Tunnel Surrounding Rock Research Articles

Large deformation analysis of tunnel-surrounding rock along the expressway from Wenchuan to Maerkang, China

The rock surrounding the Wenchuan–Malkang Tunnel, which consists of metasandstone, slate, and phyllite (including carbonaceous phyllite), is strongly affected by geological and tectonic factors. The large deformation of the tunnel-surrounding rock is a concerning problem. Based on the analysis of the geological characteristics of the tunnel-surrounding rock, Hoek predictive equation was used to study the relationship between the relative deformation of the tunnel-surrounding rock and the rock strength, geostress, geological strength index, and strength-to-stress ratio. Using the strength-to-stress ratio, we predicted the large deformation of the tunnel-surrounding rock and compared it with the deformation phenomena revealed during tunnel construction. Our study shows that the large deformation of tunnel-surrounding rock along the expressway from Wenchuan to Maerkang occurs primarily in soft rock, such as slate and phyllites, which are strongly affected by the geology and tectonics factors. Deformation of the tunnel-surrounding rock grows rapidly in soft rock with decreasing geological strength index and strength-to-stress ratio and with increasing ground stress. Moreover, the relationship between the schistosity strike of the steeply layered rock mass and the tunnel axis has an important influence on the tunnel-surrounding rock deformation. Tunnels where the schistosity of the surrounding rock has a strike at a small angle with the tunnel axis are more prone to large deformation.

Spectral Correlation Between the Non-uniform Input Ground Motion and the Dynamic Response of the Surrounding Rocks of a Long Tunnel

To generate several different time-history curves of ground motion, which have the ability to reflect local site effects, such as the traveling-wave effect and attenuation effect, for long circular tunnels, a random method for the synthesis of ground motion is employed. The dynamic response of the surrounding rocks of a long tunnel under the uniform and non-uniform input ground motions is analyzed using the vertical input method. Based on this, the spectral correlation between the input ground motion and the dynamic response of the surrounding rocks is investigated through the coherence function. Unlike the results under the uniform input ground motion, the transmission coefficient of the surrounding rock monitoring points of each section along the axial direction of the tunnel under the non-uniform input ground motion varies in the main frequency band. In addition, at the same frequency, the transmission coefficient of the monitoring points gradually increases along the tunnel’s axial direction, but the increasing magnitude is variable. The correlation function of each monitoring point along the tunnel axis under the non-uniform input ground motion generally decreases with frequency. Moreover, the further the distance from the tunnel entrance, the faster the attenuation of correlation. The maximum coherence coefficient and the axial distance of the tunnel are basically in conformity with the quadratic polynomial relationship. However, the maximum coherence coefficient of the non-uniform input ground motion is considerably greater than that of the uniform input ground motion. The gap increases with the distance, and the maximum gap is about 0.15.

Study on the Creep Characteristics of Gentle Dip Red Bed Mudstone of the Surrounding Rock Tunnel

Red bed soft rock exhibits poor physical and mechanical properties and certain creep characteristics, which cause continuous deformation of tunnels and underground engineering structures during operation. The rock mass at the bottom of a railway tunnel in Sichuan Province is mudstone of the Penglaizhen Formation of the Upper Jurassic. It has a thin to medium-thick layered structure. Moreover, the rock formation is nearly horizontal. In this paper, the shear creep test and deep learning are employed to study the creep characteristics of gentle dip red bed mudstone.The results indicate that the red bed mudstone in the tunnel site exhibits medium-low creep characteristics. When the stress level is relatively low, the rate of the creep deformation gradually reduces with time, and when it reaches a certain time, the deformation no longer increases, and the final deformation tends to a stable value. Conversely, when the stress level is relatively high, although the rate of the creep deformation gradually reduces as the time increases, it remains unchanged when it reduces to a certain value. At the initial stage of creep, the deformation of each grade is evident; at the middle stage, the deformation is slow; and at the later stage, the deformation remains unchanged, that is, it enters the stable creep stage after a rapid decay in creep rate. The long-term strength of red bed mudstone in the tunnel site is low, which easily causes continuous deformation of the surrounding rock of tunnels under the action of high ground stress. According to the long-term deformation monitoring data at the bottom of the tunnel, combined with 20 groups of red bed mudstone creep parameter samples and the upper arch deformation data of the tunnel numerical model, the deep learning inverse analysis model of the creep parameter of rock mass is established based on the deep learning algorithm. Finally, we obtain the creep parameter of the red bed mudstone via inverse analysis. The research results provide a basis for engineering structure design and long-term deformation prediction of red bed mudstone strata in this area.

