Roof Deformation Research Articles

An upper bound design method for roof bolting support in roadways with top coal

The roadways with top coal are a common type of roadways in thick coal seam mining. After excavation of such roadways, the top-coal rock mass is often loose and broken, and the roof deformation and failure are serious. Thus, the stability control of such roadways is a major concern of engineering design and construction personnel. In this paper, we take the typical roadways with top coal in Zhaolou coal mine of China’s Juye mining area as an example and propose a composite failure mechanism for roadway roof supported by rock bolting. The roof stratification and nonlinear failure characteristics of rock masses are incorporated in it. Then, a simplified design method of roof bolting support is proposed on the basis of the upper bound theorem. Furthermore, this paper shows the influence laws of varying parameters on the required supporting force of roof bolts and provides several practical recommendations for engineering applications. In addition, the effectiveness of the proposed method in this paper is further verified through a specific case analysis on a site typical roadway. The research work in this paper can provide theoretical guidance for support design and construction in roadways with top coal.

Three-dimensional physical model experiment of mining-induced deformation and failure characteristics of roof and floor in deep underground coal seams

Underground mining engineering causes complex changes in the three-dimensional stress near the working face of a mine, resulting in deformation and failure of the roof and floor rocks, as well as ground subsidence. To study the stress, deformation, and fracture field characteristics of the roof and floor strata due to mining, an indoor large-scale three-dimensional physical similarity model was developed. A novel method was used to simulate the mining process of coal seams. The results show that coal seam mining disrupted the original stress balance; consequently, a bearing pressure was generated in front of the working face, and a significant pressure relief state appeared in a particular area. The collapsed rock blocks of the overburden strata filled the goaf and played a supporting role, causing the overburden stress to increases again to a value close to the original rock stress. After complete mining, the overburden strata subsided, and the floor strata bulged. With an increasing vertical distance from the working face, the deformation of the rock formation gradually decreased. Evident fractured fields were formed in the surrounding rock of the goaf. In the horizontal section of the overburden rock layer, the cracks were distributed in a “rounded rectangular” shape. As the distance from the coal seam increased, the “rounded rectangular” boundary became smoother; the coverage area decreased; and the degree of crack opening and development in the plane decreased. The fractal dimensions of fractures with different overburden heights and different strike positions are calculated using the fractal geometry theory. We found that as the distance from the excavation face increased, the fractal dimensions of the fractures gradually became stable. In addition, numerical simulation methods were used to verify the correctness of the physical similarity model experiments. The research results can provide important references for the stability of deep underground projects such as coal mining process, tunnel excavation process, nuclear waste storage and other engineering stability.

Numerical Investigation on Time-Dependent Deformation in Roadway

The roadway deformation normally relates to time especially for underground coal roadway. The strength of soft coal is low, and therefore the deformation increases gradually under constant stress with time, which is called rheology deformation. In this study, based on a field case, the rock mass properties and deformation data of the roadway were obtained according to the field test. A 3D numerical model was then established, and the rheological deformation including horizontal and vertical deformation of the coal roadway was systematically analyzed. The results showed that the rheological deformation of horizontal sidewall accounts for almost 30% of the whole deformation, and the stable time for such roadway is around 60 days after excavation. The tendency of the roof deformation is similar to the sidewalls, and however, the floor deformation is different. Then the related suggestions for maintaining the stability of such roadway were proposed, which is useful in-field application.

Analysis on the Selection of Prefabricated Box-Shaped Steel Grid-Concrete Composite Thin-Shell Roof Structure

The new fabricated box-shaped steel grid-concrete composite thin-shell roof structure is a new structure based on the large-span steel-concrete composite thin-shell roof. An assembly unit composed of thin-walled steel ribs with bolt holes, a steel bottom plate, and concrete, and a thin-shell roof structure formed by assembly connection between the assembly units. A comparative analysis of the deformation and stress of the flat roof and arched roof structure shows that when the span is less than 30m, the difference between the deformation and stress of the two structures is not large, and it is more reasonable to choose the flat assembled composite roof structure. The construction difficulty is lower. When the span is 40m, the maximum vertical displacement of flat roof and arched roof are 53.73mm and 17.81mm respectively, and the difference gradually increases from 40m. After the span exceeds 40m, the stress between the steel box and concrete of the flat roof structure. The ratio increases sharply, and the arched roof shows a uniform change trend. The material utilization rate of the arched roof is higher than that of the flat roof.

