Crack Development Characteristics Research Articles

Experimental study on the crack propagation and acoustic emission characteristics of notched rock beams under post-peak cyclic loading

Rocks in nature are often subjected to cyclic loads caused by earthquakes, which still exist after the rock reaches its maximum bearing capacity. To obtain the crack propagation characteristics of rocks under post-peak cyclic loading, notched granite beams were tested by means of three-point bending test method combined with digital image correlation (DIC) and acoustic emission (AE) technology. The horizontal strain, horizontal displacement and crack development characteristics of rock surface were obtained by DIC. Correspondingly, the acoustic emission characteristics, such as ring count and b value, were also used to monitor and analyze the development of micro cracks and macro cracks. Our results show that the strain concentration area accumulates and propagates along both sides of the crack. In the initial post-peak cycle stage, the effective crack length first appears the characteristics of reciprocating increase, then increases rapidly until it is stable. While the crack opening displacement increases reciprocally with each cyclic loading and unloading. From the AE characteristics, the ringing counts increases gradually with the loading and a significant counts rise occurs at unloading stage. For the b value, it also shows a cyclic change with the post-peak cyclic loading. The amplitude of b value gradually increases to the maximum and then decreases to a stable level with the increase of the number of post-peak cycles. This indicates that rock fracture crack propagation undergoes a reciprocating, rapid and gradual stabilization process with the increase of cycle times under post-peak cycling.

Control of the Chamber in Extra‐Thick Coal Seam Based on Fracture Characteristics of Coal Rock and Mass

As the development characteristics of cracks of the chamber are closely related to the bolt and cable anchoring parameters, the original rock stress of the surrounding rock, and fracture degree, this paper proposes the control method for chamber in extra‐thick coal seam by the crack development characteristics. Based on the numerical model analysis, the chamber generates a large amount of shear cracks. Then, these cracks further extend and expand. When the cracks penetrate each other, the chamber bearing capacity decreases sharply, and the corresponding displacement also increases significantly. Based on the above rules, a chamber control method by high‐strength anchor bolts and grouting reinforcement is proposed to improve the rock shear strength. By optimizing the anchor bolt parameters and grouting parameters, such as spacing, length, and the grouting pressure, the cracks are significantly reduced and the cracks are prevented from penetrating. Finally, an industrial test was conducted in the chamber at Datong Coal Group, and the chamber deformation was well controlled.

Experimental Investigation on Crack Development Characteristics in Shallow Coal Seam Mining in China

The development of cracks in mining is the scientific basis for the safety and environmental exploitation of shallow multiple-seam. According to the “thickness of coal seam, interactive distance, and buried depth,” four mining coal mines are selected in Shen Fu-Dong Sheng coalfield (SFDSC). To research the mining conditions of shallow coal seam under different base-load ratio mining conditions and different working faces by the physics simulation and in-sit measurement, the key roof caves are sketched by different colors. This study shows that the typical shallow coal seams in the thin overlying bedrock and thick loose sand layer (LSL) as well as the development of the setup entry cracks (SEC) is dominated by LSL arch damage. The surface cracks are almost directly above the setup entry. The flat seam mining and the SEC development is dominated by parabolic type. The surface cracks are located inside the setup entry. With the mining height increased typically in a shallow coal seam, the rate of crack development and the extent of damaged area increased significantly. The SEC and boundary cracks are fixed. The dynamic periodic cracks (DPC) show the ability of the strata to self-repair. During the multiple-seam mining, the above three kinds of cracks have the phenomenon of activation and development. Through the reasonable coal pillar distance arrangement, the development of boundary cracks can be effectively controlled and the relatively uniform surface settlement and crack closure can be achieved. The purpose of reducing damage mining can also be achieved. Furthermore, it provides scientific support for the green mining in the shallow coal seam.

Rock-breaking mechanism and experimental analysis of confined blasting of borehole surrounding rock

The rock-breaking mechanism and effect of confined blasting were analysed by blasting and impact dynamic mechanics, fluid dynamic mechanics, fracture mechanics as well as blasting experiment. The results showed that the fracturing of surrounding rock in confined blasting condition is the result of coaction of rock pre-cracking by shock wave and stress wave and the continuing expanding crack-enhancement of confined medium, and the model of crack development of borehole surrounding rock in confined blasting condition was established. This study acquired the damage range of surrounding rock under the action of shock wave and stress wave, as well as the crack development characteristics of surrounding rock after the wedge-in confined medium into the crack space. Deep-hole confined blasting experiment on large rock showed that the high-efficient utilisation of in-hole explosive was achieved and the safety of rock blasting operation was ensured. Safe static rock-breaking under the action of high-efficient explosive blasting was achieved as well as the unification of super dynamic load of explosive blasting and static rock-breaking of water medium.

