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.

硼砂-硅酸钠碱激发矿渣砂浆干缩和微观特性试验研究

碱激发材料(AAMs)具有高强、低碳等优点,但是其相较于水泥基材料较大的干燥收缩率限制了其应用和推广。该文设计了一种复合激发剂,开展了硼砂-硅酸钠碱激发矿渣(AAS)砂浆的干缩和微观特性试验研究。采用压汞法(MIP)、X射线衍射(XRD)、扫描电子显微镜(SEM)和傅里叶变换红外光谱(FTIR)对样品进行测试和表征,分析了复合激发剂减缩机理。试验结果表明,硼砂-硅酸钠复合激发剂有效降低了AAS砂浆的干缩;XRD结果显示AAS砂浆中存在钠硼解石相(NaCaB_(5)O_(6)(OH)_(6)(H_(2)O)_(5));FTIR分析表明,最优硼砂比例下(20%),AAS砂浆的Si—O—T(T代表Si、Al或B)谱带明显增强,通过MIP分析得到AAS砂浆的中孔(<50nm)数量减少,这有助于缓解收缩应力,降低砂浆的干缩率。该研究结果可以为AAMs的减缩和应用提供参考依据,激发学生在建筑领域的碳减排思维,提升解决关键问题的能力。

干湿循环与盐溶液作用下红黏土-膨润土混合土体变与渗透特性

针对红黏土-膨润土混合土材料在干湿循环作用及复杂化学环境下的性能演化问题,开展了盐溶液入渗作用下红黏土-膨润土混合土的干湿循环试验研究,分析了干湿循环次数、膨润土掺入比、盐溶液浓度对压实混合土材料体变特征与渗透特性的影响,并结合压汞试验揭示了试样收缩变形与渗透系数变化的微观机制。结果表明:随着干湿循环次数的增加,压实红黏土-膨润土混合土试样累计收缩变形逐渐增大,收缩趋势随入渗盐溶液浓度的增加而增大;干湿循环过程中试样渗透系数呈先增大后减少的趋势,且随着盐溶液浓度增加而逐渐降低;增大混合土中膨润土掺量可以提高试样化学相容性,减少胀缩变形并减小渗透系数。压汞试验表明,盐溶液入渗及干湿循环作用导致土体孔隙“双峰”分布特征减弱,土体中的大孔数量及孔径减小,小孔略有增多;随着入渗的盐溶液浓度增加,小孔变化不明显,而土体总孔隙率及大孔数量减小,进而导致土体收缩变形增大、渗透系数减小。

弃土基可控性低强度材料静态力学特性及孔隙分布特征

针对大规模的水利水电项目通常需要一定量的土地用于建设水库、水电站等基础设施,导致产生大量的工程弃土,利用开挖弃土制备土基可控性低强度材料,采用数字图像相关技术(digitalimage correlation,DIC)和声发射技术(acoustic emission,AE)监测试件破坏特征以及损伤演化机制,通过压汞法(mercury intrusion porosimetry,MIP)和扫描电镜(scanning electron microscopy,SEM)观察试件内部孔隙分布特征。结果表明,试件受压破坏后呈现完全破碎形态,裂缝在贯穿试件的过程中沿着最初方向持续发展,荷载到达峰值后裂缝发展主要以延伸为主直至破坏,试件内部拉伸破坏和剪切破坏并无明显区别。试件内部孔隙率较高,孔隙较大,整体黏结性较低,部分孔隙有水化产物充填,在加载过程中起连结作用。本研究为科学调控弃土基可控性低强度材料力学性能提供参考。

