共查询到20条相似文献，搜索用时 453 毫秒
1.
三峡工程重力坝最大高度181 m,目前已蓄水至设计水位。大坝设计和施工过程中,通过特殊地质勘探、多种稳定计算方法对比分析、综合工程措施解决左岸坝段深层抗滑稳定问题;布置多层大孔口解决大流量、多任务的泄洪要求,运用钢筋混凝土有限元方法计算孔口配筋;运用二次风冷骨料、个性化动态通水、表面保温等技术进行温控防裂;采用富浆混凝土防渗、预埋冷却水管等技术进行碾压混凝土施工;采用封闭抽排方案、无盖重固结灌浆技术进行坝基处理。分析了大坝运行过程中纵缝开度变化、水位影响下坝踵应力变化的规律,提出了高重力坝在纵缝结构整体性、坝踵应力与应力控制标准、强震作用下大坝破坏机理及抗震措施等方面有待进一步研究的问题。 相似文献
2.
季节冻土区埋地管道水温的变化规律及其影响因素分析 总被引：2，自引：0，他引：2
埋地管道是减少寒冷地区冬季冻害的常用铺设方式,深入认识埋地管道的水温变化规律可以为减小管道埋设深度、降低管道冻害提供理论依据,对当前季节冻土区农牧民集中式供水工程的推进具有指导意义. 采用仿三维数值方法建立了管道水温的计算模型,讨论了含水量、地表温度、管道埋深等6个主要因素对埋地管道最不利水温的影响. 分析结果表明,无论上述因素如何变化,管道最不利水温均随输送距离的增加而下降. 首先,随着含水量的增加、地表温度的升高以及管道埋深的加深,管道的降温速率不断减小并具有先快后慢的特点;其次,随着管径的减小、流速的降低,管道降温速率增大,且降温速率和流速之间具有近似的倒数关系. 另外,随着入口温度的升高,管道降温速率将呈指数形式不断增加. 相似文献
3.
Kimberlite volcanism involves the emplacement of olivine-rich volcaniclastic deposits into volcanic vents or pipes. Kimberlite deposits are typically pervasively serpentinised as a result of the reaction of olivine and water within a temperature range of 130–400 °C or less. We present a model for the influx of ground water into hot kimberlite deposits coupled with progressive cooling and serpentisation. Large-pressure gradients cause influx and heating of water within the pipe with horizontal convergent flow in the host rock and along pipe margins, and upward flow within the pipe centre. Complete serpentisation is predicted for wide ranges of permeability of the host rocks and kimberlite deposits. For typical pipe dimensions, cooling times are centuries to a few millennia. Excess volume of serpentine results in filling of pore spaces, eventually inhibiting fluid flow. Fresh olivine is preserved in lithofacies with initial low porosity, and at the base of the pipe where deeper-level host rocks have low permeability, and the pipe is narrower leading to faster cooling. These predictions are consistent with fresh olivine and serpentine distribution in the Diavik A418 kimberlite pipe, (NWT, Canada) and with features of kimberlites of the Yakutian province in Russia affected by influx of ground water brines. Fast reactions and increases in the volume of solid products compared to the reactants result in self-sealing and low water–rock ratios (estimated at <0.2). Such low water–rock ratios result in only small changes in stable isotope compositions; for example, δO18 is predicted only to change slightly from mantle values. The model supports alteration of kimberlites predominantly by interactions with external non-magmatic fluids. 相似文献
4.
