Estimation of unfrozen water content of saturated sandstones using nuclear magnetic resonance, mercury intrusion porosimetry, and ultrasonic tests

The unfrozenwater content(UWC)is a crucial parameter that affects the strength and thermal properties of rocks in relation to engineering construction and geological disasters in cold regions.In this study,three different methods were employed to test and estimate the UWC of saturated sandstones,including nuclear magnetic resonance(NMR),mercury intrusion porosimetry(MIP),and ultrasonic methods.The NMR method enabled the direct measurement of the UWC of sandstones using the free induction decay(FID).The MIP method was used to analyze the pore structures of sandstones,with the UWC subsequently calculated based on pore ice crystallization.Therefore,the MIP test constituted an indirect measurement method.Furthermore,a correlation was established between the P-wave velocity and the UWC of these sandstones based on the mixture theory,which could be employed to estimate the UWC as an empirical method.All methods demonstrated that the UWC initially exhibited a rapid decrease from 0C to5C and then generally became constant beyond20C.However,these test methods had different characteristics.The NMR method was used to directly and accurately calculate the UWC in the laboratory.However,the cost and complexity of NMR equipment have precluded its use in the field.The UWC can be effectively estimated by the MIP test,but the estimation accuracy is influenced by the ice crystallization process and the pore size distribution.The P-wave velocity has been demonstrated to be a straightforward and practical empirical parameter and was utilized to estimate the UWC based on the mixture theory.This method may be more suitable in the field.All methods confirmed the existence of a hysteresis phenomenon in the freezing-thawing process.The average hysteresis coefficient was approximately 0.538,thus validating the GibbseThomson equation.This study not only presents alternative methodologies for estimating the UWC of saturated sandstones but also contribute to our understanding of the freezing-thawing process of pore water.

Determining the soil-water retention curve using mercury intrusion porosimetry test in consideration of soil volume change

It is well-known that a close link exists between soil-water retention curve(SWRC)and pore size distribution(PSD).Theoretically,mercury intrusion porosimetry(MIP)test simulates a soil drying path and the test results can be used to deduce the SWRC(termed SWRCMIP).However,SWRCMIP does not include the effect of volume change,compared with the conventional SWRC that is directly determined by suction measurement or suction control techniques.For deformable soils,there is a significant difference between conventional SWRC and SWRCMIP.In this study,drying test was carried out on a reconstituted silty soil,and the volume change,suction,and PSD were measured on samples with different water contents.The change in the deduced SWRCMIP and its relationship with the conventional SWRC were analyzed.The results showed that the volume change of soil is the main reason accounting for the difference between conventional SWRC and SWRCMIP.Based on the test results,a transformation model was then proposed for conventional SWRC and SWRCMIP,for which the soil state with no volume change is taken as a reference.Comparison between the experimental and predicted SWRCs showed that the proposed model can well consider the influence of soil volume change on its water retention property.

Prediction of loess soil-water characteristic curve by mercury intrusion porosimetry

Mercury intrusion porosimetry(MIP)is a simple and fast way to obtain the pore distribution of soil and can be used to estimate the soil-water characteristic curve(SWCC).In previous studies,soil was assumed to be a perfect wettability material,and the contact angle(CA)of the soil-water interface was taken as zero in the SWCC prediction method.However,the CA has proved to be much greater than zero even for hydrophilic soils according to some soil wettability experiments,and it has a significant effect on predicting the SWCC.In this research,a method for predicting the SWCC by MIP,which takes the CA as a fitting coefficient,is proposed.The pore size distribution curves are measured by MIP,and the SWCCs of two loess soils are measured by pressure plate and filter paper tests.When the CA is taken as70°and 50°for the wetting and drying process,respectively,the SWCCs predicted by the pore size distribution curves agree well with the measured SWCCs.The predicted suction range of the proposed method is 0-105 k Pa.The consistency of the results suggests that utilizing the MIP test to predict the SWCC with a proper CA is effective for loess.

