Soil Pore Water Pressure Research Articles

A Preliminary Study of the Seepage Hammer Effect and Its Impacts on the Stability of Layered Infinite Slope

A rapid change in the pore water pressure of unsaturated soil due to a wetting front is a crucial factor and may result in instabilities in layered slopes. This study presents preliminary research on such a change, which we define as the seepage hammer effect. Vertical infiltration with multiple soil layers by column test was implemented to investigate the mechanism of the seepage hammer effect and distinguish it from the well-known Lisse effect and reverse Wieringermeer effect. A two-phase flow model was utilized to understand the evolutions of pore water/air pressure and volumetric water content, and its result evolved into a layered infinite slope stability analysis. Thus, the impacts of the seepage hammer effect on slope stability can be analyzed. This study found that the seepage hammer effect was triggered when the wetting front reached the interface of multiple layers and impermeable layers, and the rising speed of pore water pressure was proportional to the air venting capacity of soil. Slope stability analysis showed that the safety factor may decline suddenly because of the seepage hammer effect. Its relationship with the factor of safety and the sliding velocity is proportional. The detection of the seepage hammer effect could be a potential application of the study of fast-moving landslides.

Prediction of the Soil Permeability Coefficient of Reservoirs Using a Deep Neural Network Based on a Dendrite Concept

Changes in the pore water pressure of soil are essential factors that affect the movement of structures during and after construction in terms of stability and safety. Soil permeability represents the quantity of water transferred using pore water pressure. However, these changes cannot be easily identified and require considerable time and money. This study predicted and evaluated the soil permeability coefficient using a multiple regression (MR) model, adaptive network-based fuzzy inference system (ANFIS), general deep neural network (DNN) model, and DNN using the dendrite concept (DNN−T, which was proposed in this study). The void ratio, unit weight, and particle size were obtained from 164 undisturbed samples collected from the embankments of reservoirs in South Korea as input variables for the aforementioned models. The data used in this study included seven input variables, and the ratios of the training data to the validation data were randomly extracted, such as 6:4, 7:3, and 8:2, and were used. The analysis results for each model showed a median correlation of r = 0.6 or less and a low model efficiency of Nash–Sutcliffe efficiency (NSE) = 0.35 or less as a result of predicting MR and ANFIS. The DNN and DNN−T both have good performance, with a strong correlation of r = 0.75 or higher. Evidently, the DNN−T performance in terms of r, NSE, and root mean square error (RMSE) improved more than that of the DNN. However, the difference between the mean absolute percent error (MAPE) of DNN−T and the DNN was that the error of the DNN was small (11%). Regarding the ratio of the training data to the verification data, 7:3 and 8:2 showed better results compared to 6:4 for indicators, such as r, NSE, RMSE, and MAPE. We assumed that this phenomenon was caused by the DNN−T thinking layer. This study shows that DNN−T, which changes the structure of the DNN, is an alternative for estimating the soil permeability coefficient in the safety inspection of construction sites and is an excellent methodology that can save time and budget.

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.

Dynamic pore water pressure in saturated soil due to turbine engine’s vibration

The turbine engine that is operating will generate vibrations that are transmitted by the foundation into the soil layer. This causes the pore water pressure in the soil to increase, which causes the shear strength of the soil to decrease and can reduce the carrying capacity of the soil as a foundation resting place, which results in a reduced bearing capacity of the foundation as well. The pore water pressure in the soil consists of static pore water pressure and excess pore water pressure. Static pore water pressure is hydrostatic pressure that depend on Ground Water Level (GWL), while excess pore water pressure is the pore water pressure that occurs due to changes in undrained soil stress. Therefore, a study was conducted on the effect of gas turbine engine vibration on pore water pressure in sand and clay soils with a depth of 8,5 m (fine to coarse sand), 10,5 m (silty clay), and 12,5 m (medium to coarse sand). From the research results, the value of the pore water pressure ratio for each layer of soil was 0,32, 0,02, and 0,49, which can reduce the bearing capacity of the pile, especially in sandy soils and if the value is greater than one, it can be concluded that the soil has the potential for liquefaction.

