Formation and development of salt crusts on soil surfaces

The salt concentration gradually increases at the soil free surface when the evaporation rate exceeds the diffusive counter transport. Eventually, salt precipitates and crystals form a porous sodium chloride crust with a porosity of 0.43 ± 0.14. After detaching from soils, the salt crust still experiences water condensation and salt deliquescence at the bottom, brine transport across the crust driven by the humidity gradient, and continued air-side precipitation. This transport mechanism allows salt crust migration away from the soil surface at a rate of 5 μm/h forming salt domes above soil surfaces. The surface characteristics of mineral substrates and the evaporation rate affect the morphology and the crystal size of precipitated salt. In particular, substrate hydrophobicity and low evaporation rate suppress salt spreading.     

不同温度条件下盐岩卤水浸泡后损伤自恢复特性

为了研究地下盐穴开挖扰动区（EDZ）损伤盐岩在盐穴综合利用过程中的自恢复特性,设计了损伤盐岩在卤水温度作用下的自恢复试验。结果表明：损伤盐岩经过卤水浸泡后在不同温度下烘干时力学性质可以得到恢复,在试验温度范围35～80 ℃内,其恢复效果随着温度的增加而增强。经过恢复处理的损伤盐岩试件二次加载时的声发射特征显示,其Felicity比低于0.1,Kaiser效应基本不成立,说明损伤盐岩在自恢复处理过程中其内部损伤在细观尺度上发生愈合。根据损伤盐岩试件自恢复处理后的细观形貌特征,总结出盐岩损伤恢复3种不同的细观机制：基于扩散作用的损伤微裂纹愈合,基于NaCl晶体重结晶作用的微裂隙充填以及破碎区NaCl晶体颗粒的愈合黏结。盐岩损伤恢复过程中,裂纹中充填的饱和卤水为裂纹中的物质传递提供了通道,同时提供了大量的结晶基础物质,为盐岩损伤愈合奠定了基础。温度的升高为盐岩损伤恢复提供了更高的能量,提升了损伤愈合速度,同时使氯化钠重结晶密度增加,从而提高了损伤恢复程度。     

Brine transport in porous media: On the use of Von Mises and similarity transformations

In this paper we use a Von Mises transformation to study brine transport in porous media. The model involves mass balance equations for fluid and salt, Darcy's law and an equation of state, relating the salt mass fraction to the fluid density. Application of the Von Mises transformation recasts the model equations into a single nonlinear diffusion equation. A further reduction is possible if the problem admits similarity. This yields a formulation in terms of a boundary value problem for an ordinary differential equation which can be treated by semi‐analytical means. Three specific similarity problems are considered in detail: (i) one‐dimensional, stable displacement of fresh water and brine in a porous column, (ii) flow of fresh water along the surface of a salt rock, (iii) mixing of parallel layers of brine and fresh water. This revised version was published online in July 2006 with corrections to the Cover Date.     

盐岩储气库注气排卤期剩余可排卤水分析

地下盐穴溶腔注气排卤过程中天然气和卤水共存,排卤管进入到卤水的深度及排卤速率决定了天然气是否会被卤水带出地表,如何调整后期排卤速率,降低排卤过程中带出天然气的风险,是注气排卤过程中的施工技术难题。针对该问题,采用流场分析理论对注气排卤后期盐岩储库腔底流场进行了模拟分析,得到排卤管外壁卤水向下流速;根据天然气气泡在卤水中的运移速率,分析确定了注气排卤后期不同剩余卤水深度下的安全排卤速率,为施工后期注气排卤速率调整提供了技术支撑。     

裂隙岩体流固耦合双重介质模型的有限元计算

基于孔隙-裂隙岩体的双重孔隙介质流固耦合计算的微分方程,利用伽辽金有限元法提出的相应有限元公式,并基于岩体分类指标（RQD,RMR）提出了与岩体应力状态相关的渗透系数计算公式。编制了相应的有限元程序并给出了应用算例,将计算结果与相关文献作了比较,得出相关结论。     

