Vertical Stress and Deformation Characteristics of Roadside Backfilling Body in Gob-Side Entry for Thick Coal Seams with Different Pre-Split Angles

Retained gob-side entry (RGE) is a significant improvement for fully-mechanized longwall mining. The environment of surrounding rock directly affects its stability. Roadside backfilling body (RBB), a man-made structure in RGE plays the most important role in successful application of the technology. In the field, however, the vertical deformation of RBB is large during the panel extraction, which leads to malfunction of the RGE. In order to solve the problem, roof pre-split is employed. According to geological conditions as well as the physical modeling of roof behavior and deformation of surrounding rock, the support resistance of RBB is calculated. The environment of surrounding rock, vertical stress and vertical deformation of the RBB in the RGE with different roof pre-split angles are analyzed using FLAC3D software. With the increase of roof pre-split angle, the vertical stresses both in the coal wall and RBB are minimum, and the vertical deformation of RBB also decreases from 110.51 mm to 6.1 mm. Therefore, based on the results of numerical modeling and field observation, roof pre-split angle of 90° is more beneficial to the maintenance of the RGE

Effect of Water on Mechanical Properties and Fracture Evolution of Fissured Sandstone under Uniaxial Compression: Insights from Experimental Investigation

AbstractPreexisting discontinuities and the water affect the fracture evolution process as well as the rock stability the most extensively. To ensure operational safety, the effects of water on the mechanical properties of fissured rock masses must be understood well. In this study, a series of uniaxial compressive tests is conducted on both dry and saturated fissured specimens with varying fissure angles. Real-time acoustic emission and digital image correlation are applied to monitor the fracture evolution process. The failure mode is investigated by identifying the types of cracks present in the ultimate failure forms of the fissured specimens. The results indicate that (1) the saturated and dry specimens exhibit significantly different strengths and stiffnesses, wherein the saturated specimens exhibit weaker strength by 25.64%–32.59% and a lower elastic modulus by 20.30%–29.22%. (2) The fissure angle and water jointly control the failure mode of fissured sandstone. (3) The observed fracture evolution processes can be classified into six distinct stages to facilitate the understanding of rock failure mechanisms. (4) The presence of water accelerates the nucleation of microcracks at the tips of the prefabricated fissures, enlarges the range of microcrack coalescence, and facilitates the emergence of unstable cracks owing to an increase in pore water pressure and a decrease in the friction resistance of crack surfaces

Fracture propagation law of hydraulic fracturing of rock-like materials based on discrete element method

Hydraulic fracturing is an important technical means to relieve the pressure of coal seam roof. Better understanding of fracture propagation mechanism is of great significance to the safe mining of coal seam. In order to further explore the law of hydraulic fracture propagation, aiming at rock-like specimens commonly used in the laboratory, MatDEM, a particle discrete element numerical simulation software, was used to establish a two-dimensional discrete element numerical model of hydraulic fracturing, and various hydraulic fracturing tests with different injection pressure increments were carried out. The effect of injection pressure increment on the propagation of hydraulic fractures was studied, and the mechanism of model initiation was revealed. The law of fracture generation and propagation was analyzed from mesoscale, and the propagation characteristics of hydraulic fractures were discussed. The results show that ① the effect of injection pressure increment on the model initiation pressure and initiation time presents an opposite trend. With the increase of injection pressure, the increase trend of initiation pressure is slow and gradually approaches to 5.6 MPa. The initiation time decreases with the increase of injection pressure, and the decreasing trend slows down gradually. ② The cumulative number of fractures increases exponentially with time. The hydraulic fracturing process can be divided into four stages (Ⅰ−Ⅳ): no fracture stage, slow fracture growth stage, steady fracture growth stage and rapid fracture growth stage, which correspond to the pre-crack initiation, pre-crack formation, primary fracture propagation and secondary fracture propagation processes respectively. As the injection pressure increment increases, the durations of stage Ⅰ, Ⅱ and Ⅲ decrease, while the duration of stage Ⅳ increases in a fluctuating manner. The number of cracks in each stage is the highest in stage Ⅳ, followed by stage Ⅲ and stage Ⅱ. ③ As the injection pressure increment increases, the number of secondary fractures increases from 8 to 16, and the growth rate of fractures gradually slows down before the stage Ⅲ, and increases rapidly after the stage Ⅳ. When the injection pressure increment increases from 0.03 MPa to 0.70 MPa, the final fracture length increases by 1.79 times. ④ The internal energy of the model increases with the increase of the injection pressure increment, and the energy input speed gradually becomes faster. After the model initiation, high-pressure water forms stress concentration at the crack tip, which promotes the crack to continue to extend. At higher injection pressure increment, the fracture propagation speed becomes faster, and the particle displacement decreases gradually from the pressure hole to the outside of the model. The increment of injection pressure makes the secondary fracture forming position close to the pressure hole, which inhibits the formation and expansion of the primary fracture and promotes the formation and expansion of the secondary fracture. All fracture types are tensile fractures

