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.

Support failure of a high-stress soft-rock roadway in deep coal mine and the equalized yielding support technology： a case study

Abstract There are many soft-rock roadway coal mines in China. The surrounding rocks of the high-stress soft-rock roadways in deep mine are especially difficult to be supported using the traditional supporting way. In this study, the south wing rail roadway on the second level of Yunjialing coal mine in China was used as an example to analyze the deformation and failure characteristics and influencing factors of roadway. On this basis, this study proposed the equalized yielding support idea which employs the yielding rings to realize the pressure equalization on the bolts and cables in the section. To achieve this purpose, the first bolt-mesh-cable equalizing pressure yielding support was integrated with the second grouting reinforcement. The results proved that the yield rings of the bolts and cables on the spandrel of the arched roadway firstly developed yielding deformation; then the deformation extended to the vault of the roadway; the bolts and cables achieved a yielding extreme value of 15 and 18 tonnes, respectively. The roadway surrounding rock tended to be stable at the 26th day after the maintenance. The equalizing pressure yielding supporting technology plays a moderate pressure-releasing and actively controlling role on the surrounding rocks in the soft-rock roadway with large deformation.

In-situ measure to internal stress of shotcrete layer in soft-rock roadway

In order to solve the difficult conditions of soft rock,water-trickling and hard-maintain of main air-return roadway in Tarangaole Colliery,high pretensioned stress and intensive bolt-shotcrete support program was designed and mechanical property of shotcrete layer was specially monitored through utilizing a type of concrete stress meter with oscillating chord after the program was carried out.It was indicated that,due to rock pressure and support resistance,the interior of shotcrete layer would emerge diverse stresses in axial,radial and tangential directions.With time passing internal stresses in three directions,whose average values were-0.061,0.043 and 0.517 MPa respectively,fluctuated first and then tended to stability slowly.The axial and radial stresses were relatively smaller than tangential stress which was 11,12 times the two formers respectively.Along the section of roadway,axial and tangential stresses distributed symmetrically and increased gradually from the top of arch to the waist of wall,but reduced at the foot of wall.Radial stresses reduced from the top of arch to the waist of arch first,and then increased in the waist of wall.Axial stresses were tensile substantially,except for stresses in arch vault tending to compressive,but all the radial stresses were compressive.Nevertheless,tangential stresses in the wall were compressive and tangential stresses in the arch were tensile.During the period of roadway excavating,the stress of shotcrete layer was less than its ultimate bearing capacity,with no significant stress concentration.At the end of this article,some suggests are given to shotcrete support design.

Key technologies and engineering practices for soft-rock protective seam mining

Severe gas disasters in deep mining areas are increasing,and traditional protective coal seam mining is facing significant challenges.This paper proposes an innovative technology using soft rock as the protective seam in the absence of an appropriate coal seam.Based on the geological engineering conditions of the new horizontal first mining area of Luling Coal Mine in Huaibei,China,the impacts of different mining parameters of the soft-rock protective seam on the pressure-relief effect of the protected coal seam were analyzed through numerical simulation.The unit stress of the protected coal seam,which was less than half of the primary rock stress,was used as the mining stress pressure-relief index.The optimized interlayer space was found to be 59 m for the first soft-rock working face,with a 2 m mining thickness and 105 m face length.The physicochemical characteristics of the orebody were analyzed,and a device selection framework for the soft-rock protective seam was developed.Optimal equipment for the working face was selected,including the fully-mechanized hydraulic support and coal cutter.A production technology that combined fully-mechanized and blasting-assisted soft-rock mining was developed.Engineering practices demonstrated that normal circulation operation can be achieved on the working face of the soft-rock protective seam,with an average advancement rate of 1.64 m/d.The maximum residual gas pressure and content,which were measured at the cut hole position of the protected coal seams(Nos.8 and 9),decreased to 0.35 MPa and 4.87 m^3/t,respectively.The results suggested that soft-rock protective seam mining can produce a significant gas-control effect.

