首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Reasonable failure paths are crucial in the stability assessment of a highly pressurized gas storage cavern in a rock mass using limit equilibrium analysis. In this study, the fracture patterns in the rock mass around a gas storage cavern are evaluated based on the element-free Galerkin (EFG) method with a cohesive crack model. The proposed analysis method was first validated through scaled-down model testing results before extending to a full-scale problem. Using the current approach, a parametric sensitivity analysis was performed by taking into account the influences of the stress ratio, the depth of the cavern, and the tensile strength of the rock mass. Based on the analysis results obtained, this research showed that the representative failure paths, in which the uplift evaluation is necessary, can be established from the EFG results with careful consideration of crack initiation and the propagation direction. The site having an in situ stress ratio greater than 1.2 is preferred for operation of underground gas storage caverns. By performing the limit equilibrium analyses for stability assessment of the rock mass above the pressurized cavern, we demonstrated that the factor of safety against uplift computed from the failure paths established in this study is higher than or equal to those obtained from analyses with the simplified models in previous studies without considering the influence parameters on the fracture patterns.  相似文献   

2.
Stability level of tunnels that exist in an underground mine has a great influence on the safety, production and economic performance of the mine. Ensuring of stability for soft-rock tunnels is an important task for deep coal mines located in high in situ stress conditions. The aim of this study is to investigate the effect of tunnel shape and support pattern on the deformation, failure zone and stability around a tunnel located in a coal rock mass in China and to select an appropriate tunnel shape and a support pattern to provide a stable stress-deformation condition around the tunnel. Using the available information on stratigraphy, geological structures, in situ stress measurements and geo-mechanical properties of intact rock and discontinuity interfaces, a three-dimensional numerical model was built using the FLAC software to simulate the stress conditions around the tunnel in the coal rock mass. Analyses were conducted for several tunnel shapes and rock support patterns. Results obtained for the distribution of failed zones, and stress and displacement fields around the tunnel were compared to select the best tunnel shape and support pattern to achieve the optimum stability conditions. Also, a comparison is given between the numerical predictions and field deformation monitoring results.  相似文献   

3.
To investigate the realistic ground behavior during tunneling, a new device has been developed. With the new device, model tests of tunnel excavation considering an existing tunnel and an existing building were carried out. Non-linear finite element analyses corresponding to the model tests were also conducted using FEMtij-2D software where an elastoplastic subloading t ij model was used to describe the mechanical behavior of soil. Earth pressure distribution around the tunnels and ground movements during tunnel excavation depend on the distance and position between the twin tunnels. There is a significant effect of tunneling on the existing foundation of building even in the case where the tunnel is constructed in deep underground. The numerical analyses capture well the results of the model tests.  相似文献   

4.
Face stability analysis of tunnels excavated under pressurized shields is a major issue in real tunnelling projects. Most of the failure mechanisms used for the stability analysis of tunnels in purely cohesive soils were derived from rigid block failure mechanisms that were developed for frictional soils, by imposing a null friction angle. For a purely cohesive soil, this kind of mechanism is quite far from the actual velocity field. This paper aims at proposing two new continuous velocity fields for both collapse and blowout of an air‐pressurized tunnel face. These velocity fields are much more consistent with the actual failures observed in undrained clays. They are based on the normality condition, which states that any plastic deformation in a purely cohesive soil develops without any volume change. The numerical results have shown that the proposed velocity fields significantly improve the best existing bounds for collapse pressures and that their results compare reasonably well with the collapse and blowout pressures provided by a commercial finite difference software, for a much smaller computational cost. A design chart is provided for practical use in geotechnical engineering. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

