Search

In order to prevent possible charring, oxidation and (or) vaporisation of substances other than pore water, many researchers have adopted oven-drying temperature (t) values in the range 60–90°C for water content determinations of peat and other highly organic soils. This paper investigates the oven-drying characteristics of six very different highly decomposed peaty soils retrieved from south-west China for t values of 65, 85 and 105°C. Based on the presented experimental data, it is concluded that the standardised t value of 105°C used for testing of inorganic soil is also appropriate (and preferable to using lower t values) for routine water content determinations of these soils, which is in line with the growing consensus formed by other researchers on this topic. Further, the authors recommend a wet specimen mass of approximately 50 g and a 24 h oven-drying period in performing the oven-drying tests for t = 105°C. The paper also describes an existing approach to comparing and standardising water content values determined for the same organic soil, but on the basis of different t values, with the new data presented herein for the six Chinese soils used to strengthen its wider applicability in geotechnical engineering practice and related fields.

In this paper, the nonlinear consolidation behavior of soft soil with vertical drains considering well resistance and smear effect under cyclic loadings was investigated. Using the variables separation method, a series of analytical solutions were derived to calculate the excess pore water pressure and the average degree of consolidation of the soil subjected to various cyclic loadings including trapezoidal cyclic loading, rectangular cyclic loading, triangular cyclic loading and haversine cyclic loading. The correctness of the proposed solutions was verified through degenerating into the existing solutions. Finally, the effects of different parameters on the nonlinear consolidation behavior of soil with vertical drains under cyclic loadings were analyzed.

Soft clays are problematic soils as they present high compressibility and low shear strength. There are several methods for improving in situ conditions of soft clays. Based on the geotechnical problem’s geometry and characteristics, the in situ conditions may require reinforcement to restrain instability and construction settlements. Granular columns reinforced by geosynthetic material are widely used to reduce settlements of embankments on soft clays. They also accelerate the consolidation rate by reducing the drainage path’s length and increasing the foundation soil’s bearing capacity. In this study, the performance of encased and layered granular columns in soft clay is investigated and discussed. The numerical results show the significance of geosynthetic stiffness and the column length on the embankment settlements. Furthermore, the results show that granular columns may play an important role in dissipating the excess pore water pressures and accelerating the consolidation settlements of embankments on soft clays.

This study investigates the influence of the water level fluctuation on the stability of soil slopes using coupled seepage and slope stability analysis. A simulation framework was proposed and implemented seamlessly using Python code to seek insights into three factors that have not been thoroughly studied for this issue: soil unit weight variation in the unsaturated zone, unsaturated shear strength models, and velocity of water drawdown. For this purpose, the seepage analysis was carried out by discretizing a numerical seepage analysis model using a finite element analysis platform, FEniCS. The output of the seepage analysis, i.e., pore water pressure distribution, was used as input for the slope stability analysis. Limit equilibrium methods including the Bishop Simplified method and the Ordinary Method of Slices were modified to take into consideration the unsaturated shear strength, unit weight variation in the unsaturated zone, and hydrostatic pressure changes in response to the water level fluctuation of a reservoir. Both seepage and slope analysis modules were validated against commercial programs. Analysis results obtained with the validated framework clearly revealed the distinct influences of the three factors in representative silty and sandy slopes.

Made available in DSpace on 2021-06-25T10:31:48Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 The fundamental mechanisms controlling shear strength and deformability behavior of clay-fiber mixtures have still not been well established, nor the constraints that may affect their performance of shearing under different drainage conditions. This study aims to understand the behavior of a clay soil mixed with polypropylene fibers using results from drained and undrained triaxial compression tests, and to provide necessary calibration data for a shear strength prediction model. In drained tests, shear strength increased with fiber inclusion for a given mean effective stress, represented by an increase in apparent cohesion. In the undrained tests, the shear strength was not affected by pore water pressure generation. Results from the drained and undrained tests indicate that the fiber content had a greater influence on the apparent cohesion than on the friction angle. Drainage affected the improvement in the peak shear strength of fiber-reinforced soils, with superior improvement in the drained tests. As the percent improvement in shear strength decreased with increasing effective confining stresses for both tests, the difference in behavior in the drained and undrained tests was attributed to the strain at failure, with failure occurring at large strains in the drained tests but at smaller strains in the undrained tests. UFSCar - Federal University of Sao Carlos Department of Civil Engineering UNESP - São Paulo State University School of Engineering at Bauru UCSD – University of California at San Diego UNESP - São Paulo State University School of Engineering at Bauru

Understanding diagenetic reactions in accreted sediments is critical for establishing the balance of fluid sources and sinks in accretionary prisms, which is in turn important for assessing the fluid pressure field and the ability for faults to host seismic slip. For this reason, we studied diagenetic reactions in deformation bands (shear zones and veins) within deep mud sediments from the Nankai accretionary prism (SW Japan) drilled at site C0001 during IODP Expedition 315, by means of microscopic observation, X-ray diffraction, and major- and trace-element analyses. Deformation bands are not only more compacted than the host sediment but are also enriched in framboidal pyrite, as observed under microscopy and confirmed by chalcophile-element enrichments (Fe, S, Cu, As, Sb, Pb). In tandem, one shear zone sample displays a destabilization of smectite or illite–smectite mixed layers and a slight crystallization of illite relative to its sediment matrix, and another sample shows correlated increases in B and Li in shear zones and veins compared to the host sediment, both effects suggesting a transformation of smectite into illite in deformation bands. The two diagenetic reactions of sulfide precipitation and smectite-to-illite transformation are explained by a combined action of sulfate-reducing and methanogen bacteria, which strongly suggests an increased activity of anaerobic microbial communities localized in deformation bands. This local bacterial proliferation was possibly enhanced by the liberation of hydrogen from strained phyllosilicates. We suggest that the proliferation of anoxic bacteria, boosted by deformation, may contribute to the pore water freshening observed at depth in accretionary prisms. Deformation-enhanced metabolic reactions may also explain the illitization observed in major faults of accretionary prisms. Care is therefore needed before interpreting illitization, and other diagenetic reactions as well, as evidence of shear heating, as these might be biogenic instead of thermogenic.

The riverbed sedimentation zone is an important zone of hydrochemistry, and the biogeochemical action in this zone has a significant impact on groundwater quality. As the main area where hydrochemistry occurs, studying the law of hydrochemical evolution within 1 m below the riverbed is of great significance for understanding the migration and removal of river pollutants. In this study, a combination of onsite monitoring and indoor experiments was used to analyze the variation characteristics of the hydrochemical composition of pore water during riverbank infiltration, as well as the main hydrochemical effects and influencing factors. The results show that in the process of river water infiltration, a series of redox reactions occur in the riverbed sedimentation zone, and there are differences in different infiltration depths. From 0 to 20 cm below the riverbed, strong respiration and denitrification mainly occurred. Reductive dissolution of manganese minerals mainly occurred from 20 to 60 cm, and reductive dissolution of iron minerals mainly occurred from 60 to 90 cm. River water level, dissolved organic carbon content and microbial activity had varying degrees of influence on these redox effects. The recharge of river water infiltration ensures the exploitation amount of the pumping wells, but it also leads to the increase of some components in groundwater, and the extracted water cannot be directly drunk. HIGHLIGHTS The main control effect of hydrochemical evolution in the riverbed sedimentation zone is redox, and there are differences in different infiltration depths.; The redox effects were affected by river water level, dissolved organic carbon content and microbial activity.; The recharge of river water infiltration ensures the exploitation amount of the pumping wells, but it also leads to the increase of some components in groundwater.