Failure mechanism and control technology of deep soft-rock roadways:Numerical simulation and field study

Large deformations such as roof subsidence,floor heave,and two-sided deformations occur frequently in deep soft-rock roadways.The deformation becomes more severe under the combined effect of high in-situ and mining-induced stresses,which detrimentally affect the safe mining of coal.Based on the geological conditions and roadway failure characteristics of the Nanyaotou coal mine in Shanxi province,China,we used comprehensive numerical simulations and field observations to study roadway deformation and failure.The deformation mechanism of deep soft-rock roadways under dynamic pressures is described,and the corresponding control measures are proposed.The deformation and fracture development characteristics of roadways surrounding rocks were explored with a primary support scheme,and its effects were evaluated.The radius of the plastic zone and the displacement deformation of the roadway were studied by using theoretical analysis,and a combined-support design of‘‘anchor bolt+anchor cable+shotcrete+deep and shallow borehole grouting+inverted arch”was proposed to limit deformations and relieve the stress in the surrounding rocks.Numerical simulations and field monitoring showed that the combined support scheme can effectively mitigate the large deformations of ventilation roadways and provide guidance for the stable control of deep soft-rock roadways.

高地应力软岩隧道仰拱结构受力特性与参数优化

为探索高地应力软岩隧道施工期间仰拱结构受力特性与合理支护参数,以陕西省宝汉高速公路连城山隧道工程为依托,针对仰拱施工病害及其主要影响因子,采用现场试验与数值模拟相结合的方法,探讨了不同影响因素下的仰拱结构变形与力学响应,分析了仰拱结构变形与受力对不同影响因素的敏感性,基于仰拱结构病害特征及数值模拟结果,对仰拱半径(深度)、仰拱厚度等支护参数进行了优化,并进行了工程验证。结果表明:连城山隧道施工期间仰拱二次衬砌最大接触压力达1.034 MPa,混凝土最大应力超过其抗压强度(30 MPa),出现了仰拱回填隆起、开裂等病害,仰拱设计支护参数难以保障结构稳定;地应力水平和基底围岩劣化对仰拱结构变形与受力状态均有显著影响,其中基底软化深度的影响最为突出,地应力水平次之;减小仰拱半径、增大仰拱厚度、增大仰拱钢筋直径、减小仰拱钢筋间距均能显著抑制仰拱变形,而提高混凝土强度等级对控制仰拱变形效果不明显,且经济性较差;优化后的仰拱受力得以明显改善,有效控制了仰拱结构病害,避免了频繁拆换仰拱,保障了隧道结构安全稳定。研究成果可为类似软岩隧道仰拱变形控制及病害防治提供重要借鉴。

滇中芹河隧洞软岩破碎段围岩大变形与支护结构相互作用研究

软岩大变形是滇中引水工程建设中较为突出的工程地质问题之一,以大楚段芹河隧洞4#支洞为研究对象开展软岩大变形特征及承载结构受力研究。4#支洞在施工过程中发生影响洞室稳定的问题,洞周围岩大变形不同程度侵限,导致钢拱架扭曲断裂、喷混凝土掉落现象时有发生。为了充分认识隧洞变形特征、破坏模式及成因机制,结合工程地质勘察、现场监控量测、数值反演及施工模拟分析等手段和方法对其进行综合研究。研究成果表明:破碎软岩洞段施工期围岩监测变形量大、变形速率较快,变形具有明显的时效性;围岩完整性差,洞周变形差异大;围岩以剪切破坏为主;围岩时效变形对支护结构受力影响大,部分承载结构受力超限,导致局部结构破坏。可见,针对破碎的软岩隧洞施工,需要采取超前注浆、减少减小施工扰动、及时跟进初期支护、尽快封闭成环,加强施工期围岩变形监测,选取合理的衬砌支护时机,实时指导和优化隧洞支护结构施工设计。

