Floor Reinforcement Research Articles

Numerical studies of floor heave control by the rock bolts reinforcement technology in retained gob-side gateroad

The effectiveness of modified rock bolts reinforcement technology for floor heave control in gob-side entry retaining was studied in this paper. A finite-element numerical simulation was used to analyse stress-strain state of surrounding rocks before and after immediate floor reinforcement with six floor support schemes. It was found that after immediate floor reinforcement with rock bolts with diameter 32 mm and 96 mm, floor heave in retained gob-side gateroad reduces by 2.94 – 3.6 times respectively. The modification of rock bolt reinforcement scheme by the additional installation of piles in the entry corners was proposed. Piles installation significantly reduces the zone of horizontal and vertical post-peak strains in the gateroad floor. The best variant among compared ones is a floor support scheme with two corner piles, 1 m and 2 m long. With this scheme, floor heave decreases by 3.05 times. The comparison of the materials costs of the floor support schemes were performed. As a result, the most effective floor support scheme was proposed and prospects for the further progress of floor reinforcing technologies were outlined.

Prefabricated steel-concrete composite cross joints with concrete slab: Parameter analysis and theoretical study

Nowadays, many researchers are investigating prefabricated reinforced concrete composite structural systems due to their ability to achieve the double carbon goal, which aligns with the rapid development in the construction industry. This study proposes prefabricated steel–concrete composite joints with concrete slabs, termed prefabricated composite beam joints (PCBJs). Based on existing experiments, a three-dimensional solid model of PCBJs was developed using ABAQUS. From this model, the research evaluated the influence of axial compression ratio (n), floor slab width (w), floor thickness (t), and floor reinforcement ratio (ρ) on the hysteretic behavior of PCBJs, then examined the suitability of the bearing capacity calculation methods from JGJ 138-2016 and ANSI/AISC 360-16 for PCBJs. The results indicated that n and w significantly impact the hysteresis performance of PCBJs, whereas the influence of t and pis relatively small. When n exceeds 0.4, the larger the n, the worse the joint's plastic rotation ability. The calculation method for the flexural bearing capacity presented in the JGJ 138-2016 and the ANSI/AISC 360-16 are highly conservative. The modified formula for determining the flexural bearing capacity of composite beams considers gravity's second-order effect. These calculation outcomes align closely with the FEM results.

Analysis of mechanical performance of modular steel-concrete composite joints considering floor slab composite effects

This study establishes and verifies the finite element models (FEM) of MSCCJs to analyze the mechanical performance of modular steel–concrete composite joints (MSCCJs) under monotonic static load without considering the floor slab composite effect (FSCE). Subsequently, 12 MSCCJ models incorporating the FSCE are constructed using ABAQUS. The study evaluates the effects of varying column axial compression ratios (n = 0.15, 0.25, 0.4, 0.6), floor width (w = 800, 1200 mm), floor thickness (t = 90, 110, 120 mm), and floor reinforcement ratio (r = 6 %, 8 %, 12 %) on the bending moment, initial stiffness (k0), ductility, and stress transfer of the joints. The results indicated that as n increases, the shear stress concentration in the joint core module (JCM) and the steel framework at the lower column end become more pronounced. Concurrently, the bearing moment and k0 of the joint also increase. However, once n surpasses 0.4, the joint's plastic properties diminish upon damage. With an increment in w, the k0 and ductility deformation of the joint remain stable and then decline. At w = 1000 mm, the joint's bearing capacity, stress distribution, and deformation performance reach their optimum. Since it significantly impacts stress distribution, its effect on the joint's mechanical performance is minimal. Lastly, the value of r enhances the ductility of MSCCJs and the stress concentration in the reinforcement. It is advisable to maintain r between 1.1 % and 1.7 %.

Stress-Relief–Anchor-Grouting, a Collaborative Control Technology for Severe Extrusion Floor Heave in a Deep Roadway: A Case Study

Severe extrusion floor heave is the most common type of failure of floors in deep roadways, and it is also a major problem restricting the safe and efficient mining of deep coal resources. In deep roadways, reducing floor stress is an effective means to control floor heave. In this study, the method of creating directional stress-relief zones by constructing stress-relief boreholes is applied; while the stress is released, the path of stress from the ribs transferred to the floor and to the extrusion failure path is cut off, and floor heave control is achieved. Therefore, based on the stress-boundary and rock-mass parameters of the roadway, the control effects of the borehole angle, length, diameter, and row spacing on the extrusion floor heave were studied, and the reasonable thresholds of borehole parameters were shown to ensure the stress-relief effect on the roadway. In addition, the bolt-grouting technology was used to strengthen the floor of the roadway, the broken surrounding rock was modified via grouting consolidation, the support strength of the floor was increased using high-tension bolts (cable), and there was a good floor heave control effect in the field application. On the basis of traditional floor reinforcement, the control effect of stress regulation on floor heave is fully considered in this study, and stress-relief–anchor-grouting, a collaborative control technology for floor heave in deep roadways, is developed. Based on the three factors affecting the stability of deep roadways (stress, lithology, and support), the collaborative prevention and control of severe extrusion floor heave were realized, which provides a new method for deep roadway floor heave control and has good application value.

