Search

Rock-support interaction is one of the most core issues in underground engineering, which is of major interest to supporting structure design, construction safety and cost, as well as environmental protection. In order to study the rock-support interaction in deep tunnel under complex geological conditions, taking Xianglushan Tunnel of Yunnan Water Diversion Project in China as the engineering background, two true three-dimensional physical model tests were conducted. The model test results show: (1) the surrounding rock and support are a pair of opposite and united contradictions, which are both antagonistic and cooperative; (2) the rock-lining interaction and rock-bolt interaction are distinctly different. The lining is a type of outside supporting structure to bear the load from surrounding rock and the bolt is a kind of inside supporting structure to reinforce and protect surrounding rock; (3) the impacts of weak fault on mechanical behavior of surrounding rock and supporting structure are significant. The load bearing effects of surrounding rock and support system exhibit different characteristic depending on the corresponding geological conditions. The results can contribute to the development of construction scheme and optimization of support design, and also provide an ideal data set for the calibration and validation of numerical models to simulate the rock-support interaction. [ABSTRACT FROM AUTHOR]

Deformation control of soft rock in deep roadways has always been a challenge in coal mining. The strain softening and rheological properties of high-stress soft rock not only cause large deformation of the surrounding rocks, but also lead to a long duration of deformation. Based on previous research results obtained here in China as well as abroad, this study focused on the S2S2 mining roadway in the Xiaokang Coal Mine of Liaoning Province in China for research and studied the characteristics and damage of its surrounding rock deformation. Furthermore, the sectional form that should be used in roadway construction, as well as the support structure types and parameters were proposed to control the excessive deformation of the surrounding rock. It is suggested that a circular section should be adopted as the mining roadway section, and the high-strength rock should be bolted together, employing the combination of the anchor cable support method. Industrial tests have verified that the circular roadway under the new support mode can enable relative distance changes between the roadway walls, make the roof and floor relatively flat, and reduce the convergence speed to a value lesser than that of the original support mode. The most important advantage is that under this joint support mode, the deformation and damage of the circular roadway would be less affected by mining activity, so the deformation and damage of the mining roadway can be controlled effectively. Therefore, the research results of this study can provide a reference value for similar engineering projects. [ABSTRACT FROM AUTHOR]

With the rapid rise of infrastructure construction in southwestern mountainous areas of China, tunnel engineering has become increasingly frequent in crossing faults with strong activity. However, there has been a long-term lack of an effective theoretical method for identifying the stability and controlling the deformation of extremely weak surrounding rocks inside active faults. Therefore, this paper researched stability analysis and deformation control of a tunnel with extremely weak surrounding rocks caused by strike-slip fault activity. Firstly, uniaxial and triaxial compression tests were conducted on completely decomposed granite within active faults under drained and undrained conditions, and the mechanical properties of granite after desertification and argillization were analyzed. Then, based on the upper-bound limit theory and according to the relationship between the safety factor, instability trace, and geo-stress, a theoretical method to evaluate the stability of the unsupported surrounding rock under different geo-stress levels was proposed. Furthermore, a comprehensive deformation control method, including advanced support, excavation face reinforcement, and radial grouting, was proposed, and the applicability of this method was analyzed and verified through field mechanics and deformation measurements. The results showed that under the triaxial stress state, the post-peak stress drop characteristics of completely decomposed granite basically disappear, and the plastic deformation characteristics of rock become prominent. The comprehensive strengthening scheme has a significant deformation control effect, and the surrounding rock deformation can be reduced by over 65%. In addition, the pressure on the supporting structure will be more than 3.2 times higher with no reinforcement scheme. Highlights A comprehensive deformation control scheme has been proposed to prevent and control deformation disasters in extremely weak surrounding rocks caused by strike-slip fault activity. An upper-bound limit theory considering the influence of geo-stress is established to judge the stability of the unsupported surrounding rock. The mechanical properties of completely decomposed granite caused by strike-slip fault activity under drained and undrained conditions are analyzed. [ABSTRACT FROM AUTHOR]

