The Water-Bearing Numerical Model and Its Operational Forecasting Experiments PartII: The Operational Forecasting Experiments

おhe water-bearing numerical model is undergone all round examinations during the operational forecasting experiments from 1994 to 1996. A lot of difficult problems arising from the model′s water-bearing are successfully resolved in these experiments through developing and using a series of technical measures. The operational forecasting running of the water-bearing numerical model is realized stably and reliably, and satisfactory forecasts are obtained.

Prediction Technology of Buried Water-Bearing Structures in Coal Mines Using Transient Electromagnetic Method

Buried water-conducting and water-bearing structures in front of the driving head may easily lead to water bursts in coal mines. Therefore,it is very important for the safety of production to make an accurate and timely forecast about water bursts. Based on the smoke ring effect of transient electromagnetic fields,the principle of transient electro-magnetic method used in detecting buried water-bearing structures in coal mines in advance,is discussed. Small multi-turn loop configurations used in coal mines are proposed and a field procedure of semicircular sector scanning is presented. The application of this method in one coal mine indicates that the technology has many advantages compared with others. The method is inexpensive,highly accurate and efficient. Suggestions are presented for future solutions to some remaining problems.

The Water-Bearing Numerical Model and Its Operational Forecasting Experiments Part I: The Water-Bearing Numerical Model

In first paper of articles, the physical and calculating schemes of the water-bearing numerical model are described. The model is developed by bearing all species of hydrometeors in a conventional numerical model in which the dynamic framework of hydrostatic equilibrium is taken. The main contributions are: the mixing ratios of all species of hydrometeors are added as the prognostic variables of model, the prognostic equations of these hydrometeors are introduced, the cloud physical framework is specially designed, some technical measures are used to resolve a series of physical, mathematical and computational problems arising from water-bearing; and so on. The various problems (in such aspects as the designs of physical and calculating schemes and the composition of computational programme) which are exposed in feasibility test, in sensibility test, and especially in operational forecasting experiments are successfully resolved using a lot of technical measures having been developed from researches and tests. Finally, the operational forecasting running of the water-bearing numerical model and its forecasting system is realized stably and reliably, and the fine forecasts are obtained. All of these mentioned above will be described in second paper.

Vertical variation of trace elements and its relation to the water-bearing capacity of Ordovician strata,in Datun coal field

We tested for fourteen trace elements in samples collected from the Ordovician strata in Datun coal field. The vertical concentration variation of these trace dements is reported. The relationship of the variation to the water-bearing capacity of the Ordovician strata is discussed. The minimum concentration of eleven （of 14 total） trace elements appears in the lower Majiagou formation. The maximum concentrations mainly appear in the Badou and Jiawang formations： eight maxima are located in Badou and four more are in Jiawang. The study of karst development and the water-bearing capacity of Ordovician strata shows that karst is well developed in the Majiagou formation and there is a consequent high water-bearing capacity in this formation： Badou and Jiawang formations are contrary to this situation. The results illustrate that the minimum concentrations of most trace elements within certain Ordovician formations can be taken as strong evidence for the existence of a well developed karst and a high water-bearing capacity.

Strength prediction model for water-bearing sandstone based on nearinfrared spectroscopy

The strength of water-bearing rock cannot be obtained in real time and by nondestructive experiments,which is an issue at cultural relics protection sites such as grotto temples.To solve this problem,we conducted a near-infrared spectrum acquisition experiment in the field and laboratory uniaxial compression strength tests on sandstone that had different water saturation levels.The correlations between the peak height and peak area of the nearinfrared absorption bands of the water-bearing sandstone and uniaxial compressive strength were analyzed.On this basis,a strength prediction model for water-bearing sandstone was established using the long short-term memory full convolutional network(LSTM-FCN)method.Subsequently,a field engineering test was carried out.The results showed that:(1)The sandstone samples had four distinct characteristic absorption peaks at 1400,1900,2200,and 2325 nm.The peak height and peak area of the absorption bands near 1400 nm and 1900 nm had a negative correlation with uniaxial compressive strength.The peak height and peak area of the absorption bands near 2200 nm and 2325 nm had nonlinear positive correlations with uniaxial compressive strength.(2)The LSTM-FCN method was used to establish a strength prediction model for water-bearing sandstone based on near-infrared spectroscopy,and the model achieved an accuracy of up to 97.52%.(3)The prediction model was used to realize non-destructive,quantitative,and real-time determination of uniaxial compressive strength;this represents a new method for the non-destructive testing of grotto rock mass at sites of cultural relics protection.

Prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum

This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown.A series of numerical analyses is performed to examine the effects of cover depth ratio(C/D),tunnel volume loss rate(h t)and volumetric block proportion(VBP)on the characteristics of subsurface settle-ment trough and soil volume loss.Considering the ground loss variation with depth,three modes are deduced from the volumetric deformation responses of the soil above the tunnel crown.Then,analytical solutions to predict subsurface settlement for each mode are presented using stochastic medium theory.The influences of C/D,h t and VBP on the key parameters(i.e.B and N)in the analytical expressions are discussed to determine the fitting formulae of B and N.Finally,the proposed analytical solutions are validated by the comparisons with the results of model test and numerical simulation.Results show that the fitting formulae provide a convenient and reliable way to evaluate the key parameters.Besides,the analytical solutions are reasonable and available in predicting the subsurface settlement induced by shield tunnelling in sandy cobble stratum.

Resistivity tomography study on samples with water-bearing structure

The apparent resistivity of the samples with water-bearing configuration was measured by an electrode-array and 2-D resistivity images of these samples were reconstructed then. The obtained series of tomograms reveal the dis tribution and its variation of true resistivity within the samples caused by the changes of crack and liquid distribu tion. Applying this method to the simulation experiment on the electrical properties of rocks, the fracturing and water filling process, which produces the electrical changes, can be brought to light clearly.

Physical and numerical investigations of target stratum selection for ground hydraulic fracturing of multiple hard roofs

Ground hydraulic fracturing plays a crucial role in controlling the far-field hard roof,making it imperative to identify the most suitable target stratum for effective control.Physical experiments are conducted based on engineering properties to simulate the gradual collapse of the roof during longwall top coal caving(LTCC).A numerical model is established using the material point method(MPM)and the strain-softening damage constitutive model according to the structure of the physical model.Numerical simulations are conducted to analyze the LTCC process under different hard roofs for ground hydraulic fracturing.The results show that ground hydraulic fracturing releases the energy and stress of the target stratum,resulting in a substantial lag in the fracturing of the overburden before collapse occurs in the hydraulic fracturing stratum.Ground hydraulic fracturing of a low hard roof reduces the lag effect of hydraulic fractures,dissipates the energy consumed by the fracture of the hard roof,and reduces the abutment stress.Therefore,it is advisable to prioritize the selection of the lower hard roof as the target stratum.

Deformation Mechanism and Design Countermeasures of Tunnel Portal in Volcanic Deposit Clay Stratum

Shortly after tunneling,problems such as primary-support through cracks and clearance infringement are found in the shallow-buried section of tunnel No.4 of the Jakarta-Bandung High Speed Railway(Jakarta-Bandung HSR),and orthogonal cracks can be found on the earth surface in front of the working face,which brings great challenges to the tunnel construction.In view of the above engineering problems,the sliding surface is speculated according to the geological and field conditions,and the impact of landslides is applied in the model in the form of external load.The paper uses the numerical simulation method to analyze and compare the impact of landslides on the tunnel structure and deformation,and puts forward the reinforcement measures.The conclusions of the studies are:(1)under the influence of heavy rainfall,the strength index of volcanic deposit clay stratum drops sharply,and meanwhile the multiple factors including tunnel excavation are liable to cause sliding of the front slope;(2)parallel landslide in front of the tunnel has a great impact on the tunnel,so setting-up of pre-reinforcement measures to control landslide shall be the focus of similar projects during design;(3)the deformation and stress of the tunnel structure can be significantly controlled for safe construction by strengthening the shallow-buried tunnel with pile foundation and longitudinal and transverse beam frames during landslide.

