Support design method for deep soft-rock tunnels in non-hydrostatic high in-situ stress field

Due to the long-term plate tectonic movements in southwestern China,the in-situ stress field in deep formations is complex.When passing through deep soft-rock mass under non-hydrostatic high in-situ stress field,tunnels will suffer serious asymmetric deformation.There is no available support design method for tunnels under such a situation in existing studies to clarify the support time and support stiffness.This study first analyzed the mechanical behavior of tunnels in non-hydrostatic in-situ stress field and derived the theoretical equations of the ground squeezing curve(GSC)and ground loosening curve(GLC).Then,based on the convergence confinement theory,the support design method of deep soft-rock tunnels under non-hydrostatic high in-situ stress field was established considering both squeezing and loosening pressures.In addition,this method can provide the clear support time and support stiffness of the second layer of initial support.The proposed design method was applied to the Wanhe tunnel of the China-Laos railway in China.Monitoring data indicated that the optimal support scheme had a good effect on controlling the tunnel deformation in non-hydrostatic high in-situ stress field.Field applications showed that the secondary lining could be constructed properly.

Measures for controlling large deformations of underground caverns under high in-situ stress condition--A case study of JinpingⅠhydropower station

The Jinping I hydropower station is a huge water conservancy project consisting of the highest concrete arch dam to date in the world and a highly complex and large underground powerhouse cavern. It is located on the right bank with extremely high in-situ stress and a few discontinuities observed in surrounding rock masses. The problems of rock mass deformation and failure result in considerable challenges related to project design and construction and have raised a wide range of concerns in the fields of rock mechanics and engineering. During the excavation of underground caverns, high in-situ stress and relatively low rock mass strength in combination with large excavation dimensions lead to large deformation of the surrounding rock mass and support. Existing experiences in excavation and support cannot deal with the large deformation of rock mass effectively, and further studies are needed. In this paper, the geological conditions, layout of caverns, and design of excavation and support are first introduced, and then detailed analyses of deformation and failure characteristics of rocks are presented. Based on this, the mechanisms of deformation and failure are discussed, and the support adjustments for controlling rock large deformation and subsequent excavation procedures are proposed. Finally, the effectiveness of support and excavation adjustments to maintain the stability of the rock mass is verified. The measures for controlling the large deformation of surrounding rocks enrich the practical experiences related to the design and construction of large underground openings, and the construction of caverns in the Jinping I hydropower station provides a good case study of large-scale excavation in highly stressed ground with complex geological structures, as well as a reference case for research on rock mechanics.

Effect of combined spinal and epidural anesthesia on the level of pain media, stress indicators and inflammatory factors in patients undergoing high altitude cesarean section

Objective: To discuss the effect of combined spinal and epidural anesthesia on the levels of pain media, stress indicators and inflammatory factors in patients undergoing high altitude cesarean section. Methods: Eighty patients who underwent cesarean section in our hospital from January 2017 to April 2019 were enrolled in the hospital. They were divided into two groups according to the patient's anesthesia. Fourty patients receiving epidural anesthesia were included in the control group, and another 40 patients received lumbar stiffness. The combined anesthesia patient was included in the observation group. Changes in pain mediators [Serum neuropeptide Y (NPY), endorphin (β-EP), substance P (SP)], stress indicators [Serum cortisol (Cor), C-peptide (C-P), advanced oxidative protein product (AOPP)], inflammatory factor levels [Hypersensitive C-reactive protein (hs-CRP), tumor necrosis factor-alpha (TNF-α)], and immunoglobulin levels [Serum IgA, IgG, IgM] were compared between the two groups. Results: Before anesthesia, there were no significant difference in pain media, stress index, inflammatory factor level and immunoglobulin level between the two groups (P>0.05). At 12 h after operation, the two groups of patients were NPY, β-EP, SP, Cor. The levels of C-P, AOPP, hs-CRP and TNF-α were higher than those before operation (P<0.05). The levels of IgA, IgG and IgM were lower than those before operation (P<0.05). Among them, observation group NPY, β-EP, SP, Cor, C-P, AOPP, hs-CRP and TNF-α were significantly lower than those of the control group (P<0.05). The serum levels of IgA, IgG and IgM were significantly higher than those of the control group (P<0.05). Conclusion: Combined spinal and epidural anesthesia can more effectively alleviate maternal pain in high altitude cesarean section, more effectively reduce the inflammatory stress response of patients, promote the humoral immune function of patients, and is beneficial to the early recovery of maternal postoperative, and has high clinical value.