The Effect of Steel Trusses on the Mechanical Performance of Laminated Precast Slabs

Laminated concrete slabs can deliver desirable structural properties and effectively improve the speed of construction. According to their basic specifications, laminated concrete slabs comprise a 60 mm precast concrete slab and a 70 mm concrete layer cast in situ, with a steel truss bar at a height of 80 mm. This paper studies the effects of the steel truss bar on the mechanical properties of precast slabs. A simple but accurate method is proposed for calculating the stiffness of precast slabs. The test results show that the steel truss bar has a limited effect on the stiffness of the precast slab but will weaken the compression strength of the concrete, resulting in a significant reduction in the ultimate bearing capacity of the precast slab. Further discussions show that eliminating the steel truss bar and appropriately increasing the thickness of the precast slab can effectively increase the stiffness and load-bearing capacity of the precast slab, as well as reduce the consumption of the floor reinforcement by about 26%.

Failure Mechanism and Control Countermeasures for Argillaceous Surrounding Rock of Horsehead Roadway under High Stress.

The argillaceous surrounding rock of a horsehead roadway under high stress conditions is prone to deformation and failure, and the control of its long-term stability is difficult. Based on the engineering practices that control the argillaceous surrounding rock of a horsehead roadway in the return air shaft in the Libi Coal Mine in Shanxi Province, field measurements, laboratory experimentation, numerical simulation, and industrial tests are used to analyze the main influencing factors and mechanism of the deformation and failure of the surrounding rock of the horsehead roadway. We propose principles and countermeasures to control the stability of the horsehead roadway. The main factors of the surrounding rock failure of the horsehead roadway include the poor lithology of argillaceous surrounding rocks, horizontal tectonic stress, the superimposed influence of additional stress from the shaft and construction disturbance, the small thickness of the anchorage layer in the roof, and the insufficient depth of floor reinforcement. The results show that the shaft's presence increases the horizontal stress peak and stress concentration range in the roof, and the plastic zone range. The stress concentration and plastic zones and deformations of the surrounding rock increase significantly with the increase in horizontal tectonic stress. The control principles for the argillaceous surrounding rock of the horsehead roadway include increasing the thickness of the anchorage ring, the floor reinforcement exceeding the minimum depth, and reinforced support in key positions. The key control countermeasures include an innovative prestressed full-length anchorage for the mudstone roof, active and passive reinforcement technology with cables, and a reverse arch for floor reinforcement. The field measurements show that the control of the surrounding rock using the prestressed full-length anchorage of the innovative anchor-grouting device is remarkable.

Prevention of Water Inrushes in Deep Coal Mining over the Ordovician Aquifer: A Case Study in the Wutongzhuang Coal Mine of China

Through field observation and theoretical study, we found that the Hanxing mining area has a typical ternary structure in coal mining under high water pressure of the aquifer. This ternary structure is the Ordovician limestone aquifer-aquiclude including thin limestones-coal seam. Although the aquiclude is considerably thick, there is still a great risk of water burst during mining under water pressure in the deep burial environment. Multidimensional characteristics of floor water inrush in deep mining are summarized in the paper, including water migration upwardly driven by the Ordovician confined water, the planar dispersion of the water inrush channel, the stepped increase of the water inrush intensity, the hysteretic effluent of the water inrush time and the exchange, and adsorption of the water quality. The water inrush mechanism is clarified that the permeability, dilatancy, fracturing, and ascending of the water from the Ordovician limestone aquifer form a planar and divergent flow through the transfer, storage, and transportation of thin limestone aquifers. The corresponding water inrush risk evaluation equation is also proposed. Based on the thickness of the aquiclude, the thickness of the failure zones, and the water inrush coefficient, the floor aquiclude is classified into five categories. While water inrush cannot be completely controlled by the traditional underground floor reinforcement with ultra-thick aquiclude or even zonal grouting, a comprehensive prevention and control concept of the four-dimensional floor water hazard in full time-space domain are proposed. A tridimensional prevention and control model of three-dimensional reticulated exploration, treatment, verification, and supplementation is presented. A full time domain technological quality control process of condition assessment, exploration, remediation, inspection, evaluation, monitoring, and reassurance is formed, and a water disaster prevention method with full time-space tridimensional network in deep coal mining is established. Case study in the Hanxing mining area demonstrates that the proposed methods are highly effective.

