Tunnel Excavation Process Research Articles

The Influence of Moisture Content on the Time-Dependent Characteristics of Rock Material and Its Application to the Construction of a Tunnel Portal

Uniaxial compression creep experiments were carried out for low-grade metamorphic slate samples (located in the southeastern area of Guizhou province, China) with different moisture contents, using an Instron electric-fluid servo-compression machine. Based on the experimental results, a detailed analysis was made of the effect of moisture content on the strength and deformation behaviour of the slate specimens. The three-parameter generalised Kelvin model was identified to describe the creep behaviour of the low-grade metamorphic slate with different moisture contents. There is an approximately linear negative correlation between the elastic modulus and the saturation degree, and the viscoelastic modulus and viscosity coefficient show a negative exponent correlation with the saturation degree. The Kelvin creep model considering the moisture degradation effect was established and a three-dimensional finite difference model was developed with the softwareFLAC3Dto validate the creep model. A three-dimensional numerical analysis was then performed to simulate the tunnel excavation process. The results show that the influence of moisture and creep of the surrounding rocks is needed for estimating the deformation of complex tunnel portals.

Analytical Solutions for Tunnels of Elliptical Cross-Section in Rheological Rock Accounting for Sequential Excavation

AbstractTime dependency in tunnel excavation is mainly due to the rheological properties of rock and sequential excavation. In this paper, analytical solutions for deeply buried tunnels with elliptical cross-section excavated in linear viscoelastic media are derived accounting for the process of sequential excavation. For this purpose, an extension of the principle of correspondence to solid media with time varying boundaries is formulated for the first time. An initial anisotropic stress field is assumed. To simulate realistically the process of tunnel excavation, solutions are developed for a time-dependent excavation process with the major and minor axes of the elliptical tunnel changing from zero until a final value according to time-dependent functions specified by the designers. In the paper, analytical expressions in integral form are obtained assuming the incompressible generalized Kelvin viscoelastic model for the rheology of the rock mass, with Maxwell and Kelvin models solved as particular cases. An extensive parametric analysis is then performed to investigate the effects of various excavation methods and excavation rates. Also the distribution of displacements and stresses in space at different times is illustrated. Several dimensionless charts for ease of use of practitioners are provided.

Investigating the Economic Performance of Tunnel Excavation in Iran: 1998–2013

Nowadays, the world is witnessing the ever increasing need of Tunnel excavation due to their unique features and the kind of human applied plans. This has led to increase in demand of excavating this engineering factor. Tunnel excavation process faces a lot of challenges due to environmental and technological complexities which causes the economic evaluation and investigation of this project to be difficult. It is tried to develop the proposed model with regard to efficiency concept in order to evaluate and investigate the efficiency of relative economic performance of Tunnel excavation projects and turn to its modeling and implementing by data envelopment analysis and Fuzzy DEMATEL techniques. The results in Iran showed that the proposed model can turn to investigation and evaluation of economic efficiency of Tunnel excavation by considering two optimistic (ideal) and pessimistic perspectives such that the Tunnel excavation process of “Karaj water transition” and “Cheshmelangan water transition” among 12 rock Tunnel excavation projects of Iran in the time period of 1998–2013 were respectively introduced as the most efficient and the most inefficient rock Tunnel excavation projects.

Structure Parameters Optimization of Thrust Hydraulic Cylinder under Foundation Vibration

Against the impact of strong vibration on the dynamic performance of thrust hydraulic cylinder during the process of Tunnel boring machine(TBM)'s rock break and excavation, the dynamic response of the mathematical model of hydraulic cylinder under the axial foundation vibration is built, and the correctness of the model is experimentally verified. Thrust hydraulic cylinder failure region under different vibration parameters is studied, the pressure fluctuation amplitude is positive linear correlated to vibration amplitude, and maximum when vibration frequency is near to natural frequencies, and can be considered as a constant when increase to 90 Hz. Structure parameters are optimized by response surface methodology. Optimized hydraulic cylinder can withstand vibration amplitude-frequency region wider than 45% before optimization when normally works. The optimization of hydraulic cylinder structural parameters by response surface methodology can provide theoretical basis for the design and selection of TBM thrust hydraulic cylinder.