循环流化床固硫灰路基动态回弹模量试验研究

【目的】探究循环流化床(CFB)固硫灰用作路基填料时在行车荷载下的动态性能。【方法】基于室内动三轴试验,研究了GF固硫灰与DTH固硫灰在不同养护龄期、压实度、含水率及应力水平条件下动态回弹模量特性,并结合压汞测试分析了CFB固硫灰试样孔隙分布特征与动态回弹模量的关系。【结果】结果表明:在一定范围内,CFB固硫灰的动态回弹模量随f-CaO与SO_(3)含量及养护龄期的提升而增加,在0~7 d内提升显著,7~28 d增长缓慢;压实度、含水率、围压及偏应力的提升均会使CFB固硫灰的动态回弹模量增大,其中随着压实度与含水率的上升,动态回弹模量的提升幅度逐渐下降,偏应力和围压对CFB固硫灰动态回弹模量均有较大影响,且围压的影响更显著。压汞试验的结果表明,同等条件下GF固硫灰试样总孔隙率与大孔径(>2 000 nm)密度低于DTH固硫灰,随着含水率的下降,GF固硫灰试样的总孔隙率与大孔密度增加,动态回弹模量变小。对两种CFB固硫灰不同含水率及压实度成型试件养护28 d后的动态回弹模量结果进行拟合,表明以体应力与八面体剪应力为变量的三参数理论模型预估结果与试验结果具有较高的相关性(R^(2)>0.96),可有效预测CFB固硫灰的动态回弹模量。

单、双孔隙结构非饱和黏土孔隙分布变化规律试验研究

由于孔隙分布曲线的复杂性,在非饱和过程中黏土的孔隙结构变化规律尚不明晰,这导致基于孔隙分布模型计算土-水特征曲线存在较大的误差。针对这一问题,基于干缩试验与压汞试验,对单孔与双孔结构重塑黏土在脱湿过程中孔隙分布曲线的变化规律进行了定量分析。研究表明:在脱湿过程中孔隙分布曲线存在平移、缩放等变换。构建了t分布和双t分布函数,提取了孔隙分布曲线的自由度、峰值、峰值对应的孔隙直径作为特征参数来表征孔隙分布变化规律,发现了特征参数和土样孔隙比之间存在较好的线性关系。基于试验结果,建立了含水率-孔隙比-孔隙分布曲线关系,提出了一个考虑孔隙结构变化的重塑黏土土-水特征曲线计算框架。最后,与试验测得的土-水特征曲线进行比较,验证了所提出的计算方法的准确性。

水下自护混凝土与钢筋握裹力试验研究

随着水下自护混凝土技术的推广和应用,其关键工艺参数水下保护剂浓度对水下自护钢筋混凝土结构性能的影响成为关注的热点。基于水下自护技术,在常用工作浓度范围内,对水下自护混凝土的素混凝土力学性能、混凝土与钢筋握裹力、微观孔隙结构开展了试验研究。试验结果表明:在不同水下保护剂浓度下,水下自护素混凝土抗压强度水陆强度比均超过80%;混凝土与钢筋握裹力水陆强度比约在40%~65%,水下保护剂浓度越高,混凝土与钢筋握裹力水陆强度比越低;混凝土基质区域孔隙率和混凝土与钢筋握裹力存在负相关关系;水下保护剂能够有效提升水下自护混凝土的力学性能,但水下保护剂浓度的提升会对混凝土与钢筋握裹力强度造成不利影响。因此,合理选择水下保护剂浓度并增加钢筋用量是提升水下自护钢筋混凝土工程的可靠性的重要举措。

黔西阿弓向斜北翼主采煤层孔隙结构特征研究

为研究黔西织纳煤田阿弓向斜煤储层孔隙结构特征,指导该区煤层气开发和煤矿瓦斯抽采,对研究区施工的煤层气参数井DJT1井主采煤层煤样做了压汞、煤岩鉴定等相关实验;结合实验数据分析了煤层中孔隙特征与孔隙表征参数的变化规律,探讨了该区孔隙特征的地质控制因素。结果表明:孔隙形态以开放孔为主,含一定数量的半封闭孔。总孔容在0.0225~0.0331 mL/g,小孔所占比例最高,其次是微孔。孔隙率和孔容随煤变质程度增加呈现递减变化。煤岩显微组分镜质组含量普遍超过55%,控制了微孔和小孔的含量,而矿物质含量的增加总体上对孔隙发育产生不利影响。

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.

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.

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.

