四合屯—大康保地区义县组火山—沉积岩地质特征

四合屯－大康堡地区所出露的义县组火山－沉积岩可分为上、中、下3个层位。下部层位是以玄武质、玄武安山岩质以及安山质火山岩类为主的基性、中基性火山－沉积岩;中部是以流纹质及英安质火山岩为主的中酸性火山－沉积岩;而义县组的上部层位是以玄武岩、玄武玢岩为代表的基性火山岩。薄层状的沉凝灰岩、凝灰质粉砂岩及钙质页岩等作为火山活动间歇期的产物,常不同程度地发育于义县组火山溶岩或集块岩的底部。野外工作发现：在义县组下部层位的沉凝灰岩层中发育有以鹦嘴龙为主的古脊椎动物类化石;四合屯－大康堡一带富含有热河生物群化石的沉积层属义县组火山－沉积岩系的中部层位。稀土元素分析表明,在相同层位的火山－沉积岩岩,沉凝灰岩,凝灰质粉砂岩和钙质页岩及其与火山熔岩存在密切的相关性;而不同层位间则存在一定的差异性。稀土元素配分特征不反映出,不同的义县组火山－沉积岩内、凝灰质粉砂岩和钙质页岩及其与火山溶岩存在密切的相关性;而不同层位间则存在一定的差异性。稀土元素分特征还反映出,不同的义县组火山－沉积岩层位之间具有相似的物源关系。     

季节性河流体系高流态沉积构造特征:以内蒙古岱海湖半滩子河为例*

高流态尤其是超临界流动的水动力学机制及其床沙底形演化的研究相较于次临界流动具有一定的差距。季节性河流以高流态为主要沉积搬运过程,为超临界流的形成与保存提供了有利条件,是研究超临界流沉积的重要载体。在季节性河流沉积体系研究进展调研基础上,明确了其基本定义、判别标准及沉积特征。通过对内蒙古岱海湖北部典型季节性冲积体系——半滩子河流发育的沉积构造进行研究表明:随着低流态向高流态演化,沙丘底形(Dune)逐步向上部平坦床沙底形(Upper plane bed)过渡,形成了低角度/S型交错层理;在高流态初期,形成了上部平坦床沙成因的平行层理;随着流动强度逐渐增大,流动机制演变为超临界流,平坦床沙逐渐向逆行沙丘(Antidune)过渡,形成了与平行层理伴生的逆行沙丘交错层理;当流动强度进一步增大,携带沉积物的流体发生较强的水力跳跃,形成了流槽与冲坑(Chute-and-Pool)。半滩子河流现代沉积中发育的高流态沉积与区域内气候变化具有明确的响应关系,表明河流沉积中广泛发育的高流态沉积构造指示了强烈季节性变化的气候特征。     

The Planar Shape of Rock Joints

Knowing the planar shape of discontinuities is important when characterizing discontinuities in a rock mass. However, the real discontinuity shape is rarely known, since the rock mass is usually inaccessible in three dimensions. Information on discontinuity shape is limited and often open to more than one interpretation. This paper discusses the planar shape of rock joints, the most common discontinuities in rock. First, a brief literature review about the shape of joints is presented, including some information on joint-surface morphology, inferences from observed trace lengths on different sampling planes, information based on experimental studies, and joint shapes assumed by different researchers. This review shows that joints not affected by adjacent geological structures such as bedding boundaries or pre-existing fractures tend to be elliptical (or approximately circular but rarely). Joints affected by or intersecting such geological structures tend to be rectangular. Then, using the general stereological relationship between trace length distributions and joint size distributions developed by Zhang et al. (Geotechnique 52(6):419–433, 2002) for elliptical joints, the effect of sampling plane orientation on trace lengths is investigated. This study explains why the average trace lengths of non-equidimensional (elliptical or similar polygonal) joints on two sampling planes can be about equal and thus the conclusion that rock joints are equidimensional (circular) drawn from the fact that the average trace lengths on two sampling planes are approximately equal can be wrong. Finally, methods for characterizing the shape and size of joints (elliptical or rectangular) from trace length data are recommended, and the appropriateness of using elliptical joint shapes to represent polygonal, especially rectangular, joints is discussed.     