Research on Support Technique for Excavation Process of Deep Rock Mass

In the deep rock mass surrounding, rock burst, large deformation, zonal fracturing and phenomena like these may occur in the tunnel excavation process. When zonal fracturing happens, it is essential to reconsider the types of support, the boundary of support and the approach of tunnel excavation. In this paper, the control theory about the surrounding rock stability under high pre-existing stresses was researched, and the efficient support form which was the combination of high strength anchor bar and anchor cable was ascertained to be adaptive to deep tunnel excavation. According to the deformation and zonal fracturing mechanism of the surrounding rock, a comprehensive support program that combined intensive short anchor bars and long anchor cables was established, and the numerical simulation was carried out to verify the feasibility of the support form.

Analytical Solutions for the Construction of Deeply Buried Circular Tunnels with Two Liners in Rheological Rock

The construction of underground tunnels is a time-dependent process. The states of stress and strain in the ground vary with time due to the construction process. Stress and strain variations are heavily dependent on the rheological behavior of the hosting rock mass. In this paper, analytical closed-form solutions are developed for the excavation of a circular tunnel supported by the construction of two elastic liners in a viscoelastic surrounding rock under a hydrostatic stress field. In the solutions, the stiffness and installation times of the liners are accounted for. To simulate realistically the process of tunnel excavation, a time-dependent excavation process is considered in the development of the solutions, assuming that the radius of the tunnel grows from zero until its final value according to a time-dependent function to be specified by the designers. The integral equations for the supporting pressures between rock and first liner are derived according to the boundary conditions for linear viscoelastic rocks (unified model). Then, explicit analytical expressions are obtained by considering either the Maxwell or the Boltzmann viscoelastic model for the rheology of the rock mass. Applications of the obtained solutions are illustrated using two examples, where the response in terms of displacements and stresses caused by various combinations of excavation rate, first and second liner installation times, and the rheological properties of the rock is illustrated.

The 3D Numerical Simulation and Settlement Control Study for City Tunnel Crossing High Fill Geological Area of Gravelly Soils

Three-dimensional finite element model of tunnel-soil-structures interaction was set up to analyze the causes of settlement and structural cracking when tunnel crossing complex gravelly soil area. It simulated the real tunnel excavation process of Chongqing Metro Line 3. Based on analysis and monitoring results, improved technical measures were used to control settlement, such as advance strengthening, excavation speed control and so on. The latest monitoring results indicate that vault and ground settlement are controlled, and convergence value is reduced significantly. The 3D numerical simulation analysis method provides reference for similar projects, and improvement of technical measures is conducive to settlement control.

Numerical Simulation of Primary Support Effect of Tunnel

The tunnel excavation and support process were simulated by using ANYSY. Firstly, support effects were studied on different modes of support. Secondly, numerical simulation was realized by using the function of APDL parametric design language in ANSYS. By discussing the different support effects which were arrived through changing support parameters and geometric parameters, conclusions and recommendations were put forward. At last, it could be clearly seen that the simulation results were in good agreement with the monitoring records.

Evaluation of monitoring items for adverse ground conditions in subsea tunneling

Three monitoring items, i.e. displacement vector orientation, preceding displacement, and water inflow, were compared to determine which one best provided supplementary and valuable information on the ground ahead of a subsea tunnel face when used with probe drilling. The geotechnical factors affecting tunnel stability were selected from the case studies on the construction of subsea tunnels, and six representative types of adverse ground condition were built with combinations of the factors. The capabilities of monitoring items were compared in depression and weakness zone types that were selected as major adverse ground conditions with three criteria, i.e. the capability of categorizing the type of adverse ground condition, the early-warning time, and the response capability. A three-dimensional finite element analysis program was used to simulate the process of subsea tunnel excavation, and the Analytic Hierarchy Process was used to select the optimum monitoring item. A comparison of the results showed that the vector orientation was the optimum item for categorizing ground type, and the preceding displacement and the water inflow possessed the best capability for early warning according to ground type. The response capability of water inflow was assessed as the best for three types of weakness zones, and that of vector orientation was best for depression type. In 13 cases where the priorities of comparison criteria were different, the vector orientation and the water inflow were respectively chosen in six cases, and there was little difference between the two items in the case where the criteria were equally important. While the application of one item alone may be vulnerable to a specific adverse ground condition, the monitoring capability could be overall improved by the adoption of both items.

