Pore Water Pressure Research Papers (original) (raw)

2025, Frontiers in energy research

Natural fractures and cavities are the primary spaces for oil and gas accumulation in fracture-cavity carbonate reservoirs. Establishing the connection between these spaces and the wellbore through hydraulic fracturing treatment is important for oil and gas extraction from such reservoirs. Due to the discontinuity and heterogeneity of the existing natural fracture-cavity system, anticipating the viability of hydraulic fracturing treatment is troublesome. A new method to simulate the hydraulic fracturing propagation in fracture-cavity reservoirs is proposed based on the continuous damage theory. The method considers the random spatial distribution of fractures and cavities and can simulate the arbitrary expansion of hydraulic fractures in the threedimensional direction. Based on this method, the influence of different geological and engineering factors on the propagation patterns of hydraulic fractures in the fracture-cavity reservoirs is investigated. It is found that the increase of reservoir burial depth significantly limits the propagation ranges of hydraulic fractures. The propagation modes of hydraulic fractures encountering natural fractures change with increasing burial depth, undergoing a transition from "penetrate and deflect" to "defect" and then to "penetrate". The reduction of horizontal stress difference increases the complexity of hydraulic fractures, but it is not conducive for hydraulic fractures to connect more natural fractures and cavities. The increase in fracturing pump rate is significantly beneficial for hydraulic fractures to connect more natural fractures and cavities. The viscosity of fracturing fluid has a significant impact on the morphology of hydraulic fracture propagation, which undergoes a transition from simple to complex, and then to simple with the change of the fracturing fluid viscosity from low to high. either too high or too low viscosity of the fracturing fluid is not conducive to the connection of more natural fractures and cavities by hydraulic fractures. The obtained conclusions can provide a reference for the design of hydraulic fracturing treatment for fracture-cavity carbonate reservoirs.

2025

Shear strength parameters of soils can be divided as drained and undrained conditions. Drained parameters are proper to be used for the conditions, where pore water can drain out of the soil easily, under external loading. There is no change in pore water pressure due to external loading. Drained parameters are valid for coarse grained soils and fine grained soils if the rate of the load is slow enough not to generate excess pore pressure in the system. On the other hand, undrained condition occurs when the pore water cannot drain out of the soil. The rate of the load is much quicker in undrained loading than the rate at which pore water can drain out. In undrained conditions, a large part of the load is carried by the pore water, as a result pore pressures increase. For long term stability analysis in fine grained soils, drained parameters can be used accepting the pore water can drain out of the soil. For dynamic conditions, if the rate of the loading is fast enough as in the eart...

2025, Engineering Geology

The standard cone penetration test (CPT) measures the resistance at the tip (q c ) during constant rate of penetration as well as the friction/adhesion along the sleeve (fs). The excess porewater pressures generated as a result of the penetration can also be measured by a piezometer/transducer (u 2 ) located immediately behind the cone (CPTU). The collected data help to identify several physical, hydraulic and mechanical properties of the soil layers. However, the main function of the test is soil classification. Classification has been done by using the q c and f s values at the early stages to be followed by incorporating the concept of soil behaviour type index I c . Soil behaviour type (SBT) index calculates I c and is generally calculated by normalised values of tip resistance and sleeve friction: Q and F, respectively. The porewater pressure component in the relationship is accounted for by the coefficient B q . A clear distinction between the soil classes cannot be made due to limited coverage of the parameters employed. A new parameter "i" which contributes significantly to the classification process by the use of varying porewater pressure values Δu w by depth is introduced in this paper to improve the value of I c in the classification procedure.

2025, Journal of Petroleum Exploration and Production Technology

2025, Water Research

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2025, Water Research

2025, Computers and Geotechnics

Coupled finite element analyses of the consolidation and deformation around stone columns have been performed to assess the accuracy of different analytical solutions. The numerical model reproduces the hypotheses of the closed-form solutions. In the model, a rigid load is applied to a unit cell formed by a fully penetrating column and its surrounding soil, and simple elastic or elasto-plastic soil models are used. The surface settlement, the dissipation of the pore pressure and the vertical stress concentration on the column are studied. These soil responses are accurately estimated with closed-form solutions that properly include the radial and plastic strains in the column. However, the surrounding soil does not yield for usual conditions, which reasonably justifies the elastic soil behavior assumed in the analytical solutions. The differences between drained and consolidation analyses are also evaluated. Comparing the numerical results with the closed-form solutions illustrates the implications of the assumptions of each approach.

2025

Anomalous geochemical signals inferred from elemental and isotopic analyses on spring waters and soil degassing are often detected in response to tectonic loading along faults. Recent results highlighted how the geochemical anomalies are closely related to episodes of crustal deformation. In the present study, the carbon dioxide and radon from soil degassing and the geochemical features of springs spatially related to fault zones in the Friuli-Venezia Giulia region (north-eastern Italy), a seismic-prone area, have been coupled with crustal deformation analyses to better define the possible correlations between fluctuations of geochemical parameters and seismicity, with the aim of gaining new information about local geodynamic processes. The natural CO 2 and Rn degassing was evaluated by a soil gas survey carried out by a grid of about 100 measuring sites located over the area that had been hit by strong earthquakes, in the past (Gemona -Idrija 1511, Raveo 1700, Tolmezzo 1788 and 1928, Gemona 1976). The results obtained show a significant amount of crustal-originated gases, especially CO 2 , possibly related to decarbonation reactions and stress accumulation occurring in deep-seated structures. The spring waters show, in some cases, anomalous geochemical transients, in particular concerning the chloride and Rn concentration, that are not related to seasonal changes and interpreted to reflect distinct fluid pressure regimes within the fault zone, yielding the leakage of pore fluids into the country-rock aquifers. In particular, the changes in the chloride content have been tentatively modeled in terms of pore-fluid expulsion from compacting clays during pressure gradients at shallow crustal levels. The flow regimes and chemical evolution have been related to the strain computed at the outlet sites through the Gutenberg-Richter relation parameters and the regional value of the strain rate. The information provided here may be used to start up a long-term geochemical monitoring of this seismically active area able to detect the modifications occurring in the circulating fluids to gain a better insight on the relationships between the geochemistry of the fluids and the activity of the local seismogenic faults.

