Shaking table tests on seismic measures of a model mountain tunnel

A series of three dimensional (3D) shaking table tests were carried out to investigate the mechanism and effect of seismic measures of mountain tunnel using a scaled model based on a real tunnel. Key technical details of the experiment, including similarity relations, seismic measures simulation, boundary conditions, sensor layout, modeling methods, and ground motion input were presented. Main seismic measures, including reinforcing surrounding rock with anchors, increasing lining flexibility with steel wire mesh, and installing seismic isolation layer between reinforced surrounding rock and tunnel lining, were investigated in this study. Experiment results show that: (1) adding a layer of steel wire mesh in the tunnel lining can improve the flexibility and seismic performance and also may effectively prevent radial cracks from crossing the lining; (2) installing a geofoam isolation layer between the reinforced surrounding rock and the tunnel lining reduces dynamic earth pressure by 70–90% for the lining without a seismic isolation layer; (3) the flexible joints can effectively avoid global failures of tunnel lining for they reduce dynamic strain and bending force in the tunnel lining and decrease the seismic energy transmission along the lining in axial direction; (4) reinforcing surrounding rock with anchors significantly reduces dynamic earth pressure and strain of the lining by about 50%. In addition, the length of seismic reinforcement for general mountain tunnel portal is recommended to be 50 m from the tunnel portal along the axial direction.     

海底隧道衬砌结构设计

 海底隧道围岩水通常具有稳定水位和充足补给,隧道结构受长期的水压力作用,衬砌计算中应首先确定水压力荷载大小,并综合考虑隧道涌水量的大小,由此对衬砌断面的拟定、衬砌类型的选择、衬砌结构安全性进行评价计算。正在建设的厦门翔安海底隧道衬砌结构设计时,通过不同防排水方式下衬砌背后水压力特征的模型试验表明,作用于全封闭衬砌上的水压力是不能折减的;根据陆域和海域不同地段预测全隧道涌水量,由于无法满足运营期间的排水,衬砌结构必须采用全封闭形式或限制排放形式;利用ANSYS有限元软件,根据外水压力大小与围岩压力组合下对不同的隧道衬砌断面进行对比分析计算,以得出结构受力最为经济合理的断面形式;并以此断面按荷载结构模式法进行全封闭衬砌结构计算。计算结果及建设的实际情况表明衬砌受力合理。     

考虑半渗透边界的隧道周围超孔隙水压力消散解

通过引入衬砌半渗透边界条件,将Terzaghi-Rendulic固结理论和Burgers黏弹性模型相结合建立土体固结-流变耦合模型,采用复变函数解法推导出求解黏弹性介质中半透水隧道周围超孔隙水压力的消散表达式,并以上海地铁二号线某区间隧道为工程背景分析了不同衬砌透水程度对隧道周围超孔隙水压力消散与分布的影响规律。研究发现,随着衬砌与土体相对渗透系数的增大,隧道外壁处超孔隙水压力的消散速度不断增快;隧道周围土体距离衬砌外壁越远,其初始超孔隙水压力越小,土体的超孔隙水压力消散速度也越慢。     

岩石偏压隧道动态分析及相关研究

通过系统研究岩石隧道 ,尤其是偏压隧道的围岩压力确定方法 ,及其结构计算方法 ,能够在施工过程中对隧道衬砌结构进行动态分析 ,及时调整隧道施工参数 ,达到最佳的效果。文中采用规范推荐方法确定反分析的初始参数 ,采用可变容差的单纯形法进行荷载及地层参数的反分析 ,然后利用反演参数对衬砌内力进行正分析 ,以指导支护参数的确定     

Cracking mechanism of secondary lining for a shallow and asymmetrically-loaded tunnel in loose deposits

Tunnels constructed in loose deposits with low strength and complex composition are usually subjected to asymmetrical stresses at the entrance and exit. The secondary tunnel lining is prone to excessive deformation, cracking, or even collapse, seriously affecting the safety of tunnel construction and operation. In this paper, a large shallow highway tunnel in loose deposits is used as an example to study the cracking mechanism of secondary lining. Triaxial consolidated-drained shear tests are carried out on large remolded specimens to obtain the mechanical parameters of the surrounding soil. Three-dimensional numerical modeling is conducted based on the field monitoring data to simulate the process of tunnel construction and to analyze the mechanical mechanism of cracking in the secondary lining. It is shown that even with the 30 m advance pipe roof at the tunnel entrance, the apparent difference in stiffness between the retaining wall and the surrounding soil results in an obvious stress concentration at the spring of the secondary lining near the end of the retaining wall, due to the effect of highly asymmetrical stresses. In addition, loose deposits are very sensitive to construction disturbances. Large horizontal deformation towards the lower topography occurs during tunnel construction. With increasing overburden depth, the stress concentration at the spring level and the horizontal deformation in the secondary lining increases, which are the main reasons for cracking in the secondary lining. These findings can be useful for tunnel design and construction in the similar type of loose deposits.     

