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1.
D. Benavente J. Martinez-Martinez N. Cueto S. Ordoñez M. A. Garcia-del-Cura 《Environmental Earth Sciences》2018,77(4):147
This study aims to understand the effect of salt and frost crystallisation on the petrophysical and durability properties of representative types of travertine and carbonate tufas. Results demonstrate that the studied travertines and tufas exhibit a very high durability against salt and ice crystallisation cycles, compared to carbonates rocks with similar porosity values. The variation of the loss of mass, effective porosity, capillary absorption coefficient, ultrasonic wave velocity and attenuation, and compressive strength was scarce during weathering tests. The evolution of petrophysical properties was slightly more intense after 30 cycles of salt crystallisation than 100 cycles of freeze–thaw. Petrophysical and durability properties of the travertines and carbonate tufas depend on porosity fraction and on the manner in which the vuggy porosity is connected. In the travertine facies, vuggy macropores show little connection and can be considered as separate-vug porosity. Their addition to interparticle porosity increases effective porosity and reduces their mechanical strength but does not significantly increase capillary transport and the effectiveness of salt and ice action over the stone. On the contrary, in the carbonate tufas, vugs act as touching-vug pores, as capillary imbibition coefficients reveal. However, scanning electron microscopy displays that they underwent microcracking processes related mainly to both thermal stresses and/or ice and salt pressures. These microcracks present little connection, and they do not enhance noticeably the water flow or decrease the mechanical properties. These results are finally discussed in terms of a nonlinear decay pattern, which with long periods of apparent stability might be followed by rapid and catastrophic decay. 相似文献
2.
基于现有结构面剪切力学特性研究中对简单几何形态结构面研究多,天然形态结构面研究少,力学性质演化研究多,几何形态演化研究少的研究现状,通过巴西劈裂试验制备近天然形态岩石结构面,并采用模拟材料批量复制劈裂结构面试样的方法,开展循环荷载作用下岩石劈裂结构面的剪切力学特性演化规律与影响因素研究,分析法向应力、循环剪切次数、岩壁强度以及结构面粗糙度对循环剪切作用下岩体结构面力学特性和形貌特征的影响。最终通过在黏着摩擦理论-Barton经验公式中引入与循环剪切次数Nd有关的负指数假定劣化参数,提出了岩体结构面循环剪切强度公式。研究结果表明：法向应力、岩壁强度、结构面粗糙度越大,结构面的最大剪应力越大;法向应力、循环剪切次数、结构面粗糙度越大,岩壁强度越小,则归一化粗糙度参数越小。提出的循环剪切强度公式较好地验证了试验结果,可为工程安全设计提供理论参考。 相似文献
3.
The crystallisation of soluble salts within the pores of the stone is widely recognised as a major mechanism causing the deterioration
of the stone-built architectural heritage. Temperature, in turn, is one of the main controls on this process, including salt
precipitation, the pressure of crystallisation and the thermal expansion of salts. Most laboratory experiments on decay generated
by salts are just carried out with convective heating regimes, while in natural environments building stones can undergo radiative
and convective heating regimes. The thermal response of stone to these different heating regimes is noticeably different and
might influence the crystallisation patterns of a salt within a stone. The aim of this work is to raise awareness on the different
patterns of crystallisation of NaCl within a porous stone tested with different heating regimes (convection and radiation)
and the implications that this could have on the design of experimental modelling of natural weathering conditions in laboratory
simulations. Results show that heating regime affects the sodium chloride distribution within a stone with high percentage
of microporosity. In this case, radiation heating facilitates the generation of subefflorescences, while convection heating
promotes efflorescences. This has a clear implication both on the stone decay in natural environments and on the methodologies
for testing salt decay, as subefflorescences are more destructive than efflorescences. In this sense, the use of convective
heating in laboratory experimentation might underestimate the potential damage that sodium chloride may generate. This counsels
the use of radiation heating test methods in addition to convection for the laboratory study of salt crystallisation. 相似文献
4.