平原水库库底浅层气分布特征及其诱发库底渗漏模式初探

本研究以某平原水库为研究区,基于钻探、浅地层剖面结果并结合理论分析,对浅层气致平原水库库底渗漏问题进行了研究。结果显示浅地层剖面法可有效探测平原水库库底浅层气分布。当前库底浅层气在库心沉积物中多个区域独立分布。气温的变化、近三年地下水位及水库蓄水水位的波动均无法引起研究区内水库的库底浅层气突破库底夯实黏土层。但若地下水上升最大幅度由1.1~1.2 m升高到1.4~1.6 m,或水库蓄水最小水深由3.8~4.1 m降低到0.5~3 m时,当前库底浅层气热点分布区的库底黏土防渗层将存在破坏风险。平原水库库底浅层气分布时空演化及其诱发库底渗漏过程可分四个阶段:建成初期,库底浅层气向库心汇聚阶段;极端事件引发库底气突破库底夯实黏土层致浅层气释放阶段;极端事件结束气体排泄通道/渗漏通道被限制或被关闭阶段;前两个阶段反复多次后库底沉积物饱和,库底渗漏点形成阶段。

保存条件对陆相中高熟页岩油富集与流动性保持的作用

陆相页岩烃源岩层系内部滞留烃数量与品质的控制因素除生烃母质类型、丰度、热成熟度与页岩储层储集空间外,烃源岩保存条件作为关键影响因素,在现阶段关注较少;针对该科学问题,以实例解剖为出发点,探讨保存条件在页岩油可动烃富集中的作用。研究表明,良好的保存条件主要有3方面的关键作用:①确保足够多的轻烃(C_(1)—C_(13))、中组分烃(C_(14)—C_(25))和小分子芳香烃(含1~2个苯环)留在地层中以增加页岩油流动性和流动量;②确保地层具有较高的能量场(异常高压),以推动页岩油最大量流出;③确保滞留烃保持多组分烃(轻烃、中质烃、重烃和含杂原子化合物)混相流动条件,使重烃(∑C_(25+))和重质组分(非烃和沥青质)有最佳流动度和最大流动量。经实例解剖证实,凡经济可采性较好的陆相页岩油除有机质类型、丰度与热成熟度及储集空间等有利条件外,页岩层系保存条件好,是页岩油经济成藏的关键因素,应纳入页岩油富集区/段评价标准,成为有利勘探靶体选择的必要条件。

基于建筑高度和地层厚度的城市地下空间占用深度快速评估方法——以杭州市为例

城市高密度的建筑物事实上占据了位于其下部一定深度的地下空间资源,其占用深度对城市地下空间(UUS)网络化开发具有重要影响,因此,在UUS规划前,需要掌握规划范围内地下空间占用深度和空间分布格局。UUS占用深度除地下建筑物深度外还包括下部地基持力层深度,其与建筑高度和场地地质条件相关。笔者等提出基于建筑高度和地层厚度的UUS占用深度快速评估方法,以杭州主城区为研究对象,通过实测建筑高度数据和收集建筑基础数据建立评估数学模型,利用百度建筑数据和杭州三维地质模型生成的地层厚度数据,并基于GIS平台的空间分析,实现了对杭州市主城区建筑地下空间占用深度的快速评估。研究成果为城市地下空间规划所需的大范围地下空间占用情况提供了高效的评估手段。

