Frost heaving force considering synchronous damage to tunnel lining and surrounding rocks under freeze—thaw cycles

In areas with seasonal freezing,when the tunnel lining concrete is saturated with water infiltrating the interior,the lining and the surrounding rocks will simultaneously freeze.However,the current calculation of the frost heaving force fails to consider the synchronous damage to the lining and surrounding rocks under freeze-thaw cycles.Therefore,as per the elastic calculation model of the frost heaving force and model of steady-state heat transfer of circular tunnels,this study introduces the frost heaving rate of lining and surrounding rocks.First,the analytical solution of frost heaving force is obtained for simultaneous frost heaving of lining and surrounding rocks under any steady-state temperature field.Then,based on the fracture theory and meso-damage mechanics,the damage variables of lining and surrounding rocks under freeze-thaw cycles are extracted,representing their elastic modulus and porosity.Finally,the formula of frost heaving force for synchronous damage to the lining and surrounding rocks at any steady-state temperature field is obtained.The calculation results demonstrate that the lower the temperature inside the lining,the greater the frost heaving force.With the increasing number of freeze-thaw cycles,frost heaving force tends to gradually increase initially,reaching a peak value at 85 freeze-thaw cycles,decreasing to 80%of the peak value at 140 cycles before reaching a constant value.The lining participates in frost heaving,increasing the frost heaving force.The initial increase rate of frost heaving force is 15.7%.Changing the fitting coefficients s1 and s2 of the lining and surrounding rocks can effectively control the magnitude of the frost heaving force in the tunnels.

Non-contact monitoring and analysis system for tunnel surrounding rock deformation of underground engineering

It is very important to monitor surrounding rock deformation in tunnel construction. The principle, function, development and application of the system composed of a total station and computer for monitoring and analyzing surrounding rock deformation were discussed. The new methods of two free station of 3D measurement and its mathematic adjustment mode were presented. The development of software for total station on-board and post for computer were also described. Without centering it and measuring its height, the total station controlled by the software on-board can fulfill the whole measurements to target points. Monitoring data can be processed by the post software and results of regression analysis, forecasting information of the tunnel surrounding rock deformation can be provided in time. The practical use shows that this system is practicable, highly accurate and efficient. It satisfies the needs of safety and information construction in tunnel construction of underground engineering.

Time-dependent safety of lining structures of circular tunnels in weak rock strata

Following tunnel excavation and lining completion,fractured surrounding rock deforms gradually over time;this results in a time-dependent evolution of the pressure applied to the lining structure by the surrounding rock.Thus,the safety of the tunnel lining in weak strata is strongly correlated with time.In this study,we developed an analytical method for determining the time-dependent pressure in the surrounding rock and lining structure of a circular tunnel under a hydrostatic stress field.Under the proposed method,the stress–strain relationship of the fractured surrounding rock is assumed to conform to that of the Burgers viscoelastic component,and the lining structure is assumed to be an elastomer.Based on these assumptions,the viscoelastic deformation of the surrounding rock,the elastic deformation of the lining structure,and the coordinated deformation between the surrounding rock and lining structure were derived.The proposed analytical method,which employs a time-dependent safety coefficient,was subsequently used to estimate the durability of the lining structure of the Foling Tunnel in China.The derived attenuation curve of the safety coefficient with respect to time can assist engineers in predicting the remaining viable life of the lining structure.Unlike existing analytical methods,the method derived in this study considers the time dependency of the interaction between the surrounding rock and tunnel lining;hence,it is more suitable for the evaluation of lining lifetime.