The time-dependent behavior and long-term stability of deep-buried tunnels in soft rocks have received lots of considerations in tunnel engineering and allied sciences. To better explore and deepen the engineering application of rock creep, extensive research studies are still needed, although fruitful outcomes have already been obtained in many related investigations. In this article, the Weilai Tunnel in China's Guangxi province is studied, taking its host rocks as the main research object. In fact, aiming at forecasting the time-varying deformation of this tunnel, a novel elasto-visco-plastic creep constitutive model with two variants is proposed, by exploiting the typical complex load–unload process of rock excavation. The model is well validated, and good agreements are found with the relevant experimental data. Moreover, the time-dependent deformation rules are properly established for the surrounding rocks, by designing two new closed-form solutions based on the proposed creep model and the Hoek–Brown criterion. To investigate the effects of the major creep parameters and the geological strength index (GSI) of the surrounding rocks on the time-dependent trend of the tunnel, an in-depth parametric study is carried out. It is shown that the convergence deformation of the surrounding rocks is remarkably influenced by the GSI and creep parameters. The convergence deformations calculated from the closed-form solutions conform well to the on-site monitoring data. In only 27 days after excavation, the creep deformation of the Weilai tunnel overtakes 400 mm, which is enormous. To guarantee the long-term stability of this tunnel, a robust support scheme and its long-term monitoring with appropriate remote sensors are strongly suggested. [ABSTRACT FROM AUTHOR]

Based on the Xiabeishan No.2 tunnel project of the Hang-Shao-Tai high-speed railway in China, the mechanical behavior of the anchor bolts for shallow super-large-span (SSLS) tunnels in weak rock mass is comprehensively investigated through laboratory tests, numerical simulation, and field tests. Firstly, an eight-month field test is conducted in the Xiabeishan No.2 tunnel, and it is discovered that the blasting vibration created by the construction of the middle pilot tunnel caused serious damage to the temporary support, seriously affecting the development of the bolt axial force and causing great construction risks. Then, the refined finite difference model of the SSLS tunnels is formulated, and a series of field and laboratory tests are conducted to acquire the calculation parameters. By comparing the monitored and simulated bolt axial force, the reliability of the numerical model is verified. Subsequently, the influence of the rock condition, construction scheme and bolt length on the mechanical behavior of anchor bolts is discussed. It is revealed that the rock grade significantly affects the bearing characteristics of anchor bolts. The construction scheme can greatly affect the magnitude and development mode of the bolt axial force, but the final distribution characteristics of the bolt axial force do not change regardless of the construction sequence. The axial force of the anchor bolts grows rapidly with the bolt length when the bolt length is within 18 m; meanwhile, when the bolt length exceeds 18 m, increasing the bolt length has a limited effect on the improvement in the bolt support performance. Finally, some optimization measures are proposed according to the monitoring data and simulation results. [ABSTRACT FROM AUTHOR]

Excessive deformation has been observed during the construction of large-section (over 100 m2) tunnels in soft rock all over the world. A case study of deformation control for large-section tunnel construction in fractured carbonaceous slate was conducted. Xingzishan tunnel, China, was first excavated using the three-step reserved core soil excavation method (TRCSEM); however, this resulted in serious rockfalls at the tunnel arch and local collapse. To enhance the stability of the tunnel face, three different tunnel support systems with relatively stiff structures were proposed and tested along the tunnel chainage in the same rock condition, but all of them failed. The mechanism of the TRCSEM was revealed by field measurements, highlighting the significance of the stability of the upper bench of the tunnel face. In view of this, the three-step temporary inverted arch method (TTIAM) was employed and used with advance support. With this new method, the upper bench of the tunnel face was reinforced with fibreglass bolts to mitigate the deformation. Compared with the TRCSEM, the TTIAM effectively controlled large deformation at the tunnel face during the excavation in fractured carbonaceous slate with an acceptable construction cost. [ABSTRACT FROM AUTHOR]

