Influence Of Pore Water Research Articles

Mechanical and fracture characteristics of weak microwave-absorbing sandstone under microwave irradiation: influence of pore water

Microwave radiation is an effective method to weaken the strength of hard rock, but this weakening effect is not obvious enough for weak microwave-absorbing rocks. This work focuses on the role of water in amplifying the effect of microwaves on weak microwave-absorbing rocks, by examining the bursting characteristics of the rocks as well as their physical and mechanical properties before blasting. The experimental results show that when subjected to microwave irradiation, and the time taken for this bursting decreases with higher microwave power. In addition, the surface temperature of saturated sandstone gradually rises with increased irradiation power and duration. Under high microwave power, the uniaxial compressive strength (UCS) of heated saturated sandstone notably decreases within the same irradiation duration. When the microwave power is low, the UCS of saturated sandstone remains relatively unchanged over time. The UCS of dry sandstone exhibits no significant alteration under identical irradiation power and duration. In conclusion, sandstone shows no significant change in its physical and mechanical properties during brief exposure to low-power microwave irradiation in its dry state. As water within the sandstone undergoes a phase transition from liquid to gas due to microwave irradiation, the resulting steam pressure causes the sandstone to rupture.

Numerical study of borehole instability of large diameter monopile during the window period between drilling and pile driving

Large-diameter monopiles are among the most widely used offshore wind turbine foundations. Implementing drive-drill-drive construction techniques in a decomposed granite seabed may lead to borehole instability during the window period between drilling and pile driving. In this study, the borehole stability of a large-diameter monopile in a weathered granite seabed was investigated using the discrete element method. A linear parallel bond model was employed to simulate the bonding effect among weathered granite particles, and the influence of pore water was considered. The results indicated that soil shear failure caused by excavation unloading was the primary cause of borehole instability. The exposed height of the unsupported borehole significantly influenced the occurrence of borehole instability. The greater the exposed height of the unsupported borehole, the larger the soil arch required to maintain the stability of the borehole, and the less stable the soil arch becomes. Moreover, the susceptibility to borehole instability and collapse also increased.

Overview of the Influence of Static Water Saturation on The Mechanical Properties of Concrete

This paper reviews a series of experimental and theoretical research results on the influence of existing pore water on the static and dynamic properties of concrete. This paper summarizes the current experimental research methods and conclusions, analyzes the influence mechanism of moisture content and loading speed on the elastic modulus and strength of concrete, and points out that the influence of pore water on concrete properties should be the result of the joint action of multiple factors.

Thermo-poroelastodynamic response of a borehole in a saturated porous medium subjected to a non-hydrostatic stress field

A thermo-poroelastodynamic (TPED) model incorporating the thermo-osmosis and thermal-filtration phenomena is used to analyze the transient response of a borehole subject to a non-hydrostatic stress field. The coupled TPED model is developed on the basis of equations of motion, fluid flow, heat transfer and constitutive equations so as to couple the stress wave, pressure wave and thermal wave in early times. Poroelastodynamics (PED) and thermo-elastodynamics (TED) models correspond two particular cases of the current model. The borehole problem is decomposed into the superposition of an axisymmetric mode and an asymmetric mode, corresponding to axisymmetric and deviatoric loadings, respectively. The semi-analytical solutions in the Laplace transform space are inverted numerically to obtain time-dependent displacement, pore pressure, temperature and stresses. Comparisons are performed among different sub-models to examine the influence of thermal effect on the response of pore pressure and stresses as well as the influence of pore water on the response of stress components. A direct comparison among the dynamic, quasi-static and static models shows that inertial effect is very important in the early times and it contributes to the early-time wave behavior.

Effects of aggregate types and softening effect on multiaxial mechanical properties of lightweight aggregate concrete