Association of low-voltage areas with the regional wall deformation and the left atrial shape in patients with atrial fibrillation: A proof of concept study.

BackgroundLeft atrium (LA) remodeling is associated with atrial fibrillation (AF) and reduced success after AF ablation, but its relation with low-voltage areas (LVA) is not known. This study aimed to evaluate the relation between regional LA changes and LVAs in AF patients.MethodsPre-interventional CT data of patients (n = 24) with LA-LVA (<0.5 mV) in voltage mapping after AF ablation were analyzed (Surgery Explorer, QuantMD LLC). To quantify asymmetry (ASI = LA-A/LAV) a cutting plane parallel to the rear wall and along the pulmonary veins divided the LA-volume (LAV) into anterior (LA-A) and posterior parts. To quantify sphericity (LAS = 1-R/S), a patient-specific best-fit LA sphere was created. The average radius (R) and the mean deviation (S) from this sphere were calculated. The average local deviation (D) was measured for the roof, posterior, septum, inferior septum, inferior-posterior and lateral walls.ResultsThe roof, posterior and septal regions had negative local deviations. There was a correlation between roof and septum (r = 0.42, p = 0.04), lateral and inferior-posterior (r = 0.48, p = 0.02) as well as posterior and inferior-septal deviations (r = −0.41, p = 0.046). ASI correlated with septum deformation (r = −0.43, p = 0.04). LAS correlated with dilatation (LAV, r = 0.49, p = 0.02), roof (r = 0.52, p = 0.009) and posterior deformation (r = −0.56, p = 0.005). Extended LVA correlated with local deformation of all LA walls, except the roof and the septum. LVA association with LAV, ASI and LAS did not reach statistical significance.ConclusionExtended LVA correlates with local wall deformations better than other remodeling surrogates. Therefore, their calculation could help predict LVA presence and deserve further evaluation in clinical studies.

Deformation response of roof in solid backfilling coal mining based on viscoelastic properties of waste gangue

Solid backfill mining (SBM) is a form of green mining, the core of which is to control and minimize the deformation and movement of strata above longwall coal mines. Establishing a mechanical model that can reliably describe roof deformation by considering the viscoelastic properties of waste gangue is important as it assists in improving mine designs and reducing the environmental impact on the surface. In this paper, the time-dependent deformation characteristics of gangue under different stress levels were obtained by using lateral confinement compression, that reliably represents the compaction of goaf. The viscoelastic foundation model for gangue mechanical response is different from the traditionally used elastic foundation model, as it considers the time factor and viscoelasticity. A mechanical model using a thin plate on a fractional viscoelastic foundation was established, and the roof deflection, bending moment, time-dependent, viscous and other characteristics of SBM were included and analyzed. Compared with the existing elastic foundation model, the proposed fractional order viscoelastic foundation model has higher accuracy with laboratory data. The plate deflection increases by 50.9% and the bending moment increases by 37.9% after 100 days, which the elastic model would not have been able to predict.

Fracture criterion of basic roof deformation in fully mechanized mining with large dip angle

To explore the structure evolution of overlying strata and pressure characteristics of coal mining with large dip angle, the basic roof mechanical model was established that based on the thin plate theory and the development characteristics of 1212 (3) working face of Panbei Mine. The formula was deduced that used for calculating the basic roof stress distribution in large dip angle coal seam. It revealed the mechanism evolution of mining stress and its influence on overburden deformation. Furthermore, it was also discussed that the effect of false roof on the failure of the basic roof. It showed that the false roof increases the differentiation of gangue’s filling rate in goaf and improves the evolution rate of basic roof fracture. It is the main influencing factor that the large dip angle leads to the “scoop” distribution of the stress and deformation in basic roof. It dominates the evolution of overburden fractures and the regional instability. The maximum deformation of the basic roof is located in the middle and upper part of the working face. This theoretical model is verified by means of numerical simulation and field monitoring.