As the hydropower development strategies of China continue to be implemented, a host of large hydropower projects have been completed or are being constructed in southwest China. During construction of the Jinchuan hydropower station, this study examined the stability of the surrounding rock during the excavation and unloading of hydraulic tunnels under demanding geological conditions. Microseismic (MS) monitoring technology was employed to monitor the deformation and failure of the surrounding rock online and in real time, based on engineering geological data and site surveys. To analyze the stability of the surrounding rock in the spillway tunnel and to study the temporal and spatial evolution characteristics of MS events, source parameter analysis and numerical modeling were performed. The 3D finite-difference numerical modeling software FLAC3D was used to simulate the mechanical response of the surrounding rock during the excavation and unloading of the spillway tunnel and the diversion tunnel. The numerical modeling results were compared with the monitoring results and site surveys to determine the failure mechanisms of the surrounding rock during the construction and unloading of the hydraulic tunnels. The research results can serve as a guide for studying the stability of the surrounding rock in similar hydraulic tunnels. [ABSTRACT FROM AUTHOR]

A method of load calculation in a tunnel was adopted in consideration of the state of covering depth. Due to the macropore characteristics of loess soil, the existing demarcation regulations of deep and shallow tunnels are inappropriate for large-section and shallow loess in highway tunnels. To determine the load of large-section loess tunnel and provide a proper reference for structural design, the theoretical basis for distinguishing depth of deep and shallow tunnels, as well as the characteristics of common calculation methods for surrounding rock load on depth, were analyzed. Through statistical analysis and significance analysis, the significance of the variation of surrounding rock pressure with cover depth was studied. Correlation analysis was carried out on significant results to fit the relationship between cover depth and surrounding rock pressure. The results showed that the surrounding rock pressure varied linearly with the cover depth, and the surrounding rock pressure was about 0.3 times the initial pressure in deep tunnels. The surrounding rock pressure of shallow tunnels did not change significantly with the cover depth, and the surrounding rock pressure was loose pressure. A method based on statistics was proposed to distinguish the cover depth threshold (CDT) of deep and shallow tunnels. [ABSTRACT FROM AUTHOR]

The accelerated creep plays an important role in the disasters of soft-rock tunnels under high stress. However, most of previous studies only involved attenuation creep and uniform creep. Large deformation disasters of soft rock occurred during the tunneling process in the Qianzhou–Sanyangchuan Tunnel, Gusu Province, China. In the paper, we developed the nonlinear generalized Nishihara rheological model with non-stationary parameter creep (NGNRM) to simulate the accelerated creep behaviors of soft rocks under high stress, and implemented it in ABAQUS, to reveal the mechanism of large deformation of soft rock. We proposed the multi-objective back analysis method of surrounding rock mechanical parameters based on the eXtreme Gradient Boosting and the non-dominated sorting genetic algorithm-II. In addition, the orthogonal test design method was used to determine the main parameters affecting the displacement of the tunnel. Using the proposed method, we can evaluate the large deformation mechanism of deep soft rock tunnels, and scientifically determine when to reinforce to prevent a large deformation disaster of the tunnel. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Large squeezing deformation of layered soft rock tunnel under high geo-stress has a significant time-dependent deformation behavior. In this paper, we studied the deformation mechanism during the construction period of deep-buried soft-rock tunnel by means of a combination of field observations and a numerical method. First, a new classification criterion for large deformations based on the power exponent variation law between the deformation and the strength-stress ratio is proposed. Then, the initial damage tensor reflecting the bedding plane (joint) distribution and an equivalent damage evolution equation derived from the viscoplastic strain are introduced based on the geometric research method, i.e., a new rheological damage model (RDL model) of layered soft rock is established consisting of elastic, viscous, viscoelastic, viscoplastic and plastic elements. A field test was conducted on the Maoxian tunnel in Sichuan province, southwestern China, which is in broken phyllite (layered soft rock) under high geo-stress. The tunnel has experienced large deformation due to serious squeezing pressure, thus we adopted double primary support method to overcome the supporting structure failure problems. The rheological parameters of phyllite in the Maoxian tunnel were recognized by using SA-PSO optimization, and the RDL model does a good job in describing the time-dependent deformation behavior of a layered soft-rock tunnel under high geo-stress. Thus, the RDL model was used to investigate the supporting effect and bearing mechanism of the double primary support method. Compared with the single primary support method, the surrounding rock pressure, secondary lining force, surrounding rock deformation, and the depth of the damage to the rock mass was reduced by 40%–60% after the double primary support method was used. [ABSTRACT FROM AUTHOR]

