浅埋铁路隧道CRD法施工对地表变形影响的数值分析

针对龙厦铁路石桥头隧道工程围岩软弱,埋深浅的特点,应用数值分析手段,分析了浅埋铁路隧道在CRD法下施工,对地表沉降变形的影响。结果表明:CRD法下隧道各部施工对地表沉降均有影响,掌子面上部开挖产生的地表沉降明显大于下部,纵向地表沉降随隧道开挖过程分为三个阶段。结合分析结果,文章指出了施工过程中应采取的相应措施。     

牛官头隧道锚喷支护施工

介绍了甬台温高速公路牛官头隧道锚喷支护施工新材料、新工艺、新方法,并制定出施工中出现问题的对策。     

黄土隧道施工工艺

结合工程实例,对黄土隧道洞身开挖的施工方案进行了介绍,阐述了初期支护、防排水、二次衬砌等具体的施工技术,并总结了监控测量的要点,为类似工程的施工积累了经验。     

隧道沥青路面施工技术与安全措施

随着高速公路的迅速发展,沥青混凝土以其舒适、快捷、维修养护方便、噪声小的特点已被广泛应用。越来越多的高速公路选择了在隧道内铺筑沥青混凝土路面,但隧道独特的环境因素使得铺筑隧道沥青混凝土与常见的沥青路面施工有着一定的区别。本文通过漳州招银疏港高速B1合同段伍凤山隧道沥青路面施工为例,对隧道沥青施工技术及安全保障措施进行了浅析。     

Numerical analysis of different ventilation schemes during the construction process of inclined tunnel groups at the Changheba Hydropower Station,China

During the excavation process of underground caverns, the rational selection of the ventilation scheme is very important for the safety and health of construction workers. The flood discharge tunnel groups at the Changheba Hydropower Station are selected as a case to study the design of ventilation schemes in inclined tunnel groups; these groups are characterized by a gradient of approximately 10% and a complex intersecting relationship among the tunnels. The Computational Fluid Dynamics (CFD) method is used to simulate the fluid dynamics in tunnel groups when different ventilation schemes are employed. Four ventilation schemes with the same duct at different positions along the transverse section are formulated, and the scheme approaching the right side with most of the construction adits is adopted in engineering after a comparative analysis, as it offers a well-distributed velocity field and sufficient security distance. The study reveals that flow vortices appear in the tunnels with a long axis length ranging from 5 m to 20 m; the observation that the flow velocity on the transverse sections is away from the heading face indicates that a low-velocity area is always present in the vicinity of an air duct, and the security distance on the upstream side is 60% shorter than on the downstream side with the same air-blower when the tunnels have a 10% gradient. In addition, when the excavation distance rises 200 m, the ventilation condition in the tunnels, especially in the areas around tunnel intersections, is greatly improved by the completion of pilot tunnels and shafts in advance.     

Numerical back analysis for estimation of soil parameters in the Resalat Tunnel project

Determination of in situ soil or rock geotechnical properties is a difficult task for a design engineer. Back analysis is a helpful technique for evaluation of soil properties by considering and measuring the convergence of an underground opening. In this article, the results of numerical back analysis, performed for Resalat tunnel in Tehran, Iran, are reported. The main purpose of this study was to estimate the soil cohesion and the in situ horizontal stress. Back analysis was performed by matching numerical modeling results with the measured tunnel convergence. In addition, the results of in situ direct shear, plate load and pressure meter tests are reported and compared with those from back analysis. It is shown that the back analysis presented is capable of determining the horizontal in situ stress and soil cohesion with good accuracy.     

Numerical simulation of the uplift behavior of shield tunnel during construction stage

In this study, a new 3D numerical model that considers the circumferential joint, longitudinal bolt, grout pressure, jacking force and the constraint of shield on the linings is developed to derive deeper insights into the lining uplift behavior during shield tunneling. The numerical analysis is conducted using ANSYS, which is verified by a case history in soft soils. Revealed by both the measurements and calculation results, it is found that the lining uplift due to shield tunneling in soft soils can be divided into three stages: dislocation, stretch and steady deformation stages, respectively. In the dislocation stage, the lining deformation attributes principally to the dislocation deformation between neighboring linings. In the stretch stage, the lining deformation is mainly caused by the stretch deformation of circumferential joints. The major uplift is caused during dislocation stage. Thereafter, the impacts of shield-driving parameters including gradient of grout pressure, jacking force and pre-tightening force of longitudinal bolts on the uplift behavior are investigated by a series of parametric studies. The jacking force during segment preparation and assembly shows the most significant impact on the uplift of the tunnel, while the pre-tightening force of longitudinal bolts shows negligible impact. Finally, the control criterion for lining uplift related to the allowable dislocation and opening angle of circumferential joints is proposed.     