长江漫滩折线形超深地连墙成槽施工的地层扰动研究

为探究折线形地连墙成槽施工对槽壁周围土体的扰动机理,开展了成槽全过程三维数值模拟分析,得到了阴角、阳角处两侧土体的应力分布特征和变形基本规律,并进一步探讨了不同施工条件包括超载位置、加固强度、泥浆重度,以及槽段形状包括槽段角度、长度,对两侧土体变形的影响。结果表明:阴角处的水平土拱效应使得其槽壁应力在竖向分布上较阳角处更有利,且在槽段厚度方向上的扰动范围更小,只在槽段长度方向上扰动范围略大;在相同施工条件和槽段形状条件下,阴角处变形均小于阳角处;地面超载对地表沉降的影响较大,对槽壁侧移的影响仅限地表以下20 m范围以内;当槽段角度大于195°时,折线形槽段与直线形槽段的变形差异显著增大。

渗流下砂-黏复合地层人工冻结多场耦合研究

对滨海地层进行人工冻结时,高盐度地下水渗流的存在将严重影响冻结范围和冻结效果.利用Navier-Stokes方程来描述滨海地层中液相在渗流过程中的动量守恒,考虑渗流过程中土颗粒表面对盐的吸附和解吸作用以及人工冻结时液相的非对流通量对水、盐相变的影响,建立了渗流对砂-黏复合地层人工冻结过程影响的水-盐-热-力学理论模型.基于COMSOL Multiphysics软件对渗流条件下砂-黏地层的水-盐-热-力学多场耦合理论模型进行求解,理论模型的计算结果与试验结果吻合效果较好.通过参数分析,研究了不同渗流速度对水、盐、温度和位移等各组分空间分布的影响.研究结果表明:随着渗流速度从0 m/d增加到15 m/d,在砂-黏复合地层上游土体的冻结难度加大,导致上游的冻结区域向下游缩减,下游的冻结区域沿着渗流向下游扩大,砂层和黏土层中冰的前缘位置分别向下游移动了60.3%和26.2%;砂层和黏土层中盐结晶前缘位置分别向下游移动了50.4%和26.2%;在水、盐相变的作用下,土体内部应力的增加导致土体位移的增加,在砂-黏复合地层的下游,人工冻结后黏土层的位移峰值增大了107%;冻结管在垂直于渗流方向上的影响范围被缩减,在冻结管两侧0.3 m位置处黏土层和砂层的温度分别降低了1.1℃和2.8℃,黏土层和砂层的总含盐量分别增加了8.5%和7.4%,黏土层和砂层中冰的产生范围分别缩小了10.2%和54.9%.本文研究成果为渗流条件下的滨海地层的人工冻结施工提供了理论依据和数据支撑.

浅埋砂土地层盾构带压进舱施工作业开挖面稳定性研究

[目的]解决浅埋砂土地层盾构带压进舱施工作业过程中开挖面稳定性问题。[方法]综合采用数值模拟、理论解析和工程验证的方法对盾构带压进舱施工作业过程中的极限支护压力进行研究。首先,采用数值模拟方法对浅埋砂土地层主动破坏现象进行研究,得到了相应的极限支护压力和破坏区形状;然后,基于数值模拟结果,构建了适用于浅埋砂土地层的破坏模式,并求解了相应的极限支护压力;最后,将本模型应用于杭州地铁5号线工程的盾构带压进舱施工作业,并对地面沉降情况进行了监测。[结果及结论]极限支护压力随着埋深的增大近似线性增大,随着内摩擦角的增大近似指数形式减小;失稳模式浅埋砂土地层呈现下部楔形体和上部倒圆台的形状,其中上部破坏区进一步分为破坏核心区和扰动区;通过与数值模型、文献模型对比发现,所提出的楔形体+倒圆台组合破坏模式能较好地描述因浅埋砂土地层无法成拱而导致破坏区可达地面的现象;杭州地铁5号线工程盾构带压进舱施工作业过程中,引起地面最大沉降值为9.5 mm,影响范围为隧道轴线两侧10 m范围内。