Soft‐sediment deformation of contorted and massive sandstone is common throughout much of the siliciclastic record, but clastic pipes represent a distinctive class of pressurized synsedimentary features. Remarkable centimetre to metre‐scale clastic pipe exposures in the Jurassic Navajo Sandstone of Utah (USA) establish a range of pipe sizes, expressions and relationships to the host rock in an erg margin setting, traditionally thought to be just a dry desert system. In particular, the field and laboratory characterizations of cylindrical pipes show internal concentric, annular rings that imply water fluidization, with alignment of long grain axes due to shear flow along pipe margins. Central interior parts of decimetre‐scale pipes appear massive in plan view, but display weakly developed pseudobedding from post‐pressure release, gravitational settling in the cross‐sectional view. Deformation features of conjugate fractures, ring faults, hypotrochoid patterns (geometric arcs and circles) and breccia in the host material reflect both brittle and ductile behaviour in response to the fluidization and injection of the clastic pipes. The stratigraphic context of individual pipes and the stratabound intervals of pipe features imply dynamic deformation nearly coincident with deposition in this Early Jurassic aeolian system related to multiple factors of groundwater expulsion, timing and local host sediment properties that influenced pipe development. Although the pipe features might be easily overlooked as a smaller scale feature of soft‐sediment deformation in dune deposits, these are valuable environmental indications of disrupted fluid pathways within porous, reservoir quality sands, associated with possible combinations of periodic springs, high water‐table conditions and strong ground‐motion events. These pipe examples may be important analogues where exposures are not so clear, with applications to diverse modern and ancient clastic settings internationally on Earth as well as in planetary explorations such as on Mars. 相似文献
5.
青藏铁路透壁通风管通风路基模型试验及初始温度场特征 总被引：9，自引：2，他引：7
通风路基作为一种积极主动保护冻土路基的冷却调控技术能有效的抬升多年冻土上限, 保护冻土路基的稳定性. 目前实体试验工程通风路基一般采用路基内预埋实体混凝土管或PVC管, 管壁不能透风, 管壁与土体间主要通过热传导进行换热. 一种管壁开孔、可以透风的新型通风管--"透壁通风管"既能以管内空气间的对流带走管内热量; 因其管壁透风, 低温的冷空气可以透过管壁的大孔眼穿透到通风管周围的介质中, 直接与其进行热交换, 从而改善传统通风管换热模式. 为探索透壁通风管在青藏铁路路基中的实际温控效果而进行了青藏铁路透壁通风管路基现场试验, 试验路基短期监测资料的分析结果显示, 透壁通风管对青藏铁路路基具有良好的冷却能力, 可在一定程度上抬升冻土上限; 透壁通风管路基经填土级配优化重组后更能充分发挥其路基冷却效果 相似文献
6.
Sandstone‐hosted intrusions are found in a wide variety of environments, but remain poorly understood compared with their mudstone‐hosted counterparts. In particular, they remain largely unrecognized in the subsurface, in part because they are problematic to image in seismic data. This study reports on the facies and fluid flow associated with a 20 000 km3 sandstone intrusion province in Utah, USA. Forming a small portion of this intrusion province, the intrusions cropping out in Kodachrome Basin State Park display a very wide array of facies and morphologies, factors which would make their identification in core a significant challenge. Remobilized sediment is shown to have been injected at least 200 m vertically from its source, with flow prolonged enough to concentrate heavy minerals in placer‐style deposits at the pipe margins. Evidence for lateral pipe migration and for associated broader fluidization regions is also presented. A new approach to estimating flow parameters in injectites is implemented herein, and indicates that previous work has overestimated velocities and flow Reynolds numbers by up to two orders of magnitude. Flow modelling suggests turbulent flow in the pipes that is consistent with field observations of erosive margins and chaotic internal structures. Post‐emplacement, these pipes remained as long‐term fluid conduits, as revealed by their diagenetic history, focussing and facilitating flow of extraformational fluids, despite the relatively high porosity and permeability of the aeolian host strata. 相似文献
7.
The geothermal use of concrete geostructures (piles, walls and slabs) is an environmentally friendly way of cooling and heating buildings. With such geothermal structures, it is possible to transfer energy from the ground to fluid‐filled pipes cast in concrete and then to building environments. To improve the knowledge in the field of geothermal structures, the behaviour of a pile subjected to thermo‐mechanical loads is studied in situ. The aim is to study the increased loads on pile due to thermal effects. The maximum thermal increment applied to the pile is on the order of 21°C and the mechanical load reached 1300 kN. Coupled multi‐physical finite element modelling is carried out to simulate the observed experimental results. It is shown that the numerical model is able to reproduce the most significant thermo‐mechanical effects. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
8.
