Combined Support Technology Research Articles

Gradient failure mechanism and control technology of deep roadways under the action of deviatoric stress field

Deformation control of deep roadways is a major challenge for mine safety production. Taking a deep roadway with a burial depth of 965 m in a mine in North China as the engineering background, on-site investigation found that significant creep deformation occurred in the surrounding rock of the roadway. The original supporting U-shaped steel support failed due to insufficient supporting strength. The rock mass near the roadway experienced a transition from triaxial stress conditions to biaxial and even uniaxial stress states as a result of excavation and unloading, leading to a gradient stress distribution in the surrounding rock. From the perspective of the roadway's deviatoric stress field distribution, we investigated the gradient failure mechanism of the roadway and validated it through theoretical analysis and numerical simulations. The study found that the ratio of horizontal principal stress and vertical principal stress determines the distribution shape of the surrounding rock deviatoric stress field. The gradient distribution of the stress field in the roadway will cause time-related deformation of the roadway, which will lead to large deformation and failure of the roadway. Based on this, the control mechanism of roadway gradient failure was studied, and then a combined support technology of CFST supports with high bearing capacity was proposed.

Step by step and combined supporting technique with allowable deformation + limiting shape for soft rock roadway

Aiming at the difficult problems of the large deformation in weakly cemented soft rock roadways, the reasons of large deformation are analyzed for roadways in Hongqingliang coal mine. On this basis, the principle of step by step combined support technology based on allowable deformation + limiting shape for weakly cemented soft rock roadway is proposed, and the optimal support parameters of step by step combined technology are determined by FLAC3D. Step by step combined support technology includes the primary support of anchor bolt + anchor cable + initial shotcrete and the secondary support of U-shaped steel shed + filling flexible material behind shed + control of key parts. The comparative analysis on the site shows that the deformation rate and final deformation amount of the surrounding rock after the step by step combined support are less than those of the primary support, and the deformation of the surrounding rock can be controlled effectively after the secondary support is added. Step by step combined support is superior to the traditional bolt + anchor cable combined repair in terms of economy and efficiency. The optimal construction period of each working procedure of the step by step combined technology is 28 days after the completion of the first support, and the step by step combined support based on allowable deformation + limiting shape is an effective way to control the surrounding rock of soft rock roadway.

The Failure Law and Combined Support Technology of Roadways with Weak Surrounding Rock in Deep Wells

In order to effectively address stability control technology issues of soft surrounding rock roadways in deep mines. This study analyses the deformation and failure characteristics of the surrounding rock of a −962 m horizontal track roadway with original support conditions based on a severe deformation case that occurred in a mine. Upon establishing a mechanical model of surrounding rock failure zoning for circular roadways, which is based on the relationship between the stress–strain curve of soft rocks and the secondary stress distribution and strength of surrounding rock, this study explores the influence of rock strength indicators, disturbance degree, and support resistance on the stress distribution of the surrounding rock. The failure or instability mechanism of high-stress soft and weak surrounding rock is revealed on this basis. A multi-stage strengthening combined support technology is proposed, which consists of “high-strength prestressed anchor bolt (cable) supports as the core, deep and shallow hole groutings as the foundation, bottom angle, and floor anchorage grouting reinforcements as the key.” Moreover, numerical simulation and engineering practice optimize and verify the support scheme. The results show that after adopting the multi-stage strengthening combined support technology, the deformation of the surrounding rock of the roadways was only 12.6~14.3% of that under the original supporting parameters, and the deformation rate was still less than 0.2 mm/d even after 40 days. The proposed surrounding rock support method realizes the stability control of the roadway, which also has specific reference significance for similar projects.