Morphodynamics and sedimentary structures of bedforms under supercritical‐flow conditions: New insights from flume experiments

Supercritical‐flow phenomena are fairly common in modern sedimentary environments, yet their recognition and analysis remain difficult in the stratigraphic record. This fact is commonly ascribed to the poor preservation potential of deposits from high‐energy supercritical flows. However, the number of flume data sets on supercritical‐flow dynamics and sedimentary structures is very limited in comparison with available data for subcritical flows, which hampers the recognition and interpretation of such deposits. The results of systematic flume experiments spanning a broad range of supercritical‐flow bedforms (antidunes, chutes‐and‐pools and cyclic steps) developed in mobile sand beds of variable grain sizes are presented. Flow character and related bedform patterns are constrained through time‐series measurements of bed configurations, flow depths, flow velocities and Froude numbers. The results allow the refinement and extension of some widely used bedform stability diagrams in the supercritical‐flow domain, clarifying in particular the morphodynamic relations between antidunes and cyclic steps. The onset of antidunes is controlled by flows exceeding a threshold Froude number. The transition from antidunes to cyclic steps in fine to medium‐grained sand occurs at a threshold mobility parameter. Sedimentary structures associated with supercritical bedforms developed under variable aggradation rates are revealed by means of combining flume results and synthetic stratigraphy. The sedimentary structures are compared with examples from field and other flume studies. Aggradation rate is seen to exert an important control on the geometry of supercritical‐flow structures and should be considered when identifying supercritical bedforms in the sedimentary record.     

Sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice‐contact fan deposits: A Pleistocene example (Ireland)

A pit located near Ballyhorsey, 28 km south of Dublin (eastern Ireland), displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice‐contact fan deposits. The coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies. The lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space, mainly controlled by the position of an overlying ice roof during ice‐bed decoupling. These sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments. The sorted sediments consist of fine‐grained laminated facies, cross‐laminated sand and channelized gravels, and are interpreted as subglaciofluvial sediments deposited within a subglacial de‐coupled space. The subglaciofluvial sequence is characterized by glaciotectonic deformation structures within discrete beds, triggered by fluid overpressure and shear stress during episodes of ice/bed recoupling (clastic dykes and folds). The upper deposits correspond to the deposition of successive hyperpycnal flows in a proximal proglacial lake, forming a thick sedimentary wedge erosively overlying the subglacial deposits. Gravel facies and large‐scale trough bedding sand are observed within this proximal wedge, while normally graded sand beds with developed bedforms are observed further downflow. The building of the prograding ice‐contact subaqueous fan implies an unrestricted accommodation space and is associated with deformation structures related to gravity destabilization during fan spreading (normal faults). This study facilitates the recognition of subglacial/submarginal depositional environments formed, in part, during localized ice/bed coupling episodes in the sedimentary record. The sedimentary sequence exposed in Ballyhorsey permits characterization of the temporal framework of meltwater production during deglaciation, the impact on the subglacial drainage system and the consequences on the Irish Sea Ice Stream flow mechanisms.     

Control of bioclast abundance on natural joint density in carbonate rocks: data from Oman, Provence and Languedoc (France)

Joint density in sedimentary rocks is highly dependent on many factors such as tectonic stress, fluid pressure, interbedded layers and bed thickness. Data from Cretaceous carbonate rocks in Oman, Provence and Languedoc (France) show that bed thickness has a general control on joint density in all areas but other parameters also influence joint density. In order to understand the influence of textural parameters on volume joint density, all joint sets were measured in several beds. Data show that joint density decreases when the percentage of figured grains increases in Oman and Provence but that this relationship is more complex in Languedoc. The major textural parameter controlling joint density is the percentage of bioclasts: joint density decreases with an increase of the percentage of bioclasts in the three sectors.     

Joints in the Mesozoic sediments around the Bristol Channel Basin

Analysis has been carried out at four locations on the edges of the Bristol Channel Basin to illustrate the later phases of deformation of a sedimentary basin, and to illustrate the control on joint patterns of subtle changes in the stress system. The characteristics of the joints are described and influences on joints are determined, including the roles of faults, folds and beds. There is a low coefficient of correlation between joint spacing and bed thickness, except in very thin limestone beds, which have a high density of joints. The lengths and spacings of earlier joint phases are usually greater than those of later phases. Later joints normally abut against earlier joints.The joints abut the latest faults but are not displaced by them, so the joints post-date the main Alpine contraction. The joints formed in five main phases during reduction of the Alpine stresses. Phase 1 joints are sub-parallel to the regional compression direction (160–180°). Phase 2 joints are perturbed by faults, often curving towards points of stress concentrations along the faults. Phase 3 joints are sub-parallel to the earlier E–W-striking fold axes. Phase 4 joints are cross-joints, and phase 5 joints form polygonal patterns within joint-bound blocks. Phases 2 and 3 do not occur in the absence of faults and folds, and correspond with a reduction in horizontal compression and an increase in the importance of local factors. Phases 4 and 5 occur at all locations.     