Segregations that are darker than their host basalt are locally common in the Late Pleistocene Toomba Basalt flow northwest of Charters Towers. At Basalt Corner this flow has been inflated to a thickness of 17 m and segregations are displayed in pipes, sheets, veins and vesicles. Their chemical compositions are distinct from the host hawaiite and least‐square mixing solutions provide close models involving crystallisation of olivine, plagioclase, augite and magnetite in the cooling host basalt and gas‐pressure extraction of residual melt to form the segregations. Trace‐element concentrations are consistent with this mechanism and can, in general, be modelled using mineral partition coefficients from the literature. Segregations may concentrate near the edges of the inflation structures. 相似文献
9.
以港珠澳大桥珠海连接段拱北隧道为工程实例，研究管幕冻结法的温度场发展规律，基于二维多孔介质传热理论，采用有限元软件COMSOL对积极冻结期的实际工况进行数值计算，模拟结果通过现场实测验证，研究了温度场在异形冻结管开启前后的发展与分布规律。结果表明:冻结30 d时，实顶管完全被冻土包裹，并且顶管之间开始形成连续的冻土帷幕；冻结50 d时，空顶管被冻土完全包裹；冻结90 d时，实顶管和空顶管处冻土帷幕厚度达到2.0 m，满足设计要求。在异形冻结管开启前、开启后10 d内和开启后10~20 d内，两顶管间中点处温度测点的平均温度变化速率分别为-0.86℃/d，-0.88℃/d和-0.25℃/d，之后各测点温度趋于稳定，进而形成温度较为均匀的冻土帷幕。研究成果可为类似冻结工程提供技术参考。 相似文献
10.
《Sedimentology》2018,65(5):1611-1630
This study focuses on recent debate over the value of stable isotope‐based environmental proxies recorded in riverine tufa stromatolites. A twelve‐year record (1999 to 2012) of river‐bed tufa stromatolites in the River Piedra (north‐east Spain) was recovered in this study, along with a partly overlapping fifteen‐year record (1994 to 2009) of accumulations in a drainage pipe: both deposits formed in water with near identical physico/chemical parameters. Measured water temperature data and near‐constant δ 18Owater composition allowed selection of an ‘equilibrium’ palaeotemperature equation that best replicated actual temperatures. This study, as in some previous studies, found that just two published formulas for water temperature calculation from equilibrium calcite δ 18O compositions were appropriate for the River Piedra, where tufa deposition rates are high, with means between 5·6 mm and 10·8 mm in six months. The δ 18Ocalcite in both the river and the pipe deposits essentially records the full actual seasonal water temperature range. Only the coldest times (water temperature <10°C), when calcite precipitation mass decreased to minimum, are likely to be unrepresented, an effect most noticeable in the pipe where depositional masses are smaller and below sample resolution. While kinetic effects on δ 18Ocalcite‐based calculated water temperature cannot be ruled out, the good fit between measured water temperature and δ 18Ocalcite‐calculated water temperature indicates that temperature is the principal control. Textural and deposition rate variability between the river and pipe settings are caused by differences in flow velocity and illumination. In the river, calcification of growing cyanobacterial mat occurred throughout the year, producing composite dense and porous laminae, whereas in the pipe, discontinuous cyanobacterial growth in winter promoted more abiogenic calcification. High‐resolution δ 18Ocalcite data from synchronous pipe and river laminae show that reversals in water temperature occur within laminae, not at lamina boundaries, a pattern consistent with progressive increase in calcite precipitation rate as cyanobacterial growth re‐established in spring. 相似文献
11.