2025, Proceedings of the 6th Unconventional Resources Technology Conference

Seismicity induced by the waste water injection has become an important issue in the recent years, including several regions in United States, such as Oklahoma and Texas. However, many techniques that are used to evaluate whether a particular earthquake is induced or natural are not based on the law of physics, and as a consequence these techniques do not provide much insight into nature of that type of seismicity. In this study we combine the analytic solution of coupled hydromechanical problem with numerical dynamic rupture simulation to study the influence of different properties of the rocks and fluids, as well as the geometry of the operations on the potential for earthquake triggering. We find three main driving factors are the distance between the injection well and the fault, permeability of the medium and shear modulus of the rocks. We also observe that keeping injecting the fluid at the same rate after first occurrence of seismic event, escalates the size of earthquakes with time.

2025, Canadian Geotechnical Journal

It is becoming increasingly common in the mining industry for either crushed ore or filtered mine waste to be stacked to a significant height (>100 m) in a moist state with little compaction, resulting in deposits that can be potentially loose and unsaturated. This paper presents a case history describing the characterization of stacked filtered tailings at a mine site in South America. Cone penetration tests with pore pressure and seismic velocity measurements (SCPTu) were carried out along with selected drilling, sampling, and laboratory testing. Compression wave velocity (Vp) and shear wave velocity (Vs) profiles were obtained and compared with laboratory values on reconstituted saturated and unsaturated samples. Results indicate that shear wave velocity is sensitive to suction hardening effects and appears to capture the correct unsaturated in situ behavior. The cone resistance, which is a large strain measurement, can destroy the beneficial effects of suction hardening and a...

2025, International Journal of Civil Engineering

In this study, the mechanical behavior of Vanyar dam was evaluated at the end of construction. A two-dimensional numerical analysis was conducted based on a finite element method on the largest cross-section of the dam. The data recorded by the instruments located in the largest cross-section were compared with the results of the numerical analysis at the place of instruments. The settlement, pore water pressure, and total vertical stress were the parameters used for evaluating the dam behavior at the end of construction. The results showed that the settlements obtained from the numerical analysis were in reasonable agreement with the data recorded by the instruments, which proved that the numerical analysis was implemented based on realistic material properties. In addition, the difference between the instruments and the numerical analysis in terms of total vertical stresses was discussed by focusing on the local arching around the pressure cells. Furthermore, the arching ratios were calculated based on the results of the numerical analysis and the data recorded by the instruments. Moreover, the pore water pressures and total vertical stresses, recorded by piezometers and pressure cells, respectively, were the two parameters utilized for evaluating the hydraulic fracturing phenomena in the core. The results demonstrated that the maximum settlement obtained from the numerical analysis was 1 m, which corresponded to 46 m above the bedrock on the core axis. The recorded data in the core axis indicated that maximum settlement of 0.83 m happened 40 m above the bedrock. In addition, maximum pore water pressure ratio recorded by the instruments (R u =0.43) was more than that obtained from the numerical analysis (R u =0.26); this difference was due to the local arching around the pressure cells. Furthermore, the arching ratios in Vanyar dam were found to be 0.83 to 0.90. In general, the results revealed that the dam was located on a safe side in terms of critical parameters, including settlement and hydraulic fracturing. In addition, results of the numerical analysis were consistent with those provided by the monitoring system.

2025

Soil erosion and embankment failures are serious challenges confronting our environment. In the face of these challenges, different possible solutions are been studied at different levels with special consideration on the implementation cost of such solutions. Hence, this work studied agronomical stabilization of Umuda-Isingwu erosion site using vetiver grass. The principal objective of this study was to determine the stability of an engineered slope by computing the factor of safety (FS) of the samples collected from the embankment on the erosion site. To ascertain the factor of safety, the soil samples collected from the study area were analyzed to determine its gradation by mechanical sieving and hydrometer method, while the density bottle was used to estimate the density of the samples which when multiplied by acceleration due to gravity of 9.81m/s 2 gave the unit weight of samples. The results showed that the soil samples are coarse sand and loamy sand, unit weight of bare and Vetiver rooted samples as 17.40KN/m 3 and 16.62KN/m 3 respectively, average shear strength of the bare soil samples and Vetiver rooted soil samples as 68.52KN/m 2 and 132.32KN/m 2 respectively and the factor of safety of the samples; bare and Vetiver rooted soils were computed to be 1.72 and 2.98 respectively. These computed factors of safety showed that Vetiver rooted samples are about 1.73 times more stable than the bare soil. Hence, Vetiver grass is a good embankment and erosion site stabilizer and should be put to effective use in the area erosion control and slope stabilization in Nigeria.

2025

Fractures and bedding planes within geological formations influence the exploration and development of fields in the petroleum industry, playing a vital role in reservoir characterization. However, manually identifying these features from borehole image logs (BHIs) is laborious and time-consuming. This study addresses this challenge by proposing an automated system to streamline the fracture and bedding plane picking and identification process. The model introduced in this study aims to expedite result delivery while significantly reducing the manual workload by automating the detection of fractures and bedding planes. Trained on a data set of BHIs, including formation micro-imager (FMI) and compact micro-imager (CMI) from 14 wells in Oman, the method presented proposes a transformer-based model, named Geological Beddings and Fractures Detection Transformer (GeoBFDT) for the identification, localization, and estimation of geological structural feature parameters. GeoBFDT uses a bipartite matching loss to match the predicted geological feature types and their depth, dip, and azimuth values with the ground truth in an end-to-end manner. Visual analyses, performance metrics, sensitivity tests, and comparative plots highlight the model's capability to identify subsurface features. Validation using various depth thresholds on the test set for fractures and beddings reveals F1-scores of ~65% (fractures) and ~63% (beddings) at a 3-cm depth threshold and ~75% (fractures) and ~69% (beddings) at a 5-cm threshold. Dip accuracy is ~79% (fractures) and ~65% (beddings) at a 1.5° dip threshold and ~90% for both fractures and beddings at a 3° dip threshold. Similarly, azimuth accuracy is at ~83% (fractures) and ~75% (beddings) at a 7° azimuth threshold and ~92% (fractures) and ~84% (beddings) for an azimuth threshold of 15°. The ablation study indicates that a smaller backbone yields better performance given the relatively small data set and that increasing the number of wells further enhances model performance. In addition, the dynamic logs of BHIs outperform static logs. The model's adaptability to different well inclinations was also assessed by evaluating its performance on fractures from five horizontal wells, achieving a ~55% score at a 4-cm threshold for fracture detection and localization tasks. Notably, the proposed approach surpasses the objectives of existing deep learning (DL)-based methods by accommodating multiple features in a single image, identifying beddings and fractures in complex geological areas, eliminating mask dependency, and providing an end-to-end strategy. Unlike models such as "you only look once" or mask region-based convolution neural network (R-CNN), which rely on mask generation, the proposed method focuses on different objectives, offering an alternative approach to feature picking. Although trained on limited data and validated through validation and testing sets, the GeoBFDT model offers an alternative pathway toward an end-to-end automated geological feature picking tool from BHIs. We hope that in the future, this methodology can be further explored to automate the entire feature-picking workflow in an end-to-end fashion.

