Saturated Limestone Research Articles

Experimental study on the competing effects of strain rate and water weakening on compressive strength of saturated rocks

Measuring the rock compressive strength under combined effects of strain rate and water weakening is of great importance and at the same time a major issue for engineers. In this study, we explore the ability to detangle the contributions of strain rate and water-weakening effects on rock compressive strength within a wide static and dynamic strain rate range. To this end, we conduct a series of compression tests and acoustic emission (AE) tests on two types of rock with specific mineral compositions (i.e., limestone and granite). The correlations between rock compressive strength, including static compressive strength σcs and dynamic compressive strength σcd, and water-weakening factors fw with strain rate are derived. The experimental AE waveform data is analyzed using a new methodology named statistical analysis of dominant frequency, from which we infer the intrinsic rock progressive failure and evaluate the competing effects of water weakening and strain rate. Our results show that water saturation causes a drastic loss in the compressive strength of limestone and a small reduction in the compressive strength of granite. The strain rate effect governs the changes in the compressive strength of dry rocks, characterizing a reduction in low dominant frequencies of AE waveforms with increasing strain rates. Whether the strain rate effect or water-weakening effect plays a dominant role depends largely on the rock types and loading regimes. We proposed that the primary effects on σcs of saturated limestone are strain rate under relatively low static strain rate (lower than 8.33 × 10−5 s−1) and pore water pressure under relatively high static strain rate (beyond 8.33 × 10−5 s−1), respectively, and that on σcd of saturated limestone is strain rate. The variations of σcs and σcd of saturated granite are both determined by the strain rate effect within the strain rate range investigated. Additionally, the exertions of various water-weakening effects of limestone and granite at different strain rates, which are responsible for their fw variations, are evaluated in detail.

Fluid distribution effect on seismic dispersion and attenuation in biphasic saturated limestone- Direct measurement

Fluid distribution effect on seismic dispersion and attenuation in biphasic saturated limestone- Direct measurement

Surface water–groundwater interactions of Xiluodu Reservoir based on the dynamic evolution of seepage, temperature, and hydrochemistry due to impoundment

AbstractReservoir construction greatly affects the regional ecological environment, particularly surface water–groundwater interactions around the reservoir. Xiluodu Reservoir, a representative large‐scale reservoir in China, has had substantial impacts on surface water–groundwater interactions at the dam site since impoundment. This study analysed the dynamic characteristics of surface water–groundwater level, temperature, and hydrochemistry to determine the evolution of surface water–groundwater interaction before and after the impoundment. The levels of groundwater and some surface water rose by more than 100 m after impoundment and the water level of saturated limestone gradually stabilized, whereas basalt saturation in the affected area continued to expand. The groundwater temperature did not decrease significantly, whereas the hydrochemical types and ion contents of both surface water and groundwater experienced significant changes. Calculation of the saturation index indicated spatiotemporal changes in the saturation state of minerals. The replenishment source of each type of water and their mutual relationships were determined using cluster analysis and isotope characteristics. The results confirmed continuous, significant, and variable surface water–groundwater interactions at the dam site, which were partially reversed after impoundment. Changes in surface water–groundwater interactions were due to impoundment, the impact of which decreases with distance from the dam, as well as the unique geological conditions and artificial construction.

Applicability Analysis of Microseismic Technology in Tunnel Water Inrush Monitoring

Water inrush disaster is one of the most serious geological disasters in tunnel construction. There are still some problems in the existing researches, such as the activity information of surrounding rock is difficult to obtain, the mechanism of water inrush disaster is unclear, the correlation between water inrush disaster and microseismic (MS) information is missing, which have caused the water inrush disaster to be passively controlled. Combining with the practical experience of tunnel engineering, the application problems of MS technology in tunnel engineering is summarized, which provides ideas for monitoring of surrounding rock activity. The formation mechanism of water inrush disaster caused by rock mass fracturing and filling medium instability has been revealed. The MS characteristics of the water inrush channel in different water inrush disasters have also been revealed. The MS response characteristics of water inrush and rockburst disasters are compared, which provides guidance for the improvement of MS monitoring technology and the analysis of effective MS information. The compression failure test of limestone under saturated and natural conditions is carried out. The results show that the presence of water weakens the ability of rock to store energy. The acoustic emission (AE) phenomenon is weaker in the process of saturated limestone failure, which increases the difficulty of AE monitoring. The number of AE events of natural limestone and saturated limestone shows a slow increase to a sudden increase in the process stress loading, which can be regarded as an important precursor of rock failure.

