基于COMSOL的地下水封油库围岩流固耦合特征模拟研究

地下水封油库通常建造于完整性好的结晶岩体内部,利用隙存水封的原理将油气封闭于地下洞室内部,洞库围岩在施工及运营期间具有典型的流固耦合特征。论文基于裂隙岩体流固耦合理论,采用COMSOL Multiphysics 软件对洞库围岩不同工况下流固耦合特征进行了模拟研究。研究结果表明:地下洞库在不设置人工水幕情况下,开挖后洞室顶部地下水位明显下降,并形成降落漏斗,可能导致洞室油气外溢; 设置人工水幕后,洞室顶部地下水位下降趋势得到明显控制,有效确保了水封的可靠性; 在设置水幕的情况下,洞室直墙及洞室拱顶与底板角点处出现明显的应力集中,但围岩仍未出现连贯塑性区,洞室最大位移不超过5mm,洞室围岩稳定性良好。分析成果对于指导洞库优化设计及施工具有一定的参考价值。     

Features of the accretion in the EX Hydrae system: Results of numerical simulation

A two-dimensional numerical model in the axisymmetric approximation that describes the flow structure in the magnetosphere of the white dwarf in the EX Hya system has been developed. Results of simulations show that the accretion in EX Hya proceeds via accretion columns, which are not closed and have curtain-like shapes. The thickness of the accretion curtains depends only weakly on the thickness of the accretion disk. This thickness developed in the simulations does not agree with observations. It is concluded that the main reason for the formation of thick accretion curtains in the model is the assumption that the magnetic field penetrates fully into the plasma of the disk. An analysis based on simple estimates shows that a diamagnetic disk that fully or partially shields the magnetic field of the star may be a more attractive explanation for the observed features of the accretion in EX Hya.     

Numerical simulation and land subsidence control for deep foundation pit dewatering of Longyang Road Station on Shanghai Metro Line 18

In terms of controlling groundwater in deep foundation pit projects, the usual methods include increasing the curtain depth, reducing the amount of pumped groundwater, and implementing integrated control, in order to reduce the drawdown and land subsidence outside pits. In dewatering design for confined water, factors including drawdown requirements, the thickness of aquifers, the depth of dewatering wells and the depth of cutoff curtains have to be considered comprehensively and numerical simulations are generally conducted for calculation and analysis. Longyang Road Station on Shanghai Metro Line 18 is taken as the case study subject in this paper, a groundwater seepage model is developed according to the on-site engineering geological conditions and hydrogeological conditions, the excavation depth of the foundation pit as well as the design depth of the enclosure, hydrogeological parameters are determined via the pumping test, and the foundation pit dewatering is simulated by means of the three-dimensional finite difference method, which produces numerical results that consistent with real monitoring data as to the groundwater table. Besides, the drawdown and the land subsidence both inside and outside the pit caused by foundation pit dewatering are calculated and analyzed for various curtain depths. This study reveals that the drawdown and the land subsidence change faster near the curtain with the increase in the curtain depth, and the gradient of drawdown and land subsidence changes dwindles beyond certain depths. In this project, the curtain depth of 47/49 m is adopted, and a drawdown-land subsidence verification test is completed given hanging curtains before the excavation. The result turns out that the real measurements basically match the calculation results from the numerical simulation, and by increasing the depth of curtains, the land subsidence resulting from dewatering is effectively controlled.     

Numerical simulation and land subsidence control for deep foundation pit dewatering of Longyang Road Station on Shanghai Metro Line 18

In terms of controlling groundwater in deep foundation pit projects, the usual methods include increasing the curtain depth, reducing the amount of pumped groundwater, and implementing integrated control, in order to reduce the drawdown and land subsidence outside pits. In dewatering design for confined water, factors including drawdown requirements, the thickness of aquifers, the depth of dewatering wells and the depth of cutoff curtains have to be considered comprehensively and numerical simulations are generally conducted for calculation and analysis. Longyang Road Station on Shanghai Metro Line 18 is taken as the case study subject in this paper, a groundwater seepage model is developed according to the on-site engineering geological conditions and hydrogeological conditions, the excavation depth of the foundation pit as well as the design depth of the enclosure, hydrogeological parameters are determined via the pumping test, and the foundation pit dewatering is simulated by means of the three-dimensional finite difference method, which produces numerical results that consistent with real monitoring data as to the groundwater table. Besides, the drawdown and the land subsidence both inside and outside the pit caused by foundation pit dewatering are calculated and analyzed for various curtain depths. This study reveals that the drawdown and the land subsidence change faster near the curtain with the increase in the curtain depth, and the gradient of drawdown and land subsidence changes dwindles beyond certain depths. In this project, the curtain depth of 47/49 m is adopted, and a drawdown-land subsidence verification test is completed given hanging curtains before the excavation. The result turns out that the real measurements basically match the calculation results from the numerical simulation, and by increasing the depth of curtains, the land subsidence resulting from dewatering is effectively controlled.     