Disaster Control of Roof Falling in Deep Coal Mine Roadway Subjected to High Abutment Pressure

The roof falling accident is a serious threat to the lives of miners in deep coal mining, especially when the coal mine is more than 1000 meters deep. In regard to the 5306 coalface in the Tangkou coal mine, Shandong, China, the depth of coal seam is 992.8 m and the stress concentration coefficient of the roadway surrounding rock is 3.33. This leads to a serious deformation of the roadway roof, thereby producing a high risk of the roof falling disaster. In this pursuit, based on the mechanical analysis of roadway roof subjected to a high abutment pressure, the mathematical expressions of the setting load and movable column length of supports were introduced. Furthermore, the stability control mechanism of the roadway roof was analyzed and the optimized support parameters of supports are provided. The results showed that the longtime effective support of the roadway roof required the strength and deformation coupling of supports and anchored surrounding rock. The support length of the belt roadway should be at least 57.7 m, with 0-30 m away from the coalface supported by hydraulic supports and 32-57.7 m supported by single props. In addition, the maximum setting load and movable column length of hydraulic supports were 21.67 MPa and 280.3 mm and 12.44 MPa and 177.1 mm for single props, respectively. By applying the optimized support parameters of supports to the belt roadway of the 5306 coalface, the effective control of the roadway roof and the disaster control of roof falling were realized.

ВИЗНАЧЕННЯ РАЦІОНАЛЬНИХ ПАРАМЕТРІВ ЗВЕДЕННЯ ЗАКЛАДНИХ МАСИВІВ ПРИ СЕЛЕКТИВНІЙ ТЕХНОЛОГІЇ ВИЙМАННЯ ТОНКИХ ВУГІЛЬНИХ ПЛАСТІВ

Purpose. Substantiation of the backfill massif parameters in fully mechanized selective mining thin coal seams, taking into account the influence of technological and mining-and-geological conditions. Methods. The integrated approach which includes the analysis and generalization of scientific developments in the field under study, analytical and numerical methods for determining technological parameters is used in the work. Findings. The results of studies of the influence of complex technological and mining-and-geological conditions on filling massif parameters while selective mining are given in the paper. Using the example of numerical calculation methods for the selected initial characteristics of the mined coal seam the following trends are revealed: the shrinkage value of the filling material Eв from the ultimate rock strength σст and the relative density γв; the length of the filling mined-out space lз and the size of the undercut rocks mпр, the filling density γв and the technological gap Δhтех; the initial height of the filling massif formation hЗ and the effective seam thickness mеф from the support resistance Pк and the rock strength of the filling material σст. Originality consists in the determination of the change regularities in the roof subsidence and deformation of the filling massif from the technological parameters of the site and the face support while effective coal seam development by technological scheme of selective coal extraction. Practical implication. The research results can be used in the design of technological schemes for coal mining with backfilling and leaving waste rocks in the worked-out area. Key words: backfilling of worked-out space, selective technology, parameters, regularities.

