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.

Numerical analysis on mechanical difference of sandstone under in-situ stress,pore pressure preserved environment at depth

Deep in-situ rock mechanics considers the influence of the in-situ environment on mechanical properties,differentiating it from traditional rock mechanics.To investigate the effect of in-situ stress,pore pressure preserved environment on the mechanical difference of sandstone,four tests are numerically modeled by COMSOL:conventional triaxial test,conventional pore pressure test,in-situ stress restoration and reconstruction test,and in-situ pore pressure-preserved test(not yet realized in the laboratory).The in-situ stress restoration parameter is introduced to characterize the recovery effect of in-situ stress on elastic modulus and heterogeneous distribution of sandstone at different depths.A random function and nonuniform pore pressure coefficient are employed to describe the non-uniform distribution of pore pressure in the in-situ environment.Numerical results are compared with existing experimental data to validate the models and calibrate the numerical parameters.By extracting mechanical parameters from numerical cores,the stress-strain curves of the four tests under different depths,in-situ stress and pore pressure are compared.The influence of non-uniform pore pressure coefficient and depth on the peak strength of sandstone is analyzed.The results show a strong linear relationship between the in-situ stress restoration parameter and depth,effectively characterizing the enhanced effect of stress restoration and reconstruction methods on the elastic modulus of conventional cores at different depths.The in-situ pore pressurepreserved test exhibits lower peak stress and peak strain compared to the other three tests,and sandstone subjected to non-uniform pore pressure is more prone to plastic damage and failure.Moreover,the influence of non-uniform pore pressure on peak strength gradually diminished with increasing depth.

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.

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.

Stress Corrosion Cracking of High-strength Drill Pipe in Sour Gas Well

In high sour gas reservoir drilling process, it happens occasionally that high-strength drill pipe suffers brittle fracture failure due to stress corrosion cracking, and poses serious hazard to drilling safety. To solve this problem, this paper studied the stress corrosion cracking mechanism and infl uencing factors of highstrength drill pipe in sour environment with hydrogen permeation experiments and tensile tests. We simulated practical conditions in laboratory and evaluated the stress corrosion cracking performance of the high-strength drill pipe under conditions of high stress level. For the problems occurring in use of high-strength drill pipe on site, the paper proposed a technical measure for slower stress corrosion cracking.

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.

基于FLAC^(3D)数值模拟的回风平巷变形破坏机理分析

随着开采的逐步深入,山西华晋吉宁煤业逐步面临着高应力环境下回采巷道掘进难以及支护难等问题。以该矿2208回风平巷为研究对象,借助FLAC 3D通过数值模拟的方式用控制变量法分别从地质条件、支护方式、施工工艺这3个方面分析对巷道围岩变形量(顶板下沉量、底板鼓起量,侧帮变形量)、破坏区深度、破坏体积的影响。研究发现断层地质构造对回采巷道及周围煤岩体稳定性影响显著,应当在回采巷道揭露断层地质构造时加强对回采巷道的支护工作。锚杆支护能够有效改善巷道围岩变形以及应当采用及时支护方式对回采巷道进行加固,并尽量减少顶板暴露面积,从而最大限度地维护巷道围岩稳定。

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.

An experimental study of ultra-high temperature ceramics under tension subject to an environment with elevated temperature,mechanical stress and oxygen

Ultra-high temperature ceramic(UHTC) composites are widely used in high-temperature environments in aerospace applications. They experience extremely complex environmental conditions during service, including thermal, mechanical and chemical loading. Therefore, it is critical to evaluate the mechanical properties of UHTCs subject to an environment with elevated temperature, mechanical stress and oxygen. In this paper, an experimental investigation of the uniaxial tensile properties of a ZrB_2-SiC-graphite subject to an environment with a simultaneously elevated temperature, mechanical stress and oxygen is conducted based on a high-temperature mechanical testing system. To improve efficiency, an orthogonal experimental design is used. It is suggested that the temperature has the most important effect on the properties, and the oxidation time and stress have an almost equal effect. Finally, the fracture morphology is characterized using scanning electron microscopy(SEM), and the mechanism is investigated. It was concluded that the main fracture mode involved graphite flakes pulling out of the matrix and crystalline fracture, which indicates the presence of a weak interface in the composites.

夏季老年人典型局部皮肤温度的确定及其应用

为探究夏季老年人皮肤温度特征,快速判断老年人热应激状态,选择保定市某老年公寓24名老年人为受试者进行现场测试,获取1900组环境生理指标数据。分析夏季不同环境温度下老年人11个局部皮肤温度分布特征,基于局部皮肤温度的环境敏感性和局部皮肤温度之间的相关性,选择1个典型局部皮肤温度,最终提出典型局部皮肤温度在现场测量中的具体应用。结果表明:手背温度的环境敏感性最高,与其他局部皮肤温度最为显著相关,手背温度为典型局部平均温度;平均皮肤温度与手背温度呈二次多项式关系;手背温度对应的热应激分级区间为无或轻度[35.6℃,35.8℃]、中度(35.8℃,36.8℃]、重度(36.8℃,39.1℃]。通过测量手背温度,可快速估算均匀及稳态环境下的平均皮肤温度和评价老年人热应激状态。本研究可为实际现场快速判断老年人热应激风险提供参考。