Correlation of excess pore water pressure ratio on flow liquefaction phenomenon in Sibalaya – Central Sulawesi Province

On September 28, 2018, liquefaction in Sibalaya damaged irrigation canals and hit 51.2 hectares fields and roads. This phenomenon was triggered by an earthquake of magnitude 7.5 that shook Sigi Regency, Central Sulawesi Province. As an increase in soil pore water pressure is one of the causes of liquefaction, the pore water pressure ratio (ru) at the study site was analyzed. Then, this figure is used as a point of reference to determine the liquefaction potential. Standard Penetration Test (SPT) data and laboratory tests from four boreholes resulting from soil investigations in 2021 with a maximum depth of 20 meters were utilized in this study, along with microtremor data down to the depth of bedrock from test results in 2023. Based on the data, the liquefaction potential was assessed using the one-dimensional nonlinear site response approach, the GQ/H + PWP model, and the DEEPSOIL V.7 program. At multiple layers of boreholes, ru is more than or equal to 0.8, indicating that the Sibalaya liquefaction flow area is still susceptible to liquefaction.

Field observations of soil moisture, suction and movement of cornfield in tropical highland with and without vetiver system

An increasing large number of cornfield have been cultivated in highland of many Southeast Asian countries. In most cases, this corn plantation is done without proper soil & water conservation such as vetiver system (VS), thus causing land degradation and shallow slide. This study is aimed at investigating the field behaviour of slopes with corn plantation with and without vetiver system in Chiang Mai, Northern Thailand. Tensiometers, soil moisture sensors, in-place inclinometers and tiltmeters were installed at a slope in two locations, with and without vetiver system from surface to 2m depth. The monitoring results show that for the vetiver treatment, the soil moisture tended to be higher and response faster to rainfall than the cornfield without vetiver. However, the pore-water pressure in the root zone (about 0.5m) was higher for the vetiver treatment than the cornfield which only has the root depth of about 0.2m. For cornfield without vetiver, the seasonal variation of the soil moisture and pore-water pressure was also larger. Tiltmeter indicates a larger surface movement in the cornfield without VS. However, the inclinometer readings suggested that for slope with VS there was some cyclic movement toward hillside at the surface. This could be an indication of non-uniform settlement of soil layers or influence of groundwater rising.

Measurement of Excess Pore-Water Pressure in Frozen Soil at Subfreezing Temperatures Close to 0°C

Response of pore-water pressure has crucial effect on the engineering geological performance of permafrost ground. However, there is a dearth of literature on the measurement of pore-water pressure in frozen soils due to challenges with regard to technical and operational method. To validate the generation of pore-water pressure and to reveal its variation property in frozen soils at subfreezing temperatures close to 0°C, a miniature pressure transducer was utilized to conduct a number of confined compression tests. Double-wall structure avoided damage to the transducer during frozen soil sampling. The transducer at sample bottom perceived a pressure fluctuation as varying air pressure imposed on sample surface, proving the connectivity among the pores in frozen soils with a hysteretic effect on pressure transmission. Pore-water pressure experienced a progressive increase followed by a slow dissipation under invariable load and temperature conditions when water drainage was permitted, while a monotonic increase in pressure was observed for an undrained sample. With decreasing temperature, a smaller peak and a more dilatory dissipation were displayed. When the sample was exposed to a stepwise warming process, a similar performance for the pressure was obtained with abrupt rise at the turning point of temperature.