Joint development during fluctuation of the regional stress field in southern Israel

Four trends of joint sets (WNW–ESE, NW–SE, NNW–SSE and NE–SW) are found in upper Turonian carbonate rocks within the Neqarot syncline of south-central Israel. The two most predominant sets strike parallel to the trend of maximum compressive stress directions (S_H) associated with the plate-related Syrian Arc stress field (SAS; WNW–ESE) active during the Cretaceous to present and the perturbed regional stress field (NNW–SSE) related to stress accumulation on the Dead Sea Transform during the Miocene to the present. Eighty-two percent of the beds in this study contain joints parallel with the latter trend, whereas 42% contain joints parallel to the former trend. All beds with layer thickness to spacing ratio (FSR)>1.5 have NNW–SSE joint sets compatible with the Dead Sea Transform stress field (DSS), whereas all joints sets that are not compatible with the DSS stress field fall beneath this value for FSR. Considering lithology, joints in five of six chalky limestone beds and all marly limestone beds are compatible with the DSS, whereas joints compatible with the SAS do not develop in these marly and chalky limestone beds. In the study area, the joint sets lack a consistent formation sequence where more than one set is found in a single bed. We use these observations to conclude that all studied joints are Miocene or younger, that the regional stress field from the Miocene to the present fluctuated, between DSS and SAS states, and that the higher FSRs correspond to a greater amount of joint-normal strain in response to the DSS.     

Cambrian sedimentary dykes in the Proterozoic basement of the Västervik area (southeast Sweden): episodic formation inferred from macro- and microfabrics

Fabrics of Cambrian sedimentary dykes formed in Proterozoic granites of the Västervik area (Southeast Sweden) evidence repeated opening/filling and mineralisation/cementation events under varying conditions. Diagnostic features include (1) wall-parallel boundaries between epiclastic fillings and (2) early formed dyke sediments that appear as lithoclasts in subsequently formed sedimentary fillings. The psammitic components mostly consist of well-rounded quartz grains related to a coastal environment and fragments from the granitic host rock. Platy calcitic fragments embedded in the epiclastic matrix originally formed as microveins within already-lithified dyke sediments and the adjacent host rock. Convex downward-pointing, internal sagging structures, together with the preferred orientation of compositional boundaries and long axes of grains/rock fragments parallel to the dyke walls, are interpreted as the result of suction-controlled flow of unconsolidated fillings during episodes of downward dyke growth. Pressure solution of quartz grains are evidence of extensional phases with dyke propagation that were interrupted by phases of horizontal compression normal to the dyke walls. The N–S and NE–SW striking sedimentary dykes formed by opening of a pre-existing joint set during NW–SE oriented rifting during the Cambrian.     

A unified model for bedform development and equilibrium under unidirectional,oscillatory and combined‐flows

The development of bedforms under unidirectional, oscillatory and combined‐flows results from temporal changes in sediment transport, flow and morphological response. In such flows, the bedform characteristics (for example, height, wavelength and shape) change over time, from their initiation to equilibrium with the imposed conditions, even if the flow conditions remain unchanged. These variations in bedform morphology during development are reflected in the sedimentary structures preserved in the rock record. Hence, understanding the time and morphological development in which bedforms evolve to an equilibrium stage is critical for informed reconstruction of the ancient sedimentary record. This article presents results from a laboratory flume study on bedform development and equilibrium development time conducted under purely unidirectional, purely oscillatory and combined‐flow conditions, which aimed to test and extend an empirical model developed in past work solely for unidirectional ripples. The present results yield a unified model for bedform development and equilibrium under unidirectional, oscillatory and combined‐flows. The experimental results show that the processes of bedform genesis and growth are common to all types of flows, and can be characterized into four stages: (i) incipient bedforms; (ii) growing bedforms; (iii) stabilizing bedforms; and (iv) fully developed bedforms. Furthermore, the development path of bedform; growth exhibits the same general trend for different flow types (for example, unidirectional, oscillatory and combined‐flows), bedform size (for example, small versus large ripples), bedform shape (for example, symmetrical or rounded), bedform planform geometry (for example, two‐dimensional versus three‐dimensional), flow velocities and sediment grain sizes. The equilibrium time for a wide range of bed configurations was determined and found to be inversely proportional to the sediment transport flux occurring for that flow condition.     