坝基两道防渗墙水头分担情况有限元分析

深覆盖层坝址上的高心墙堆石坝,在河床覆盖层中常设置两道混凝土防渗墙防渗。采用开发的有限元软件,参照砂卵石覆盖层深度近50 m的某心墙堆石坝工程的情况,分析了主、副防渗墙6种设置方案中坝基的稳定渗流场,得到了主墙、副墙和覆盖层的水头分担比例。所有方案中河床覆盖层上的水头都小于3 %。当主、副两道墙下部灌浆情况相同、端部之间设置灌浆帷幕封堵绕渗时,副墙承担的水头接近主墙;如果取消封堵绕渗的帷幕,副墙承担的水头下降到总水头的20 %～30 %;而副墙底部和主、副墙两端均不设帷幕的情况,副墙上承担的水头比例下降到总水头的8 %～11 %。副墙位于主墙的下游侧时,其上承担的水头比例比副墙位于主墙上游侧的情况略高。防渗墙承担的水头比例取决于墙整体的防渗能力,而对防渗墙本身的厚度变化不敏感。     

A fluorescent approach to the identification of grout injected into fissures and pore spaces

A new fluorescent approach was developed to visualize grouting processes. The evaluation of the effect of grouting is carried out by methods based mainly on physical measurements such as permeability and porosity characteristics. However, these estimates do not necessarily correlate with practical grouting data. In this paper, the distributions of various grout mixtures containing fluorescent substances were clearly visualized under ultraviolet light, using a borehole television system or a microscope. Since this approach enabled direct observation of grout distribution, it is considered that this approach is useful for analysis of grouting mechanisms, designing grout curtains, etc.     

岩溶水库坝基防渗帷幕灌浆幕深与幕长的结构形式及处理

防渗帷幕灌浆是处理岩溶地区水库坝基坝肩渗漏的主要方法之一，它可以杜绝深、浅层的复杂的岩溶漏水问题，帷幕设计的合理性及其效果取决于水文地质、地下水的补排条件，水工建筑物结构之间的帷幕体的搭接形式，布置格局和边界范围。本文根据34处渗漏水库的灌浆实践，提出确定帷幕的深度和长度的原则，并得出了相关曲线和经验公式，对岩溶地区水库的渗漏处理进行探讨。     

“华北型”煤田岩溶水害及防治现状

“华北型”煤田的开采普遍受到煤层底板岩溶承压水的威胁，近年来，煤田岩溶水害的机理研究取得突破性进展，认为岩溶裂隙水网络是发生突水的物质基础，隔水层的岩石水学性质及厚度是突水的制约因素，断裂构造是突水的关键因素，采矿活动是突水的诱发因素；在水害防治方面，采用疏水降压、注浆改造、帷幕截流等技术方法，取得了明显的技术效果，本文旨在介绍水害现状，分析探讨治理对策，为治理煤田水害提供参考。     

皖浙山区大坝坝址环境水特征与作用

大坝建成水库蓄水,坝址水环境发生明显变化,致使水岩间相互作用加剧。在渗透压力作用下,弱酸性的水库底层水侵蚀力加强;水对岩石和混凝土的作用造成了坝基地下水的酸性和碱性化;坝基地下水地球化学环境的改变,是造成坝基排水孔胶状析出物排出的主要原因。大坝两侧岸坡和坝基地下水坡降增大,绕坝渗漏的存在,是造成大坝岸坡坝基不稳定的主要因素。     

On the use of pore pressure measurements in safety reassessments of concrete dams founded on rock