Pore water data of thallium (Tl) in marine environments are scarce. It has been suggested that anoxic sediments are a sink for dissolved Tl likely due to its incorporation into Fe sulfides. However, recent studies indicated that Tl is removed from solution prior to the onset of sulfidic conditions and that Tl is involved in biological cycles in coastal seawater. To assess the Tl behavior in marine sediments, pore waters of a high energy beach (Spiekeroog Island, Germany) were sampled during different seasons and on different spatial scales. The study site provides a perfect set of samples to assess trace metal behavior under various redox conditions. Samples were analyzed for the dissolved trace metals Tl, molybdenum (Mo), uranium (U), and rhenium (Re). Additionally, sediments were incubated to monitor trace metal removal or release under controlled conditions. On-site redox conditions were characterized using dissolved oxygen (O2), manganese (Mn), and iron (Fe) concentrations. Our results indicated high enrichments of Tl in pore waters concurrently to aerobic organic matter (OM) degradation, exceeding seawater concentrations up to 6-fold. In contrast, Tl was completely removed in weakly reducing pore water characterized by more than 1 µM Mn or Fe. The spatial Tl distribution in intertidal pore waters responded to the present dissolved Mn and Fe level, which varied in space and with season. We suggest, Tl release to be attributed to OM degradation, particle desorption, or reoxidation, whereas Tl removal is likely related to the presence of trace amounts of dissolved sulfide. In conclusion, the fast reaction kinetics of Tl led to fast and complete removal in comparison to Mo, U, and Re and we suggest the following order of removal: Tl > Re > U > Mo. The removal behavior as well as the high enrichments of Tl in pore waters implicate that sinks and sources in the marine environment are not yet fully understood. Although the intertidal sediments form an overall sink for Tl (U and Re), especially under mostly anoxic conditions in summer, sediments turn into a Tl net source in winter, when sediments are more oxic. For global marine Tl balances, Tl fluxes have been estimated based on pore water Tl/Mn ratios. Contrastingly, Tl removal from pore waters at low threshold concentrations of Mn at our site indicated that these Tl flux estimations may not be applicable in permeable sandy beach sediments and in many other types of sediments, which host mildly sulfidic conditions.

The self-healing of a GCL with a circular hole is examined in experiments where the GCL, overlain by geomembrane, is hydrated from a silica sand subgrade (SSS) having three different pore water chemistries. Factors considered included: hole size, subgrade initial moisture content wfdn, GCL mass per unit area, and overburden stress (20–100 kPa). GCL self-healing is better for wfdn = 16% than for wfdn = 10%, which is better than for 5%, when the SSS pore water has negligible cations (ionic strength, I

Using the dense linear multihole to control the directional hydraulic fracturing is a significant technical method to realize roof control in mining engineering. By combining the large-scale true triaxial directional hydraulic fracturing experiment with the discrete element numerical simulation experiment, the basic law of dense linear holes controlling directional hydraulic fracturing was studied. The results show the following: (1) Using the dense linear holes to control directional hydraulic fracturing can effectively form directional hydraulic fractures extending along the borehole line. (2) The hydraulic fracturing simulation program is very suitable for studying the basic law of directional hydraulic fracturing. (3) The reason why the hydraulic fracture can be controlled and oriented is that firstly, due to the mutual compression between the dense holes, the maximum effective tangential tensile stress appears on the connecting line of the drilling hole, where the hydraulic fracture is easy to be initiated. Secondly, due to the effect of pore water pressure, the disturbed stress zone appears at the tip of the hydraulic fracture, and the stress concentration zone overlaps with each other to form the stress guiding strip, which controls the propagation and formation of directional hydraulic fractures. (4) The angle between the drilling line and the direction of the maximum principal stress, the in situ stress, and the hole spacing has significant effects on the directional hydraulic fracturing effect. The smaller the angle, the difference of the in situ stress, and the hole spacing, the better the directional hydraulic fracturing effect. (5) The directional effect of synchronous hydraulic fracturing is better than that of sequential hydraulic fracturing. (6) According to the multihole linear codirectional hydraulic fracturing experiments, five typical directional hydraulic fracture propagation modes are summarized.

Little attention has been paid to investigating borehole deformation characteristics during drilling in soil and rock mixtures commonly encountered in the construction of ground anchors, micropiles, etc., raising questions as to the pile quality. This unique study investigates the deformations of micropile boreholes during rotary drilling in a compacted soil-limestone mixture (S-LM) by developing model tests. Three sets of experiments were carried out, in which three groundwater conditions (no water flow, 40 cm water level, and 80 cm water level) were applied at each of the three boreholes, which had diameters of 32, 44, and 56 mm. The variations in vertical displacement, deep horizontal displacement, pore water pressure, and soil pressure were recorded during the drilling stage. The test results showed that, in general, the vertical displacement at the ground surface, radial horizontal movement, and soil pressure induced by rotary drilling were strongly correlated with the borehole diameter. It was observed that the larger the borehole diameter was, the higher the values of these parameters. Furthermore, the 80-cm water level resulted in borehole collapse during the drilling stop periods since a negative displacement area and a soil pressure varying from negative to zero were observed. This research broadens the limited study of borehole deformation conducted on soil and rock mixtures via model tests. Additionally, it can provide a reference for micropile designers and contractors planning to drill in similar soil-rock mixtures.

The deep oceanic sediments were collected from the Challenger Deep in the southwestern part of the Mariana Trench. Considering the salt in the pore water, a modified method for determining the physical and mechanical properties of the deep-sea sediments was proposed, by which the geological engineering indices were measured and corrected. Through the scanning electronic microscope (SEM), the microstructures of the sediments were found to be composed of flocculation, with a large number of diatom debris and empty shells of organism around it. As a consequence, the porosity and compressibility are high; internal friction angle and cohesion are low. Besides high water content, high porosity, high liquid limit, high plasticity, high consolidation coefficient, low compressive modulus, low shear strength, low density, and low specific gravity, the deep-sea mining machine may slip and subside. This research can improve the understanding of the deep-sea sedimentary environment of the Challenger Deep in the southwestern part of the Mariana Trench and provide an essential reference for the parameter calibration as well as the basis for walking-characteristic study and optimization design of the deep-sea mining vehicle.

The study on hydromechanical coupling properties of rocks is of great importance for rock engineering. It is closely related to the stability analysis of structures in rocks under seepage condition. In this study, a series of conventional triaxial tests under drained condition and hydrostatic compression tests under drained or undrained condition on sandstones were conducted. Moreover, complex cyclic loading and unloading tests were also carried out. Based on the experimental results, the following conclusions were obtained. For conventional triaxial tests, the elastic modulus, peak strength, crack initiation stress, and expansion stress increase with increased confining pressure. Pore pressure weakened the effect of the confining pressure under drained condition, which led to a decline in rock mechanical properties. It appeared that cohesion was more sensitive to pore pressure than to the internal friction angle. For complex loading and unloading cyclic tests, in deviatoric stress loading and unloading cycles, elastic modulus increased obviously in first loading stage and increased slowly in next stages. In confining pressure loading and unloading cycles, the Biot coefficient decreased first and then increased, which indicates that damage has a great impact on the Biot coefficient.

Underwater drilling blasting technique is often adopted to clear away the obstructed reef and dredge-cut in the mountainous waterway dredging engineering. However, the vibration of the underwater blasting and excavation of the riverbed has a certain influence on the stability of bank slopes. Combined with the partial bank collapse phenomenon in the waterway regulation project between two dams in the Three Gorges reservoir area, the change of pore water pressure of unsaturated soil under heavy rainfall and the increase of permanent displacement of soil under blasting vibration in the reservoir area are discussed. This paper explains the weakening effect of rainfall infiltration and blasting vibration on the stability of the bank slope. By studying the law of slope failure deformation under the separate action and coupling action, it is found that rainfall infiltration promotes the increase of slope permanent displacement and the blasting vibration enlarges the infiltration area of the soil, which demonstrated the accelerated failure mechanism of the rainfall-blasting slope.

