Tunnel Surrounding Rock Research Articles

An Algorithm for Calculating Blasting Parameters of the Complex Surrounding Rock Tunnel Undercrossing Nearby Roadbed

An Algorithm for Calculating Blasting Parameters of the Complex Surrounding Rock Tunnel Undercrossing Nearby Roadbed

Research on Tunnel Surrounding Rock Failure and Energy Dissipation Based on Cyclic Impact and Shear Loading

Aiming at the cyclic impact deformation and failure of tunnel surrounding rock under shear stress, a self-developed rotation-impact simulation test platform was used to determine the number of failures, stress-strain curves, and energy in the process of cyclic impact failure. The failure process of rock under different impact velocities and shear stresses has been systematically studied. Results show that, under the same impact speed, the shear stress will increase with the increase in the rotation speed, but an upper limit will exist. When the rotation speed reaches this upper limit, the shear stress will no longer increase. The presence of shear stress will reduce the number of impacts required for rock failure. When the impact speed is 7.2 m/s, the number of impacts at the maximum rotation speed is 60% of the static state. When the impact velocity is 16.8 m/s, this value is only 33.3%. At the same impact velocity, the stress-strain curves under different rotation speeds do not change significantly, but with the increase in the rotation speed, the slope of the elastic stage of the stress-strain curve gradually decreases, and the corresponding stress of the rock sample decreases when the maximum strain is reached. With the increase in shear stress, the crushing specific energy required for rock failure gradually decreases. The greater the impact velocity, the more obvious the impact of shear stress on energy dissipation. In the tunnel process, when the surrounding rock is subjected to impact loads from different directions, only the axial strain analysis will have certain safety hazards, and timely support and reinforcement work are required.

RETRACTED ARTICLE: Research and application of automatic monitoring system for tunnel-surrounding rock measurement based on GIS

This paper establishes a geological three-dimensional coordinate model and uses GIS to obtain the thickness of the overburden. The tunnel displacement monitoring points mainly include: vault settlement measurement points, foot settlement measurement points, and gap convergence measurement points. This paper constructs a GIS-based section tunnel entrance safety evaluation system, which provides a reference for the safety evaluation of the section tunnel entrance. The determination of the construction parameters and support parameters of the tunnel engineering is deeply affected by the stress conditions of the tunnel engineering. Under the conditions of limited economy and time, before tunnel construction, the mechanical parameters of the tunnel-surrounding rock are determined mainly through limited drilling. Although it is somewhat difficult, the construction parameters of tunnel engineering are also determined accordingly. The calculation results may cause the actual deformation of the surrounding rock to be quite different from the predicted deformation, and accidents may be caused according to the original construction plan. Therefore, the supervision and measurement of tunnel engineering is particularly important. At the same time, a risk evaluation system is established to achieve the control of risk evaluation indicators, which can intuitively express the size of the tunnel entrance affected by the evaluation factors, calculate the mechanical parameters of the surrounding rock of the tunnel, determine the construction parameters and support parameters of the tunnel project, and analyze the measured displacement changes to ensure long-term stable construction and support. Through the actual application of the project, it can be seen that the risk assessment system can also conveniently and quickly query and analyze the monitoring data of the tunnel, and it can realize online operation and analyze the stability of the same surrounding rock. This proves the rationality of the planning and framework of the detection system, and it has high application value.

Experimental Study on the Failure Mechanism of Tunnel Surrounding Rock under Different Groundwater Seepage Paths

The influence of groundwater on tunnel engineering is very complicated. Due to the complexity of water flow water pressure transfer and uncertain defects in the stratum, all of which are key factors with regard to the design of tunnel engineering. Therefore, the variation of surrounding rock during excavation and the deformation and failure of soft surrounding rock under different seepage paths of underground water after excavation systematically. Experimental results showed that the stress change of surrounding rock caused by tunnel excavation can be divided into 3 stages: stress redistribution, stress adjustment, and stress rebalancing. In the process of water pressure loading, water flow rate is closely related to the experimental phenomenon. The between stable loading water pressure pore water pressure of the tunnel surrounding rock and the distance from the measuring point to the edge of the tunnel obey the exponential function of the decreasing growth gradient. With the increase of loading pressure, the pore water pressure and stress at the top of the tunnel increase, and the coupling of stress field and seepage field on both sides of surrounding rock more and more intense. The failure process of the tunnel can be divided into 6 stages according to the damage degree. The final failure pattern of the surrounding rock of the tunnel is mainly determined by the disturbed area of excavation. The arched failure area and the collapse-through failure area are composed of three regions. The surrounding rock is characterized by a dynamic pressure arch in the process of seepage failure, but it is more prone to collapse failure at low water pressure. The results of this study are the progressive failure mechanism of tunnel under different groundwater seepage paths and would be of great significance to the prevention of long-range disasters.