Mechanical Characteristics and Mesostructural Damage of Saturated Limestone under Different Load and Unload Paths

To study the evolutionary characteristics of mesostructural damage to saturated limestone under different loading and unloading paths, three types of loading and unloading tests involving three different loading rates and initial peak stresses were performed. Nuclear magnetic resonance technology and scanning electron microscopy were used to investigate the evolutionary characteristics of pore water during the loading and unloading of the limestone. The results indicated that, with an increase in the initial peak stress, the rock viscoplasticity gradually decreased, and the variation of pore radius and the reduction of bound water decreased. With an increasing loading rate, the mesostructure evolution law under disturbance‐increasing amplitude (DIA) cycling was opposite to those under increasing amplitude (IA) and repeated‐increasing amplitude (RIA) cycling. With the increasing loading stress level, the porosity decreased and then increased. Under increasing amplitude cycling, a larger initial porosity resulted in higher pore compaction and expansion limits. Reducing the initial peak stress inhibited the pore expansion, whereas it had the opposite effect under RIA and DIA cycling. During loading and unloading, bound water exists in pores of organic matter and mesopores, and free water exists in macropores of intergranular and transgranular fractures. These changes indicate certain laws under different loading and unloading paths. The results of this study indicate that the mesostructure characteristics of rock depend on the loading and unloading paths.

Limestone Acoustic Emission Evolution Characteristics Under Different Experimental Loading and Unloading Conditions

To study the acoustic emission evolution characteristics of saturated limestone under different loading and unloading paths, three cyclic loading and unloading tests were conducted with different loading rates and initial cyclic peak stresses, and acoustic emission monitoring was performed simultaneously. The results indicate that, during loading and unloading, the intermediate-frequency signals of saturated rock exhibit a variation trend of sparse–dense–sparse signals, whereas the low-frequency signals are continuously and massively produced. With the increase in the loading rate, the development trends of cumulative hits and energy become closer, and the development form of ringing count changes from N-type to U-type and then to N-type. The slight increase period and attenuation period are extended, whereas the intense growth period and postpeak calm period are shortened. With an increase in the initial cyclic peak stress, the change in cumulative energy is more obvious than that in cumulative hits near the rock failure. The development form of the ringing count changes from U-type to W-type and then to N-type, and each period is first shortened and then extended. With the increase in loading rate, the increase in the slow-change period tends to change from gradually increasing to increasing and then decreasing. By contrast, the increase in the step tends to change to a gradual increase. With the increase in the initial cyclic peak stress, the duration of and increase in the energy in the step and the slow-change period tend to decrease and then increase.

Influence of Loading Rate on the Energy Evolution Characteristics of Rocks under Cyclic Loading and Unloading

To analyse the effect of loading rate on the energy evolution of rocks under cyclic loading and unloading, tests on saturated limestone were conducted at loading rates of 0.15, 0.2, and 0.3 mm/min, and the evolution characteristics of plastic, elastic, dissipation, and input energies were examined under different loading rates. The results indicated that the plastic strain in the entire test was directly proportional to the loading rate. In addition, strength, residual stress, plastic energy, and dissipation energy under residual resistance were inversely proportional to the loading rate. The plastic strain exhibited a decreasing–stabilising–increasing trend, and the smaller loading rate delayed the “increasing” trend. The increasing extent of each energy exhibited the following trend: input > elastic > plastic > dissipation energy. Furthermore, the first three types of energy exhibited a slow–fast–slow–fast increase trend. The dissipation energy exhibited a fast–steady–fast–slow–fast increase trend. Additionally, the elastic energy index exhibited a large increase–steady increase–decrease trend, which was proportional to the loading rate. The damping ratio exhibited a decrease–increase–decrease–increase–decrease trend which was proportional to the loading rate in the compaction stage and inversely proportional to the plastic stage.