非平衡建筑超载下软弱地层地铁深基坑变形特性及加固方案研究

软弱地层中某地铁深基坑外侧作用有建筑物偏压超载,对深基坑开挖存在较为不利影响。为研究外部建筑物偏压超载对软弱地层中基坑支护结构的变形影响,确定合理的隔离桩及基底加固方案,采用有限元方法进行了不同加固方案下基坑开挖模拟计算,并与实测结果对比分析。结果表明:临近深基坑的外部建筑物超载将对基坑支护结构产生明显的偏压效应,偏压超载对坑底软弱地层范围内支护结构影响最为明显;基坑外侧设置隔离桩加固,可有效减小地下连续墙水平位移,隔离桩变形在软弱地层范围最大,增加桩长可使桩底产生支点约束效应,但不能有效减小支护结构位移及支撑轴力;同样,改变隔离桩刚度对支护结构位移及支撑轴力影响较小;仅采用基底加固方案,可减小坑底范围内支护结构位移,但对上部支护结构变形影响较小,采用隔离桩+基底加固组合方案可有效减小支护结构变形及支撑轴力,降低了偏压荷载对基坑的不利影响,具有较好的加固效果。

红沙梁东井田含煤地层特征及沉积环境分析

通过对红沙梁东井田下白垩统老树窝群含煤地层展布规律的研究,结合区域构造及沉积环境等方面进行综合分析,结果表明:含煤地层呈现为一个小型煤盆地形态,其含煤性呈中西部好,向四周逐渐变差的趋势;含煤地层沉积环境主要有扇三角洲、湖泊、湖泊三角洲,其间的三角洲平原泥炭沼泽与滨湖沼泽环境为全区的有利成煤环境,形成了区内的4层可采煤层。

浅埋厚煤层开采地表采动裂缝发育演化规律研究

基于串草圪旦煤矿典型生产工作面覆岩赋存情况及地表采动裂缝发育特征,采用现场实测、理论分析和数值计算相结合,研究了覆岩关键层失稳运动形式及其对地表采动裂缝发育形态的影响,以及基采比对地表采动裂缝演化规律的影响。结果表明:浅埋厚煤层开采过程中,关键层失稳运动对地表采动裂缝发育类型具有控制作用,关键层滑落失稳引起地表产生台阶型裂缝,关键层回转失稳引起地表产生张开型裂缝;覆岩关键层失稳运动过程导致地表采动裂缝尺度参数发生动态变化,随着基采比的增大,地表采动裂缝的垂直错动量呈减小趋势,水平张开量呈增大趋势,裂缝水平张开量与关键层回转角线性相关。

广州地区复合地层大直径铁路隧道盾构选型及适应性分析

盾构法施工凭借效率高、扰动小等优势已然成为隧道工程建设中常用的手段。不同工程的地质水文环境不尽相同,盾构装备能否适应地质水文环境是决定施工能否高效、安全开展的关键因素,这在复合地层大直径隧道施工时更为明显。依托广州南站联络线隧道工程,识别出工程区间存在盾构选型适应性、刀盘刀具磨损、大直径浅埋盾构掘进控制三种重大风险,基于此针对盾构选型、刀盘刀具、推进驱动系统进行适应性选型设计。实践证明,经针对性设计后的盾构装备在此区间地层适应性优良,能够提升施工效率,保障施工安全。

富水砂层地质大型拉森锁扣钢管桩围堰施工关键技术

中交第二公路工程局有限公司依托安罗高速原阳至郑州段黄河特大桥,深入研究富水全砂层等复杂条件下深大基坑支护的施工技术。安罗黄河特大桥位于黄河河道内,河道宽浅,水流散乱,冲淤变化迅速,地质条件基本为全砂层,摩擦系数大且地下水丰富。经过项目前期调研对比分析,并根据现场施工需要及结合工程特点,将钢管桩围堰及钢板桩围堰的各类特点有机结合,并配合围堰外侧降水及卸土,形成一项新的施工技术,即富水砂层地质大型拉森锁扣钢管桩围堰施工技术,该技术已实际成功应用于安罗黄河特大桥主墩承台施工时基坑开挖支护。