Numerical Study on the Impact Instability Characteristics Induced by Mine Earthquake and the Support Scheme of Roadway

Rockburst of deep roadway was induced by the superposition of mine earthquake disturbance and high static stress exceeding the limit strength of coal‐rock mass. To study the roadway impact instability characteristics caused by mine earthquake disturbance and to propose an optimized support scheme, the discrete element model of the roadway structure was established based on the 1305 working face of the Zhaolou Coal Mine. The influence of mine earthquake amplitude and hypocenter location on the roadway was analyzed. The mesocrack evolution characteristics of the roadway were simulated and reproduced. Characteristics of stress field, crack field, displacement field, and energy field of the disturbed roadway with different support schemes were studied. The results showed that the greater the amplitude of the mine earthquake was, the severer the roadway impact failure was. The upper and left hypocenters had a significant influence on the roadway. The superposition of the high static stress and the dynamic stress due to the far‐field mine earthquake resulted in the impact instability of coal‐rock mass around the roadway, causing severe roof subsidence as well as rib and bottom heave. The evolution of tensile cracks caused the severe impact failure of roadway from a mesoscopic perspective. Using the flexible support to reinforce the roadway retarded the stress decline in roof and rib, improved the self‐stability, reduced the number of near‐field cracks, and decreased the displacement. Meanwhile, it allowed the roof and rib deformation, which was conducive to releasing elastic energy in surrounding rocks and reducing mine earthquake energy. The cracks and deformation in the floor were controlled by using the floor bolt. The optimal support scheme for a roadway to resist mine earthquake disturbance was proposed: “bolt‐cable‐mesh‐steel strip‐π‐beam + floor bolt.” The research results have a specific guiding significance for the support of the coal mine roadway.

Three‐Dimensional Physical Simulation and Control Technology of Roof Movement Characteristics in Non‐Pillar Gob‐Side Entry Retaining by Roof Cutting

An overlying rock structure plays a key role in controlling the roof deformation of nonpillar gob‐side entry retaining by roof cutting. On the bases of the actual geological conditions of II 632 Haulage Roadway at the Hengyuan coal mine, a similar three‐dimensional simulation experiment of roof precutting is conducted. Thereafter, the caving characteristics and migration law of the roof strata in the strike and dip directions are obtained. Moreover, the roof of the retained roadway and key strata of the goaf can form a hinge structure of the key blocks. By monitoring the deformation of the surrounding rock and stress distribution of the roof, the skew deformation characteristics of roadway roof are obtained. By observing the borehole peeping technology, the roof subsidence near the goaf is determined to be greater than that of the solid coal side, and the roof subsidence of the gob‐side entry retained by roof cutting is greater than that of the floor heave and two sides approaching. Results of the three‐dimensional similar simulation experiment indicate that the mechanical structure model of the key block of the retained roadway roof is constructed, and the mechanical analytical solution of the required support resistance of the retained roadway roof is obtained. This study proposes the constant resistance and large deformation anchor cable reinforcement support method to control the roof deformation of the retaining roadway. Through engineering application, the maximum value of the roof and floor movement of the retained roadway is stable at approximately 650 mm. The retained roadway can meet the demand of the next mining face.

Analysis of Roof Deformation Mechanism and Control Measures with Roof Cutting and Pressure Releasing in Gob‐Side Entry Retaining

The mechanical model of the basic roof fracture structure is established on the basis of key block theory to study the roof breaking mechanism of gob‐side entry retaining under roof cutting and pressure relief, and the analytical formula of roof support resistance is derived when the key block of the basic roof is stable. The influence of roof cutting angle and cutting height on roof support resistance is also analyzed. Determining the cutting seam parameters of the retained roadway roof is necessary to identify the support resistance of the roadway roof due to the correlation between the roof cutting parameters and the support resistance. Taking the II 632 haulage drift of the Hengyuan coal mine as the engineering background, FLAC3D numerical simulation is used in this paper to analyze the influence of different roof cutting angles and cutting heights on the surrounding rock structure evolution of retained roadways. Results show that the roof cutting angle and cutting height respond to the support resistance of the retained roadway roof, and the support resistance required by the roof increases with the roof cutting angle and cutting height. This condition ensures that the side roof of the gob can be cut off smoothly, and the support resistance required by the roof of retained roadways is within a reasonable range. Through theoretical and numerical simulation analysis, the reasonable roof cutting height of II 632 haulage drift is 8 m and the roof cutting angle is 15°. The theoretical analysis and numerical simulation results reveal that the required support resistance to maintain the stability of the roadway roof is 0.38 MPa. The supporting scheme of the roof of the II 632 haulage drift in the Hengyuan coal mine is then designed. Finally, the field industrial test is used for verification. The borehole imaging results show that the overall line of the retained roadway roof is small based on the description of field monitoring results. The deformation of the surrounding rock surface of the retained roadway is less than 100 mm, and the roadway is 40 m from the lagging working face. The deformation rate of surrounding rock decreases with the increase in distance from the working face. The integrity of the retained roadway roof is good, and the deformation of the surrounding rock is effectively controlled.