Effect of curing regime on long-term mechanical strength and transport properties of steam-cured concrete

Steam curing is a common method of producing prefabricated elements, achieving high early strength to meet economic benefits. However, this rapid curing method is extremely detrimental to the microstructure and long-term performance of concrete. Therefore, choosing an appropriate measure to remission this adverse effect is critical to the development of long-term performances of steam-cured concrete. In this study, two steam-curing regime and four subsequent curing conditions were employed on the curing of concrete. The long-term compressive strength, surface permeability and microstructure were measured to analyze the effects of curing condition on performance of steam-cured concrete. The results indicate that step-curing is beneficial to the formation of pre-structures, thereby improving the long-term mechanical properties and impermeability of steam-cured concrete. Among the four subsequent curing conditions, saturated limestone immersion is most beneficial to the long-term performance of steam-cured concrete, while water immersion is the most unfavorable.

ЕЛЕКТРИЧНІ Й АКУСТИЧНІ ПАРАМЕТРИ НИЖНЬОПЕРМСЬКИХ КАРБОНАТНИХ ПОРІД ЗАХІДНОЇ ЧАСТИНИ ГЛИНСЬКО-СОЛОХІВСЬКОГО ГАЗОНАФТОНОСНОГО РАЙОНУ ДДЗ

The main objective of this article is to study electrical parameters of Lower Permian carbonate rocks of Western part of the Hlynsko-Solokhivskyi gas-oil-bearing district of the Dnieper-Donets Basin (DDB) in normal (atmospheric) and modeling (reservoir) conditions. In atmospheric conditions it has been revealed that the resistivity of dry extracted limestones (the specific electrical resistivity of framework of grains was measured) varies from 12.147 kΩ⋅m to 111.953 MΩ⋅m (mean 1.542 MΩ⋅m). The resistivity of saturated limestone samples with kerosene varies from 44.478 kΩ⋅m to 14.449 MΩ⋅m (mean 1.435 MΩ⋅m). The resistivity of dry and saturated with kerosene samples is almost the same. The resistivity of limestones saturated with model of reservoir water (salinity M = 190 g/l) is lower and varies from 1.11 Ω⋅m to 23.16 Ω⋅m (mean 3.12 Ω⋅m). It has been determined that formation resistivity factor of limestones in atmospheric conditions varies from 13.5 to 230 Ω⋅m (mean 32.5 Ω⋅m). In addition to resistivity, the parameter of relative permittivity of investigated limestones was studied. It was determined that relative permittivity of dry limestones varies from 3.0 to 7.5 (mean 4.2). Relative permittivity saturated samples of limestones with kerosene varies from 2.8 to 8.8 (mean 4.5) and practically does not differ from dry ones but significantly lower than values of samples saturated with model of reservoir water (from 655 to 9565, mean 4280). That means when pores of limestones are saturated with NaCl solution their relative permittivity increases rapidly – from hundreds to thousands times (on average 944 times). It can be explained by the high conductivity of model of reservoir water. Limestones saturated with NaCl solution have velocities of P-waves in the range from 3346 m/s to 4388 m/s (mean 4030 m/s), and velocities of Swaves – from 1753 m/s to 2121 m/s (average 1942 m/s). If rocks are saturated with kerosene then velocities have strictly higher values – P-waves from 3433 m/s to 4514 m/s (mean 4011 m/s) and S-waves – from 2137 m/s to 2464 m/s (average 2344 m/s). Physical modelling of reservoir conditions (temperature 50 °С, pressure 30 MPa) showed that the specific electrical resistivity varies from 0.81 Ω⋅m to 13.19 Ω⋅m (mean 2.67 Ω⋅m), and limestones – from 0.49 Ω⋅m to 7.81 Ω⋅m (mean 1.95 Ω⋅m). Also, "specific electrical resistivity – pressure" connection was investigated. Due to the closure of microcracks and the deformation of the pore space, the electrical resistance of rocks increases with increase of pressure. The regression dependence of the formation resistivity enlargement factor with pressure for the studied rocks has a linear character. It was determined that in reservoir conditions the range of the formation resistivity factor for limestones varied from 17.3 to 271.9 Ω⋅m (mean 50.7 Ω⋅m), and range of variation of porosity coefficient was from 0.040 to 0.169 Ω⋅m (mean 0.118 Ω⋅m). The comprehensive analysis of petrophysical data has been resulted in a set of correlation ratios between reservoir, electric and elastic parameters of studied limestones in normal and modeling conditions.