A critical review on the developments of rock support systems in high stress ground conditions

Extreme ground behaviour in high-stress rock masses such as rockburst prone and squeezing ground conditions are encountered in a range of underground projects both in civil and mining applications.The occurrence of such ground behaviour types are difficult to predict and special design and construction measures must be taken to control them.Determining the most appropriate support system in such grounds is one of the major challenges for ground control engineers because there are many contributing factors to be considered,such as the rock mass parameters,the stress condition,the type and performance of the support systems,the condition of major geological structures and the size and geometry of the underground excavation.The main characteristics and support requirements of rockburst-prone and squeezing ground conditions are herein critically reviewed and characteristics of support functions are discussed.Different types of energy-absorbing rockbolts and other support elements applicable for ground support in burst-prone and squeezing grounds are introduced.Important differences in the choice and economics of ground support strategies in high-stress ground conditions between civil tunnels and mining excavations are discussed.Ground support benchmarking data and mitigation measures for mines and civil tunnels in burst-prone,squeezing and heavily swelling grounds conditions are briefly presented by some examples in practice.

Experimental study on the effect of flexible joints of a deep-buried tunnel across an active fault under high in-situ stress conditions

During dislocation,a tunnel crossing the active fault will be damaged to varying degrees due to its permanent stratum displacement.Most previous studies did not consider the influence of the tunnel’s deep burial and the high in-situ stress,so the results were not entirely practical.In this paper,the necessity of solving the anti-dislocation problem of deep-buried tunnels is systemically discussed.Through the model test of tunnels across active faults,the differences in failures between deep-buried tunnels and shallow-buried tunnels were compared,and the dislocation test of deep-buried segmental tunnels was carried out to analyze the external stress change,lining strain,and failure mode of tunnels.The results are as follows.(1)The overall deformation of deep-buried and shallow-buried tunnels is both Sshaped.The failure mode of deep-buried tunnels is primarily characterized by shear and tensile failure,resulting in significant compressive deformation and a larger damaged area.In contrast,shallow-buried tunnels mainly experience shear failure,with the tunnel being sheared apart at the fault crossing,leading to more severe damage.(2)After the segmental structure design of the deep-buried tunnel,the “S”deformation pattern is transformed into a “ladder”pattern,and the strain of the tunnel and the peak stress of the external rock mass are reduced;therefore,damages are significantly mitigated.(3)Through the analysis of the distribution of cracks in the tunnel lining,it is found that the tunnel without a segmental structure design has suffered from penetrating failure and that cracks affect the entire lining.The cracks in a flexible segmental tunnel affect about 66.6% of the entire length of the tunnel,and cracks in a tunnel with a short segmental tunnel only affect about 33.3% of the entire length of the tunnel.Therefore,a deep-buried tunnel with a short segmental tunnel can yield a better anti-dislocation effect.(4)By comparing the shallow-buried segmental tunnel in previous studies,it is concluded that the shallow-buried segmental tunnel will also suffer from deformation outside the fault zone,while the damages to the deep-buried segmental tunnel are concentrated in the fault zone,so the anti-dislocation protection measures of the deep-buried tunnel shall be provided mainly in the fault zone.The results of the above study can provide theoretical reference and technical support for the design and reinforcement measures of the tunnel crossing active fault under high in-situ stress conditions.

