A stable implicit nodal integration-based particle finite element method(N-PFEM)for modelling saturated soil dynamics

In this study,we present a novel nodal integration-based particle finite element method(N-PFEM)designed for the dynamic analysis of saturated soils.Our approach incorporates the nodal integration technique into a generalised Hellinger-Reissner(HR)variational principle,creating an implicit PFEM formulation.To mitigate the volumetric locking issue in low-order elements,we employ a node-based strain smoothing technique.By discretising field variables at the centre of smoothing cells,we achieve nodal integration over cells,eliminating the need for sophisticated mapping operations after re-meshing in the PFEM.We express the discretised governing equations as a min-max optimisation problem,which is further reformulated as a standard second-order cone programming(SOCP)problem.Stresses,pore water pressure,and displacements are simultaneously determined using the advanced primal-dual interior point method.Consequently,our numerical model offers improved accuracy for stresses and pore water pressure compared to the displacement-based PFEM formulation.Numerical experiments demonstrate that the N-PFEM efficiently captures both transient and long-term hydro-mechanical behaviour of saturated soils with high accuracy,obviating the need for stabilisation or regularisation techniques commonly employed in other nodal integration-based PFEM approaches.This work holds significant implications for the development of robust and accurate numerical tools for studying saturated soil dynamics.

Author Correction to “Saturated Cavity Ring-Down Spectroscopy of ^(12)C^(16)O_(2) near 1.57 μm”

We regret to announce that there is an error in one of fund numbers in the acknowledgements of the paper titled“Saturated Cavity Ring-Down Spectroscopy of ^(12)C^(16)O_(2) near 1.57μm”due to the author’s typing errors.The acknowledgements were published in Chin.J.Chem.Phys.37,17(2024).

The existence of saturated vapors in the deep source region of 2017Pohang earthquake evidenced from seismic tomography

Geothermal resources are a promising approach to clean renewable energy;90%of them are deep reservoirs of hot dry rock that require hydraulic fracturing to create a network of connections among wells to enable efficient heat exchange,known as an Enhanced Geothermal System(EGS).The Pohang EGS project in south Korea led to a devasting Mw5.5 earthquake,triggered by the reservoir's EGS stimulation,the largest earthquake known to have been induced by EGS development.Detailed investigations have been conducted to understand the cause of the Pohang earthquake;the conclusion has been that overpressurized injected fluids migrated into an unknown fault triggering this large earthquake.Detailed velocity images for the source zone of the 2017 Pohang earthquake,which could be helpful for further understanding its inducing mechanism,are unavailable.However,we have assembled detailed aftershock data recorded by 41 local stations installed within about three months after the Mw5.5 Pohang earthquake,and have then applied the V_(p)/V_(s)model's consistency-constrained double-difference seismic tomography method to determine the high-resolution three-dimensional Vp(compressional wave velocity),Vs(shear wave velocity),and V_(p)/V_(s)models of the source region that we report here,as well as earthquake locations within the source region.The velocity images reveal that the deep source area of the 2017 Pohang earthquake is dominated by low Vp,high Vs,and low V_(p)/V_(s)anomalies,a pattern that can be caused by overpressurized vapors due to high temperatures at these depths.Based on aftershock locations and velocity features,our studies support the conclusion that the 2017Pohang earthquake was triggered by injected EGS fluids that migrated into a blind fault.

Vertical distribution characteristics of soil saturated hydraulic conductivity under different land use patterns in the Mu Us sandy land