5.
The vibrations of existing service tunnels induced by blast-excavation of adjacent tunnels have attracted much attention from both academics and engineers during recent decades in China. The blasting vibration velocity (BVV) is the most widely used controlling index for in situ monitoring and safety assessment of existing lining structures. Although numerous in situ tests and simulations had been carried out to investigate blast-induced vibrations of existing tunnels due to excavation of new tunnels (mostly by bench excavation method), research on the overall dynamical response of existing service tunnels in terms of not only BVV but also stress/strain seemed limited for new tunnels excavated by the full-section blasting method. In this paper, the impacts of blast-induced vibrations from a new tunnel on an existing railway tunnel in Xinjiang, China were comprehensively investigated by using laboratory tests, in situ monitoring and numerical simulations. The measured data from laboratory tests and in situ monitoring were used to determine the parameters needed for numerical simulations, and were compared with the calculated results. Based on the results from in situ monitoring and numerical simulations, which were consistent with each other, the original blasting design and corresponding parameters were adjusted to reduce the maximum BVV, which proved to be effective and safe. The effect of both the static stress before blasting vibrations and the dynamic stress induced by blasting on the total stresses in the existing tunnel lining is also discussed. The methods and related results presented could be applied in projects with similar ground and distance between old and new tunnels if the new tunnel is to be excavated by the full-section blasting method.  相似文献   

6.
The large-scale construction of railway tunnels in China is hindered by several challenges, including large depths, large tunnel cross-sections, and fragile geological conditions. In this paper, we explored a new physical and numerical simulation method that improves upon the currently used methods to investigate the deformation and failure modes of weak rocks surrounding a tunnel. We also compared the results from physical tests and numerical simulations with the field measurements to demonstrate the effectiveness of the proposed numerical simulation method. In the physical model test, an artificial speckle field was developed by staining quartz sand particles and mixing the particles with barite powder and petroleum jelly in preset proportions. The artificial speckle field was employed in the digital speckle correlation method (DSCM) to monitor the evolution of the strain field on the surface of the plain strain model for tunneling during loading. A secondary strain-softening constitutive model using the numerical modeling code FLAC3D was developed (degradation constitutive model) by considering the deformation modulus degradation in the numerical simulation. The failure mode of weak rocks surrounding a tunnel in the physical model test was examined using the developed degradation constitutive model. Both the physical and numerical results revealed that the least stable area was the shear wedge along the minimum principal stress, which was confirmed in the damage zone of the surrounding rocks. The results were consistent with previous research findings. The results of the DSCM in the physical model test indicated that the shear wedge in the middle part of the tunnel and the cracks around the arch of the tunnel were induced by shear strain, whereas the collapse of the arch was attributed to a combination of tensile strain and shear strain. A comparison of the physical and numerical simulation results demonstrated that the degradation constitutive model can be used to describe the extent and depth of the excavation damage zone of tunneling. A comparison of the displacements from the numerical simulation and field measurements indicated that the degradation model can be used to capture the displacement of weak rocks surrounding tunnels.  相似文献   

7.
Damage and fracture propagation around underground excavations are important issues in rock engineering. The analysis of quasi-brittle materials can be performed using constitutive laws based upon damage mechanics. The finite element code RFPA2D (Rock Failure Process Analysis) based on damage mechanics was used to simulate a loading-type failure process around an underground excavation (model tunnel) in brittle rock. One of the features of RFPA2D is the capability of modeling heterogeneous materials. In the current model, the effect of the homogeneous index (m) of rock on the failure modes of a model tunnel in rock was studied. In addition, by recording the number of damaged elements and the associated amount of energy released, RFPA2D is able to simulate acoustic activities around circular openings in rock. The results of a numerical simulation of a model tunnel were in very good agreement with the experimental test using the acoustic emission technique. Finally, the influence of the lateral confining pressure on the failure mechanism of the rock around the model tunnel was also investigated by numerical simulations.  相似文献   