Stability Analysis of Surrounding Rock of Water-Rich Tunnel and Optimization of Blasting Construction Method

Tian, G.B.; Dai, J.; Wu, Y., and Zhai, H.H., 2020. Stability analysis of surrounding rock of water-rich tunnel and optimization of blasting construction method. In: Bai, X. and Zhou, H. (eds.), Advances in Water Resources, Environmental Protection, and Sustainable Development. Journal of Coastal Research, Special Issue No. 115, pp. 514-517. Coconut Creek (Florida), ISSN 0749-0208.In order to solve the technical problems of tunnel construction in water-rich area, the deformation and stress change of surrounding rock caused by three blasting methods, such as entire section method, bench method and single side heading method, are analyzed. The bench method produces the minimum displacement of the vault, and the displacement of the first row hole is slightly larger than that of the second row hole. After the tunnel excavation, the tensile stress concentration area appears in the inverted arch, the maximum tensile stress value produced by the entire section method is the smallest, and the bench method is the largest. The single side heading method has the least influence on the surrounding rock of the first tunnel. Finally, it is determined that the first tunnel of the water-rich tunnel is excavated by entire section method and the rear tunnel is excavated by Single side heading method. Through the field implementation, the method is proved to be feasible.

A Modified Engineering Classification Method for Schistose Surrounding Rocks of Tunnel

For schistose surrounding rocks of tunnel, engineering classification of rock masses by the widely used BQ method in China are often inconsistent with the reality. In this study, microtests and uniaxial compression test were performed on three types of quartz mica schist. Microtests reveal that the schist is characterized by natural orientation and interbedded distribution of minerals and microfissures are prone to be distributed directionally along the smooth edge of flaky minerals. Mechanical test shows that the compressive strength of schist samples has U-shaped change with the varied loading direction. Moreover, the strength anisotropy degree of the schist is positively correlated with the development of schistosity planes, and the strength anisotropy increases significantly after saturation. When the direction of uniaxial load applied to the samples changes gradually, the splitting-tensile, shear-slip and shear failure occur respectively, indicating that the dominant factors affecting the strength of schist specimens are not uniform. In particular, the strength of specimens with transverse schistosity planes is less affected by the weak planes. Based on the experimental study, a new model considering the schistosity development degree was constructed, which is served as the evaluation of the basic quality of schistose rock mass. By regression analysis on 168 sets of practical data, an optimized BQ equation was further developed. Then a correction coefficient table was put forward based on numerical simulation, which is helpful to correctly determine the final engineering grade of surrounding rock. Case study shows that the improved BQ method is more reliable for classifying engineering grade of schistose surrounding rock.

Comparative Analysis on Elastic-plastic Analytical Methods for Tunnel Surrounding Rocks

Comparative Analysis on Elastic-plastic Analytical Methods for Tunnel Surrounding Rocks

Field Experimental Study on Mechanical Characteristics of Primary Supporting in Weak Surrounding Rock Tunnel

Since the poor self-stability of weak surrounding rock when applied the full-face excavation in a tunnel construction, a large surrounding rock deformation are tended to occur, which causes a big security risk. Under the engineering background of gaojiaping tunnel of zheng-wan high-speed railway, the stress of surrounding rock, steel frame, initial shotcrete stress, bolt axial force and extrusion deformation of working face of the tunnel are monitored and analyzed respectively. The results show that the surrounding rock stress, steel frame stress and initial shotcrete stress of the tunnel are significantly affected by surrounding rock lithology and construction disturbance. The plastic zone of surrounding rock can be preliminarily determined as 3m according to the peak value of bolt axial force. The extrusion deformation of the tunnel working face shows that the surrounding rock integrity of the test section is good. The experimental study is helpful to collect the deformation of weak rock mass and provide reference for establishing scientific and reasonable support system.