深井松软围岩煤巷采动增跨效应及防控技术

针对深井松软煤巷围岩变形严重、巷道支护困难等问题,以城郊煤矿LW21106工作面沿空巷道为工程背景,建立了采动巷道增跨模型,揭示了采动增跨效应演化机理。通过构建巷道顶板横纵弯曲梁模型,指出顶板横向受力、巷道等效跨度、煤岩强度是巷道围岩损伤破坏的主控因素,提出了采动增跨效应防控对策并进行工业性试验。研究结果表明:受采动影响,巷道经历“初始围岩稳定—围岩裂隙发育扩展—围岩剪切破坏加剧—等效跨度增加”过程;巷道顶板最大正应力与应力集中系数、顶板等效跨度、巷道断面尺寸及埋深成正相关关系;巷道顶板在高应力环境下易发生拉剪破坏,增加顶板锚索数量以及锚索预紧力有利于增强顶板初期完整性。基于巷道变形破坏主控因素,提出“围岩加固–卸压–强化支护”协同防控策略;针对现场条件,采用煤柱侧向切顶+注浆加固并对破碎区域补充锚索强化支护的防控技术。现场监测结果表明,煤柱帮最大移近量为18.89cm,顶板下沉量为25.86cm,两帮移近量为29.65 cm,有效控制了煤巷围岩变形,为深井松软围岩巷道变形控制提供了参考。

软弱围岩掘锚一体化快速掘进关键技术与工程实践

软弱围岩掘锚一体化快速掘进关键技术与装备是煤矿安全高效开采以及智能化建设的迫切需求。以具备膨胀性、节理化等软岩特征的煤矿回采巷道工程为背景,梳理了国内外掘锚一体机快速掘进技术发展现状,剖析了软弱围岩条件下掘锚一体机快速掘进面临3个方面的难题,包括全宽截割对围岩的扰动控制,软弱围岩及时高效永久支护,软弱围岩快速掘进煤帮临时支护。提出了软弱围岩掘锚一体化快速掘进的5项关键技术,包括:(1)低扰动截割技术。主要包括椭型全宽截割滚筒、截齿排布优化、截割动力学优化等。(2)减小空顶空帮距的及时支护技术。该技术是在掘锚一体化技术基础上,研制了集双圆柱导向、多连杆升降、支护油缸撑顶撑底、随动挡矸帘防护于一体的多钻机整体滑移平台,将掘锚一体机作业空顶距由2.5 m降至1 m,作业空帮距由3.5 m降至1 m。(3)软弱围岩多维度协同支护技术。综合考虑锚杆锚索支护参数间的时空协同效应和支护体与围岩的协同效应,掘进工作面采用低密度强力锚杆支护控制顶板,后部同步实施增强永久支护。(4)钻锚一体化技术。主要包括锚杆结构和力学特性、锚固剂材料及泵注技术等。(5)煤帮喷涂临时支护技术。主要包括快反应高延伸率喷涂材料、高比例精度喷涂泵送、不规则煤壁表面自适应轨迹控制、矿用防爆高精度机械臂、喷涂材料配套补给等。基于以上内容,研制了可控作业空顶距掘锚一体机,并进行了井下试验。试验表明,该装备有效缩短了作业空顶距和空帮距,实现了作业空顶距“可控”,适应于软弱围岩巷道快速掘进,掘进效率提高了1倍。

极高地应力软岩隧道非对称变形机理及支护优化研究

针对极大断面公路隧道施工中出现的非对称大变形问题,考虑高地应力第一主应力与隧道轴线关系、层状软岩夹层与互层状态、掌子面软岩空间不对称、地下水等因素,基于对工程地质条件、围岩与支护结构失效及破坏特征的分析,结合岩样物理力学特性室内试验研究及地应力实测情况,探究了非对称大变形形成机理并提出针对性的支护结果优化方案。结果表明:高地应力层状软岩隧道围岩不对称变形是在岩层倾角α、最大水平主应力与隧道轴线夹角β和岩层夹角γ、围岩岩性和地下水综合作用下的大变形,围岩不对称部位由以上几种因素共同决定;当主应力σ1与隧道轴线既不垂直也不平行时,会产生挤压性偏压构造水平地应力,使隧道横断面侧向受力不对称,发生偏压性非对称大变形;通过改变锚杆的布设方式、提高超前注浆小导管的长度和刚度、喷射临时封闭、在防水板与喷射砼间增加高密度橡塑海绵板缓冲层等措施,可以有效的减少变形量,防止围岩因开挖扰动而松动和坍塌。