2025, Scientific Reports

Both intra-pore hydrate morphology and inter-pore hydrate distribution influence the physical properties of hydrate-bearing sediments, yet there has been no pore-scale observations of hydrate habit under pressure in preserved pressure core samples so far. We present for the first time a porescale micro-CT study of natural hydrate-bearing cores that were acquired from Green Canyon Block 955 in UT-GOM2-1 Expedition and preserved within hydrate pressure-temperature stability conditions throughout sub-sampling and imaging processes. Measured hydrate saturation in the sub-samples, taken from units expected to have in-situ saturation of 80% or more, ranges from 3 ± 1% to 56 ± 11% as interpreted from micro-CT images. Pore-scale observations of gas hydrate in the sub-samples suggest that hydrate in silty sediments at the Gulf of Mexico is pore-invasive rather than particle displacive, and hydrate particles in these natural water-saturated samples are pore-filling with no evidence of grain-coating. Hydrate can form a connected 3D network and provide mechanical support for the sediments even without cementation. The technical breakthrough to directly visualize particlelevel hydrate pore habits in natural sediments reported here sheds light on future investigations of pressure-and temperature-sensitive processes including hydrate-bearing sediments, dissolved gases, and other biochemical processes in the deep-sea environment.

2025, Scientific Drilling

The pore habits of gas hydrate in natural sediment matrices provide essential clues for understanding physical (mechanical, thermal, hydraulic, and electrical) properties of hydrate-bearing sediments, yet there are no tools that can directly visualize the pore habits of natural gas hydrate other than indirect interpretation based on core-scale or field-scale observations. A significant challenge is to obtain a mini-core from pressure cores retrieved from natural reservoirs for high-resolution micro-CT (computed tomography) scans while maintaining pressure and temperature conditions required for stability of gas hydrate during all operational steps including manipulation, cutting, transferring, sub-coring and CT scanning. We present a new set of tools for pore-scale micro-CT imaging of natural hydrate-bearing sediments while maintaining pressure and temperature control. The tests with laboratory-prepared cores and pressure cores successfully demonstrate the capability of this set of tools to subsample a mini-core from pressure cores, transfer the mini-core to an X-ray transparent core holder, and conduct micro-CT scans. Successfully obtained CT images prove the functionality of this set of tools.

2025

The effects of porous medium heterogeneity on methane hydrate formation, water flow through the heterogeneous hydrate-bearing sand, and hydrate dissociation were observed in an experiment using a heterogeneous sand column with prescribed heterogeneities. X-ray computed tomography (CT) was used to monitor saturation changes in water, gas, and hydrate during hydrate formation, water flow, and hydrate dissociation. The sand column was packed in several segments having vertical and horizontal layers with two distinct grain-size sands. The CT images showed that as hydrate formed, the water and hydrate saturations were dynamically redistributed by variations in capillary strength of the medium (the tendency for a material to imbibe water), which changed with the presence and saturation of hydrate. Water preferentially flowed through fine sand near higher hydrate-saturation regions where the capillary strength was elevated relative to the lower hydrate saturation regions. Hydrate dissociat...

2025, Review of Scientific Instruments

Understanding mechanical interactions between hydrate and hosting sediments is critical for evaluating formation stability and associated environmental impacts of hydrate-bearing sediments during gas production. While core-scale studies of hydrate-bearing sediments are readily available and some explanations of observed results rely on pore-scale behavior of hydrate, actual pore-scale observations supporting the larger-scale phenomena are rarely available for hydrate-bearing sediments, especially with methane as guest molecules. The primary reasons for the scarcity include the challenge of developing tools for small-scale testing apparatus and pore-scale visualization capability. We present a testing assembly that combines pore-scale visualization and triaxial test capability of methane hydrate-bearing sediments. This testing assembly allows temperature regulation and independent control of four pressures: influent and effluent pore pressure, confining pressure, and axial pressure. ...

2025, Marine and Petroleum Geology

Establishing the geomechanical stability of marine sediments in the vicinity of a production well is one of the key design considerations in planning offshore gas production from marine hydrate reservoirs. This paper presents an assessment of the sediment stability at India's National Gas Hydrate Program, Expedition 2 (NGHP-02) Site 16 Area B offshore eastern India, for which gas production is to be carried out by depressurization. One important feature of the study is that extensive calibration of constitutive model parameters has been conducted based on laboratory test data from pressured core samples. From analysis perspective, the site is challenging because the hydrate reservoir consists of thin layers of hydrate-bearing sands interbedded with mud. Moreover, depressurization at the depth of a reservoir more than 2750 m below sea surface will lead to a pore pressure drop, and accordingly an effective confining stress increase as high as 25 MPa. In dealing with thin interbedded hydrate-bearing strata, meshing requirements for flow and geomechanical analysis are quite different from those for reservoirs with thicker massive layers, An axisymmetric model and one-way coupling simulations were thus adopted for this study, in which the geomechanical study utilizes pore pressure and hydrate saturation output from the flow study, but the flow study does not takes the porosity changes from the geomechanical analysis. Instead, the reduction of porosity due to sediment deformation in the flow study is based on a pressure-dependent pore compressibility relationship derived from geomechanical modeling. The rationality is validated through back computing the pore compressibility from the geomechanical deformation results. The study shows that large compression in the reservoir will result in movement of the sediments from above and below, as well as laterally in smaller magnitudes; and the sediment is deemed stable during the gas production period.