弹性半空间中衬砌隧道对瑞利波的散射

 采用一种高精度的间接边界积分方程法,对弹性半空间中衬砌隧道对入射瑞利的二维散射问题进行求解分析。结果表明：衬砌隧道和非衬砌隧道对瑞利波的散射具有显著的差别,衬砌刚度对波的散射规律具有重要影响。隧道附近地表动力响应和隧道衬砌动应力集中主要取决于衬砌和围岩的刚度比、隧道的埋深和直径、入射波频率等因素。对于柔性衬砌,浅埋隧道对低频瑞利波会产生显著的位移放大效应;对于刚性衬砌,衬砌内壁的动应力集中效应十分明显。整体上看,随着埋深的增大,隧道周围波的散射逐渐减弱。     

The importance of longitudinal stress effects on the static conditions of the final lining of a tunnel

The effects of stresses acting in the longitudinal direction (parallel to the tunnel axis) in certain cases take on an important role in the definition of the static conditions of the final lining, and if they are not foreseen, can lead to instabilities that often require difficult and expensive repair interventions. The case in which the final lining shows a marked irregularity of thickness along the tunnel axis is typical, for example, when the preliminary supports are of a truncated-cone type placed in advancement ahead of the excavation face. The produced anomalous stresses are basically due to the difference in transverse stiffness (and, therefore, in the radial displacements) between the adjoining lining sections. A simple calculation procedure has been set up in this work which permits the estimation of the three-dimensional stress state inside the concrete in the presence of a thickness anomaly and of a homogeneous and uniform radial load at the lining extrados. The approach followed is able to furnish the trend of the safety factor regarding the rupture of concrete, in function of the distance from the thickness anomaly, in such a way as to be able to design the lining thickness and any necessary steel reinforcements.     

Single-shell In-situ concrete tunnel lining: Experience in the Federal Republic of Germany

Although traffic tunnel construction in West Germany typically has used in-situ concrete as a double-shell lining, this method is both time-consuming and costly to apply. Recent research efforts have focused on the possibilities of single-shell in-situ concrete tunnel lining. This paper describes tests performed recently in West Germany on the use of (1) shotcrete and (2) steel-fibre-reinforced pumped concrete. The discussion deals with problems involved in these types of construction, the site and laboratory tests performed, and recommendations/prospects for application of these types of tunnel linings. The article also reports on two recent research projects, involving: (1) tunnel lining for large cross-sections with steel plate skin and unreinforced backfill concrete; and (2) construction and economic possibilities for creating tunnels in monocoque design.     

Voids delineation behind tunnel lining based on the vibration intensity of microtremors

In-situ microtremor measurements and numerical simulations were carried out to study the microtremor characteristics of tunnel linings. Power spectrum density (PSD) of microtremor signals measured from three spans of a tunnel lining with or without defects (cracks and voids) was calculated and analyzed. The results revealed that the normalized ratio of comparative power spectrum density (NRPSD) obtained by calculating the ratios RPSD, which is the ratio of PSD between different orientations (axial, radial and circumferential), of damaged spans to that of the healthy span, can be used as an indicator for the void delineation. For a damaged lining where voids exist, the vibration intensity is enlarged greatly in the radial direction, resulting in a pronounced value of NRPSD by comparing the NRPSD of the radial orientation to that of other orientations. Influences of properties of rock–concrete interfaces, geometric properties (location, arc length, and depth) of voids, and mechanical properties of rocks and concrete on the values of NRPSD were estimated via numerical simulations. As a preliminary study, these results provide clear evidence that the vibration intensity characteristics of microtremors have a strong correlation with the existence of voids located between lining concrete and surrounding rock masses, which has high potential to be developed to an effective approach for health assessment of tunnel linings in the future.     