高中生班级环境和学业压力的关系:一个有调节的中介模型

为探讨高中生班级环境与学业压力的关系及其内部机制,本研究构建了一个有调节的中介模型,采用问卷调查法对870名高中生进行调查。结果表明:(1)班级环境的师生关系、同学关系负向预测学业压力;班级环境的竞争、学习负担正向预测学业压力;(2)学业社会比较的比较取向、自我贬低在班级竞争和学业压力之间起中介作用;(3)自我概念清晰性可以调节“班级竞争→比较取向→学业压力”中介模型的前半段以及“班级竞争→自我贬低→学业压力”中介模型的前半段。结论:班级竞争通过学业社会比较取向和自我贬低负向预测学业压力,同时自我概念清晰性可以调节比较取向和自我贬低的中介作用。

温度与应力耦合作用下高强钢海水腐蚀行为研究

目的保证船舶设备安全,明确船用Ni-Cr-Mo-V高强钢在不同海水温度中的服役状态变化。方法在实验室模拟环境中,通过四点弯曲装置向Ni-Cr-Mo-V高强钢施加不同应力,并结合电化学测试、腐蚀形貌和产物分析,研究温度与应力耦合对Ni-Cr-Mo-V高强钢在不同温度海水环境中腐蚀行为的影响及规律。结果温度升高会加快Ni-Cr-Mo-V高强钢腐蚀产物的生成,但是在较高温度海水中,会使高强钢由点蚀转变为均匀腐蚀,因此较高温度海水中对高强钢施加外加应力未发现点蚀坑加深。较高温度海水相对于低温海水条件下,高强钢腐蚀产物层中的Cr、Ni含量增加,低温海水中施加应力致使腐蚀产物层中的Cr、Ni含量降低,而较高温度海水中施加应力对腐蚀产物成分的影响不大。温度对Ni-Cr-Mo-V高强钢的腐蚀作用明显强于外加应力对其的腐蚀作用。结论在不同温度海水中,较高的温度使得Ni-Cr-Mo-V高强钢的耐蚀性能降低,但是相对于低温海水中,较高温度海水条件下施加应力对Ni-Cr-Mo-V高强钢腐蚀的影响较小,因此对于高强钢在海水中的腐蚀,温度对高强钢的影响明显大于应力的影响。

高锰钢在模拟海洋环境中的应力腐蚀行为

以低温高锰钢为研究对象,采用光学显微镜、扫描电镜、透射电镜、X射线能谱分析仪等设备对高锰钢进行微观观察,采用恒载荷应力腐蚀试验研究其在人工海水溶液中的应力腐蚀行为,采用电化学手段测试其腐蚀性能。结果表明:低温高锰钢晶粒度大小不一,显微组织主要为形变奥氏体,试样内存在位错及孪晶,晶界上未见明显析出物;在低温高锰钢的使用过程中,其缺陷部位优先发生腐蚀,在恒定应力条件下,材料表面局部生成微裂纹,且扩展速率较慢,材料对应力腐蚀不敏感;当应力发生变化时,试样中微裂纹与应力的平衡被打破,加速了裂纹的扩展和新微裂纹的萌生,材料在腐蚀环境下易发生应力腐蚀开裂。

动车侧窗固定密封用胶粘剂理化特性分析评估

高铁动车侧窗在运行过程中是暴露在外界的环境中,外界因素会影响胶粘剂的粘接性以及可靠性。因此,对高铁动车上使用较为广泛的某款胶粘剂进行可靠性评估,确定其对不同环境的敏感特性。确定胶粘剂的使用位置,评估胶粘剂在实际使用过程中的可能经历的环境条件;对胶粘剂按照相关标准进行制样,进行模拟实际环境条件下的环境适应性考核;对经历不同环境条件下胶粘剂样品进行理化性能分析,确定胶粘剂的主要敏感应力。通过对胶粘剂环境可靠性的评估,确定胶粘剂的敏感环境应力,为胶粘剂后期的使用及更换提供参考。

高原环境因素与自由基反应

高原环境是一个特殊的生态环境系统,其复杂多变的自然地理条件使移居和新进高原环境的人群或生物出现高原反应或发生“高原(山)病”。大气压低、氧分压低、太阳辐射强所导致的氧化应激反应是高原反应或高原病的主要原因之一。本文从高原气候因素与自由基反应,不同海拔高度对不同民族人群自由基反应的影响,相同海拔高度不同人群的自由基反应,海拔高度与机体抗氧化营养物质变化的关系,不同海拔高度紫外线强度与自由基反应及高原环境地球化学异常与自由基反应等6个方面,论述了高原环境因素与不同人群自由基反应的关系,不仅对探讨环境应激反应所产生的自由基反应与世居高原地区人群起源和进化有重要意义,而且对研究移居人群高原反应和高原病的预防、治疗及经济、国防建设具有现实应用价值。