Diffusion control of garnet growth,Harpswell Neck,Maine, USA

A detailed analysis of chemical zoning in two garnet crystals from Harpswell Neck, Maine, forms the basis of an interpretation of garnet nucleation and growth mechanisms. Garnet apparently nucleates initially on crenulations of mica and chlorite and quickly overgrows the entire crenulation, giving rise to complex two‐dimensional zoning patterns depending on the orientation of the thin section cut. Contours of Ca zoning cross those of Mn, Fe and Mg, indicating a lack of equilibrium among these major garnet constituents. Zoning of Fe, Mg and Mn is interpreted to reflect equilibrium with the rock matrix, whereas Ca zoning is interpreted to be controlled by diffusive transport between the matrix and the growing crystal. Image analysis reveals that the growth of garnet is more rapid along triple‐grain intersections than along double‐grain boundaries. Moreover, different minerals are replaced by garnet at different rates. The relative rate of replacement by garnet along double‐grain boundaries is ordered as muscovite > chlorite > plagioclase > quartz. Flux calculations reveal that replacement is limited by diffusion of Si along double‐grain boundaries to or from the local reaction site. It is concluded that multiple diffusive pathways control the bulk replacement of the rock matrix by garnet, with Si and Al transport being rate limiting in these samples.     

Dologrus: The impact of meteoric-water-controlled diagenesis following early-marine dolomitization

Carbonate rocks that have suffered early near-surface dolomitization followed by extended meteoric exposure commonly undergo partial delithification, a process that results in the formation of dolomitic silts and sands, herein termed dologrus. Dologrus is interpreted to form as a result of diffuse dissolution in porous and permeable dolostones prior to burial and compaction. Such dissolution occurs at the crystal–pore-water interface, causing individual crystals to corrode along interfacial boundaries, eventually leading to delithification and the formation of sediment composed of corroded crystals. The resulting sediment grain size is likely controlled in part by the crystal size of the precursor dolostone. Loss of rock competency through the process of dologrus formation in the shallow subsurface can lead to collapse of overlying bedrock and the formation of dolines common to karstic carbonate landscapes.     

Salt and subsidence in Cheshire,England

Rock salt occurs in the Keuper Marl Series of Cheshire. There are two saliferous beds, the lower being 190 m and the upper 404 m thick. However, most of the Triassic rocks in Cheshire are covered by thick superficial deposits. Nevertheless natural brine springs occur at the surface and salt has been evaporated from these springs since pre-Roman times.Subsidence occurs as a result of wild brine pumping. Gradual collapse takes place above the subterranean brine runs giving rise to cambered depressions at the surface, the flanks of which are often interrupted by tension scars. Flashes occupy many of these depressions. The most disastrous subsidences occurred towards the end of the nineteenth century due to bastard brine pumping, that is, pumping, with reckless abandon, from old mine workings. The associated subsidences were rapid and caused the destruction of many buildings. One of the awkward characteristics of subsidence in salt due to wild brine pumping is that it is unpredictable, indeed subsidence may occur several kilometres from the point of extraction. This means that an individual brine pumper could not and still cannot be proved responsible for subsidence. Accordingly, the Cheshire Brine Subsidence Compensation Board was established by act of Parliament at the end of the nineteenth century which obliged each brine pumper to contribute towards the compensation fund. Because controlled solution mining has not given rise to subsidence in its 40 years of operation this form of extraction is eventually to be extended throughout the whole of the salt field, another field is now being developed. It is hoped to phase out wild brine pumping by the 1980's.     

