Influence of confined water on the limit support pressure of tunnel face in weakly water-rich strata

In the process of shield tunneling through soft soil layers,the presence of confined water ahead poses a significant threat to the stability of the tunnel face.Therefore,it is crucial to consider the impact of confined water on the limit support pressure of the tunnel face.This study employed the finite element method(FEM)to analyze the limit support pressure of shield tunnel face instability within a pressurized water-containing layer.Subsequently,a multiple linear regression approach was applied to derive a concise solution formula for the limit support pressure,incorporating various influencing factors.The analysis yields the following conclusions:1)The influence of confined water on the instability mode of the tunnel face in soft soil layers makes the displacement response of the strata not significant when the face is unstable;2)The limit support pressure increases approximately linearly with the pressure head,shield tunnel diameter,and tunnel burial depth.And inversely proportional to the thickness of the impermeable layer,soil cohesion and internal friction angle;3)Through an engineering case study analysis,the results align well with those obtained from traditional theoretical methods,thereby validating the rationality of the equations proposed in this paper.Furthermore,the proposed equations overcome the limitation of traditional theoretical approaches considering the influence of changes in impermeable layer thickness.It can accurately depict the dynamic variation in the required limit support pressure to maintain the stability of the tunnel face during shield tunneling,thus better reflecting engineering reality.

Characterizing large-scale weak interlayer shear zones using conditional random field theory

The shear behavior of large-scale weak intercalation shear zones(WISZs)often governs the stability of foundations,rock slopes,and underground structures.However,due to their wide distribution,undulating morphology,complex fabrics,and varying degrees of contact states,characterizing the shear behavior of natural and complex large-scale WISZs precisely is challenging.This study proposes an analytical method to address this issue,based on geological fieldwork and relevant experimental results.The analytical method utilizes the random field theory and Kriging interpolation technique to simplify the spatial uncertainties of the structural and fabric features for WISZs into the spatial correlation and variability of their mechanical parameters.The Kriging conditional random field of the friction angle of WISZs is embedded in the discrete element software 3DEC,enabling activation analysis of WISZ C2 in the underground caverns of the Baihetan hydropower station.The results indicate that the activation scope of WISZ C2 induced by the excavation of underground caverns is approximately 0.5e1 times the main powerhouse span,showing local activation.Furthermore,the overall safety factor of WISZ C2 follows a normal distribution with an average value of 3.697.

Prediction Research of Deformation Modulus of Weak Rock Zone under In-situ Conditions

Weak rock zone (soft interlayer, fault zone and soft rock) is the highlight of large-scale geological engineering research. It is an important boundary for analysis of rock mass stability. Weak rock zone has been formed in a long geological period, and in this period, various rocks have undergone long-term consolidation of geostatic stress and tectonic stress; therefore, under in-situ conditions, their density and modulus of deformation are relatively high. Due to its fragmentary nature, once being exposed to the earth's surface, the structure of weak rock zone will soon be loosened, its density will be reduced, and its modulus of deformation will also be reduced significantly. Generally, weak rock zone can be found in large construction projects, especially in the dam foundation rocks of hydropower stations. These rocks cannot be eliminated completely by excavation. Furthermore, all tests nowadays are carried out after the exposure of weak rock zone, modulus of deformation under in-situ conditions cannot be revealed. In this paper, a test method explored by the authors has been introduced. This method is a whole multilayered medium deformation method. It is unnecessary to eliminate the relatively complete rocks covering on weak rock zone. A theoretical formula to obtain the modulus of deformation in various mediums has also been introduced. On-site comparative trials and indoor deformation modulus tests under equivalent density conditions have been carried out. We adopted several methods for the prediction researches of the deformation modulus of weak rock zone under in-situ conditions, and revealed a fact that under in-situ conditions, the deformation modulus of weak rock zone are several times higher than the test results obtained after the exposure. In a perspective of geological engineering, the research findings have fundamentally changed peoples' concepts on the deformation modulus of weak rock zone, provided important theories and methods for precise definition of deformation modulus of deep weak rock zone under cap rock conditions, as well as for reasonable engineering applications.

Numerical simulation of rock progressive failure on samples with a pre-existed weak zone during brittle failure

Considering the heterogeneity of geomechanical materials, seismicity during brittle rock failure under compressive loading on the sample with an original weak zone is simulated by using rock failure process analysis code (RFPA2D). The run-through process of weak zone, the forming of new fault and associated micro-seismicities are studied. The modeling demonstrates the total process of source development of earthquake from deformation, micro-failure to collapse and the behavior of temporal-spatial distribution of micro-seismicities. The stress, strain and the temporal-spatial distribution of micro-seismicities life-likely portrayed the phenomena of localization and temporal-spatial transitions, which is similar to those observed in our real crust. Also, the results obtained in simulations are in agreement with or similar to the reported experimental observations.