Background,aim,and scope Soil saturated hydraulic conductivity(K_(s))is a key parameter in the hydrological cycle of soil;however,we have very limited understanding of K_(s) characteristics and the factors that inf luence this key parameter in the Mu Us sandy land(MUSL).Quantifying the impact of changes in land use in the Mu Us sandy land on K_(s) will provide a key foundation for understanding the regional water cycle,but will also provide a scientific basis for the governance of the MUSL.Materials and methods In this study,we determined K_(s) and the basic physical and chemical properties of soil(i.e.,organic matter,bulk density,and soil particle composition)within the first 100 cm layer of four different land use patterns(farmland,tree,shrub,and grassland)in the MUSL.The vertical variation of K_(s) and the factors that influence this key parameter were analyzed and a transfer function for estimating K_(s) was established based on a multiple stepwise regression model.Results The K_(s) of farmland,tree,and shrub increased gradually with soil depth while that of grassland remained unchanged.The K_(s) of the four patterns of land use were moderately variable;mean K_(s)values were ranked as follows:grassland(1.38 mm·min^(-1))<tree(1.76 mm·min^(-1))<farmland(1.82 mm·min^(-1))<shrub(3.30 mm·min^(-1)).The correlation between K_(s) and organic matter,bulk density,and soil particle composition,varied across different land use patterns.A multiple stepwise regression model showed that silt,coarse sand,bulk density,and organic matter,were key predictive factors for the K_(s) of farmland,tree,shrub,and grassland,in the MUSL.Discussion The vertical distribution trend for K_(s) in farmland is known to be predominantly influenced by cultivation,fertilization,and other factors.The general aim is to improve the water-holding capacity of shallow soil on farmland(0-30 cm in depth)to conserve water and nutrients;research has shown that the K_(s) of farmland increases with soil depth.The root growth of tree and shrub in sandy land exerts mechanical force on the soil due to biophysical processes involving rhizospheres,thus leading to a significant change in K_(s).We found that shallow high-density fine roots increased the volume of soil pores and eliminated large pores,thus resulting in a reduction in shallow K_(s).Therefore,the K_(s) of tree and shrub increased with soil depth.Analysis also showed that the K_(s) of grassland did not change significantly and exhibited the lowest mean value when compared to other land use patterns.This finding was predominantly due to the shallow root system of grasslands and because this land use pattern is not subject to human activities such as cultivation and fertilization;consequently,there was no significant change in K_(s) with depth;grassland also had the lowest mean K_(s).We also established a transfer function for K_(s) for different land use patterns in the MUSL.However,the predictive factors for K_(s) in different land use patterns are known to be affected by soil cultivation methods,vegetation restoration modes,the distribution of soil moisture,and other factors,thus resulting in key differences.Therefore,when using the transfer function to predict K_(s) in other areas,it will be necessary to perform parameter calibration and further verification.Conclusions In the MUSL,the K_(s) of farmland,tree,and shrub gradually increased with soil depth;however,the K_(s) of grassland showed no significant variation in terms of vertical distribution.The mean K_(s) values of different land use patterns were ranked as follows:shrub>farmland>tree>grassland;all land use patterns showed moderate levels of variability.The K_(s) for different land use patterns exhibited differing degrees of correlation with soil physical and chemical properties;of these,clay,silt,sand,bulk density,and organic matter,were identified as important variables for predicting K_(s) in farmland,tree,shrub,and grassland,respectively.Recommendations and perspectives In this study,we used a stepwise multiple regression model to establish a transfer function prediction model for K_(s) for different land use patterns;this model possessed high estimation accuracy.The ability to predict K_(s) in the MUSL is very important in terms of the conservation of water and nutrients.

Assessing the impact of concurrent high-fructose and highsaturated fat diets on pediatric metabolic syndrome:A review

High-saturated fat(HF)or high-fructose(HFr)consumption in children predispose them to metabolic syndrome(MetS).In rodent models of MetS,diets containing individually HF or HFr lead to a variable degree of MetS.Nevertheless,simultaneous intake of HF plus HFr have synergistic effects,worsening MetS outcomes.In children,the effects of HF or HFr intake usually have been addressed individually.Therefore,we have reviewed the outcomes of HF or HFr diets in children,and we compare them with the effects reported in rodents.In humans,HFr intake causes increased lipogenesis,hypertriglyceridemia,obesity and insulin resistance.On the other hand,HF diets promote low grade-inflammation,obesity,insulin resistance.Despite the deleterious effects of simultaneous HF plus HFr intake on MetS development in rodents,there is little information about the combined effects of HF plus HFr intake in children.The aim of this review is to warn about this issue,as individually addressing the effects produced by HF or HFr may underestimate the severity of the outcomes of Western diet intake in the pediatric population.We consider that this is an alarming issue that needs to be assessed,as the simultaneous intake of HF plus HFr is common on fast food menus.