Research on Creep Deformation and Control Mechanism of Weak Surrounding Rock in Super Large Section Tunnel

In order to solve the difficulties of creep deformation of surrounding rock in super large section tunnel, taking Letuan tunnel of Binlai expressway, a typical super large cross-section tunnel as research background, the creep mechanical characteristics of surrounding rock are taken into consideration, and the influence of different supporting forms such as bolt reinforcement, rock grouting, high-strength arch and concrete lining on surrounding rock deformation and failure mechanism is comprehensively studied. The creep failure mechanism and high strength control mechanism of surrounding rock are obtained. Research results show that the surrounding rock shows obvious creep mechanical characteristics, the continuous growth of surrounding rock deformation has brought severe challenges to the tunnel support; the surrounding rock of super large cross-section tunnel shows unstable creep deformation failure mechanism with obvious acceleration of creep stage under the condition of no support; the influence mechanism of different support forms on the control effect of surrounding rock creep deformation is systematically studied, and the evaluation indexes of deformation control rate and creep control rate of surrounding rock prove that confined concrete, as a high-strength support type, has significant advantages for surrounding rock creep control. Based on the large-scale mechanical test system of tunnel, the mechanical test of confined concrete arch is carried out, and the bearing mechanism and mechanical characteristics of confined concrete arch are clarified. The field application results show that the confined concrete arch can effectively control the creep deformation. The research results can provide theoretical basis for relevant projects.

Analysis of deformation and failure characteristics of soft and broken surrounding rocks of super-large section tunnel constructed using benching tunneling method

The benching tunneling method can overcome the problems of insufficient working space and low construction efficiency in the soft and broken surrounding rock tunnel with super large section, but the design and construction theory and method are under developing. In order to solve the problem of insufficient basis for the design of the large-section bench method in the weak and broken surrounding rock, a three-dimensional elastoplastic model was established. The deformation and fracturing of the surrounding rock outside the tunnel excavation profile and in front of the tunnel face were used as indicators to analyze the deformation and failure characteristics of the weak and broken surrounding rock under benching tunneling method. The calculation results show that the grade of surrounding rock worsens (grade IV-V). Depending on the initial support design conditions, instability of the supporting structure or the tunnel face may occur. In the condition that grade of surrounding rock does not lose stability, the leading deformation accounts for a larger proportion of the whole deformation, indicating that the leading deformation is the key to the stability control in the benching tunneling method. When the tunnel face is unstable, the surrounding rock within 4.5m in front of the tunnel and 1.5m above the arch collapses, and the deformation and damage develop from the vault down to the foot of the wall.

Anchoring Parameters Optimization of Tunnel Surrounding Rock Based on Particle Swarm Optimization

In the highway tunnel project, due to the uncertainty and complexity of geotechnical parameters, it is difficult to design and optimize the anchorage parameters. In order to solve this problem, based on the Zhenfengling tunnel project as the research object, 3D tunnel model was established by ANSYS software, the model was imported into FLAC3D software for numerical analysis and calculation for the displacement and stress of surrounding rock during construction, using orthogonal experiment methods to analyze factors affecting the stability of surrounding rock. The influence of anchor length, anchor spacing, anchor diameter, the thickness and elastic modulus of spray layer on the displacement of arch waist, arch crown and arch bottom of the tunnel was obtained by using range and variance analysis. The regression model of the relationship between arch surrounding rock displacements and anchorage parameters was determined by fitting regression. The particle swarm optimization algorithm was used to optimize the anchorage parameters in combination with the tunnel section cost formula, and the parameters were compared with those not optimized. Finally, the anchor length is designed as 3 m, the anchor spacing is designed as 1.4 m, the anchor diameter is designed as 21 mm, the thickness of spray layer is designed as 24 cm, and the elastic modulus of spray layer is designed as 24 GPa. The stability requirements can be met, and the economic efficiency is also greatly improved. The cost of support with optimized parameters is 19.4% lower than that of the original design parameters.