Influence of Dry Density on Soil-Water Retention Curve of Unsaturated Soils and Its Mechanism Based on Mercury Intrusion Porosimetry

The soil-water retention curve(SWRC)can be used to evaluate the ability of unsaturated soils to attract water at various water contents and suctions. In this study, drying SWRCs for a kind of sandy soil were obtained in the laboratory by using self-modified SWRC apparatus. In addition, the porosity and the pore size distribution of the samples were investigated by a mercury porosimetry test in order to analyze the effect of dry density. Results showed that the soil-water retention of the soil specimens was strongly dependent on the dry density. Under zero suction, soil specimens with a higher dry density exhibited lower initial volumetric water content. The higher the dry density of soil, the more slowly the volumetric water content decreased with the increase of suction. There was a general and consistent trend for a soil specimen to possess a larger air-entry value and residual suction, while smaller slope of SWRC when it had a higher density. This was probably attributed to the presence of smaller interconnected pores in the soil specimen with a higher dry density. The proportion of large diameter pores decreased in comparison to pores with small diameters in the soil tested. The measured total pore volume of the soil specimen, which had a larger dry density, was lower than that of the relatively loose specimens.

Research on pore microstructure features for dredger fill based on mercury intrusion method

The material composition and microstructure have a comprehensive influence on geological engineering properties of dredger fill.The porosity of the dredger fill is an important characteristic of microscopic structure.Taken dredger fill from Binhai New Area in Tianjin as research object,the distribution trend of pore is obtained by granularmetric analysis,mineral composition analysis and mercury intrusion method.By discussing the variation regulation of dredger fill in two different kinds of processing methods,certain theoretical basis is provided for evaluating the engineering geological properties of dredger fill.It can be concluded from the test results that after drainage treatment,the porosity decreased and the structure unit changed from the relatively loose state to aggregate state.In certain depth range,the consolidation effect of dredger fill with drainage treatment is better than that without drainage treatment.

Pore Structure Characteristics and Permeability of Deep Sedimentary Rocks Determined by Mercury Intrusion Porosimetry

Pore structure characteristics of rock are a great concern for researchers and practitioners in rock mechanics and rock engineering fields. In this study, mercury intrusion porosimetry（MIP） was used to measure pore size distribution, as well as several important index parameters of pore structure, for seven common types of deep sedimentary rocks with a total of fifty rock samples. Results show a similar pore size distribution pattern of the rock samples in the same lithological group, but remarkable differences among different lithological groups. Among seven investigated rock types, mudstone has the smallest porosity of 3.37%, while conglomerate has the largest value of 18.8%. It is also found that the porosity of rock types with finer grain size is lower than those with coarser grain size. Meanwhile, a comparison of frequency distribution at ten intervals of pore-throat diameter among seven types of sedimentary rocks reveals that different rock types have different dominant pore-size ranges. Furthermore, permeability of the investigated sedimentary rock samples was derived based on MIP data using reported theoretical equations. Among seven rock types, mudstone has the lowest averaged permeability（3.64×10^（-6） mD） while conglomerate has the highest one（8.59×10^（-4） mD）. From mudstone to conglomerate, rock permeability increases with an increase of grain size, with only an exception of siltstone which has a relatively larger porosity value. Finally, regression analysis show that there is a good fitting（R^2=0.95） between permeability and porosity which could be easily used to derive reliable permeability values of similar kinds of engineering rocks.

Fractal analysis of small-micro pores and estimation of permeability of loess using mercury intrusion porosimetry