Control Mechanism and Support Technology of Deep Roadway Intersection with Large Cross-Section: Case Study

Conventional bolt–shotcrete support technology is usually single-layered, which does not meet the requirements of strength and stiffness for roadway support. Therefore, in this paper, new combined support technology, including a multiple-layered staggered dense arrangement of bolts, multiple-layered laying of steel meshes, multiple-layered pouring of shotcrete, strengthening support of long cables, and full cross-section grouting, is proposed. Specifically, the following new combined support technology process is proposed: first layer of shotcrete (80 mm), first layer of mesh, first layer of bolt, second layer of shotcrete (50 mm), second layer of mesh, second layer of bolt, reinforced cable, third layer of shotcrete (50 mm), and grouting. The results show the following: (1) In the system of a superimposed coupling strengthening bearing arch, compared to a cable bearing arch, changing the support parameters of the bolt bearing arch can significantly vary the bearing capacity. A range of bolt spacing between 0.4 m and 0.7 m is more conducive for a high performance of the bearing capacity of the superimposed coupling strengthening bearing arch. (2) With the increase in the single-layer shotcrete thickness (from 50 mm to 100 mm), the bearing capacity of the shotcrete structure increased rapidly in the form of a power function. (3) After the multi-level bolt–shotcrete support structure was adopted, the ring peak zone of the deviatoric stress of the surrounding rock at the roadway intersection was largely transferred to the shallow part, and the plastic zone of the surrounding rock of the roadway was reduced by 43.3~52.3% compared to that of the conventional bolt–shotcrete support. The field practice model showed that the final roof-to-floor and rib-to-rib convergences of the roadway intersection were 114 mm and 91 mm after 26 days, respectively. The rock mass above the depth of 3 m of the roadway’s roof and sides was complete, the lithology was dense, and there was no obvious crack. The new technology achieves effective control of a deep roadway intersection with a large cross-section.

A New Combined Support Technology to Prevent the Failure of the Existing Metro Station Induced by Unilateral Excavation

This study establishes a 3-D simulation model based on a real project, which reveals the problem that the metro structure deformation induced by unilateral excavation without any support exceeds the safety threshold. According to the metro structure deformation warning area, this study proposes a support technology that combines cover plate braces and diagonal steel braces. The research shows that the lateral deformation reduction ratio of the metro station under the diagonal steel brace is about 10% – 20%. The deformation reduction ratio under the cover plate brace is about 35% – 40%. To ensure construction safety, this study adopts the optimal support combination of 3 cover plates and 6+9+11 steel pipes. Monitoring feedback and simulation prediction shows that the comprehensive support system can reduce structural deformation by 56.1%, and effectively control the deformation within a safe range.

Failure Characteristics and Deformation Control Methods of the Bottom Drum of Roadways during Repeated Mining of Multiple Coal Seams

As the problems of serious bottom drum and roadway broken surrounding rock are influenced by repeated mining in multiple coal seams, the factors affecting the surrounding rock deformation of a +980 m roadway in Faer coal mine by analyzing the rock composition and obtaining borehole video data are investigated. The mechanism of the overburden caving affected by repeated mining of multiple coal seams is analyzed theoretically, and the numerical simulation is conducted to evaluate the deformation mechanism of roadway bottom drum. A combined support technology is proposed consisting of bolts, anchor cables, grouting, and pressure relief grooves. The measurements obtained during a 50 d monitoring period indicate that the deformations of the roof, floor, and both sides of roadway in the repaired and reinforced section are only 26, 56, and 26 mm, respectively. The fissures filled with slurry in the rock surrounding roadway can prevent further deformation of the rock mass.

Research of Surrounding Rock Control of Gob-Side Entry Retaining Based on Deviatoric Stress Distribution Characteristics