Physical model tests and numerical simulation for assessing the stability of brick-lined tunnels

Nowadays, numerical modelling is increasingly used to assess the stability of tunnels and underground caverns. However, an analysis of the mechanical behaviour of existing brick-lined tunnels remains challenging due to the complex material components. In order to study the mechanical behaviour of the masonry in brick-lined tunnels, this paper reports a series of small scale physical tunnel model tests to represent the true behaviour of a real tunnel under extreme loading. Advanced monitoring techniques of laser scanning and photogrammetry are used to record tunnel deformation and lining defects. This investigation shows how these techniques may substitute or supplement the conventional monitoring procedures. Moreover, numerical analyses based on continuum and discontinuum approaches are carried out. The numerical results are compared with physical model tests to assess the overall stability of these tunnels. Predictions using numerical models under various conditions have also been carried out to show the mechanical behaviour of masonry tunnel and to quantify the influence of the boundary and loading conditions.     

隧道初支与二衬间接触压力统计分析

复合式衬砌一般由初期支护和二次衬砌共同组成,二者相互作用关系是隧道工程中的研究热点,本文通过对43座隧道79个监测断面初支与二衬接触压力的统计分析,探讨了接触压力的总体分布特征及其与围岩等级、隧道埋深、跨度等因素的关系,研究了二衬荷载分担比在洞周的分布规律,讨论了接触压力随时间的变化规律及其空间分布特征。结果表明:初支与二衬接触压力值分布在10~200 kPa之间;接触压力及其离散程度随隧道埋深增大而增大,Ⅴ级围岩增大趋势比Ⅳ级围岩更明显;二衬荷载分担比集中在0~20%范围内;接触压力有明显的时间效应,随时间的变化表现为快速增长至峰值之后减小,进而缓慢增大趋于稳定,稳定所需时间在二衬浇筑后30 d左右;接触压力空间分布规律为拱顶→拱肩→拱腰→拱墙增大,拱墙→拱脚→拱底减小。研究结论可为隧道结构受力分析与优化提供参考。     

爆破震动下地下工程围岩稳定与支护设计

随着我国地下工程的大量建设,在新建硬岩隧道与既有隧道间距较小的情况下进行爆破开挖,产生的爆破震动波会危及隧道支护结构的安全和稳定。因此,研究隧道爆破开挖对既有隧道和开挖隧道支护结构的稳定性影响,具有重要的理论意义和工程实用价值。本文运用便携式微机控制数字输出测震仪进行爆破震动测量,同时,采用软件进行非线性数值模拟计算,分析隧道爆破开挖对既有隧道和开挖隧道支护衬砌的影响,讨论爆破震动影响下隧道支护方式的优化。     

2D numerical investigation of segmental tunnel lining behavior

The application field of shield tunneling has extended in recent years. Most shield-driven tunnels are supported by segmental concrete linings. Although many well documented experimental, numerical and analytical results exist in literature concerning the functioning of segmental tunnel linings, their behavior under the influence of joints is still not clear.This paper presents a numerical study that has been performed to investigate the factors that affect segmental tunnel lining behavior. Analyses have been carried out using a two-dimensional finite difference element model. The longitudinal joint between segments in a ring has been simulated through double node connections, with six degrees of freedom, represented by six springs. The proposed model allows the effect of not only the rotational stiffness but also the radial stiffness and the axial stiffness of the longitudinal joints to be taken into consideration. The numerical results show a significant reduction in the bending moment induced in the tunnel lining as the joint number increases. The tunnel behavior in terms of the bending moment considering the effect of joint distribution, when the lateral earth pressure factor K₀ is equal to 0.5, 1.5 and 2, is almost similar and differs when K₀ is equal to unity. It has been seen that the influence of joint rotational stiffness, the reduction in joint rotation stiffness under the negative bending moment, the lateral earth pressure factor and Young’s modulus of ground surrounding the tunnel should not be neglected. On the other hand, the results have also shown an insignificant influence of the axial and radial stiffness of the joints on segmental tunnel lining behavior.     

大跨度隧道CRD法穿越含水软弱层沉降变形控制

 正在施工的厦门翔安海底隧道两端陆域段采用CRD法长距离穿越含水软弱层,为保证施工安全快速的通过,施工中通过差分软件计算分析及结合现场监控量测数据,探讨CRD法隧道拱顶下沉量及其在各个导坑开挖过程中的分配比例以及导坑施工顺序对沉降的影响。计算及现场量测结果都表明,CRD1开挖产生的拱顶沉降所占整体沉降的比例约为40%,拱顶下沉通常为最后收于一稳定值的台阶状上升曲线,初期支护全封闭后,结构整体仍有一定量的下沉,一般小于10%,尽快闭合仰拱对减小拱顶下沉有很大帮助。施工时应控制施工进尺,相邻导坑间距不大于10～15 m,并尽早设置临时仰拱,使支护结构成环。     