Inverse Estimation of Soil Hydraulic Parameters in a Landslide Deposit Based on a DE-MC Approach

Extreme rainfall is a common triggering factor of landslide disasters, for infiltration and pore water pressure propagation can reduce suction stress and shear strength at the slip surface. The subsurface hydrological model is an essential component in the early-warning system of rainfall-triggered landslides, whereas soil moisture and pore water pressure simulated by the Darcy–Richards equation could be significantly affected by uncertainties in soil hydraulic parameters. This study conducted an inverse analysis of in situ measured soil moisture in an earthquake-induced landslide deposit, and the soil hydraulic parameters were optimized with the Differential Evolution Markov chain Monte Carlo method (DE-MC). The DE-MC approach was initially validated with a synthetic numerical experiment to demonstrate its effectiveness in finding the true soil hydraulic parameters. Besides, the soil water characteristic curve (SWCC) and hydraulic conductivity function (HCF) described with optimized soil hydraulic parameter sets had similar shapes despite the fact that soil hydraulic parameters may be different. Such equifinality phenomenon in inversely estimated soil hydraulic parameters, however, did not affect the performance of simulated soil moisture dynamics in the synthetic numerical experiment. The application of DE-MC to a real case study of a landslide deposit also indicated satisfying model performance in terms of accurate match between the in situ measured soil moisture content and ensemble of simulations. In conclusion, based on the satisfying performance of simulated soil moisture and the posterior probability density function (PDF) of parameter sets, the DE-MC approach can significantly reduce uncertainties in specified prior soil hydraulic parameters. This study suggested the integration of the DE-MC approach with the Darcy–Richards equation for an accurate quantification of unsaturated soil hydrology, which can be an essential modeling strategy to support the early-warning of rainfall-triggered landslides.

Debris Flow Prediction Based on the Fast Multiple Principal Component Extraction and Optimized Broad Learning

In the current research of debris flow geological disaster prediction, determining reasonable disaster-inducing factors and ensuring the accuracy and rapidity of the prediction model are considered vital issues, and also, essential foundations for disaster early warning and disaster prevention and mitigation. Aiming at the problems of low prediction accuracy and long prediction time in the current debris flow research, firstly, six debris flow impact factors were selected relying on the fast multiple principal component extraction (FMPCE) algorithm, including rainfall, slope gradient, gully bed gradient, relative height difference, soil moisture content and pore water pressure. Next, based on the broad learning (BL) algorithm, the debris flow prediction model based on FMPCE and the optimized BL is established with the input of debris flow-inducing factors and the output of debris flow probability. Then the model is optimized using matrix stochastic approximate singular value decomposition (SVD), and the debris flow disaster prediction model, based on SVDBL, is constructed. The prediction results of the optimized model are compared with those of the gradient descent optimized the BP neural network model(GD-BP), Support Vector Machines model(SVM) based on grid search and BL model. The results show that the accuracy of SVDBL is 7.5% higher than that of GD-BP, 3% higher than that of SVM and 0.5% higher than that of BL. The RMSE sum of SVDBL was 0.05870, 0.0478 and 0.0227 less than that of GD-BPSVM and BL, respectively; the MAPE sum of SVDBL was 1.95%, 1.66% and 0.49% less than that of GD-BPSVM and BL; the AUC values of SVDBL were 12.75%, 7.64% and 2.79% higher than those of the above three models, respectively. In addition, the input dataset is expanded to compare the training time of each model. The simulation results show that the prediction accuracy of this model is the highest and the training time is the shortest after the dataset is expanded. This study shows that the BL can be used for debris flow prediction, and can also provide references for disaster early warning and prevention.

Suction penetration characteristics and resistance calculation of bucket foundation in sand

• Based on the suction penetration test of bucket foundation, the distribution regularity of the excess porewater pressure of soil and soil pressure on both sides of bucket wall and bucket end are revealed. • Based on finite element method, the seepage characteristics of the bucket foundation during the penetration process are analyzed, and the change regularity of the effective stress and resistance of soil during the penetration process of bucket foundation is obtained. • Considering the effect of effective stress on seepage, a calculation method for required suction of bucket foundation with few easy-obtained parameters is established. The accurate estimation of penetration resistance of the bucket foundation is the key step for its installation, and the core part of the estimation of the penetration resistance is the exact prediction of the drag reduction effect due to suction. Therefore, in the present paper, the change regularity of the excess porewater pressure along the bucket wall and at the tip is analyzed by combining the model test and finite element analysis method, along with the soil pressure of the bucket foundation during the suction penetration process in sand. The results showed that, during the suction penetration process of the bucket foundation, the soil pressure and excess porewater pressure change approximately linearly with the depth of the bucket wall, and the reduction degree of lateral resistance due to seepage increases in a power function growth trend. Based on the effective stress principle of soil and basic theory of seepage and considering the effect of seepage on penetration resistance, the change regularity of the effective stress of soil along the bucket wall during the penetration process is obtained. Besides, the calculation method for penetration resistance and required suction of bucket foundation in sand soil is established, and the effectiveness of the present method is verified by comparing with the model test and engineering case, which can provide theoretical basis for engineering design and construction of bucket foundation.