In this paper, we study seismic responses to an earthquake source in horizontally stratified transversely isotropic porous media with a vertical axis of symmetry that is, transversely isotropic porous media. We present a semi‐analytical method to simulate the three‐dimensional time–space–domain seismic wavefields. We obtain the solution in the frequency–wavenumber domain by the global matrix method and transform it to the time–space domain by the discrete wavenumber method and fast Fourier transform. Our method incorporates the moment tensor source so that it allows simulating seismic responses to an earthquake. We validate our method by degenerating the transversely isotropic porous media into the isotropic porous media and transversely isotropic solid media, respectively, and compare the results with the corresponding reference solutions. We then investigate the characteristics of seismic wavefields in the transversely isotropic porous media by considering an explosive source, a shear‐wave source and a double‐couple source. The results reveal interesting observations in the transversely isotropic porous media versus the isotropic porous media. For example, the qSV wave can have a response to the pore pressure during its propagation in a transversely isotropic porous medium while the shear‐wave does not generate any disturbance of the pore pressure. Our method is semi‐analytical and computationally efficient and it can be used for rapid evaluation of the seismic responses in transversely isotropic porous media.

Generally numerical modelling can provide an accurate and cost-effective approach to understand the behaviour of geosynthetic-reinforced column-supported embankment. When the problem geometry cannot be simplified to the two-dimensional plane-strain or axisymmetric, a full three-dimensional solution is required to obtain sensible results. This study presents a modelling of the geosynthetic-reinforced composite ground supporting a road embankment. Response of soft soil is captured by adopting Modified Cam-Clay model. In addition, Hoek-Brown constitutive model is considered to simulate non-linear stress-dependent yield criterion for Concrete Injected Columns (CIC) that describes shear failure and tensile failure by a continuous function. To assess whether the proposed numerical model can capture real behaviour of composite ground, field monitoring data of deep soft clay deposit improved by CIC from Gerringong Upgrade is used to validate the model. The settlement and lateral displacements of ground, stress transferred to column, and pore water pressure results for the embankment during and after the construction, measured using the field instrumentations including settlement plates, inclinometers, earth pressure cells on CIC, and pore pressure transducers, are compared with numerical predictions. In addition, the numerical results provide insights to investigate load transfer mechanism in the composite ground, capturing response of soil – column - embankment system.

A microgravity data set presented in a previous study exhibits distinct short-wavelength anomalies over a longwall coal mine panel at Soma-Darkale Coalfield. Nevertheless, our preliminary models suggest that the wavelength after the coal removal from a panel at a moderate depth and fracturing alone should be incomparably greater than that of the measured anomalies. Understanding the mechanism that causes these anomalies usually becomes critical to provide credible evidence for longwall mining-related legal cases. This study improves the model by including the post-subsidence drainage as it occurs because of fracturing that causes an increase in water storage and local density change. Since no water-level information was available at the site, we attempted to infer the drained zone from the dc-resistivity sounding measurements acquired shortly before the gravity field survey. The wavelengths of the model anomalies became reasonably comparable with that of the residual anomalies after the inclusion of the inferred drainage information. This presented approach that does not require water level measurements shows that the inclusion of the inferred drained zone to the model became an amplifying indicator of a coal panel at a moderate depth. Therefore, it may easily find application in settling the mining-related legal cases, understanding the longwall mining-related geohazard, and environmental impact assessments.

Plate bending-related normal faults (i.e. bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction zone. Numerous geophysical studies and numerical simulations suggest that bend-faults play a key role by providing pathways for seawater to flow into the oceanic crust and the upper mantle, thereby promoting hydration of the oceanic plate. However, deep penetration of seawater along bend-faults remains controversial because fluids that have percolated down into the mantle are difficult to detect. This report presents anomalously high helium isotope (3He/4He) ratios in sediment pore water and seismic reflection data which suggest fluid infiltration into the upper mantle and subsequent outflow through bend-faults across the outer slope of the Japan trench. The 3He/4He and 4He/20Ne ratios at sites near-trench bend-faults, which are close to the isotopic ratios of bottom seawater, are almost constant with depth, supporting local seawater inflow. Our findings provide the first reported evidence for a potentially large-scale active hydrothermal circulation system through bend-faults across the Moho (crust-mantle boundary) in and out of the oceanic lithospheric mantle.

Pore pressure is an important parameter in coalbed methane (CBM) exploration and development; however, the distribution pattern and mechanism for pore pressure differences in the Upper Permian CBM reservoirs are poorly understood in the western Guizhou region of South China. In this study, lateral and vertical variations and mechanisms for pore pressure differences are analyzed based on 126 injection-falloff and in-situ stress well test data measured in Permian coal reservoirs. Generally, based on the pore pressure gradient and coefficient in coal reservoirs of the western Guizhou region, five zones can be delineated laterally: the mining areas of Zhina, northern Liupanshui, northern Guizhou, northwestern Guizhou and southern Liupanshui. Vertically, there are two main typical patterns: i) the pore pressure gradient (or coefficient) is nearly unchanged in different coal reservoirs, and ii) the pore pressure gradient (or coefficient) has cyclic variations in a borehole profile with multiple coal seams, which suggests the existence of a “superimposed CBM system”. The mechanism analysis indicates that coal permeability, thermal evolution stage and hydrocarbon generation contribute little to pore pressure differences in coal reservoirs in the western Guizhou region. The present-day in-situ stress field, basement structure and tectonic activity may be the dominant factors affecting lateral pore pressure differences. The sealing capacity of caprocks and the present-day in-situ stress field are significant parameters causing vertical pore pressure differences in coal reservoirs. These results are expected to provide new geological references for CBM exploration and development in the western Guizhou region.

Pore pressure is the pressure associated with fluids in the pore spaces of sedimentary rocks. This pressure varies from hydrostatic to severe overpressure. It is classified as abnormal pressure when it deviates from hydrostatic pressure. Incorrect prediction or the absence of pore pressure evaluation can lead to severe damage of the drilling platform, loss of personnel, waste of resources and environmental pollution. This study was carried out in an offshore field in Niger Delta with an objective of predicting the abnormal pressure regime from the seismic volume using seismic inversion technique. First, we employed the Eaton’s and Bower’s model of predicting pore pressure from Well log. The predicted pore pressure from the well was used to calibrate the P-impedance that was used in the inversion process. A pressure-based model for the seismic inversion process was developed. This was constrained by the relationship between the P-impedance and pore pressure in the study area. The predicted pore pressure from the Well logs aligned with the measured pore pressure in the formation. At about 3600 m to end of the Well, depicts a pressure regime that is a deviation from the hydrostatic pressure trend. The abnormal pressure regime is marked by the region where a change is observed in the normal compaction trend line. The cross plot of acoustic impedance against pore pressure reveals a linear relationship; with a direct relationship indicating a normal pressure interval and the indirect relationship at the abnormal pressure regime. The inverted 3D pressure result from the seismic volume validates the normal compaction trend line and also the pressure values estimated from the Well logs. The abnormal pressure regime in the study area is predicted to be found towards the end of Agbada Formation and through the Akata Formation due to the un-compacted shales.