Single-borehole measuring method for broken rock zone in gently inclined thin layer weakness structure

According to the structural characteristics of gently inclined thin layer rock mass in which lots of weak interlayer existed,the concept of gently inclined thin layer weakness structure was proposed.If single-borehole measuring method of the acoustic along the conventional arrangement mode was used in measuring the broken rock zone in this structure,the change of the relationship curves (Vp-L) between acoustic p-wave velocity (Vp) and borehole depth (L) would present the irregular feature due to the mechanical characteristics of layered rock mass and harmful effects of weak interlayers,and the scope of broken rock zone couldn't be defined quickly.Based on the analysis of the me- chanical characteristics of layered rock mass,the propagation rule of acoustic and distri- butions characteristics of plastic zone and slip zone in layered rock mass,new arrange- ment mode of acoustic measuring boreholes for broken rock zone in gently inclined thin layer weakness structure was proposed.Namely,the measuring boreholes in two sides were parallel to the strata,the measuring boreholes in the roof and floor perpendicular to the strata.Besides the controlling depth of the measuring boreholes in the scope of the large plastic zones or the large slip zones should be increased.Engineering example showed that new acoustic measuring boreholes arrangement mode had the better appli- cability and could determine the scope of the broken rock zone in the gently inclined thin layer weakness structure quickly.

基于多区组合煤体的煤与瓦斯突出动力学机制

煤与瓦斯突出(以下简称“突出”)严重影响煤炭安全开采,其背后涉及的众多科学问题仍未解决。为降低煤体力学性质各向异性对突出研究的困扰,构建多区组合煤体模型;基于上覆岩层应力分布特征及应力波传播机制确定“弱区”煤体位置,将研究对象由“突出中心体”具体为“弱区”。由于外部动载扰动是导致突出的激发条件,采用冲击试验研究应力波在层状组合煤岩体中的传播规律,构建组合煤岩体应力-应变本构模型。进而明确卸载波作用下,煤体轴向多层层裂是煤体质点内撞击形成加载冲击波在自由面反射形成拉应力波导致的;煤体径向平面,由于泊松效应形成卸载波追赶塑性加载波的情形,生成多个径向裂隙及环向裂隙,得到煤体层裂片厚度动态演化规律。从而明确在外部动载扰动下,煤体“弱区”最先破坏,轴向产生多层层裂、径向平面产生多个径向及环向裂隙的三维损伤路径。基于此,提出一种基于多区组合煤体的突出动力学机制,将突出划分为准备、启动、发展、终止四个阶段。突出准备阶段,煤体上覆岩层应力转移、集中,高瓦斯压力梯度形成,为后续煤体失稳破坏创造条件;突出启动阶段,煤体受外部动载扰动,轴向“弱区”煤体最先发生破坏、形成多层层裂,径向平面形成多个径向及环向裂隙;突出发展阶段,吸附态瓦斯解吸与游离态瓦斯积聚形成高压瓦斯抛出煤体,导致突出继续向深部煤体发展,形成二次损伤;突出终止阶段,积聚形成的瓦斯压力低于煤体抗拉强度,形成稳定的纺锤形突出腔体,突出终止。该机制初步解释了突出过程中“响煤炮”“口小腔大”突出孔洞等动力现象成因,为矿井防突工作提供了新思路。

冀东金厂峪金矿剪切带控矿规律及找矿建议

冀东金厂峪金矿为典型受构造作用控制的矿床,金矿体主要产于NNE向脆-韧性片理化带内的强变形带之中,直接控矿构造为叠加于强变形带之上的NNE向燕山期脆性断裂构造。本文在详细的野外调查基础上进行了构造分期配套,建立了弱变形域控岩+强变形带赋矿的透镜体控矿模式,结合矿体赋存和矿化富集规律总结,提出了韧脆性片理化带深部、两侧次级平行构造等找矿方向。