In probabilistic stability analyses of concrete dams founded on rock, the uplift pressure is often a parameter of major importance. In previous literature, it has been suggested that assessing uplift with pore pressure measurements, instead of using empirical assumptions, could improve the calculated dam safety. This paper presents a coherent methodology to investigate whether incorporating pore pressure measurements has any impact on the calculated dam safety, based on Bayesian linear regression of pore pressure data in combination with series-system and the first-order reliability method. The study concludes that the probability of sliding failure is closely related to the probability of an extreme increase in uplift. Hence, measured uplift should only be incorporated while this probability remains sufficiently small, which requires proper programs both for uplift monitoring and for maintenance of drains and grout curtains.     

砂漏型岩溶地面塌陷防治原则和方法

武汉地区在近东西向的多个褶皱构造中分布有6条石灰岩条带是岩溶地面塌陷多发区。其岩溶地面塌陷可分为砂漏型、土洞型、真空吸蚀型等三种基本类型,每种类型有其特定的地质条件及对应的塌陷机理。文章重点对灾害后果最严重、防治难度最大的砂漏型塌陷的地质条件及塌陷机理进行了分析,认为地下水（岩溶水和孔隙水）渗流是导致砂漏发生的关键因素,其中岩溶水渗流是原始动力。基于此,认为设置帷幕截断岩溶水渗流是防治砂漏型塌陷的根治措施,并提出地铁车站和区间盾构防治砂漏型塌陷的原则和方法,取得了良好效果。      

苏州软土地区的基抗支护工程

苏州是我国典型的软土地区，其坑支护难度较大。基坑支护类型的钢板桩支护、悬臂式、锚杆锚拉式、钢筋砼内支撑梁式钻孔灌注桩排桩支护、土钉墙支护、组合结构支护等。止水帷幕有压密注浆、高压旋喷桩、水泥土搅拌桩等。降水多采用轻型井点或管井降水。土方开挖是基坑工程的有机组成部分，对挤土桩，须重视地应力释放问题。监测技术与信息化施工得到了广泛应用，但系统性、完整性、规范性尚欠缺。介绍了部分典型工程实例。     

莲花台水电站岩溶发育特征及工程意义

根据地质调查和勘探资料,阐明莲花台水电站坝址区岩溶发育形态、规模及空间展布特征,归纳岩溶发育规律。结果表明:坝址区岩溶发育主要受岩性和地质构造控制,岩溶现象分布范围广,岩溶发育较为密集,具有垂向分带性及空间分布不均匀性的特征;岩溶发育对工程的影响主要表现在岩溶渗漏和岩溶塌陷稳定问题两个方面,岩溶渗漏可能造成电站无法达到设计正常蓄水水位,岩溶空间的存在可能引起坝基抗滑稳定问题。因此,建议设置防渗帷幕,并对坝基开挖揭露的溶洞进行换填加固及固结灌浆等工程处理措施,通过处理,可有效避免岩溶发育对工程的影响。      

Construction of grout curtain in karstic environment case study: Salman Farsi Dam

Salman Farsi is an arch-gravity dam. It is 125 m high and located on the Ghareh-Agaj River in Fars province, south of Iran. From the geological and hydrogeological point of view, this dam is one of the most complicated sites in Iran. Existence of 40 springs at the river level (including hot springs), and many faults and crushed zones are part of these complications. The dam site is famous for its numerous big caverns. Main characteristics of the rock mass are: (1) low permeable limestone of moderate to high strength, (2) high karstification generally localized around intersection of faults or discontinuities. The main purpose of grout curtains is to change the hydrogeological characteristics (reducing the permeability) of the rock mass. Constructing a grout curtain in a karstic environment with a high random distribution of karst features contains some uncertainties and surprises cannot be excluded. During the excavation of grouting galleries, some big caverns at both abutments were discovered. The volume of the biggest one (Golshan’s Cave) exceeds 150,000 m³. A large-scale underground geotechnical treatment is needed to improve the water tightness of the dam site.     