In view of the difficulty of the surrounding rock control of retaining a roadway along a goaf, this paper takes the 5504 working face of the Hongshuliang Coal Mine as the engineering context. The uniaxial compressive strength and tensile strength of concrete filling material in the retained roadway are determined by laboratory tests. Through theoretical analysis, field investigation, numerical simulation and field measurement, the distribution characteristics of deviatoric stress and damage zone of the roadway surrounding rock in the mining process of the 5504 working face are studied here. Based on the failure of rock mass element caused by deviatoric stress tensors, the study shows that the thickness of the concrete wall is 2.2 m and the compressive strength of the concrete wall can reach 10.87~11.64 MPa in 3 days to 4 days, which can meet the support strength of the retained roadway. From the position of 90 m in front of the working face to the position of 100 m behind the working face, the distribution form of the roadway surrounding rock deviatoric stress is: symmetrical butterfly shape → single butterfly shape → narrow oblique strip → oblique 8 shape → wide oblique strip shape. When the distance between the retained roadway and the working face is 49 m, the retained roadway tends to be stable. Based on the distribution characteristics of the deviatoric stress outline line and the damage zone outline line of the retained roadway surrounding rock, the retained roadway surrounding rock is divided into three regions, and the combined support technology of “bolt + anchor cable + single pillar + reinforcement combined with steel plate to strengthen concrete wall” is proposed. Through field engineering practice, the maximum displacement of roof, floor, solid coal side and concrete wall side in the retained roadway is 136.6 mm, 78.8 mm, 62.3 mm and 43.3 m, respectively, and the surrounding rock control effect of the retained roadway is good.

Determination of coal pillar width for gob‐side entry driving in isolated coal face and its control in deep soft‐broken coal seam: A case study

AbstractLarge deformation control of surrounding rock in deep soft‐broken coal roadway has always been a key scientific and technological problem restricting the deep coal resources exploitation. Taking the gob‐side entry driving (GED) in isolated coal face under deep soft‐broken coal as research object, the prominent difficulties of surrounding rock control were clarified. Through numerical simulation, the evolution laws of deviatoric stress and plastic zone of GED under different coal pillar widths were studied. Combined with rational calculation, reasonable coal pillar width was determined to be 7.0 m. The study shows that severe disturbance distance in the front section of the coal face is 22 m, and makes it clear that coal pillar and roof are the key control areas. A subregional asymmetric combined support technology named anchor cable truss in roof and coal pillar + anchor cable in solid coal + single prop reinforced support in 25 m ahead of the coal face was proposed. The field application and ground pressure observation results show that good control effect has been achieved after adopting subregional asymmetric support technology under 7 m coal pillar width. The research results have important reference significance for safe mining in deep coal resources.

Study on deformation mechanism and control technology of surrounding rock during reuse of gob side entry retaining by roof pre-splitting

In this study, we aiming at the problems of severe surrounding rock deformation and support failure during the reuse of gob side entry retaining, we conducted field observations, theoretical analyses, numerical simulations and engineering projects to analyze the surrounding rock deformation mechanism, and we proposed a corresponding combined support technology. The results show that: (1) the surrounding rock failure is mainly affected by the advance abutment pressure, followed by the lateral abutment pressure, and the lateral abutment pressure has a certain lag. (2) According to borehole detection and theoretical analyses, multiple dynamic pressures influence the relationship between roadway support system and surrounding rock state. (3) The high proportion of inelastic zone volume is the main cause of severe surrounding rock deformation. Consequently, we developed a combined support technology, and applied it to an engineering project, realizing roadway stability; thus, the study provides a reference for similar engineering projects.

Research on Stress Distribution Characteristics for Uniquely Shaped Roadway with Hard Roof in Steeply Inclined Coal Seam and Support Technology of Reducing Vibration Impact

This paper presents a comprehensive study of the stress distribution and stability analysis of a uniquely shaped roadway having a steeply dipping hard roof. The coal seam and its roof have a certain impact tendency, which is the internal condition of rock burst. The syncline tectonic stress causes the original rock stress to reach a higher level. The large amount of coal produced in the coal mine and the large movement range of the upper strata cause the huge mining additional stress around the stope. The impact load caused by “cantilever beam” fracture of hard roof can induce and strengthen rock burst. Its engineering geological setting encompasses the mining process and surrounding rock conditions of No. 6 Coal Seam in the 2130 coal mine of Xinjiang. Numerical simulations with theoretical analysis and field measurements investigated a proposed new truss combined support scheme for implementation. A comparison was made of the differences in the state parameters of the road under the new and old support conditions. The application of the new combined support technology changed the form of the stress distribution around the road. Apart from the displacements of the two coal sidewalls, the new support system notably reduced the displacement of roof and floor by 67.8% and 83.6%, respectively. After the implementation of the new support scheme, the frequency of the original rock burst in the working face is greatly reduced, the surrounding rock control and field application effects also remained good, and personnel and equipment safety and production plan have a good guarantee.