顺层深路堑边坡滑带土强度特性和基底预留厚度预警分析

含软弱夹层的顺层深路堑边坡在边坡工程中普遍存在,滑带土强度和基底预留厚度(开挖边坡基底到软弱夹层的距离)是影响其稳定性的2个关键性因素。以杨宣(杨柳-宣城)高速K42路堑边坡为例,分析了边坡变形演化过程和基底隆起变形特征,通过适合研究大剪切位移下土体抗剪强度的环剪试验揭示了边坡深部滑带土的特性,应用滑带土的饱和残余强度参数进行了边坡开挖基底预留厚度分析。结果表明:K42滑带土有明显的应变软化特性,且法向应力越小滑带土应变软化特性表现越明显;由峰值抗剪强度到残余抗剪强度,黏聚力和内摩擦角均表现出衰减效应,且黏聚力衰减程度大于内摩擦角;滑带土残余抗剪强度参数中的残余黏聚力随剪切速率的变化很小,而残余内摩擦角和剪切速率呈对数函数φ=0.1303ln v+7.3197关系变化,当剪切速率<2 mm/min时,滑带土残余抗剪强度参数对剪切速率较为敏感,反之敏感性较差;最后,依据边坡不同临界状态的回归方程h_(1)、h_(2)、h_(3)将不同坡率下的基底预留厚度分成A(失稳)、B(欠稳定)、C(基本稳定)以及D(稳定)4个区,并且在此基础上建立了基底预留厚度判据和边坡开挖基底预留厚度预警模型。

邢台震区应力场特征及M_(L)3.5以上地震的发震背景分析

邢台老震区构造背景复杂,发育多组断裂,属构造较不稳定地带,且区域中小地震频发。2017年至2021年发生6次M_(L)3.5以上地震,其中有两次M L4以上地震。本文基于搜集的震源机制解资料,反演区域现今地壳应力场,模拟震源机制与地壳应力场的关系,计算地壳应力场在地震发震断层面上的相对剪应力和相对正应力,分析地震的发震背景。结果表明,6次M_(L)3.5以上地震中,有2次震源机制节面接近应力场的最大剪应力节面,有4次震源机制节面远离应力场的最大剪应力节面。说明地震不是完全按照震源机制节面上具有最大剪应力的破裂方向发生,有时可能发生在某些薄弱带上。因此,在进行地震预测时,不能只关注最大剪应力破裂方向,还应多关注其边缘的地质薄弱带,这一结果可能会为后续分析该区域的地震危险性,研究地震孕育机制及动力学过程提供一定的参考依据。

煤层巷道顶板复合岩层组合特征与支护设计研究

煤层巷道顶板岩层组合结构复杂多变,顶板支护设计若缺乏有效指导,会导致冒顶事故发生。本文以羊场湾煤矿为工程背景,综合采用现场实测和理论分析方法,探测巷道顶板岩层结构组合特征,研究巷道顶板横向裂隙带和煤薄弱离层区域分布规律,提出支护设计方案。研究结果表明,巷道顶板岩层主要由顶煤、细粒砂岩、粉砂岩、砂质泥岩和中粒砂岩复合组成,浅部顶板0~2.5 m范围存在较多的横向裂隙破碎带和煤线发育区,中部顶板3~4 m范围岩层稳定,深部顶板5.0~6.5 m范围存在薄弱易离层五花肉“煤层+砂质泥岩+煤层”的组合结构,该结构整体厚度为1.0~1.5 m,此区域易发生离层膨胀和剪切错动,提出的支护设计方案能够满足现场安全生产要求,此设计方法能够为煤矿巷道顶板事故的防治提供科学合理的支护措施。

自由贸易试验区建设与企业实体投资

我国自由贸易试验区建设的主要目的是推动实体经济发展以实现产业转型升级并建成开放型经济格局。本文研究发现自由贸易试验区建设显著提高企业实体投资率,其中的重要作用机制是融资约束缓解、金融化投资绝对收益水平下降、实体投资绝对风险水平下降。此外,本文检验了自由贸易试验区建设后企业金融化投资规模和投资倾向的变化,并对比了企业采取不同投资决策的财务业绩表现。本文在微观企业层面证明了自由贸易试验区建设助力实体经济发展目标实现及其路径,为进一步完善相关制度建设和促进企业发展提供现实依据和有益参考。

协调发展视角下中国式现代化的水平差异与分区调控

从6个维度构建指标体系对各省中国式现代化水平进行测度,运用CRITIC权重法、Da-gum基尼系数、耦合协调度模型、障碍因子诊断模型对其区域差异、协调分区进行探索,明晰不同区域主要短板因素及调控路径。结果表明:中国式现代化水平总体差距趋于扩大,子维度中创新现代化发展不平衡程度最高。从区域内差异来看,西部地区现代化发展差距最大,东北地区差距最小;从区域间差异来看,与东部地区关联的地区间差距较大,子维度中创新现代化和经济现代化发展差异较大;从区域差异贡献率来看,现代化发展不平衡的主要原因来自地区间差异。通过耦合中国式现代化综合水平与协调度关系,将各省现代化发展划分为优先提升区、重点提升区、潜在提升区、协同优化区、适度优化区5个类型,以“找短板,齐发展”为调控路径,因地制宜探索不同分区差异化的提升路径,以实现中国式现代化“双高”发展目标。