Study on Ground Motion Intensity Measures for Seismic Response Evaluation of Circular Tunnel

Ground motion intensity measure (IM) is a key link between the seismic hazard analysis and structural seismic response analysis, which play an important role in the performance-based earthquake engineering framework. In order to find suitable IM for seismic response evaluation of circular tunnel, nonlinear dynamic time-history analyses are conducted on a two-dimensional finite element model of tunnel-surrounding rock interaction in this study. The near field ground motions without velocity pulse and far field ground motions as recommended by FEMA-P695 are used as the input ground motions for the numerical model. Besides, the overall lining damage indices in compression and in tension are used as engineering damage measures (DMs) to estimate the lining damage state. The applicability of 20 existing ground motion IMs commonly used in engineering practice are investigated in this study. Statistically regression analysis is carried out for results obtained from nonlinear time-history analyses. Based on the criteria of efficiency and sufficiency, Arias intensity is identified as the optimal IM for seismic response prediction of circular tunnel structure.

Study of the Growth Process of Original Crack in the Surrounding Rock of Tunnel under the Adjacent Explosive Load

The surrounding rock damage of a tunnel under adjacent explosive load is often manifested as the growth of the original crack. In order to thoroughly understand the crack growth mechanism, in this study, the growth process of the original crack was investigated in detail by the dynamic caustics experiment. The experimental study shows that the growth of original crack is the result of the combined action of explosion stress wave and explosive gas. The quasi-static stress generated by the explosive gas was superimposed on the weakened stress field, resulting in the formation of the peak of the main stress difference in the surrounding rock, moving towards the adjacent tunnel in the form of an arc wave. With the arc wave moving towards the original crack, the growth rate of the original crack increases rapidly. During the period of 200 μs to 250 μs, the crack growth rate oscillates at the peak, and its size is approximately equal to the moving speed of the arc wave. Based on the experimental results and microscopic damage mechanics, the high stress concentration at the original crack tip under the stress wave first causes damage localization and the weakest chain is formed by the penetration of the damage localization zones by microcracks by special distribution law. Subsequently, the original crack starts to initiate and grow along the direction of the weakest chain.

Stability Analysis of Surrounding Rock in Circular Tunnels Based on Critical Support Pressure

Accurate calculation for the critical support pressure of tunnels plays an important role in tunnel stability evaluation and support design. In this study, a mechanical model for circular tunnels is developed. Considering the intermediate principal stress and strain‐softening characteristic of rock mass, the critical support pressure when the plastic zone and damage zone begin to occur is determined based on the unified strength criterion and strain‐softening model. Through the example study, the critical support pressure under different intermediate principal stress coefficient is solved. Furthermore, the effect of initial field stress, softening coefficient, and maximum damage variable on the critical support pressure are also discussed. The results show that the critical support pressure and radii of plastic and damage zones all decrease with the increase of the intermediate principal stress coefficient. The larger the initial field stress, the larger the critical support pressure. The softening coefficient and maximum damage variable of rock mass has no influence on the critical support pressure when the plastic zone begins to form, but has a significant effect on the critical support pressure when the damage zone begins to form. As softening coefficient increases and maximum damage variable decreases, the critical support pressure when the damage zone which begins to form increases. Data presented in this contribution provide significant theoretical insights into evaluating tunnel stability and support system reliability.

Model Test on Bearing Characteristics of Basalt Fiber‐Reinforced Concrete Lining

Adding fiber can improve the brittleness of plain concrete. Compared with plain concrete, basalt fiber‐reinforced concrete has the advantages of strengthening, toughening, and crack resistance. Compared with steel fiber‐reinforced concrete, basalt fiber‐reinforced concrete has better construction performance. Basalt fiber concrete is a type of inorganic material with environmental protection and high mechanical properties, which has an important mechanical advantage for controlling the deformation of the soft surrounding rock tunnel. Through the indoor model test of mechanical behavior of reinforced concrete and basalt fiber‐reinforced concrete lining, the bearing characteristics of basalt fiber‐reinforced concrete lining was studied. The results show that, compared with reinforced concrete, the initial crack load of basalt fiber‐reinforced concrete is increased by 20%; the toughness of lining structure is enhanced by adding basalt fiber, and the lining can still bear large bending moment and deformation after the initial crack appears; after the initial crack appears, the bearing characteristic curve of reinforced concrete lining rises slowly and converges rapidly; the bearing characteristic curve of basalt fiber‐reinforced concrete lining rises slowly, and there is no sign of convergence when it reaches 2 times of initial crack load. For the soft surrounding rock tunnel, it is necessary to seal the rock surface as early as possible, provide support as soon as possible, and have a certain deformation capacity. Basalt fiber‐reinforced concrete can better meet these needs.