2025, Journal of Petroleum Science and Engineering

We used x-ray computed tomography (CT) to image and quantify the effect of a heterogeneous sand grain-size distribution on the formation and dissociation of methane hydrate, as well as the effect on water flow through the heterogeneous hydrate-bearing sand. A 28 cm long sand column was packed with several segments having vertical and horizontal layers with sands of different grain-size distributions. During the hydrate formation, water redistribution occurred. Observations of water flow through the hydratebearing sands showed that water was imbibed more readily into the fine sand, and that higher hydrate saturation increased water imbibition in the coarse sand due to increased capillary strength. Hydrate dissociation induced by depressurization resulted in different flow patterns with the different grain sizes and hydrate saturations, but the relationships between dissociation rates and the grain sizes could not be identified using the CT images. The formation, presence, and dissociation of hydrate in the pore space dramatically impacts water saturation and flow in the system.

2025, Scientific Reports

2025, Journal of Soils and Sediments

Purpose There is a growing understanding that methane hydrates (MHs) distributed globally in permafrost and deep sea sediments present an enormous unconventional reservoir of methane (CH 4 ); however, there is also increasing concern about their role in the global climate change. The study focuses on the evaluation of the environmental conditions in the deep Adriatic Sea during the Last Glacial Maximum (LGM, 21.5-18.3 ka BP) and presently with respect to MHs potential occurrence. Materials and methods The MHs phase stability diagram was calculated in order to evaluate the methane hydrate stability zone (MHSZ) by using the Croatian Legacy Data and the digital bathymetry map of the Adriatic Sea obtained from the Croatian Hydrocarbon Agency (CHA). Environmental data from different surveys published in the scientific literature were used to assess the environmental conditions in the deep Adriatic Sea during the LGM and present. The sea level rise of 100 m since the end of the LGM was taken into consideration. The volume of methane in place (MIP) as an estimation of the amount of CH 4 stored in MHs deposits at standard conditions of pressure and temperature (SPT, T 0 = 273.15 K, P 0 = 0.101325 MPa) was calculated by using combined gas law V SPT = (P×V/T) × (T SPT /P SPT ). Results and discussion Evaluation of the MHs phase stability diagram for the Adriatic Sea in present environmental conditions has revealed that MHs are exactly at the boundary of stability. This has been calculated for the potential temperature of 13 °C, the salinity of 3.87% (data measured at the E2-M3A deep ocean observatory of the Southern Adriatic), and the average geothermal gradient of 17 °C km -1 reported in the literature and verified by the Croatian Legacy Data of CHA. According to the published literature, LGM deep sea temperature was 2-4 °C lower and seawater was saltier. Consequently, the estimation of MHSZ during the LGM taking into consideration the temperature of 10 °C and salinity of 3.98% revealed a potential deposit of methane in place (MIP) of more than 415 × 10 9 m 3 , the majority of which probably dissociated in the sea/atmosphere system in the last 18 ka. Conclusions The results have shown that MHs reservoir in the deep sea Adriatic basin shows boundary instability for MHs occurrence which might be of importance for studying the role of MHs in climate change. Further research is needed as follows: (1) thermodynamic modeling in order to understand if the MHs dissociation is concluded; and (2) in the case of the transient condition, seismic data analysis in order to reveal the presence of a relic bottom simulating reflection.

2025, E3S web of conferences

Instabilities mostly happen in fully saturated and loose non-cohesive geomaterials like sands or silts or tailings, but it is also possible in unsaturated geomaterials. When unsaturated they can experience a reduction in effective stress and strain soften during water (and air) undrained loading, attaining a very low residual strength. This study focuses on modelling the conditions required to cause instability in unsaturated silty tailings, giving particular consideration to the presence of air and the way it alters the ability for volume change when it remains trapped inside the tailings. A gold tailings is used to calibrate the UNSW bounding surface plasticity model. The effect of air, including the volumetric change caused by air compression, the alteration of air pressure, the contribution of suction to the effective stress, and suction hardening, are explored. Collapse lines (sometimes referred to as instability lines or flow liquefaction lines which represent boundaries between stable and potentially unstable stress states) in the 𝑞𝑞 -𝑝𝑝′ plane are explored. The undrained shear strength ratios and slopes of the collapse lines are compared to those of other tailings and sands when unsaturated.

2025, E3S Web of Conferences

Shallow rainfall triggered slope failures occur frequently in loess and loess-derived deposits across the South Island, New Zealand. These failures, which occur in both natural slopes and engineered cuttings, impact road infrastructure, residential housing and rural land use. When dry, the loess can form near vertical cuttings. However, with increase in moisture content loess slopes become susceptible to shallow slope failures. To date, the influence of negative pore-water pressure (suction) on the stability of loess slopes in New Zealand has not been well understood. In this paper, data from long term in situ field monitoring of rainfall, suction and volumetric water content from a loess slope in Banks Peninsula, Canterbury are presented with laboratory triaxial test results undertaken on undisturbed unsaturated loess samples. Field and laboratory soil responses to wetting and drying are compared, and the characteristics of rainfall events which reduce suction in situ and therefore...