Determination of groundwater flow regimes in underground storage caverns using tritium and helium isotopes

Understanding groundwater flow and chemical transport is crucial for operating underground storage caverns. Groundwater flow in the study area is mainly affected by cavern operating conditions, and groundwater chemistry in the study area is modified by disinfection activities for removing possible biological clogging and by mixing with cement pore water. It is significant to discern these two effects because wells affected by the disinfection activities, in particular, may have hydrological connections with water curtains in which disinfectant water was injected to remove the biological clogging. Concentration of tritium (³H) and helium isotopes (⁴He), and groundwater chemical compositions were used to confirm that there are hydrological connectivities between the water curtain and the well. Groundwater along the fault areas contains low total dissolved solid (TDS) and high ³H, suggesting that the faults may act as fast flow conduits, which is not inconsistent with previous studies. Certain diagnostic conditions (high concentrations of Na⁺, Cl⁻ and TDS and high pH) are presumed by the effect of disinfection activity, indicating that there are hydrological connections between the water curtain and the wells. This hypothesis is valid in YK2U and YK2L, but is not in YK12L, implying a closed system or an immobile water to explain the isotopic results.     

Field experiments and numerical simulations of whirlpool foundation pit dewatering

A whirlpool foundation pit is a small-diameter, deep circular pit. Because of its depth and small diameter, a large drawdown is required, and a limited number of wells can be installed inside the pit. During excavation, partially penetrating wells inside and outside the foundation pit have to be installed to lower the water level when the aquifer is too thick. However, partially penetrating wells near partially penetrating curtains cannot be treated by analytical methods. Therefore, it is necessary to use numerical methods to predict dewatering during excavation. Field experiments were performed on whirlpool foundation pit 1880 of Baosteel Group, Shanghai, China, to obtain pumping rates and drawdown, pumping with a single well and two wells in the confined aquifer. The results indicate that the drawdown inside the pit induced by pumping wells outside the foundation pit was small, whereas it was large for pumping wells inside the pit. The pumping wells inside and outside the pit had to be combined to lower the water level. A three-dimensional numerical model was developed to simulate the dewatering process. The hydraulic conductivities of the confined aquifers were inversed by using the pumping tests. Operation schedules were simulated with the corrected model for different combinations of wells inside and outside the pit. The results suggest that different schedules and operation conditions affect drawdown. The monitored results during dewatering indicate that the simulation and field measurements were in agreement. The results can be applied to similar situations.     

Seepage problems in the right abutment of the Shahid Abbaspour dam, southern Iran

In this study, seepage phenomena through the right abutment of Shahid Abbaspour dam are investigated. The Shahid Abbaspour dam is a 200 m high arch dam, which regulates the waters of the Karun River, serves power generation, and flood control and irrigation needs. The dam site lies in the Zagros Mountains of southern Iran. This region presents continuous series of mainly of karstic limestone, marl, shale and gypsum ranging in age from Jurassic to Pliocene. The region has subsequently been folded and faulted. Seepage from the Shahid Abbaspour reservoir occurs mainly through the karstic limestone.The basic foundation treatment of the dam consisted of consolidation grouting, a high-pressure grout curtain and a drainage curtain. Moreover, a 144 m high and 30 m wide concrete cutoff wall was built to prevent reservoir seepage through a clay-filled fracture zone in the right abutment. The grout curtain penetrates the “Principal Vuggy Zone” only beneath the central portion of the dam and below the cutoff wall. In the right abutment fan curtains were constructed to reduce drainage flows, but the seepage problem could not be solved. In order to determine the seepage direction and karstification pattern, hydrogeological studies have been carried out. Additional investigation boreholes have been drilled to monitor fluctuations in groundwater level. Besides these, water chemistry, dye tracer, pinhole and XRF tests have been carried out. As a result of these studies, seepage paths have been identified in the karstic limestone in the right abutment of the dam.     

