Roof Deformation Research Articles

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.

Investigation of wind induced vibration and acoustic performance interactions for a flexible roof through multiphysics approach

This paper analyses structural and acoustic performance interactions of a building covered with a cable net and membrane roof following a multiphysics approach. The problem has three different variables: the roof time-depending deformed shape under wind action (duration 1800 s), the extremely variable position of a singer on the stage (30 s speaker recorded movements were expanded through a 6th order Hermite chaos polynomials to cover all the potential acoustic source positions) and finally, the listeners’ location (assumed according to Beranek for a listener located in the middle of the aisle between two stalls). The Initial Time Delay Gap was assumed as a measure of speech or song diffusion. In addition, reverberation time, clarity and early decay time were estimated for both undeformed and deformed roof shapes to evaluate acoustic performance variations. Roof deformation was calculated using time-history nonlinear structural analyses done by applying wind action measured in wind tunnel.

A study of the mechanical structure of the direct roof during the whole process of non-pillar gob-side entry retaining by roof cutting

The non-pillar entry (roadway) retained by roof cutting serves the two adjacent working faces. As compared with the conventional mining roadways, the roadway retained by roof cutting has a longer life cycle and receives more complicated influence from mining. Determining the location where the roof deformation and maximum deformation occur can provide an important basis for roadway support. Here, the direct roof of the roadway is studied by assuming it as an elastic deformation body. The stress features of the direct roof of the gob-side entry retained by roof cutting are analyzed, and the roof deformation is divided into five stages. The stress superposition principle is employed, and the equivalent concentrated load within the roadway is introduced. The mechanical model of the direct roof is established for the whole process of gob-side entry retaining by roof cutting. Next, the calculation formula for the concentration of direct roof at different positions is obtained for the whole process of gob-side entry retaining by roof cutting. The application scope of the calculation formula and the determination method of the key parameters are analyzed. The relationship between direct roof deformation of the roadway and stiffness of the support system is studied. The results show that the direct roof deformation has a symmetrical distribution about the midline. The maximum roof deformation occurs in the middle of the roadway, and it gradually decreases as the coal seam stiffness increases. During the example calculation, the maximum roof deformation is 280 mm for the gob-side entry retaining under primary mining. The measured maximum roof deformation is 320 m, and the error rate is 12.5%. It is then verified that the uniform mechanical model proposed in this study applies to the calculation of direct roof deformation in the gob-side entry retained by roof cutting.

Combined support technology for main roadway passing through goaf: A case study

AbstractControlling the surrounding rock of the main roadway passing through a goaf during the reconstruction and expansion of a merger and reorganization mine is a common challenge in underground mining practices. In this study, a combined support technology of roof “anchorage‐mesh‐shotcrete” and a double‐H‐type space frame structure for a main roadway passing through a goaf was studied using field investigations, theoretical analysis, and engineering practice. It was observed that the main roadway control difficulties lie in the strongly mining‐induced roof strata in the early stages, with collapsed gangues not connected to an unsupported roof, large goaf sections, and multiple superpositions of surrounding rock stress fields with complex distributions. Based on the results, a double‐H‐type space frame structure support system comprising a “reinforced concrete pillar + reinforced concrete longitudinal beam + cross steel I‐beam” was constructed. This provided strong pillar support, enhanced the shock resistance of the roof, improved the bending and lateral pressure resistances of the frame structure, and produced airtight spaces for the main roadway. Accordingly, a “double systems” support scheme was designed. The results of the engineering practice indicated that the deformation of the goaf roof and force of the supporting structure were controlled within a safe range, meeting the requirements for mine ventilation, pedestrians, and haulage. Consequently, the surrounding rock control problem for the main roadway passing through the goaf was effectively solved, and theoretical and technical bases were provided for the stability control of a roadway passing through a goaf under similar conditions.