2025, Journal of Geotechnical and Geoenvironmental Engineering

Ottawa sand specimens premixed with 0, 3, and 5% bentonite by dry mass of sand were tested under undrained static and cyclic loading to investigate the effects of bentonite on the static and cyclic shear strength of the sand. The results show that allowing the bentonite to hydrate within the sand pore space increases the cyclic resistance of the sand. For the same skeleton relative density and cyclic stress ratio, cyclic tests on specimens with sufficient hydration times showed a significant increase in the number of cycles required for liquefaction compared with clean sand. When the specimens were allowed an extended postconsolidation aging period, the cyclic resistance increased further. Resonant column and cyclic triaxial tests showed that this is a result of the delay in the generation of excess pore pressure in the presence of the bentonite suspension in the pore space. The improvement in cyclic behavior does not occur at the expense of the static resistance of the soil under working loads because undrained static triaxial tests on specimens with bentonite showed only a minor decrease in the small-strain internal friction angle compared with the clean sand, while the critical-state internal friction angle remained unchanged. To address the need to deliver the bentonite suspension in a sand deposit, a method for engineering the rheology of concentrated bentonite suspensions through the addition of sodium pyrophosphate (SPP) was developed. With the addition of 0.5% SPP by mass of clay, the viscosity of concentrated (10%) bentonite dispersions dropped to a value that allowed delivery of the bentonite into the sand matrix through permeation. Over time, the bentonite suspension recovered the thixotropic properties that ensured its effectiveness in mitigating liquefaction. As a result, sand specimens permeated with 10% bentonite suspensions showed a large increase in liquefaction resistance. Changes in the rheological properties of the pore fluid with time also explain the increase with aging of the cyclic resistance of the sand-bentonite specimens.

2025, Géotechnique

The paper examines the effect of small percentages of bentonite on pore pressure generation in loose sands, from small strains all the way to liquefaction. It relies on resonant column, static triaxial and cyclic triaxial tests conducted on specimens prepared by dry-mixing Ottawa sand and bentonite, at a skeleton relative density of 35% ± 5%. Two main variables are investigated: the percentage of bentonite (3% and 5% by dry mass of the sand), and the duration of the ageing period preceding shear (1 to 10 days). The presence of bentonite increases the shear strain needed to initiate the generation of excess pore pressures in resonant column tests; in cyclic tests it reduces the mean pore pressure generated per loading cycle and allows the specimen to sustain an increased loss of effective stress before liquefaction initiates, both effects contributing to an increased resistance to liquefaction. These effects are further enhanced with prolonged pre-shear ageing. Additionally, under st...

2025, Geotechnical Testing Journal

This paper investigates the undrained shear stiffness of sand-bentonite specimens (with 0 %, 3 %, and 5 % bentonite by dry mass of the sand) prepared at the same skeleton void ratio (D rsk ¼ 35 % to 40 %) using a dry pluviation technique. The experimental program consisted of (1) small strain tests using a resonant column apparatus and (2) large strain tests using a cyclic triaxial apparatus. The resonant column tests were performed at three confining stress levels (50, 100, and 193 kPa) under drained and undrained conditions. A comparison of the shear modulus reduction with shear strains for both drained and undrained conditions is presented; the effects of changes in effective stresses and the rate of modulus reduction as a function of the effective stress are discussed to describe the discrepancy between the two sets of data. The results show a marginal decrease in G max for specimens with bentonite, which is attributed to the presence of bentonite at the sand grain contacts. However, the presence of bentonite increases the linear elastic threshold, particularly in the case of undrained tests, in which a noticeable delay in excess pore pressure generation was measured. The strain level required in order to initiate excess pore pressure generation increased with increasing bentonite content. A similar trend was noted in cyclic triaxial tests, in which, for a given strain, specimens with bentonite generated lower excess pressure than sand specimens tested under similar conditions. Finally, a combined normalized G/G max curve from both tests is presented for specimens with 0 %, 3 %, and 5 % bentonite at 100 kPa.

2025, Géotechnique

Boom clay, a stiff clay, has been selected as a potential host formation for the geological disposal of radioactive waste in Belgium. The underground research facility HADES has been constructed to enable various in situ experiments to be performed on Boom clay so as to study the feasibility of high-level radioactive waste disposal, and to provide reliable data on the performance of Boom clay as a host formation. Among the various laboratory studies performed on samples extracted from the HADES facility to investigate the thermo-hydro-mechanical behaviour of Boom clay, relatively few were devoted to the time-dependent behaviour, limiting any relevant analysis of the long-term behaviour of the disposal facility. The present work aims at investigating the time-dependent behaviour of Boom clay under both thermal and mechanical loading. High-pressure triaxial tests at controlled temperatures were carried out for this purpose. The tests started with constant-rate thermal and/or mechanica...

2025

Aceh -Indonesia, is a province that is prone to the earthquake strike because of the position of it which is close to earth fault. There are subduction tectonic fault, Indo-Australia, Euo-Asia tectonic faults, and Sumatra fault. The aim of this research was to analyse the probability of sand soil failure (liquefaction potency) as the earthquake strike. The earthquake waves when it reaches the saturated of sand soil layer as a cyclic loads, leads the sand soil layers to fail (soil liquefaction). The soil formation will be change due to the cyclic loads and increase the pore water pressure, as a result the soil shear strength will decrease or even loss strength and becomes like fluida. The location of the research is in Krueng Raya beach in Aceh Besar -Aceh province. The data were obtained from N-SPT test and showed that the soil layers are dominant with sand soil layers. Seed et al (1976) and Castro (1975) were used to analyse the liquefaction potency. The research shows that liquefaction occurs in the depth of 3 m -15 m for Seed et al (1976) method whereas no indication of liquefaction shows from Castro (1975) methods in any depths.

2025

A thesis submitted in fulfilment of the regulations governing the award of the degree of Doctor of Philosophy.