Remediation and monitoring of a burning coal refuse bank affecting the Southsea Looproad at Brymbo, North Wales

Southsea Looproad at Brymbo suffers large and varied settlements where the highway crosses a smouldering coal refuse bank. A sudden surge in combustion activity during 1991 resulted in considerable subsidence within the carriageway and posed recurring and persistent difficulties for road safety and highway maintenance. Initial investigations involved subsurface temperature measurements to delimit the hot spots and provide a basis for the design of remedial works. The aim of remediation was to extinguish the migrating fire in the outer loop area and to control the burning throughout the remaining areas. The principal strand of the remediation strategy involved excavating the burning coal refuse, cooling, mixing with pulverized fuel ash and compacting. Supplementary containment measures included limestone-filled cut-off trenches, cementitious grout curtains and impervious clay blankets. The works achieved the design objectives, however, small pockets of smouldering material remained within the inner loop. Subsequent monitoring of the site disclosed two markedly different patterns of temperature response on each side of the road. On the outer rim of the looproad temperature trends were steadily downwards in accordance with expectations and indeed reached ambient temperature within about one year. However, on the inside of the looproad seasonal surges in temperature have been recorded during winter months every year since the completion of the remedial works in 1993. The explanation for this unusual pattern of combustion activity is thought to be related to climatic effects and particularly the combined influence of rainfall, atmospheric pressure, air temperature and wind strength and direction. The relative contribution of these factors remains uncertain. Temperature monitoring continues in order to identify the eventual end of combustion activity and determine the appropriate time to complete reinstatement of the carriageway.     

水下清淤人工冻结板温度场数值分析

为研究水下清淤人工冻结板温度场的发展规律以及冻土帷幕形成的过程,通过有限元分析软件,采用单因素分析法进行数值分析,研究了水下人工冻结板在几何及物理环境变化条件下的冻结规律。结果表明:冻结板不同几何尺寸与清淤深度的相关性较弱,调整冻结板的几何尺寸仅能改变清淤面积;对清淤环境来说,土层的导热系数越大,比热容越小,原始地温越低,其降温速度越快,清淤越高效;砂土的冻结效果要明显优于黏土;相变潜热对土体降温的影响十分有限;盐水降温计划中最低温度对清淤深度有较大影响,在-50℃以前,冻土帷幕发展较快,每降低10℃冻土帷幕的发展厚度增加约0.4 m,而在-50℃以后冻土帷幕的发展较慢,每降低10℃冻土帷幕厚度的发展仅约为0.05 m。因此,在工程实际中,冻结初期通过调节盐水降温计划可以较好的实现冻结效果;建议盐水降温计划最低温度设置为-50℃,此时可以得到的有效清淤深度约1.5 m。研究结果可为今后的相关实际工程提供参考依据。      

SEDIMENTATION IN THE RIFT ZONE OF THE JUAN DE FUCA RIDGE

The sediments of the upper Swartkops River are almost exclusively gravels and boulder beds derived from the Cretaceous Uitenhage Group and the Paleozoic Cape Supergroup rocks. Many of the cobbles and boulders are second-cycle clasts, the great majority of which are quartzitic in composition. Pebble size and shape were examined and fabric analysis was performed on samples from 22 sites in the study area. Pebble imbrication planes dip consistently upstream at angles of 20? to 50? and pebble long axes generally are aligned normal to the flow direction. Clasts in the braid-plain deposits range from a few millimeters to tens of centimeters (large boulders over a meter in diameter are not uncommon). Pebble roundness ranges from 0.2 to 0.9 (averaging 0.43) and sphericity values range from 0.3 to 0.9 (averaging 0.59). The gravel clasts are angular to well-rounded, but are predominantly subrounded. Zingg diagram plots show a majority of discoidal pebbles, but there is a diversity of shapes reflecting the complex source area from which some resedimented clasts originated.

Channel and bar morphology is complex, with gravel bars often merging laterally and longitudinally with main and secondary channels. Both channels and bars are terraced stepwise downstream and across the braid plain. Bar tops are armored by both small and large clasts, whereas channels may be lined with cobbles or boulders, but often exhibit small pebble lags. Algal mats occur as fresh curtains in all standing pools of water and dried crusty deposits on pebbly substrates in inactive channels.

Imbrication studies demonstrate conclusively that pebble imbrication is the most meaningful indicator of flow direction in a gravel deposit and is far more reliable than rare cross-bedding encountered in bar-top sands, where bedforms often migrate laterally rather than downstream. The Swartkops braid-plain gravels resemble the ancient deposits of the Ventersdorp Contact Reef, both deposits being characterized by boulder-rich gravels, poor clast sorting, resedimented pebbles from a proximal fault-bounded source, and algal mats. Although heavy minerals are lacking in the Swartkops, trapping of fines by algal filaments appears to occur during low-flow conditions.