高地应力软岩隧道长期稳定性分析

研究目的:高地应力软岩具有明显的流变特性,流变过程中岩体参数随时间发生变化。本文结合梁王山隧道的设计施工方案,采用Cvisc模型对其施工过程及运营期间的围岩和支护的受力和变形情况进行分析,查明了隧道在施工阶段和长期运营阶段的应力、应变和变形特性以及隧道支护结构的内力与变形随时间发展规律。研究结论:(1)在软岩隧道工程施工中,施工时应对隧道初支拱脚处适当加固,控制拱脚变形;(2)不仅要保证施工期的安全,更需要关注隧道在后期运营过程中的长期稳定性;(3)需根据全寿命周期内的围岩流变稳定状态设计支护结构的刚度,从而确保隧道结构长期稳定;(4)本研究成果可为高地应力软岩隧道施工安全和长期稳定性研究提供参考。

深部破碎软岩巷道超前控顶加固及控制爆破技术

随着矿山开采深度逐渐增加,深部破碎围岩工程地质条件转为复杂多变,极大程度上影响巷道等工程施工过程及后续使用安全;为确保深部破碎软岩巷道施工过程中安全及质量,提出了软岩巷道超前控顶加固及控制爆破技术。针对钟九铁矿-550 m水平6号交岔点岩体裂隙极为发育、稳定性差等特点,拟采用超前控顶措施加固顶板围岩,提高深部破碎软岩巷道的承载力。为便于6号交岔点掘进施工,沿6号交岔点东北侧方向划分17个掘进区,并采用“四步”台阶法分段施工。针对同段起爆数码电子雷管,起爆器系统可随机设置单发雷管起爆间隔时间为3~5 ms,实现同段炮孔单孔单响,降低爆破振动对6号交岔点影响。根据不同掘进区总体岩性情况,优化支护方式(管棚支护、W型钢带及锚索支护等联合支护方式等),确保6号交岔点后续使用期安全。试验结果表明:采用超前控顶加固、控制分区爆破技术,降低破碎软岩巷道顶板偏帮、下沉,保证6号交岔点断面成型效果,削减其支护、后期维护等综合成本达8.7%,该技术可为类似巷道施工提供一定指导建议。

施工期铁路隧道软岩大变形快速分级方法研究

研究目的:西南复杂艰险山区等典型构造活跃区的构造地质环境复杂,断裂、褶皱发育,构造应力显著,铁路隧道围岩大变形问题突出,随着构造活跃区铁路隧道工程日益增加,将面临更严峻的大变形问题。在隧道施工开挖过程中,快速判别可能发生的大变形等级,有利于施工工法的调整和支护措施的制定。研究结论:(1)深入分析构造软岩大变形工程案例,以施工期掌子面开挖揭示围岩分级数据为基准,结合区域地应力、岩层厚度、岩性等大变形关键控制因素,快速判定大变形等级,提出了施工期铁路隧道围岩大变形快速分级方法,并结合典型工程案例对分级方法的有效性和准确性进行了验证;(2)本研究成果可应用于施工期间铁路隧道开挖围岩大变形的快速分级,适用于工程地质勘察领域。