8.
When evaluating the long-term stability of existing tunnels, the creep behavior of soft rock around the tunnel should be properly considered. It is also important to understand the failure mechanism of soft rock when designing the mitigation and remediation of the failure around a tunnel. In this paper, an elasto-viscoplastic model is first modified so that the overconsolidation effect and the structure effect of soft rock can be considered. Then, the performance of the modified model is confirmed with drained triaxial compression tests and creep tests on a manmade rock produced with gypsum and diatom clay. Based on the modified model, finite element analyses are conducted to simulate the model tests of an existing tunnel constructed within manmade rock. Two kinds of model tests are simulated: one is loading failure test and the other creep failure test. The good agreement between the numerical results and the test data validates the performance of the modified constitutive model and the applicability of the corresponding FEM for evaluating the creep failure behavior of an existed tunnel constructed in soft rock.  相似文献   

9.
As part of the HG-A experiment in the Mont Terri Rock Laboratory, large-scale in situ water/gas injection experiments was conducted in a microtunnel. This research work focuses on the numerical analysis of the experimental data and the in situ observations. Concerning a temporary change of the hydromechanical properties of Opalinus Clay during experimental operations, three phases were numerically interpreted. These included the generation of excavation damaged zone during tunnel excavation, in which highly permeable flow paths around the tunnel have been formed; the self-sealing effect during water tests; and the pressure evolution during a long-term gas injection test. A coupled two-phase flow and mechanics model, taking into account the strong anisotropic properties of Opalinus Clay, was developed to interpret the measured data. The hydraulic anisotropy was described by a transversely isotropic permeability tensor. An elasto-plastic model was established to consider both stiffness anisotropy and strength anisotropy. Anisotropic plasticity was studied using the microstructure tensor method.  相似文献   

10.
Modeling and monitoring in a soft argillaceous shale tunnel   总被引：1，自引：1，他引：0  
Taking advantage of measurements from an in situ monitoring program and an elastoplastic model using the finite-difference method, this paper simulates and evaluates the deformation and stability of a tunnel in soft argillaceous shale. The elastoplastic model is implemented in FLAC3D program to simulate the deformation and the stress of the soft argillaceous shale during construction. In situ tests performed in the soft argillaceous shale tunnel show that the results from numerical simulations are in good quantitative agreement with the measured in situ data. Results of the simulations also suggest that deformation rate is high during the initial phase of tunnel excavation, compared with the later phase, but the time to reach a steady state remains long. Entire primary support has been undergoing plastic deformation before construction of the secondary lining, which takes the form of so-called “shear yield” from the middle to the bottom of the arch. Some auxiliary measures, especially the anchor, should be applied to enhance stabilization because of the large compressive stress located at the arch springing of the tunnel. The methodology applied in this article can be used to investigate the effect of construction on the performance of tunnels in soft argillaceous shale.  相似文献   

11.
The construction of quasirectangular tunnels at shallow depths is becoming increasingly common in urban areas to efficiently utilize underground space and reduce the need for backfilling. To clarify the mechanical mechanism of the stresses and displacements around the tunnels, this study proposes analytical solutions that precisely account for quasirectangular tunnel shapes, the ground surface, the tunnel depth, and the ground's elastic/viscoelastic properties. The Schwarz alternating method combined with complex variable theory is employed to derive the elastic solution, and convergent and highly accurate solutions are obtained by superposing the solutions in the alternating iterations. Based on the solution and the extended corresponding principle for the viscoelastic problem, the time-dependent analytical solutions for the displacement are obtained for the ground assuming any viscoelastic model. The analytical solutions agree well with the finite element method (FEM) numerical results for models that are completely consistent, and qualitatively agree with field data. Furthermore, based on the stress solution combined with the Mohr-Coulomb failure criterion, the predicted initial plastic zone and propagation directions around the tunnels are qualitatively consistent with those determined by the limit analysis. A parametric study is performed to investigate the influences of the rectangular/quasirectangular tunnel shape, burial depth, and supporting pressure on the ground stresses and displacements.  相似文献   