Softening effect refers to the inherent property of porous media materials of having their strength decrease over time under water saturation compared with that under dry condition. Typical porous media materials, such as ceramsite and ceramsite-based concrete, exhibit a softening effect. This study investigated the softening effect of shale ceramsite (SC) and different types of lightweight aggregate concrete (LWACs). Mix ratios of LC30 all-lightweight shale ceramsite concrete (also known as all-lightweight concrete, ALWC) whose SC and shale pottery (SP) were selectively or simultaneously replaced with limestone gravel (LSG) and river sand (RS) with the same volume fraction, respectively, were prepared for comparison with gravel lightweight concrete (GLWC), sand lightweight concrete (SLWC) and hybrid aggregate lightweight concrete (HALWC) were formed. The four kinds of LWACs (ALWC, GLWC, SLWC and HALWC) were cast into their corresponding specification and size specimens and demoulded after indoor curing for 24 h, with their target ages (7–180 d) maintained under standard and hydrostatic curing. Then, the strength and initial elastic modulus under uniaxial stress, ultimate compressive strength and stress–strain curves under triaxial stress of the specimens were tested to analyse the influence of aggregate types and curing methods on the mechanical properties and softening effect of LWACs. According to the test results, the cube compression, prism compression, splitting tensile, conventional triaxial compression and elastic modulus decreased after 180 d of hydrostatic curing; the experimental age of the conventional triaxial compression test was after 90 d. ALWC demonstrated the most evident decrease, followed by SLWC, HALWC and GLWC. The trend indicates that normal aggregates can significantly improve the softening effect of LWACs. The failure modes of the triaxial compression specimens changed from splitting failure to shear failure, and a plastic platform phenomenon was apparent on the stress–strain curves, with their descending section appearing gentler than those in the uniaxial compression test with the increase in confining pressure. The relationship between ultimate compressive strength and confining pressure of the LWACs can be accurately described by the Mohr–Coulomb single-parameter failure criterion, Hsieh–Ting–Chen four-parameter failure criterion and Willam–Warnke five-parameter failure criterion. However, the three failure criteria demonstrated application limitations based on meridian equation and deviatoric plane analysis. The extension trend of the compression meridian of the LWACs after 90 d of hydrostatic curing was generally the same, and the types of aggregates exerted a minimal effect on the meridian and deviatoric plane limit trace. The softening effect of LWACs was mainly caused by the softening effect of the SC itself and the influence of pore water on the matrix concrete.

Neodymium Isotope Records From the Northwestern Pacific: Implication for Deepwater Ventilation at Heinrich Stadial 1

AbstractDuring Heinrich Stadial 1 (HS1, 18.0–14.7 kyr ago), the Bering and Okhotsk Seas in the western Subarctic Pacific (SAP) exhibited boundary conditions that enhanced intermediate water convection. However, little is known about the quantitative contribution of the intermediate waters from the Bering and Okhotsk Sea (BSIW and OSIW) to ventilation in the open SAP intermediate–deep layers. In this study, we analyzed the neodymium (Nd) isotopes of fish debris (εNd‐FD) from sediment cores in the Northwestern Pacific, and observed a reduction in εNd (up to −2.6) from the Last Glacial Maximum to HS1 at Sites MD01‐2420 (2,101 m) and KH99‐3 ES (2,388 m). The relevance of reduced HS1 εNd‐FD shifts across the cores cannot be explained by the porewater influence, which generally changes authigenic εNd in opposite ways. Instead, as the εNd‐FD shifts concurred with a reduction in the 14C ventilation age, HS1 εNd‐FD shifts suggest the entrainment of younger and distinct εNd water mass sinking in the Okhotsk and/or Bering Seas. A mixing model applying Nd isotopes, their concentrations, and 14C ventilation ages of BSIW, OSIW, and the Lower Circumpolar Deep Water showed that during HS1, BSIW (36%–41%) was more conducive to the water mass at Site MD01‐2420, compared to OSIW (4%–8%). We argue that the Bering Sea has wider and deeper connections (Kamchatka and Near Straits, ∼4,400–2,200 m) with the western SAP, and the deep conduit would enable BSIW to more effectively flow out into the open Northwestern Pacific deep layer.

Influence of Pore Water on the Gas Storage of Organic-Rich Shale

Previous studies that utilize dry samples have been conducted on the nanoporosity of organic matter in shale. However, underground shales contain pore water that may greatly influence their pore structures and adsorbed gas content. To address this, a typical organic-rich, marine, gas-bearing shale in China was analyzed in this study. Water content and isothermal adsorption under different saturation conditions were determined, and the adsorbed and free gas contents were quantified. Across scales, water occurs within clays, between grains, and in fissures. In micropores and mesopores, gas is mainly adsorbed onto the surface of kerogen, as clay surfaces are water-saturated. In macropores and fractures, gas mainly exists in a free state. Adsorbed and free gas contents decrease with increasing water saturation in shale reservoirs. In high-production reservoirs, a limited amount of adsorbed gas is stored within micropores, while a relatively large amount of free gas is stored in larger pores and natural fractu...