Comparison between Percutaneous Lateral Osteotomy and Endonasal Lateral Osteotomy in Primary Rhinoplasty

Introduction: Open rhinoplasty is a popular method to correct nasal deformities, which is commonly carried out by percutaneous or endonasal techniques. Despite their advantages, these two techniques can also be associated with some disadvantages. The present study was carried out in order to examine the functional and aesthetic outcomes of percutaneous and endonasal osteotomies.
 Material and Methods: The present comparative study was carried out on 50 patients who underwent percutaneous osteotomy (25 cases) and endonasal osteotomy (25 cases) from August 2018 to September 2019. Before and three days, eight days, and three months after the surgeries, the required data were collected through medical and psychological assessments.
 Results: According to the results, the mean age of the patients was 28.7±6.5 years, and most of them were females with a female-to-male ratio of 4:1. It was also concluded that percutaneous and endonasal lateral osteotomies were not significantly different in terms of the postsurgical pain felt by the patients, epistaxis, skin scars 21 days and three months after the rhinoplasty, nasal obstruction, closing the open roof deformity, state of correction, patient satisfaction, age, and gender (p>0.05). However, they were significantly different regarding periorbital edema, periorbital ecchymosis, and skin scars during the first eight days after the surgery (p<0.05).
 Conclusion: Both percutaneous and endonasal lateral osteotomies were found to be useful methods to carry out rhinoplasty because both led to acceptable functional and aesthetic results regarding decreased pain, epistaxis, periorbital edema and ecchymosis, skin scar, nasal obstruction, closing the open roof deformity, and nasal deviation correction and increased patient satisfaction.

A comprehensive assessment of bus rollover crashes: integration of multibody dynamic and finite element simulation methods

Rollover crashes have the highest fatality rate and exhibit complex and unpredictable mechanisms in terms of vehicle-ground and vehicle-occupant interactions. The objective of this study is to evaluate the tilt table and modified dolly rollover (MDR) crash tests in terms of how these crash tests can represent those interactions and compare their results with two real-world rollover crashes. An application of combined dynamic and finite element (FE) simulations was presented to assess the cutaway bus rollover crash. First, the numerical models were validated against the experimental MDR test. Then, two real-world rollover crashes were simulated in PC-Crash to find the kinematics of the bus prior to the first vehicle-to-roof impact phase. Next, the impact phase of these real-world crashes was simulated using LS-DYNA and the results were compared with the two rollover crash tests. The FE simulations were conducted using a 2-point belted 50th Hybrid III FE model. The results of this study indicate that the common impact mechanism among these rollover scenarios was the impact between the bus’s roof corner (roof connection to the sidewall) and ground which caused lateral deformation patterns. Furthermore, unlike passenger cars where the vertical roof deformation can cause severe injuries in rollover crashes, the intrusion of the bus’s passenger compartment was not identified as a main source of injury. In addition, the highest head, neck, and chest injury risk were predicted during the MDR simulation where the ATD was partially ejected through the side window. Lastly, possible future works and limitations were explained.

Instability Mechanism of a Multi-Layer Gangue Roof and Determination of Support Resistance Under Inclination and Gravity

A multi-layer gangue roof of a steeply dipping coal seam with a large mining height face area was analyzed using physical simulation, numerical simulation, theoretical analysis, and field measurement methods to evaluate the roof deformation and the mechanisms associated with the instability of the hard gangue and soft coal interlayer. The results indicated that the first weighting step of the multi-gangue roof was larger than that of a non-gangue roof, but periodic weighting steps were similar. The overburden collapse height was lower in the multi-gangue roof than in the non-gangue roof due to the buffering and supporting function of the collapsed gangue. Moreover, the failure of the coal interlayer was the key factor in the collapse of the multi-layer gangue. A mechanical model was established for the hard gangue and soft coal interlayer based on a revised Prandtl squeezing theory. The limited load of the interlayer and maximum resistance of the shield support was thus modeled. The maximum resistance of the support increased with the dip angle of the seam and burial depth. It also increased with the interlayer thickness at thicknesses below 2.75 m. It reached a peak when the interlayer thickness was between 2.75 and 3 m and exhibited a decreasing trend when the thickness was greater than 3 m. The results were confirmed using physical simulation and a field test. Certain measures were proposed to control the stability of the gangue roof, including zoning control of the mining height and resistance and advancing the support while maintaining roof contact, thus ensuring the integrity of the support and surrounding rock system.

Spontaneous Repositioning of Isolated Blow-In Orbital Roof Fracture: Could Wait and See Be a Strategy in Asymptomatic Cases?