Numerical study on failure mechanism of tunnel in jointed rock mass

During underground excavation many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this paper, a numerical code called RFPA was used to study the influence of different dip angle of layered joints and the lateral pressure coefficient on the stability of tunnel in jointed rock mass. Numerical analysis indicated that both the dip angle of joints and the lateral pressure coefficient have significant impacts on the failure mode and displacement characters of tunnel. The progressive failure processes of tunnel in jointed rock mass were presented and the mechanisms were discussed. The applicable condition of geographical method by Goodman is also discussed. These results offer a guideline in support design.     

Design and optimisation of the lining of a tunnel in the presence of expansive clay levels

This paper describes the study made of the Trasvasur tunnels (Canary Islands, Spain), which were excavated in rocky formations of volcanic origin presenting metric levels of expansive clays. The building of these tunnels had to be abandoned 30 years ago, owing to the problems caused by the expansivity of the ground. It was subsequently decided to resume the project, making joint use of geotechnical investigation campaigns, convergence measurements and numerical simulations, thereby contributing towards the optimisation of the cross-section of the tunnelled area, support and lining. The work done has shown that when building tunnels in the presence of expansive clays it is advisable to use circular or similar cross-sections. It has also been found to be advisable to seal off the excavation as quickly as possible to prevent alteration due to the decompression of the expansive clay levels and their absorbing water from the tunnel itself.     

Probabilistic assessment of tunnel construction performance based on data

A probabilistic model for estimating tunnel construction time is learnt with data from past tunnel projects. The model is based on the Dynamic Bayesian Network technique. The model inputs are determined through an analysis of data from three tunnels built by means of the conventional tunneling method. The data motivate the development of a novel probability distribution to describe the excavation performance. In addition, the probability of construction failure events and the delay caused by such failures are estimated using databases available in the literature. The model is applied to a case study, in which it is demonstrated how observations from the tunnel construction process can be included to continuously update the prediction of construction time.     

Influence of stress path on tunnel excavation response – Numerical tool selection and modeling strategy

The actual stress path in a rock mass during tunnel excavation is complex. To capture the correct tunnel excavation response, it is important to correctly resemble the stress path in situ in the numerical tools.FLAC and Phase² are two powerful two-dimensional continuum codes for modeling soil, rock, and structural behavior, in the fields of geotechnical, geomechanics and in civil and mining engineering. FLAC is based on explicit finite difference formulation while Phase² is based on implicit finite element formulation. When the two codes are applied to the analysis of tunnel excavation problems, difference in results might occur simply due to the different formulation methodologies used in these codes. It is shown that for linear elastic tunnel excavation problems, both codes provide the same result because stress path is unimportant. For tunnel excavation in elasto-plastic materials using long-round drill and blast method, there is significant difference in terms of yielding zone distribution by the two codes if conventional modeling approach is used, especially when the rock strength is low relative to the in situ stress magnitude. The mechanism of the difference is investigated and recommendation provided for choosing appropriate tools and modeling strategies for tunnel excavation problems. The importance of honoring the true stress path in tunnel excavation response simulation is illustrated using a few examples.     

Deformation and mechanical characteristics of tunnel lining in tunnel intersection between subway station tunnel and construction tunnel

Deformations and stress distributions in tunnel intersection areas are more complicated than those in common tunnels. The literature on deformations and stress distributions in tunnel intersections, in which the intersecting tunnel is in a different section, is limited. The Shangxinjie subway station in Chongqing, China, was selected to investigate the deformation, stress and plastic zone responses of a tunnel intersection using numerical simulations. Based on the numerical results, the scopes of influence with respect to the deformation, stresses and possible failure modes of the tunnel lining were further studied. The numerical results show that the deformation in a section close to the tunnel intersection was larger than the deformations in distant sections. Compared with the common section, the crown settlement reached the maximum value at the tunnel intersection, and the maximum rate of increase was approximately 28%. The range of the plastic zone at the tunnel intersection was much larger than that in the other areas, and it was mainly located in the side wall and tunnel crown. In the longitudinal direction, the lengths of the scopes of influence were 2.4 B and 1.6 B with respect to the deformation and stress, respectively. The magnitudes of the internal forces in the longitudinal and circumferential directions were almost equal. The bending moments of the tunnel lining within 135° and 225° significantly changed, but the axial force decreased dramatically. Tensile and compressive failures may occur at the tunnel intersection and in a section 5 m away. Locally thickening the supporting structures is suggested to improve the stability of the tunnel.     