Hideki Shimada Saeid Khazaei Kikuo Matsui 《Geotechnical and Geological Engineering》2004,22(2):161-186
In order to protect the safety of workers construction, as well as for environmental and cost reasons, efficient small-diameter
shallow tunneling methods have recently become increasingly important in regards to outside plant engineering such as for
water supplies, electricity, telecommunications and gas. The effects of the above projects in overcrowded urban areas are
significant and often result in substantial impact and traffic delays associated with a loss of travel time. Clearly the solution
to these utility placement problems, if the full impact of trench excavation is to be avoided, is trench less technology.
In particular, for construction work near existing facilities, underground tunnels that are excavated by slurry pipe-jacking
are being increasingly employed in order to avoid problems. Slurry pipe-jacking was firmly established as a special method
for the non-disruptive construction of the underground pipelines of sewage systems. Pipe-jacking, in its traditional form,
has occasionally been used for short railways, roads, rivers, and other projects. Basically the system involves the pushing
or thrusting of a drivage machine through concrete pipes ahead of jacks. This method utilizes mud slurry that is formed around
the pipes in order to stabilize the surrounding soil. Moreover, in recent years, the rectangular shape of the concrete pipe
in using slurry pipe-jacking was introduced due to the effective uses of the space. Based on his reason, the rectangular shape
of the concrete pipe is often adopted in Japan. From this point of view, this paper discusses the effect shapes have on the
stability of surrounding soil by means of the numerical analysis. Secondly, this paper discusses the performance of the mud
slurry around the drivage pipes by means of the two-dimensional Eulerian-Lagragian seepage analysis. Moreover, in slurry pipe-jacking,
the performance of the mud slurry plays an important role in the pushing process. Finally, the thrusts in slurry pipe-jacking
can be predicted accurately by evaluating the resistance between the mud slurry and the concrete pipes and the resistance
between the soil and the pipes in the curved jacking area.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
Formation of fluidization pipes during liquefaction: examples from the Uratanna Formation (Lower Cambrian), South Australia 总被引：2，自引：0，他引：2
JEFFREY F. MOUNT 《Sedimentology》1993,40(6):1027-1037
ABSTRACT Usually well preserved fluidization pillars and sand filled fluidization pipes occur within submarine channel sands of the basal Uratanna Formation (Lower Cambrian) in the Adelaide Geosyncline of South Australia. The morphology of these structures reflects complex lateral and vertical movement of fluids during liquefaction and dewatering. Fluidization pipes acted as conduits for highly concentrated, upward directed fluid flow. The formation and maintenance of these pipes was dependent upon the development of a pipe wall composed of clay plugged fine sand. Formed during initial fluidization, this lining acted as a permeability barrier, confining and concentrating fluidized flow within the pipe. Each of the pipes is surrounded by a cylindrical fluidization halo in which leakage through the pipe lining produced partial fluidization of the surrounding sediment. Fine scale structures within these haloes indicate that fluids flowed radially and upward out of the fluidization pipes at an acute angle. These fluids merged with and influenced the orientation and size of adjacent fluidization pillars. The fluidization pipes of the Uratanna Formation may represent unusual preservation of the unstable fluid flow conditions that occur during incipient fluidization of sand beds. 相似文献
13.
14.