Magnesium sulphate salts on monuments in Saxony (Germany): regional geological and environmental causes 总被引：1，自引：0，他引：1
Heiner Siedel 《Environmental Earth Sciences》2013,69(4):1249-1261
A record of mortar and salt analyses from the last 20 years on various monuments in Saxony demonstrates the close relation between the occurrence of magnesium sulphate salts and the use of dolomitic lime mortars in a regional frame. The regional distribution scheme of dolomitic lime in historic mortars depends on the geological setting of the territory, i.e. the natural occurrence of dolomite deposits. Sulphation of these mortars with the formation of magnesium sulphate and gypsum is mainly due to environmental pollution, as can be shown by sulphur stable isotope analyses. Exposure of the sulphated mortar surfaces to rain leads to the preferential dissolution and advective transport of the novel formed magnesium sulphate salts, which effloresce or subfloresce on the mortar surface or can be accumulated in the structure of adjoining porous building materials like natural stones. These processes may cause severe damages in mortars by the weakening of the binder and in porous stones by salt crystallisation of phases like epsomite and hexahydrite. 相似文献
5.
Black crusts are very common on limestones in polluted urban environments, but white crusts are less frequently developed. On the soft, porous and inherently weak oolitic limestone of Budapest both crusts are frequent, and indeed white ones are more common on the stone walls of the studied fortress. In this paper, black and white crusts and the host rock have been described using morphological criteria, mineralogical analyses (XRD, DTA), elements analyses (microprobe) and micro-morphological (SEM) tests. The analyses have shown that on white crusts the surface dissolution is combined with the precipitation of gypsum and calcite in the pores and accumulation of gypsum on the underside of the crust. Thin white crusts are removed by a combination of salt crystallisation (gypsum) and frost action while very thick stone layers scale off due to freeze-thaw cycles. Black crusts are enriched in gypsum relative to white crusts. Gypsum accumulates on the crust surface and signs of dissolution have not been observed. Airborne particulates (flyash, silt-sized quartz, and organic debris) adhere to the crust surface of sheltered black crusts. These particles are later incorporated into the expanding gypsum crystals, that are visible on the underside of the crust. The host rock also contains gypsum, but it is washed off the surface when the crust is removed. Further exposure of the host rock may lead to the dissolution of calcite crystals as it is observed by SEM. The micro-environment influences the crust formation and adherence of the crusts. On frequently wet and dry surfaces crust removal is more common. The crust serves as a protective layer on the stone surface, but this protection is temporary since trigger mechanisms such as salt crystallisation or frost action can cause rapid surface loss.Special Issue: Stone decay hazards 相似文献
6.
以锦屏二级水电站大理岩室内三轴压缩试验结果为基础,推导了考虑体积应力效应的塑性内变量公式,并研究了大理岩强度参数及剪胀特性随内变量的变化规律,结果表明,大理岩在峰前阶段凝聚力稍有降低,在峰后阶段迅速减小;内摩擦角随内变量增加而增大,并在内变量为0.8～0.9时达到最大值;不同围压下大理岩剪胀角均随内变量增大,且表现为先增大后减小的变化趋势,但低围压和高围压条件下剪胀角变化趋势不同。在此基础上建立了大理岩考虑体积应力效应的力学模型,并通过FLAC3D模拟了大理岩室内常规三轴压缩试验,模拟结果与室内试验结果吻合很好,表明该模型可较好地反映大理岩的主要力学特性。研究方法和成果可为其他深部脆性岩体的变形破坏分析提供重要的参考价值和借鉴意义。 相似文献
7.
“一带一路”规划的高速铁路频繁穿梭于盐质荒漠区,沿线优质不含盐路基填料极其匮乏。为解决粗粒盐渍土填筑高速铁路路基面临的技术难题,结合伊朗德伊高铁建设,以现场粗粒盐渍土路基填料为对象,开展了温度循环下压实粗粒盐渍土水盐迁移与变形响应试验研究。结果表明,每次温度循环后温度波幅值由土层浅表向深层土体衰减传递,土体埋深越浅、恒温时间越长,温度波幅值越大;水盐均匀分布的压实粗粒盐渍土经历多次温度循环后逐渐演化成非均匀分布,水盐向土体表面迁移聚集,越靠近土体表面水盐增量越大;前5次温度循环中压实粗粒盐渍土产生了塑性盐胀或塑性融沉,随着温度循环次数增加,盐渍土塑性盐胀或塑性融沉显著减小甚至消失;盐渍土层上设置非盐渍土层具有迟滞盐分向上迁移和消能减胀作用,粗粒盐渍土构筑高速铁路路基宜采用结构分层技术,非盐渍土层设置厚度一般不宜小于当地温度辐射影响显著深度;粗粒盐渍土路基设计宜考虑多次温度循环后形成的水盐非均质分布及其可能诱发的盐胀与融沉增大效应,路基压实度不宜过高。研究成果将为盐渍土地区高速铁路路基工程建造起到示范参考作用。 相似文献
8.