Analytical Model for Predicting the UCS from P-Wave Velocity, Density, and Porosity on Saturated Limestone

Rock mechanics and rock engineering projects require determining, among other parameters, the uniaxial compressive strength (UCS) of rock. For such a purpose, it is not uncommon to perform ultrasonic pulse laboratory tests. Many researchers have found experimental relationships between strength and P-wave velocity, but these relationships are based mainly on dry conditions and without considering any other physical or chemical characteristics of the studied rock. Specifically, for limestone, there are 11 correlations reported in the literature, eight of which are simple and the remaining three are multiple, and, among the latter, only two of them consider the saturation. In order to evaluate the combined effect of P-wave velocity, density, and porosity on the UCS of saturated limestone, simple and multiple regression analyses were carried out on the test results of 13 saturated limestone specimens to determine the parameters of both previously mentioned predictive models. The results showed that density is not correlated with strength.

Transport of a PAH-degrading bacterium in saturated limestone media under various physicochemical conditions: Common and unexpected retention and remobilization behaviors.

Laboratory saturated columns packed with granular limestone grains were used to explore the retention and remobilization of functional bacteria FA1 under various physicochemical conditions. The unique surface properties of limestone and FA1 caused some unexpected phenomena. Solution IS, cation type, temperature and surface biological property all affected FA1 retention in the columns. The IS effect was temperature dependent and initial solution pH showed little influence due to the strong buffering ability of limestone. Perturbations of solution IS caused slight release of previously retained bacteria in some columns with NaCl as the background electrolyte, while increase in flow rate caused no release at all. When CaCl2 was the background, bacterial remobilization only occurred following both cation exchange and IS reduction. DLVO forces incorporating with surface roughness calculation were determined to assist with interpretation of interaction mechanisms. All the experimental evidences suggest the importance of cation bridging, cation exchange, surface roughness, and hydrophobic interaction in controlling bacterium transport in saturated limestone porous media.

Effect of cation type in mixed Ca-Na systems on transport of sulfonamide antibiotics in saturated limestone porous media.

Retention and transport of sulfonamides (SAs) in subsurface can strongly affect groundwater quality. In this work, a range of laboratory batch sorption and column transport experiments were conducted to determine the effect of cation type in mixed Ca-Na systems on the retention and transport of two typical SAs, sulfadimethoxine (SDM) and sulfacetamide (SCA), in saturated limestone porous media. Column experimental data showed divalent cation Ca2+ played a more important role than monovalent cation Na+ in decreasing the transport of only SDM in co-cation systems in the saturated limestone media. Further, in the single-cation (i.e., including either Ca2+ or Na+) system, increasing ionic strength (IS) of either NaCl or CaCl2 had little effect on SCA transport; however, increasing of IS of CaCl2 promoted the retention of SDM in the saturated limestone porous media. This is mainly due to the cation bridging effect of Ca2+ on SDM and limestone. Overall, SDM showed much higher retention in the limestone columns than SCA, which can be attributed to the two SAs' different physicochemical properties. Moreover, limestone showed stronger ability to retain the two SAs than quartz sand. Findings in this study suggest that cation type and the concentration of certain electrolyte (e.g., CaCl2) as well as medium type play an important role in controlling the environmental fate and transport of antibiotics.

The strength of ice-saturated extraterrestrial rock analogs

In situ resource utilization (ISRU) activities have been identified by the National Research Council as one of the most important scientific endeavors of the coming decade. The failure of the MUPUS-PEN experiment on Rosetta's Philae lander to penetrate the surface of comet 67P demands knowledge of the mechanical properties of extraterrestrial materials in such environments. To such an end we conducted laboratory strength measurements at cryogenic conditions of two terrestrial rocks, Bishop tuff and Indiana limestone as potential cometary and asteroid analogs, respectively. We measured failure strength of dried and fully saturated samples under constant displacement rate compressional loading at temperatures of 77 K–295 K and (for most) confining pressure of 5 MPa. The strength of saturated samples increased dramatically with decreasing temperature below the ice point: saturated limestone from 30 MPa at 295 K to >200 MPa at 150 K and below, and saturated tuff from 26 MPa at 240 K to 160 MPa at 150 K. Some ductility or distributed fracturing was evident in both saturated rock types above 150 K. The saturated tuff was stronger than pure ice at all conditions but its transition from brittle to ductile deformation with temperature closely paralleled that of ice. The results of this study will be useful to future sample retrieval missions or ISRU maneuvers. The fully saturated state of our samples and use of Bishop tuff as an unconsolidated cometary analog likely means our results are upper estimates for substrates we may encounter in our solar system. Pending corroboration and refinement of these preliminary measurements, the large increase in compressive strength we observed in the saturated materials at cryogenic temperatures suggests that future missions must prepare technology with the energetic and mechanical capability to penetrate very hard substrates.