Load capacity and crack development characteristics of HCWA–DSF high strength mortar ferrocement panels in flexure

In accordance to current technological advancements in the field of sustainable construction materials, high calcium wood ash (HCWA), a by-product from the biomass power generation sector, has been established as a highly viable supplementary binder material for the production of concrete and mortar. The research study was performed with the aim to investigate the effects of the inclusion of HCWA as a supplementary binder material. These effects were measured on the structural parametric response, crack development behaviour and ultimate failure mode of fabricated ferrocement flexural panels using HCWA mortar. Ferrocement flexural panels were subjected to four point flexural test till ultimate failure throughout the study. Mortars used in the fabrication of the ferrocement panels contained varying HCWA cement replacement levels from 2% to 10% by total binder weight. At the same time, all other experimental parameters of the ferrocement panels remained constant. The experimental results of 21 ferrocement panels indicated that the fabricated ferrocement panels fabricated with HCWA content up to 4% by binder weight exhibited superior structural performance as compared to the control ferrocement panels with no HCWA content. Structural performance parameters used for comparisons were the first crack load, ultimate failure load, deflection of energy absorbed to trigger ultimate failure, flexure stress–deflection response and flexure stress–concrete strain response. The number of cracks developed at failure was also taken into account with measurements of average crack width, crack spacing and failure mode. The inclusion of HCWA in the mortar within the ferrocement panels not only enhances the engineering performance of the panels but also contributes to potential binder material savings and resource conservation.

Different Design Parameters Analysis of Unbonded Precast Reinforced Concrete Frame Structure

This thesis studies deeply the crack development characteristics, failure pattern, hysteresis curve and the displacement ductility of unbonded precast reinforced concrete frame, by analyzing one unbonded precast reinforced concrete frame under low reversed cyclic load test. We build a model using finite element analysis software to the test piece model analysis, the analysis result agree well with the experimental results. So we build finite element analysis models with different design parameters to analysis the impaction for seismic performance. Numerical analysis results can provide a scientific reference for the unbonded precast frame structure design.

Different Design Parameters Analysis of Unbonded Precast Reinforced Concrete Frame Structure

This thesis studies deeply the crack development characteristics, failure pattern, hysteresis curve and the displacement ductility of unbonded precast reinforced concrete frame, by analyzing one unbonded precast reinforced concrete frame under low reversed cyclic load test. We build a model using finite element analysis software to the test piece model analysis, the analysis result agree well with the experimental results. So we build finite element analysis models with different design parameters to analysis the impaction for seismic performance. Numerical analysis results can provide a scientific reference for the unbonded precast frame structure design.

Research on Seismic Performance of Prestressed Precast Reinforced Concrete Intelligent Structure

This thesis studies deeply the crack development characteristics, failure pattern, hysteresis curve and the displacement ductility of this new prestressed precast reinforced concrete intelligent structure, by analyzing one prestressed precast reinforced concrete frame under low reversed cyclic load test. Prestressed precast reinforced concrete frame is a new assembly architecture intelligent structure. We build a model using finite element analysis software to the test piece model analysis, the analysis result agree well with the experimental results. Experimental studies indicate that this new prestressed precast reinforced concrete intelligent structure has a good seismic performance. This prestressed precast reinforced concrete frame is a new kind of structural system complying with the development of architectural industrialization, which is worthy of popularization and application in the earthquake area.

Experimental Research on Seismic Behavior of Unbonded Precast Reinforced Concrete Frame

Unbonded precast reinforced concrete frame is a new assembly architecture structure. This thesis studies deeply the crack development characteristics, failure pattern, hysteresis curve and the displacement ductility of unbonded precast reinforced concrete frame, by analyzing one unbonded precast reinforced concrete frame under low reversed cyclic load test. We build a model using finite element analysis software to the test piece model analysis, the analysis result consistent with the experimental results. Experimental studies indicate that assembly of prestressed reinforced concrete frame structure has a good seismic performance. This unbonded precast reinforced concrete frame is a new kind of structural system complying with the development of architectural engineering, which is useful in application in the earthquake area.

Carbon Fiber Cloth in Structural Engineering Application

The frame beam end uses the carbon fiber cloth restraint, then uses the steel stranded wire assembly,which is a new assembly architecture structure. This thesis studies deeply the crack development characteristics, failure pattern, hysteresis curve and the displacement ductility of prestressed precast reinforced concrete frame, by analyzing one prestressed precast reinforced concrete frame under low reversed cyclic load test. We build a model using finite element analysis software to the test piece model analysis, the analysis result agree well with the experimental results. Experimental studies indicate that assembly of prestressed reinforced concrete frame structure has a good seismic performance. This prestressed precast reinforced concrete frame is a new kind of structural system complying with the development of architectural industrialization, which is worthy of popularization and application in the earthquake area.