Nested Saturated Control of Uncertain Complex Cascade Systems Using Mixed Saturation Levels

This study addresses the problem of global asymptotic stability for uncertain complex cascade systems composed of multiple integrator systems and non-strict feedforward nonlinear systems. To tackle the complexity inherent in such structures, a novel nested saturated control design is proposed that incorporates both constant saturation levels and state-dependent saturation levels. Specifically, a modified differentiable saturation function is proposed to facilitate the saturation reduction analysis of the uncertain complex cascade systems under the presence of mixed saturation levels. In addition, the design of modified differentiable saturation function will help to construct a hierarchical global convergence strategy to improve the robustness of control design scheme. Through calculation of relevant inequalities, time derivative of boundary surface and simple Lyapunov function,saturation reduction analysis and convergence analysis are carried out, and then a set of explicit parameter conditions are provided to ensure global asymptotic stability in the closed-loop systems. Finally, a simplified system of the mechanical model is presented to validate the effectiveness of the proposed method.

A high-temperature resistant and high-density polymeric saturated brine-based drilling fluid

Three high-temperature resistant polymeric additives for water-based drilling fluids are designed and developed:weakly cross-linked zwitterionic polymer fluid loss reducer(WCZ),flexible polymer microsphere nano-plugging agent(FPM)and comb-structure polymeric lubricant(CSP).A high-temperature resistant and high-density polymeric saturated brine-based drilling fluid was developed for deep drilling.The WCZ has a good anti-polyelectrolyte effect and exhibits the API fluid loss less than 8 mL after aging in saturated salt environment at 200°C.The FPM can reduce the fluid loss by improving the quality of the mud cake and has a good plugging effect on nano-scale pores/fractures.The CSP,with a weight average molecular weight of 4804,has multiple polar adsorption sites and exhibits excellent lubricating performance under high temperature and high salt conditions.The developed drilling fluid system with a density of 2.0 g/cm^(3)has good rheological properties.It shows a fluid loss less than 15 mL at 200°C and high pressure,a sedimentation factor(SF)smaller than 0.52 after standing at high temperature for 5 d,and a rolling recovery of hydratable drill cuttings similar to oil-based drilling fluid.Besides,it has good plugging and lubricating performance.

Saturated absorption spectrum of cesium micrometric-thin cell with suppressed crossover spectral lines

Micrometric-thin cells(MCs)with alkali vapor atoms have been valuable for research and applications of hyperfine Zeeman splitting and atomic magnetometers under strong magnetic fields.We theoretically and experimentally study the saturated absorption spectra using a 100-μm cesium MC,where the pump and probe beams are linearly polarized with mutually perpendicular polarizations,and the magnetic field is along the pump beam.Because of the distinctive thin chamber of the MC,crossover spectral lines in saturated absorption spectra are largely suppressed leading to clear splittings of hyperfine Zeeman transitions in experiments,and the effect of spatial magnetic field gradient is expected to be reduced.A calculation method is proposed to achieve good agreements between theoretical calculations and experimental results.This method successfully explains the suppression of crossover lines in MCs,as well as the effects of magnetic field direction,propagation and polarization directions of the pump/probe beam on saturated absorption spectrum.The saturated absorption spectrum with suppressed crossover lines is used for laser frequency stabilization,which may provide the potential value of MCs for high spatial resolution strong-field magnetometry with high sensitivity.

Effects of transient temperature gradient on frost heave of saturated silty clay in an open system

Frost heave in seasonally frozen regions is a one-dimensional process that could severely damage infrastructure subgrades.Stress state,temperature and water migration are important factors for frost heave.This work investigated the effects of soil temperature and volumetric water content on the transient frost heave ratio during the freezing of saturated silty clay in an open system and analyzed the relationships between the transient frost heave ratio and freezing rate and between temperature gradient and frost heave rate.The results show that the frost heave ratio,frost heave rate,and freezing rate are positively correlated with the temperature gradient since the temperature gradient drives the water migration during freezing,indicating the transient temperature gradient could be used to evaluate the frost heave of saturated silty clay.The transient freezing rate and transient frost heave ratio are logarithmically related to the transient frost heave ratio and transient temperature gradient,respectively.The effects of transient temperature gradient on frost heave are the principal mechanism responsible for different frost heave characteristics and uneven frost heave along a subgrade of the same soil type.