艾丁湖盐角草种群动态生命表及其对温度变化的响应

艾丁湖地处亚洲中部极端干旱区,夏季酷热,地势闭塞,环境条件独特。本研究在该地区选择3个具有不同水分特征和盐角草(Salicornia europaea)种群特征的样地(A样地:地形偏高,4月之后地表无积水,盐角草密度相对较低;B样地:位于地表径流覆盖范围内,地表长期有积水,种群密度相对中等;C样地:地表早期有积水,种群密度相对最大,盖度最高)进行调查,根据盐角草的生长情况,从3月至10月每月调查1~2次,共10次,每次统计样方内盐角草的株数。利用动态生命表以及相关性分析的方法来研究该地区盐角草种群变化及其与环境温度之间的关系。结果表明,艾丁湖盐角草种群密度在5月前基本呈增长状态,5月末至6月由于温度升高、水分下降和营养物质减少引发了种群自疏,出现第1次死亡率高峰期;7月至8月,A、B两个种群出现第2次死亡率高峰期,主要原因是连续长达34d的40℃以上的极端高温;9月A种群出现第3次死亡率高峰期,主要原因可能是高温以及高温加速土壤水分蒸发引起的土壤返盐、水分丧失,从而导致的高温胁迫和盐胁迫。相关性分析表明,A、B种群死亡率与高温显著相关(P<0.05)。C种群仅有一次死亡率高峰期,且与温度相关不显著(P>0.05),与A、B种群差异较大的原因可能是由于C样地水分条件好、种群密度高缓解了高温的胁迫作用。A、B两个种群存活曲线属于Deevy-Ⅲ型,即初期死亡率较高,9月之后趋于稳定;C种群属于Deevey-Ⅱ型存活曲线,呈对角线型,即各个龄级存活率基本一致。

离心机臂动特性分析

在高线加速度下热与振动复合环境试验中 ,通常用离心机来实现高线加速度环境 .由于离心机臂端安装振动台、温度箱、夹具、试件 ,其总重量很大 ,在高转速下将产生很大的离心力 ,造成离心机臂伸长 ,从而影响加速度输出精度 .因此 ,利用有限元方法 ,对离心机在不同转速下机臂位移场进行计算 ,分析了离心机臂伸长对加速度输出精度的影响 ,并对离心机固有振动特性进行了分析 ,得出了一些有意义的结论 .

矿井高温高湿职业危害及其临界预防点确定

为预防矿井高温高湿热害对矿工身心健康造成不良影响,对矿井热源以及高温高湿环境导致的职业危害进行分析。选取等效温度(TET)和综合温度指标(TZ)作为热应力指标,调查研究矿井高温高湿环境造成的矿工疲劳问题和烦恼问题。提出在矿井特殊环境下导致矿工疲劳和烦恼的临界预防点—TET指标临界值和TZ指标临界值分别为28.48℃和26.14℃,并给出矿井临界深度745 m。结果表明:提出的临界预防值与国内外已经制定的标准有一定的一致性。矿井开采超过临界深度后,矿工疲劳、烦恼影响程度将随开采深度急剧增加。不同深度矿井应该采取不同的降温标准。

深部高应力动态环境下水平矿柱开采稳定性研究

深部水平矿柱开采的稳定性问题 ,是地下金属矿山迫切需要解决的共性技术难题之一。采用数值模拟和相似材料模拟方法对此进行了研究 ,结果表明 ,在双回路回采初期 ,水平矿柱中出现了应力集中 ,之后应力逐步减小 ,与此同时 ,水平矿柱下部充填体承载能力迅速提高 ,充分发挥了充填体支撑围岩与吸收地应力的作用。模拟实验表明 ,在整个回采过程中 ,水平矿柱并没有出现应力高度集中或突然降低现象 。

高温、噪声及二者结合对大鼠血浆部分生化指标的影响

为探讨环境因素对飞行人员的影响，８０只Ｗｉｓｔａｒ大鼠随机分为：高温组、噪声组、两组条件相加的复合组和对照组。用特异性放射免疫法测定各组血浆心钠素（ＡＮＰ）、心脏扩张素（ＣＤＤ）、内源性洋地黄因子（ＥＤＬＳ）、血管紧张素Ⅱ（ＡⅡ）及内皮素（ＥＴ）含量。高温组血浆ＡＮＰ含量明显低于对照组（Ｐ＜０．０５）。高温组、噪声组血浆ＣＤＤ含量明显高于对照组（Ｐ＜０．０５）。高温组、噪声组及复合组血浆ＡⅡ明显高于对照组（Ｐ＜０．０５）。复合组血浆ＥＴ含量明显低于对照组（Ｐ＜０．０５）。各组ＥＤＬＳ含量无显著差异。提示：ＡＮＰ、ＣＤＤ、ＡⅡ含量变化与高温、噪声引起大鼠脱水、失盐及交感神经兴奋、肾素分泌增加有关，为机体的代偿反应。