Stability assessment of permanent and temporary roadways in process flowchart design

For the stability assessment of underground structures, the authors analyze the mechanisms of deformation, movement and fall in damaged and nonuniform rock mass. Weak floor reinforcement and roof bolt designs are determined to ensure safe and efficient mine operation.

Numerical Analysis of the Water-blocking Performance of a Floor with a Composite Structure under Fluid–solid Coupling

The diversity of geological structure combinations in the coal seam floor makes it difficult to characterize, prevent and control floor water inrush in the Chenghe mining area in the Weibei coalfield, China. Based on a comparative study of the structure of the floor strata and the sedimentary characteristics of the no. 5 coal seam floor in the Chenghe mining area, the floor strata were categorized into four types. Fluid–solid coupling numerical simulation software was used to study floor water-blocking performance. We found that mining failure depth was the shallowest and water-blocking capacity was the best for the “soft-hard-soft” type of floor, followed by two interbeds of soft and hard type floors, while the mining failure depth was the deepest and the water-blocking capacity the worst for the “hard-soft-hard” type of floor. These conclusions were applied to guide the floor grouting reconstruction project at the 22,507 working face in the Dongjiahe coal mine. The “hard-soft-hard” type of floor was transformed into an "interbedded soft and hard" type of floor with a better water-blocking capacity, avoiding blind grouting, reducing grouting costs and the risk of water inrush, and allowing safe mining above the confined aquifer. The research results revealed how floor strata combinations control the water-blocking characteristics of the floor and provides scientific guidance for floor reinforcement and grouting projects.

Designing of Slab-Column Structures Due to Additional Loads

The introduction of Eurocodes in the designing practices led to the change of methodology of the floor reinforcement, particularly for slab-column floors. Until now, the most important decisive factor was the determination and arrangement of reinforcement due to the limit states; any other problems were treated as additional information. At present designers - constructors of reinforcement in slab-column structures have to follow Eurocodes (PN-EN 1990:2004, PN-EN 1991-1-1:2004, PN-EN 1991-1-7:2008) in taking into account first and foremost the following threats accidental loadings and fires, as they influence further stages of the designing process. The article presents the most important design guidelines for slab-column structures due to accidental loads.

Comparing suture with N-Hexyl Cyanoacrylate glue for mesh fixation in inguinal hernia repair, a randomised clinical trial

PurposeInguinal hernia is a common surgical problem and different methods are currently used to repair it. In The Lichtenstein technique, the inguinal floor defect is buttressed with a prosthetic mesh and commonly, sutures are used for mesh fixation. N-Hexyl Cyanoacrylate is a gluelike product that can be used for mesh fixation as a substitute with fewer complications. This study was done for comparing therapeutic outcomes of mesh fixation with suture and N-Hexyl cyanoacrylate glue in inguinal hernia repair with the Lichtenstein method. MethodsIn a two-arm parallel-group randomised controlled trial with blinded patients, 58 hernia cases who were candidates for hernia repair with the Lichtenstein method entered the study and randomly divided into two groups. In the control group, the mesh that was used for inguinal floor reinforcement was fixed with sutures and in the intervention group with N-Hexyl Cyanoacrylate glue. The results including acute and chronic pain, hospital stay, complications, and recurrence rate after one year were compared. ResultsThere was no recurrence. According to the numeric rating scale (NRS), mean postoperative pain (acute pain) was 6.5 and 5.7 points in the suture and N-Hexyl Cyanoacrylate glue groups respectively, with significant difference (P = 0.006). Mean duration of surgery was 73.3 and 64.5 min in the suture and N-Hexyl cyanoacrylate glue groups respectively, with significant difference (P = 0.014). Complications, hospital stay days, and chronic pain did not differ across the groups (P > 0.05). ConclusionMesh fixation with N-Hexyl cyanoacrylate glue in hernia repair with the Lichtenstein method can lower postoperative pain and duration of surgery and this product might be used as a substitute for suture.