Failure Mechanism Analysis and Support Technology for Roadway Tunnel in Fault Fracture Zone: A Case Study

This paper introduces a case study on the failure mechanism and support design of a roadway tunnel in the fault fracture zone of the 106 mining area in the Yuandian no.2 coal mine. Based on the on-site geological conditions (in-situ stress test, borehole television imaging, and lithological analysis), the failure mechanism of the roadway tunnel in the fault fracture zone was studied. The test results showed that the high tectonic stress, fractured rock, and poor lithology are the primary reasons for the roadway instability. According to the support principles of grouting reinforcement, pre-reinforced support, and rational support range, a new type of combined support technology was proposed, including advanced grouting, grouting bolts, and grouting anchor cables. A 100 m roadway section was selected for field testing using the new support scheme, and detailed deformation monitoring was performed. Monitoring results showed that the roadway deformation under the new support was significantly reduced. During the roadway excavation process, no roof collapse phenomenon occurred, and the safety of roadway excavation was ensured. This successful case provides an important reference for similar roadway projects in the fault fracture zone.

Combined support mechanism of rock bolts and anchor cables for adjacent roadways in the external staggered split-level panel layout

Using the spatial structure of the external staggered split-level panel layout, a combined support technology for adjacent roadways was developed and analyzed for a rock bolt and anchor cable mechanism. The influence of the side rock bolt and anchor cable parameters on the mechanical properties of the anchorage body and the support stress distribution of the lateral coal body were revealed using the FLAC3D software. The optimal support parameters of the side rock bolts and anchor cables were subsequently determined, and the support effect of gob-side entry in a mining scenario was verified. The results show that the support of the side rock bolts and anchor cables improves the mechanical properties and stress state of the anchorage body, producing a good protective effect on the coal body of the air-intake entry roof and side wall. This is beneficial to the stability of the side wall and the realization of the suspension effect for roof rock bolts and anchor cables, which in turn makes the surrounding rock maintenance of the gob-side entry to a thick coal seam more favorable.

Stability and Control of Retracement Channels in Thin Seam Working Faces with Soft Roof

To reduce the risk of roof falling and rib spalling during equipment retracement in thin coal seam faces with soft roofs, the 25070 working face of Xuehu Coal Mine was taken as the research object, and theoretical analysis, numerical simulation, and field practice methods were used. Under different space relationships between retracement channels and main roof fracture, the load of hydraulic supports was quantitatively analyzed. The relationship between the working resistance of the hydraulic support and the sinking rotation angle of the immediate roof was analyzed, and a reasonable time for the arrangement of the retracement channel was determined. The sublevel excavation technology and the combined support technology of roof anchor cables and coal rib anchors were proposed. The field application shows that the falling height and rate of movable prop of the hydraulic supports, working resistance of the hydraulic supports, and the roof subsidence all meet the requirements of safety production during the terminal mining period, and the surrounding rock control effect of retracement channel was determined to be good. The safe and efficient mining of the coal mine is ensured, and the research results can provide guidance for similar working faces.