The Plastic Zone of Tunnel Surrounding Rock under Unequal Stress in Two Directions Based on the Unified Strength Theory

For the deficiencies that the existing calculation theory for the Plastic Zone of Tunnel Surrounding Rock (PZTSR) does not consider the effect of the intermediate principal stress σ2 and interaction between the surrounding rock and support structure on the PZTSR under unequal stress, the Unified Strength Theory (UST) for the rock is adopted to replace the often used Mohr-Coulomb (M-C) strength criterion to consider the effect of σ2 on the PZTSR. Meanwhile, the interaction mechanism between the surrounding rock and support structure is also considered in the proposed model. Finally, the effect of the initial elastic displacement of the surrounding rock, stiffness of the support structure, and the coefficient b of the intermediate principal stress on the plastic zone is discussed. The results show that the PZTSR will increase nonlinearly with increasing the initial elastic displacement of the surrounding rock, and when it increases to a certain value, its increase extent will be much obvious. With increasing the stiffness of the support structure, the PZTSR will gradually decrease nonlinearly, but the decrease extent is not very much. With increasing b, the PZTSR will decrease; namely, σ2 can improve the stress condition of the surrounding rock and reduce the PZTSR.

Cracking Characteristics of the Surrounding Rocks of a Hydraulic Tunnel Under High Geothermal Conditions: A Model Test

In the present study, a physical model test was used to investigate the cracking characteristics of the surrounding rocks of hydraulic tunnels under high geothermal conditions. Based on similarity theory, a similar material was developed to simulate the intact and hard rocks in thermo-hydro-mechanical (THM) coupling fields; this material was used to cast a large-scale model tunnel. A new loading system, including a temperature loading system and a water pressure loading system, was designed to improve upon conventional laboratory hydraulic tunnel testing and provide a means of better understanding the fracture behavior of solid media. An acoustic emission (AE) monitoring system, thermocouples and osmometers were used to reveal the real-time evolution of the temperature field, seepage pressure field and crack propagation. The test results showed that compared to a hydraulic tunnel without high geotemperature, the critical internal water pressure of the hydraulic tunnel under high geothermal conditions decreased significantly. After the initiation of main cracks was induced by hydraulic fracturing, due to THM coupling, a certain number of secondary cracks initiated and developed between the main cracks. In this process, the trend of the secondary crack tip deviated from the radial direction, resulting in a more developed and complicated evolution of cracks (including main cracks and secondary cracks). This was different from the cracking behavior of surrounding rocks without a high geothermal gradient, in which only a few main cracks due to hydraulic fracturing were observed. An obvious multifield THM coupling effect was observed under high-geotemperature conditions, and cracks propagated and damage increased in the surrounding rocks in a discontinuous and step-like manner. The number and source locations of the cracks recorded by the AE monitoring system were in good agreement with the evolution of the temperature field and seepage pressure field. In addition, FLAC3D numerical simulations based on the thermo-hydro-mechanics and damage (THMD) model revealed that high geotemperatures and in situ stresses significantly influenced on the cracking mode of the surrounding rocks of hydraulic tunnels under high geotemperatures. The results obtained in this study provide a better understanding of the cracking characteristics of the surrounding rocks of hydraulic tunnels under high geothermal conditions and are useful for the design of hydraulic tunnels.

SEISMIC INTENSITY MEASURES FOR THE DAMAGE EVALUATION OF CIRCULAR TUNNELS

The seismic intensity measure (IM) is a key parameter affecting the accuracy of seismic risk assessment, which plays an important role in the performance-based earthquake engineering framework. A reasonable IM can make the prediction of structural seismic responses more accurate. To study on seismic IMs which are suitable for the damage evaluation of circular tunnels, a two-dimensional finite element model was established for the nonlinear dynamic time history analyses of circular tunnel-surrounding rock interaction. The near-field ground motions without velocity pulses and far-field ground motions recommended by FEMA-P695 were used as the input in the numerical model. The overall lining damage indices in compression and in tension were used as the engineering damage measures to estimate the damage states of the lining. The applicability of 20 ground motion IMs commonly used in the engineering practice were investigated. The results show that based on the criteria of efficiency, practicality, proficiency and sufficiency, the best seismic IM for the damage evaluation of circular tunnels is the sustained maximum acceleration (SMA), and the second best is the acceleration spectrum intensity (ASI).

Displacement Prediction of Surrounding Rock in Tunnel Based on cellular ant algorithm

The deformation of tunnel surrounding rock is the key factor to analyze the stability of surrounding rock. However, due to the influence of many factors and the strong non-linear relationship between the factors, it is difficult to predict the deformation effectively. In this paper, a method based on cellular ant neural network model is proposed to simulate the displacement of surrounding rock with time. The results show that this method is efficient and feasible, and can meet the requirements of engineering and control.