Stress rise precursor to earthquakes in the Tibetan Plateau

Earthquake prediction thus far has proven to be a very difficult task, but changes in situ stress appear to offer a viable approach for forecasting large earthquakes in Tibet and perhaps other continental regions. High stress anomalies formed along active faults before large earthquakes and disappeared soon after the earthquakes occurred in the Tibetan Plateau. Principle stress increased up to ~2 -?5 times higher than background stress to form high stress anomalies along causative faults before the Ms 8.1 West Kunlun Pass earthquake in November 2001, Ms 8.0 Wenchuan earthquake in May 2008, Ms 6.6 Nimu earthquake in October 2009, Ms 7.1 Yushu earthquake in April 2010 and the Ms 7.0 Lushan earthquake in April 2013. Stress near the epicenters rapidly increased 0.10 - 0.12 MPa over 45 days, ~8 months before the Ms 6.6 Nimu earthquake occurred. The high principle stress anomalies decreased quickly to the normal stress state in ~8 -?12 months after the Ms 8.1 West Kunlun Pass and the Ms 8.0 Wenchuan earthquakes. These high stress anomalies and their demise appear directly related to the immediate stress rise along a fault prior to the earthquakes and the release during the event. Thus, the stress rise appears to be a viable precursor in prediction of large continental earthquakes as in the Tibetan Plateau.

In-situ stress distribution and coalbed methane reservoir permeability in the Linxing area, eastern Ordos Basin, China

Understanding the distribution of in-situ stresses is extremely important in a wide range of fields such as oil and gas exploration and development, CO2 sequestration, borehole stability, and stress-related geohazards assessment. In the present study, the in-situ stress distribution in the Linxing area of eastern Ordos Basin, China, was analyzed based on well tested parameters. The maximum horizontal principal stress （SHmax）, minimum horizontal principal stress （Shmin）, and vertical stress （Sv） were calculated, and they were linearly correlated with burial depth. In general, two types of in-situ stress fields were determined in the Linxing area： （i） the in-situ stress state followed the relation Sv 〉 Snmax 〉 Shmin in shallow layers with burial depths of less than about 940 m, indicating a normal faulting stress regime; （ii） the Snmax magnitude increased conspicuously and was greater than the Sv magnitude in deep layers with depths more than about 940 m, and the in-situ stress state followed the relation Snmax 〉 Sv 〉 Shmin, demonstrating a strike-slip faulting stress regime. The horizontal differential stress （Snmax-Shmtn） increased with burial depth, indicating that wellbore instability may be a potentially significant problem when drilling deep vertical wells. The lateral stress coefficient ranged from 0.73 to 1.08 with an average of 0.93 in the Linxing area. The coalbed methane （CBM） reservoir permeability was also analyzed. No obvious exponential relationship was found between coal permeability and effective in-situ stress magnitude. Coal permeability was relatively high under a larger effective in-situ stress magnitude. Multiple factors, including fracture development, contribute to the variation of CBM reservoir permeability in the Linxing area of eastern Ordos Basin.

高速列车转向架区域积雪问题的数值研究

当高速列车在高寒雨雪地区行驶时,转向架区域容易形成积雪,对高速列车的安全行驶造成威胁。在积雪轨道上行驶的高速列车,其转向架区域积雪中雪粒来源于地面积雪,因此基于壁面切应力,建立风致积雪雪粒运动模型,研究地面积雪中雪粒在列车风作用下的运动情况。采用欧拉-拉格朗日方法,基于雪粒沉积准则,建立转向架区域雪粒沉积边界模型,研究风致雪粒运动情况下转向架区域积雪分布。研究结果表明:高速气流在转向架正下方区域出现高速上扬的现象;转向架区域的车体板件、构架和轴箱等为主要的积雪部位;转向架区域雪粒沉积数量与转向架的位置、雪粒的密度和直径及壁面条件有关。