The Use of Soil Moisture and Pore-Water Pressure Sensors for the Interpretation of Landslide Behavior in Small-Scale Physical Models.

This paper presents some of the results and experiences in monitoring the hydraulic response of downscaled slope models under simulated rainfall in 1 g. The downscaled slope model platform was developed as part of a four-year research project, “Physical modeling of landslide remediation constructions’ behavior under static and seismic actions”, and its main components are briefly described with the particular focus on the sensor network that allows monitoring changes in soil moisture and pore-water pressure (pwp). The technical characteristics of the sensors and the measurement methods used to provide the metrics are described in detail. Some data on the hydraulic and mechanical responses obtained from the conducted tests on slope models built from different soil types under different test conditions are presented and interpreted in the context of rainfall-induced landslides. The results show that the sensor network used is suitable for monitoring changes in the soil moisture and pwp in the model, both in terms of the transient rainfall infiltration through partially saturated soil and in terms of the rise in the water table and pwp build-up under fully saturated conditions. It is shown how simultaneous monitoring of soil moisture and pwp can be used to reconstruct stress paths that the monitored points undergo during different test phases. Finally, some peculiarities related to hydraulic hysteresis and surface erosion that were observed in some of tests are discussed, as well as possible difficulties in achieving and maintaining the targeted initial moisture distribution in slope models.

Effects of sediment yield fluctuations on the niche-like ephemeral gully formation in granite red soil

The granite red soil area in southern China has been afflicted by severe and large-scale gully erosion, locally known as “Benggang” erosion. It is generally believed that Benggang develops from the earlier gully; however, this remains disputed. Therefore, we investigated the rills and ephemeral gullies in the Yanglong watershed of the Hubei Province to explore the initial developmental process of Benggang. The results indicate that a unique gully with a niche-like morphology was found, which was named niche-like ephemeral gully (NEG). The NEG morphology was as follows: a distinct rill upstream, steep bank, a narrow upper bank, and a wide and deep gully bed. The NEG was formed on the exposed sandy soil layer and a local slope which was steeper than 30°. The field runoff scouring experiment simulating NEG formation was conducted on two slopes (20° and 40°) and with two runoff flows (3 L/min and 6 L/min) on three naturally exposed soil layers due to early surface soil erosion (B1 and B2 red clay, and sandy soil layers). The experimental results revealed that the total sediment yield of the sandy soil layer was at most 24.39 times higher than that of the B1 layer under the same treatment. Furthermore, compared to upper red clay layers, the deeper sandy soil layer formed more bank collapse due to faster soil moisture variations and higher soil pore water pressure, thus prompting more drastic sediment yield fluctuations and NEG formation. Therefore, the NEG was primarily formed in the sandy soil layer and was influenced by gravitational erosion represented by bank collapse. The amount of bank collapse and sediment yield differed in the three exposed soil layers, which could be essential for the development of rill into the NEG. Therefore, the NEG is a critical stage where the rill evolves into Benggang from the predominant hydraulic erosion into gravity erosion. These findings provide a new possibility for the origin of Benggang.