Many popular models have been proposed to study the fractal properties of the pores of porous materials based on mercury intrusion porosimetry(MIP).However,most of these models do not directly apply to the small-micro pores of loess,which have a significant impact on the throat pores and tunnels for fluid flow.Therefore,in this study we used a combination of techniques,including routine physical examination,MIP analysis,and scanning electron microscope(SEM)image analysis,to study these small-micro pores and their saturated water permeability properties.The techniques were used to determine whether the fractal dimensions of six MIP fractal models could be used to evaluate the microstructure types and permeability properties of loess.The results showed that the Neimark model is suitable for analysis of small-micro pores.When applied to saturated water permeability,the results from this model satisfied the correlation significance test and were consistent with those from SEM analysis.A high clay content and density cause an increase in the number of small-micro pores,leading to more roughness and heterogeneity of the pore structure,and an increase in the fractal dimensions.This process further leads to a decrease in the content of macro-meso pores and saturated water permeability.Furthermore,we propose new parameters:the*Ellipse and its area ratios(*EAR).These parameters,coupled with 2D-SEM and 3D-MIP fractal dimensions,can effectively and quantitatively be used to evaluate the types of loess microstructures(from typeⅠto typeⅢ)and the saturated water permeability(magnitude from 1×10^(-4)cm/s to 1×10^(-5)cm/s).

Evaluation of the effect of sodium silicate addition to mine backfill,Gelfill-Part 2:Effects of mixing time and curing temperature

The effects of mixing time and curing temperature on the uniaxial compressive strength （UCS） andmicrostructure of cemented hydraulic fill （CHF） and sodium silicate-fortified backfill （Gelfill） wereinvestigated in the laboratory. A series of CHF and Gelfill samples was mixed for time periods rangingfrom 5 min to 60 min and cured at temperatures ranging from 5 C to 50 C for 7 d, 14 d or 28 d.Increasing the mixing time negatively influenced the UCS of Gelfill samples, but did not have a detectableeffect on CHF samples. The curing temperature had a strong positive impact on the UCSs of both Gelfilland CHF. An elevated temperature caused rapid UCS development over the first 14 d of curing. Mercuryintrusion porosimetry （MIP） indicated that the pore size distribution and total porosity of Gelfill werealtered by curing temperature.

The pore structure of tight limestone-Jurassic Ziliujing Formation, Central Sichuan Basin, China

The pore structure of the tight limestone in the Daanzhai Member of the Ziliujing Formation, Jurassic System, in central Sichuan Basin, China, is complex but essential to the exploration and development of tight oil. The pore structure of the tight limestone is studied by using scanning electron microscopy （SEM）, nitrogen adsorption, high-pressure mercury intrusion, and nuclear magnetic resonance （NMR）. The experimental results suggest that the pores are mainly slit pores and mesopores and macropores contribute to the pore volume and specific surface. The displacement pressure, average pore size, and homogeneity coefficient correlate with porosity and permeability and can be used to evaluate the pore structure. The full pore-size distribution was obtained by combining nitrogen adsorption and high-pressure mercury intrusion. We find that the limestone mainly contains mesopores with diameter of 2-50 nm. The T2 distribution was converted into pore-size distribution, well matching the full pore-size distribution. The relation between T2 and pore size obeys a power law and the geometric mean of T2 correlates with the pore structure and can be used in the pore structure evaluation.

Analysis of Pore Structures and Their Relations with Strength of Hardened Cement Paste

Three cement samples were prepared, includi ng OPC consisted of 100wt% portland cement, PFA consisted of 70wt% portland cemen t and 30wt% fly-ash, and CA consisted of 70wt% portland cement and 30wt% modifi ed fly ash. The strength of hardened cement paste of these samples was tested an d their pore structures were determined by a mercury intrusion porosimeter. More over,the data of the pore structures of three samples were comprehensively analy zed. The relations between the pore structures and the compressive strength of t he three samples were studied. The experimental results show that the relations between the porosity determined by the mercury intrusion porosimeter and the com pressive strength are not notable, and the total pore surface area, the average pore diameter and the median pore diameter could be used to explain the differen ce of the strength of the tested samples.