江陵凹陷富钾锂卤水矿田地质特征及成藏模式研究

江汉盆地江陵凹陷内的高温高压高盐度卤水,富含钾、锂、硼、溴、碘、铷、铯等,达到工业品位或超过综合利用品位,构成富钾锂卤水矿,长期以来其矿体定位一直是难题,对于钾锂卤水的富集与矿田构造的关系还没有完全查清。本研究以现代矿田地质学为指导,以地球物理勘探、钻井和野外地质等资料为基础,综合分析江陵富钾锂卤水的矿田建造、矿田构造与矿田成矿作用。江陵凹陷富钾锂卤水矿田建造分为构造沉积岩相矿田和构造火山岩相矿田。江陵凹陷内各地区由于受所处构造位置的影响,在不同时期发育了不同类型的局部构造,这些局部构造在空间上有序的分布与叠置形成了大量的构造圈闭,为钾锂卤水的聚集提供了有利的场所。从古新世沙市组到早始新世新沟嘴组沉积时期,江汉盆地的古气候条件总体为高温干旱,利于古盐湖的蒸发作用,火山活动带来丰富的钾锂物质,从而利于钾锂卤水的富集。江陵凹陷富钾卤水属构造—储层耦合成藏模式:江陵凹陷盐湖沉积特征,决定了有大量卤水储存在其地层中。这些卤水最大的储集体就是砂岩孔隙,而构造产生的大量裂缝大部分位于泥岩和火成岩中,也成为储集卤水的场所。在构造褶皱及埋藏作用下,卤水开始从盐类晶间,首先进入砂岩体孔隙内,而后可能进入裂隙系统及火山岩系统。     

Creep of rocksalt

A review is presented of the fundamental flow properties and processes in experimentally deformed natural and synthetic halite single crystals and polycrystalline aggregates. Included in the summary are discussions of: (a) microstructures induced during steady-state creep; (b) creep-rupture of rocksalt; (c) experiments associated with “Project Salt Vault” and more recent field studies; and (d) brine migration. A representative steady-state flow law determined for natural aggregates and maximum natural deviatoric stresses deduced from subgrain sizes are applied briefly to considerations of creep in waste repositories and of salt dome dynamics. While the mechanical behavior of rocksalt is probably better understood than for all other rock types, further investigations, especially on load path, stress history and creep-rupture are clearly mandated. Furthermore, additional investigations of brine migration and of bench and field-scale deformations are needed, the latter incorporating realistic rocksalt flow properties into numerical simulations of natural rock-mass response.     

Small-scale transport of trace elements Nb and Cr during growth of titanite: an experimental study at 600?°C, 0.4 GPa

Trace element distribution in titanite overgrowths on rutile has been investigated experimentally at 600?°C, 400?MPa and f_O2 near NiNiO buffer. Compositionally homogenous Cr- or Nb-doped synthetic rutile single crystals or Nb-containing natural rutile crystals were the source of Cr, Nb and Ti to synthesize titanite using the double-capsule technique. All element exchange with the source of Si, Ca and Al occurred via a NaCl–H₂O fluid. Titanite forms quickly and exclusively around the rutile crystals. The titanite overgrowth separates rutile from the bulk fluid, and all elements from rutile dissolution have to pass through the titanite rim. Trace element concentrations in titanite show a considerable scatter in experiments with and without Al, although the average concentrations of Cr or Nb of titanite around compositionally homogeneous synthetic rutile approach the expected values for closed system conditions. Variability of Al with Cr or Nb in the titanite is not correlated. The Al zoning is irregular and patchy, and also the distribution of trace elements does not show systematic trends in the spatial distribution. In experiments using zoned natural rutile, the concentrations of Nb in titanite are related to the Nb zoning in rutile, but the contents also vary unsystematically. Under the controlled conditions of the experiment, the explanation for the strongly irregular spatial distribution is most likely due to variations in elemental concentrations during transport from the rutile along the titanite grain boundaries. The transport pathway is complex because grain boundary migration is important during titanite growth. Such irregular element distribution is also found in a natural sample of titanite overgrowth on rutile from an eclogite with retrograde overprint in the amphibolite facies. Transport of Ti and trace elements was focused on grain boundaries and shielded from the rutile as a source of these elements. We conclude that this type of zoning is not related to changes in P–T or composition in an open system, but solely controlled by transport in and through the titanite rim.     