Investigation of Dynamic Compaction and Vibro-compaction to Mitigate Liquefaction: A Case Study

Liquefaction is one of the phenomena that can be triggered by an earthquake. Earthquake causes an increase in pore-water pressure in soil, reducing soil’s effective stress to zero or near-zero. In this state, the soil loses its strength and behaves like a liquid. This is known as liquefaction. When soil loses its strength, so it also loses its bearing capacity, causing damage or failure to structures. The soil type that is most prone to liquefaction is loose saturated fine sand. Such soil can be found in many of coastal areas in Indonesia. Indonesia is also one of the most earthquake prone countries in the world, hence liquefaction is one of the natural hazards that Indonesia has to face. Earthquake cannot be prevented, and its occurrence cannot be accurately predicted. Fortunately, liquefaction can be prevented by doing soil improvement to increase the sand density. The two most commonly used ground improvement techniques to increase sand density is dynamic-compaction and vibro-compaction. A case study from Aceh province, where both ground improvement techniques were used, is presented in this paper to compare the performance of dynamic compaction and vibro-compaction.

A repository of measured soil freezing characteristic curves: 1921 to 2021

Abstract. Soil freeze–thaw processes play a fundamental role in the hydrology, geomorphology, ecology, thermodynamics, and soil chemistry of cold regions' landscapes. In understanding these processes, the temperature of the soil is used as a proxy to represent the partitioning of soil ice and water content via a soil freezing characteristic curve (SFCC). This mathematical construct relates the soil ice content to a specific temperature for a particular soil. SFCCs depend on many factors, including soil properties (e.g., porosity and composition), soil pore water pressure, dissolved salts, (hysteresis in) freezing/thawing point depression, and the degree of saturation, all of which can be site-specific and time-varying characteristics. SFCCs have been measured using various methods for diverse soils since 1921, but, to date, these data have not been broadly compared. This is in part because they had not previously been compiled in a single dataset. The dataset presented in this publication includes SFCC data digitized or received from authors, and it includes both historic and modern studies. The data are stored in an open-source repository, and an R package is available to facilitate their use. Aggregating the data has pointed out some data gaps, namely that there are few studies on coarse soils and comparably few in situ measurements of SFCCs in mountainous environments. It is hoped that this dataset (https://doi.org/10.5281/zenodo.5592825; Devoie et al., 2022a) will aid in the development of SFCC theory and improve SFCC approximations in soil freeze–thaw modelling activities.

Stability Analysis of Shield Inclined Tunnel Faces under the Change Effect of Soil Heterogeneity and Pore Water with Buried Depth

The purpose of this work is to look at how soil heterogeneity and pore water pressure impact shield inclined tunnel excavation face stability as burial depth varies. The calculation model of excavation face stability was established, and the supporting pressure of maintain the excavation face stability was solved via the upper bound method. The results showed that the soil heterogeneity coefficient and pore water pressure coefficient had substantial effects on the supporting pressure. The location of failure face and failure range of shield inclined tunnel under varied heterogeneity coefficient and pore water pressure coefficient were presented. In addition, the boundary depth of shallow tunnel under the influence of soil heterogeneity and pore water was obtained, which supplemented the relevant tunnel code.

Water Adsorption–Induced Pore-Water Pressure in Soil

Water Adsorption–Induced Pore-Water Pressure in Soil

A semi-analytical undrained solution for cylindrical cavity expansion in K 0-consolidated anisotropic soils under plane stress condition

To remove the limitation that the plane stress problem cannot be considered using cylindrical cavity expansion and to explore surface response of cylinder expansion in shallow soil, a semi-analytical undrained solution is developed for cylindrical cavity expansion in anisotropic modified Cam-clay model soils under the plane stress condition. The constitutive relationship is described by the K 0-consolidated anisotropic modified Cam-clay (K 0-AMCC) model, which can properly simulate the mechanical behaviour of the K 0-consolidated natural clays. The problem is equivalent to solving ordinary differential equations to determine the effective stresses, vertical strain, and excess pore water pressure (EPWP). Parametric analyses are conducted to investigate the effective stresses, vertical strain, and EPWPs around the expanded cavity under plane stress condition. The results show a clear influence of over-consolidation ratio on the stresses, vertical strain, EPWP around the cavity, and effective stress paths for a soil particle at the cavity wall. Axial expansion or uplift of soil and negative pore water pressure are observed during cavity expansion under the plane stress condition. There are obvious differences in effective stress components around the cavity under two plane conditions. The effective axial stress around the cavity wall is generally smaller than that under the plane strain condition.

