Concrete-filled Steel Tube Support Research Articles

Study on the failure mechanism of deep roadways considering gradient stress and the control technology of CFST supports

The surrounding rocks showed gradient failure after excavation. And according to the different stress states, the surrounding rock of the excavated roadway is divided into severe damage area, moderate damage area and light damage area. An indoor triaxial unloading test was designed to simulate the damage of surrounding rock under different stress states. It was found that it has the composite failure characteristics of splitting and shearing, and the peak stress is also between the conventional uniaxial and triaxial test results. The relative stress gradient was introduced, and a mechanical model of gradient failure in deep tunnels was proposed and established based on the stress field strength method. Based on the gradient damage mechanism, a combined support scheme of annular concrete-filled steel tube support is proposed, which has a better effect on controlling the deformation of the roadway in the field.

Application research on composite support technology of concrete-filled steel tube support in high stress and large deformation soft rock roadway: A case study

Aiming at the surrounding rock control problem of high stress and large deformation soft rock roadway. This article takes the 141712 coal haulage uphill as the engineering background in Guizhou Panjiang Mining Area. Through field investigation, theoretical calculation, numerical simulation, and industrial tests, the deformation characteristics of surrounding rock and the mechanism of roadway instability and failure were revealed. And a composite support scheme of "bolt (cable) + grouting + concrete-filled steel tube support" was designed. A strengthening support mechanical model of “Three-arch” based on the concrete-filled steel tube support technology was established. The ultimate bearing capacity of the design scheme above is calculated, which meets the support load and can maintain the stability of the soft rock roadway. Through numerical simulation analysis, the distribution characteristics of the plastic zone, stress field and displacement field of the design scheme are obtained, and the rationality of the scheme is verified. The industrial tests were successfully applied and the field monitoring results show that the deformation is within the controllable range, effectively controls the deformation of the 141712 roadway. The research results can provide a reference case for the control of soft rock roadway with high stress and large deformation under similar complex conditions.

Experimental research and engineering application on bearing capacity of concrete-filled steel tube circular arch

The bearing property and deformation failure law of the CFST circular arch were investigated in order to provide direction for the optimization of the concrete-filled steel tube (CFST) support. The flexural bearing capacity test of the 194 mm × 10 mm CFST was performed initially in this study. It was primarily explored how bearing capacity and deformation of circular arches were affected by the slip of the arch foot and anti-bending strengthening, and the neutral layer migration rule and anti-bending strengthening mechanism of circular arches were examined. The bearing performance of the circular arch under the condition of the concentrated load of the vault and the usual uniform load of the entire span is then simulated in an orthogonal test by numerical simulation in order to extend the experimental investigation. The effect of variables including the steel tube’s outer diameter, thickness, slip of the arch foot, and the ratio of the arch rise to span on the bearing capacity of the circular arch is examined. The study demonstrates that under focused stress on the arch top or full-span normal uniform loading, the arch foot slip is the most important element impacting the CFST support’s bearing capacity. In steel tubes with the same outer diameter and wall thickness, the vector span ratio has a bigger influence than anti-bending strengthening. When the span ratio is the same, the influence of the outer diameter and wall thickness are equal and outweigh the influence of bending strengthening. The circular arch with an outside diameter of 168 mm, a wall thickness of 10 mm, and a rise-span ratio of 0.207 has the best performance characteristics under the influence of concentrated load, and the ultimate failure mechanism is local waist drum deformation failure. Based on the aforementioned study findings, the circular CFST support’s buckling deformation and drum deformation are examined, and a composite support consisting of “anchor net spray + CFST support” is directed for the north three deep track downhill of Yangcheng Coal Mine. Two failure types expose the failure mechanism and provide a technique for optimization. The support had contributed to the circular CFST arc arch’s best bearing performance in the event of waist drum deformation and failure.

Research on application of annular concrete-filled steel tube support in deep roadway

In this paper, through on-site investigation and monitoring, the characteristics of roadway deformation and the causes of deformation and damage are analyzed. Among them, the unreasonable support system is an external factor, and the nature of rock mass, deterioration degree of surrounding rock, and high ground stress are internal factors. A simulation method of CFST considering initial defects in core concrete is proposed and utilized to analyze the mechanical properties of CFST supports. Building upon numerical simulation results, we introduce an optimized support scheme comprising annular CFST support, segmental fissure surrounding rock grouting, and bolts. Field comparison tests demonstrate that the application of the new repair technology yields remarkable enhancements in the bearing capacity of surrounding rock and supporting structures while ensuring a more uniform stress distribution within the rock mass.

