柱状节理坝基岩体三维各向异性数值分析

在分析柱状节理不连续性和各向异性的工程特性基础上,对某拱坝及坝基的柱状节理岩体进行三维数值模拟分析。考虑河谷初始地应力场和岩体各向异性力学性质,采用各向同性本构和各向异性弹塑性本构进行对比分析。计算表明,坝基柱状节理岩体各向异性特性对工程整体应力、变形的影响比较明显,采用各向异性弹塑性模型计算更能反映柱状节理的特殊性。其结果为该坝区岩体工程各向异性力学分析提供了示例。     

库车坳陷东部晚白垩世古隆起及构造应力场恢复

库车坳陷东部具有丰富的油气资源,其构造变形机制与南天山造山带密切相关。综合采用露头共轭节理及白垩系残余厚度分布,分析了库车坳陷东部晚白垩世古隆起特征及构造应力场属性。吐格尔明、克孜勒努尔沟、库车河、卡普沙良河、吉迪克以及库车河西6条剖面的共轭节理分析表明,库车坳陷东部新生代构造挤压应力为NNW-SSE向,而中生代的构造挤压应力为NE-SW向。原型盆地恢复显示,库车坳陷白垩纪的沉积中心大致位于大北1井―吐北2井―克拉2井一线,且发育秋里塔格―新和―牙哈―提尔根古隆起带,白垩系原始沉积厚度总体上北厚南薄。在晚白垩世区域抬升剥蚀的构造背景下,坳陷东部受压隆升遭受剥蚀,白垩系残余厚度减薄,呈西厚东薄的趋势。位于坳陷东部的吐格尔明背斜在石炭纪―三叠纪为一个长期存在的继承性沉积古隆起,晚白垩世进一步隆升形成构造古隆起,背斜周缘的白垩系残余厚度进一步减薄。吐格尔明背斜和背斜周缘白垩系残余厚度等值线以及库北1井和库车河剖面周缘白垩系残余厚度等值线的长轴方向均为NW-SE向,进一步证实了库车坳陷东部晚白垩世的构造应力为NE-SW向。库车坳陷东部晚白垩世古隆起与构造应力场属性主要与特提斯造山带中地体增生和拼贴作用导致的特提斯北缘盆地群中发生的区域性抬升有关。     

北京南口地区构造特征与虎峪水坝渗流稳定性分析

南口地区地处军都山隆起与京西丘陵平原区的过渡部位。系统的野外调查、地形地貌解析、节理统计分析,结合基岩样品显微组构研究表明,区内上口-南口断裂总体表现为正断性质,自燕山早期形成以来,其经历了由压性转变为张性的力学过程,南口地区主应力σ1在侏罗纪为NW-SE向,早白垩世以来为NEE-SWW向。上口-南口断裂最晚活动时期为晚更新世晚期,库区构造背景较不稳定。虎峪水库现今储水不满,下游地下潜流发育,是由于基岩中密集发育的节理渗流而引起的,且主要受控于早期区域NW-SE向挤压运动产生的顺河流走向节理。为了提高水库储水能力,建议对其进行防渗加固处理。     

云南泸水市压扭性构造对银厂坪白云岩岩溶系统发育控制作用

银厂坪岩溶系统由溶蚀洼地和溶洞系统组成,溶蚀洼地内发育15个规模和形态不同的落水洞以及多条溶沟。根据断层面擦痕反演构造应力张量和共轭剪节理反映的应力场特征, 结合区域地质背景,认为研究区于始新世—早中新世主要受 SEE-NWW 向挤压和 NNE-SSW 向拉张应力场控制,形成 NW 向左旋压扭性构造,其几何学和运动学特征符合里德尔剪切模式。走滑拉分阶区所形成凹陷具有汇水功能,利于岩溶作用形成溶蚀洼地,内部发育的共轭节理交汇部位是良好的导水构造,叠加在走滑微拉分阶区内,促进白云岩溶蚀作用形成落水洞。地下岩层受构造挤压发生层间滑动形成微裂隙,经溶蚀扩大,形成顺倾斜岩层发育的岩溶洞穴。左行走滑断裂造成地表河流和山脊发生系统左旋位错,发育断层崖于山脚处形成倒石堆,在构造抬升和剥蚀作用下,岩壁不断后退,地下河频繁袭夺使早期溶洞成为干洞,现代地下河于斜坡下游通过地下河出口转为明流。     