2025, Soil and Tillage Research

In the last 250 years the Aquands (depth-limited and waterlogged-volcanic ash soils) in southern Chile were exposed to an intensive land use change inducing physical degradation of these fragile soils. The aim of this work was to evaluate the effect of cyclic loading on soil structural properties and the resilience capacity after simulating one event of soil waterlogging as usually occurs in the field. In undisturbed soil samples, collected from two horizons (2-5 cm, Hz1 [A 1 ] and 20-23 cm, Hz2 [B s1 ]) of a Duric Histic Placaquand under secondary native forest (sNF) and naturalized grassland (NG), the precompression stress (Pc), deformation and recovery indices derived from cyclic loading tests (20, 80 and 200 kPa) were determined. The air permeability (Ka) and soil volume changes were measured during the entire test. The land use change from sNF to NG increased the rigidity of the pore system due to plastic deformation. However, the cyclic loading provokes changes in the pore system (e.g. increase in bulk density as well as decrease in wide coarse pores, which finally induce a decrease in air permeability: 1.89 to -0.17 log μm 2 and 1.03 to 0.37 log μm 2 in Hz1 of aNF and NG, respectively) even at loads lower than Pc highlighting the fragility of the soils. As the applied load increases to levels higher than Pc, the plastic deformation induces an increase in pore water pressure and mechanical strength, affecting the pore network and in turn the air permeability of the soil. After one event of ten days of waterlogging conditions, the resilience capacity of the pore system was low. CT-images show that the soil under sNF recovered apart of the deformed porosity allowing an increase in Ka (0.55 ± 0.15 log μm 2 ) after waterlogging conditions, however, no changes were identified for the soil under NG (final Ka = 0.57 ± 0.26 log μm 2 ). Therefore, both land use change and increasing loads on these fragile soils imply the loss of their resilience capacity generating a further soil settlement.

2025

The long-term behavior of concrete can be influenced by its composition and environment exposure. Leaching is a chemical process of degradation caused by water, leading to dissolution of cement components, increasing the permeability and reducing mechanical properties. Backfill concrete with fly ash was used in Itaipu dam, in a region subjected to water flow. Chemical analyses have been done since the 1980's and concrete samples were recently extracted to perform laboratory tests, showing increase in resistance, despite partial loss of calcium caused by leaching, by what it is understood as a localized small change, with no implications to the dam safety.

2025

The dissected relief of Slovene mountains with steep slopes above narrow valley bottoms is the result of very active geomorphic past and the playing-ground of vigorous recent geomorphic processes such as rockfalls, landslides, flash-floods etc. These occasional events are the main constituent part of recent geomorphic activity in the mountains, and at the same time, a real threat to the local population and infrastructure which is mainly concentrated in narrow valley bottoms along rivers and smaller streams. The situation in the Dinaric mountains is completely different -there, karst is a predominant feature, corrosion of carbonate rocks is a main geomorphic process and mass movements are exceptional. In the paper, a selection of large-scale geomorphic events is studied from two perspectives: as natural hazards and as principal components of recent landform evolution. The main focus is on three largest geomorphic events in last twenty years: the debris flow of Log pod Mangartom on November 17, 2000, and catastrophic flash-floods in the Savinja river drainage basin on November 1, 1990 and in the villages of Rateče and Ugovizza (Italy) on August 31, 2003. During the first event, man was only a powerless observer of raging nature, while for the second event the contribution of man to the extent of the disaster was rather obvious, especially due to inappropriate location of settlements and economic activities in narrow floodplains and on alluvial fans.

2025, Journal of Korean Society of Coastal and Ocean Engineers

Seabed beneath and near the coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If the liquefaction occurs in the seabed, the structure may sink, overturn, and eventually fail. Especially, the seabed liquefaction behavior beneath a gravity-based structure under wave loading should be evaluated and considered for design purpose. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using 2-dimensional numerical wave tank. The 2dimensional numerical wave tank was expanded to account for irregular wave fields, and to calculate the dynamic wave pressure and water particle velocity acting on the seabed and the surface boundary of the structure. The simulation results of the wave pressure and the shear stress induced by water particle velocity were used as inputs to a FLIP(Finite element analysis LIquefaction Program). Then, the FLIP evaluated the time and spatial variations in excess pore water pressure, effective stress and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the analysis, when the shear stress was considered, the liquefaction at the seabed in front of the structure was identified. Since the liquefied seabed particles have no resistance force, scour can possibly occur on the seabed. Therefore, the strength decrease of the seabed at the front of

2025, Journal of the Korean Geotechnical Society

This study extended the Lee et al.'s (2015a) solution which improved the existing analytical solution for prediction of the residual pore water pressure into progressive wave and flow coexisting field. At this time, the variation of incident wave period and wave length should be incorporated to Lee et al.'s (2015a) analytical solution, which does not consider flow. For the case of infinite thickness, the new analytical solution using Fourier series was compared to the analytical solution using Laplace transformation proposed by . It was verified that the new solution was identical to the Jeng and Seymour's solution. After verification of the new analytical solution, the residual pore water pressure head was examined closely under various given values of flow velocity's magnitude, direction, incident wave's period and seabed thickness. In each proposed analytical solution, asymptotic approach to shallow depth with the changes in the soil thickness within finite soil thickness was found possible, but not to infinite depth. It is also identified that there exists a discrepancy case between the results obtained from the finite and the infinite seabed thicknesses even on the same soil depth.

2025, Journal of Korean Society of Coastal and Ocean Engineers

Seabed beneath and near coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If liquefaction occurs in the seabed, the structure may sink, overturn, and eventually increase the failure potential. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank to account for an irregular wave field. In the condition of an irregular wave field, the dynamic wave pressure and water flow velocity acting on the seabed and the surface boundary of the composite breakwater structure were estimated. Simulation results were used as input data in a finite element computer program for elastoplastic seabed response. Simulations evaluated the time and spatial variations in excess pore water pressure, effective stress, and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the results of the analysis, the liquefaction potential at the seabed in front and rear of the composite breakwater was identified. Since the liquefied seabed particles have no resistance to force, scour potential could increase on the seabed. In addition, the strength decrease of the seabed due to the liquefaction can increase the structural motion and significantly influence the stability of the composite breakwater. Due to limitations of allowable paper length, the studied results were

2025, Arabian Journal of Geosciences

This study presents a controlled laboratory evaluation of the high vacuum densification method (HVDM) for improving extremely soft soil using a 1 g physical model. Following several trials on the physical model, the experiment was carried out using samples obtained from the field site, where HVDM was applied to improve the soil properties. The successful application of HVDM within the physical model resulted in achieving 94% relative compaction, accompanied by significant enhancements in soil strength: specifically, a 37% increase in unconfined compressive strength and a 38% rise in triaxial deviator strength, as well as a significant improvement in cohesion and angle of internal friction relative to untreated conditions. Also, the experimental observations, including the pore pressure response, settlement behavior, and visual evidence, all indicate a significant enhancement in soil stiffness following HVDM treatment, accompanied by rapid consolidation and increased density. The application of HVDM enables the achievement of the desired soil stiffness within the shortest possible timeframe.