The Early Christian Munazio Ireneo cubicle in Cagliari (Sardinia) is carved into the rock and is one of the rare monuments of Sardinia belonging to Early Christian Age. It is 166 cm under the planking level and is a semi-confined chamber in which a gate allows exchange with the outside. In 1888, when it was discovered, it was completely painted, but over the years, it suffered a serious damage and all the paintings are nearly disappeared. Now the site shows a high moisture and a differential damage characterised by delamination, powdering, salt crystallisation and biological colonisation. The research offers a multidisciplinary approach to study the salt crystallisation damage, which is a phenomenon still not completely understood today. Studies and analyses highlight that different kinds of damage can be recognised. The cement mortar and the air pollution cause crystallisation of the sulphates. Constant capillary rising and the presence of water infiltration due to the rains, which travelled into the site from the vault, were detected during qualitative inspection. Although the microclimate did not change much in the site and the humidity was almost constant during the monitoring period, the variations in temperature allowed the phase transitions of sodium sulphate, especially in summer. The greatest damage of the porous stone is associated with the phase transitions and crystallisation inside the stone of sodium sulphate, one of the most harmful salts for porous materials because of its high crystallisation pressure. 相似文献
9.
干湿和冻融循环作用下黄土强度劣化特性试验研究 总被引：9，自引：4，他引：5
通过室内试验模拟土体季节性的干湿和冻融交替变化,采用直剪试验测试了原状黄土经干湿和冻融循环作用后的抗剪强度及抗剪强度参数的变化,并进行了直剪后试样的易溶盐总量测定.结果表明：干湿和冻融循环作用对原状黄土物理力学性质影响极大,是造成黄土边坡破坏的主要因素.随着干湿循环次数的增加,试样的抗剪强度逐渐减小,黏聚力逐渐减小,内摩擦角先增加,后逐渐趋于稳定,盐分迁移现象明显,土样下部易溶盐含量逐渐减少,上部易溶盐含量逐渐增加,并且试样的质量损失逐渐增加;随着冻融循环次数的增加,试样的抗剪强度逐渐减小,黏聚力逐渐增大最后趋于稳定,而内摩擦角和盐分迁移现象不明显. 相似文献
10.
为完善坡面水流的基础理论研究,基于定床水槽试验,以甘油溶液为试验流体,采用超声波测量技术,进行了4种粗糙度、5种坡度和13种单宽流量条件下的组合试验,研究了坡面流层流区的动力学特性及滚波特征。研究结果表明:在雷诺数为8~160的范围内,流态指数在理论值0.33附近波动,且随粗糙度的增大呈现先增大后减小的变化趋势,在粗糙度为0.10 mm附近达到峰值;阻力系数受坡度和粗糙度影响显著,可较好地由坡度、粗糙度和雷诺数的关系式表示;随着雷诺数的增大,滚波波速和波峰均呈幂函数形式递增,滚波周期大小无明显变化;坡度的增大会使层流失稳临界单宽流量减小,粗糙度的增大会使临界弗劳德数的均值减小。 相似文献
11.
为研究泥皮、粗糙度对桩-土接触面力学特性的影响规律,根据灌注桩成孔后的孔径-深度曲线,应用统计分析法获得了桩侧凸出尺寸和粗糙度的分布频率规律,以此构建了表面光滑和梯形凹槽混凝土板来模拟实际桩侧表面粗糙度。在此基础上,开展了不同泥皮厚度、粗糙度条件下的混凝土-砂土接触面大型直剪试验。其研究结果表明：无泥皮条件下粗糙接触面,其剪切应力-切向位移关系曲线呈软化型;泥皮厚度为5、10 mm条件下,呈硬化型。剪切模量G0.02随泥皮厚度增加而衰减。对光滑混凝土板,其接触面峰值剪切强度和峰值摩擦角随泥皮厚度的增加呈指数关系衰减;对粗糙混凝土板,峰值剪切强度和峰值摩擦角随泥皮厚度的增加近似呈线性衰减。初始泥皮越厚,试验后的泥皮土和泥皮越厚,接触面剪切强度越低。无泥皮条件下粗糙度对接触面峰值剪切强度的影响规律：存在一个临界粗糙度Icr =10 mm,当混凝土板的粗糙度I< Icr时,接触面峰值剪切强度和峰值摩擦角随粗糙度的增大而增大;当I≥Icr时,二者随着接触面粗糙度的增大而减小,泥皮存在会影响改变这一规律。 相似文献
12.