Bearing Capacity of Concrete Filled Steel Tube Circular Arch under the Six‐Point Uniformly Distributed Loading and Its Engineering Application

The influence of rise‐span ratio on the bearing performance of concrete filled steel tube (CFST) circular arch was studied in this paper, three groups of CFST circular arch specimens with different rise‐span ratios (0.154, 0.207, and 0.26) were selected, the six‐point uniformly distributed loading was performed, and bearing performance experiments on CFST circular arch specimens with fixed ends were carried out. In this study, the ultimate bearing capacity and deformation failure characteristics of CFST circular arch specimens were obtained. The comparative analysis shows that the deformation evolution of CFST circular arch specimens has experienced compaction stage, elastic stage, elastic‐plastic stage, and plastic stage. In the elastic‐plastic and plastic deformation stages, the circular arch shows good ductility and bearing capacity. The bearing capacity of the circular arch is significantly affected by the rise‐span ratio. Compared with circular arch specimens with a rise‐span ratio of 0.154, the yield load of specimens with a rise‐span ratio of 0.207 and 0.26 is increased by 50.8% and 61.5%, and the ultimate bearing capacity is increased by 42.7% and 68.3%, respectively. The larger the rise‐span ratio, the greater the yield load and ultimate bearing capacity of the specimen and the stronger the deformation resistance of circular arch. The numerical simulation on the bending resistance process of circular arch was performed by ABAQUS to present the compression failure process of steel tube and core concrete. The simulation results are in good agreement with the experimental results. The experimental and simulation results show that the circular arch first yields at the inner side of the arch foot, and the curvature of different positions of the specimen is no longer consistent. When the ultimate bearing capacity is reached, the steel pipe at the arch foot obviously heaves, and the hooping effect of the steel pipe on the concrete is invalid. Based on the above research results, a closed composite support scheme of “bolt mesh shotcrete + vertical elliptical CFST support + steel fiber concrete shotcrete layer + reinforced anchor cable” was proposed for the extremely soft rock roadway and successfully applied in the Qingshuiying coal mine.

Preliminary Design and Cross-Sectional Form Study of Closed-Type Concrete-Filled Steel Tube Support for Traffic Tunnel

In view of the structural form and common construction methods of traffic tunnels, the bearing performance of the closed-type CFST support designed for traffic tunnels is studied. The closed-type CFST support, which consist of a CFST girder with external shotcrete, is improved from the CFST support used in mine roadways. The reasonable cross-sectional form of closed-type CFST support is analyzed by the FEM. The closed-type CFST support is mainly composed of CFST arches, a shotcrete layer, sleeves, and blind flanges. The post-buckling analysis of the closed-type CFST circular arch members using circular-shaped, rectangular-shaped, triangular-shaped, and trapezoidal-shaped steel tubes is implemented. The result shows that the closed-type CFST support has better performance than the traditional tunnel support. The study also found that for closed-type CFST support, the triangular-shaped steel tube section has the highest bearing capacity, stiffness, and steel utilization rate, which is the preferred cross-sectional form. The bearing capacity of the circular-shaped steel tube section is acceptable. Moreover, the circular-shaped steel tubes are more convenient to obtain and process, so it is also an optional cross-sectional form. The square-shaped and trapezoidal-shaped steel tube sections have neither performance advantages nor economic efficiency, so these two forms are not recommended.

Analysis on deformation and structural safety of a novel concrete-filled steel tube support system in loess tunnel

Because the conventional support system has its own limitations, it is hard to stabilize the surrounding soil which frequently causes the tunnel damage in loess area. Therefore, there has been aroused a great concern for controlling the large deformation during loess tunnel construction. Based on a successful application of the concrete-filled steel tube (CFST) in mining engineering, a novel support type of CFST support system is proposed in this article. The new support system highlights to strengthen the primary lining and to improve the stress distribution between primary and secondary lining. The convergence confinement method and finite element analysis were adopted to investigate the performance of CFST support system and conventional support system, respectively. The results showed that CFST support system presented a better support performance with higher stiffness and greater bearing capacity compared with the conventional support system. In addition, CFST support system effectively decreased the tunnel deformation and extensively increased the safety reserve of secondary lining during the tunneling process. Also, a parametric study was conducted and included investigations on the inner concrete strength, the thickness of the steel tube and the diameter of the CFST. These results help to improve the loess tunnel design and construction.