Influence of Pore Water (Ice) Content on the Strength and Deformability of Frozen Argillaceous Siltstone

Influence of Pore Water (Ice) Content on the Strength and Deformability of Frozen Argillaceous Siltstone

Influence of Pore Water on the Mechanical Properties of Water-Saturated Rock under Very Low Temperatures

Influence of Pore Water on the Mechanical Properties of Water-Saturated Rock under Very Low Temperatures

Influence of pore water in the seabed on dynamic response of offshore wind turbines on monopiles

The well-known p-y curve method provides soil-structure interaction that does not account for the pore pressure effect for dynamic analysis of offshore wind turbines (OWTs). In order to avoid overly conservative designs, reliable estimates of the dynamic response should be taken into account. The turbine is introduced using a simplified model to assess the eigenfrequencies and modal damping, accounting for pore water flow and excess pore pressure around the monopile. Thus the effect of pore pressure and load frequency are illustrated by implementing a poroelastic model to present more realistic dynamic properties and compare them with results obtained by the p-y curve method. A cyclic loading is considered and the soil stiffness based on the Winkler and Kelvin models is calculated and compared while the soil damping for the Kelvin model is computed. Developed finite element programs are employed to present the results for a two-phase system consisting of a solid skeleton and pore fluid, based on the u-P formulation. Here, u is grain displacement and P is pore water pressure. The developed codes have been validated with commercial software and are implemented to perform free vibration tests to evaluate the eigenfrequencies. A linear poroelastic material model is utilized. An equivalent masses-dashpots-springs system at the pile-cap level is calculated and compared by using Winkler and Kelvin models to highlight the effect of pore pressure and load seepage damping.

Sorption of uranium(VI) onto Opalinus Clay in the absence and presence of humic acid in Opalinus Clay pore water

The U(VI) sorption onto Opalinus Clay (OPA), a natural clay rock from Mont Terri, Switzerland, was investigated in the absence and presence of humic acid under aerobic conditions using synthetic OPA pore water ( I = 0.34 M, pH 7.6) as background electrolyte. The results show that the U(VI) sorption onto OPA is low and not influenced by humic acid. This can be attributed to the dissolution of calcite, a mineral constituent of the clay. The resulting calcium ions (up to 25 mM) in the pore water influence both the U(VI) speciation and the speciation of humic acid. In OPA pore water the U(VI) speciation is dominated by the neutral complex Ca 2UO 2(CO 3) 3(aq) both in the absence and presence of humic acid. Its predominance was verified by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Speciation estimations for humic acid show that calcium ions saturate the humic acid binding sites almost completely. Thus, only few humic acid binding sites are available for U(VI) complexation at pH 7.6. For the sorption of U(VI) and humic acid onto OPA distribution coefficients, K d, were determined and amount to 0.0222 ± 0.0004 m 3/kg and 0.129 ± 0.006 m 3/kg, respectively. In conclusion, calcium ions determine the interaction processes of U(VI) and humic acid in the OPA system.

Fundamental Study on Large Deformation Analysis of Composite Breakwater by Improved Elastoplastic MPS Method

Deformation analyses of rubble mound as an elastoplastic body have been already carried out, however, in these conventional analyses, large deformation to tilt a caisson on a mound cannot be reproduced. On the other hand, the MPS method used in this study can be applied for such a large deformation, however, in a conventional elastoplastic MPS method, an influence of pore water in a mound cannot be taken into account. Therefore, in this study, an improved elastoplastic MPS method based on effective stress model is developed, and a few fundamental examination of its validity are executed.