陶瓷抛光废料制备UHPC的耐久性能试验研究

为探究陶瓷抛光废料(CPW)对超高性能混凝土(UHPC)耐久性能的影响,采用CPW分别取代部分水泥、粉煤灰和硅灰制备UHPC,主要研究了CPW对UHPC孔隙结构、力学性能、体积稳定性、抗氯离子渗透性能以及抗硫酸盐侵蚀性能的影响。结果表明,随着CPW分别取代水泥、粉煤灰、硅灰量的增加,UHPC的孔隙率增大,导致UHPC的抗氯离子渗透性能下降。CPW取代粉煤灰会增大UHPC的自收缩,而取代水泥和硅灰会减小UHPC的自收缩。CPW取代水泥会降低UHPC的抗压强度,但对硫酸盐侵蚀后UHPC的抗蚀系数和抗压强度有所提升;当CPW取代20%(质量分数)的水泥时,硫酸盐侵蚀90 d的UHPC的抗压强度达到最高。

低–中阶煤压汞实验可靠性分析与压缩性校正

低−中阶煤煤质软、在高压条件下煤基质压缩效应明显,应用压汞实验能否得到可靠的孔隙结构存在争议。选取4种低−中阶煤样品,通过对比不同粒度样品的进汞曲线、压汞前后的宏观与显微特征,建立高压段进汞量的校正方法,研究了压汞实验对低−中阶煤中孔隙测试结果的可靠性。结果表明:(1)柱状样品能保留更多的原生裂隙,有效避免低压阶段的粒间孔与麻皮效应,更适用于低−中阶煤的压汞测试;(2)宏观与微观尺度下均未发现汞在高压下对煤基质与孔隙的破坏作用,压汞孔容偏高主要是煤基质压缩效应的结果,压缩性校正后压汞测孔隙率与氦气测孔隙率基本一致,6~100 nm的孔容校正后与低温N2吸附结果的差值降低了29.87%~55.49%,表明压汞实验可以应用于低−中阶煤中孔隙结构的测定;(3)针对高压阶段的煤基质压缩效应,建立了压缩性累积校正方法,对大于20 MPa高压段数据进行校正后,进汞量降低了0.0170~0.0323 mL/g,纳米孔隙与低温N2吸附实验结果更为接近;(4)低−中阶煤中孔隙的孔容主要源于大孔,褐煤与长焰煤孔隙发育差异显著,褐煤压汞孔容为0.1687 cm^(3)/g,长焰煤压汞孔容介于0.0272~0.0720 cm^(3)/g,孔隙特别发育的样品,植物组织胞腔孔是孔容的主要来源。

磷石膏基发泡建筑石膏的热传导与强度特性研究

为了进一步提高磷石膏的综合利用率,本文采用单因素试验,研究了α-烯基磺酸钠(AOS)、动物蛋白、十二烷基硫酸钠(K12)质量比为1∶1∶1的复合发泡剂稀释化对磷石膏基发泡建筑石膏孔隙率及孔隙结构的影响,并研究了孔隙率与强度、导热系数之间存在的关系。研究结果表明,当表观密度在600~800 kg/m^(3)时,磷石膏基发泡建筑石膏的热工性能要优于其他四组泡沫保温材料,当表观密度大于900 kg/m^(3)时,抗压强度要远远高于其他石膏基泡沫材料,导热系数与孔隙率之间的关系符合Maxwell-Euchen1模型,而抗压强度与孔隙率之间的关系更符合Hasselmann方程。本研究可为磷石膏基发泡建筑石膏生产提供数据支撑。

新疆油页岩升温过程中孔隙结构演化特征

孔隙结构是油页岩描述的重要特征,直接影响页岩油气的储存和运移。因此,研究孔隙结构演化对指导油页岩原位开采具有重要意义。本文以新疆巴里坤油页岩为研究对象,利用热重(TG)、低温氮气吸附(LTNA)与压汞(MIP)等试验,结合LTNA-MIP联合精确表征方法,揭示巴里坤油页岩热解失质量规律及升温过程中孔隙发育特征,并对孔隙结构演化过程和机理进行研究。结果表明:新疆油页岩热重可分为低温缓慢失质量阶段(20~360℃)、中温快速失质量阶段(360~500℃)和高温缓慢失质量阶段(500~600℃),由于该油页岩具有低挥发分、高含油率、高灰分的特点,中、高温阶段是主要的失质量阶段;巴里坤油页岩内部孔隙类型复杂,升温过程中,微、小孔由狭缝形演变为导管状,中、大孔始终以墨水瓶状为主。墨水瓶状孔隙在300~400℃和500~600℃这2个温度区间集中发育,有效孔隙则在400~500℃大量发育。低温段以原生大孔为主,在自由水蒸汽压、矿物热膨胀和沥青质软化共同影响下,孔隙结构变化较小;中温段有机质集中热解,产生扩孔效应,单位孔隙体积大幅增加,孔隙类型以中孔为主;高温段黏土矿物失水、石英相变产生膨胀压力,大孔、中孔进一步扩展。