2025, Geophysical Research Letters

Injection and extraction of fluids from the subsurface can induce earthquakes (e.g., . Induced seismicity can be intentional and beneficial. This is the case in the context of Enhanced Geothermal Systems where hydrofractures and shear-fractures are used to enhance permeability . In the context of CO 2 storage, fracturing of the underburden and the rock volume beneath the target reservoir could enhance the storage capacity. Most commonly, though, seismicity is viewed as a source of hazard that can compromise the safe operation of a geothermal field or of a CO 2 storage site . In any case, there is much need for a better understanding of how such operations could induce earthquakes. It is well established that the Coulomb Failure Stress change, ΔCFS, can assess the risk of induced seismicity due to a stress change at a particular location . An increase of ΔCFS can in principle result from an increase of shear stress, an increase of pore pressure, or decrease of normal stress. In the case of fluid injection or extraction, ΔCFS at a given location might be due to pore pressure diffusion

2025, Landslides

Rainfall is one of the most important triggers of slope failure. Weathered pyroclastic (tephra) 2 deposits are especially vulnerable to slope failure because they commonly form slopes of high 3 porosity and high clay content. Empirically-derived thresholds for the triggering of landslides 4 are commonly based on rainfall conditions and have been widely applied in volcanic soils. However, so far only few researchers utilized pore water pressure in the slope as additional 6 variable for the threshold calibration. Here we derived a new rainfall threshold for initiating the 7 decrease in effective stress in the slope by analyzing a long-term record of rainfall and piezom-8 eter data from a slide-prone coastal area in northern New Zealand that consists of clayey, hal-9 loysitic tephra deposits. The level of effective stress decrease increases with rainfall intensity 10 and duration. We observed highest effective stress decrease of up to 36 % during rainfall events 11 that triggered landslides in our study area. The effective stress threshold exhibits a satisfactory 12 predictive capability. The probability of correctly predicting a decrease in effective stress is 13 53 %. The effective stress threshold contributes towards the implementation of the decrease in 14 effective stress into rainfall thresholds for the occurrence of landslides. 15 16 Keywords landslides; rainfall threshold; effective stress; weathered tephra; spheroidal hal-17 loysite; rainfall-induced slope failure 18 19 et al., 2018a). In their recent review, Segoni et al. (2018a) summarized that most rainfall thresholds were 46 derived for shallow landslides and debris flows, whereas only few rainfall thresholds for deep-seated 47 landslides, rockslides, and earthflows had been studied. Furthermore, Segoni et al. (2018a) recognized 48 that most studies solely rely on rainfall data when calibrating rainfall thresholds. They found only two 49 case studies -Baum and Godt (2010) and Napolitano et al. (2016)in which pore water pressure data 50 provided additional insight into the trigger mechanism of landslides. Understanding changes in pore 51 water pressure due to rainfall is needed to calculate changes in effective stress in the soil slope (Duncan 52 et al., 2014) and its evaluation would therefore offer a new beneficial perspective in the determination 53 of rainfall thresholds (Segoni et al., 2018a). 54 55 1.1 Suitability of study area 56

2025, Energies

Natural gas hydrates (primarily methane hydrates) are considered to be an important and promising unconventional source of hydrocarbons. Most natural gas hydrate accumulations exist in pore space and are associated with reservoir rocks. Therefore, gas hydrate studies in porous media are of particular interest, as well as, the phase equilibria of pore hydrates, including the determination of equilibrium pore water content (nonclathrated water). Nonclathrated water is analogous to unfrozen water in permafrost soils and has a significant effect on the properties of hydrate-bearing reservoirs. Nonclathrated water content in hydrate-saturated porous media will depend on many factors: pressure, temperature, gas composition, the mineralization of pore water, etc. In this paper, the study is mostly focused on the effect of hydrate-forming gas pressure on nonclathrated water content in hydrate-bearing soils. To solve this problem, simple thermodynamic equations were proposed which require da...

2025

The equilibrium “pore water in sediment–gas hydrate-former–bulk gas hydrate” was experimentally studied. This residual pore water corresponds to a minimal possible amount of water in the sediment, which is in thermodynamic equilibrium with both gas and the bulk hydrate phase. This pore water can be defined as non-clathrated water by analogy to unfrozen water widely used in geocryological science. The amount of non-clathrated water depends on pressure, temperature, type of sediment, and gas hydrate former. The presence of residual pore water influences the thermodynamic properties of hydrate-saturated samples. The paper’s purpose is to describe a new experimental method for determining the amount of non-clathrated water in sediments at different pressure/temperature conditions. This method is based on measuring the equilibrium water content in an initially air-dried sediment plate that has been placed in close contact with an ice plate under isothermal, hydrate-forming gas pressure c...

2025

Increasingly, industrial operations adjoin residential communities. As the demand for natural resources increases, this problem is only more likely to exacerbate in coming decades. Thus, it is imperative to fully understand all potential damage mechanisms that may imperil nearby structures. This paper presents a case history that introduces a potential new mechanism, namely the unintentional triggering of liquefaction due to industrial blasting. The site in question is an early twentieth century town in the southeastern United States located adjacent to a granite quarry. Despite diligent control of blasting levels, there is a clear pattern of repeated damage radiating from the quarry area. This paper presents evidence collected to date that the damage mechanism is blasting-induced partial, repetitive liquefaction.