Large deformation has always been a focus and difficult issue in the construction of deep-buried tunnels in squeezing rock. Previous studies mainly focused on the large deformation of medium and small span railway/highway tunnels in soft ground. However, there are limited researches on the large deformation control methods for large-span (three-lane) highway tunnels constructed in unfavorable geological environment. Based on the Lianchengshan Tunnel of the Baoji-Hanzhong expressway in Shaanxi Province, China, this paper studied the deformation behaviors and mechanical mechanisms of a large-span tunnel excavated in chlorite schist formation with single primary lining method and double primary lining method by in-situ test and numerical simulation. The achieved results indicate that the double primary lining method is much more effective than that of the single primary lining method in restraining the deformation of surrounding rock, and the maximum vertical displacement and horizontal convergence are reduced by 67% and 66%, respectively. The support method of double HK200b-type steel sets combined with large-diameter foot reinforcement bolt (FRB) and deep invert could effectively control the large deformation of the case tunnel, which effectively avoided the supporting structure failure, repeated clearance invasion and multiple reshaping work caused by the single primary lining method and conformed to the energy-saving construction concept of "no clearance interfering, no support reshaping" of tunnels in squeezing ground. Simulation analysis of surrounding rock deformation, supporting structure stress and plastic zone distribution was performed to evaluate the support effect of the two deformation-controlled methods. Finally, the deformation and stress characteristic curves of rock-support of the two deformation-controlled methods were established, which revealed the supporting mechanism of double primary linings for large-span tunnels in chlorite schist. The research results can provide a theoretical basis and practical reference for the large-deformation control of similar large-span tunnels in squeezing rock. [ABSTRACT FROM AUTHOR]

For tunnels excavated in soft layered rock strata, the secondary lining is susceptible to asymmetrical pressure and substantial concrete cracking. To solve this problem, a supporting system that combines a secondary lining with a highly deformable layer is proposed. First, field investigations were conducted to reveal the mechanical behaviors of the secondary lining of two typical tunnels situated in phyllite formation in China. Then, similarity model tests were used to analyze the mechanical responses of the secondary lining in layered rock stratum with different inclination angles. Finally, numerical simulation was adopted to systemically investigate the yielding mechanism of yielding layer in different cases. The results show that: (1) The distribution of inner force and deformation of lining is non-uniform due to the anisotropy of rock mass and geo-stress field, with the positive bending moment and larger axial force appearing mainly in the region where the tangent of the tunnel contour is parallel or vertical to the weak planes, respectively. (2) The existence of yielding layer has no influence on the distributed feature of inner force and displacement around tunnel perimeter, while it can significantly lower the magnitude of inner force and displacement of the lining. (3) The distinctly compressive zones of yielding layer coincide with the zones of positive bending moment, and the line connecting the central points of the evidently compressive zones on both sides will deflect towards the direction of minor principal stress to a certain extent. (4) The inner force and deformation of lining increase with the increase in the strength or decrease in the thickness of yielding layer, and this changing trend is related to the different supporting curves for linings with yielding layer of different strength and thickness. [ABSTRACT FROM AUTHOR]

The reasons why large deformations of inclined and laminar stratum occur in complicated geological conditions during tunnelling remain unclear. In this study, the geological conditions, the initial design of excavation and support and specific deformation failure modes of the laminar stratum and initial support system were first introduced at the Yangjiaping tunnel in China. Thereafter, field surveys, laboratory tests and numerical simulation were performed to investigate this complicated deformation and mechanical behaviour. Meanwhile, by combining buckling and catastrophe theory, the occurrence criteria of the deformation and failure of such stratum were established. Finally, excavation and support adjustments were proposed to control the rock mass deformation. The theoretical criterion reveals that buckling failure of the laminar structure has an obvious influence on the large deformation occurrence. By adopting the adjusted excavation and support measures, the rock mass deformation and contact pressure between the surrounding rock mass and initial lining are both dramatically decreased. The largest decline in the average horizontal convergence is approximately 25 cm; the maximum contact pressure value is approximately 1.149 MPa at the right haunch, which is about 64% of the value at the same location when using the original excavation and support method. [ABSTRACT FROM AUTHOR]