Large-Scale Triaxial Experiments on the Creep Behavior of a Saturated Rockfill Material

AbstractLarge-scale triaxial compression and creep experiments were conducted with a saturated limestone rockfill material. The relationships between dilatancy ratio and stress ratio during loading...

Dynamic failure of dry and fully saturated limestone samples based on incubation time concept

This paper outlines the results of experimental study of the dynamic rock failure based on the comparison of dry and saturated limestone samples obtained during the dynamic compression and split tests. The tests were performed using the Kolsky method and its modifications for dynamic splitting. The mechanical data (e.g. strength, time and energy characteristics) of this material at high strain rates are obtained. It is shown that these characteristics are sensitive to the strain rate. A unified interpretation of these rate effects, based on the structural–temporal approach, is hereby presented. It is demonstrated that the temporal dependence of the dynamic compressive and split tensile strengths of dry and saturated limestone samples can be predicted by the incubation time criterion. Previously discovered possibilities to optimize (minimize) the energy input for the failure process is discussed in connection with industrial rock failure processes. It is shown that the optimal energy input value associated with critical load, which is required to initialize failure in the rock media, strongly depends on the incubation time and the impact duration. The optimal load shapes, which minimize the momentum for a single failure impact, are demonstrated. Through this investigation, a possible approach to reduce the specific energy required for rock cutting by means of high-frequency vibrations is also discussed.

Application of S-Transform and Simultaneous Seismic Inversion to Interpret Bright Spots

Bright spots are usually seen in seismic sections that can be interpreted as gas reservoirs. These local anomalies are identified as an increase in amplitudes on a seismic section. However, bright spots are not always gas indicators. They are also produced because of lithology changes. In this case, to prevent great costs of drilling, we need to understand the cause of bright spots. In this paper we use two methods which are mainly based on frequency and velocity analysis of seismic waves. Therefore, we apply simultaneous seismic inversion and S-transform on a 2D pre-stack seismic data which in its CDP gathers, several bright spots are seen. We just choose two of these bright spots arbitrarily. If they are due to hydrocarbon, P-wave velocity decreases sharply while S-wave velocity increases slightly, therefore decreases. Similarly, high frequencies being eliminated in the hydrocarbon areas. In contrast, if the bright spot is produced due to lithology change (gas saturated limestone/ limestone interface) then frequency and P-wave velocity will increase while S-velocity decreases.

Influence of clay particles on Al2O3 and TiO2 nanoparticles transport and retention through limestone porous media: measurements and mechanisms

Utilization of nanoparticles (NPs) for a broad range of applications has caused considerable quantities of these materials to be released into the environment. Issues of how and where the NPs are distributed into the subsurface aquatic environments are questions for those in environmental engineering. This study investigated the influence of three abundant clay minerals namely kaolinite, montmorillonite, and illite in the subsurface natural aquatic systems on the transport and retention of aluminum oxide (Al2O3, 40 nm) and titanium dioxide (TiO2, 10–30 nm) NPs through saturated limestone porous media. The clay concentrations in porous media were set at 2 and 4 vol% of the holder capacity. Breakthrough curves in the columns outlets were measured using a UV–Vis spectrophotometer. It was found that the maximum NPs recoveries were obtained when there was no clay particle in the porous medium. On the other hand, increase in concentration of clay particles has resulted in the NPs recoveries being significantly declined. Due to fibrous structure of illite, it was found to be more effective for NPs retention in comparison to montmorillonite and kaolinite. Overall, the position of clay particles in the porous media pores and their morphologies were found to be two main reasons for increase of NPs retention in porous media.