Stone columns, which are frequently employed to stabilize the liquefiable soil, are susceptible to accumulation of soil particles. The progressive accumulation of the soil particles causes clogging of the stone column which decreases its drainage capacity. The stone column can be encased with geotextile to sustain its long term drainage function. The encasement prevents the movement of the soil particles into the stone pores. In the present paper, a mathematical model is presented to assess the filtration performance of the geotextile encasement to prevent the clogging. The filtration capacity of the geotextile is related to its maximum pore size, porosity and soil characteristics. It is observed that the encased stone column dissipates the excess pore pressure at a faster rate compared to the stone column without encasement. The peak maximum excess pore water pressure (Umax) is not significantly affected due to selection of the opening size of the geotextiles for single earthquake. However, the opening size can significantly affect the peak Umax value for multiple earthquakes. Depending on the capture coefficient of the stone column, the clogging can be fully prevented for higher hydraulic gradient if geotextile with maximum opening size in between D10 to D5 is used as encasement.

Seepage-type gas hydrate accumulation in subsea shallow formations involves complicated thermo-hydro-solid coupling processes and matching problem between various accumulation elements. The formation physical properties control local natural gas migration pathway and thus the final reservoir characteristics of hydrates. In this paper, a novel mixed-flux model for gas hydrate accumulation is established and then used to simulate the process of methane gas migration into the shallow stratum to form a hydrate reservoir. The effects of reservoir heterogeneity and gas source conditions on the distribution of pore fluid and hydrate accumulation are examined. The simulation results show that reservoir heterogeneity is conducive to the retention and lateral migration of CH4 in a hydrate stability zone. CH4 can contact more pore water to form a large hydrate reserve, but the formed hydrate is often dispersed. Low-permeability layers enhance the trapping of CH4 and form a uniform and large hydrate saturation. Besides, gas source conditions have an important impact on the hydrate accumulation in reservoirs. Large gas flux, small pore water flux, continuous gas supply, high content of heavy components in natural gas, and numerous gas source points contribute to large amounts of hydrates generation in a certain time period. The presented work will deepen our understanding of the controls of natural gas hydrate systems in subea shallow formations.

The focus of the present paper is on utilizing a comprehensive diagnostics workflow that combines coupled hydro-mechanical modeling with production data-driven diagnostics for optimization of stimulation candidate selection process. Reservoir fluids production and production-induced depletion affect reservoir mechanical environment due to reduced pore pressure and increased effective stress and the consequent porosity and permeability reduction, depending on rock sensitivity to stress changes. The coupled formation damage index (CFDI) is implemented in the traditional stimulation candidate selection workflow to capture the effect of production-induced stress changes on the near-wellbore permeability over time. The top potential stimulation candidates are recognized based on heterogeneity index, static formation damage index, and the CFDI parameter. CFDI is a dynamic parameter for stimulation candidate selection through estimating time-dependent permeability changes induced by stress state and fluid pressure. Probabilistic type curves and decline curve analysis of candidate wells versus reservoir unit are also applied to complement the stimulation and production enhancement candidate selection.

Cemented paste backfill (CPB) is extensively used for underground mine support and/or tailings management. However, CPB behavior under cyclic loadings might be affected by the chemistry of its pore-water, which often contains sulphate ions. Till today, no studies have addressed the effect of sulphate on the response of CPB to cyclic loadings by using shaking table technique. This study presents new findings of assessing the effect of the sulphate in the pore water of CPB on its geotechnical response to cyclic loading by using shaking table. CPB mixtures were prepared (with and without sulphate), poured into a flexible laminar shear box, cured to 4 h, and then exposed to cyclic loading using one-dimensional (1D) shaking table. Several parameters (e.g. pore water pressure, settlement, lateral deformation, acceleration, electrical conductivity, effective stress, and liquefaction susceptibility) were monitored or determined before, during, and after shaking. Obtained results indicate that the sulphate-bearing CPB cured to 4 h can be prone to liquefaction under the studied conditions. However, sulphate-free CPB samples are resistant to liquefaction. These results are expected to contribute to a better understanding of the effect of water chemistry on the cyclic behavior of CPB, consequently enhancing the cost-effective design of CPB structures.

Volumetric expansion of water by 9% in saturated pores and cracks causes substantial frost deformation in rock masses. Frost deformation is an important index reflecting the frost resistance of rocks; however, water saturation has a great influence on the frost deformation characteristics. In this research, the frost strains and acoustic emission activities of red sandstone with different water saturations are monitored under freeze–thaw conditions. The experimental results show that both the peak and the residual frost heaving strains greatly increase for sandstone beyond 85% water saturation. However, there is no significant frost heaving strain that occurs in low-saturation red sandstone (less than 85% water saturation). The acoustic emission activities show the same change trend and further confirm the existence of this critical saturation. In addition, the pore size distribution also has a great influence on the frost heaving strain and freeze–thaw damage. All the liquid pore water in this red sandstone is frozen at − 20 °C because the pores are larger than the critical freezing radius (2.58 nm at − 20 °C) according to the measured pore size distribution. Based on the pore micromechanics and Gibbs–Thomson equation, a developed frost heaving model is proposed considering the effects of water saturation and the pore size distribution. The proposed model can be used to predict the frost heaving strain at any freezing temperature for unsaturated red sandstone. This study thus provides the frost deformation characteristics of red sandstone and contributes to a better understanding of the freeze–thaw damage mechanism of unsaturated sandstone.

Forecasting the pore or formation pressure is crucially significant in every well drilling operation to determine whether the pore pressure gradient is abnormal or subnormal. Abnormal pore pressure gradient means that the pore pressure gradient exceeds the gradient of the normal pressure, while when the opposite happens it means that the pore pressure is subnormal. Both cases required high care with special control of the mud weight to overcome the vital situation. Accurate pore pressure determination is rigorous in drilling engineering to plan for drilling hydrocarbon wells with appropriate mud program with less effort and cost. Precise forecasting of formation pore pressure prevents occurring various drilling hazards such as lost circulation, stuck pipe and well kick as a result of abnormal pore pressure. In the present work, a new technique was proposed to predict the pore or formation pressure from the specific energy. A new formula of specific energy was used involving the rock properties and the drilling parameters. The new specific energy formula is functioned later in Eaton’s equation to obtain a new suggested formula of pore pressure. There is a lack of researches in the literature that determine the real-time pore pressure without depending on well logs. Abnormal and subnormal pressure zones can be determined accordingly based on the fact that abnormal pressure intervals possess low effective stress and require less energy to drill than the intervals that have normal pressure at the same depth. The new proposed formula of pore pressure was tested in two oil wells in North Rumaila field (N14 and N15) in Basrah province south of Iraq. The obtained pore pressure from the new technique based on the suggested specific energy formula that involves the physical properties of the rock being excavated and the drill bit is compared with the actual (measured) pore pressure derived from other wells in North Rumaila field using measurements while drilling logs, drill stem test and real formation test. There was a good rapprochement between the predicted and the measured pore pressure. The present approach depends mainly on the value of the slope (m) which is determined and varied from one place to another. The new method could provide an alternative method for estimating the pore pressure especially for wells being planned to be drilled where the actual pore pressure is unknown and there is shortage in well logs and formation tests, where most of the previous articles in the literature depend mainly on well logs of adjacent wells in predicting the pore pressure of a specific well. The findings of this study can help for better understanding the prediction of formation or pore pressure that helps to choose the appropriate mud weight to control the well without collapsing and preventing well kick that might occur.