考虑湿度应力的深部软岩隧道大变形控制研究

为探明深部高地应力软岩隧道大变形产生机理,制定适应大变形控制措施,以月直山隧道为工程依托,首先明确求解围岩形变压力与松动压力的Kastner与Caquot公式,基于岩体弹塑性力学与连续介质理论建立围岩湿度应力解析解,采用收敛-约束法绘制出3种围岩应力作用下围岩与初期支护特征曲线,分析断面变形过程中围岩与支护结构相互作用规律及3种应力占比演化规律。分别以混凝土与型钢钢架作为二衬支护结构对月直山隧道围岩稳定性进行计算分析,明确考虑湿度应力与松动压力条件下隧道二衬最优支护时机与支护参数,以支护结构安全系数FS评判出最优支护方案并对隧道软岩大变形进行治理。结果表明:当围岩径向位移达到550 mm时,仅考虑形变压力Pi时围岩对支护结构的压力P仅为0.813 MPa,考虑湿度应力Pw与松动压力Pa时P增大为1.372 MPa,湿度应力与松动应力总占比达40.7%,仅考虑形变压力而设计的支护结构不满足围岩稳定性要求;根据“卸压支护”理念,确定以“位移释放峰值upeak=0.325 m”与“间距d=0.7 m”作为增设第二层钢架的最佳支护时机与支护参数,现场二次钢架设置24天后使围岩变形收敛于50.8 mm,围岩大变形得到控制,研究成果可为今后相关隧道工程设计与施工提供参考。

卸围压下弱胶结软岩分数阶蠕变损伤本构模型

为研究地下硐室开挖卸荷诱发的软岩蠕变损伤特征,以西部矿区弱胶结软岩为研究对象,利用GDS HPTAS开展了分级卸围压蠕变试验,研究了不同含水条件下弱胶结软岩卸围压下蠕变特征和蠕变速率特征。基于稳态蠕变速率倒数的方法,确定了弱胶结软岩长期强度和含水率的数学指数函数关系。基于蠕变速率曲线特征提出了一种确定衰减蠕变与等速蠕变分界点t_1和等速蠕变与加速蠕变分界点t_2的新方法。引入Riemann-Liouville分数阶积分算子和负时间指数损伤演化变量,定义了非线性损伤Abel黏壶,建立了一个包括弹性元件、黏弹性损伤元件、黏性元件和非线性黏塑性损伤元件的六元件分数阶蠕变损伤本构模型。基于试验结果,采用Trust-Region算法进行了模型参数识别和敏感性分析。结果表明,所建立的模型具有物理意义明确、与试验值吻合度较高等特点,可较为准确地反映开挖卸荷条件下弱胶结软岩蠕变损伤特性,对保障地下工程长期稳定性具有重要的意义。

软岩隧道支护让压体系优化及安全状态易损性评价

软岩隧道围岩参数变异性大,支护体系与围岩相互作用不确定性强,易发生大变形等安全问题,为此国内外开展了隧道让压支护优化等工作以应对上述风险,但对其安全状态评价仍面临诸多难题。设计了一种新型柔-刚型让压接头,并基于可靠度分析方法,从易损性出发,综合拱顶沉降及初衬强度破坏准则,提出了基于概率的隧道开挖安全状态易损性评价方法。其通过利用概率有限元分析围岩‒支护相互作用,拟合形成极限状态功能函数响应面,经由随机抽样获得隧道开挖失效概率与可靠度指标;以此为基础,建立拱顶沉降与结构应力响应之间的拟合关系,提出了基于拱顶沉降的结构极限状态条件概率计算方法,并根据概率分布区间划定易损区进行支护安全性评价。基于上述理论方法,结合工程实际,开展了新型让压支护与传统刚性支护的易损性对比分析,验证了让压支护体系在大变形承载可靠性方面的优势。

NPR锚索对跨断层软岩大变形隧道控制技术研究

为探究NPR锚索对东马场跨断层软岩大变形隧道控制效果,首先对NPR锚索进行静力拉伸试验,验证其恒阻大变形的能力和具有良好的抵御外力的效果;随后开展NPR锚索对东马场隧道围岩变形控制的三维物理模型试验。试验现象和数据表明:在开挖过程中,隧道围岩也没有出现较大垮落和坍塌,NPR锚索对软岩隧道围岩有较好的支护效果。在加载完成后,NPR锚索对非断层处的隧道围岩最大位移约为14 mm,断层处的围岩最大位移约为21 mm,隧道区域所受应力分布的不规律性,导致隧道围岩出现挤压变形,位移曲线呈振荡状。在NPR锚索的支护下,围岩应力最大发生在左拱肩,围岩临空面3 cm处切应力最大(0.3 MPa),隧道未出现大规模的不对称破坏现象,隧道总体呈现出“小塌而不垮”,变形总体可控。