高应力断层构造区巷道冲击破坏特征研究

断层构造区静动载应力耦合作用加剧了井下断层区围岩冲击危险性,断层构造区巷道围岩应力分布规律及冲击动载响应特征存在显著特殊性。目前对于断层构造区的冲击研究主要集中于工作面采场附近,但对于断层构造区巷道冲击破坏鲜有研究。以陕西某矿深埋高应力断层构造区巷道为工程背景,分析了断层构造区巷道围岩变形破坏力学特征:①断层面存在明显应力阻隔效应,正断层附近存在上盘应力集中区和下盘应力降低区2个特殊应力区。巷道由于断层面影响,巷帮静载集中应力呈现非对称分布特征,远离断层面侧应力集中程度大于靠近断层面侧,该侧巷道围岩冲击破坏危险程度增大。②断层面对于应力波传递产生明显阻隔作用,正断层上盘动载响应大于下盘动载响应,由于巷道两帮应力非对称分布特征,右帮动载响应明显大于左帮。基于上述特征,提出了断层构造区巷道围岩“卸(大直径钻孔卸压)−支(梯次加固成层式吸能防冲支护)”协同防冲控制技术,工程试验结果表明:①巷道围岩采取“卸−支”协同防冲处理措施后,巷道两帮应力集中区往围岩深部转移3~5 m,应力峰值降低18.5%~20.3%,巷道帮部围岩应力集中程度显著降低。②采用“卸−支”协同防冲处理措施前,巷道顶底板及两帮变形量分别为856,334,325,567 mm,巷道围岩变形破坏严重,采用“卸−支”协同防冲处理措施后,巷道围岩变形量降低35.69%~62.03%,巷道围岩稳定性增强。③钻孔煤粉量显著低于临界粉煤量,巷道围岩动力显现降低。

黄土高填方挖填结合区桩基础数值模拟研究

为了分析黄土地区桩基础的力学响应特性,文中建立了桩基础的仿真模型,模拟分析了不同材料参数条件下桩基础的变形及受力特性。结果表明,桩基础的侧阻力随着深度的增加呈现先稳定后增加(正摩阻力)、再反向增加(负摩阻力)的变化规律,增加筏板和抬升坡度均可有效增加桩侧的摩阻力;桩基础的桩身轴力随着深度的增加呈现先增加(桩体埋深小于20 m)后降低(桩体埋深20~30 m)的变化规律,增加筏板、抬升坡度及增加桩径均可有效降低桩身的轴力,抬升坡度可有效降低桩身侧向的土压力。

高应力区综采工作面回撤通道施工工艺及支护技术研究

虎龙沟矿81511工作面回撤通道施工时受地质构造影响,采用传统施工工艺时存在效率低、成本费用高、围岩控制维护难度大等技术难题。通过技术研究,对81511工作面回撤通道施工方案进行对比,采用自成巷法施工工艺,并对高应力区回撤通道顶板采用“切顶卸压+注浆加固+锚索钢带+锚索棚”联合支护,对煤壁采用“L型钢棚+水力膨胀锚杆”联合支护技术。应用效果表明,回撤通道采用自成巷法施工工艺后,施工周期缩短了8.5 d,减少设备安装数量;采用联合支护技术后,减少了高应力区回撤通道顶板破碎、煤壁片帮现象。回撤通道施工后现场实测顶底板最大移进量为0.24 m,帮部最大收敛量为0.32 m,取得了显著应用成效。

高应力区软岩煤层巷道掘进支护优化

基于长平煤矿53101巷掘进期间受地质构造应力影响,围岩出现破碎、巷帮垮落现象,分析了围岩破碎机理,对垮落巷帮采取柔性注浆加固技术,对顶板采取“桁架锚索+L型拉棚+梯形钢棚”联合支护,从现场实际应用效果来看,通过对巷帮及顶板采取联合支护技术后,提高了巷道围岩稳定性,两帮最大收缩量为0.32 m,顶底板移近量为0.21 m,取得了显著应用成效。

旭龙水电站进水塔抗震稳定性分析

旭龙水电站所处工程区的地震基本烈度为Ⅷ度,属于高地震区。为研究进水塔结构的抗震设计,采用三维有限元分析软件,运用振型分解反应谱法计算进水口在静动力各工况下的变形和应力分布,并对进水塔的整体稳定和基底应力进行了验算。结果表明:在各工况下,进水塔各部位一般应力均在规范许可的范围内,整体稳定及基底应力均满足规范要求,旭龙水电站进水塔结构抗震性能良好。研究成果可为类似进水塔结构设计提供参考。

基于微震监测技术的矿山高应力区采动研究

冬瓜山铜矿是目前国内开采最深的金属矿山之一,岩石具有典型的岩爆倾向性,最大应力为38MPa,为控制岩爆的发生及制定高应力区采矿的战略,2005年矿山引进南非ISS国际公司的微震监测系统,实现对采矿引起的岩体应力、应变状态的实时监测。简单介绍冬瓜山矿微震监测系统的布置;基于一段时间内监测到的有效事件,对井下首采区地震事件的时间与空间分布进行研究;利用可视化工具JDI对事件的相对集中区域进行圈定,并与井下生产活动相结合,分析原因;还提出对井下工程岩体危险识别的手段,并用实际发生的事件验证;综合研究成果,制定以微震监测技术为基础的高应力区采动分析的工作程序,为目前矿山的安全生产提供依据。

