paper, the consolidated undrained (CU) test of the Yellow River silt is carried out by using GDS triaxial apparatus. The effects of confining pressure, relative density and loading rate on the stress-strain relationship, strength parameters, generalized shear stress ratio and pore water pressure variation of the Yellow River silt are explored. The results show that, under the same axial strain, the deviator stress increases with the increase of confining pressure and relative density, and decreases with the increase of loading rate; compared with the relative density, the effect of the confining pressure and loading rate on the generalized shear stress ratio is insignificant. The friction angle is affected by relative density and confining pressure in varying degrees, but less by loading rate. The secant modulus and initial tangent modulus increase with the increase of confining pressure and relative density. The pore water pressure first increases to the positive peak value, and then decreases to a negative value gradually with the increase of axial strain under most conditions. The pore water pressure variation is affected by the confining pressure and relative density obviously, while affected by the loading rate insignificantly.

The Influence of Shell Permeability on Stability of Upstream Slope during Rapid Drawdown – Khassa Chai Earth Dam as a Case Study

Several factors affect the stability of earth dam during sudden drawdowns such as permeability and mechanical properties of soil, upstream side slope, drawdown ratio, and drawdown rate. This paper investigates the influence of shell permeability on earth dam upstream slope stability and its role in the change of pore water pressure at different locations of the embankment during the sudden drawdown, using different limit equilibrium methods. To accomplish the objective of this study, (Geo Studio 2012 Software) as one of the powerful geotechnical programs was used for the modeling and numerical analysis. The study shows that decreasing in the shell permeability resulted in the reduction of pore water pressure dissipation and variation of shell hydraulic conductivity plays a vital role in the overall stability of the upstream slope under rapid drawdown conditions.

Tracking and modelling water percolation process in modern intensive farming loess terraces

Loess slopes along the Yellow River in China are prone to failure in response to intensive irrigation. Existing studies found that the wetting front depth subjected to intensive farming water could barely reach 6 m in loess terrace. Long-term field monitoring revealed that irrigation water takes a short time to recharge the groundwater. Yet the dynamic process and mechanism of irrigation water percolation through thick unsaturated loess remains unrevealed. To address this problem, the Heifangtai terrace was selected as the study area and a series of unique full-scale controlled field irrigation experiments were carried out combined with numerical modelling. The variations in water content, pore-water pressure, and electrical resistivity over time were monitored. From the field testing, the unsaturated stratified loess layer could be divided into two vadose zones based on the water percolation characteristics, namely, transient flow zone (0–6.5 m) and steady flow zone (>6.5 m). Variation in water content presented a hysteresis effect in the transient flow zone compared with the steady flow zone. In the whole seepage process, the vertical percolation rate of 0.5 m/day was double that of the horizontal percolation rate. Furthermore, the irrigation water percolating process was modelled using a finite element code, PANDAS, which was validated by the field testing. Numerical simulation results demonstrated that the movement of wetting front was hampered by the air outflow within transient flow zone and that irrigation water reached the deep groundwater table through the thick unsaturated stratified loess within 100 days, which was consistent with the field monitoring data. This research aids in a better understanding of the irrigation water percolation process in unsaturated stratified loess in the loess region.

Effect of Seismic Loading on Variation of Pore Water Pressure During Pile Pull-Out Tests in Sandy Soils

Experimental model was done for pile model of L / D = 25 installed into a laminar shear box contains different saturation soil densities (loose and dense sand) to evaluate the variation of pore water pressure before and after apply seismic loading. Two pore water pressure transducers placed at position near the middle and bottom of pile model to evaluate the pore water pressure during pullout tests. Seismic loading applied by uniaxial shaking table device, while the pullout tests were conducted through pullout device. The results of changing pore water pressure showed that the variation of pore water pressure near the bottom of pile is more than variation near the middle of pile in all tests. The variation of pore water pressure after apply seismic loading is more than the variation before apply seismic loading near the middle of pile and near the bottom of pile and in loose and dense sand. Variation of pore water pressure after apply seismic loading and uplift force is less than the variation after apply seismic loading in loose sand at middle and bottom of pile.

Investigation on the Responses of Overburden Stress and Water Pressure to Mining under the Reverse Fault

This paper focuses on the responses of overburden stress and pore water pressure in confined aquifer to mining under the Ordovician limestone aquifer and the reverse fault. Taking 32 coal seam mining in the first eastern mining area of Qianyingzi coalmine in China as engineering background, on the basis of the mining hydrogeological and engineering geological model of the study area, a numerical calculation model considering the fluid-solid interaction is established. Simulation results indicate that the variation characteristics of pore water pressure in confined aquifer and overburden stress are affected by both mining effect and geological tectonics and are closely related to the shear failure of the reverse fault plane caused by mining effect and the failure characteristics of the overburden strata in the stope. According to the variation of pore water pressure before and after the roof water inrush, the reduction range of pore water pressure can be used as one of the early warning indicators for water inrush accidents. These new understandings are of reference value to the mining water inrush under the combined action of reverse faults and confined aquifers and to the establishment of corresponding forecasting and early warning systems.