Failure Mechanism and Control Technology for a Large-Section Roadway under Weakly Cemented Formation Condition

The roof of a large-section roadway will usually undergo progressive deformation and failure under the action of deep surrounding rock stress. The large-section rectangular roadway is more prone to sudden roof caving accident under the weakly cemented formation condition, which poses great threats to operating personnel and mechanical equipment and brings about considerable difficulties to roof monitoring and evaluation. A large-scale caving accident that occurred on a large-section rectangular roadway in Bojianghaizi Mine in Inner Mongolia was taken as the study object. The factors that triggered the roadway roof caving were analyzed by investigating the roof caving mechanism of weakly cemented overlying strata, and an effective roof supporting method was proposed. A numerical mechanical analysis model was established for surrounding rocks of the roadway by using the discrete element method, and numerical simulation results showed that obvious vertical cracks would be generated at two ends of the roof under the action of shearing stress. With upward crack propagation and transverse crack penetration at the roof separation, a dangerous caving zone penetrated by cracks formed inside the roof. The permeation of the upper aquifer would reduce the rock strata strength at the roof and further aggravate the risk of roadway caving. In accordance with the numerical simulation and comprehensive analysis of field exploration data, the main reasons for the roadway caving accident were concluded as follows: (1) low rock strata strength at the roof and the influence of tectonic stress in deep surrounding rocks, (2) unreasonable original support pattern, and (3) permeation of the upper aquifer. On this basis, an improved support scheme was proposed, and field monitoring data showed that the maximum separation amount of the roof was controlled at 14 mm, and the roof deformation was well controlled, thus meeting the safety production requirements. The proposed method can provide a reference for the control of weak roadway roof and its support scheme design.

Assessing support alternatives for longwall gateroads subject to changing stress

Longwall gateroad entries are subject to changing horizontal and vertical stress induced by redistribution of loads around the extracted panel. The stress changes can result in significant deformation of the entries that may include roof sag, rib dilation, and floor heave. Mine operators install different types of supports to control the ground response and maintain safe access and ventilation of the longwall face. This paper describes recent research aimed at quantifying the effect of longwall-induced stress changes on ground stability and using the information to assess support alternatives. The research included monitoring of ground and support interaction at several operating longwall mines in the U.S., analysis and calibration of numerical models that adequately represent the bedded rock mass, and observation of the support systems and their response to changes in stress. The models were then used to investigate the impact of geology and stress conditions on ground deformation and support response for various depths of cover and geologic scenarios. The research results were summarized in two regression equations that can be used to estimate the likely roof deformation and height of roof yield due to longwall-induced stress changes. This information is then used to assess the ability of support systems to maintain the stability of the roof. The application of the method is demonstrated with a retrospective analysis of the support performance at an operating longwall mine that experienced a headgate roof fall. The method is shown to produce realistic estimates of gateroad entry stability and support performance, allowing alternative support systems to be assessed during the design and planning stage of longwall operations.