Study on Micro-expansive Concrete-Filled Steel Tube Support for Controlling the Stability of Surrounding Rock in Deep Roadway

The overall supporting capacity of ordinary concrete-filled steel tube support (CFSTS) can be decreased due to the self-shrinkage of concrete and the cracks of hardened concrete. The micro-expansive CFSTS is put forward in this paper. Firstly, the optimum proportion of micro-expansion concrete was determined by concrete strength testing. Then, the deformation of micro-expansion CFSTS and ordinary CFSTS under the same load w studied by numerical simulation. Finally, the micro-expansion CFSTS and ordinary CFSTS were applied to the roadway respectively. The results show: The expansive agent content and water reducer content is 11 and 0.5% in the optimum proportion of micro-expansive concrete, respectively. Under the same load, the deformation of the ordinary CFSTS was much larger than that of the micro-expansion CFSTS. The deformations of roof–floor and two sides of roadway supported by the micro-expansion CFSTS were obviously smaller than that of roadway supported by the ordinary CFSTS. The micro-expansion CFSTS has stronger supporting capacity than ordinary CFSTS.

Experimental Research on Propagation Evolution with Rock-Like Cracks of the CFST Short Columns

To accurately grasp the failure mechanism of surrounding rock in Nanguan deep coal mines, and improve the ability of the concrete filled steel tube support effectively. First, the large size specimens made by rock-like material were compressed under different biaxial loading rates and different intermediate principal stress, meanwhile, the acoustic emission (AE) were used to characterise the crack propagation of the target specimens. In addition, the crack propagation and peeling accurately in the whole progress of uniaxial compression experiment in micro aspects were simulated by using ABAQUS software with cohesive elements in three-dimensional. Finally, the effect of different biaxial loading rates and different intermediate principal stress on crack evolution in large size specimens was analyzed together with the SAEU2S real-time monitoring system of AE behavior characteristics of these specimens. Experimental results clearly indicate that the trend of AE characteristics showed obvious stages when the stress changed by true triaxial testing machine and the rock failure process can be reflected significantly, which proved the efficiency of the proposed cohesive element in ABAQUS.

R&D and Application of Curved D-Shape Concrete-Filled Steel Tube Support in Roadway Support

The concrete-filled steel tube support (CFSTS) has been proposed as a new passive support form for controlling the stability of surrounding rock in underground structures, especially for the case of high ground stress. In order to improve the application of the CFSTS in the high stress soft rock roadway, this paper made a comparison between the commonly used U36 steel support and the CFSTS, and the advantages of the CFSTS were determined by theoretical calculation; By using the numerical simulation to optimize the ordinary CFSTS, the D-shape concrete-filled steel tube support (D-CFSTS) was designed, then the compression analysis was carried out; Based on the engineering background of the Pingdingshan ten mines, the D-CFSTS was applied to the support of the soft rock roadway. The results show: The supporting force of the CFSTS is far greater than that of the U-steel support. Under the same load, the deformation of the D-CFSTS is smaller than that of the circular CFSTS, especially D-CFSTS is more suitable for the deep roadway where the horizontal stress is greater than the vertical stress. In the Pingdingshan ten mines, the U-steel support was damaged prematurely, but the D-CFSTS had good effect and could maintain long-term stability.

Design Research and Application of D-shape Expansive Concrete-filled Steel Tube Supports in Roadway Support

In order to perfect the application of concrete-filled steel tube support (CFSTS) in roadway support, aiming at the shortcomings of the existing common CFSTS, this paper put forward the D-shape expansive concrete-filled steel tube support (D-ECFSTS). Firstly, this article uses the numerical simulation to carry on the optimization of circular steel tube, designs the D-shape steel tube, and carries on the comparative analysis of D-shape concrete-filled steel tube support (D-CFSTS) and circular concrete-filled steel tube support (CFSTS). Then, the scheme of expansive concrete is put forward, and the ratio of expansive concrete is tested by the test method. Finally, the D-ECFSTS was made by D-CFSTS and expansive concrete, then used in roadway support. The results show: The deformation of D-CFSTS is much smaller than that of circular CFSTS under the same load; The best ratio of expansive concrete includes that the ratio of cement, sand, gravel is 1:1.31:2.65, water cement ratio is 0.41, expansion agent ratio is 11% and water-reducing agent ratio is 0.5%; In the support of Pingdingshan coal mine roadway, the supporting effect of D-ECFSTS is much better than that of U36 support. So, D-ECFSTS is a good roadway support method.