Characterization of microstructural features of Tamusu mudstone

Tamusu mudstone formation, located in the Alxa area in western Inner Mongolia, is considered a potential host formation for high-level radioactive waste(HLW) underground disposal in China. In this study, complementary analyses with X-ray diffraction(XRD), field emission scanning electron microscopy(FE-SEM), mercury intrusion porosimetry(MIP), and N_(2) physisorption isotherm were conducted on the Tamusu mudstone to characterize its physical characteristics and microstructural features, such as mineral compositions and pore structure. Several minerals, including carbonates, feldspar, clays and analcime, were identified in Tamusu mudstone by XRD. Images from FE-SEM show that pores in the Tamusu mudstone were dominantly on nanometer scale and generally located within their mineral matrix or at the interface with non-porous minerals. The combination of the MIP and N_2 physisorption curves indicated that the Tamusu mudstone has diverse pore sizes, a porosity varying from 2.34% to 2.84%, and a total pore volume in the range of 0.0065—0.0222 cm^(3)/g with the average pore diameter ranging from 9.6 nm to 19.23 nm. The specific surface area measured by MIP(2.572—5.861 m^(2)/g) was generally higher than that by N_(2) physisorption(1.29—3.04 m^(2)/g), due to the pore network effect, pore shape(e.g. ink-bottle shape), or technique limits. The results related to pore information can be applied as an input in the future to model single-or multi-phase fluid flow and the transport of radionuclides in porous geomedium by migration and diffusion.

Evaluation of the effect of sodium silicate addition to mine backfill,GelfillLPart 1

In this paper, the mechanical properties of sodium silicate-fortified backfill, called Gelfill, were investigated by conducting a series of laboratory experiments. Two configurations were tested, i.e. Gelfill and cemented hydraulic fill（CHF）. The Gelfill has an alkali activator such as sodium silicate in its materials in addition to primary materials of mine backfill which are tailings, water and binders. Large numbers of samples of Gelfill and CHF with various mixture designs were cast and cured for over 28 d. The mechanical properties of samples were investigated using uniaxial compression test, and the results were compared with those of reference samples made without sodium silicate. The test results indicated that the addition of an appropriate amount of an alkali activator such as sodium silicate can enhance the mechanical（uniaxial compressive strength） and physical（water retention） properties of backfill. The microstructure analysis conducted by mercury intrusion porosimetry（MIP） revealed that the addition of sodium silicate can modify the pore size distribution and total porosity of Gelfill, which can contribute to the better mechanical properties of Gelfill. It was also shown that the time and rate of drainage in the Gelfill specimens are less than those in CHF specimens made without sodium silicate. Finally, the study showed that the addition of sodium silicate can reduce the required setting time of mine backfill, which can contribute to increase mine production in accordance with the mine safety.

Transient infiltration tests in pyroclastic soils with double porosity

Fallout volcanic deposits of SommaVesuvius(Campania,southern Italy),characterized by the presence of layers with contrasting textural and hydraulic properties,are frequently affected by shallow landslides during rainwater infiltration.The soils of the stratigraphic sequence present intraparticle pores,originated by the gases escaped during magma decompression in the volcanic conduit,thus are characterized by double porosity(i.e.,intraparticle and interparticle pores),which is expected to affect their hydraulic behaviour,and to play a key role in rainwater infiltration through layered deposits.To understand the effect of double porosity on the hydraulic behaviour of the involved soils,controlled experiments have been carried out in an infiltration column.The experimental apparatus is provided with newly designed non-invasive Time Domain Reflectometry(TDR)probes,not buried in the investigated soil layers so as to minimize disturbance to the flow,allowing water content measurement during vertical flow processes.Specifically,transient flow experiments are carried out through reconstituted specimens of black scoriae and grey pumices,both loose pyroclastic granular soils from fallout deposits of Somma-Vesuvius,featuring double porosity with different pore size distributions,that were estimated by X-ray tomography and Mercury Intrusion Porosimetry.The experimental results highlight the effects of the double porosity and clearly indicate the different behaviour of the two soils during wetting and drying processes,mainly related to the different dimensions of intraparticle pores.