Numerical modelling of gas pumping in inner in-terlocked tail roadway of coal mine based on coupled fracture-seepage model

1. CHEN J., He H., ZHANG Y., 2011, Dynamic and static analysis of mechanism of loosen zone in sur-rounding rock of tunnels, Chinese Journal of Geotechnical Engineering, 33 (12), 1964–1969. Google Scholar

Research on Deformation Control Measures of Surrounding Rock in Soft Rock Tunnel

In order to study the control measures of soft rock tunnel surrounding rock deformation, based on the restraint effect of shotcrete anchor support on it, a support model was constructed, and numerical simulation was used to compare and analyze the restraint effects of different bolts controlling the surrounding rock deformation. The results show that: With the reduction of the bolt spacing (d), the resin bolt has a significant supporting effect compared with the mortar bolt support, the maximum displacement of the surrounding rock is reduced by 70.69%, and the maximum stress is reduced by 58.81%. With the increase of bolt length (L), compared with mortar bolt support, resin bolt has a more obvious restraint on surrounding rock deformation. The maximum displacement of surrounding rock is reduced by 57.89% and the maximum stress is reduced by 40.23%. When 4.5m <L< 6.m, 0.6m< d< 0.7m, the resin bolt has a significant effect on controlling the deformation of surrounding rock. In other cases, the use of mortar bolts or resin bolts to support the surrounding rock deformation has little significant difference.

Study on Seismic Response and Damping Measures of Surrounding Rock and Secondary Lining of Deep Tunnel

Tunnel construction is gradually developing to areas with high in situ stress; the deeper the tunnel construction, the more intense the earthquake disturbance. Under the background of frequent earthquakes, the seismic characteristics of tunnels become an important content related to the safety and stability of engineering structures. In view of the key problems of seismic response and vibration reduction measures for complex deep buried tunnels, the methods of advanced grouting and foam concrete aseismic are studied in this paper. Firstly, through geological survey, the in situ stress and geological conditions of the study area are analyzed. The structural characteristics of surrounding rock and related rock mechanics parameters are analyzed. The failure criterion of concrete lining under dynamic load is studied theoretically, and the relevant numerical calculation parameters are modified. A numerical model based on viscous boundary conditions is established. Through numerical calculation, the seismic response of tunnel surrounding rock and lining under different damping measures is analyzed. The research results have theoretical research value and social and economic benefits for ensuring the safety and stability of tunnel structure and improving the seismic fortification level.

Temporal and Spatial Effect of Surrounding Rock and Supporting Construction of a Large Soil Tunnel

Based on the Zaosheng No. 3 tunnel of the Yinchuan‐Xi’an high‐speed railway, the surrounding rock pressure, contact pressure of the primary support, and secondary lining and internal force of the secondary lining concrete are systematically tested using a vibrating wire sensor, and the correlation between the advance construction distance and the surrounding rock release rate is studied with finite element software. The results show that the pressure on the surrounding rock is low when the deeply buried soil tunnel is excavated and can be divided into three stages: rapid growth, slow growth, and flattening with time. It is more reasonable to calculate the surrounding rock pressure by using tunnel planning calculations. For the contact pressure, although the value of each measuring point in the inverted arch changes a little, the arch pressure obviously has the characteristics of rapid growth and a sharp rebound. Most of the test points of the second lining concrete show a compression state, which is far less than the ultimate compressive strength. At the same time, the initial support of the tunnel bears a large load, while the secondary lining bears a relatively small force, and the load sharing ratio of the two ranges between 0.1 and 0.7; with the progress of the excavation section, the surrounding rock deformation (deformation release rate) increases gradually. When the excavation face is close to the monitoring section, the deformation (deformation release rate) is the most severe. With the increase in the distance between the excavation section and the monitoring section, the deformation (deformation release rate) tends to be flat.

Calculation of Damage Caused by Blasting Vibration on Surrounding Rocks of Water-conveyance Tunnel across the Yellow River

The commonly used method for tunnel excavation is the drilling and blasting method, but the surrounding rock will accumulate damage under the action of blasting, leading to engineering accident, and the consequences of the accident in the Yellow River-crossing tunnel will be more serious. The work proposed a quantitative evaluation calculation of the damage on surrounding rocks caused by tunnel blasting excavation to study the effect of tunnel blasting on the damage of surrounding rock. analyzes the damage plasticity model theoretically, and determines the rock constitutive curve used in the numerical calculation of vibration damage, based on which plane physical model is established to adopt several different stress control standards to calculate the vibration damage of surrounding rock. The results proved that in the damage settlement of planar model 1, the damage variable around the tunnel was 0.14 at the maximum and 0.10 at the minimum. In the curtain grouting area, the maximum damage variable was 0.05, and the minimum was 0.01. In the damage settlement of planar model 2, the damage variable around the tunnel was 0.45 at the maximum and 0.05 at the minimum. In the curtain grouting area, the maximum damage variable was 0.20, and the minimum was 0.05.the impact of blasting vibration on the surrounding rock is mainly concentrated near the cavern, Thus, with the rock depth increasing, the damage decreased. the damage in the grouting curtain area is relatively small. The results accurately reflected the damage caused by blasting vibration on surrounding rocks and provided references for engineering construction.