When tunneling through deep-buried layered soft strata, asymmetric deformation of surrounding rock and asymmetric mechanical behavior of supporting structures are often encountered. This paper investigates the anisotropic mechanical properties of deep-buried carbonaceous phyllite and its influence on the asymmetrical mechanical behavior of supporting structures in the Zhegu mountain tunnel in Sichuan Province, China. It is a typical road tunnel that suffered from large asymmetrical deformation and cracking of the secondary lining due to layered strata and high geo-stresses. Firstly, experimental tests were conducted to investigate the influence of bedding angle on the mechanical properties and failure behavior of phyllite. Then, the UDEC numerical software was adopted to study the effects of the lateral pressure coefficient, rock layer inclination angle, bedding spacing and shear stress on the mechanical behavior of supporting structures. Moreover, a field test was conducted to measure the pressure between the surrounding rock and the primary support as well as the internal force of the steel arch and the secondary lining. Based on the field data and numerical simulation results, it can be concluded that the asymmetrical deformations of surrounding rock and the cracking of secondary lining in the Zhegu mountain tunnel were results of the coupling effect of layered soft rock and shearing action along the foliation. [ABSTRACT FROM AUTHOR]

At present, there is no unified support design criterion for the construction of super-large cross-section tunnel. The design of initial supporting components is based on engineering analogy method, lacking theoretical and experimental guidance. The spacing of arch and longitudinal connection strength have significant influence on the bearing capacity of initial support system, so in-depth study in this area is very important. Therefore, based on the typical super-large cross-section tunnel-Letuan Tunnel of Binlai Expressway in China, laboratory test and numerical test are carried out in this paper to study the combinational bearing mechanism of multiple spatial arches in initial supporting system. This paper also clarifies the mechanical characteristics of spatial supporting system and the influence mechanism different designing parameters such as arch spacing, longitudinal connection spacing. The cost performance of each design scheme of the spatial supporting arch system is established. The research results show that the influence of arch spacing and longitudinal connection spacing on arch bearing capacity is remarkable. Strength of combined arch structures is 3.14–3.92 times of single arch frame. The influence of arch spacing is more obvious than that of longitudinal connection spacing. The research results can provide reference for related projects. [ABSTRACT FROM AUTHOR]

To evaluate tunnel ground vibrations induced by fault-slip in underground mine, it is crucial to resolve the peak ground velocity (PGV) and the peak ground acceleration (PGA). To quantify PGV and PGA in three-dimensional space, the forces acting on the fault and the seismic wave radiation pattern were investigated. A qualitative method for ground vibration of tunnels induced by fault-slip in underground mine was proposed and applied to the Yongshaba Phosphate Mine, China. Firstly, the moment tensor of the significant fault-slip event was obtained using a full waveform source inversion method based on the recorded seismograms. It describes the forces acting on the fault and the seismic wave radiation pattern. Then, the inverted source was used as a reference to evaluate the ground vibrations under possible larger seismic magnitudes and probable slip models. The vibrations along the tunnels resulted from different slip models were calculated using the representation theorem by the convolution of the Green's function and the corresponding moment tensor. The velocity series and the acceleration series were obtained. Results show that the spatial distribution of the ground motions are closely related to sensor-source distance, the sensor-source azimuth, as well as the strike, dip, and rake configuration of the slip model. The seismic magnitude has an exponential effect on the distribution of the PGVs and PGAs. The PGV and PGA have similar spatial distribution patterns. The PGV values of the north and vertical components show nearly 5 times higher than the east component. The vertical vibrations affect the widest area. The ground support principles were suggested considering the parameters including the PGVs, the PGAs, the rock mass rating, and the dynamic loads. [ABSTRACT FROM AUTHOR]

To ensure the safety of the tunnel construction, it is very important to take the appropriate treatment measures after the collapse happened. Especially the tunnel goes through the fault fracture zone. This paper sets forth the process of the collapse that occurred in the Yezhuping Tunnel affected by the fault fracture zone and introduces the treatment for the collapse. The deformation characteristics of the surrounding rock are analyzed according to the monitoring results. Based on the research regarding the effect of the fault on the tunnel by using the general Hoek–Brown failure criterion and the field monitoring results, it is shown that the fault is the main reason for the collapse; it induces the attenuation of the Young modulus and the compressive strength and the enlargement of the plastic zone. The research results have some reference significance for similar projects. [ABSTRACT FROM AUTHOR]