《Applied Geochemistry》1994,9(4):431-454
Thousands of solution-collapse breccia pipes crop out in the canyons and on the plateaus of northwestern Arizona; some host high-grade uranium deposits. The mineralized pipes are enriched in Ag, As, Ba, Co, Cu, Mo, Ni, Pb, Sb, Se, V and Zn. These breccia pipes formed as sedimentary strata collapsed into solution caverns within the underlying Mississippian Redwall Limestone. A typical pipe is approximately 100 m (300 ft) in diameter and extends upward from the Redwall Limestone as much as 1000 m (3000 ft).Unmineralized gypsum and limestone collapses rooted in the Lower Permian Kaibab Limestone or Toroweap Formation also occur throughout this area. Hence, development of geochemical tools that can distinguish these unmineralized collapse structures, as well as unmineralized breccia pipes, from mineralized breccia pipes could significantly reduce drilling costs for these orebodies commonly buried 300–360 m (1000–1200 ft) below the plateau surface.Design and interpretation of soil sampling surveys over breccia pipes are plagued with several complications. (1) The plateau-capping Kaibab Limestone and Moenkopi Formation are made up of diverse lithologies. Thus, because different breccia pipes are capped by different lithologies, each pipe needs to be treated as a separate geochemical survey with its own background samples. (2) Ascertaining true background is difficult because of uncertainties in locations of poorly-exposed collapse cones and ring fracture zones that surround the pipes.Soil geochemical surveys were completed on 50 collapse structures, three of which are known mineralized breccia pipes. Each collapse structure was treated as an independent geochemical survey. Geochemical data from each collapse feature were plotted on single-element geochemical maps and processed by multivariate factor analysis. To contrast the results between geochemical surveys (collapse structures), a means of quantifying the anomalousness of elements at each site was developed. This degree of anomalousness, named the “correlation value”, was used to rank collapse features by their potential to overlie a deeply-buried mineralized breccia pipe.Soil geochemical results from the three mineralized breccia pipes (the only three of the 50 that had previously been drilled) show that: (1) Soils above the SBF pipe contain significant enrichment of Ag, Al, As, Ba, Ga, K, La, Mo, Nd, Ni, Pb, Sc, Th, U and Zn, and depletion in Ca, Mg and Sr, in contrast to soils outside the topographic and structural rim; (2) Soils over the inner treeless zone of the Canyon pipe show Mo and Pb enrichment anf As and Ga depletion, in contrast to soils from the surrounding forest; and (3) The soil survey of the Mohawk Canyon pipe was a failure because of the rocky terrane and lack of a B soil horizon, or because the pipe plunges. At least 11 of the 47 other collapse structures studied contain anomalous soil enrichments similar to the SBF uranium ore-bearing pipe, and thus have good potential as exploration targets for uranium. One of these 11, #1102, does contain surface mineralized rock. These surveys suggest that soil geochemical sampling is a useful tool for the recognition of many collapse structures with underlying ore-bearing breccia pipes. 相似文献
15.
16.
R. G. Cawthorn C. Harris F. J. Kruger 《Contributions to Mineralogy and Petrology》2000,140(1):119-133
Discordant ultramafic pipes cut most of the layered sequence of the Bushveld Complex. We have studied one pipe in detail,
the Tweefontein pipe, which cuts the Critical Zone, eastern Bushveld Complex, because it is well-exposed in a new road cutting.
Field relations suggest that these pipes were emplaced while the layered rocks were extremely hot and incapable of brittle
failure. The existence of displaced chromitite and anorthosite fragments in this discordant body is suggestive of an intrusive magmatic, rather than metasomatic,
mode of emplacement. Initial Sr isotopic ratios of plagioclase from the pipe are in the range 0.7073 to 0.7079, which contrast
with typical ratios of 0.7055 to 0.7065 for the Critical Zone, and >0.708 for Main Zone. These data preclude an origin for
the pipe as residual magmas from the adjacent layered rocks. The compositions of, and extensive exsolution in, pyroxenes in
the pipe indicate temperatures of formation comparable to those of the layered sequence itself, and that they underwent slow
cooling comparable to the surrounding layered rocks, such that they both have similar closure temperatures. Preferential replacement
of leuconoritic layers suggests a temperature of emplacement in excess of the plagioclase–pyroxene cotectic temperature. The
per mil δ18O difference between plagioclase and pyroxene (Δplag–px) for samples from within the pipes ranges from 0.4 to 1.0, and averages 0.7 (for nine pairs), compared to Δplag–px of 0.4 to 0.6 for host rocks, again consistent with magmatic temperatures of formation. Oxygen isotope ratios for plagioclase
and pyroxene in the pipes and layered host rocks are comparable, and preclude a significant fluid contribution from metamorphosed
sediments in the floor of the Bushveld Complex in the formation of the primary mineralogy. The presence of hornblende, and
occasional higher Δplag–px values than in the normal layered sequence rocks suggest lower temperature equilibration in the pipe, probably in the presence
of a fluid. Higher absolute δ18O values for both minerals in a few of the pipe and host samples suggest reaction with a later fluid. These discordant ultramafic
pipes are considered to form by emplacement of magma batches, which are Sr-isotopically distinct from those which produced
the adjacent layered rocks of the Bushveld Complex, but were nevertheless extremely closely related in time to the main intrusive
events. Dissolution of host rocks, rather than purely mechanical dilation, provided the space for pipe emplacement. However,
the pipe may have acted ultimately as a channelway for low-temperature hydrothermal fluids related to later faulting in the
immediate vicinity.