Failure mechanism and control countermeasures of surrounding rock at deep large section chamber intersection in the Wanfu Coal Mine

In order to solve the problem of large deformation at the intersection of deep large section soft rock roadway,this paper takes the intersection of kilometer-deep roadway in the Wanfu Coal Mine as an engineering example and applies Negative Poisson’s Ratio(NPR)steel anchor cable in roadway support for the first time.By combining numerical simulation indoor test,theoretical analysis and field test,the deformation mechanism of surrounding rock at the intersection of deep-buried roadway was analyzed,and the control strategy with micro NPR steel anchor cable as the core was put forward.Through numerical simulation,the numerical analysis model of roadway intersection with different intersection angles and excavation sequence was constructed,and the impact of two key variables of rake angle and excavation sequence on the stability of surrounding rock at roadway intersection was studied.The optimal dip angle is 90°and the optimal excavation sequence was determined as pump house-pump house passage-substation.The mechanical properties of the micro-NPR steel anchor cable were studied through the static tensile test in the laboratory.The results showed that the micro-NPR steel anchor cable showed high constant resistance,uniform tensile,no yield platform,and no obvious necking phenomenon during breaking.Through theoretical derivation,it was calculated that the vertical stress of roadway intersection is 45 MPa,and the bearing capacity of superposed arch composed of micro NPR steel anchor cable is 1257 kN,which is enough to guarantee the overall stability of intersection.Support application test and monitoring were carried out on site,and it was verified that the combined support strategy of short and long micro NPR steel anchor cable has a good control effect on large deformation of surrounding rock at intersection,which provides a new support material and support means for the safety and stabilization control of surrounding rock at intersection.

充填体-围岩接触带损伤破坏特征试验研究

由于充填体和围岩性质差异明显,两者接触带附近总会发生变形。因此,确定接触区破坏特征是矿山安全生产的前提。以金川三矿区为研究区,根据充填体-围岩接触带几何形状的不同,将其划分为平直型、嵌入型和折线型接触,采用现场调查和物理模型试验相结合的方法,研究接触区的损伤破坏特征。研究结果表明,嵌入型强度最大,损伤最初发生在拐点附近;折线型的强度次之,损伤最初发生在接触带,裂纹总是首先出现在垂直接触面上;平直型强度最低,损伤始于接触带,破坏主要集中在充填体,且剪切破坏占主导地位。研究结果可为金川矿区以及相似地质条件、采矿方法的矿山提供参考。

基于FLAC3D的隧道开挖过程围岩稳定性研究

针对隧道在施工开挖过程中产生的复杂应力场和位移场,应用FLAC3D 6.0三维有限差分软件进行数值模拟。地层采用Drucker-Prager准则作为岩体塑性屈服准则,计算得到隧道开挖及支护后的隧道应力场、位移场分布规律,进而确定隧道需要支护的关键位置。结果表明,支护能够抑制应力和位移的扩大,显著提高围岩的承载力。

新建老鲁箐水库蓄水对大尖山隧道的影响研究

为定量分析库区蓄水对隧道的影响,以玉-磨铁路大尖山隧道为例,运用地下水渗流计算理论,分析新建老鲁箐水库对大尖山隧道涌水量影响变化规律,利用MIDAS/GTS有限元软件作剖面二维渗流模拟,开展库区蓄水对隧道影响的数值模拟研究。结果表明:理论计算结果显示库区蓄水至校核洪水位后隧道涌水量增加量在35.77%以内。有限元软件计算结果显示库区蓄水前与蓄水至校核洪水位时引起的隧道拱顶位移在1.8 mm以内,变化量为20.9%,隧道水平收敛在1.3 mm以内,变化量为27%;轴力最大部位出现在拱脚处,库区蓄水前后轴力最大的变化幅度为31.7%;弯矩最大部位为墙脚,蓄水前后变化幅度约为10.5%;库区蓄水后最小安全系数为4.3,仍满足规范要求,衬砌处于安全状态。所得结论可为近隧址区修建水库对隧道的影响评价及灾害防治提供理论指导,具有一定的理论和实践意义。

Geological conditions and key rock mechanics issues in the Western Route of South-to-North Water Transfer Project

In terms of special geological conditions of the Western Route of South-to-North Water Transfer Project, the classification method for surrounding rocks is discussed by combining with the construction method of tunnel boring machine （TBM）. The classification standard of surrounding rocks is put forward on the basis of physical simulations and engineering practices. Damage, deformation and evolution of surrounding rocks induced by TBM excavation are discussed. Meanwhile, the long-term deformation mechanisms and stability of surrounding rocks are also studied. On this basis, a three-dimensional constitutive model for interbedded sandstone slate and a fiat shell-joint element-foundation system for calculating internal forces of segment lining are established. The deformation features of surrounding rocks of deep and steep interbedded sandstone slate and their influences on internal forces of segment lining are presented. Finally, the design methods of segment lining constructed in deep and steep flysch are proposed.