不同降雨条件下露天矿含泥岩弱层边坡稳定性分析

为了研究不同降雨条件下露天矿含泥岩弱层边坡的稳定性变化规律,以新疆维吾尔自治区某露天煤矿西端帮边坡为工程背景,采用滤纸法获得了泥岩土-水特征曲线,借助COMSOL软件对不同降雨条件下的西端帮进行了渗流与应力耦合计算。结果表明:不同降雨条件下边坡安全系数在降雨期间均快速下降,降雨结束后均缓慢回升,但在较长一段时间内仍低于边坡初始安全系数;短时强降雨比长时弱降雨对边坡稳定性的影响更剧烈,但在降雨结束后安全系数回升得更快;塑性应变首先产生于泥岩弱层中并沿泥岩弱层逐渐向边坡深部发展,最终形成贯通边坡的塑性区。

伊犁矿区弱胶结覆岩导水裂缝带发育高度探测

以伊犁四矿23223工作面为研究对象,分别采用地面瞬变电磁法的导高探测、井下钻孔并行电法的导水裂缝带高度探测,以及数值模拟等方法对煤层开采上覆岩层导水裂缝带发育高度及规律进行了现场探查与研究。结果表明:弱胶结覆岩条件下,工作面垮采比为3.0,裂采比为5.3。研究结果能进一步为弱胶结覆岩下采动安全开采提供科学借鉴。

底辟模糊区成像处理的关键技术

底辟带具有巨大的油气勘探潜力,但受浅层气云的影响,该领域地震资料成像品质差、构造形态不准确,对周缘含油构造潜在目标的落实带来了困难。为解决底辟模糊区成像问题,本文分析近年海上新采集资料的优势及新老资料的共性特征,提出弱信号保护的保幅处理、高精度速度建模及Q深度偏移等关键技术,形成对不同采集方案具有普适性的处理对策。采用上述方法在莺歌海盆地L工区进行实际资料的应用,得出底辟模糊区核部地震资料信噪比得到提升,有效地层清晰成像,井震相关系数比原老资料提高了38%,深度域构造与测井吻合,特别是老资料重处理的效果明显,成像质量不亚于新采集资料,验证了本方法对于底辟模糊区成像挖潜的有效性,可为后续类似领域的采集及处理提供借鉴。

软弱夹层厚度对巷道围岩稳定性影响研究

为得出软弱夹层厚度对巷道围岩稳定性影响规律,以3上712工作面运输巷为工程背景,采用数值模拟和现场监测等综合研究方法,研究了不同软弱夹层厚度与巷道围岩变形特征及应力分布之间关系,并对3上712工作面运输巷提出了支护优化措施。结果表明,随着软弱夹层厚度的增加,巷道顶板上方下位坚硬岩层区域应力值逐渐减小,巷道顶板塑性区破坏面积逐渐增大;且不同软弱夹层厚度会导致不同的顶板破裂形态,巷道含软弱夹层顶板出现了明显的非连续破坏,顶板破裂区具有明显的隔层扩展特性。经现场实践,巷道位移量在40 d后基本趋于稳定,巷道的顶板、两帮及底鼓量分别达到53 mm、46 mm、41 mm,有效控制了巷道围岩变形量。

A sand production prediction model for weak sandstone reservoir in Kazakhstan

Weakly consolidated reservoirs are prone to sand production problem,which can lead to equipment damages and environmental issues.The conditions for sand production depend on stresses and properties of rock and fluid.Accurate sand volume estimation is,however,still a challenging issue,especially for reservoirs in weak formations.The weak reservoirs containing viscous or heavy oil are mainly discovered in shallow depths in Kazakhstan,with moderate temperature and pressure.Many prediction models developed for open-hole completions where the reservoir materials usually possess certain strength are not applicable for the local reservoirs where the materials are significantly weaker even if casing is used to support the wellbore with oil produced through the perforation tunnels.In this context,a prediction model was proposed where the volume of the produced sand was estimated as the volume of the plastic zone of the failed materials surrounding the perforation tunnels.The model assumes an evolving truncated conical shape for the damage zone and takes into account stress distributions and shear failure in this zone.Then,the proposed model was used to estimate sand volumes in 20 wells during oil production with sequential increase of flow rates.The predictions match well with the measured sand volumes in a local oil field.Finally,a sensitivity analysis was conducted on the model performance.It shows that the permeability of the plastic zone was the most significant controlling factor in the prediction results.