动力扰动下深部采空区围岩力学响应及充填作用效果

针对深部采空区承受高静载同时受到周边采场爆破地震波扰动的具体情况,为研究采场围岩的稳定性,应用应力波方法分析了采空区围岩受到侧崩时的动力响应及充填的支护效果,采用有限差分软件FLAC3D模拟了安徽省铜陵的冬瓜山铜矿典型采场受到周边开采爆破侧崩时的动力特征及全尾胶充填的支护效果。分析结果表明:爆炸地震波传播过程中,围岩应力场受到扰动,采空区自由面振动速度幅值约为围岩内部的2倍,围岩产生新的塑性变形,质点位移增加;对采场进行充填能够降低接触面振动速度,减少围岩塑性变形及质点位移,从而保护了采场间柱,提高采场围岩稳定性。

大北地区高陡构造异常高压地层地应力测井计算方法

塔里木盆地库车坳陷大北地区是异常高压发育地带,高孔隙压力和强烈的构造运动使得地应力的大小及分布变得较为复杂。针对大北地区地层倾角较大、地层异常高压、地应力强的实际情况,基于应力分布的几何空间三角函数关系,以地应力实验和压裂试采实测值为刻度基准,利用地层倾角测井和声电成像测井解释得到的地层倾角数据,引入地层倾角DIP对地应力的影响系数,建立适合于大北地区高陡地层地应力的测井计算方法。处理了工区多口井的测井资料,其地应力计算值与实测值较为一致,能满足工程应用要求,值得推广应用。

庐江-枞阳矿集区深部结构与成矿

为探测长江中下游成矿带庐江-枞阳白垩纪火山岩盆地和铁、硫矿集区深部构造和地壳结构,探讨成矿深部控制条件,作者完成了穿越火山岩盆地的深反射地震剖面(记录30s)和罗河铁矿区浅层高分辨反射地震剖面,揭示了矿集区全地壳精细结构,同时开展区域构造测量和应力场反演研究,获得了新的认识。证实"耳状"的庐-枞火山岩盆地是一个沿北东向罗河断裂向东发育的非对称火山盆地,排除了另一半被断在西侧红层之下的判断;罗河断裂是一条切穿MOHO的深断裂,倾向南东,是引导地幔流体和岩浆上涌和喷发的通道;鉴别出多层界面,火山岩-侏罗系砂岩厚约4-5km(其中火山岩厚度约3km),三叠系-震旦系变形层底界深度大致18-20km,变质基底组成中下地壳,MOHO平缓向西北倾,深度33-31km;追踪郯-庐断裂带的深部产状,陡立延伸到MOHO,宽约10km。

高地应力区深埋隧道三维应力场数值模拟

结合高地应力区某深埋隧道工程,通过三维弹塑性有限元数值模拟,分析隧道掌子面推进过程中的围岩空间应力场状态和演化趋势。结果表明:当掌子面接近和通过某一断面时,围岩主应力大小和方向发生相应的变化。隧道开挖对平面σx、σy的主要影响范围约为0.5B,对围岩空间主应力和剪应力的影响范围约1.0B,对围岩位移和屈服接近度的影响范围分别为2.0B和1.0B。对高地应力区深埋隧道围岩稳定性分析、确定合理的支护措施以及制定合理的开挖方案具有重要的意义。

女鞋鞋跟高度对前掌动态稳定性的影响

旨在研究女性穿着不同跟高的鞋子行走时前掌压强和受力面积的变化,再根据前掌受力面积和压强的变化客观地评估高跟鞋前掌处的稳定性。研究发现,当高跟鞋跟高超过5.5 mm以后,前掌压强急剧增加,受力面积减少。这将严重影响高跟鞋的稳定性。

金川矿区深部高应力矿床开采关键技术研究与发展

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