Multi-dimensional chemo-osmotic consolidation of clays

A model of chemo-osmotic consolidation of clays in multi-dimensional domains is presented, with volumetric strains induced by both changes in the chemistry and osmotically driven pore water flow considered. Three fully coupled governing equations considering force equilibrium, pore water transport and chemical transport are presented and solved using the transient finite element method. The proposed approach is verified via consideration of chemo-osmotic consolidation of a compacted clay landfill liner and then applied to investigation of a hypothetical case with a local leachate leak in the compacted clay liner. An assessment of the impact of the two-dimensional nature of the system is made. The consolidation process is found to be dominated by osmotic consolidation in the early stages and subsequently by chemical consolidation. It is found that the surface settlement and the leachate concentration in the compacted clay liner may be highly overestimated by a one-dimensional analysis. Moreover, the peak negative excess pore pressure predicted by the two-dimensional solution remains in a shallow region under the leak while in the one-dimensional solution it moves progressively downwards.     

Formulation of discontinuous deformation analysis (DDA) — an implicit discrete element model for block systems

Continuum-based numerical methods have played a leading role in the numerical solution of problems in rock mechanics and engineering geology. However, for fractured rocks, a continuum assumption often leads to difficult parameters to define and over-simplified geometry to be realistic. In such case, discrete representations of fractures and individual blocks must be adopted. In this paper, a newly emerged member in the family of discrete element methods (DEM), the discontinuous deformation analysis (DDA), is presented, including its variational principle, governing equations, solution techniques and contact representation and detection algorithms. Its relative advantages and shortcomings are compared with the explicit distinct element method and the finite element method. An example of the analysis of tunnel stability is provided to demonstrate the capability of this new method.     

Effects of orientation on the diffusive properties of fluid-filled grain boundaries during pressure solution

An unresolved issue in the study of pressure solution in rock materials is the dependence of grain boundary structure and diffusive properties on the mutual orientation of neighbouring grain lattices. We report electrical measurements yielding the diffusivity of differently oriented halite–glass and halite–halite contacts loaded in the presence of brine. The halite–glass contact experiments show pressure solution of the halite and an effect of halite lattice orientation on grain boundary transport. Post-mortem observations show an orientation-dependent grain boundary texture controlled by the periodic bond chains in the halite structure. It is inferred that this texture determines the internal grain boundary structure and properties during pressure solution. In the halite–halite experiments neck-growth occurred, its rate depending on twist-misorientation. The results imply that deformation by pressure solution may lead to lattice-preferred orientation development, and that polymineralic rocks may deform faster at lower stresses than monomineralic rocks.     

隧道开挖的双重介质水力耦合模型有限元分析

基于混合物理论孔隙-裂隙岩体的双重孔隙介质水力耦合计算的微分方程,利用伽辽金有限元法提出了相应的有限元公式,并基于岩体分类指标（RQD,RMR）提出了与岩体应变状态相关的渗透系数计算公式。编制了裂隙岩体双重介质流固耦合的2-D有限元程序,给出的验证算例表明,该程序是合理和实用的。同时将该程序用于隧道开挖的模拟计算,探讨渗流效应对开挖隧道围岩变形与渗流场的影响。计算结果表明,在隧道设计中不考虑渗流的影响是偏于不安全的。     

库车盆地铜矿化与盐丘系统的关系

库车盆地新近系发育一系列盐丘体,遥感解译和野外地貌调查共发现36个盐丘体,主要分布在南部的秋里塔格构造带和北部的克拉苏构造带,沿近东西向断裂呈带状分布.在盐丘体的发育过程中,盐丘体、围岩及围岩中发育的断裂与破碎带等构成一个盐丘体系统.调查显示铜矿化发育在盐丘体附近,位于盆地南、北两大构造带(背斜带)轴部偏两翼处,共有砂岩型、泥岩型、灰岩型3种类型,主要矿物为氯铜矿,矿化层位于上新统的康村组和中新统的吉迪克组.扫描电镜分析发现,盐丘体中盐岩样品含有自然铜、氯铜矿,表明盐丘体可以为地表铜矿化提供铜源,而卤水中的盐分来自盐丘体中盐、膏的溶解.盐丘系统不但为地表铜矿化提供铜源,而且其卤水对铜的富集、运移起到载体作用.存在于盐丘系统围岩并与后期盐丘体相伴生的断裂、节理、破碎带,为含铜卤水的迁移提供通道,盐丘体后期的构造挤压力,成为含铜卤水的运移动力.因此,盐丘系统发育过程对碎屑岩型铜矿形成起到关键性控制作用.     