2025, Geophysical Research Letters

Results of a coupled fluid flow and deformation model indicate that megasplay fault slip may impact excess pore pressures within an accretionary prism. In a simulation with homogeneous low permeability representative of clay-rich sediment, excess pore pressures build where compression occurs in the hanging wall and directly beneath the splay fault. In another simulation with heterogeneous permeability, the impact of high permeability fault zones and turbidite horizons lessens the effect of the megasplay fault slip. Overall, excess pore pressures are lower for the heterogeneous simulation than for the simulation with uniform low permeability. Within the footwall of the megasplay fault zone, simulated pore pressures increase across a transition from more permeable uplifted turbidites to less permeable clay-rich sediments. Strong permeability contrasts might provide an alternate explanation for a previously observed decrease in seismic velocity beneath the megasplay fault of the Nankai Trough subduction zone. Citation:

2025, Journal of Geophysical Research: Solid Earth

The basic triggering mechanism underlying induced seismicity traces back to the mid‐1960s that relied on the process of pore‐fluid pressure diffusion. The last decade has experienced a renaissance of induced seismicity research and data proliferation. An unprecedent opportunity is presented to us to synthesize the robust growth in knowledge. The objective of this article is to provide a concise review of the triggering mechanisms of induced earthquakes with a focus on hydro‐mechanical processes. Four mechanisms are reviewed: pore‐fluid pressure diffusion, poroelastic stress, Coulomb static stress transfer, and aseismic slip. For each, an introduction of the concept is presented, followed by case studies. Diving into these mechanisms sheds light on several outstanding questions. For example, why did some earthquakes occur far from fluid injection or after injection stopped? Our review converges on the following conclusions: (a) Pore‐fluid pressure diffusion remains a basic mechanism ...

2025, Geophysical Research Letters

2025, Geophysical Journal International

In volcanic regions ascending magma is subject to depressurization and is generally accompanied by exsolution of volatiles. We assume a process in which these volatiles propagate upward across newly fractured and permeable rock layers, bringing a sharp increase of pore pressure and temperature within a thin disc-shaped region (inclusion). Thermo-poro-elastic (TPE) inclusion models provide a mechanism to explain seismicity and deformation induced by p and T changes in absence of new magma emplacement in volcanic contexts. They are also suitable to represent the mechanical effects due to fluid extraction and re-injection in geothermal fields. In the present work analytic solutions are provided for the displacement, strain and stress fields assuming a TPE unbounded medium. Significant deviatoric stress is generated by positive increments of pore pressure and temperature: the stress field is fully deviatoric outside the TPE inclusion, but a strong isotropic stress component is present within, leading to highly heterogeneous faulting mechanisms: if the disc plane is horizontal, thrust faulting mechanisms are favoured within the TPE disc over optimally oriented faults and normal mechanisms above. The model is easily generalized to a vertically thick disc with variable temperature and pore-pressure changes: then, an extensional environment can be obtained even within the TPE inclusion assuming upward decreasing of pore pressure and temperature changes. The supplied analytical solution may be used to model near-field TPE inclusion effects and to validate more complex numerical modelling.

2025, Geophysical Journal International

SUMMARY In volcanic regions ascending magma is subject to depressurization and is generally accompanied by exsolution of volatiles. We assume a process in which these volatiles propagate upward across newly fractured and permeable rock layers, bringing a sharp increase of pore pressure and temperature within a thin disc-shaped region (inclusion). Thermo-poro-elastic (TPE) inclusion models provide a mechanism to explain seismicity and deformation induced by p and T changes in absence of new magma emplacement in volcanic contexts. They are also suitable to represent the mechanical effects due to fluid extraction and re-injection in geothermal fields. In the present work analytic solutions are provided for the displacement, strain and stress fields assuming a TPE unbounded medium. Significant deviatoric stress is generated by positive increments of pore pressure and temperature: the stress field is fully deviatoric outside the TPE inclusion, but a strong isotropic stress component is p...

2025, Geosynthetics International

This paper describes an investigation into the performance of geosynthetics in enhancing the resistance to liquefaction of medium dense (Dr = 50%) sand deposits. Cyclic torsional shear tests were carried out on 99 laboratory test specimens under a confining pressure of 98 kPa and a loading frequency of 0.1 Hz. A series of shear stress ratios was used to evaluate the behaviour of sand under cyclic loading conditions. Different types of geotextile (woven, nonwoven) and different arrangements of geotextiles (one, two, three and four layers) were tested. Test results revealed that the liquefaction resistance of sand deposits can be significantly increased by geosynthetic reinforcement. Nonwoven geotextiles were found to perform better than woven geotextiles as reinforcement materials. The results indicate that both the type and the arrangement of reinforcements are crucial in increasing the liquefaction resistance of medium dense sands, and there can be significant variations in the beh...

2025, Interpretation

A working petroleum system was established on the shelf in offshore Labrador with the Bjarni H-81 discovery in 1973 in the Hopedale Basin. The same reservoirs as those targeted on the shelf are present in the deep water, which is currently receiving attention as the result of newly acquired seismic data. To date, only a very small number of wells have been drilled in the deep water, i.e., Blue H-28, Orphan Basin, and none off mainland Labrador. The wells that were drilled in the deep water had encountered significant overpressure, e.g., kicks that indicated overpressures of 26,850 kPa in the Mid-Cretaceous. Therefore, it was reasonable to assume that pore pressures be similarly high for any new deepwater prospects identified. To help reduce the risk in unexplored environments, we developed an approach that can be adopted to model pore pressure in deepwater settings, with Labrador as the main case study area featured, but also we discussed other global examples such as the Vøring Bas...

2025, Advances in Water Resources

In this work semi-analytical solutions for saturation, temperature, pressure and in situ reservoir stress are found for immiscible nonisothermal injection into a radial porous medium. A model for advectiondominated, nonisothermal, two-phase flow from a previous work is used to estimate the reservoir pressure and stress that result from injection of cold CO 2 . Flow is assumed to be one-dimensional and purely advective, while temperature has radial advection in the reservoir and transverse diffusion into the surrounding media. A simplified thermal solution is developed to allow for easier analysis of the reservoir stress. Two pressure models are presented, one which requires numerical integration of the pressure in the two-phase region, and one which is fully analytical, but simplifies the pressure profile. Two models are used to calculate reservoir stress, one which uses the full pressure and temperature profiles and must be numerically integrated, and one which uses the simplified models and has a closedform analytical solution. The resulting radial and tangential (hoop) stress profiles in the reservoir are compared and it is shown that the simplified model is adequate for estimating the reservoir stresses. The impact of outer boundary conditions on reservoir pressure and stresses is also explored.