Collapsed Building Detection Using 3D Point Clouds and Deep Learning

Collapsed buildings should be detected with the highest priority during earthquake emergency response, due to the associated fatality rates. Although deep learning-based damage detection using vertical aerial images can achieve high performance, as depth information cannot be obtained, it is difficult to detect collapsed buildings when their roofs are not heavily damaged. Airborne LiDAR can efficiently obtain the 3D geometries of buildings (in the form of point clouds) and thus has greater potential to detect various collapsed buildings. However, there have been few previous studies on deep learning-based damage detection using point cloud data, due to a lack of large-scale datasets. Therefore, in this paper, we aim to develop a dataset tailored to point cloud-based building damage detection, in order to investigate the potential of point cloud data in collapsed building detection. Two types of building data are created: building roof and building patch, which contains the building and its surroundings. Comprehensive experiments are conducted under various data availability scenarios (pre–post-building patch, post-building roof, and post-building patch) with varying reference data. The pre–post scenario tries to detect damage using pre-event and post-event data, whereas post-building patch and roof only use post-event data. Damage detection is implemented using both basic and modern 3D point cloud-based deep learning algorithms. To adapt a single-input network, which can only accept one building’s data for a prediction, to the pre–post (double-input) scenario, a general extension framework is proposed. Moreover, a simple visual explanation method is proposed, in order to conduct sensitivity analyses for validating the reliability of model decisions under the post-only scenario. Finally, the generalization ability of the proposed approach is tested using buildings with different architectural styles acquired by a distinct sensor. The results show that point cloud-based methods can achieve high accuracy and are robust under training data reduction. The sensitivity analysis reveals that the trained models are able to locate roof deformations precisely, but have difficulty recognizing global damage, such as that relating to the roof inclination. Additionally, it is revealed that the model decisions are overly dependent on debris-like objects when surroundings information is available, which leads to misclassifications. By training on the developed dataset, the model can achieve moderate accuracy on another dataset with different architectural styles without additional training.

Tectonic and sedimentary deformational structures within the first Mid-Polish lignite seam – Konin Basin, central Poland

This paper focuses on deformational structures seen at macro and mesoscales within the first Mid-Polish lignite seam (MPLS-1) currently exploited by the Konin Lignite Mine. In fact, the majority of examples presented herein come from the Jóźwin IIB and Tomisławice opencasts. The deformations are divided into two groups; they are tectonic and sedimentary ones. The first group includes deformations of the floor, faults, cleats, and seismically-induced structures such as breccia and deformed lamination. The second group covers compactionally-induced deformations of MPLS-1 roof, sedimentary breccia, and slumps. All these deformations are described and then briefly interpreted in this paper. Although in a few cases in the formation of sedimentary deformations, the contribution of the tectonic factor as a trigger mechanism seems obvious. This is supported by the fact that the mentioned lignite seam is mined in the areas of grabens that were tectonically active during the development of the Mid-Miocene mires in the Konin Basin.

Nonlinear Creep Model of Deep Gangue Backfilling Material and Time-Dependent Characteristics of Roof Deformation in Backfilling Mining

With the gradual increase in mining depth of coal resource exploitation, deep backfilling mining has effectively solved the impact of strong deep mine pressure and strong mining disturbances. However, after deep backfilling mining, the backfilling material is subjected to high stress for a long time, and its viscoelasticity has a significant impact on the roof control effect. This paper uses a large-scale bulk confinement test device to analyze the viscoelastic properties of gangue, establishes a high-precision fractional viscoelastic creep model, and identifies the gangue parameters. The established fractional viscoelastic model was used as the foundation model of the beam, and the roof model based on the fractional viscoelastic foundation was solved. The top deformation characteristics of elastic foundation and fractional foundation were compared and analyzed, and the time effect, viscoelastic effect, and order effect of the fractional order viscoelastic foundation beam were discussed. The results show that the viscosity of gangue increased under the action of deep high stress. As time increased, the roof deformation also increased. In order to more effectively control the long-term deformation of the roof, the viscosity coefficient of the backfilling material should be greater than 20 MPa. This research provides relevant guidance for the requirements of backfilling materials for deep backfilling mining and the prediction of long-term dynamic deformation of the roof in underground excavations.