Quantitative characterization of shale pore connectivity and controlling factors using spontaneous imbibition combined with nuclear magnetic resonance T_(2)and T_(1)-T_(2)

Shale oil can be extracted from shale by using interconnected pore networks.The migration of hydrocarbon molecules within the shale is controlled by pore connectivity.However,assessing the pore connectivity of shale oil reservoirs is uncommon.To characterize pore connectivity and clarify its controlling factors,this study used spontaneous imbibition(SI)combined with nuclear magnetic resonance(NMR)T_(2)and T_(1)-T_(2)technologies on shale oil reservoirs selected from the Shahejie Formation in the Dongying Sag,Bohai Bay Basin.According to the findings,the SI processes of shales include fast-rising,slow-rising,and stable stages.The fast-rising stage denotes pore connectivity.The shales studied have poor connectivity,with lower imbibition slopes and connected porosity ratios,but large effective tortuosity.During the SI process,micropores have the highest imbibition saturation,followed by mesopores and macropores.Furthermore,n-dodecane ingested into micropores appears primarily as adsorbed,whereas n-dodecane appears primarily as free states in mesopores and macropores during the SI process.The pore connectivity of the shales under study is primarily controlled by inorganic minerals.Quartz and feldspar develop large and regular pores,resulting in better pore connectivity,whereas clay minerals and calcite with plenty of complex intragranular pores do not.Organic matter negatively influences pore connectivity because the dissolution of calcite by organic acid produced during hydrocarbon generation leads to a more complex and heterogeneous pore structure.This study sheds light on the pore connectivity and controlling factors of the shale oil reservoir and aids in the understanding of shale oil mobility.

Analysis on Pore Structure of Non-Dispersible Underwater Concrete in Saline Soil Area

In this paper,mercury intrusion porosimetry(MIP)is used to test the pore structure of non-dispersible underwater concrete so as to study the influence of pouring and curing environment,age and slag powder on the pore characteristics of concrete,analyze the pore characteristics,porosity and pore distribution of concrete in different hydration stages,and reveal the relationship between pore structure and permeability of concrete.The results show that the pore-size distribution of concrete in fresh water condition is better than that in sulfate environment and mixed salt environment,and therefore,sulfate as well as mixed salt are not conducive to the development of pore structure of non-dispersible underwater concrete;chlorine salt has little effect on the pore structure of nondispersible underwater concrete;under the three conditions of sulfate,chlorine and mixed salt,the porosity of concrete mixed with slag powder is lower than that of concrete without slag powder.The results indicate that the addition of slag powder can ameliorate the pore size distribution of non-dispersed underwater concrete,reduce the porosity,and make the concrete structure more compact,which is beneficial to improve the permeability resistance of concrete at the macro level.

Pore Structure of Cement Pastes Mixed with Inorganic Salts

The influence of salts on concrete durability,pore structure of cement pastes with inorganic salts,including CaCl2,NaCl,Na2SO4,NaNO2,Ca(NO3)2 and Ca(NO2)2,was studied through mercury intrusion porosimetry (MIP),and hydration degree of each paste was also tested.The results show that porosity of the paste with inorganic salt cured for 3 d or 28 d was related with its hydration degree.For the pore size distribution,the pores smaller than 50 nm in paste with salts cured for 3 d increased;the amount of pores larger than 100 nm increased because of the addition of Ca (NO3)2 at 3 d,but these coarse pores turned into fine pores and reduced significantly at 28 d;coarse pores lager than 1000 nm in cement pastes containing NaCl and Na2SO4 increased.

Pore Structure Characteristics of Taiyuan Formation Shale in Qinshui Basin

Qinshui Basin is located in the southeast of Shanxi Province, China. Taking the shale of Taiyuan Formation in Qinshui Basin as the research object, the study analyzed the pore size of the shale of Taiyuan formation in detail from micropore to macropore by the methods of mercury injection, liquid nitrogen analysis and combination of liquid nitrogen and mercury injection. The results show that: 1) the visible pores and macropores are poorly developed and distributed unevenly in the shale of Taiyuan formation, and the micropores are well developed in the shale, and there are more open pores in the pore diameter range, and the pore connectivity is good;2) the liquid nitrogen experiment shows that the pores of Taiyuan Shale are relatively developed between 15 nm and 20 nm, and the formation of hysteresis loop may be caused by some narrow slit pores with similar layered structure;3) the comprehensive analysis of liquid nitrogen and mercury injection experiments shows that the shale of the Taiyuan formation mainly develops micropores, the Mesopores is not developed, the pore volume at 10 - 100 nm is more developed than other parts, and the specific surface is mainly contributed by micropores, which can improve the efficiency of shale gas resolution;at the same time, it provides a channel for Shale gas migration, which is beneficial to the development of shale gas.