Treatment of isolated blow-in orbital roof fractures is still debated due to their anatomical complexity and the potential ocular and neurological related injuries. Surgery is advised in symptomatic cases while there is still controversy regarding the preferred treatment for those patients asymptomatic. To explore the suitability of a conservative management with close imaging follow-up in asymptomatic isolated blow-in orbital roof fractures. A single-case experience has been integrated into a systematic review of the literature to support the discussion on this specific traumatic lesion. Studies written in English and pertaining adult human subjects were further filtered according to the following eligibility criteria: clear definition of fracture's pattern, absence of concomitant cranio-facial injuries requiring management, proper description of treatment timing and outcome. The literature regarding treatment of isolated orbital roof fractures is of poor quality partly due to the rarity of such lesions. A total of 4 studies limited to small case series with 13 patients in total discuss thoroughly management options and timing of treatment. In particular, displaced blow-in fractures were treated conservatively in 4 patients with only 2 benefitting from this approach. Our patient showed a spontaneous realignment of a posttraumatic blow-in orbital roof deformity and at 12-month follow-up conservative management appeared a safe and effective strategy. A short-term wait-and-see approach with aggressive follow-up imaging could probably represent a reasonable option for treatment of isolated blow-in orbital roof fractures without neurological or ocular symptoms. Since literature remains confined to limited case series, future multicenter studies adopting shared evaluation parameters would help in standardizing the indications for this subset of craniofacial injuries.

Effect of Geometric Nonlinearity on Membrane Roof Stability in Air Flow

Membrane materials are widely used in construction engineering with small mass and high flexibility, which presents strong geometric nonlinearity in vibration. In this paper, an improved multiscale perturbation method is used to solve the aerostatics stability of membrane roofs on closed and open structures by quantifying the effect of geometric nonlinearity on the single-mode aeroelastic instability wind velocity. Results show that the critical wind velocities of two models are smaller when the geometrical nonlinearity of the membrane material is neglected. In addition, under normal wind load, the influence of geometrical nonlinearity of the membrane on the aerodynamic stability of the roof can be neglected. However, under strong wind load, when the roof deformation reaches 3% of the span, the influence of geometric nonlinearity should be considered and the influence increases with the decrease of transverse and downwind span of the membrane roof. The results obtained in this paper have an important theoretical reference value for the design membrane structures.

Rockburst Risk Analysis During High-Hard Roof Breaking in Deep Mines

Mining operations continue to advance to greater depths to address the demand and supply of coal. However, deep mining occurs in complex and dangerous environments where mines are often subject to rockbursts induced by high-hard roof breaking (HHRB). Here, we use the #2233 working face of the Hengda coal mine as a case study to investigate the mechanism of HHRB-induced rockbursts by means of stress, electromagnetic radiation (EMR) and hydraulic support resistance. We propose an elastoplastic plate theory model to study the relationship between impact load energy and maximum roof deformation and verify the dynamic evolution of rockbursts generated by HHRB by FLAC3D numerical modeling. The results show that rockbursts are more likely to occur when the coal-rock mass under high static stress conditions is subjected to superposition of continuous dynamic stress. This is accompanied by an abrupt increase in stress, increase in hydraulic support resistance, accumulation of strain energy that is not easily dissipated and a decrease in EMR intensity. The peak dynamic stress value determines the deformation mode of the elastoplastic plate model, and the impact damage behavior of the coal-rock mass is the most apparent, whereas the maximum deformation displacement lags slightly behind the arrival time of the peak stress. The occurrence of rockbursts is accelerated by long-term and high-amplitude dynamic disturbances.

Establishing the need to model the actual state of stress along rock bolts

Proper design of rock bolt support in underground mines is critical to avoid incidents, accidents and loss of production. The traditional design approach only considers the axial (tensile) capacity and this is clearly not the situation in situ, where a rock bolt is subjected to both axial and shear/bending loads which determines its overall performance and failure behaviour. To demonstrate and analyse the shear displacement in bedded roof, scaled physical models of underground excavation were created. From the models it was found that the shear displacement between the layers depends on the vertical roof deformation and thickness of beds. To analyse the effect of combined loading on rock bolt design for suspension and beam building models, analytical methods were used to calculate the required spacing of rock bolt for a given safety factor. Numerical models were then created using Rocscience RS2 software to establish the stresses on the rock bolt. The results show a significant reduction in safety factor for suspension as demonstrated in an example (reduced from 3.5 to 2.0) and beam building (2.0 to 1.36) when the rock bolt capacities are calculated considering the effect of combined loading as opposed to just the axial or shear loads.

