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.

Heterogeneity identification method for surrounding rock of large-section rock tunnel faces based on support vector machine

Purpose–The purpose of the study is to quickly identify significant heterogeneity of surrounding rock of tunnel face that generally occurs during the construction of large-section rock tunnels of high-speed railways.Design/methodology/approach–Relying on the support vector machine(SVM)-based classification model,the nominal classification of blastholes and nominal zoning and classification terms were used to demonstrate the heterogeneity identification method for the surrounding rock of tunnel face,and the identification calculation was carried out for the five test tunnels.Then,the suggestions for local optimization of the support structures of large-section rock tunnels were put forward.Findings–The results show that compared with the two classification models based on neural networks,the SVM-based classification model has a higher classification accuracy when the sample size is small,and the average accuracy can reach 87.9%.After the samples are replaced,the SVM-based classification model can still reach the same accuracy,whose generalization ability is stronger.Originality/value–By applying the identification method described in this paper,the significant heterogeneity characteristics of the surrounding rock in the process of two times of blasting were identified,and the identification results are basically consistent with the actual situation of the tunnel face at the end of blasting,and can provide a basis for local optimization of support parameters.

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.

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.

Engineering Geological Classification of Surrounding Rock Stability in Coal Mine Tunnels and Its Engineering Applications

The stability type and spatial distribution of surrounding rock are an important basis for the layout of hae tunuels and the selection of support patterns in a mine design. Based on a lot of investigations and testing studies,a new engineering geological classification scheme of surrounding rock stability is put forward,which is easy to be applied,and reliable verified by examples. According to the classification system,the spatial divisions of surrounding rock stability can be delineated in an exploration progamme, providing relevant engineering geological informations for mine designers to prevent them from making the uurealistic tunnel layout and support

Study on the new shell bolting and shotcrete support and its application in soft rock tunnels

A new kind of tunnel support was put forward on the basis of the anchor spraysupport principle. The mechanics of the new three-dimensional steel bar shotcrete liningsupport was studied and the structure's internal forces were analyzed. The model experiment was done relying on the industrial test. The conclusion of numerical calculationsproved that the ANSYS program is reasonable and creditable. It was compared to otherkinds of support that are commonly used in soft rock tunnels. The technique and economiccontrasts of the typical tunnel with support three-dimensional steel bar were completed.

收敛约束法在挤压性围岩隧道中的应用

由于挤压性围岩隧道围岩性质与应力环境的特殊性,其围岩特征曲线与常规隧道有明显差异。为研究挤压性围岩隧道围岩-支护相互作用关系,考虑支护效应修正围岩特征曲线,研究不同变形等级对修正围岩特征曲线的影响规律,优化挤压性围岩双线铁路隧道初期支护。研究结果表明,毛洞状态下,受双线隧道断面应力集中影响,拱脚和墙脚为安全控制位置;随着变形等级和侧压力系数增加,支护特征曲线与修正围岩特征曲线不再相交;Ⅰ、Ⅱ级变形采用单层支护可满足安全要求,锚杆只需布置在拱部和边墙位置,Ⅱ级及以上变形锚杆需要全环布置;Ⅳ级变形在采用双层支护的同时,需考虑改善洞室形状、超前加固等措施。

锚杆钻车运行中支护承载结构及围岩受力变形分析

目的针对单轨液压锚杆钻车运行过程中支护承载结构及围岩受力变形难以观测分析的问题。方法利用研发的CMMD4-35煤矿用单轨液压锚杆钻车,结合长城五矿1902S回风巷巷道现场情况综合分析钻车在大断面大倾角巷道动态运行的支护、承载及围岩协同受力变形特征。结果研究表明,钻车运行过程中吊挂板的受力变形在悬吊点处均达到峰值,工字钢在悬吊点的部分位移最小,与钻车直接接触的部分受力最大;锚索中部主要受到拉应力,靠近巷道一侧主要受到剪应力,而巷道两帮的锚杆拉应力主要分布在靠近巷道内部一侧;巷道顶板悬吊点处位移最大,两帮靠近顶板位移高于底板处,而巷道偏向低帮处底板的位移大于高帮处;以单轨液压锚杆钻车为核心的新型配套工艺可以有效控制围岩变形,支护效果良好,比传统以掘锚一体机为中心的机器化工艺掘进效率更高。结论研究明确了CMMD4-35煤矿用单轨液压锚杆钻车在实际应用的可行性,解决了现有掘锚一体机难以在复杂地质条件下大断面煤巷自动化掘进支护的问题,提升了煤巷支护效果掘进效率,为CMMD4-35煤矿用单轨液压锚杆钻车的现场应用提供了理论依据。