12.
Swelling deformations leading to convergence of tunnels may result in significant difficulties during the construction, in particular for long term use of tunnels. By extracting an experimental based explicit analytical solution for formulating swelling strains as a function of time and stress, swelling strains are predicted from the beginning of excavation and during the service life of tunnel. Results obtained from the analytical model show a proper agreement with experimental results. This closed-form solution has been implemented within a numerical program using the finite element method for predicting time-dependent swelling strain around tunnels. Evaluating effects of swelling parameters on time-dependent strains and tunnel shape on swelling behavior around the tunnel according to this analytical solution is considered. The ground-support interaction and consequent swelling effect on the induced forces in tunnel lining is considered too. Effect of delay in lining installation on swelling pressure which acting on the lining and its structural integrity, is also evaluated. A MATLAB code of “SRAP” is prepared and applied to calculate all swelling analysis around tunnels based on analytical solution.  相似文献   

13.
The rock around tunnels used for gas storage is subject to high pressures, reaching 30 MPa in the case of compressed air energy storage. Uplift failure of the overlaying rock mass up to the surface represents the main hazard scenario in such cases. The present paper investigates this problem by using the upper bound theorem of limit analysis assuming a continuum rock mass model obeying the Mohr Coulomb failure criterion with tension cut‐off. Tools of the calculus of variations are used to assess the geometry of the failure surface. The effects of geometrical and geotechnical parameters on uplift pressure are analyzed systematically. Charts are then provided, which enable a quick estimation of the upper bound of uplift pressure across a wide range of geotechnical and geometrical conditions.  相似文献   

14.
缓倾角层理各向异性岩体隧道稳定性的物理模型试验研究   总被引：4，自引：1，他引：3  
李丹  夏彬伟  陈浩  白世伟 《岩土力学》2009,30(7):1933-1938
层状岩体的广泛分布是地下工程无法回避的现实。以渝湘高速公路共和隧道为工程背景,采用自行研制的弹脆性模型相似材料,制作出层状岩体隧道模型。采用大型真三轴岩土工程模型试验机进行加载试验,采用围岩应变监测、洞室内窥摄影、试件破坏形态的研究与分析,从而对缓倾角层理岩体中隧道的二次应力分布特征及破坏机制进行研究。试验中还通过超载系数,提供了一个安全储备的定量评估指标。试验的破坏特征与隧道实际破坏一致,说明了模型试验的正确性,同时也为顺层偏压隧道的加固机制研究及加固设计提供了试验基础。  相似文献   

15.
A numerical model is proposed for the simulation of rock blasting. A bonded particle system is utilized to mimic the behavior of rock. The particles interact at the contact points through normal and shear springs to simulate rock elasticity. To withstand the deviatoric stresses, the particles are glued to each other. If the applied force exceeds the contact strength, local failure occurs and microcracks are developed in the synthetic rock. For simulation of gas flow, the smooth particle hydrodynamic method is implemented. The interaction of gas particles with the rock grains is assumed to follow a perfect plastic collision model in which the initial momentum of the colliding particles is preserved. A detailed examination of the interaction of gas with blast hole is investigated. It is shown that the proposed hybrid model is capable of simulating the induced shock waves in the gas together with wave propagation in the rock material. The model successfully mimics crack propagation in rock. In particular, the crushed zone around the borehole, radial cracks, and surface spalling are all captured successfully. The results of numerical analysis suggest that gas–rock interaction can, in fact, generate a few successive compressive waves in the rock specimen, causing further extension of radial cracks with time as the weaker secondary and tertiary waves interact with the crack tips.  相似文献   

16.
This paper studies dynamic crack propagation by employing the distinct lattice spring model (DLSM) and 3‐dimensional (3D) printing technique. A damage‐plasticity model was developed and implemented in a 2D DLSM. Applicability of the damage‐plasticity DLSM was verified against analytical elastic solutions and experimental results for crack propagation. As a physical analogy, dynamic fracturing tests were conducted on 3D printed specimens using the split Hopkinson pressure bar. The dynamic stress intensity factors were recorded, and crack paths were captured by a high‐speed camera. A parametric study was conducted to find the influences of the parameters on cracking behaviors, including initial and peak fracture toughness, crack speed, and crack patterns. Finally, selection of parameters for the damage‐plasticity model was determined through the comparison of numerical predictions and the experimentally observed cracking features.  相似文献   