Experiment and Application Study on the Load-Bearing Properties of Shallow Arch Circular Concrete Filled Steel Tube Support

Shallow arch circular concrete filled steel tube support has a good load-bearing capacity, which is used in soft rock roadway supporting to solve the problem of supporting instability and to reduce the amount of anti-invert excavation. In this paper, concrete filled steel tube supports of Φ168 ×6 are designed according to shallow arch circular concrete filled steel tube structures and their load-displacement curves, ultimate bearing capacity and support failure mode are especially tested in experiment. This shallow arch circular concrete filled steel tube support is also applied in very soft rock roadway supporting of No. 1 mine well of Chaganzhuoer in Xilinhot, Inner Mongolia and proved to be of good supporting effect. The shallow arch circular concrete filled steel tube support is of higher load-bearing capacity and of outstanding advantages in solving extremely soft rock roadway supporting problems, as is proved in both theoretical test and application.

Bearing Performance Test Research of Shallow Arch Circular Concrete Filled Steel Tube Support

Concrete filled steel tube Support has a good load-bearing capacity, in this paper, shallow arch circular concrete filled steel tube support was designed, two kinds supports of Φ194×8 and Φ168×6 are to experiment according to shallow arch circular steel concrete structures and their load-displacement curves, ultimate bearing capacity and support failure mode are especially tested in experiment.

Analysis of circular concrete-filled steel tube (CFT) support in high ground stress conditions

Concrete-filled steel tubular (CFT) support has been proposed as a new passive support form for controlling the stability of surrounding rock in underground structures, especially for the case of high ground stress. This paper presents a numerical study on the mechanical performance of CFT support. A plastic damage model is used for the concrete and two interface models are adopted to describe the behaviors between the concrete and the steel tube. The feasibility and accuracy of the numerical method are verified by comparing the calculated results with the test observations. The interface behaviors of CFT support has an important influence on its mechanical performance and the friction coefficient of 0.4 is proposed. The results indicate that the load–displacement response of the CFT support could be generally divided into three stages, elastic, elastic–plastic and plastic stages and the CFT support exhibits a stable deformability and never loses its load capacity in a sudden manner. The mechanical performance of the CFT support increases by increasing the concrete strength and the steel ratio; however, the load capacity decreases as the support radius increases.

Research on Supporting Theory of Pressure-Bearing Ring and Yield Supporting Technology in Extremely Soft Rock Roadway

The soft rock roadway is classified by uniaxial compressive strength of rock and water-physical properties, which includes hard surrounding rock in deep mine, soft surrounding rock, and extremely soft surrounding rock. Aimed to the situation of being hard to support the extremely soft rock roadway, with combination of the specific project of return airway crossheading roadway of sea area NO.2 mining district in Beizao coal mine, a compound roadway supporting technology based on the concrete-filled steel tube support, reinforced concrete lining, with combination of yield supporting technology was used for this specific project, for which the mechanical model of the pressure-bearing ring structure was analyzed and calculated by using fixed-end arch theory in structural mechanics and Lame formula in Elastic theory. The field test results showed that this new compound roadway supporting technology was an ideal method to support the extremely soft rock roadway, which could control the deformation of roadway and realize the stability of roadway, effectively.

Research on Mechanical Property and Economic Effect of Contractible Concrete Filled Steel Tube Support

The finite models of U-steel support, grid steel frame, hollow steel tube support and concrete filled steel tube support were established, of which mechanical property and influencing factor such as bearing capacity, support effect etc. was analyzed. Comparative analysis of economic benefit was carried out through research of material dosage and support effect index. The contractible joint for concrete filled steel tube was designed, and their mechanical characteristic was analyzed through test. The results show that the supporting performance of concrete filled steel tube support is related to confinement coefficient. Compared with traditional support, the concrete filled steel tube support has high bearing capacity, intensive later strength, good ductility, various standards and well economic benefits, and in conjunction with contractible joint, it is able to implement functions of quantitatively increasing resistance and yielding. Properly designed through optimization analysis on associated effects, the concrete filled steel tube support can meet supporting demand of deep soft rock and joint broken rock.

Supporting Effect and Economic Benefit Analysis on New Type Concrete-Filled Steel Tube Supports

The finite element contrast model such as concrete filled steel tube support, U-steel support and hollow steel tube support were established with ANSYS software, combining with engineering practice and relative design scheme of concrete filled steel tube test, respectively analysis their influencing factors and mechanical properties such as support effect, bearing capacity and so on. The economic benefit of each support was been analysised by comprehensive comparison of the material using condition and mechanical performance. The results show that, comparing with traditional U-steel support, retractable concrete filled steel tube support is a new style support with high bearing capacity, a large variety of sizes, higher economic benefit, and hence fit to support the deep soft rock broken jointed rock mass.