含二阶起伏体的模拟岩体节理试样剪切特性试验研究

利用规则的小尺寸锯齿构造二阶起伏体,对不同二阶起伏体高度的人工节理进行常法向应力下的直剪试验,研究了节理剪切力学特性。对节理的剪切强度、变形特征进行了分析,并对破坏特征做出解释。试验结果表明：二阶起伏体对节理剪切力学特性有重要影响,含二阶起伏体节理的剪切力学特性与只含有一阶起伏体节理的剪切力学特性不同,只含一阶起伏体的节理剪应力只有一个峰值,含二阶起伏体的节理会出现波浪状的剪胀曲线和多峰值剪应力,且峰值剪应力随剪切位移增大依次出现并逐个减小;随着二阶起伏体高度增大,节理峰值剪切强度增大,节理依次出现磨损破坏、多次性剪断破坏、一次性剪断破坏。     

The temporal relationship between joints and faults

Examples are presented of three temporal relationships between joints and faults: joints that pre-date faults; joints that are precursors to, or synchronous with, faults; and joints that post-date faults. Emphasis is placed on strike-slip faults in carbonate beds, but other examples are used. General rules are given for identifying the three temporal relationships between joints and faults. Joints that formed before faults can be dilated, sheared or affected by pressure solution during faulting, depending on their orientation in relation to the applied stress system. Faulted joints can preserve some original geometry of a joint pattern, with pinnate joints or veins commonly developing where faulted joints interact. Joints formed synchronously with faults reflect the same stress system that caused the faulting, and tend to increase in frequency toward faults. In contrast, joints that pre- or post-date faults tend not to increase in frequency towards the fault. Joints that post-date a fault may cut across or abut the fault and fault-related veins, without being displaced by the fault. They may also lack dilation near the fault, even if the fault has associated veins. Joints formed either syn- or post-faulting may curve into the fault, indicating stress perturbation around the fault. Different joint patterns may exist across the fault because of mechanical variations. Geometric features may therefore be used in the field to identify the temporal relationships between faults and joints, especially where early joints affect or control fault development, or where the distribution of late joints are influenced by faults.     

持续开挖效应下结构面剪切力学性质与能量特征研究

基于地下岩体工程开挖扰动的实际情况,开展考虑持续开挖效应,充分反映岩体结构面应力调整过程的结构面剪切试验更具理论意义和工程应用价值。采用人工劈裂方法制备岩体结构面,开展了常规应力路径和持续开挖效应下的结构面剪切试验,系统研究了两种条件下结构面剪切力学性质、声发射特征和能量的演化规律。研究结果表明：开挖扰动荷载强度越大,结构面发生剪切破坏时的剪应力降整体上越大,但持续开挖效应下的剪应力降最大值仅为常规应力路径下剪应力降的48.57%;考虑持续开挖效应的结构面剪切过程中声发射活动主要集中于结构面受剪破坏和剪应力降产生时,且声发射活动强度与开挖扰动强度正相关,声发射振铃计数变化率极值明显小于常规应力路径下的相应值;持续开挖效应下试样裂纹发育密集度、结构面磨损区域及破坏程度均随开挖扰动强度增加而增加,但试样裂纹发育的密集程度和结构面破坏程度相对常规应力路径下的情况轻;考虑持续开挖效应的结构面发生剪切破坏时弹性应变能随扰动荷载增大而增大,均低于常规应力路径条件下的弹性应变能值,持续开挖效应降低了结构面剪切破坏的强度,但更易引发结构面发生剪切破坏。     

Dynamics of sediment-laden underflows passing over a subaqueous sill: glacier-fed Peyto Lake, Alberta, Canada

The dynamic behaviour of sediment-laden underflows was examined in Peyto Lake, Alberta, Canada, which contains a midlake sill 7 m high. Sediment-laden underflows are driven by the downslope component of negative buoyant gravity multiplied by the current's thickness. Our measurements of wind, lake currents and water properties indicate that underflows pass over the sill due to the active storage of turbid suspension near the bottom in the deepest proximal region. Sill overflows occurred only when a hydrological threshold of the inflowing river was exceeded, causing quasicontinuous underflow and associated sedimentation in the distal region of the lake basin.     