The Influence of Saturated and Bilinear Incidence Functions on the Dynamical Behavior of HIV Model Using Galerkin Scheme Having a Polynomial of Order Two

Mathematical modelling has been extensively used to measure intervention strategies for the control of contagious conditions.Alignment between different models is pivotal for furnishing strong substantiation for policymakers because the differences in model features can impact their prognostications.Mathematical modelling has been widely used in order to better understand the transmission,treatment,and prevention of infectious diseases.Herein,we study the dynamics of a human immunodeficiency virus(HIV)infection model with four variables:S(t),I(t),C(t),and A(t)the susceptible individuals;HIV infected individuals(with no clinical symptoms of AIDS);HIV infected individuals(under ART with a viral load remaining low),and HIV infected individuals with two different incidence functions(bilinear and saturated incidence functions).A novel numerical scheme called the continuous Galerkin-Petrov method is implemented for the solution of themodel.The influence of different clinical parameters on the dynamical behavior of S(t),I(t),C(t)and A(t)is described and analyzed.All the results are depicted graphically.On the other hand,we explore the time-dependent movement of nanofluid in porous media on an extending sheet under the influence of thermal radiation,heat flux,hall impact,variable heat source,and nanomaterial.The flow is considered to be 2D,boundary layer,viscous,incompressible,laminar,and unsteady.Sufficient transformations turn governing connected PDEs intoODEs,which are solved using the proposed scheme.To justify the envisaged problem,a comparison of the current work with previous literature is presented.

Experimental Analysis of Hydraulic Conductivity for Saturated Granular Soils

Hydraulic conductivity is the ability of a porous media to transfer water through its pore matrix. That is a key parameter for the design and analysis of soil fluid associated structures and issues. This paper presents the test results of the vertical hydraulic conductivity kv carried out on one poorly graded sand and three gap graded gravely sand. It was found that the vertical hydraulic conductivity of saturated soil depends on the grain size distribution curve, on the initial relative density of the soil. Compilation of these current test results and other test results published, shows that the common approaches predict well to some extent the vertical hydraulic conductivity kv for the poorly graded sand materials and underestimate the kv values for gap graded gravely sand materials. Therefore, new approaches are developed for the prediction of the vertical hydraulic conductivity in saturated poorly graded sand and gap graded gravely sand. The derived results from the new approaches lie in the range of the recommended values by (EAU 2012) and (NAVFAC DM 7 1974).

Shale porosity measurement by the saturated oil method: Removing the contribution from oils dissolved in kerogen

Shale porosity measurements have crucial scientific and economical applications in unconventionalpetroleum systems. As a standard technique, liquid saturation methods, including water saturation (WS)and oil saturation (OS), have been widely used to measure the porosity of many rock types. For clay-richshale reservoirs with high organic matter content, it is well known that the WS method may cause clayswelling and induce structural changes in the pore system. The OS method affects the accuracy ofporosity measurements because of some of the oil being dissolved by kerogen within the shale;however,this has not received sufficient research attention. In this study, we compare the previously reported andnewly tested OS porosities with helium (He) expansion porosity. Results show that OS porosity generallyexceeds the He porosity. Furthermore, the higher the total organic carbon (TOC) content and lower thematurity of shale, the greater the difference between the OS and helium porosities. When using the OSmethod, the effect of kerogen-dissolved oil causes an overestimation of the shale porosity by ~30%. To thebest of our knowledge, this is the first time to note the kerogen-dissolve oil effects on OS porosity. Herein,we propose a new, simple, and effective correction method for estimating OS porosity that involvessubtracting the kerogen-dissolved oil content from raw OS porosity. In addition, the quantification modelof kerogen-dissolved oil capacity is established, taking into account the abundance and maturity oforganic matter. Taking the He porosity as the benchmark, the absolute error of the corrected OS porositydoes not exceed 1% and the average relative error is only ~10%. The obtained results can help improve theaccuracy of shale porosity evaluation methods.