Experimental Study on Load Bearing Characteristics of Steel Fiber Reinforced Concrete Lining in the Soft Surrounding Rock Tunnel

Tunnels in soft rock with high ground stress will encounter the problem of large deformation of surrounding rock. The study of new high‐performance tunnel lining materials is of great significance to improve the safety of tunnel excavation in soft rock with high ground stress. In this paper, the bearing characteristics of the plain concrete, the reinforced concrete, and the steel fiber reinforced concrete lining are studied by the indoor model experiment. By extracting the displacement and stress data of typical parts of lining, the bearing characteristics of the steel fiber reinforced concrete lining are analyzed and summarized. The test results show that the initial crack load and ultimate load of the steel fiber reinforced concrete lining are significantly higher than those of the other two materials, and the crack development path is more tortuous, and the number of cracks is greater. Steel fiber can improve the bearing capacity and deformation capacity of the lining structure so that the failure mode of the lining structure changes from brittle shear failure to ductile bending failure. It is concluded that steel fiber reinforced concrete can improve the toughness of lining. Because of its excellent mechanical properties, steel fiber reinforced concrete can completely replace the conventional reinforced concrete as a new lining material for soft rock tunnel. The above research results are of great significance to the design and construction of tunnel lining in the soft surrounding rock.

Dynamic Optimization Classification Model for Submarine Tunnel Surrounding Rocks and Its Application in Engineering

Hou, F.-J.; Xie, X.-K.; Shi, S.-S.; Song, S.-G.; Bu, L.; Li, L-P., and Zhou, Z.-Q., 2019. Dynamic optimization classification model for submarine tunnel surrounding rocks and its application in engineering. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 311–315. Coconut Creek (Florida), ISSN 0749-0208.In order to make the classification of tunnel surrounding rocks more reasonable and accurate, a multi-index matter-element extension evaluation model was proposed for the advanced optimization classification of submarine tunnel surrounding rocks based on the extension evaluation method. Firstly, the rock mass integrity index Kv, Young's modulus E, the longitudinal wave velocity Vp, Poisson's ratio l, and groundwater W were selected as the evaluation indices. Secondly, the TSP detection technology was employed to collect quantitative indices. The main influencing factors, which were non-dimensional, were used to set up the matter-elements in order to make the evaluation indices comparable. Lastly, the matter-element extension evaluation model was applied to a submarine tunnel construction project in China and the evaluation results were compared against the excavation conditions on site.

Study on Key Steps of Three-lane Weak Surrounding Rock Tunnel Construction

For tunnel excavation with poor stability of surrounding rock, controlling the construction of key steps in each construction method is of great significance to tunnel construction. Taking Fengshuao and Daping tunnels as examples, this paper uses FLAC software to simulate three construction methods, i.e. double sides heading tunnel method, three-step method and CRD method. Through the analysis of displacement deformation in the numerical simulation results of three construction methods, it is concluded that the corresponding steps of maximum displacement deformation in different construction methods are the key steps in construction: the both sides heading method needs to strictly control the excavation of double-sided upper steps, the excavation of inverted arch and the dismantlement of middle-wall; the three-step method mainly controls the excavation of curved guide tunnel of upper steps, the excavation of inverted arch and the strike of locked bolts. The control steps of CRD method are the excavation of upper steps on the left wall, the excavation of upper steps on the right wall and the dismantlement of the middle wall. Therefore, strictly controlling the key steps of each construction method can improve the safety and efficiency of this kind of highway tunnel construction, and provide reference for future construction.

Stability Analysis of Surrounding Rock in Tunnel Crossing Water-Rich Fault Based on Catastrophe Theory

The failure of surrounding rock in tunnel crossing water-rich fault is a sudden damage phenomenon with obvious nonlinear and abrupt characteristics, which is characterized by the uncertainty of deformation, the nonlinearity of constitutive relation and the mutation of failure process. Based on the mechanical model of tunnel-fault system, the cusp catastrophe model of the failure of surrounding rock in tunnel crossing water-rich fault is established. Combining with the field monitoring data, the model is employed to judge the stability of surrounding rock. Results show that the deformation curve of tunnel vault has a good correlation to the cusp catastrophe model, and the results for stability analysis is consistent with the actual situation. The influences that the strength of rock mass, groundwater and fault width have on the failure of tunnel are further discussed, which provides scientific guidelines to the construction of tunnel.