Received: 10 October 1998 / Accepted: 22 May 2000 相似文献
17.
This paper investigates the pipe–soil interaction for pipes buried in expansive soil when subjected to swelling soil movement due to increase in moisture content. A laboratory experiment has been undertaken on a plastic pipe in a large-scale pipe box. A three dimensional numerical model is developed to analyse the pipe response, using FLAC3D computer program. The pipe is assumed to behave as a linearly elastic material, while the soil is modelled as a nonlinear material with Mohr–Coulomb failure criterion. The water flow and soil/pipe deformations are decoupled, where water flow is calculated using simplified capillary rise theory on the basis of measurements made. A reasonably good agreement between the experimental results and model predictions is reported. 相似文献
18.
Numerical modelling of concrete cracking requires robust models able to describe opening and propagation of cracks. Structural concrete codes provide practical relations to describe crack openings. However, these empirical methods were developed for specific structures and cannot be used for general applications. Here, a continuous modelling approach based on damage mechanics is used to compute crack openings in a tie‐beam concrete structure. We propose a post‐processing method to extract crack openings from a continuum damage finite element computation. This method can be applied to all continuum damage/plasticity models. The tie‐beam concrete is characterized by a weak stress gradient; this aspect complicates predictions of crack positions and number. A stochastic method is used to take into account the spatial variability in concrete properties and create a spatially correlated random property field. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
19.
富水性斜坡易产生滑坡进而形成泥石流,斜坡排水是防止地质灾害的重要手段。虹吸排水具有实时性和免动力等优势,但因斜坡排水涉及高扬程,在虹吸管内的低压环境中流动液体会发生强烈的空化现象,从而产生气液两相流。在间歇性虹吸排水过程中,如果不及时将析离的气泡带走,气泡会积聚在虹吸管顶点附近,最终破坏虹吸过程。通过对管内两相流型分析,发现只有形成完整的弹状流,才能将气泡带走,保证虹吸的长期有效。采用流体数值计算软件FLUENT的VOF模型,分别对管径为4、5、6、8 mm的虹吸管内气液两相流型进行模拟。结果表明：管径小于5 mm的条件下,表面张力起主要作用,形成完整弹状流;管径大于6 mm的条件下,形成附壁弹状流。该结论通过物理模型试验也得到证明。 相似文献
20.
本文聚焦碳酸盐岩微观渗流特性与破裂机制的研究,开展了岩石破裂过程中管道-裂隙水流动可视化试验,基于岩石块体尺度试验结果定量分析管道流体向裂隙流体过渡的流态演化过程,研究多级荷载对管道-裂隙水流动特性的影响。试验结果表明:碳酸盐岩流态稳定性与破裂状态相关,管壁破坏初期管道流主要以层流为主,局部管壁劈裂造成管道流体时域性流态交替,管道流体向裂隙流体转变的前兆特征主要表现为过渡流态临界转换点。碳酸盐岩破裂过程中管道流体向裂隙流体过渡过程具有分数演化特征,分数指数能够定量刻画管流和裂隙流的临界过渡过程。 相似文献