露天矿顺倾软岩边坡内排追踪压帮治理工程——以贺斯格乌拉南露天煤矿首采区南帮为例

软岩露天煤矿实现安全高效开采的重点是边坡稳定。为解决露天矿顺倾软岩边坡稳定性治理难题,在分析边坡稳定性主控因素的基础上,提出了露天矿顺倾软岩边坡内排追踪压帮治理工程。以贺斯格乌拉南露天煤矿首采区南帮为工程背景,兼顾采场与内排土场边坡稳定性,采用极限平衡法和数值模拟相结合的手段,设计了采场边坡的空间形态,提出了采场与内排土场边坡协同治理方案,可最大限度地安全回收边坡压覆煤炭资源。研究结果表明:弱层暴露长度是露天矿顺倾软岩边坡稳定性的主控因素,控制采场与内排土场间的追踪距离是改善边坡稳定性的有效途径;随着追踪距离的增加,边坡破坏模式从以圆弧为侧界面、弱层为底界面的切层-顺层-剪出滑动逐渐过渡为以圆弧为侧界面、弱层为底界面的切层-顺层滑动,边坡稳定性逐渐下降;内排土场及其与采场构成的复合边坡稳定性随破坏底板弱层回填岩石范围的增大呈指数函数规律提高;贺斯格乌拉南露天煤矿首采区南帮浅部边坡留设40 m运输平盘、15 m保安平盘,底帮深部边坡角29°,追踪距离控制在50 m之内时可满足安全要求;内排土场基底弱层完全破坏并回填岩石倾向长度60 m时可满足安全要求。研究成果为软岩露天煤矿边坡稳定性治理提供了新思路。

软岩地基中新型倒肋式风机基础力学性能有限元分析

目的 提出一种新型倒肋式风机基础,解决软岩地基中采用梁板式风机基础带来的挖方量大、模板支设繁琐、施工成本高、周期长等问题。方法 以2.5 MW风机为例,采用ABAQUS有限元分析软件,建立相同尺寸的倒肋式与梁板式风机基础模型,对比两种基础在极端工况下的倾斜率、水平位移、破坏特征等,并结合挖方量、模板工程量对两者的经济性进行分析。结果 倒肋式基础的水平位移为0.444 mm、倾斜率为0.012 1%,均满足规范要求;倒肋式基础的肋梁受力特征与悬臂梁相似,在基底反力作用下肋梁与墩台连接处承受的剪力及弯矩较大,容易开裂破坏,可通过增加肋梁截面高度改善;倒肋式基础相较于梁板式基础土方挖量可节省54%、模板工程量可节省48%。结论 倒肋式基础充分发挥出了倒置肋梁与软岩地基之间齿槽嵌固的优势,相较于梁板式基础不仅具有更优的抗滑移稳定性和受力性能,而且减少了挖方和模板工程量,经济效益显著。

模拟软岩蠕变特性相似材料的研制及试验分析

为快速、有效地反映软岩介质的蠕变特性,根据模型试验的相似原理,通过配比和力学试验,研制出一种具有快速蠕变特性的软岩相似材料,它由沥青、河砂、铁粉和橡胶粉按一定配比搅拌压实而成。瞬时抗压强度测定、弹性模量测定,以及分级加载下的单轴蠕变试验表明:相似材料的物理参数变化范围大,具有瞬时弹性特征;轴向蠕变过程具有衰减、等速和加速蠕变三个阶段特性;相似材料能在短时间内模拟软岩蠕变特性。有望为软岩工程提供一种短期、高效、准确的软岩蠕变新模型。