Three calcitic marble types often used as cladding material and different in lattice preferred orientation (texture), grain shape preferred orientation, grain size distribution and grain interlocking are investigated to study the combined effect of thermal cycles (day-night) and moisture on the decay of marble, particularly on the bowing phenomenon. Repetitive heating-cooling under dry conditions leads to considerable inelastic residual strain only in the first thermal cycle. The residual strain continuously increases again if water is present, whereby the moisture content after a thermal cycle has a certain impact on the decay rate. The water-enhanced thermal dilatation strongly correlates with the deterioration rate obtained from the laboratory bow test. All applied approaches reveal that the texture in combination with the grain shape preferred orientation control the intensity and anisotropy of marble deterioration, thus, the cutting direction of facade panels has to be considered in terms of durability. On-site analysis from building facades confirm the laboratory results such as the bowing tendency of different marbles, directional dependence, relevance of moisture content during cyclical heating and the loss of strength due to environmental impact.Special Issue: Stone decay hazards 相似文献
14.
裂隙是油气储层主要的储集空间及流体渗流通道,影响油气的运移规律,是油气勘探开发的重要指标。以冀中坳陷任丘油田任10井为例,运用数值模拟方法研究了裂隙开展宽度和裂隙面粗糙度对岩石渗流特性的影响规律。研究结果表明,(1)裂隙开展宽度较小时,孔隙内流体压力仅在入口处小范围内呈扇形分布,裂隙中压力分布曲线呈正切函数型,流体流速在裂隙和孔隙中都较小;随着裂缝开展宽度的增加,孔隙内流体压力逐渐增大,裂隙中压力分布曲线逐渐向直线型转变,流体流速在入口处先减小后稳定,在裂隙中先增加后稳定;(2)裂隙面粗糙度对裂隙岩石渗流特性的影响与裂隙开展宽度有关,在裂隙开展宽度较大时,裂隙面粗糙度对流体压力的分布影响较大;随着裂隙面粗糙度增大,孔隙内流速逐渐增大,而裂隙中流速逐渐减小;(3)随着裂隙开展宽度的增大,影响裂隙流体流动的主控因素逐渐由裂隙开展宽度转变为裂隙面粗糙度。 相似文献
15.
含盐土渗透系数变化特征的试验研究 总被引：4，自引：0，他引：4
对含盐土的渗透系数进行了室内试验研究.结果表明:在干容重相同的情况下,渗透系数随着含盐量的增加而减小;对同一类型土,随着含盐量的增加,硫酸盐土的渗透系数要比氯盐土渗透系数减小显著;在干容重和盐类相同的情况下,细颗粒含盐土的渗透系数要比粗颗粒含盐土的渗透系数减小显著.在含盐量相同的情况下,同一种土的渗透系数随着干容重的增大而减小.当干容重在一定的范围内时,渗透系数与干容重呈线性关系,但当干容重超过该范围时,渗透系数与干容重呈幂函数关系. 相似文献
16.