The occurrence of harmful algae blooms has been increasing in large lakes worldwide. The mechanism of heavy metals mobilization in sediments during algae blooms is not well understood. As a major pollutant in the sediments of Taihu Lake, cobalt (Co) has been selected to study heavy metal mobilization during algae blooms. Rhizon and HR-Peeper sampling techniques have been used for in situ investigation and indoor simulation experiments to collect information on dissolved Co, manganese (Mn), and UV absorbance at 254 nm (UV254) in sediments. Excitation–emission matrix (EEM) was combined with parallel factor (PARAFAC) to determine the change of dissolved organic matter (DOM) components during algae blooms. The chemical morphology of Co in pore water was analyzed by visual MINTEQ model. The Stern–Volmer model was used to characterize the stability of different DOM components and Co(II). Algae blooms significantly increased the dissolved Co concentration in sediments. The release of Co was closely related to DOM in the algae bloom sediments, which was reflected by the similar distribution and significant positive correlation between the dissolved Co and DOM in pore water, during both in situ and laboratory simulation algae blooms experiments. On the other hand, the saturation of oxygen in the sediment–water interface (SWI) rapidly decreased from 100 to 0% during algae blooms, resulting in high mobilization of Co and reduction of Mn oxides in sediments. This was supported by the simultaneous increase of dissolved Co and Mn and significant positive correlation between dissolved Co and Mn in the simulation aerobic–anaerobic sediments. The transformation of most Co(II) into DOM-Co(II) complexes, as calculated by the Visual MINTEQ model, further demonstrated that the mobilization of Co was mainly controlled by the DOM content in the sediments during algae blooms. Further studies revealed that tyrosine-like substance released by algae played a major role in their complexation with Co, possibly due to their relatively high content and high stability after binding Co. The mobilization of Co in sediments during algae blooms was mainly controlled by DOM through complexation, reflected by the observation that dissolved Co concentration and UV254 increased simultaneously and had significant positive correlation during in situ monitoring and indoor simulations experiments. More than 80% of dissolved Co in the pore water during algae blooms was DOM-Co complexes, supporting this conclusion. It was further observed that tyrosine-like substances played an important role in Co complexation.

Due to the economic and tourist importance of Bandar-e Anzali coastal zone and also the high seismic risk in this area, this article provides an experimental seismic study using shaking table test on the sandy soil of Bandar-e Anzali. Modeling the laboratory conditions and applying seismic forces were carried out using a transparent tank on a shaking. Additionally, digital instrumentations of horizontal displacement transducers, pore water pressure gauge and data entry device via computer were used. In this study, data collection was conducted by creating saturated samples with relative densities of 20%, 30% and 50% and accelerations of 0.15 g, 0.3 g and 0.53 g and the variation of pore water pressure, horizontal displacement and settlements were measured. The results indicate the high effect of input acceleration on the occurrence of liquefaction and amount of the settlements, especially in low relative density. The effect of higher density on reducing the liquefaction potential and settlement is also significant.

The diffusive gradients in thin films (DGT) technique has been successfully and widely applied to investigate the labile fractions of inorganic contaminants in soils and sediments, but there have been almost no applications to organic contaminants. Here we developed and tested the approach for the pesticide Atrazine (ATR) in a controlled soil experiment and in situ in an intact lake sediment core. The soil study explored the relationships between soil solution, DGT measured labile ATR and solvent extractable ATR in dosed soils of different organic matter, pH status and incubation times. The results are further interpreted using the DIFS (DGT-induced fluxes in soils and sediments) model. Resupply of ATR to the soil solution was partially sustained by the solid phase in all the soils. This was due to small labile pool size and slow kinetics, with soil pH being an important controlling factor. The in situ sediment study successfully used a DGT probe to examine labile ATR distribution through the core on the subcm scale. It demonstrated-for the first time-an easy to use in situ technique to investigate the effects of redox on resupply kinetics and biogeochemical processes of trace organic contaminants in sediments.

Thickness and stratigraphic settings of soils covering slopes potentially control susceptibility to initiation of rainfall-induced shallow landslides due to their local effect on slope hydrological response. Notwithstanding the relevance of the assessment of hazard to shallow landsliding at a distributed scale by approaches based on a coupled modelling of slope hydrological response and slope stability, the spatial variability of soil thickness and stratigraphic settings are factors poorly considered in the literature. Under these premises, this paper advances the well-known case study of rainfall-induced shallow landslides involving ash-fall pyroclastic soils covering the peri-Vesuvian mountains (Campania, southern Italy). In such a unique geomorphological setting, the soil covering is formed by alternating loose ash-fall pyroclastic deposits and paleosols, with high contrasts in hydraulic conductivity and total thickness decreasing as the slope angle increases, thus leading to the establishment of lateral flow and an increase of pore water pressure in localised sectors of the slope where soil horizon thickness is less. In particular, we investigate the effects, on hillslope hydrological regime and slope stability, of irregular bedrock topography, spatial variability of soil thickness and vertical hydraulic heterogeneity of soil horizons, by using a coupled three-dimensional hydrological and a probabilistic infinite slope stability model. The modelling is applied on a sample mountain catchment, located on Sarno Mountains (Campania, southern Italy), and calibrated using physics-based rainfall thresholds derived from the literature. The results obtained under five simulated constant rainfall intensities (2.5, 5, 10, 20 and 40 mm h−1) show an increase of soil pressure head and major failure probability corresponding to stratigraphic and morphological discontinuities, where a soil thickness reduction occurs. The outcomes obtained from modelling match the hypothesis of the formation of lateral throughflow due to the effect of intense rainfall, which leads to the increase of soil water pressure head and water content, up to values of near-saturation, in narrow zones of the slope, such as those of downslope reduction of total soil thickness and pinching out of soil horizons. The approach proposed can be conceived as a further advance in the comprehension of slope hydrological processes at a detailed scale and their effects on slope stability under given rainfall and antecedent soil hydrological conditions, therefore in predicting the most susceptible areas to initiation of rainfall-induced shallow landslides and the related I-D rainfall thresholds. Results obtained demonstrate the occurrence of a slope hydrological response depending on the spatial variability of soil thickness and leading to focus slope instability in specific slope sectors. The approach proposed is conceived to be potentially exportable to other slope environments for which a spatial modelling of soil thickness would be possible.

The influence of crab disturbances on nitrogen migration and the transformations of pore water and overlying water in a coastal tidal flat wetland were investigated at the lab scale, and the nitrogen exchange flux at the sediment-water interface was calculated. The results showed that crabs, combined with tidal effects, had significant effects on the microtopography of the studied crab box. In addition, there was no significant difference in the concentrations of NH4+-N, NO3−-N, or TN between two points in the horizontal direction (P > 0.05), and there were significant differences in the concentrations of NH4+-N and TN in the vertical direction (P 0.05). The NO3−-N concentration in the surface pore water of the crab box had a downward trend with time. Furthermore, the NH4+-N and TN contents in the overlying water in the crab box were significantly higher than those of the control box, indicating that crab disturbances also had significant effects on the concentrations of NH4+-N, NO3−-N, and TN in the overlying water. The existence of crab caves greatly promoted the nitrogen exchange flux at the sediment-water interface, and the mean exchange fluxes of NH4+-N, NO3−-N and TN were 51.40 mmol (m2 day)−1, −13.44 mmol (m2 day)−1 and 39.74 mmol (m2 day)−1, respectively (much higher than those measured in the control box), implying that NH4+-N and TN were released from the sediment to the overlying water, while NO3−-N was released from the overlying water to the sediment.