Experimental research on variation of porosity in destruction process of cement stabilized soil

Based on the process of reinforcing soft soil using cement in laboratory, the porosity of test samples under different pressures conditions were determined through mercury intrusion porosimetry. The experiment was introduced and the law of porosity variation was summarized. The results show that when stress is between 0 and 0.15--0.2 qu, porosity decreases along with the pressure, then porosity has increased in the wake of the pressure until the sample damaged. It can provide an experimental basis for exploring the failure mechanism of cement stabilized soil from the microscopic view and the study to establish the microcosmic constitutive model of cement stabilized soil.

Significance of compaction time delay on compaction and strength characteristics of sulfate resistant cement-treated expansive soil

The addition of cement for stabilization of expansive soils is one of the most commonly used methods.As with every calcium-based stabilizer,the time delay between the physical mixing of the stabilizer and compaction plays an important role in achieving the desired results after stabilization.However,a clear insight on the determination of optimum time delay for achieving the maximum desired compaction properties of cement-stabilized soils is yet to be established.Furthermore,the recent studies highlighted the use of sulfate to mitigate the negative effect of compaction time delay.The only drawback with the use of sulfate along with calcium-based stabilizers is the formation of ettringite,which deteriorates the stabilized soil matrix.In view of this,the present study is aimed at using the sulfate resistant cement(SRC)as a stabilizer along with the controlled addition of sulfate solutions to mitigate the negative effect of compaction time delay in stabilizing the expansive soil.To bring out the above effects,three periods of time delays(0 h,6 h and 24 h)and three sulfate concentrations of 5000 parts per million(ppm),10,000 ppm and 20,000 ppm were adopted.The experimental results showed that the delay in compaction resulted in the formation of clogs and reduction of strength of SRC-stabilized expansive soil.Upon sulfate addition to SRC-stabilized expansive soil,the formation clogs was not curtailed and resulted in the formation of ettringite clusters.These formations were captured with the help of scanning electron microscope(SEM)images and validated with electron dispersive X-ray spectroscopy(EDAX)analysis.Further,an attempt is also made to explain the mechanism of density and strength reduction with the aid of physico-chemical properties and mercury intrusion porosimetry(MIP)studies.

Pore Size Distribution of Clayey Soils and Its Correlation with Soil Organic Matter

Soil pore size distribution(PSD) directly influences soil physical,chemical,and biological properties,and further knowledge of soil PSD is very helpful for understanding soil functions and processes.In this study,PSD of three clayey soils collected from the topsoil(0-20 cm) of Vertisols in Northern China was analyzed using the N_2 adsorption(NA) and mercury intrusion porosimetry(MIP) methods.The effect of soil organic matter(SOM) on the PSD of clayey soils was also evaluated.The differential curves of pore volume of clayey soils by the NA method exhibited that the pores with diameter < 0.01 μm accounted for more than 50%in the pore size range of 0.001 to 0.1 μm.The differential pore curves of clayey soils by the MIP method exhibited three distinct peaks in pore size range of 60 to 100,0.3 to 0.4 and 0.009 to 0.012 μm,respectively.In the three clayey soils,the ultramicropores(5-0.1μm) were determined to be the main pore class(on average 35.5%),followed by macropores(> 75 μm,31.4%),cryptopores(0.1-0.007μm,16.0%),micropores(30-5 μm,9.7%) and mesopores(75-30 μm,7.3%).The SOM greatly affected the pore structure and PSD of aggregates in clayey soils.In particular,SOM removal reduced the volume and porosity of 5-100 μm pores while increased those of <5 μm pores in the 5-2 and 2-0.25 mm aggregates of clayey soils.The increase in the volume and porosity of < 5 μm pores may be attributed to the disaggregation and partial emptying of small pores caused by the destruction of SOM.