Developing a soil column system to measure hydrogeophysical properties of unconsolidated sediment

AbstractGeophysical methods have been increasingly used to characterize the Earth's critical zone (CZ) and monitor hydrological processes occurring within it. For a quantitative interpretation, geophysical studies of CZ materials are necessary, and thus require more sophisticated laboratory setups. In this study, we develop a hydrogeophysical soil column system to measure key hydraulic and electrical properties of regolith in CZs. The developed soil column system consists of two components: (a) a novel hydrogeophysical probe that measures pore water pressure and electrical potential in soils and (b) a cylindrical cell to hold soil samples. The system can be arranged to perform both saturated flow and drainage tests. The saturated flow test is similar to the traditional constant head experiment for determining the hydraulic conductivity and streaming potential coupling coefficient. The drainage tests can produce transient responses of cumulative overflow, pore water pressure, and streaming potential. These transient data can be used to estimate the sample's electrical and hydraulic properties with the coupled, stochastic hydrogeophysical inversion. A sand sample is used to demonstrate the procedures of applying this new system. The measured saturated hydraulic conductivity and streaming potential coupling coefficient of the sand are within the typical ranges of sands reported in the literature. The inversion‐estimated soil parameters can well reproduce the measured transient responses during the drainage test of the sample. Moreover, the inversion‐estimated saturated properties are in good agreement with those independently measured in the saturated flow test, showing the robustness of the developed system.

Seismic responses of two bucket foundations for offshore wind turbines based on shaking table tests

Sand liquefaction under seismic load causes severe failure of bucket foundations for offshore wind turbines. This study conducted shaking table tests for two different types of bucket foundations: mono bucket foundation (MBF) and composite bucket foundation (CBF). Furthermore, five groups of EI-Centro seismic waves with different intensities were applied. The excess pore water pressure and acceleration of the foundation soil were measured. The influences of bucket foundations on the seismic behavior of sand were explored by comparing the excess pore water pressure and acceleration at different positions. Moreover, the seismic responses of two types of bucket foundations were compared, and the effects of bulkheads in CBF on the seismic performance of foundation soil were clarified. The test results show that the seismic response of the soil inside the bucket is clearly suppressed compared with the soil outside the bucket, and thus the risk of liquefaction is lower. Furthermore, the seismic response of the CBF is significantly weaker than that of the MBF, and the anti-liquefaction performance of the CBF soil foundation is better. This implies that CBFs are safer than MBFs during earthquakes.

Centrifuge modeling of geosynthetic-reinforced soil retaining walls subjected to the combined effect of earthquakes and rainfall

Local fine-grained soils were usually used as backfill for geosynthetic-reinforced soil retaining walls (GSRWs). However, there are few studies on the seismic response in this case, especially under the influence of rainfall. In this study, three centrifuge shaking table tests were performed at 30 gravities to investigate the performance of GSRWs subjected to the combined effect of earthquakes and rainfall. Two stages were designed in this study. In the first stage, three conditions were simulated, i.e., post-rainfall earthquake (Test-1), rainfall and earthquake occurring simultaneously (Test-2), and post-earthquake rainfall (Test-3). The results show that if there was enough time for rainwater seepage, the suction force generated in unsaturated GSRW enhanced the soil strength. When GSRW was subjected to heavy rainfall and no time for seepage, the deformation of the GSRW was largest due to the high excess pore water pressure of local saturated soil in GSRW. In the second stage, seismic failure models of GSRWs with different water contents were studied. Under the excitation of a series of continuous earthquakes, a large tensile crack was formed in the unsaturated GSRW, whereas no cracks were found in the saturated GSRW, but its panel demonstrated a large bulging deformation.