Failure Mechanism and Control Technology of Thick and Soft Coal Fully Mechanized Caving Roadway under Double Gobs in Close Coal Seams

The surrounding rock of the roadway under double gobs in the lower coal seams is partially damaged by the mining of the upper coal seam and the stress superimposition of the stepped coal pillars. What is worse, the upper layer of the roof is collapse gangue in double gobs, which makes the anchor cable unable to anchor the reliable bearing layer, so the anchoring performance is weakened. The actual drawing forces of the anchor bolt and anchor cable are only approximately 50 kN and 80 kN, respectively. The roadway develops cracks and large deformations with increasing difficulty in achieving safe ventilation. In view of the above problems, taking the close coal seam mining in the Zhengwen Coal Mine as the engineering background, a theoretical calculation is used to obtain the loading of the step coal pillars and the slip line field distribution of the floor depth. The numerical simulation monitors the stress superimposition of stepped coal pillars and the distribution of elastoplastic areas to effectively evaluate the layout of mining roadways. The numerical simulation also analyzes the effective prestress field distribution of the broken roof and grouting roof anchor cable. A laboratory test was used to monitor the strength of the grouting test block of the broken coal body. Then, we proposed that grouting anchor cable be used to strengthen the weak surface of the roof and block the roof cracks. From on-site measurement, the roadway was seen to be arranged in the lateral stress stabilization area of the stepped coal pillars, the combined support technology of the grouting anchor cable (bolt) + U type steel + a single prop was adopted, the roadway deformation was small, the gas influx was reduced, and the drawing force of the anchor bolt and the anchor cable was increased to approximately 160 kN and 350 kN, respectively. The overall design and control technology of the roadway can meet the site safety and efficient production requirements.

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.

Combined Support Technology of Retained Entry in Large Mining Height Face with Double Roadways Layout

The stability of retained roadway plays an important role in the safety production of coal mine underground working face. Taking the 21,101 auxiliary haulage gate in Yaping Mine as the engineering background, the supporting technology was systematically studied. Firstly, based on the previous situation of pillar setting and surrounding rock failure and deformation in double roadway layout, the reasonable size of pillar between roadways was studied. The width of the broken zone was realized as 2.95 m by theoretical analysis, and then the width of pillar between roadways was determined as 7.95 m. On this basis, the law of stress evolution and retained roadway deformation with the pillar width of 6 m, 8 m, 10 m, 12 m, 15 m under the influence of two times mining were analyzed, comprehensive analyzed the above research results, 8 m in width of pillar between roadways was determined. Secondly, the failure rules of pillar between roadways, the failure rules and the failure process of retained roadways during two times mining were revealed: the range between 70 m in front of the work and 80 m behind the work was determined as the mining influence area according to the damage degree of coal pillar, the failure depth of surrounding rock in retained roadway during the two times mining was the largest in the pillar side, the second in the roof and the coal wall side, the smallest in the floor, and the damage degree was the largest in pillar side, the second in floor, the smaller in roof and wall, and the overall failure of roadway was asymmetric. Finally, on the basis of the above research results, considering all kinds of influencing factors and technical difficulties of retained roadway surrounding rock support, the system analysis method was used to determine the combined support technology with high strength allowable cables support + asymmetric cables support + bolts support system + concrete floor-allowable pressure non-repeated supports dynamic strengthening support. Practice shows that the combined support technology is scientific and reliable, which can meet the safety mining requirements in large mining height face with double roadways layout.

Failure mechanism and safety control strategy for laminated roof of wide-span roadway

The laminated roof of wide-span roadway is characterized by large subsidence, easy instability and difficult support. The open-off cut of #30102 working face in Nanliang coal mine is taken as an example to expound the roof failure mechanism. The roof exploration test are carried out to reveal geologic characteristics. The parametric asymmetric Voronoi block generation program is developed by Python, and the parametric modeling of laminated strata is first implemented in UDEC, then, the numerical model of roadway is established by combining the results of exploration test, microproperties calibration, tension and shear test of rockbolt, and bearing characteristics of timber. It can be concluded that the main types of joint failure are dominated by tensile through numerical calculation. The joint failure height is independent of the roadway width, and when the roadway width is greater than the limit span of the combination beam, there will be roof caving. Based on above analysis, the “rockbolt + timber” combined support technology is proposed, which can combine the roof strata and further reduce the roof span. Numerical simulation results and field application results show that this support scheme can effectively realize the safety control of the laminated roof of the wide-span roadway.