Multiple Source-Detector Reflected Wave Method in the Intercity High-Speed Rail Tunnel Application

In the tunnel excavation process, often encounter fault belt, soft interlayer and abnormal water-bearing body does not directly predict adverse geological structure, not timely prediction and control these geological disasters will affect the safety of production. In many prediction methods in geophysical technology with nondestructive, accurate, efficient, fast and be recognized, many shot-geophone reflected wave method in different geological conditions on the apparent impedance response, the migrated results can accurately distinguish the lithologic interface, in many projects has been confirmed. The paper introduces the multiple source-detector reflection wave observation system based on, combined with the specific project example, elaborated how the shot-receiver reflected wave method in tunnel face geological disaster prediction in rats.

Study on the Impact of Stability around Tunnel Surrounding Rock in Construction Program

In order to analyze the different construction program under the tunnel surrounding rock stress, strain and plastic zone changes, we take water tunnel group of nuclear power plant as basic project and the application of software FLACIS3D numerical simulation.The results show that: During the tunnel excavation and support group process, the different rock tunnel construction program can produce different stress, displacement and plastic zone extended range of distribution and other aspects.To interval-type excavation program,although previously disturbing effect of the excavation of the tunnel construction and tunnel excavation of rock, it can generate less impact on the stability of surrounding rock. For the latter excavation of the tunnel, the tunnel project area affected by the first digging,the stress can be released, the stability of the first excavation of the tunnel effect is also small.Comparing to sequential and parallel program-type excavation program, the use of interval-style group of rock tunnel excavation will help stabilize the body.

Finite Element Analysis for the Displacement Characteristics of Loess Tunnel with Weak Surrounding Rock

Backed up by Dayoushan loess tunnel of Xining in Qinghai province, the displacements of vault settlement, peripheral convergence, surface deformation and post-construction settlement caused by tunnel construction are numerically simulated and analyzed. First, 2-D elastic-plastic model is founded to simulate the tunnel excavation process with up and down steps method. Second, considering the rheological characteristics of loess, 2-D visco-elastic-plastic constitutive model is founded to simulate the creep deformation of rock displacement characteristics. Finally, combined with the serious collapsible feature of loess foundation in supported project, the post-construction settlements under different conditions are simulated to obtain the settlement values of tunnel vault and bottom. The results can explain the deformation laws of tunnel displacement characteristics reasonably and show the importance of foundation reinforcement measures for loess tunnel.

Development of swing method with sequential data assimilation (SDA-SWING) and its application to groundwater problems in real tunnel construction

Tunnel excavation in Japan is beset by difficulties related to complicated geology and groundwater. Controlling the groundwater inflow to the tunnel during excavation is a challenging issue for both tunnel construction and for environmental assessment. The SWING (System for Water INformation of Ground) method was developed to enable predictions regarding groundwater inflow to the tunnel and also to allow evaluation of the impact of excavation on the surrounding groundwater environment. The SWING method is based on the closed-form solution of Dupuit quasi-uniform flow and can follow the tunnel excavation process by reconstructing the hydraulic conductivity fields using data obtained at construction sites. Herein, the original SWING system was modified by the Ensemble Kalman Filter (EnKF) in order to automatically optimize the hydraulic parameters. The newly developed SWING method, SDA-SWING (Sequential Data Assimilation-SWING), was applied to two different tunnel construction sites in Japan and its applicability was discussed by comparison with the results obtained from the original SWING method. The effects of initial hydraulic conductivity and the frequency of data acquisition on the predicted results were also investigated using the SDA-SWING method. The SDA-SWING method can automatically optimize the hydraulic parameters using EnKF algorism without the need for highly skilled personnel and thus leads to a significant reduction in working times. The estimation of groundwater inflow by the SDA-SWING method generally agrees well with results obtained by the original SWING method and also with observations at the tunnel site.

Three Dimensional Load Analysis of Tunnel Linings Including Weathering Processes of the Shotcrete

In this study a three-dimensional finite element model was applied to simulate the process of tunnel excavation and lining installation. The emphasis was placed on the prediction of deformation and forces acting on the primary shotcrete lining during a NATM excavation in rock modelled with Mohr-Coulomb elasto-plastic material behaviour. Further investigations and development of the model were done by taking into consideration long-time behaviour of the primary support elements by decreasing the strength and stiffness parameters of the shotcrete shell and the influence on the final lining caused by this.