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.

基于MIP试验下的煤微观结构研究和分形定量表征

为了解地下煤火对煤裂隙孔隙的影响,将压汞法(MIP)和分形计算相结合,研究高温处理下的煤孔隙裂隙发展的规律并计算分维数,分析煤孔隙裂隙发展与分维数之间的关系。结果表明200℃高温处理的煤样(C200)总孔体积(0.171 5 mL/g)大于400℃高温处理后的煤样(C400)总孔体积(0.120 9 mL/g),均大于原煤的0.113 5 mL/g,孔体积增加主要是中孔和大孔,C200中孔和大孔体积占比为70.15%以及C400占比59.97%。MIP分维数随温度的升高呈现降低的趋势,温度越高煤样贯通性越好,C200和C400孔体积和三维分维数的变化呈现相反的趋势与煤基质在不同温度下受力不同有关。温度越高分维数越小,裂隙孔隙的贯通程度越好,煤的内部微观结构不同尺寸的分布相对均匀。

煤的孔隙结构分形定量研究

煤是一种具有复杂孔隙结构的物质，难以用传统的欧几里德理论予以描述．分析用压汞法测出的煤中不同孔径段的比孔容资料，发现最小孔半径在６５～８７ｎｍ的大孔和中孔具有分形特点．可以用分形维数定量表征煤的孔隙特征．分形维数能反映组成煤的煤岩组分的复杂程度和煤结构遭受破坏的严重程度．在煤的变质系列中，中变质程度烟煤的分形维数最大．

恒速压汞法在致密储层孔隙结构表征中的适用性

在深入分析恒速压汞法原理的基础上,结合鄂尔多斯盆地延长组致密油岩心实验结果,研究了该方法在致密油孔隙结构表征中的适用性。结果表明:运用恒速压汞法能够区分孔隙和喉道,获得孔隙半径、喉道半径及孔喉半径比分布,可以更全面地表征孔隙结构并揭示其对渗流能力的影响;恒速压汞法以准静态进汞,能够消除润湿滞后效应,同时修正了高压下介质变形的影响,实验数据相比于高压压汞法更为准确。然而,受最高驱替压力的限制,恒速压汞法最大汞饱和度较低,无法表征半径小于0.12μm的孔喉。总体而言,恒速压汞法在表征致密油孔隙结构方面有一定的优势,但还需要结合其他方法才能表征致密油完整的孔隙结构。

氮气吸附法和压汞法在测试泥页岩孔径分布中的对比

泥页岩比表面大,孔隙小,结构复杂,易吸水膨胀,一般方法很难准确描述其孔径分布情况。对泥页岩孔径分布的研究在石油钻井,完井,储层描述,泥页岩盖层封闭性等方面有着重要的意义。实验分别使用氮气吸附法和压汞法对同一泥页岩进行孔径分析。氮气吸附法中使用BJH原理分析泥页岩的中孔径,使用DA原理分析泥页岩的微孔径;压汞法中使用Wasburn公式分析泥页岩整体孔隙,对两种方法实验结果进行对比。氮气吸附法在泥页岩微孔和中孔分析方面有优势,能分别对泥页岩的微孔和中孔进行详细的描述;而压汞法受泥页岩孔径分布不均一性影响相对较小,能弥补氮气吸附法在大孔分析方面的不足。把氮气吸附法和压汞法测得的孔径分布结果结合使用,可以得到泥页岩从微孔到大孔的孔径分布情况。