17.
Water outbursts from the floor during underground mining, and those from the surrounding rock mass of tunnels, involve the basic principle of hydraulic fracturing. Based on the hydraulic-fracturing mechanism, considered to be dependent on the coupling between seepage and damage, it is deemed that the variation of the pore-fluid pressure coefficient must be taken into account during this coupled process, in order to correctly establish the crack propagation mechanism during hydraulic fracturing. The coupled seepage-damage model is validated using numerical simulations of hydraulic fracturing around one hole and three holes; the model may also enable scientific and reasonable explanation of the dominance of hydraulic gradient on the crack propagation path in permeable rock. Finally, the water outburst from the floor at a coal mining site in Hebei Province, China, is numerically simulated, and the coupled seepage and damage mechanism during the mining-induced rock failure is clarified. The numerical simulation implies that the seepage-damage is the main mechanism for controlling the water outburst. Therefore this mechanism should be considered in the numerical simulation to understand the essence of water outburst induced in mines.  相似文献   

18.
李元鑫  朱哲明  刘凯  范君黎 《岩土力学》2014,35(Z1):189-194
采用模型试验和数值模拟方法,研究单轴压缩载荷下带裂纹直墙拱形隧道在不同的裂纹面与隧道垂直边墙之间的夹角 时围岩损伤破坏规律。试验采用水泥砂浆制作成具有不同夹角 的直墙拱形隧道模型,养护30 d后进行加载。数值模拟采用混凝土损伤塑性模型,计算出隧道周边各点的应力和裂纹尖端的应力强度因子,与模型试验结果吻合较好。结果表明,拱肩处的裂纹会降低隧道的整体稳定性及强度,在裂纹尖端及侧壁产生很大的应力集中,但随着 角度的变化,强度降低的程度有所不同;当 = 60?和 = 130?时,裂纹对其整体稳定性及强度的影响最大,其裂纹尖端的应力集中现象最为明显,而且破坏应力峰值仅为无裂纹模型的40.9%和41.8%。  相似文献   

19.
The heterogeneity of tight reservoirs significantly influences hydrofracturing behaviours, such as crack morphology, type, initiation, propagation, and distribution. The accurate characterisation of the influencing mechanisms has become a pivotal issue in enhancing the fracturing stimulation of tight reservoirs, as well as in the prediction of tight oil and gas production. In this study, the hydrofracturing behaviours of heterogeneous glutenites and their influencing mechanisms were numerically investigated based on bonded particle models (BPMs). The geometry and mechanical properties of the natural glutenites were obtained using microfocus computed tomography (CT) and triaxial tests and were used to construct heterogeneous BPMs. The hydrofracturing behaviours of the heterogeneous BPMs under various in‐situ stresses were analysed with hydro‐mechanical coupling effects considered and compared with those of homogeneous BPMs under the same conditions. The numerical results show that gravels in heterogeneous glutenites inhibit crack propagation. The shear cracks that appear in the initial stage of crack development subsequently propagate and distribute around the injection hole, and there are fewer hydraulic shear cracks than tensile cracks. The crack morphologies of BPMs are found to be consistent with the experimental forms. The numerical simulation provides a way to understand the mechanisms that govern the hydrofracturing crack types and propagation of heterogeneous reservoirs.  相似文献   

20.
Summary A combined experimental and numerical approach is adopted to investigate crack propagation in sandstone. Experiments on two types of sandstones show a simular behaviour as found in tests on concrete specimens. The heterogeneity of the material in combination with the stress situation, as a result of the applied load, governs the direction of crack propagation. Cracks that develop are not continuous, but overlaps exist mainly around the grain particles in the material. A simple lattice model, in which the material is schematized as a network of small beams, is adopted to simulate the experiments. Using the simulations carried out with the lattice model, the control parameter for stable displacement controlled four-point-shear tests was determined. The crack patterns obtained with the model are in good agreement with the experimental observations. However further study is needed to predict the load-displacement response correctly.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号