既有隧道不同扩挖宽度下锚杆参数的优化

以黄山洞隧道工程为依托,通过对现场数据的监测和利用有限元分析软件Midas GTS NX进行数值模拟,分析了不同扩挖宽度下隧道拱顶沉降值、周边收敛值和围岩有效应力变化的规律,并改变锚杆的长度和锚杆间距,分析在不同锚杆长度下围岩有效应力、衬砌应力以及锚杆应力的变化规律,确定了不同扩挖宽度下最优的锚杆长度和锚杆间距.研究结果表明:随着扩挖宽度的增加,围岩有效应力由大至小依次为拱脚处压应力、拱腰处压应力、拱顶处压应力和仰拱处拉应力;拱顶处压应力随扩挖宽度的增大而减小,拱腰处压应力随扩挖宽度的增大而增大,但增大趋势不明显;受单侧扩挖方式的影响,扩挖侧的应力大于非扩挖侧;拱脚处受到应力集中的影响,其压应力随着扩挖宽度的增大而增大;扩挖宽度为1.5~2.5 m时的最优锚杆长度和间距分别为2.5 m和1.7 m,扩挖宽度为3.5~4.5 m时二者分别为3.0 m和1.2 m.

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。

天山胜利隧道敞开式TBM钢管片支护作用效果研究

针对TBM穿越断层破碎带地层洞壁围岩松动掉块严重的问题,依托乌尉天山胜利隧道,采用数值模拟的方法,通过对比研究传统支护方式与新型钢管片支护方式下围岩变形和围岩塑性区情况,研究钢管片支护的作用效果;同时,为说明不同支护的适用条件,采用现场调研方法开展不同支护方式下施工效率和经济性对比分析。结果表明:1)断层破碎带地层中,当围岩出露护盾后,变形量与塑性区范围增大,围岩破坏程度加剧,以锚杆和钢拱架为主的传统支护方式无法较好地控制围岩变形和塑性区发展。2)断层破碎带地层中,钢管片支护较传统支护的围岩累计沉降值降低53%,围岩变形收敛快,能更好地控制围岩变形和发展。3)钢管片支护较传统支护的围岩塑性区范围小,其中边墙的最终塑性区缩小44%,且钢管片支护可实现早封闭、及时支护,塑性区均匀,更有利于围岩的稳定。4)一般地层中,传统支护方式的经济性和效率更佳;断层破碎带地层中,钢管片支护方式可提供安全作业空间,减小钢拱架+喷锚支护作业量,较传统支护经济性和施工效率更佳。

TBM隧洞围岩分级方法及支护体系研究

目前TBM隧洞设计施工主要采用基于矿山法的围岩分级方法,但由于TBM法与矿山法隧洞施工存在很大差异,传统矿山法的围岩分级方法难以适用于TBM施工。为解决该问题,依托北疆供水二期工程,综合考虑围岩稳定性和围岩可掘性,选取围岩基本质量指标BQ、岩石单轴饱和抗压强度Rc、岩体完整性系数KV和岩石磨蚀性指数CAI作为评价隧洞围岩性质的主要指标,统计18台TBM集群施工收集的近3000组BQ、Rc、KV等岩性指标数据,分析各项岩性指标与纯掘进速度PR及安全系数FS的变化规律,将TBM隧洞围岩分为Ⅰ~Ⅴ级共10个亚级。在此基础上,分析了敞开式TBM的施工特性,进而采用数值模拟方法,对各级围岩在不同支护参数下的稳定性进行对比分析,提出了适用于北疆地区水工隧洞各级围岩的隧洞支护体系及支护参数,共形成7套支护体系设计图,并结合现场实际工程对本文提出的围岩分级支护体系进行验证。现场监测数据表明,本文提出的TBM隧洞围岩分级支护体系有较好的适用性。

锚杆支护方式对深埋洞室隔冲击效果影响的数值模拟研究

与浅埋洞室相比,随着埋深增加而产生的高地应力现象使深埋洞室安全性评价更加复杂。本研究在考虑地应力平衡的前提下,采用有限元与无限元相结合的方法,对冲击荷载作用下深埋洞室的锚杆支护方式进行了设计与优化。计算结果表明:在平衡初始地应力之后,Mises应力会随着锚杆长度、疏密程度的增加略有增长。当锚杆长度和疏密程度增至某一特定值时,洞室洞壁的位移和塑性应变将达到最小值,洞室围岩将达到相对安全状态。锚杆间隔布置下,长锚杆数量的增加将提高洞室围岩的安全性。当对洞室拱脚进行重点支护时,整个洞壁的位移均有所减小。