A Novel Safety Evaluation Method for Mountain Tunnel Surrounding Rock Based on Vague Set

A Novel Safety Evaluation Method for Mountain Tunnel Surrounding Rock Based on Vague Set

Stress‐Strain Calculation Method of Composite Lining considering the Creep Characteristics of Tunnel Surrounding Rock

Tunnels are generally designed for a sustained usage of 80 to 100 years, during which the safety of tunnel structures must be guaranteed. A common supporting form utilized in contemporary tunnel engineering is composite lining. To derive applicable parameters of the supporting form and therefore ensure the long‐term safety of the tunnel structure, it is imperative to determine the extra acting force exerted onto the composite lining by the creep of the rock surrounding the tunnel and to calculate the stress‐strain characteristics of composite lining. In the current study, this paper proposes an approach termed surrounding reinforcement, which is based on the homogenization method. Specifically, this paper defined the bolt force as the internal force of the surrounding rock, analyzed their viscoelastic‐plastic properties using the unified strength theory, and derived an equation for calculating the stress‐strain relationship of the composite lining. To further validate the method in tunnel structures, this paper applied the derived equation to a representative instance. The results of this paper show that the initial support force has also increased during the creep process of the surrounding rock, indicating that engineers should pay close attention to the coordination between the strength of initial support and the secondary lining and thus ensure an optimal distribution of the pressure from the surrounding rock when designing composite lining tunnel within weak strata. This paper proposes that the initial support not only would guarantee the tunnel safety during the construction stage but also could cooperate with the secondary lining to brace the stress caused by the creep, ensuring that the supporting structure stays stable across the whole period of tunnel operation. This paper provides an alternative to previous methods that is more comprehensive, with simpler calculations, and more applicable to the composite lining supporting design within weak strata.

Application of Improved Grey Model Based on Cumulative Method to Deformation Prediction of Tunnel Surrounding Rock

The traditional GM(1,1) model was improved by using the cumulative to increase its prediction accuracy. Based on the measured data of the Laomu tunnel in section 10 of shiqian to yuping expressway, the traditional grey prediction model and the improved grey prediction model were used to predict the surrounding rock deformation of the tunnel. The research shows that the improved model prediction can reduce the probability of outliers and the data series fluctuation of traditional gray prediction model, and makes the predicted value closer to the measured value. Although the improved gray prediction model has a slightly single modeling step, it can effectively increase the prediction accuracy of the model in a short period of time, and has certain reference value for similar tunnel surrounding rock deformation monitoring projects.

Complex Analytical Study of the Stability of Tunnel-Surrounding Rock in a Layered Jointed Rock Mass

A barrier function method based on the fmincon optimization function in MATLAB was used to determine the function to map a tunnel boundary to the unit circle in the complex plane, and a structural failure criterion of the mapping convergence was established based on the reliability theory of underground engineering. The joints were approximated as cracks around the tunnel, the anisotropy of the stress intensity factor due to the crack inclination and position changes was studied, and the modified scoring parameter of the layered joints around the tunnel for the rock geomechanics classification (RMR) was proposed and used at points around the tunnel. The calculation method for the supporting stress was required to balance the bias load. The results showed the following: (1) When taking the structural failure criterion as the convergence condition of the mapping function, the mapping function converged when the mapping accuracy was δ ≥ 31.74 % . (2) The crack with an inclination angle of β = 45 ° was the dominant structural plane of the jointed rock mass around the tunnel. The anisotropy of the stress intensity factor K II at the tip of the mode II crack indicated that the corresponding cracks at the various points around the tunnel had inconsistent influences on the tunnel. The position had the greatest influence, followed by the straight wall area, and then by the top and floor areas. (3) When the crack inclination β was equal to the inclination angle β 0 of the dominant joint plane, the secondary crack was parallel to the unloading surface of the corresponding tunnel. (4) The bias load formed by the layered joints around the tunnel reduced the stress threshold of the failure of the rib spalling.