多夹层盐矿水采沉渣空隙特征与储气能力评价

在低品位、多夹层盐矿地层中建设地下储库,利用水采溶腔（盐穴）底部不溶物沉渣空隙储气有望较大幅度扩大储气库库容,但需要开展沉渣空隙储气可行性和适用性评估。首先,采用不溶物沉渣制备大尺寸CT扫描试样,构建了沉渣空隙三维重构模型,定性分析了沉渣空隙尺寸和空隙连通性,发现沉渣空隙尺寸大且连通性好;其次,采用自主研制的盐矿水采沉渣储气试验装置,利用不溶物小颗粒和夹层垮塌大尺寸块体混合堆积样品进行注气排卤试验,测定注气排卤前后沉渣空隙率,分析了沉渣空隙率变化的原因;最后,建立沉渣空隙体积预测模型,提出了盐腔采动空间和沉渣可排卤水体积的计算公式。通过考虑盐层不溶物小颗粒连续堆积,又考虑夹层垮塌大尺寸块体无序堆积,计算了沉渣堆积体积及可排卤储气体积,计算结果与现场采卤数据吻合较好。该研究可为评价低品位、多夹层盐矿沉渣空隙储气能力提供参考。     

基于细观变形理论的盐岩塑性本构模型研究

唯象学本构模型不能很好解决诸如夹杂含量、温度、应变速率等对盐岩力学性质的影响,更难以解释盐岩变形机制。盐岩为石岩晶体组成,其变形机制主要由多晶结构所控制,故基于固体位错理论研究方法建立的盐岩塑性本构模型更能反映盐岩的变形机制。研究表明,盐岩的塑性-蠕变交互作用机制是（亚）晶粒内部位错的滑移与（亚）晶界及其干涉面内位错的攀移运动之间的耦合。基于此,可确定亚晶（或晶粒）平均尺寸与流动应力之间的关系、（亚）晶内的位错平均密度;建立微观参量（位错、亚晶直径、亚晶界宽度等）演化模式;根据Orowan定律建立盐岩微观-宏观变形联系,从而导出盐岩塑性本构方程。导出的本构方程体现了盐岩塑性-蠕变变形的物理机制,相对于传统的塑性本构方程具有更好的物理意义。     

东营凹陷沙四段盐湖的深水成因模式

东营凹陷下第三系沙四段广泛发育的蒸发岩类与暗色泥、页岩和深水浊积砂体呈现明显韵律层,为厚度达千米的盐湖沉积。通过分析了该地区蒸发岩地层的沉积特征和沉积条件,认为东营凹陷沙四段蒸发岩类的物质基础是深层卤水 深部古老地层中的盐类物质是其盐源 凹陷中北部的同沉积深大断裂是沟通凹陷与地壳深部盐类物质的通道。在此基础上提出东营凹陷沙四段盐湖的深水成因模式,可与东非裂谷基伍湖和东濮凹陷下第三系深水成因盐湖对比。     

HYDRATION SWELLING OF WATER-ABSORBING ROCKS: A CONSTITUTIVE MODEL

Water-absorbing rocks are formed from minerals that can hold water in their crystal structure or between grain boundaries. Such water absorption is often accompanied by a change in the crystal dimension that manifests itself as a swelling of the rock. Swelling is particularly pronounced in rocks containing phyllosilicates because of the ease with which these minerals hydrate; it is thus of geological and geotechnical relevance in shales, clay-rich soils and zeolitized tuffs. The model of hydration swelling that we present here is based on extended versions of the equations of poroelasticity and Darcy's transport law, which we derive using a non-equilibrium thermodynamics approach. Our equations account for the hydration reaction under the assumption that the reaction rate is fast in comparison with the rate at which hydraulic state changes are communicated through the rock, i.e. that local physico-chemical equilibrium persists. Using a finite-element scheme for solving numerically the governing equations of our model, we simulate the creep of shales during a routine swelling test and calculate the stress and strain distributions around wellbores drilled in shale formations that undergo swelling. We show that swelling effects promote tensile failure of the wellbore wall.