Interaction of tunnel linings and soft ground

Although soil-lining interaction is highly dependent on the tunnelling technology used, most of the available design methods for tunnel linings fail to take into consideration this important factor. During tunnel excavation, the in-situ stresses are significantly altered, depending on the tunnelling technique as well as the configuration of the tunnel and the characteristics of the soil deposits. The reduced radial stresses are the starting point of the soil-lining interaction at lining activation. This paper presents a method of lining design that considers the details of the excavation procedure and lining installation. Interaction between the tunnel lining and the ground is analysed in two stages—excavation and interaction. The excavation stage is responsible for determining the pre-lining soil deformations and the reduced in-situ stresses. The interaction stage models the soil-lining system together. Soil continuum, tunnel lining, and the interface between them are idealized in the whole system using nonlinear finite-element techniques. The deformations of the soil-lining system, as well as the lining internal forces, and equilibrium soil pressures are determined. Finally, results of the proposed analytical method as well as commonly used procedures are compared with field measurements compiled during the construction of two tunnels in which a precast segmental lining and rib and lagging lining were used.     

Excavation and support design of the Dicle–Kralkizi water tunnel: an overview

Tunneling projects have their uniqueness in terms of engineering problems. The expertise gained from analyzing these projects establishes a sound basis for future application. This paper conveys experiences gained during the construction and support of the design of the Dicle–Kralkizi water tunnel, Turkey. Tunnel stability problems including overbreaks and surface subsidence are evaluated. An analysis of the breakdowns, factors controlling advance rate and the overall performance of tunnel are covered. The accumulated information presented here is believed to be useful and reliable for a successful tunnel excavation in similar formations.     

某下穿危房管线工程对建筑物影响分析

针对某下穿危房管线工程实例,采用国际标准,运用解析方法评估了隧道施工对建筑物的影响;并通过数值模拟评价了隧道拆除临时支撑及二衬施作对结构、地层的影响;为隧道成功穿越提供了理论支持和实践指导。     

隧道衬砌混凝土质量主要通病的预防和控制

在隧道施工中,二次衬砌混凝土存在质量问题(即质量通病)。针对隧道衬砌混凝土质量通病加以分析,提出一些预防和控制的方法,对提高隧道二次衬砌混凝土的施工水平具有借鉴意义。     

海底隧道排水衬砌渗流场解析

现有海底隧道渗流场计算模型未考虑上覆土层对围岩压力水头的影响。本文采用保角变换法,根据层间流量相等原则求得在上覆土层条件下带衬砌隧洞的渗流量及其周边水头分布,并验证其可靠性。计算结果表明:(1)海底土层的渗透系数对渗透量影响较大,尤其当土层水力通道不佳时要考虑土层的影响;(2)衬砌水压力折减系数随衬砌渗透系数变化逐步趋于稳定,折减系数宜取其与渗透量的交线处,此时衬砌与注浆圈渗透系数比值k_{L/kg=0.075;(3)注浆圈比衬砌承担更大的水压力,注浆圈厚度加大能有效减小渗透量,当kL/kg<0.05时,注浆圈厚度的增加对渗透量影响不大。}     

Subsurface exploration and transient pressure testing from a deep tunnel in fractured and karstified limestones (Lötschberg Base Tunnel,Switzerland)

This paper summarizes the results from a subsurface exploration campaign carried out in fractured and karstified limestones and marls of the Lötschberg Base Tunnel in the Swiss Alps. The exploration program in the 3.2 km long Doldenhorn Section consisted of 50 cored and 13 destructive horizontal predrillings of 250–300 m length each (in total 14,853 m of predrillings). These boreholes were used to locate possible tunnel inflows and characterize their hydraulic properties. A new efficient hydrogeological test protocol has been developed and was systematically and successfully applied. The test protocol consists of short constant rate outflow and recovery tests in open boreholes. The on-site test analysis allowed reliable predictions of the hydrogeological conditions ahead of the advancing tunnel face in brief period of time, leading to decisions regarding further reconnaissance drillings, tunnel driving or sealing measures. Detailed analysis of the transient pressure responses of the hydrogeological tests carried out after tunnel completion led to important new findings regarding flow model identification (type and orientation of conductive fractures), aquifer parameters and boundary effects. Even though the hydrogeological tests had to be carried out within a short time frame (a few hours) they allowed characterization of large scale aquifer properties relevant for long term tunnel inflow behavior.