Dynamic deformation and fracture characteristics of a deep roadway surrounding rock based on the machine vision monitoring method

AbstractThe deformation and fracture of surrounding rock in deep underground engineering have the characteristics of time mutation and space continuity. In order to monitor and provide early warning of the dynamic deformation and fracture characteristics of deep surrounding rock, a real‐time digital displacement measuring instrument was developed in this paper. The proposed device represented a kind of surrounding rock deformation and fracture monitoring method, which had the continuous and real‐time advantages. Based upon the simulation experiments, the dynamic deformation and fracture of deep roadway surrounding rock were measured synchronously using the digital displacement measuring instrument testing system (DDMITS) and the V‐STARS measurement system. Comparative measurement results indicated that the DDMITS had a higher reliability. The deformation of roadway surrounding rock gradually increased with the increase of loading. The roof deformation and caving changing patterns in coal seam mining were studied using similar simulation experiments based on the DDMITS. The vertical displacement response of rock strata was more obvious than the horizontal displacement. There was a sharp increase in the vertical displacement during the collapse of the rock strata. Additionally, the vertical displacement velocity showed fluctuations. Meanwhile, the fluctuations in the vertical displacement acceleration increased significantly. The DDMITS could achieve full‐field measurement and the noncontact measurement of three‐dimensional deformation.

Geomechanics model test research on automatically formed roadway by roof cutting and pressure releasing

The N00 mining technology is a new coal mining method of automatically formed roadway (AFR). The roadway is created by roof cutting and pressure releasing (RCPR). Compared with the traditionally longwall method, this new technology does not require excavating mining roadways and reserving protective coal pillars (no-pillar). In order to make an in-depth study on the law of the mining pressure behavior, the first working face of N00 mining technology around the world is taken as the engineering background in this manuscript. A three-dimensional geomechanics model test system is independently developed for the N00 mining technology and the model test is carried out. Combined with numerical comparative analysis, the law of surrounding rocks stress evolution and overlying strata movement of AFR is obtained. The variation law of roof and floor convergence deformation of AFR has obvious zoning characteristics, which can be divided into four significant stages. These stages are the pressure releasing stage, the dynamic pressure deformation rising stage, the dynamic pressure deformation stabilizing stage, and the compaction stabilisation stage, respectively. The overload test results indicate that the key damaged parts are the shoulder corner of solid coal side, and the gangue rib of AFR. The research results can be used as a reference for theoretical research, engineering design and field application of the N00 technology.

Model experiment study on the stability mechanisms of box culvert excavation faces under the effect of pipe roof in a shallow bury

The pipe roof box culvert construction method is widely used in short-distance crossing projects. The shallow buried tunnel can reduce the wiring length, thus saving on the project’s construction costs. However, if not handled properly, roof collapse may occur in the tunnel. In this study, we created a model experiment design based on the Tianlin Road pipe roof box culvert project and conducted an experiment involving a pipe roof box culvert excavation surface stability model under different bury depths and pipe roof stiffness levels as well as a support plate moving forward or backward. This was done to explore the process of the excavation face instability and the development mechanism of ground deformation. The excavation face support plate was moved during the experiment to simulate the failure process of the excavation face limit equilibrium state. The DIC binocular camera and the fiber Bragg grating fiber were used to monitor the surface deformation and pipe roof deformation, respectively. The experiment results reveal the environmental influence law of the supper shallow buried pipe roof box culvert construction method and the failure shape of the excavation surface. The results further indicate that the development of the surface deformation of the under-excavation gradually changes from “straight” to “parabolic” with the change of the stiffness of the pipe roof. Furthermore, without the pipe roof, both the deformation value and the ground deformation under the over-excavation do not exceed 63.4% and 20.6%, respectively. The maximum vertical deformation of the over-excavation pipe roof is located at about 1 H of the excavation surface, and the maximum deformation of the under-excavation occurs at a distance near 2 H. The results of the model experiment can provide guidance in the application of the pipe roof box culvert construction method under supper shallow buried conditions.