Application and Research of Multiple Support Types in the Combination of Deep Foundation Pits

We are studying the foundation pit support technology is currently the most common engineering problem in foundation pit engineering, and this is very important for the selection of support structure. We found that construction techniques such as soil-nailed walls, cast-in-place piles, triaxial cement mixing piles, row piles, anchors (rods), deep well dewatering, and internal support in foundation pits are more common construction methods in deep foundation pit support technology. During the design and construction process, according to the different environmental conditions, engineering geological conditions and support requirements of the construction site, we can flexibly adopt a variety of support types to form a safe and reliable support system. Using this method can ensure the foundation pit is opened. Safety during digging. We found in the project an example of the design of the full-type technology of the support group of “filled pile + internal support”. We applied the rational foundation pit algorithm to the excavation process of the soft soil deep foundation pit under the row pile support. The variation of the moment of the pile body, the lateral deformation of the pile body and the ground settlement around the foundation pit due to excavation were analyzed. In the project, we combined the monitoring information of the foundation pit, and the experimental results resulted in this type of support combined support technology. In the foundation pit support technology, the limited deformation results are good, and the impact on the surrounding foundation is small. Studies have proved that this technology can provide a reference for similar engineering practices, and the technology has practical research significance.

Roadway Surrounding Rock under Multi‐Coal‐Seam Mining: Deviatoric Stress Evolution and Control Technology

Multi‐coal‐seam mining creates surrounding rock control difficulties, because the mining of a coal face in one seam can affect coal faces in another. We examine the effects of multi‐coal‐seam mining on the evolution of the deviatoric stress distribution and plastic zone in the roadway surrounding rock. In particular, we use numerical simulation, theoretical calculation, drilling detection, and mine pressure observation to study the distribution and evolution characteristics of deviatoric stress on Tailgate 8709 in No. 11 coal seam in Jinhuagong mine when the N8707 and N8709 coal faces in No. 7‐4 coal seam and the N8707 and N8709 coal faces in No. 11 coal seam are mined. The evolution laws of deviatoric stress and the plastic zone of roadway surrounding rock in the advance and behind sections of the coal face are studied, and a corresponding control technology is proposed. The results show that the peak value of deviatoric stress increases with the advance of the coal face, and the positions of the peak value of deviatoric stress and the plastic zone become deeper. The deflection angle of the peak stress after mining at each coal face and the characteristics of the peak zone of deviatoric stress and the plastic zone of the roadway surrounding rock under the disturbance of multi‐coal‐seam mining are determined. In conclusion, the damage range in the roadway roof in the solid‐coal side and coal pillar is large and must be controlled. A combined support technology based on high‐strength and high pretension anchor cables and truss anchor cables is proposed; long anchor cables are used to strengthen the support of the roadway roof in the solid‐coal side and coal pillar. The accuracy of the calculated plastic zone range and the reliability of the combined support technology are verified through drilling detection and mine pressure observation on site. This research can provide a point of reference for roadway surrounding rock control under similar conditions.

Bolt-grouting combined support technology in deep soft rock roadway

Analyzing the mineral composition, mechanical properties and ground stress testing in surrounding rock, the study investigated the failure mechanism of deep soft rock roadway with high stress. The bolt-grouting combined support system was proposed to prevent such failures. By means of FLAC3D numerical simulation and similar material simulation, the feasibility of the support design and the effectiveness of support parameters were discussed. According to the monitoring the surface and deep displacement in surrounding rock as well as bolt axial load, this paper analyzed the deformation of surrounding rock and the stress condition of the support structure. The monitor results were used to optimize the proposed support scheme. The results of field monitors demonstrate that the bolt-grouting combined support technology could improve the surround rock strength and bearing capacity of support structure, which controlled the great deformation failure and rheological property effectively in deep soft rock roadway with high stress. As a result, the long term stability and safety are guaranteed.