Bedform and stratification characteristics of some modern small-scale washover sand bodies

Washover sand bodies commonly develop along microtidal coastlines in beach/barrier island or spit settings. Wave runup, usually in conjunction with an abnormally high water level, may overtop the most landward berm of the beach and the foredune crest, if one exists, to produce overwash and subsequent runoff across the more landward subaerial surface. Two main elements of the resulting deposit are the washover fan and runoff channel. Newly formed, small-scale washover deposits were examined along the Outer Banks, North Carolina, near Pt Mugu, California, and at Presque Isle (Lake Erie), Pennsylvania. The fans were formed in response to unidirectional landward transport, and the runoff channels in response to unidirectional flow usually in a landward direction, but sometimes in shore-parallel then seaward direction. Where overwash carried across the fan surface and entered a pond or lagoon, a small-scale delta (microdelta) developed. In this case, the washover fan consisted of two subfacies, the wetted, but ‘subaerial’ part of the fan and the subaqueous washover delta. Flow associated with the development of the fan and runoff channel produced distinctive sets of bedforms and internal stratification. High velocity discontinuous surges moving across the fan surface resulted in the development of a plane bed and subhorizontal to low-angle (landward dipping) planar stratification which comprised the major part of the fan. Similarly, rhomboid forms were produced by high velocity sheet flow across the fan surface. Where flow carried into a standing body of water, delta-type foreset strata developed. For this case, the lateral structural sequence was subhorizontal, planar stratification merging landward into landward dipping, delta (tabular) foreset strata. In the runoff setting, where flow became channelized and continuous, both upper-flow and lower-flow regime currents were typical. Upper-flow regime bedforms included antidunes, standing waves, and plane beds. The most commonly observed lower-flow regime bedforms included microdelta-like bars, low-amplitude bars, linguoid ripples, and sinuous-crested current ripple trains. The sets of sedimentary structures comprising modern washover sand bodies provide criteria for the identification of similar deposits in ancient sediments and for more specific interpretation of the environment.     

Shallow-water gravity-flow deposits, Chapel Island Formation, southeast Newfoundland, Canada

A remarkable suite of shallow-water, gravity-flow deposits are found within very thinly-bedded siltstones and storm-generated sandstones of member 2 of the Chapel Island Formation in southeast Newfoundland. Medium to thick siltstone beds, termed unifites, range from non-graded and structureless (Type 1) to slightly graded with poorly developed lamination (Type 2) to well graded with lamination similar to that described for fine-grained turbidites (Type 3). Unifite beds record deposition from a continuum of flow types from liquefied flows (Type 1) to turbidity currents (Type 3). Calculations of time for pore-fluid pressure dissipation support the feasibility of such transitions. Raft-bearing beds consist of siltstone with large blocks or‘rafts’ of thinly bedded strata derived from the underlying and adjacent substrate. Characteristics suggest deposition from debris flows of variable strength. Estimates of debris strength and depositional slope are calculated for a pebbly mudstone bed using measurable and assumed parameters. An assumed density of 2.0 g cm^-1 and a compaction estimate of 50% gives a strength estimate of 79.7 dyn cm^-2 and a depositional slope estimate of 0.77°. The lithologies and sedimentary structures in member 2 indicate an overall grain-size distribution susceptible to liquefaction. Inferred high sediment accumulation rates created underconsolidated sediments (metastable packing). Types of sediment failure included in situ liquefaction (‘disturbed bedding’), sliding and slumping. Raft-bearing debrites resulted from sliding and incorporation of water. Locally, hummocky cross-stratified sandstone directly overlies slide deposits and raft-bearing beds, linking sediment failure to the cyclical wave loading associated with large storms. The gravity flows of the Chapel Island Formation closely resemble those described from the surfaces of modern, mud-rich, marine deltas. Details of deltaic gravity-flow deposition from this and other outcrop studies further our understanding of modern deposits by adding a third dimension to studies primarily carried out with side-scan sonar.     

Bed shear stress over subaqueous dunes, and the transition to upper-stage plane beds

Plane beds that replace small bedforms (e.g. ripples) on the backs of subaqueous dunes are dynamically similar to upper-stage plane beds. Local bed shear stresses at the position on dunes where plane beds develop may be two to three times larger than on a completely plane bed under the same general hydraulic conditions. These observations help explain the transition from dunes to a wholly upper-stage plane bed.     