Experimental Study on the Basic Properties of a Green New Coal Mine Grouting Reinforcement Material

Waste tires are internationally recognized as hazardous waste. Many waste tires storing in the open air for a long time will not only waste the land resources but also pollute the environment after the incineration. Meanwhile, the cumulative accumulation of fly ash in China has also been one of the largest sources of solid waste in coal mines. Under the action of high winds, the accumulated fly ash forms flying dust, which pollutes the environment and endangers human health. Herein, a new type of grouting material for floor reinforcement was developed based on solid waste products using the waste tire rubber particles and fly ash. Using this new material, disaster accidents such as flooding and casualties caused by the inrush of the floor-confined water due to floor fractures, activation, and expansion in the mining process can be greatly reduced, thereby ensuring the safety of coal mine production. The grout body was prepared using a large amount of fly ash, waste tire rubber particles and clay, and mixing additives. The ratio optimization test, uniaxial compressive strength test, permeability characteristic test, stability test, and microanalysis of mine water environment were performed. From the test results, the macrophysical and chemical properties including optimal mix ratio, compressive strength, permeability coefficient, and stability of mine water environment were obtained. The microstructural properties of the grouts were analyzed using scanning electron microscopy microanalysis methods. Considering the situation of the coal floor and attempting to use as many solid waste products as possible, the optimized proportion that can meet the requirements of low cost, high bonds, and dense filling is as follows: 20% of rubber particles, 65% of fly ash, 15% of clay, and 1% of nanosilica. Furthermore, this study can provide scientific reference for large-scale floor grouting reinforcement and large-scale utilization of solid waste products.

Mechanism of Water Inrush and Controlling Techniques for Fault-Traversing Roadways with Floor Heave Above Highly Confined Aquifers

Floor heave and water inrush accidents are likely in fault-traversing roadways above highly confined aquifers. In this paper, the deflection curve equation for the key floor stratum of a fault-traversing roadway in the Zhaogu no. 2 coal mine was derived based on the cantilever beam model, and the line strain in the failure zone, e, was introduced to characterize the relationship between floor heave and deformation of deep intact rock layers. Then, three- dimensional pre-grouting technology was established for floor reinforcement. Analysis indicated that the rock surrounding the fault-traversing roadway was highly fractured, increasing the risk of water hazards. Numerical UDEC simulations showed that the plastic zone of the roadway was greater due to the faults; the floor heave, in this case, was 2.6 times greater than without faults. However, water pressure applied to the floor had a limited impact on deformation of the surrounding rock. The measured maximum deflection of the stratum was 644 mm, and the line strain e in the failure zone in the floor was 67 mm, which resulted in a difference of 3.5% compared with the modelled results. The apparent resistivity in the grouted areas, observed through comprehensive geophysical explorations, was increased, suggesting that the grouting reinforcement had been successful.

Experimental study on properties of a new type of grouting material for the reinforcement of fractured seam floor

In this paper, a grouting material with low cost and high density was proposed for the reinforcement of large-scale floor cracks. The component screening test, mechanical property test, rheological properties test, and impermeability test were conducted to obtain the strength, rheological properties, and permeability of the new grouting materials. In order to fully understand the physicochemical properties of the new grouting material, a total of 12 sets of test pieces were produced using cement, clay, and fly ash as the main body, and foaming agent as the auxiliary material. Each set of the test pieces had different proportions of ingredients, pores conditions, and auxiliary chemical materials (water reducing agents, defoamers). The test results showed that: (1) The optimal proportion of ingredients for the new grouting material (including 1% foaming agent) was: 40% of cement, 30% of clay, and 30% of fly ash. (2) The optimal amount of fly ash for the new grouting material was 30% and the optimal foaming amount for the new grouting material was 1%. The impermeability of the grouting material was 0.7MPa, which reached Level P6. The new grouting material was suitable for the HB rheology model. (3) The pores were uniformly distributed inside the solidified body of the new grouting material. In the later stage, the strength of the solidified body was stable, and the flow loss was reduced. At present, the corresponding proportion of ingredients and the performance parameters of the new grouting material were tested in the laboratory. In the future, it is necessary to further determine the effect of the grouting material in the reinforcement of the floor crack of the coal seam and to improve the proportion of ingredients for the grouting material in the mine sites.

Study on Time-dependent Viscosity of Slurry and Its Diffusion Model

Floor water disasters have occurred frequently, which can be treated by grouting and reinforcement of floor. The purpose of this paper is to study on time-dependent viscosity of slurry and its diffusion model for guiding grouting and reinforcement engineering by observing of the change of slurry viscosity with time in laboratory. The result showed that the slurry viscosity had an exponential trend with time. A slurry diffusion model based on the time-dependent viscosity of slurry is derived, according to the diffusion model of grouting in horizontal single fracture under hydrostatic condition. These results will provide theoretical basis for grouting process adjustment and regional grouting transformation.