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。

高瓦斯大断面煤巷智能快掘条件下围岩控制研究

针对高河煤矿高瓦斯大断面煤巷智能快掘条件下的围岩控制问题,根据悬吊理论、普氏理论对E2312进风顺槽锚杆、锚索支护参数进行理论计算,初步确定了部分参数,采用数值模拟方法对智能快掘巷道围岩控制效果进行模拟分析,揭示锚杆、锚索协同锚固效应及其双层锚固平衡拱结构形成机理,并确定快掘条件下的最终支护参数。通过对不同支护参数和掘进速度分别制定了多组数值模拟方案,对比分析巷道围岩锚固效应、塑性区发育范围以及顶板下沉量和两帮移近量变化曲线,结合现场工程应用综合分析得出,在一定范围内提高掘进速度的同时,结合对支护参数的优化,更加有利于巷道的围岩稳定控制。

TBM掘进煤矿巷道力学及变形分析

以保安采区8号煤南回风巷为研究对象,基于CVISC蠕变模型,对其TBM掘进过程进行分析,研究不同支护方式下巷道的位移及力学性能变化规律,并将其数值模拟结果与实际监测数据进行对比,以验证数值模拟结果的准确性。结果表明:采用锚索和锚杆对煤矿巷道进行支护能减小其隧道围岩的受力,其中,采用锚索+钢筋网的支护方式效果最优;各工况下的竖向应力均大于其水平应力,煤矿巷道的受力主要以竖向为主,最大应力均出现在围岩的顶部和底部,不同支护方式下围岩发生的位移具有一定的差异性,采用锚索+钢筋网的支护方式产生的位移量最小,煤巷道稳定性较高,未采取支护措施的围岩位移量最大,此时煤矿巷道的稳定性较差,易发生变形。

基于Mohr-Coulomb强度准则的锚杆支护效应研究

从围岩与锚杆相互作用的力学特性出发,基于围岩增强理论,采用数值模拟手段,探究锚杆支护作用下隧道开挖后围岩的力学特性,得到围岩特性曲线(GRC曲线)。通过对比各种锚杆支护参数下与未支护状态下围岩特性曲线的差异,建立锚杆密度与围岩收敛降低比例之间的关系。结果表明:锚杆对围岩收敛的限制作用显著,能很好地控制围岩变形,且锚杆密度越大,支护效果越明显,但当锚杆密度大于3时,收敛限制效果开始减弱;锚杆对围岩收敛的约束作用存在极限值,锚杆密度与收敛减低比例之间满足二次函数关系,Ⅳ级围岩限制比例极限为40.9%,Ⅴ级围岩限制比例极限为33.8%;锚杆支护对围岩收敛的约束作用与围岩性质有关,Ⅳ级围岩的约束效果显著优于Ⅴ级围岩。

沙特NEOM隧道项目Q系统围岩分类及支护体系研究

沙特NEOM隧道支洞项目采用挪威法施工,依据地质素描判定的Q值划分围岩类别,确定工程所需的支护结构参数。在对Q系统围岩分类法的各项参数及计算方法进行详细分析的基础上,从超前预测、掌子面判定、隐蔽工程记录等方面,形成了“超前探孔-地质素描-TDMS隧道文件管理系统”的地质工作流程;同时,应用Q系统分类法划分围岩支护等级、选取相应支护参数,当围岩等级较好时可主要使用注浆锚杆+喷射混凝土的支护方式,当围岩等级较弱时,还需要借助格栅钢架/型钢钢架+钢筋网片的方式确保支护体系的安全。

引江补汉雾渡河段深埋隧洞渗流与稳定性分析

深埋隧洞往往会穿越复杂的地质结构,隧洞在穿越富水断层面临严重的涌水突泥问题,其中围岩内的渗流过程以及应力状态是隧洞围岩稳定的关键影响因素。以雾渡河段为研究对象,基于数值模拟方法研究了富水断层内隧洞开挖过程中的渗流过程以及隧洞围岩的稳定性。结果表明,隧洞开挖会导致隧洞围岩内渗流过程改变,隧洞衬砌会承受较大的外水压力;灌浆圈有效地阻隔了地下水,水流通过排水孔流出,二者组合能降低衬砌70%的外水压力;断层围岩物理力学性质较差,开挖后变形明显,水平向的位移大于铅直向;采用超前灌浆与超前支护处理后,围岩位移降低50%~60%,衬砌应力显著降低;综合比选后,推荐使用长4.5 m、搭接长度1 m、外插角为15°的小导管和长30 m、搭接长度3 m、外插角3°的管棚进行超前支护。