Froude supercritical flow bedforms in deepwater slope channels? Field examples in conglomerates,sandstones and fine‐grained deposits

Active margin continental slope outcrops from the Eocene Juncal Formation, the Eocene La Jolla Group and the Miocene Capistrano Formation display sedimentary structures and depositional geometries that suggest deposition from Froude supercritical flow, based on comparison to strata produced by flume experiments. These deposits range from boulder‐size soft clasts and cobble‐size hard clasts to silt and mud, and display long‐wavelength and low‐amplitude convex‐up and concave‐up geometries that range from centimetre to hundreds of metres scale, low‐angle foresets and backsets, and common internal and bounding erosion surfaces from centimetres to tens of metres in depth. In places, planar laminations, structureless beds and normally graded beds are laterally or vertically associated with such structures. In other places, consistent backsets or deep and steep‐sided scours occur. This study aimed to discuss the origin of the observed bedforms, contributed to recognition of supercritical flow deposits on continental slopes and expanded the outcrop examples of supercritical flow deposits to silt and mud. This work implies that the erosive and powerful Froude supercritical flow turbidity currents may have a substantial impact on erosional and depositional dynamics on deepwater slopes, especially on active margins due to the steep gradients and high sediment supply.     

Fractal properties of simulated bed profiles in coarse-grained channels

Bed roughness characteristics in coarse-grained channels are fairly complex. A hierarchy of roughness elements can be observed, ranging from variable particle sizes and shapes and small-scale sedimentary structures, to large-scale bedforms such as riffle-pool sequences. The effects of these scales of roughness on the flow geometry still remain to be thoroughly investigated. The semivariogram has been suggested in the past as a means of quantifying bed roughness effects on streamflow, as well as for distinguishing between scales of roughness. However, field measurements are rather time-consuming. The low number of bed profiles measured in the field precludes the identification of generally applicable relationships between the statistical properties derived from the semivariograms (such as the Hausdorff dimensions and the scale of autocorrelation corresponding to each fractal band) and the bed configuration itself (geometrical and sedimentological properties). Simulation results of gravel-bed profiles are, therefore, presented in order to complement the original investigation of Robert (1988a). The simulation experiments, based on grain characteristics of sizes and shapes and on morphological properties of small-scale bedforms, yield very significant information on boundary roughness at the microscale and give insight into the interpretation of empirical semivariograms (derived from field measurements). Bed-material sorting, variable grain shapes, and height and spacing of cluster bedforms control the fractal dimensions obtained from the semivariograms, as well as the location of the break of slope and the range of the process.     

Upper flow regime sheets, lenses and scour fills: Extending the range of architectural elements for fluvial sediment bodies

Fluvial strata dominated internally by sedimentary structures of interpreted upper flow regime origin are moderately common in the rock record, yet their abundance is not appreciated and many examples may go unnoticed. A spectrum of sedimentary structures is recognised, all of which occur over a wide range of scale: 1. cross-bedding with humpback, sigmoidal and ultimately low-angle cross-sectional foreset geometries (interpreted as recording the transition from dune to upper plane bed bedform stability field), 2. planar/flat lamination with parting lineation, characteristic of the upper plane bed phase, 3. flat and low-angle lamination with minor convex-upward elements, characteristic of the transition from upper plane bed to antidune stability fields, 4. convex-upward bedforms, down- and up-palaeocurrent-dipping, low-angle cross-bedding and symmetrical drapes, interpreted as the product of antidunes, and 5. backsets terminating updip against an upstream-dipping erosion surface, interpreted as recording chute and pool conditions. In some fluvial successions, the entirety or substantial portions of channel sandstone bodies may be made up of such structures. These Upper Flow Regime Sheets, Lenses and Scour Fills (UFR) are defined herein as an extension of Miall's [Miall, A.D., 1985. Architectural-element analysis: a new method of facies analysis applied to fluvial deposits. Earth Sci. Rev. 22: 261–308.] Laminated Sand Sheets architectural element. Given the conditions that favour preservation of upper flow regime structures (rapid changes in flow strength), it is suggested that the presence of UFR elements in ancient fluvial successions may indicate sediment accumulation under the influence of a strongly seasonal palaeoclimate that involves a pronounced seasonal peak in precipitation and runoff.     