Mine Pressure Behavior Characteristics and Control Methods of a Reused Entry that Was Formed by Roof Cutting: A Case Study

Noncoal pillar mining with automatic formation of a roadway is a new coal mining method that is tailored to improve the coal resource recovery rate and reduce the investment in roadway tunneling. Using this proposed method, a reuse entry is formed by roof cutting instead of tunneling. In this paper, the S1201-II working face of the Ningtiaota Coal Mine was used as a case study. The stress distribution of surrounding rock and the roof deformation characteristics of the reused entry during the mining process of the second working face were studied through FLAC3D numerical simulations combined with field measurements. The results indicate that the zone close to the reused entry led to higher stress in advance. If this stress is superimposed with the lateral pressure of the adjacent mined working face, it will be more difficult to maintain the reused entry. In the engineering case study described here, the reused entry created a stress increase zone and a severe deformation zone in the range of 0–80 m in front of the working face, and its range was approximately 37.5% larger than an ordinary entry. The stress peak in the stress increase zone increased by approximately 34.7% over that of an ordinary entry. The maximum amount of deformation within the severe deformation zone increased by 94.4% over that of an ordinary entry. To properly control the surrounding rock stress and deformation of the reused entry, a dynamic pressure bearing support in front of the working face with adaptability to the large roof deformation and high support strength is proposed here. Field application results showed that the final roof deformation with the dynamic pressure bearing support can be satisfactorily controlled within 110∼130 mm. These findings can provide a reference for researchers and field engineering technicians when engaging in the support work of reused entry.

Research on an automatic roadway formation method in deep mining areas by roof cutting with high-strength bolt-grouting

The excavation of deep mining roadways with traditional mining methods leads to various issues, such as the occurrence of large deformations, the waste of coal resources, complex conditions and the high cost of advanced support measures. In this study, we examined the roadway damage mechanism of the traditional gob-side entry driving method with coal pillars using the Suncun Coal Mine, the deepest mine in China, as an engineering case study. A method for the automatic formation of roadways in deep mining areas by roof cutting with high-strength bolt-grouting was proposed, and several quantitative evaluation indicators, namely, the roadway deformation control rate, anchor cable strength utilization ratio, and hydraulic prop strength utilization ratio, were established. The impacts of controlling the deformation of the surrounding rock were comparatively analysed in consideration of numerous factors, such as the mechanical parameters of the surrounding rock, roof cutting height, roof cutting angle, grouting anchor cable length, and hydraulic prop spacing. On this basis, the proposed method was applied in the field. The results showed that the automatically formed roadway cross-section exhibited decreased convergence deformation; moreover, the roof deformation was effectively controlled, and the passive hydraulic prop supports could be effectively replaced with the active support of grouting anchor cables, verifying the effect of the proposed method.

Long High-Performance Sustainable Bolt Technology for the Deep Coal Roadway Roof: A Case Study

High-efficiency maintenance and control of the deep coal roadway roof stability is a reliable guarantee for safe production and sustainable development of a coal mine. With belt haulage roadway 3108 in MenKeqing coal mine as the research background, in situ investigation, theoretical analysis, numerical simulation, and engineering practice were carried out to reveal the law of improving the bearing state of bolts by increasing the thickness of the roof anchoring layer. Also, the mechanism of the high-efficiency and long anchoring of the roof is revealed. Results show that increasing thickness of the roof anchorage layer could mobilize deep rock mass to participate in the bearing and promote the bolt to increase the resistance in a timely manner to limit the deformation of rock mass. Through the close link between shallow soft rock mass and deep stable rock mass, the deformation of the shallow rock mass is well controlled and so are the development and expansion of the roof separated fissures from shallow to deep. Long high-performance sustainable bolt technology for roof are proposed and carried out to control the stability of the deep roadway roof. Engineering practice indicates that deformations of roof could be efficiently controlled. The maximum deformations of the roof and sidewall-to-sidewall are 17 mm and 24 mm, respectively. No obvious separation fissures are found in the anchoring range of roof. This study provides a reference for roof stability control of deep roadway under similar conditions.

Study on Stability Analysis and Control Technology of Floor Rock Roadway in Dynamic Pressure Stope

Taking the floor rock roadway of 10414 working face of Yangliu Coal Mine in Huaibei as the engineering technology background, this paper uses theoretical analysis and numerical simulation technology to analyze the stability of floor rock roadway caused by stope mining. According to the dynamic pressure of stope, the support stage is divided into three stages: timely support scheme after excavation, pre-mining reinforcement support stage and post-mining repair support stage, and corresponding suggestions are put forward. Support scheme, through field practice, the overall maintenance of roadway affected by dynamic pressure is in good condition, the deformation of roof, floor and both sides are within the controllable range, and the roadway section can meet the requirements of normal use.