In this research, the conventional triaxial compression experiments for intact red sandstone specimens and the specimens with a single persistent joint at different inclination angles, i.e., 0°, 30°, 45°, and 90°, were conducted at first. Based on the results of the conventional tests, the effects of the confining pressure and the joint inclination angle on the mechanical properties including deformation behavior and strength parameters were summarized and analyzed, respectively. We find that the strength and deformation of jointed red sandstone are enlarged due to the increment of confining pressure, and the mechanical parameters of specimens show a U-shaped development with the rise of the joint angle. Besides, to investigate the effects of the pore pressure on seepage characteristics of rocks with joint angles at 0°, 45°, and 90°, a series of triaxial compression drainage tests on the jointed red sandstone were performed. The results show that the pore pressure has a weakening effect on the strength of jointed specimens, which can reduce the strengthening effect induced by confining pressure. Meanwhile, the tested specimens mostly present shear failure modes. As a result, the mechanical responses, seepage characteristics, and cracking modes in red sandstone containing a single persistent joint under triaxial compression are revealed.

International audience; This study aims at investigating the lime treatment effect on the changes in microstructure and water retention property of compacted saline soil, with consideration of the aggregate size effect. Two soil powders with different maximum aggregate sizes (Dmax = 0.4 and 5 mm) were prepared and stabilized by 2% lime. The microstructure, total suction and matric suction were determined at various curing times. Results showed that the lime treatment caused a rapid decrease in micro-pores and an increase in macro-pores due to the flocculation of soil particles. During curing, the percentage of micro-pores decreased and that of nano-pores increased slightly. Due to the modification of microstructure, the matric suction increased significantly at 90-day curing. However, the curing time effect on the total suction was insignificant. This was due to the fact that the Ca2+ and Mg2+ in soil pore water and the Ca2+ from hydrated lime were consumed in the precipitations of CaCO3 and Mg(OH)2, cation exchanges and pozzolanic reaction, resulting in a reduction in osmotic suction. Therefore, the increase in total suction was slight, as the increase in matric suction was balanced by the decrease in osmotic suction. The treated specimens with larger aggregates exhibited a larger modal size and thus had a smaller air entry value. The aggregate size effect on the water retention property of total suction and matric suction was found to be insignificant, which could be explained by the similar pore size distribution at micro-pore range and the same soil mineralogy for specimens with different aggregates.

A common and important task in mining industry is to estimate the settlement or final volume of the tailings or backfill associated with sedimentation and self-weight consolidation. Up to now however, most existing analytical solutions were developed by only considering the settlement induced by consolidation. In this paper, the process of shrinkage tests has been compared with those of sedimentation and consolidation. It was shown that the pore water and particles movement in the sedimentation are very similar to that in the normal shrinkage. The void ratio at the end of sedimentation is thus for the first time considered to be equal to the void ratio at desaturation onset of shrinkage tests. An analytical solution was then proposed to estimate the settlement of tailings or backfill by considering the sedimentation and consolidation. To validate the proposed analytical solution, tailing deposition tests were conducted in two molds to simulate the tailings impoundment and underground mine stope. The required parameters were obtained through shrinkage and consolidation tests. Good agreements were obtained between the measured settlements and those calculated by the proposed solution. The proposed solution can thus be considered as validated and used to evaluate the settlement of tailings or backfill slurry.

One of the vital parts of mining activity is optimizing the mine waste dump. It means that the capacity needs to be conserved by the various aspects of feasibility study. Hydrogeology is one of the main aspects of mine waste stability that needs to be controlled to ensure slope stability. The research aims to determine the influence of water balance toward mine waste dump stability, especially for inclined basement. The analysis was carried out by distributing the constituent material grain size, mapping of permeability value, determining the water balance behaviour between recharge and discharge, and watering behaviour inside mine waste dump material. It was also about the fragmentation analysis that was carried out to determine the layer of porosity value, while the permeability test was used to examine the rainfall infiltration rate. It is important to decide on the equilibrium water flow between the recharge and the discharge rates to ensure no water accumulates to mine waste dump. The fragmentation analysis results showed that the top layer of the waste is composed of sand-boulder-sized material with porosity towards the contact zone and a little clay. The hydraulic conductivity material values range from 6 × 10–6 m/s and 3 × 10–2 m/s at the top and the bottom layers of mine waste dump. The rainfall and the seepage are interrelated because a rise follows an increase in rainfall in seepage debit. The large permeability difference between the in-situ material and the layer slope is approximately 14°, therefore, the water tends to flow following the contact zone and forms a seepage. Pore pressure can be minimized, and stability of the mine waste dump slope maintained.

Desorption of phosphorus (P) bound to iron-containing minerals (Fe-P) is a crucial component of the eutrophication process in lakes. However, the main process and regulation mechanism of iron (Fe) and sulfur (S) on P release is little known because of a lack of in situ high-resolution data. High-resolution measurement evidence is needed to assess the availability and diffusion kinetic process of P at the water–sediment interface. Soluble reactive phosphate (SRP), ferrous ion (Fe2+), and sulfide (S2−) fluxes through the water–sediment interface in a freshwater lake were detected using the novel double-sided diffusive gradients in thin films (DGT) technique. Different P forms in solid sediment were also measured using the sequential extraction procedure. The diffusion fluxes across the water–sediment interface and dynamic diffusion parameters between solid sediment and solution were calculated using the DGT-induced fluxes in sediments and soils (DIFS) model. There was a clear decrease of the SRPDGT, Fe2+DGT, and S2−DGT fluxes from ~5 cm sediment depth to the water–sediment interface. The significant positive correlation between SRPDGT and Fe2+DGT fluxes in the whole profile demonstrates that Fe-P was a vitally important source of labile P in the solution phase. The significant positive fluxes of SRPDGT and Fe2+DGT indicated upward diffusion from the sediment particle toward the overlying water. This process further indicated the desorption and resupply of SRP and Fe2+ from the solid sediment phase and the synergistic effect between these two parameters. In addition, a gentler decline of R curves fitted with the DIFS model was found as the sediment depths increased, which suggesting the continuous resupply process from solid phase to pore water, especially under anaerobic conditions. The novel DGT technique in combination with DIFS analysis confirmed the considerable remobilization and transport capacity of labile P fractions including loosely adsorbed MgCl2-P and reductive Fe-P. These pools can diffuse from sediment particles to the interstitial and the overlying water, and can be further assimilated by organisms in shallow lacustrine ecosystem.

Reservoir geomechanical studies play a decisive role in identifying wellbore instability and weak zones in offshore petroleum reservoirs. In this study, an integrated workflow developed with 1D Mechanical Earth Models (1D MEM), uniaxial compressive strength and swelling tests using well logs, drilling, and core data of production and exploratory wells from the North-Heera field, Mumbai offshore, India. Lithology-based correlations are utilized for calculating continuous profiles of rock mechanical properties by taking well logs as a primary source of input. Insights of fracture gradients and stresses are generated by interpretation of the pore pressure. UCS created from the well logs shows the low value of 15 MPa and high Poison's ratio of 0.38–0.45. Fracture pressure analysis of the wells specifies the lower fracture initiation pressures at 300 m are 5ppg–15ppg, which are shale and clay formation. Shale swelling tests are performed to know the hydration properties of shales present at shallow depths. The core samples' loading tests' results are very close to the UCS models constructed from the well logs. The combined analysis examines fracture pressures around wellbores, hydration of shales, weak zones identification, and wellbore instability.