Analytical solution of a circular lined tunnel with alterable mechanical property under hydrostatic stress and internal pressure

The influence of the interaction between surrounding rock and lining on the long-term behaviour of a tunnel in service is significant.In this paper,we proposed a mechanical model of the circular lined tunnel with the alterable mechanical property under hydrostatic stress and radially inner surface pressure of the lining.The alterable mechanical properties of the surrounding rock and the lining are embodied by the changing of their elasticity modulus with service time and radial direction of the tunnel,respectively.The proposed mechanical model is successfully validated by comparison with the existing theoretical models and the numerical simulation,respectively.The influences of the main parameters of the proposed mechanical model,such as the radial power-law indexes and the time-varying coefficients of the surrounding rock and the lining,as well as the radially inner surface pressure of the lining,on the interface displacement and pressure between surrounding rock and lining are investigated.The research results can provide some valuable references for timely diagnosis and correct evaluation of the long-term behaviours of a tunnel in service.

Load laws of composite lining in mountain tunnel model tests and numerical simulation validation

Currently,model tests are increasingly being used to simulate the construction of mountain tunnels,but the support structure of the model tests does not show the composite lining,and the force laws of the composite lining are not yet clear.In this research,the force variation of composite lining under three cases in model tests of deep-buried tunnels were carried out with the surrounding rock grade and installation time as the variation factors.The test results reveal that:(1)The suitable method to reduce the contact load between the secondary lining and primary support is to enhance the primary support in the soft and weak surrounding rock.Correspondingly,for ClassⅢsurrounding rock and better quality of surrounding rock,the primary support can lag behind the excavation face a certain distance.(2)The axial forces of the bolts tend to rise with concentration of 0.4 kN-0.7 kN after the secondary lining was installed.(3)With or without two to three excavation cycles delayed,the load sharing ratio of the secondary lining of the Class III surrounding rock is less than 10%.Finally,the numerical simulation verifies the feasibility of the model tests.

隧道围岩-衬砌接触面剪切特性模拟研究

探究隧道围岩-衬砌接触面在不同法向应力及不同粗糙度条件下的剪切特性规律,对进一步研究隧道围岩与衬砌间的相互作用及岩体稳定性具有重要的理论和工程意义。为考虑粗糙度条件,利用分形理论,通过改变分形公式中的分形维数D及分形粗糙度G生成5种不同接触面,基于二维颗粒流程序(PFC^(2D)),建立接触面数值剪切模型,尺寸为150 mm×150 mm。开展同一接触面在不同法向应力下,数值模拟剪切试验及不同接触面在同一法向应力下的数值模拟试验;将数值剪切试验与室内剪切试验获得的剪切应力-剪切位移曲线进行对比,验证数值剪切模拟的可靠性。研究结果表明:(1)数值模型剪切破坏产生的裂隙主要集中于中间接触面处,破坏后的应力主要集中于接触面粗糙度最大处,破坏裂纹可分为剪切裂纹和张拉裂纹,其中张拉裂纹占主要优势;(2)剪切应力-剪切位移过程曲线存在爬坡、啃断、滑移三大阶段,具有明显的峰值强度和残余强度,法向位移随着剪切位移的增加而增大,产生剪胀效应;(3)随着法向应力增加,剪切和张拉裂纹数量增加,破坏现象越明显,峰值强度和残余强度增大,剪胀效应减小;(4)随着粗糙起伏度增大,即分形维数D的增大或者分形粗糙度G的减小,破坏裂纹数量增加,其中张拉裂纹增加较明显,峰值强度和残余强度增大,剪胀效应增大。