Numerical Analysis of Bolt Support at Roadway Intersection in Yanghui Mine, Vietnam

The stress of surrounding rock at roadway intersection is complex. U-shaped steel support has been used at the roadway intersection of Yanghui Mine in Vietnam, but there are many problems, such as blocked ventilation and limited passing capacity. In this paper, FLAC3D numerical simulation software is used to simulate the support effect of U-shaped steel and bolt based on the field data of Yanghui Mine. The deformation of roof, floor and two sides are compared. The results show that the bolt support can be applied to the intersection of roadways in the mine to improve the support of the mine.

Osteotomies-When, Why, and How?

An ideal nasal osteotomy should deliver precise, predictable, and reproducible cosmetic and functional results while minimizing soft-tissue trauma and postoperative complications. In addition to closing an open roof deformity after hump reduction, other common indications for osteotomies include the crooked nose and a wide bony vault. The literature has reported numerous and diverse osteotomy techniques as well as differences in timing of osteotomies. Each has its own merits and indications, and its proponents. In this article, we review the anatomy and nomenclature relating to osteotomies. We review the locations and paths of the osteotomies-lateral, intermediate, medial, and superior/transverse. We consider the percutaneous and endonasal approaches, as well as timing of osteotomies and other considerations. We also discuss technical considerations in the selection of instrumentation for osteotomies.

Secondary Gob-side Entry Retaining Technology with Double Side Roof Cutting and Pressure Relief in Thin Coal Seam

In order to solve the problems of stress concentration and large deformation of surrounding rock of secondary gob-side entry retaining in thin coal seam caused by hard overhanging roof, the method of cutting off overhanging roof on both sides of roadway by manual pre-cutting seam is adopted. It can transfer high stress to goaf on both sides of roadway and reduce roadway deformation. The mechanism of roadway formation, the conditions of double side overhanging roof subsidence and the stress reduction of roadway side support of secondary gob-side entry retaining after double side roof cutting are given. This paper studies the pressure relief law of secondary gob side entry retaining after double side roof cutting in thin coal seam. After double side roof cutting, the stress of roadway side support is reduced by 76%, the maximum vertical displacement of roof is reduced by 84%, and high stress is transferred to goaf. The influence of different double side roof cutting thickness and angle on the pressure relief effect is analyzed. On the premise that the collapsed gangue can fill the goaf, the smaller the thickness of double side roof cutting is, the better the pressure relief effect is, and the greater the double side roof cutting angle is, the better the pressure relief effect is. It has been successfully applied in the left five roadway of No. 69 coal seam in Xinqiang coal mine, and the deformation of roof and floor is reduced by 47% and the deformation of two sides is reduced by 56% after double side roof cutting. It has important reference value for the future secondary gob-side entry retaining.

Дослідження деформацій та оптимізація параметрів дегазаційних свердловин

Purpose. Investigation of deformation of the mouth of the degassing well depending on the deformation of the rocks around the preparatory work Methodology. The deformation of the mouth of the degassing well as a function of deformations of the roof rocks of the preparatory workings from which the well was drilled is considered. The dependence of the required depth of well sealing on the level of methane leakage and roof deformation is established. Results. It is experimentally proved that in the zone of active shifts behind the operating lava, where the main amount of explosive methane is released from the massif, the mouths of degassing wells change and the main types of irreversible deformations take place. With the distance from the contour of the preparatory production, the distance between adjacent concentrated deformations of the wellbore increases according to the logarithmic dependence, and these deformations are distributed according to the normal law. The average value of the concentrated deformation of the degassing well is in logarithmic dependence on the displacements on the contour of the preparatory work. The tensile deformation of the degassing well axis decreases with distance from the production contour into the array. Stratification of rocks leads to gas leakage and air suction, which reduces the efficiency of degassing. Permissible concentrated deformations of the degassing wellbore should not exceed its radius. Originality. The empirical power dependence of the required length of sealing of the degassing well on the allowable leaks and displacements of the roof of the preparatory workings from which the well was drilled is established. Practical value. Methods for calculating the required sealing depth of the degassing well have been developed and measures have been proposed to increase its stability, which increase the reliability of the degassing system as a whole and help increase the safety of underground coal mining.