The rapid drawdown of reservoir may have a significant impact on the stability of adjacent slopes. In order to avoid potential risks, it is important to calculate the change of slope safety factor prior to the reservoir operation. The finite element method is used to analyze the transient seepage during drawdown, and then the pore water pressures are introduced into the stability computation based on limit equilibrium to obtain the transient safety factor. Computations show that for slopes with a specific geometry, the safety factor ratio depends on the parameters K/(Syv) (where K is the permeability coefficient, v is the drawdown speed, and Sy is the specific yield) and c′/(γHtan ϕ′) (where c′ and ϕ′ are the effective cohesion and friction angle, γ is the soil unit weight, and H is the slope height). By considering a wide range of K/(Syv) and c′/(γHtan ϕ′) values and different slope geometries, the percent reduction in critical safety factor of slope during drawdown relative to that during steady-state seepage is obtained. The drawdown condition that causes a large percent reduction in safety factor is judged as a rapid drawdown, and the opposite is a slow drawdown, which does not affect the slope design. This paper presents a series of charts for engineers and designers to judge rapid and slow drawdown conditions. Before the reservoir operation, the appropriate drawdown speed is selected according to the charts to ensure a slow drawdown for adjacent slope, while in the slope stabilization design, only the rapid drawdown stability analysis needs to be performed.

Generally, the electrical method of geophysics is potentially valuable in typifying the subsurface conductivity and its surrounding medium. Sixteen datasets of 1-D electrical resistivity survey was integrated with 8 core samples, which were taken in the neighbourhood of eight of the sixteen VES datasets. The two sets of data were intertwined with geological and hydrogeological datasets to enhance the realization of unique results used in assessing the aquifer geo-matrix and pore water geo-resistivity in four counties in the coastal province of Akwa Ibom State, southern Nigeria. The current electrode separations of 1-D resistivity data were extended up to 300 m to ensure that the prolifically exploited water-bearing units were assessed. The VES data were manually and electronically modeled and each of them showed characteristic four geo-electric layers with KH, HK, KQ, HA and A group of curves. The core samples, which cut across the local Government Areas under survey, included sandy clay (12.5%), fine-grained sand (50.0%), medium-grained sand (12.5%) and coarse sand (25.0%). Bulk resistivities of water-bearing units and other primary geo-electrical indices were measured in all sixteen locations. However, in the eight aquifer core sample locations, water resistivities were measured in situ. The core samples were taken to the laboratory for measurements of fractional porosity and volumetric water content. The measured fractional porosity ranged from 0.189 to 0.267 with an average of 0.232, whilst volumetric water content varied from 0.23 to 0.31 with an average value of 0.268. The transmission coefficients were computed from volumetric water content and other parameters in the work. The values ranged from 0.4135 to 0.5612 with an average value of 0.4945. Fractional porosity was also modeled from field parameters and the results showed a good match with laboratory measurement as the root—mean square error was just 1.3%. Intrinsic specific resistance and conductivity of soil aquifer matrix were found to be $$3.333 \times 10^{3} \;\Omega {\text{m}}$$ and $$3.000 \times 10^{ - 4} \;{\text{Sm}}^{ - 1}$$ respectively. The study has provided useful information about the geo-electrical and geo-pore properties of the prolifically exploited aquifers in the study area. The aquifer parameter contour maps have been delineated and these, together with other parameter relations generated in this study could help in predicting the volumetric conductivity between pore water and the matrix texture of hydrogeological units in the study area and other areas with similar geology.

SUMMARY We have developed a new method for introducing the effects of pore water distribution into the interpretation of P-wave velocity (VP) dispersion in a partially saturated rock. Pore water in an unsaturated rock is distributed as patches, and mesoscopic-scale wave-induced fluid flow (WIFF) from saturated patches to empty patches is known as a key mechanism for interpreting P-wave dispersion. Mesoscopic WIFF depends on permeability and the scale of the saturated patch, thus evaluating their influences is important for estimating the relationship between water saturation (${S_{\rm{w}}}$) and VP. The simplest and conventional law for simulating the ${S_{\rm{w}}} - {V_{{P}}}$ relation considering the mesoscopic WIFF is White's model, which describes the patch size changes proportional to the saturation. However, White's model assumes homogeneity in the size and distribution of pores, and does not consider the effects of pore water distribution in a partially saturated rock. In the rock, pore water is distributed heterogeneously according to the pore radius, causing non-linear changes in the permeability and size of the saturated patches against the water saturation. In this study, we modified White's model by introducing relative permeability and a new coefficient describing the nonlinear change of the patch size into the conventional version, and applied the modified model to better interpret our experimental ${S_{\rm{w}}} - {V_{{P}}}$ relations, which were measured by an ultrasonic technique at 200 and 500 kHz for two types of Berea sandstone samples with different permeabilities as their water saturation was decreased by evaporative drying. The relative permeabilities were determined by applying the Mualem–van Genuchten model into the capillary pressure curves from mercury intrusion porosimetry. Furthermore, we proposed a calculation method for the new coefficient using tortuosity, which corresponds to the pore water connection. The modified White's model could reproduce the experimental ${S_{\rm{w}}} - {V_{{P}}}$ relations better than other conventional models. Consequently, our modification, considering the effect of pore water distribution, would be useful for more quantitative interpretation of P-wave velocity and attenuation under coexisting multifluid conditions.

We present an aerosol injection technique (AIT) to accelerate the consolidation of soft soils for ground improvement. We employ high-pressure aerosol injections at different depths to enhance the drainage in soft soils for faster consolidation. The technique is briefly described. A well-instrumented field test is carried out to demonstrate its performance. Compared to the traditional methods, our approach gives rise to faster dissipation of excess pore pressure and larger ground settlement. This method is particularly attractive for the improvement in soft ground in medium depths.

Water-bearing porous rocks can be greatly strengthened by freezing; its microscopic mechanisms lie in how subzero temperature modifies pore structure but have not yet been clearly defined. In this study, we link the mechanical properties of frozen sandstone to phase composition of pore water (i.e., relative amount of unfrozen water and ice). Both the strength (uniaxial compressive strength and tensile strength) and the phase composition of pore water (tested through the nuclear magnetic resonance (NMR) method) of frozen sandstone at nine subzero temperatures were measured. The results showed the following: (1) subzero temperature strengthened saturated sandstone significantly, both the strengths increased in a three-stage mode and each stage showed an approximately linear trend as temperature decreased from 0 to – 20 °C; and (2) change of phase composition with freezing displayed two distinct stages: the rapid decreasing stage of unfrozen water content (0 to – 4 °C), when bulk water and capillary water froze almost completely, and the slow decreasing stage (− 4 to – 20 °C), when adsorbed water froze partially. Based on direct observations on microscopic pore structure of sandstone and detailed discussion on the mechanical interactions between water, ice, and pore wall, phase composition may modify the mechanical properties of frozen rocks through the following effects: the supporting effect of ice under compression, the crack-filling effect of ice, the cementing effect of unfrozen water film under tension or under shearing load, and the frost damage effect. The former three are strengthening effects, while the latter one is weakening effect.

Diatomaceous soils are comprised of the silica frustules of diatom microalgae that are present in marine and lacustrine environments throughout the world. Owing to their unique origin, diatomaceous soils are typically characterized by high intraparticle porosity, complex particle shapes, and uniform mineralogy, causing them to exhibit atypical physical and engineering behaviors. A substantial deposit of diatomaceous silt was observed during site exploration for construction of the Buck Creek Bridge on OR140 near Klamath Falls, OR, USA. A comprehensive laboratory and in situ testing program indicated that the diatomaceous soil possessed “non-textbook” engineering properties. Specifically, tested samples had high liquid limits (≈100%-140%) with natural water contents at or near the liquid limit. Geologically, the soil is expected to be normally consolidated, yet high apparent overconsolidation ratios (OCR) (≈15-40) were observed both in oedometric consolidation tests and through cone penetration test (CPT) correlations. Standard penetration test (SPT) results show a corrected standard penetration resistance consistent with a medium-dense sand (i.e. N160≈25). CPT results include corrected tip resistances (qt) of approximately 7-10 MPa and excess pore pressures (u2) of up to 4 MPa. In CPT dissipation tests, pore water pressures (PWPs) returned to hydrostatic pressure in less than one hour. In this work, we synthesize these seemingly disparate material properties in an attempt to infer appropriate engineering properties for the diatomaceous deposit at the Buck Creek Bridge and attempt to provide insight into the underlying reasons for the observed behavior.