Application of the complex variable function method in solving the floor heave problem of a coal mine entry

With the increase of mining depth in Chinese coal mines, the entry floor heave becomes one of the major engineering problems. This paper has studied the stress and displacement distribution around an entry in Buertai coal mine, China. The mechanism of floor heave is analyzed using the method of complex variable function. The influences of floor mechanical properties, longwall face advance, and mine water on the stability of the floor are then identified. The results show that (1) the floor moves towards the center under the concentration of the tangential stress, resulting in floor heave; (2) the floor stability is mainly influenced by the mechanical properties of the floor and the confining stress from the surrounding rock; and (3) the unnoticeable movement of the floor may be enlarged by the mining activity (face advance) and mine water. The proposed theoretical model is validated by the numerical modeling and the in situ. Good agreements are found between the theoretical analysis and the numerical modeling results and the in situ. It is thus believed that the complex variable function method can be used for analyzing the floor heave problem. Based on the mechanism of floor heave, we divide the control techniques into two categories: creation of a stress-relief entry and floor reinforcement. The techniques were practiced at two Chinese coal mines with good ground control effects.

Improving the robustness of R.C. buildings by the activation of the elasto-plastic catenary behaviour

According to the latest technical standards, the design capacity to survive actions even extraordinary (explosion, impact and consequences of human errors) is left to the owner. Nevertheless, the analysis of some collapses occurred in the last years shows that it is necessary to give sufficient robustness (i.e. ability of a structure to withstand events or consequences of human errors without being damaged to an extent disproportionate to the original cause) to every building. This fact is also confirmed by the possibility to protect human lives in extreme conditions, completely sacrificing the functionality, by simple measures, sometimes regarding detailing, without substantially increasing the cost of a structural system. In this scenario this article aims to propose a simplified numerical approach able to evaluate the amount of floor reinforcement necessary to activate the elasto-plastic catenary behaviour of R.C. floor slabs.

Multiple-iteration springback compensation of tailor welded blanks during stamping forming process

The forming and springback of tailor welded blanks (TWBs) are more complicated than those of conventional sheet metals because of the influence of weld seam. The current study investigated the microstructure and fracture of TWBs through metallographic microscopy and scanning electron microscopy. Tensile tests show that thin and thick materials possess similar mechanical properties. The maximum elongation and yield strength of the TWBs decrease, whereas the tensile strength of the TWBs is larger than that of the base materials. We proposed the use of multiple-iteration springback compensation to improve the accuracy of springback compensation for the TWBs. The simulation of the entire forming processes, which includes drawing, trimming and piercing, as well as springback analysis, was used to explore the stamping forming of the TWBs by automotive floor reinforcement. Forming parameters were optimised in drawing process. In addition, springback calculation was performed to predict the springback of the formed part. Furthermore, multiple-iteration springback compensation was applied to drawing tools and verified by experiments. The experimental results agree with the simulation results.

Seismic risk assessment of low rise RC frame structure

Seismic evaluation and financial risk analysis of typical low rise reinforced concrete frames are performed. The financial risk assessment is determined on the basis of results of incremental dynamic analysis (IDA) of reinforced concrete frames analyzed using nonlinear time history analyses on IDARC platform with a suite of 20 ground motion records used by Vamvatsikos and Cornell (2002) for mid-rise buildings. Three frames were analyzed with capacity design concepts taking into account shear capacity, flexural capacity and contribution from floor reinforcement to beams. Maximum inter-story drift ratios obtained from time-history analyses are plotted against ground motion intensities. Results are statistically interpreted to develop cumulative distribution functions for frames. Fragility curves are plotted for HAZUS damage states of conventional structures. Fragility curves thus drawn are used to estimate the expected annual loss (EAL) of low rise RC frames using quadruple integral formula based on probabilistic financial risk assessment framework.

Application of a combined support system to the weak floor reinforcement in deep underground coal mine

More and more coal mines begin to exploit deep resource, leading to more serious supporting problems. Common supporting measures for shallow roadways can hardly apply to the deep geological conditions, which are mainly reflected by high ground pressure, more broken and weak surrounding rock. This paper takes a winch room in China׳s Gubei coal mine as an example to study a new kind of combined supporting system for weak floor under adverse geological conditions. The stability of the winch room is simulated by FLAC3D. The deformation characteristics and stress distribution of the surrounding rock is obtained. Then, a new kind of combined supporting system as well as monitoring measures for the floor is proposed. A new type of hollow grouting cable which has many advantages is introduced in the supporting system. The results show that the combined supporting system is satisfactory.