Finite Characteristic Ratio Theory Model Analysis for the Thin Rock Pillar of a Twin Tunnel

The machnical response of the thin rock (and/or soil) pillar of a twin tunnel with super-large-span and small-spacing is described upon a model of finite characteristic ratio constitutive theory (FCRT). The analysis result is compared with the results from in situ monitoring and the D-P model of the classic plastic constitutive theory; it shows that the deformation characteristics of the middle pillar during tunnel excavation process can be reasonably described by the FCRT model, and the method of parameter determined of the FCRT model is relatively simple than the classic plastic model due to the model has a clear physical background and with little randomness.

Risk Quantification for Tunnel Excavation Process

Risk Quantification for Tunnel Excavation Process

An application of three-dimensional analysis around a tunnel portal under construction

Deformation of a tunnel portal during tunnel excavation is very complex, and it can affect adjacent portal structures. During the construction of the Seoul Metro Line 7, a temporary vertical shaft was constructed by cut and cover method to take out a shield machine and to excavate subsequent tunnel by New Austrian Tunneling Method. Due to the complex structure of tunnel portals, the temporary support system of the vertical shaft was expected to be subjected to an additional load during the tunnel excavation. Thus, three-dimensional analysis of the vertical shaft, including tunnel excavation process, was performed in order to ensure the safety of overall system. This paper presents behavior of the vertical shaft based on the three-dimensional numerical analysis results during the construction sequence.

Investigation of Tunnel-Soil-Pile Interaction in Cohesive Soils

Underground tunnels are considered to be a vital infrastructure component in most cities around the world. Careful planning is always necessary to ensure minimum impact on nearby surface and subsurface structures. This study describes the experimental investigation carried out to examine the effect of existing piles installed in cohesive soil and extended to bedrock on the circumferential stresses developing in a newly constructed tunnel supported by a flexible lining system. A small scale testing facility was designed and built to simulate the process of tunnel excavation and lining installation in the close vicinity of preinstalled model piles. Lining stresses were measured for different separation distances between the lining and the existing piles Consistent decrease in the lining load was observed when the piles are located within a distance of one tunnel diameter from the tunnel. The results presented in this study indicated that measuring the lining response near existing pile foundations may be used to evaluate the extent of the interaction between the lining and the surrounding piles.

나일론섬유보강 터널 라이닝 콘크리트의 내구성능 평가

Tunnel structures are widely used for transportations in mountains areas. To shorten the construction period and to cut down the construction expenditure, a construction technique that a tunnel excavation process and a tunnel lining process are simultaneously performed is often applied in the field. However, due to the vibration and impact caused by excavation process, cracking and deterioration of tunnel lining concrete could happen. This research experimentally investigated the effective role of the usages of blended cement and recently developed nylon fibers for tunnel lining concrete. It has been observed that both nylon fibers and blended cement improve the durability and physical properties of concrete.

3D Effects on Earth Pressure and Displacements During Tunnel Excavations

Three-dimensional model tests of tunnel excavation and the corresponding numerical analyses were carried out to investigate the influence of tunnel excavation on surface settlement and earth pressure surrounding a tunnel. Numerical analyses were performed with the finite element method using elastoplastic subloading tij model. Two types of apparatuses were used in the model tests, namely-trap door apparatus and pulling out tunnel apparatus. The minimum excavation length along the excavation direction is 8 cm in the trap door apparatus. However, the process of real tunnel excavation is more continuous. For simulating real tunnel excavation in 3D, a new apparatus was develped, which is called as the pulling out tunnel apparatus. This apparatus can simulate tunnel excavation in sequential way. Both experiments and analyses were conducted with various ground depths for simulating the influence of soil cover on tunnel excavations. Surface settlements are measured at the transverse cross-section of the ground. Earth pressures at the top of the tunnel in the trap door apparatus are measured. However, in the tests performed with the pulling out tunnel apparatus, earth pressures are measured adjacent to the tunnel cross section. In this paper, the effects of 3D excavation on surface settlements and earth pressures are discussed. It is revealed that arching is formed in both transverse and longitudinal directions of tunnel excavation. Numerical results show very good agreement with the results of the model tests. In the three-dimensional analyses performed in a sequential way, earth pressure is almost zero at the excavation front, irrespective of the soil cover. In 2D analyses and 3D analyses using the trap door apparatus, the earth pressure at the excavation front does not vanish, as observed in 3D sequential analyses.