Laboratory modelling of shear behaviour of soft joints under constant normal stiffness conditions

Shear behaviour of regular sawtooth rock joints produced from casting plaster are investigated under constant normal stiffness (CNS) conditions. Test results obtained in this investigation are also compared with the constant normal load (CNL) tests. It is observed that the peak shear stress obtained under CNL conditions always underestimates the peak shear stress corresponding to the CNS condition. Plots of shear stress against normal stress show that a nonlinear (curved) strength envelope is acceptable for soft rock joints subjected to a CNS condition, in comparison with the linear or bilinear envelopes often proposed for a CNL condition. Models proposed by Patton (1966) and Barton (1973) have also been considered for the predictions of peak shear stress of soft joints under CNS conditions. Although Patton's model is appropriate for low asperity angles, it overestimates the shear strength in the low to medium normal stress range at higher asperity angles. In contrast, while Barton's model is realistic for the CNL condition, it seems to be inappropriate for modelling the shear behaviour of soft joints under CNS conditions. The effect of infill material on the shear behaviour of the model joints is also investigated, and it is found that a small thickness of bentonite infill reduces the peak stress significantly. The peak shear stress almost approached that of the shear strength of infill when the infill thickness to asperity height ratio (t/a) reached 1.40. This paper also introduces an original, empirical shear strength envelope to account for the change in normal stress and surface degradation during CNS shearing. © Rapid Science Ltd. 1998     

Lithologic and structural controls on fluvial knickzones in basalts of the Paraná Basin,Brazil

Knickzones are common features along rivers on the basaltic plateaus of the Paraná Basin. According to current conceptual models, knickpoints are formed in massive basalts that have a high density of vertical joints. Vesicular–amygdaloidal basalts and those with horizontal joints tend to form reaches of low slope due to their lower resistance to erosion. However, field surveys revealed complexities in this general relationship. The research presented here sought to verify the controls on the genesis of knickzones in this type of geological environment. We studied a 61 km-long mixed bedrock–alluvial river. The longitudinal profile of the river was surveyed on a topographic map with 5 m contour intervals. Tectonic lineaments oriented transverse to the channel and longitudinal lineaments in which the river lies were identified from maps. A detailed field survey of the lithologic characteristics of the riverbed was also performed. The results show that knickzones may form in any litho-structural zone in the flood basalts. On the other hand, low slope zones are predominantly sculpted into vesicular–amygdaloidal basalts, which are less resistant to erosion. The fracture densities of vesicular–amygdaloidal basalts are similar in low slope zones and in knickzones (4.86 and 4.93 m/m², respectively). This indicates that knickzones in this type of basalt are not caused by higher resistance to erosion. Approximately 60% of the 18 knickzones identified are associated with tectonic lineaments, irrespective of the structural characteristics of the basalts. Vesicular–amygdaloidal basalt and/or basalt with horizontal joints allow the fastest knickzone migration and aid in the formation of convexities. Knickpoints in these basalts do not migrate, but erosion in the pools advances downstream and breaks the bedrock steps, thus increasing the slope. Massive basalt with vertical joints causes slower migration, and its presence at convexities indicates local uplift. Convex segments are only formed upstream of faults.     