TiO2 nanoparticle transport and retention through saturated limestone porous media under various ionic strength conditions

The impact of ionic strength (from 0.003 to 500mM) and salt type (NaCl vs MgCl2) on transport and retention of titanium dioxide (TiO2) nanoparticles (NPs) in saturated limestone porous media was systematically studied. Vertical columns were packed with limestone grains. The NPs were introduced as a pulse suspended in aqueous solutions and breakthrough curves in the column outlet were generated using an ultraviolent–visible spectrometry. Presence of NaCl and MgCl2 in the suspensions were found to have a significant influence on the electrokinetic properties of the NP aggregates and limestone grains. In NaCl and MgCl2 solutions, the deposition rates of the TiO2-NP aggregates were enhanced with the increase in ionic strength, a trend consistent with traditional Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Furthermore, the NP aggregates retention increased in the porous media with ionic strength. The presence of salts also caused a considerable delay in the NPs breakthrough time. MgCl2 as compared to NaCl was found to be more effective agent for the deposition and retention of TiO2-NPs. The experimental results followed closely the general trends predicted by the filtration and DLVO calculations. Overall, it was found that TiO2-NP mobility in the limestone porous media depends on ionic strength and salt type.

Transport and aggregation of Al2O3 nanoparticles through saturated limestone under high ionic strength conditions: measurements and mechanisms

Aluminum oxide (Al2O3) nanoparticles (NPs) are being utilized in a broad range of applications; thus, noticeable quantities of these particles are being released into the environment. Issues of how and where these particles distribute into the subsurface remain major challenges. In this study, mechanisms governing the transport and aggregation of Al2O3-NPs (Alpha-40 nm) through saturated limestone porous media under different ionic strength conditions were evaluated. For this aim, 50 mg of Al2O3-NPs was dispersed in 1 L of different electrolyte solutions including NaCl and CaCl2. Ionic strength range was selected from deionized water up to 500 mM. Breakthrough curves in the column effluent were measured by UV–VIS spectrometry. It was found that the presence of NaCl and CaCl2 in the suspensions led to formation of ion bridges among NPs. Thus, the stability of Al2O3-NPs significantly declined and NPs started to flocculate and form bigger clusters. Furthermore, ionic strength caused considerable delay in NPs breakthrough in the effluents and reduction of NPs recovery. CaCl2 compared to NaCl was found more effective in instability and deposition of Al2O3-NPs. In addition, the obtained results from transport experiments were checked against classical filtration and Derjaguin–Landau–Verwey–Overbeek (DLVO) theories. The results were found to be in agreement with named theories.

Multi-channel Analysis of Surface Waves (MASW) in Karst Terrain, Southwest Georgia: Implications for Detecting Anomalous Features and Fracture Zones

Multi-channel analysis of surface waves (MASW) was used to map bedrock topography, image anomalies in the soil overburden, and detect variations in the degree of limestone weathering in covered, karst terrain near Albany, Georgia. Surface-wave data were acquired along seven parallel lines and two perpendicular cross-lines. Two surveys using a hammer and moving van-source were conducted to address the trade-off between lateral resolution and depth penetration. Resolution matrices show that the depth ranges most effectively imaged are 0.5–4 m for half-spread hammer data, 3–12 m for full-spread hammer data, and 8–20 m for van-source data. A steep S-velocity gradient marked by the 350 m/s contour at depths of 9–12 m is interpreted as the bedrock surface, in agreement with coincident borehole data. The models indicate variations within limestone bedrock (S-velocity: 350–700 m/s) and anomalous zones within the sandy-clay overburden. Standard penetration tests at two locations 45-m apart confirm variations in limestone rigidity suggested by the velocity models. At one location, a dissolution feature (N-value: 0) within highly weathered, saturated limestone (N-values: 12 and 19) correlates with low S-velocities (<350 m/s). Borehole data from the second location shows more rigid limestone (N-values: 25 and 34) that correlates with S-velocities between 350–400 m/s. A zone of weathered rock at depths of 12–20 m imaged along a suspected fracture zone is consistent with borehole data and sinkhole formation at the ground surface. An anomaly associated with a burn pit at the intersection of two perpendicular profiles was imaged at two different scales. S-velocity models and distinct changes in apparent velocity of direct P-waves and surface waves across shot gathers constrain the lateral and vertical extent of the anomaly, and borehole data verify changes in soil composition and depth (5 m) to the base of the anomaly.