Numerical analysis of tunnel thermal plume control using longitudinal ventilation

A CFD model of the 4th Beijing subway line was used to study the effect of longitudinal ventilation on heat and smoke plume movement in the tunnel. The critical ventilation velocity is correlated with the heat release rate for both a simplified heat fire source model and a complete combustion fire source model with methane gas as fuel. The influences of the heat source length and the fuel gas inlet geometry on the critical velocity are investigated for both fire source models. The results show that the influences of the combustion process and fire source area variation are not included in models based on Froude number preservation theory. Thus, Ri is no longer suitable as a dimensionless number for the critical ventilation velocity when the fire geometry or combustion conditions influence the results. The back-layering air temperature above the front of the fire source can be used to explain the different critical velocity variation regimes for all the simulation conditions.     

较差地质连拱隧道开挖方案及施工顺序的探索

通过对云南富广高速公路银厂连拱隧道施工过程的分析,并对比邻近在建连拱隧道的不同施工方法,分析了偏压连拱隧道在采用不同开挖顺序施工时各阶段围岩的应力、应变状况,得出了一些结论,为今后类似连拱隧道的施工提供了合理建议。     

On numerical simulation of tunnel installation

The design of tunnels requires a proper estimate of surface settlements and lining forces. In engineering practice different design methods tend to be used, varying from simple empirical and analytical formulations to advanced finite element analyses. This paper begins with a review of empirical and analytical analyses for settlements and lining forces placing emphasis on the sequences of excavation and installation of support. Such installation procedures range from open face to closed face tunnelling and they tend to have a significant effect on deformations and lining forces. Hereafter the focus is on two-dimensional FE-analyses; again both for open face and for closed face tunnelling. Results for different installation procedures will be presented on the basis of two case studies. It is shown that installation procedures are most important to be considered in order to arrive at proper predictions for tunnelling settlements, horizontal deformations and lining forces. For the installation of closed face shield tunnelling a novel simulation method is presented, named the grout pressure method. It is shown that the grout pressure method yields the best predictions for both ground movements and structural forces.     

新建隧道下穿既有高铁隧道施工方案研究

针对如何确保新建隧道的施工尽可能少的影响既有隧道运营安全这一课题,以新建宁德白马港铁路支线天池山隧道与已建成通车的杭深铁路天池山隧道为例,分析其工程特点,列举相关工程措施,描述相应施工方案,为同类工程提供指导。     

高速铁路软弱围岩隧道洞口滑坡体地段施工技术

对高速铁路软弱围岩隧道洞口滑坡体地段明洞段、暗洞段施工时出现变形开裂的情况作了分析,并采取了一系列有效加固处理措施,稳步推进完成洞口段二次衬砌,度过了施工高风险区,在类似工程实践中具有一定的参考意义。     

宝成铁路新109号隧道快速施工方法

结合宝成铁路新109号隧道实际情况,简要介绍了该隧道施工方案,着重阐述了新109号隧道快速施工方法,包括开挖、衬砌、仰拱三方面内容,经实践证明,该快速施工法取得了良好效益,值得推广。     

Effects of steel fiber reinforced high-strength shotcrete in a squeezing tunnel

In order to quantitatively clarify the effects of steel fiber reinforced high-strength shotcrete (SFRS) applied to a squeezing tunnel, a non-linear numerical analysis is carried out, in which the stress–strain–time constitutive relationships of SFRS and the time-dependent movement of the ground surrounding the tunnel are taken into account. Through a comparison of field measurement and analytical results, it is recognized that SFRS can be applied as a reasonable primary lining for tunnels excavated in grounds with severe geological conditions. In particular, high strength during the early stages of the execution and ductility after its peak strength both contribute to the safe construction of squeezing tunnels.     

邵家台隧道千枚岩施工变形演变研究

以湖北省谷(城)竹(溪)高速公路邵家台隧道千枚岩隧道工程为例,结合监控量测信息,探讨软弱千枚岩不良地质段隧道施工变形机理及其影响因素,提出应对施工优化方案,为类似工程提供了一定指导。