基于不同围岩特性的隧洞衬砌厚度优化分析

基于不同围岩特性的隧洞衬砌厚度优化既能实现安全要求又可以降低工程投资。结合某电站引水隧洞,采用有限元分析法对隧洞在不同围岩特性下的受力情况进行数值模拟,计算分析在不同衬砌厚度下的应力、配筋及裂缝宽度情况,综合考虑安全性和经济性对结果进行分析比较,提出了针对不同围岩特性的隧洞衬砌厚度优化方案。研究结果表明,隧洞衬砌在运行期的应力情况是影响衬砌配筋的关键因素,不同围岩特性下衬砌厚度的选择应充分考虑隧洞衬砌应力、所需配筋及裂缝宽度因素影响,当衬砌达到一定厚度后,所需配筋及裂缝宽度趋于稳定。

考虑衬砌减薄及脱空的公路隧道地震易损性研究

衬砌背后脱空、衬砌厚度不足是我国运营隧道的典型质量缺陷,这些缺陷的存在会直接影响隧道结构的抗震性能,加剧隧道的地震损伤。近年来,基于质量缺陷对隧道抗震性能影响的研究多采用确定性方法,缺少考虑地震波随机性的定量评估。依托云南某两车道运营公路隧道,采用增量动力分析(increment dynamic analysis,IDA)方法开展了考虑衬砌减薄及脱空组合缺陷的一系列隧道地震响应时程分析。根据隧道地震易损性分析理论,建立了组合缺陷影响下的公路隧道地震易损性曲线,分析了组合缺陷程度、缺陷位置、围岩等级和地震波入射方向等因素对隧道地震易损性的影响。结果表明:衬砌减薄及脱空组合缺陷程度、缺陷位置、围岩级别和地震波入射方向均对隧道地震易损性有重要影响。组合缺陷的存在增大了隧道结构的易损性,随组合缺陷程度的增大,衬砌地震损伤概率呈非线性增加。质量缺陷对隧道易损性的影响程度随发生部位不同而异,拱肩缺陷对隧道易损性的影响大于拱顶缺陷。围岩等级越差,隧道易损性受组合缺陷的影响就越大。隧道在横向地震作用下的易损性大于竖向地震作用下的易损性,且易损性受地震波方向的影响随缺陷位置的不同而异。缺陷位于拱肩部位时,隧道结构易损性受竖向地震动的影响更大,而缺陷位于拱顶时受横向地震动的影响更大。

寒区隧道衬砌渗水挂冰试验研究

为揭示寒区隧道衬砌渗水挂冰发育规律,研制出一套模拟地表水补给条件下寒区隧道衬砌渗水挂冰发育的模型试验装置,实时监测渗水断面围岩温度和挂冰发育过程;采用Image-J软件测量挂冰图像截面积和线性回归分析方法分析挂冰发育过程,研究不同风速和围岩初始温度条件下渗水点围岩温度和挂冰堵塞率演变规律。结果表明:1)挂冰开始发育时刻,随着风速的增大和围岩初始温度的升高,渗水点围岩临界温度逐渐升高;渗水点围岩温度随冷却时间逐渐降低,近似呈对数函数关系;风速越小、围岩初始温度越高,平均降温速率越慢,挂冰发育持续时间越长;当风速分别为0.6 m/s和1.2 m/s时,由于渗水断面围岩冻结圈的形成和衬砌内壁冰体封堵渗水点导致衬砌挂冰停止发育。2)挂冰堵塞率与时间近似呈线性关系,风速越小、围岩初始温度越高,挂冰开始发育的时间越晚,冻害严重程度越高,而紧急程度越低。