Pyroclastic dune bedforms: macroscale structures and lateral variations. Examples from the 2006 pyroclastic currents at Tungurahua (Ecuador)

Pyroclastic currents are catastrophic flows of gas and particles triggered by explosive volcanic eruptions. For much of their dynamics, they behave as particulate density currents and share similarities with turbidity currents. Pyroclastic currents occasionally deposit dune bedforms with peculiar lamination patterns, from what is thought to represent the dilute low concentration and fluid‐turbulence supported end member of the pyroclastic currents. This article presents a high resolution dataset of sediment plates (lacquer peels) with several closely spaced lateral profiles representing sections through single pyroclastic bedforms from the August 2006 eruption of Tungurahua (Ecuador). Most of the sedimentary features contain backset bedding and preferential stoss‐face deposition. From the ripple scale (a few centimetres) to the largest dune bedform scale (several metres in length), similar patterns of erosive‐based backset beds are evidenced. Recurrent trains of sub‐vertical truncations on the stoss side of structures reshape and steepen the bedforms. In contrast, sporadic coarse‐grained lenses and lensoidal layers flatten bedforms by filling troughs. The coarsest (clasts up to 10 cm), least sorted and massive structures still exhibit lineation patterns that follow the general backset bedding trend. The stratal architecture exhibits strong lateral variations within tens of centimetres, with very local truncations both in flow‐perpendicular and flow‐parallel directions. This study infers that the sedimentary patterns of bedforms result from four formation mechanisms: (i) differential draping; (ii) slope‐influenced saltation; (iii) truncative bursts; and (iv) granular‐based events. Whereas most of the literature makes a straightforward link between backset bedding and Froude‐supercritical flows, this interpretation is reconsidered here. Indeed, features that would be diagnostic of subcritical dunes, antidunes and ‘chute and pools’ can be found on the same horizon and in a single bedform, only laterally separated by short distances (tens of centimetres). These data stress the influence of the pulsating and highly turbulent nature of the currents and the possible role of coherent flow structures such as Görtler vortices. Backset bedding is interpreted here as a consequence of a very high sedimentation environment of weak and waning currents that interact with the pre‐existing morphology. Quantification of near‐bed flow velocities is made via comparison with wind tunnel experiments. It is estimated that shear velocities of ca 0·30 m.s^?1 (equivalent to pure wind velocity of 6 to 8 m.s^?1 at 10 cm above the bed) could emplace the constructive bedsets, whereas the truncative phases would result from bursts with impacting wind velocities of at least 30 to 40 m.s^?1.     

Effects of in-situ stress and joint on permeability of the coal bed in Linfen block,southeastern Ordos Basin,China

Effects of in-situ stress and joint on permeability of the coal bed depend on orientation relationships between in-situ stress and joint. In-situ stress orientations of Linfen block of southeastern Ordos Basin were determined by systematical measurements of the loess joints. In-situ stress magnitudes were calculated based on well logging and hydraulic fracturing data. Joint orientations of the No. 5 coal bed and density distributions of the overlying sandstone bed were investigated. The results show that the NE-oriented maximum horizontal principal stress, approximately parallel to the predominant joint orientation of the coal bed, is favorable to the openness of the predominant joints. The minimum horizontal principal stress, with its orientation perpendicular to the predominant joint orientation, tends to induce the closure of the predominant joints. The stress state of No. 5 coal bed is o_v > 0_H > O_h, which is favorable for the openness of subvertical joints and an increase in the permeability. The permeability of No. 5 coal bed increases obviously with increasing effective vertical stress and effective horizontal maximum stress and decreases with increasing effective horizontal minimum stress. Besides, the permeability of No. 5 coal bed exhibits a good exponential relationship with the density of predominant joint set. Therefore, predominant joints with the orientation of 45° mainly contribute to increases in the permeability of the No. 5 coal bed in Linfen block. Multidimensional analysis show good exponential relationships among the permeability, predominant joint density, and effective stress of the No. 5 coal bed.     

红层泥岩水岩作用特征研究

红层是红色陆相沉积为主的碎屑沉积岩层,岩性以砂岩、泥岩、粉砂岩和页岩为主。该类岩层多为软岩与硬岩相间,呈互层状产出,层间结合力弱。受区域构造影响,岩层扭曲褶皱强烈,多中高倾角,结构面发育,有泥化现象。红层中的泥岩具有透水性弱、亲水性强,遇水易软化、塑变,抗风化能力弱,易崩解等特性。特别是遇水后岩体及结构面抗剪强度大幅度降低,并且具有遇水膨胀、失水收缩的工程特性。水岩作用对边坡的影响主要有,结构面遇水泥化导致楔形体失稳,泥岩塑性变形引起边坡蠕变,同时红层还具有很强的崩解性,边坡开挖后发生崩解等现象。