Numerical Simulation to Research on the Fracture Mechanism of the Surrounding Rock in Deep Tunnels

In order to further explored the mechanical mechanism of surrounding rock zonal disintegration in deep buried tunnels, Numerical simulation was used in this paper to analyze the variation of different rock mass mechanical parameters (c, φ, µ) of surrounding rock and variation of the zonal disintegration under horizontal tectonic stress. Through the research and analysis, the influence law of rock mass mechanical parameters (c, φ, µ) on the zonal disintegration of surrounding rock of deep buried tunnel was obtained. The increase of the cohesive force and internal friction angle of the rock mass can reduce the range of partition failure. However, the influence of Poisson’s ratio on the zonal disintegration range presents nonlinear characteristics. At the same time, the horizontal tectonic stress directly determines whether the zonal disintegration phenomenon occurs, and it is the key factor for the regional failure of the surrounding rock of the deep tunnel. The above conclusions had certain reference value for in-depth study of the failure problem in deep buried tunnels, and provided theoretical support for further discussion of its mechanical mechanism.

A Prediction Model of Tunnel Surrounding Rock Deformation Based on Induced Ordered Weighted Averaging Theory and its Application

For the different prediction accuracy of tunnel surrounding rock deformation prediction model are different. Based on induced ordered weighted averaging theory(IOWA), IOWA modified combined forecasting model of tunnel surrounding rock deformation has been put forward with the relationship between the accuracy and the weight of a single prediction model. With the monitoring data of Mila Mountain tunnel of highways from Lasa to Linzhi, coupling the time series prediction model of deformation and exponential smoothing model of two kinds of single tunnel, IOWA modified combination prediction model for tunnel surrounding rock deformation has been built up. The result shows that predicted displacement of IOWA modified combination prediction model for tunnel surrounding rock deformation is closer to the measured value and has higher accuracy. The combined model for the prediction of tunnel surrounding rock deformation is feasible.

Numerical Calculation of Instability of Tunnel Surrounding Rock Based on Elastic Hole Theory

The instability and unloading of surrounding rock structure in tunnel under TBM construction condition can easily induce large-scale rock caving in heading face, which seriously restricts safe and efficient tunneling. Aiming at the instability problem of surrounding rock structure of tunnel constructed by TBM, four types of slope induced by excavation disturbance are summarized systematically based on elastic hole theory, and the instability mechanism of roof structure and surrounding rock of tunnel is analyzed; the instability mechanism and catastrophic characteristics of surrounding rock structure of tunnel are analyzed by FLAC3D finite element numerical calculation software, and the roof transportation of tunnel after supporting is carried out. The amount of movement is greatly reduced and the overall failure degree of overlying strata is slowed down. The results show that the roof is prone to structural instability under the influence of tunneling disturbance. Tunnel support can effectively hinder the movement of overlying rock roof and floor, alleviate the probability of rock mass catastrophe, effectively control the dynamic disasters, and achieve safe tunneling.

Construction Monitoring and Numerical Simulation Analysis of the Yangwujian Soft Rock Tunnel

Tunnel construction monitoring plays a key role in excavation construction of soft surrounding rock tunnel, it can be accurately judged stability of surrounding rock, its provide more priority information to design and construction. This paper adopts to construction of New Austrian Tunnel-ling Method (NATM), by strengthening the supporting and actual measurement on the spot, obtained displacement curve above vault settlement and clearance convergence. Selection parameter of supporting structure property by using Midas-GTS finite element analysis software, as well it has obtained both upper guide and down guide clearance convergence displacement-excavation step curve and valut settlement-excavation step curve. It’s found that: the faster stage of changing velocity is the first 10 days; the optimal execution time of the secondary lining is that the tunnel was excavated 30 days. It’s almost anastomosis both numerical simulation analysis and actual monitoring, it is better confirmed correctnass to establish the tunnel model, which provide reference for design and construction.

Analysis of Deformation Characteristics of Surrounding Rock in Shallow Excavation Tunnel

This paper takes the section of the excavation section SK25+490 of Nanzhi Road Station of Harbin Metro Line 2 as the background. Through collecting field monitoring data, the diachronic variation curves of surface subsidence and vault subsidence are drawn. By using FLAC3D software, a 3d model is built based on the engineering profile of the tunnel. Through comprehensive comparison of numerical analysis results and field monitoring data, it is found that the deformation of tunnel surrounding rock can be divided into three stages: rapid deformation, slow growth and basic stability with the advance of palm face. The similarity between the field monitoring data and the numerical analysis of the surrounding rock deformation law is high, which is of guiding significance for the reasonable selection of construction methods and types of supporting lining.