Hilde De Clercq Maja Jovanović Kirsten Linnow Michael Steiger 《Environmental Earth Sciences》2013,69(5):1751-1761
The behaviour of two types of limestones having a different porosity, Maastricht and Euville limestone, laden with aqueous solutions of equimolar mixtures of sodium sulphate/sodium nitrate or sodium sulphate/potassium sulphate was investigated. At 50 % RH, the efflorescences on Maastricht samples during the first 30 h of drying consisted of similar amounts of thenardite and darapskite in case of an equimolar mixture of sodium sulphate/sodium nitrate while those on Euville samples under the same conditions contained mainly darapskite. After drying at 20 °C and 85 % RH, thenardite, formed through the precipitation and dehydration of mirabilite, was mostly detected in the efflorescences on both Maastricht and Euville samples. Re-wetting by increasing the RH from 50 to 85 % resulted in substantial damage on Maastricht stone laden with an equimolar mixture of sodium sulphate/sodium nitrate as a consequence of high supersaturation of mirabilite. In case of a contamination with equimolar amounts of sodium sulphate and potassium sulphate, the efflorescence on both limestones during drying at 50 % RH contained predominantly aphthitalite. The observed crystallisation behaviour is compared to the theoretical behaviour. The results indicate a strong influence of stone properties on the crystallisation behaviour of salt mixtures. 相似文献
17.
盐渍土化学固化法是解决盐渍土盐胀、溶陷和腐蚀等不良工程问题的有效方法之一。通过无侧限抗压强度试验、X射线衍射试验、化学成分分析和扫描电镜试验研究了石灰粉、煤灰、水玻璃联合固化硫酸盐渍土的强度特征,分析探讨了其固化机制。试验结果表明：石灰含量小于8%时,石灰、粉煤灰、水玻璃联合固化硫酸盐渍土的抗压和抗剪强度较石灰粉煤灰固化土有大幅度提升,固化土强度随水玻璃浓度几乎呈线性增长。水玻璃固化硫酸盐渍土强度增加的机制在于：水玻璃的碱激发粉煤灰作用和水玻璃与盐渍土中化学成分的吸附作用所生成各类凝胶的填充和包裹,使得骨架颗粒的接触面积增大,颗粒之间的孔隙逐步减小,骨架颗粒由点接触变为面接触,固化盐渍土通过凝胶而黏结成为一个紧密的空间网状整体结构,土体强度得以提高。同时,复杂的物理化学作用大幅度降低了固化盐渍土中 含量,有效地抑制了硫酸盐渍土的盐胀特性。 相似文献
18.
对初始状态相同南阳膨胀土试样进行1～6次干湿循环,选取其中的1、3、6次循环后的试样,采用饱和盐溶液蒸汽平衡法测定其含水率、孔隙比、饱和度等与吸力的关系,并对比分析干湿循环对南阳膨胀土的持水能力影响。在1～6次干湿循环过程中,以环刀为参照物拍摄每次烘干后试样上表面照片,用数字图像处理提取图像中的裂隙与收缩面积,以此分析试样烘干过程中裂隙与收缩与干湿循环次数的关系。试验结果表明,干湿循环过程中相同吸力的试样含水率略降低、孔隙比略增大、持水能力略降低,烘干过程中试样收缩面积增大,裂隙展开面积增大,但上述性质变化幅度都随干湿循环次数增加而减小。试验成果为研究膨胀土的持水能力和湿胀干缩变形性质随干湿循环的变化规律提供实测数据。 相似文献
19.
冻融循环作用下富平黄土微观结构几何类型变化研究 总被引：1，自引：1，他引：0
冻融循环作用可通过影响寒区土体结构致使基础设施发生破坏,而导致工程失稳宏观现象的根源来自于冻融作用改变了土体的微观结构。为探索冻融作用下土体微观结构变化规律,将富平黄土作为研究对象,分别对其进行0、4、6、8、10、50、100次冻融循环下的电镜扫描观测试验,得到对应次数下的微观照片,对其从颗粒形态、连结方式、排列形式对孔隙的影响三方面进行分析,并且将微观照片中出现的颗粒接触方式以几何模型的方式进行归类,研究几何模型随冻融循环次数增加后的变化规律。结果表明：随着冻融循环次数的增加,土颗粒大小朝着均一性的方向发展,平均粒径呈先减小后增大趋势;颗粒的连结形式从面胶结为主逐渐演变为点接触为主最终再回归为面胶结为主;土体在0~6次冻融循环时孔隙率呈下降趋势,6~8次冻融循环时孔隙率快速上升,之后随着冻融循环次数的增加孔隙率逐渐减小;粒状粒子几何模型变化规律从棱边接触逐渐过渡为粒面接触,扁平状粒子几何模型变化规律从初始粒面接触为主逐渐演变为棱边接触为主,最终再演变为粒面接触。 相似文献