西藏某水电站导流隧洞塌方过程与稳定性分析

【目的】为了确定水电站导流隧洞塌方段的安全性,需要对塌方段施工期、运行期的稳定性及相应处理措施进行研究。【方法】以西藏某水电站为典型案例,结合其导流隧洞塌方过程进行分析,通过计算最小岩体覆盖厚度、相邻隧洞最小围岩厚度和衬砌结构配筋等3个指标来分析隧洞塌方段运行期的稳定性。【结果】计算得出,1号导流隧洞塌方段岩体实际厚度大于理论最小围岩覆盖厚度,相邻隧洞最小围岩厚度大于2倍开挖洞径(洞宽),实际配筋面积大于理论配筋面积。【结论】在水电站导流隧洞设计施工过程中,通过3个指标的计算分析表明该隧洞满足施工期和运行期的稳定性要求。

浅埋软弱围岩巷道支护技术研究

巷道支护对煤矿井下安全生产意义重大,传统的锚杆锚索支护技术对浅埋软岩巷道支护的针对性差,难以满足矿井精细化生产要求。利用注浆加固技术结合钢筋混凝土衬砌结构对浅部软岩巷道进行支护,增强了软弱围岩的强度和自稳性能,提高了巷道围岩的整体性和稳定性,同时由于注浆加固的扩散作用,对巷道掘进前方的煤岩体产生一定的加固作用,提高了巷道掘进的安全性,实践表明,该支护技术对浅部软弱围岩巷道具有很强的针对性。

富水黄土隧道围岩软化对结构受力影响研究

以银百高速榆林子隧道为依托工程,通过有限元软件ABAQUS温度场模块摸拟隧道施工围岩软化过程,研究了富水黄土隧道围岩在不同软化阶段和软化范围工况下,隧道围岩、初期支护、仰拱填充层的位移和应力的变化规律。结果显示:拱顶沉降和仰拱填充层隆起随软化范围的扩大而增大,而隧底隆起减小,仰拱填充层隆起在软化范围3 m时趋于稳定;围岩软化对仰拱填充层中心影响最大,而仰拱填充层拱脚处几乎不受影响;围岩软化后在初期支护拱脚位置产生最大拉应力,拱墙和拱顶应力变化不明显;塑性区以内是围岩软化的主要影响范围,需特别关注塑性区内的地下水赋存状态。

黄土隧道台阶法施工过程围岩压力的实测与影响因素分析

以甘肃省内某一黄土隧道工程为研究对象,进行实测,分析了台阶法施工过程围岩压力的变化特征。采用智能压力传感器,分别连续采集隧道下台阶、仰拱、二次衬砌施工前后7 d的围岩压力数据;同时,采用数据处理软件,分析了隧道施工各工序对隧道围岩压力的影响。分析发现:隧道二次衬砌施工对隧道围岩压力影响最大,其次是下台阶施工,而仰拱施工对围岩压力的影响最小;隧道下台阶施工对隧道拱腰部位围岩压力的影响最大;隧道二次衬砌施工后,围岩压力呈先下降后升高的趋势。

软弱围岩隧道衬砌结构参数优化研究

针对隧道建成后二衬分配荷载较大,出现混凝土开裂,甚至掉块等普遍存在的问题,以药草台隧道工程为例,运用ANSYS数值计算软件建立荷载-结构模型,对Vb型衬砌类型的不同二衬厚度条件下进行结构安全性检算。结果表明:减薄二衬厚度对于改善二衬受力状态有明显作用,二衬厚度从原设计值50 cm减少到30 cm时,二衬结构安全系数仍满足规范要求,二衬有进一步优化减薄的空间。

围岩蠕变作用下偏压隧道衬砌结构稳定性分析

为了研究围岩蠕变作用下不同偏压角度对隧道衬砌结构的影响,本文采用FLAC3D有限元软件建立三维隧道模型,基于Burgers蠕变模型对不同偏压角度隧道进行了模拟,分析了围岩蠕变作用对偏压隧道衬砌结构的稳定性影响。研究结果表明:隧道建成后的30年间,隧道衬砌结构受到围岩蠕变作用比较明显,随着偏压角度的增加,左拱腰收敛水平有加速增加的趋势,隧道衬砌应力分布的非对称性逐渐加剧。