Characterizing the permeability variation in fractured rocks is important in various subsurface applications, but how the permeability evolves in the foundation rocks of high dams during operation remains poorly understood. This permeability change is commonly evidenced by a continuous decrease in the amount of discharge (especially for dams on sediment-laden rivers), and can be attributed to fracture clogging and/or hydromechanical coupling. In this study, the permeability evolution of fractured rocks at a high arch dam foundation during operation was evaluated by inverse modeling based on the field time-series data of both pore pressure and discharge. A procedure combining orthogonal design, transient flow modeling, artificial neural network, and genetic algorithm was adopted to efficiently estimate the hydraulic conductivity values in each annual cycle after initial reservoir filling. The inverse results show that the permeability of the dam foundation rocks follows an exponential decay annually during operation (i.e. K/K0 = 0.97e−0.59t + 0.03), with good agreement between field observations and numerical simulations. The significance of the obtained permeability decay function was manifested by an assessment of the long-term seepage control performance and groundwater flow behaviors at the dam site. The proposed formula is also of merit for characterizing the permeability change in riverbed rocks induced by sediment transport and deposition.

Understanding the complex interplay of mass transport, heat transport and deformation in swelling cellulose based materials is a challenging task. To aid in this endeavour a multiphysics model is developed within the mixture theory framework. The model is macroscopic and accounts for swelling, non-equilibrium mass exchange of water, elastic deformation and multiphase transport phenomena, where non-isothermal conditions are considered. The investigated material is viewed as an immiscible mixture of cellulose fibers, pore gas and inter-fiber pore water separated by interfaces. Fiber and gas are considered as miscible mixtures of dry fiber and fiber water, and dry air and water vapor, respectively. The constitutive equations are obtained in a coupled and thermodynamically consistent manner by exploitation of the dissipation inequality. As an application of the model, conditions representative of the retorting process for liquid packaging board are simulated using the proposed constitutive model. The influence of the process control parameters during the heating, cooking and cooling steps of the retorting procedure are analysed. It was found that through-plane temperature gradients and the presence of dry air in the retort had a significant impact on the moisture uptake and the moisture distribution. Spatial distribution of hydrophobicity had a great effect on the distribution of fiber water and inter-fiber water.

The reservoir permeability of tight sandstone gas reservoirs is low, which makes it difficult to carry out displacement flow experiments on real cores underground conditions, so the microscopic flow mechanism can be hardly studied. Based on the lattice Boltzmann method (LBM), this paper simulated the flow process of formation water displaced by tight gas under the simulated reservoir conditions of high temperature and high pressure to clarify the distribution of bound water in the reservoir. Then, reservoir drying was experimentally studied using the laser etching model, and numerical simulation of reservoir drying was simplified by referring to the visualization results of the experiment. Finally, the influence of reservoir drying on the seepage capacity of tight gas was studied by means of numerical simulation. And the following research results were obtained. First, when the lattice Boltzmann model is used for high temperature and high pressure reservoirs, it satisfies the Laplace law and its numerical solution of two-phase Poiseuille flow rate is basically consistent with the analytical solution, which indicates that this model can be used to simulate gas–water immiscible displacement under reservoir conditions. Second, tight gas preferentially breaks through in large porous media connected channels, and after the breakthrough, the displacement rate of formation water decreases significantly. Third, the contact angle between formation water and rock wall has a significant influence on gas–water two-phase flow. The stronger the water wettability of the rock is, the lower the displacement rate is. Fourth, the bound water in tight sandstone gas reservoirs can be classified into four types, including adsorbed water film, blind end pore water, dead pore water and trapped water. In porous media, a large number of connected micro-channels are occupied by trapped water and adsorbed water film and the phenomenon of “water lock” is obvious, which seriously influences the seepage capacity of tight gas in the porous media of reservoir. Fifth, drying agent can react with bound water to produce a large number of bubbles, which will consume adsorbed water film, trapped water and blind end pore water, so as to improve the gas seepage capacity. Sixth, in the “water lock” regions formed by trapped water, the gas seepage capacity can be effectively improved by increasing the drying strength. On the whole, the tight gas permeability increases with the increase of drying strength, but its increase amplitude decreases gradually when the drying strength exceeds a certain degree.

This paper presents the results from a case study highlighting the difficulties of pile driving in diatomaceous soils. In the companion (first) paper to this article, results of an extensive laboratory and in situ testing program were presented while the results from pile driving and further analysis of field observations were presented herein. Unexpected high pile rebound (HPR) was observed during driving of a closed-end pipe pile, with refusal occurring at a depth of less than 5 m. Subsequent open-ended piles were thus driven. Piezometer and case pile wave analysis program (CAPWAP) data were collected during driving of both closed- and open-end piles. Piezometer data indicated that negative pore water pressures (PWPs) were generated while the closed-ended pile exhibited high rebound. Results from in situ tests indicated change in material stiffness and strong dilative tendencies near the depth of refusal. A hypothesis for observed behavior was proposed that considers the soil beneath the pile as a medium with an effectively infinite bulk modulus.

This study investigates the behaviour of bored tunnels in the Port-Said very soft to firm clay deposit in El-Tina Plain, north-eastern Egypt. Recent studies provided full characterization of the physical, mechanical and time-dependent properties of Port-Said Clay. This characterization enabled simulating its constitutive behaviour using the stress-dependent Modified Cam Clay model. The finite difference method is utilized to simulate the interaction between the tunnel and Port-Said Clay. The results are presented in terms of the pore water pressure regime, shear strain level, ground surface settlement and tunnel lining bending moment. The results show significant effect of the face and grouting pressures on the tunnel’s short and long-term behaviours. The term “reference hydrostatic pressure” is introduced to evaluate short-term face stability as a more practical and easy-to-quantify parameter compared to the conventional stability number. New empirical equations are developed to describe the long-term surface settlement trough (maximum settlement and trough width) in terms of the grouting pressure and tunnel diameter for tunnels in similar soft clay deposits.

Pore bulk modulus in continuum apparent permeability models was generally treated as an independent parameter or deduced from the Betti-Maxwell reciprocal theorem neglecting the sorption effect, which is not appropriate for the unconventional reservoirs with strong gas sorption. In this work, pore bulk modulus was firstly derived from the Betti-Maxwell theorem with the consideration of the gas sorption strain and was incorporated into the solid–fluid coupling apparent permeability model. Numerical simulation was then conducted under the uniaxial strain condition and the stress confined condition to investigate the gas transport characteristics. The results showed that when taking into account for the sorption effect in the Betti-Maxwell theorem, the pore bulk modulus dramatically decreased with the falling pore pressure during the gas transport process under two loading conditions. Moreover, gas transport ability under the stress confined condition was greatly degraded while it was hardly changed under the uniaxial strain condition. Both the pore bulk modulus and the stress distribution in the reservoirs were found responsible for the variation of gas flow capacity. Finally, the effects of the parameters associated with the pore bulk modulus were examined to further discuss the impact of involving the sorption effect in the Betti-Maxwell theorem.