Strength characteristics of dry and saturated rock at different strain rates

The strength of rock materials is largely affected by water and loading conditions, but there are few studies on mechanical properties of saturated rocks at high strain rates. Through compressive tests on dry and saturated sandstone specimens, it was found that the dynamic compressive strength of both dry and saturated sandstone specimens increased with the increase of strain rates. The saturated rock specimens showed stronger rate dependence than the dry ones. The water affecting factor （WAF）, as the ratio of the strength under dry state to that under saturated state, was introduced to describe the influence of water on the compressive strength at different strain rates. The WAF under static load was close to 1.38, and decreased with the increase of strain rate. When the strain rate reached 190 s^-1, the WAF reduced to 0.98. It indicates that the compressive strength of saturated specimens can be higher than that of dry ones when the strain rate is high enough. Furthermore, the dual effects of water and strain rate on the strength of rock were discussed based on sliding crack model, which provided a good explanation for the experimental results.

Creep experiment and rheological model of deep saturated rock

By the methods of uniaxial single-stage loading and graded incremental cyclic loading, the creep experiments were performed on the deep saturated rock from Dongguashan Mine, and the creep curves of saturated rock under different loading stresses were obtained. By comparing with the creep rule of dry rock in the same location, the creep rule of deep saturated rock was analyzed. Based on the united rheological mechanical model, the rheological model of deep saturated rock was recognized, and the parameters of the model were determined. The results show that the creep curves are very smooth under low stress, but the phenomena of wave and catastrophe turn up under high stress, and the bearing capacity of rock is weakening over time. The rheological properties of saturated and dry rocks are very different under tlie condition of deep high stress, especially when unloading, degradation and damage of rock quality is more serious, and the effect of water cannot be neglected. The H--HIN--NJS model （Schofield-Scott-Blair model） was selected to represent the rheology rule of deep saturated rock, and the fitting curves of model agree well with the experiment data, so the selected model is reasonable.

Distinctive roles of unsaturated and saturated fatty acids in hyperlipidemic pancreatitis

AIM: To investigate how the saturated and unsaturated fatty acid composition influences the susceptibility of developing acute pancreatitis. METHODS: Primary pancreatic acinar cells were treated with low and high concentrations of different saturated and unsaturated fatty acids, and changes in the cytosolic Ca2+ signal and the expression of protein kinase C(PKC) were measured after treatment. RESULTS: Unsaturated fatty acids at high concentrations, including oleic acid, linoleic acid, palmitoleic acid, docosahexaenoic acid, and arachidonic acid, induced a persistent rise in cytosolic Ca2+ concentrations in acinar cells. Unsaturated fatty acids at low concentrations and saturated fatty acids, including palmitic acid, stearic acid, and triglycerides, at low and high concentrations were unable to induce a rise in Ca2+ concentrations in acinar cells. Unsaturated fatty acids at high concentrations but not saturated fatty acids induced intra-acinar cell trypsin activation and cell damage and increased PKC expression.CONCLUSION: At sufficiently high concentrations, unsaturated fatty acids were able to induce acinar cells injury and promote the development of pancreatitis. Unsaturated fatty acids may play a distinctive role in the pathogenesis of pancreatitis through the activation of PKC family members.