侏罗系弱胶结顶板采动破坏规律与发育高度预测

煤层采动后形成的顶板导水裂隙带是沟通顶板充水含水层的主要通道之一,同时也是顶板水害防治需要重点研究的关键问题。近年来,西部矿区已成为我国煤炭资源主要开采区,其主采侏罗系含煤地层与东部石炭-二叠系有着明显差异,并具有典型的孔隙度高、胶结程度差等特征,顶板采动导水裂隙的演化特征也与东部矿区具有较大差异,相关的研究尚未形成普适性成果。因此,本文选取典型的弱胶结地区——新疆哈密大南湖矿区为例,采用UDEC数值模拟、现场三维钻孔电视成像等方法,并结合“S-R”稳定理论,以垮落带高度为自变量,建立砌体梁承载强度与垮落带高度关系式,全面揭示该区煤层开采过程中顶板的采动破坏过程与演化特征,并以此为依据确定顶板导水裂隙带的发育高度。在此基础上,通过收集侏罗系同类型煤矿导水裂隙带高度的实测数据,采用回归分析方法,拟合并修正现有经验公式。研究表明:研究区顶板导水裂隙带发育高度的范围是60.07~62m,裂采比为17.67~18.24,整体形态呈“梯台”型特征,结合邻矿现场实测对比证实了此次实测结果的可靠性;开采范围内导水裂隙带发育高度受垮落带高度增量、岩块回转角变化的影响呈现:“快速增加-缓慢增加-逐渐稳定”的发展与演化规律;验证计算结果表明,论文提出的回归公式预测精度一般在10.30%~17.25%之间,相较于传统经验公式平均误差降低了51.84%,显著提高了导水裂隙带高度的预测精度。论文的相关研究成果可为新疆地区相似开采条件下顶板导水裂隙带发育高度计算提供理论依据。

LCL型并网逆变器新型电容电压有源阻尼策略

在弱电网条件下,数字控制延时会导致虚拟阻抗呈现负阻性,无法起到阻尼效果,因此并网逆变器在电网阻抗变化情况下不能稳定运行,鲁棒性受到严重威胁。针对上述问题,提出一种双线性正反馈有源阻尼策略,以扩大系统的有效阻尼区。为了节省传感器成本,将其优化为电容电压正反馈有源阻尼策略,在电容电压两端添加合适的正反馈阻尼环节,使得系统的有效阻尼区扩大为(0,0.477f3)。分析结果表明该策略使得并网逆变器在弱电网条件下始终具有良好的鲁棒性,即使谐振频率等于1/6采样频率时,系统也具有较好的稳定性。最后,以三相LCL型并网逆变器为例进行实验验证,实验结果验证了该策略的正确性。

基于高陡交填界面软弱带影响下黄土填方边坡失稳模式研究

近年来,我国黄土高原地区为了扩大土地可利用资源,开展了大范围的填沟造地、平山造城等工程建设。针对高陡原始坡-填方坡交填界面可能存在的灾变隐患开展了室内物理模型试验,发现黄土填方边坡在连续强降雨下会沿高陡交填界面发生整体滑移失稳。进一步通过有限元数值模拟对交填界面处无软弱带、不同软弱带厚度与弱化系数等工况进行了对比分析,证明了交填界面通过该处滋生的相对软弱带对填方边坡的稳定性产生影响,软弱带的不断发展在降低填方边坡稳定性系数的同时也改变了潜在最危险滑面的位置。设定的弱化系数对稳定性系数的影响可划分为3个阶段:无影响阶段、等速陡降控制阶段、等速缓降控制阶段;其中定义的“关键弱化系数”是对边坡稳定性开始产生影响的临界弱化系数,在实际工程中应采取相应措施来避免软弱带弱化系数降到其“关键弱化系数”之下。降雨诱发基于高陡交填界面软弱带影响下黄土填方边坡的失稳模式可归纳为:坡表侵蚀并形成冲沟→坡脚多级局部滑塌、交填界面软弱带逐步发展→土体沿交填界面滑移下错及坡脚剪出→剪切裂缝贯通、填方体整体滑移失稳。研究成果可为修筑在陡坡上的黄土填方边坡防灾减灾工作提供理论支撑。