Relations between fracture patterns, seismicity and plate motions in the Lesser Antilles

Measurements of orientations of joints that have been made on the Leeward and Windward Islands (Lesser Antilles) from St. Martin to St. Vincent are reported. The preferred orientations of the joints have been determined by a statistical analysis. Assuming the joints to be shearing phenomena, the principal directions of the stress field that caused them, can be calculated. The latter are in very good agreement with the principal stress directions obtained by a statistical analysis of fault plane solutions of earthquakes in the area; the inferred maximum compression direction being NW-SE (ca. N 130°E). This corresponds to a model which assumes that the American plate is subducted in that direction beneath the Caribbean plate.     

锦屏复杂结构谷坡应力场反演模拟与特征分析

在野外实际地质条件调查的基础上,分析整理前人对锦屏有关地应力场的实测数据、模拟计算成果,研究多种地应力反演模拟手段,结合此次应力场的模拟目的,对锦屏一级水电站的地应力场进行更为细致、全面地反演计算。以II1勘探剖面为研究对象,对其进行细致概化,形成具有复杂结构的概念模型。同时,对河流下切历史进行分析,根据各阶地的下切速度和发育时间,设计岸坡线和风化线的演化过程。通过分析锦屏构造特征、地应力数据及前人的研究成果,经多次试算后确定,在VI级阶地重力场模型上,同时施加12 MPa和8 MPa的均布应力在两个垂直边界上,所得到的拟合结果最佳。对比分析模拟结果与实测地应力数据后认为,谷底应力包的量值和分布范围都有着较高精度的拟合,与前人的计算成果也有着较大的相似性。分析锦屏现今河谷地应力场特征认为,左右岸应力非对称分布,左岸受倾坡外断层、黄斑岩脉影响,应力分布情况比右岸复杂,其应力分异强烈带、卸荷范围均比右岸深。     

Environmental significance of bedrock jointing in Southern Ontario,Canada

The bedrock surface of many glaciated areas is obscured by thick drift deposits. In southern Ontario, Canada, the buried bedrock surface is dissected by channels, infilled with glacial deposits as much as 150 m thick, that are part of a wider mid-continent preglacial fluvial system that predates formation of the modern Great Lake basins. The infills of bedrock channels form major groundwater aquifers, influence regional groundwater flows and contaminant migration to Lake Ontario, and may localize the release of thermogenic methane and radon within heavily urbanized surface environments. A quantitative comparison of the regional pattern of bedrock joints and the orientation pattern of buried bedrock channels and modern river valleys shows that all these orientation patterns are virtually coincident. Buried bedrock channels in south-central Ontario are not part of a simple antecedent drainage system but were likely predesigned by bedrock joint patterns that have subsequently been propagated upward into overlying Pleistocene sediments. Joints in sediments are of considerable environmental significance (for example, subsurface contaminant and gas migration in fine-grained clayey sediments) and of many origins (stress release, desiccation, etc.) but are widely assumed to be a predominantly surface-related phenomena; the existence of deeper joints has been noted by some authors but their origin is obscure. Data presented herein from south-central Ontario confirm that, in addition to surface-related joints, a second population of bedrock-related joints, reflecting the upward propagation of bedrock fractures, is present in Pleistocene sediments of south-central Ontario.     

岩石节理在固定法向压力刚度条件下的剪切理论研究

节理在固定法向压力刚度（CNS）条件下的剪切过程比较复杂,剪切中由于剪胀的存在使得法向压力增大,而法向压力的增加又限制了剪胀的发生。根据CNS剪切过程中某一瞬时状态下法向压应力大小,以节理在该法向压应力下法向剪胀位移与剪切位移的关系为基础,建立一个楔形物理模型。通过循环迭代求得CNS剪切过程中每一步的法向压应力值,进而得到整个过程的剪切应力值。通过该模型,讨论了节理各参数对CNS剪切过程的影响,结果表明,其剪切应力值受法向压应力刚度与节理法向变形参数共同协调控制（包括单轴压缩变形及剪胀角的磨损）,节理在剪切过程中越不易发生压缩变形,其剪切应力值越大。     

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.     

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.     

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.     