Dietary saturated fatty acid and polyunsaturated fatty acid oppositely affect hepatic NOD-like receptor protein 3 inflammasome through regulating nuclear factor-kappa B activation

AIM: To investigate the effect of different dietary fatty acids on hepatic inflammasome activation.METHODS: Wild-type C57BL/6 mice were fed either a high-fat diet or polyunsaturated fatty acid (PUFA)-enriched diet. Primary hepatocytes were treated with either saturated fatty acids (SFAs) or PUFAs as well as combined with lipopolysaccharide (LPS). The expression of NOD-like receptor protein 3 (NLRP3) inflammasome, peroxisome proliferator-activated receptor-&#x003b3; and nuclear factor-kappa B (NF-&#x003ba;B) was determined by real-time PCR and Western blot. The activity of Caspase-1 and interleukine-1&#x003b2; production were measured.RESULTS: High-fat diet-induced hepatic steatosis was sufficient to induce and activate hepatic NLRP3 inflammasome. SFA palmitic acid (PA) directly activated NLRP3 inflammasome and increased sensitization to LPS-induced inflammasome activation in hepatocytes. In contrast, PUFA docosahexaenoic acid (DHA) had the potential to inhibit NLRP3 inflammasome expression in hepatocytes and partly abolished LPS-induced NLRP3 inflammasome activation. Furthermore, a high-fat diet increased but PUFA-enriched diet decreased sensitization to LPS-induced hepatic NLRP3 inflammasome activation in vivo. Moreover, PA increased but DHA decreased phosphorylated NF-&#x003ba;B p65 protein expression in hepatocytes.CONCLUSION: Hepatic NLRP3 inflammasome activation played an important role in the development of non-alcoholic fatty liver disease. Dietary SFAs and PUFAs oppositely regulated the activity of NLRP3 inflammasome through direct activation or inhibition of NF-&#x003ba;B.

Effects of microalgal polyunsaturated fatty acid oil on body weight and lipid accumulation in the liver of C57BL/6 mice fed a high fat diet

Dietary polyunsaturated fatty acids （PUFAs）, which are abundant in marine fish oils, have recently received global attention for their prominent anti-obesogenic effects. Among PUFAs, eicosapentaenoic acid （EPA; 20：5n-3） and docosahexaenoic acid （DHA; 22：6n-3）, which are n-3 long-chain PUFAs widely referred to as omega-3 oils, were reported to prevent the development of obesity in rodents and humans. In the present study, we evaluated the anti-obesity effects of microalgal oil on high-fat induced obese C57BL/6 mice, compared with commercial omega-3 fish oil and vegetable corn oil. Microalgal oil is an inherent mixture of several PUFAs, including EPA, DHA and other fatty acids produced from a marine microalgal strain of Thraustochytriidae sp. derived mutant. It was found to contain more PUFAs （〉80%） and more omega-3 oils than commercial omega-3 fish oil （PUFAs 〉31%） and corn oil （PUFAs 59%）. All three types of oils induced weight loss in high-fat-induced obese mice, with the loss induced by microalgal oil being most significant at 9 weeks （10% reduction）. However, the oils tested did not improve blood lipid levels, although microalgal oil showed an apparent inhibitory effect on lipid accumulation in the liver. These findings may be attributed to the higher PUFA content, including omega-3 oils of microalgal oil than other oils. Collectively, these findings suggest that microalgal oil, derived from Thraustochytriidae sp. derived mutant, is a prominent candidate for replacement of omega-3 fish oils based on its apparent anti-obesity effect in vivo.

Dynamic and quasi-static bending of saturated poroelastic Timoshenko cantilever beam

Based on the three-dimensional Gurtin-type variational principle of the incompressible saturated porous media, a one-dimensional mathematical model for dynamics of the saturated poroelastic Timoshenko cantilever beam is established with two assumptions, i.e., the deformation satisfies the classical single phase Timoshenko beam and the movement of the pore fluid is only in the axial direction of the saturated poroelastic beam. Under some special cases, this mathematical model can be degenerated into the Euler-Bernoulli model, the Rayleigh model, and the shear model of the saturated poroelastic beam, respectively. The dynamic and quasi-static behaviors of a saturated poroelastic Timoshenko cantilever beam with an impermeable fixed end and a permeable free end subjected to a step load at its free end are analyzed by the Laplace transform. The variations of the deflections at the beam free end against time are shown in figures. The influences of the interaction coefficient between the pore fluid and the solid skeleton as well as the slenderness ratio of the beam on the dynamic/quasi-static performances of the beam are examined. It is shown that the quasi-static deflections of the saturated poroelastic beam possess a creep behavior similar to that of viscoelastic beams. In dynamic responses, with the increase of the slenderness ratio, the vibration periods and amplitudes of the deflections at the free end increase, and the time needed for deflections approaching to their stationary values also increases. Moreover, with the increase of the interaction coefficient, the vibrations of the beam deflections decay more strongly, and, eventually, the deflections of the saturated poroelastic beam converge to the static deflections of the classic single phase Timoshenko beam.