Microhabitat effects on Cd/Ca and δ13C of benthic foraminifera

Cd/Ca and δ13C were measured on bottom and pore water samples, and samples comprising dead individuals of six species of benthic foraminifera, including Cibicidoides wuellerstorfi, Uvigerina peregrina and Melonis barleeanum, from throughout the sediment mixed layer at three well-characterised sites in the Northeastern Atlantic. ‘Living’ (i.e., Rose Bengal stained) U. peregrina and M. barleeanum from one of the three sites were also analysed. Co-existing living and dead foraminifera of the same species from the same site have similar Cd/Ca and δ13C, and show no significant down core variability. Therefore, comparison of δ13C in foraminifera with bottom water and pore waters was used to estimate average calcification depths within the sediment for each species and thereby determine DCd based on the Cd concentrations at these depths. Pore waters are 2–4 times more enriched in Cd than bottom waters; consequently, DCd values are different from estimates based on bottom water Cd. Results give DCd of ∼1 for all the infaunal species, with no significant water depth dependence. DCd for C. wuellerstorfi based on bottom water Cd are 3.2±1.1 at 3600 m water depth and 3.9±1.3 at 1900 m water depth, being consistent with DCd estimated from culture experiments. The results suggest that the depth dependence of DCd based on bottom water Cd may be partly explained by a pore water influence on the test chemistry for infaunal species.

Vertical distributions and stable isotopic compositions of live (stained) benthic foraminifera from the North Carolina and California continental margins

The vertical distributions of live (Rose Bengal stained) benthic foraminifera were determined in Soutar box cores from six sites on the North Carolina continental margin (337–1477 m) and three sites on the California continental margin (786–3705 m). Stained specimens of the most abundant taxa were analyzed for their carbon and oxygen isotopic compositions. Bottom water δ 13C values and pore water δ 13C profiles were determined at seven of the sites to aid in interpretation of the live benthic foraminiferal δ 13C data. The abundance profiles of most benthic foraminiferal species show consistent patterns within the sediments at each site. These patterns enable us to characterize taxa as epifaunal and shallow, intermediate, and deep infaunal. The vertical range of the living assemblage is small (2–4 cm) in several of the cores, presumably as a consequence of the relatively high organic carbon fluxes and correspondingly small oxygen penetration depths in these continental margin environments. At each site, species with deeper within-sediment microhabitats have lower average δ 13C values than do shallow-dwelling species. The δ 13C offset from bottom water for each species is larger at high bottom water oxygen sites (North Carolina) than at low bottom water oxygen sites (California). Both of these observations are consistent with a pore water influence on benthic foraminiferal δ 13C. The Atlantic-Pacific differences rule out a constant species-specific fractionation as the explanation for the δ 13C values of these foraminifera. Despite substantial downcore changes in pore water δ 13C, foraminiferal δ 13C values for most species change very little over the entire depth range of stained individuals within each core. This lack of vertical δ 13C variation may imply that calcification takes place in a relatively small sub-zone of the microhabitat range suggested by the distribution data.

Late Triassic transition from biogenic to arc sedimentation on the Peninsular terrane: Puale Bay, Alaska Peninsula

The thick (∼700 m) section of Upper Triassic (upper Norian) carbonates, cherts, and volcaniclastics exposed at Puale Bay, Alaska Peninsula, preserves an excellent record of early Mesozoic arc-related sedimentation on the Peninsular Terrane. The Puale Bay sedimentary basin was probably part of a back-arc basin with two stages of evolution: (1) an initial upward-deepening sequence, as reflected in shallow-water carbonates succeeded by spicular chert deposits; and (2) increased magmatic-arc activity and an upward-shallowing sequence near the Triassic-Jurassic boundary, as shown by increased influx of volcaniclastics and deposition of thick, coarse-grained turbidites. This deepening-shallowing cycle of the basin is recorded in kerogen types and in authigenic carbonates that precipitated under marine pore-water influence during the deepening phase, and under meteoric or hydrothermal pore-fluid influence during the upward-shallowing phase. The marine-dominant phase is characterized by types I and II kerogen, δ 13 C (calcite) ratios near 0.0‰ PDB, and Sr values near 700 ppm. The upward-shallowing phase is characterized by type III kerogen, δ 13 C (calcite) ratios with large negative excursions (up to -7.2‰ PDB), and low Sr values down to 33 ppm. The increased volcanic activity, the transition to a terrestrial kerogen source, and the dominance of nonmarine pore fluids near the Triassic-Jurassic boundary are all suggestive of the development of a nearby volcanic arc. This early Mesozoic arc volcanism may reflect closure of ocean basins, between the Peninsular, Wrangellia, and Alexander terranes. Hence, this initiation of arc volcanism may represent an early phase of tectonic amalgamation in southern Alaska.