Joint initiation in bedded clastic rocks

Two general types of sedimentary structures serve as initiation points (IP) for cross-fold joints in siltstone beds of the Ithaca Formation, Appalachian Plateau, New York: planar bed boundaries and geometrically complex features such as bedforms, trace fossils, and soft-sediment deformation structures. The relative abundance of each IP type varies with the stratigraphic position of the jointed body. When they are mechanically isolated by thicker shales, siltstone bodies have a higher percentage of IP associated with complex features. This association supports the hypothesis that sedimentary structures serve to concentrate stress, thus becoming preferred sites for primary joint initiation. Secondary joint initiation occurs at planar bed boundaries through interaction with pre-existing joints in adjacent siltstone beds that are mechanically coupled to form composite joints. The propagation path of joints passing through planar bed boundaries of composite joints can be traced backward to primary IP at complex sedimentary structures. Modeling suggests that when beds are mechanically coupled, the modest joint-tip stress concentration across a shale layer (e.g., < 3× for a 1-cm thick bed) is equivalent to the stress concentration in the vicinity of a bedform. Consequently, in mechanically coupled siltstone beds, sedimentary structures such as bedforms compete with pre-existing joint tips in adjacent beds to initiate new joint segments.     

Recognition of strong seasonality and climatic cyclicity in an ancient,fluvially dominated,tidally influenced point bar: Middle McMurray Formation,Lower Steepbank River,north‐eastern Alberta,Canada

Inclined heterolithic stratification in the Lower Cretaceous McMurray Formation, exposed along the Steepbank River in north‐eastern Alberta, Canada, accumulated on point bars of a 30 to 40 m deep continental‐scale river in the fluvial–marine transition. This inclined heterolithic stratification consists of two alternating lithologies, sand and fine‐grained beds. Sand beds were deposited rapidly by unidirectional currents and contain little or no bioturbation. Fine‐grained beds contain rare tidal structures, and are intensely bioturbated by low‐diversity ichnofossil assemblages. The alternations between the sand and fine‐grained beds are probably caused by strong variations in fluvial discharge; that are believed to be seasonal (probably annual) in duration. The sand beds accumulated during river floods, under fluvially dominated conditions when the water was fresh, whereas the fine‐grained beds accumulated during the late stages of the river flood and deposition continued under tidally influenced brackish‐water conditions during times of low‐river flow (i.e. the interflood periods). These changes reflect the annual migration in the positions of the tidal and salinity limits within the fluvial–marine transition that result from changes in river discharge. Sand and fine‐grained beds are cyclically organized in the studied outcrops forming metre‐scale cycles. A single metre‐scale cycle is defined by a sharp base, an upward decrease in sand‐bed thickness and upward increases in the preservation of fine‐grained beds and the intensity of bioturbation. Metre‐scale cycles are interpreted to be the product of a longer term (decadal) cyclicity in fluvial discharge, probably caused by fluctuations in ocean or solar dynamics. The volumetric dominance of river‐flood deposits within the succession suggests that accumulation occurred in a relatively landward position within the fluvial–marine transition. This study shows that careful observation can reveal much about the interplay of processes within the fluvial–marine transition, which in turn provides a powerful tool for determining the palaeo‐environmental location of a deposit within the fluvial–marine transition.     

节理角度对预裂爆破成缝效果的影响研究

预裂爆破的现场实践表明,诸如节理、软弱夹层和断层等地质不连续面是影响预裂爆破效果的一个重要因素。运用LS-DYNA 3D程序研究了不同角度的节理对预裂爆破效果的影响。通过数值模拟发现,岩体中节理的存在对预裂爆破效果影响显著,其吸收应力波能量并阻碍应力波的传播,且影响预裂缝产状。研究结果表明,节理附近的预裂缝大多沿节理垂直方向开裂,逐渐与被破坏节理连接,节理夹角较小时,易形成锯齿状裂缝,且较难贯通。随着节理与炮孔连线夹角的增大,应力波在节理处的透射率越大,节理附近位置上的质点振速也越大,预裂缝更趋于平直且更易贯通。当节理垂直炮孔连线时透射率最大,所形成的预裂缝与炮孔连线基本重合,不会出现锯齿形裂缝,相对成缝效果最佳。