BISQ model based on a Kelvin-Voigt viscoelastic frame in a partially saturated porous medium

Taking into account three important porous media mechanisms during wave propagation （the Biot-flow, squirt-flow, and solid-skeleton viscoelastic mechanisms）, we introduce water saturation into the dynamic governing equations of wave propagation by analyzing the effective medium theory and then providing a viscoelastic Biot/squirt （BISQ） model which can analyze the wave propagation problems in a partially viscous pore fluid saturated porous media. In this model, the effects of pore fluid distribution patterns on the effective bulk modulus at different frequencies are considered. Then we derive the wave dynamic equations in the time-space domain. The phase velocity and the attenuation coefficient equations of the viscoelatic BISQ model in the frequency-wavenumber domain are deduced through a set of plane harmonic solution assumptions. Finally, by means of numerical simulations, we investigate the effects of water saturation, permeability, and frequency on compressional wave velocity and attenuation. Based on tight sandstone and carbonate experimental observed data, the compressional wave velocities of partially saturated reservoir rocks are calculated. The compressional wave velocity in carbonate reservoirs is more sensitive to gas saturation than in sandstone reservoirs.

Test Investigation on Liquefied Deformation Structure in Saturated Lime-Mud Composites Triggered by Strong Earthquakes

Three identical model boxes were made from transparent plexiglass and angle iron. Using the method of sinking water and according to the sedimentary rhythm of saturated calcium carbonate （lime-mud） intercalated with cohesive soil, calcites with particle sizes diameters of ≤ 5 μm, 10–15 μm and 23–30 μm as well as cohesive soil were sunk alternatively in water of three boxes to build three test models, each of which has a specific size of calcite. Pore water pressure gauges were buried in lime-mud layers at different depths in each model, and connected with a computer system to collect pore water pressures. By means of soil tests, physical property parameters and plasticity indices （Ip） were obtained for various grain-sized saturated lime-muds. The lime-muds with Ip ranging from 6.3 to 8.5 （lower than 10） are similar to liquid saturated silt in the physical nature, indicating that saturated silt can be liquefied once induced by a strong earthquake. One model cart was pushed quickly along the length direction of the model so that its rigid wheels collided violently with the stone stair, thus generating an artificial earthquake with seismic wave magnitude greater than VI degree. When unidirectional cyclic seismic load of horizontal compression-tension-shear was imposed on the soil layers in the model, enough great pore water pressure has been accumulated within pores of lime-mud, resulting in liquefaction of lime-mud layers. Meanwhile, micro-fractures formed in each soil layer provided channels for liquefaction dewatering, resulting in formation of macroscopic liquefaction deformation, such as liquefied lime-mud volcanoes, liquefied diapir structures, vein-like liquefied structures and liquefied curls, etc. Splendid liquefied lime-mud eruption lasted for two to three hours, which is similar to the sand volcano eruption induced by strong earthquake. However, under the same artificial seismic conditions, development of macroscopic liquefied structures in three experimental models varied in shape, depth and quantity, indicating that excess pore water pressure ratios at initial liquefaction stage and complete liquefaction varied with depth. With size increasing of calcite particle in lime-mud, liquefied depth and deformation extent increase accordingly. The simulation test verifies for the first time that strong earthquakes may cause violent liquefaction of saturated lime-mud composed of micron-size calcite particles, uncovering the puzzled issue whether seafloor lime-mud can be liquefied under strong earthquake. This study not only provides the latest simulation data for explaining the earthquake-induced liquefied deformations of saturated lime-mud and seismic sedimentary events, but also is of great significance for analysis of foundation stability in marine engineering built on the soft calcium carbonate layers in neritic environment.