STATIC ANALYSIS AND FREE VIBRATION ANALYSIS OF THE PYRAMIDAL LATTICE SANDWICH STRUCTURE BASED ON LAYERWISE/SOLID-ELEMENTS METHOD

The layerwise/solid element method（ LW/SE） was used to study the static and free vibration problems of lattice sandwich structure under different boundary conditions. First,the layerwise theory was used to analyze the behavior of the shell of composite face sheets,and the three-dimensional solid elements were employed to obtain the governing equations of the core. And then,based on the governing equations of the face sheets and core,the finial governing equation of sandwich structure was assembled by using the compatibility conditions,which was used to ensure the compatibility of displacements at the interface between face sheets and core. The numerical results of the proposed method were compared with those obtained from the 3 D elastic model developed in finite element software,and good agreements are achieved. Furthermore,a series of numerical analyses are conducted to further explore the effects of the thickness of the face sheets on the static responses and free vibration responses of composite lattice sandwich structures

STUDY ON FREE VIBRATION ANALYSIS FOR HONEYCOMB SANDWICH STRUCTURE WITH DOUBLE CORES

The free vibration problem of the honeycomb sandwich structure with double cores was studied based on the Layerwise/Solid-Elements（ LW/SE） and Fixed-interface Modal Synthesis Technique（ FMST） of the dynamic substructure method. The governing equation and the total modal space of the honeycomb sandwich structure were assembled based on LW/SE and FMST,respectively,and the final governing equation on the basis of the modal spaces was assembled based on the governing equation and the total modal space. This method obtains the natural frequency of the honeycomb sandwich structure with double cores accurately and reduces memory requirement. The numerical results of the method are compared with those obtained by the 3D solid finite element,and good agreements are achieved

Research on abutment stress distribution of roof-cutting coalface: numerical simulation and field measurement

Abstract During the processing of deep mining, revealing the distribution of abutment pressure is significant for controlling stability of the entry. In this study, the abutment pressure distribution of roof-cutting coalface was investigated by FLAC3D and self-developed flexible detection unit (FDU). In the numerical simulation, the double-yield model was built to analyze the goaf abutment pressure under the fracturing roofs to maintain entry (FRME). Compared with the non-fracturing side, the peak value of the advanced abutment pressure on the fracturing side is reduced by 19.29% on average, the influence range (span) increases by 30.78% and the distance between the peak value and the working face increases by 66.7%. The goaf abutment pressure within 23m near the cutting side is significantly higher than other areas along the dip. The FDU was employed in the coalface to record the change of advanced abutment stress. And the field measured results are in well agreement with the numerical results

Which Stage of ADPKD Is More Appropriate for Decortication? A Retrospective Study of 137 Patients from a Single Clinic.

To study retrospectively the efficacy of decortication in patients with different stages of ADPKD and to determine which stage for decortication is more appropriate.We analyzed 137 patients with ADPKD from 2001 to 2010. All patients were divided into three stages. A total of 70 patients underwent decortication, and we studied intraoperative indicators and postoperative indicators at 1 and 3 years follow-up.In 70 patients who underwent decortication, significant differences were observed in operative duration and bleeding volume between patients with stage I and II ADPKD (P<0.05), but no significant differences were observed in intestinal recovery time, pain medication dose, and the days of postoperative hospitalization (P > 0.05). The total complication occurrence rate was significantly different between them (P < 0.05). The serum creatinine (Scr) levels in patients with stage I ADPKD were within normal limits 1 and 3 years postoperatively and did not differ significantly (P > 0.05). Scr levels were significantly decreased in patients with stage II ADPKD in the 1st postoperative year (P < 0.05), but these were not significant differences in the 3rd postoperative year (P > 0.05). In the 1st postoperative year, VAS value, blood pressure and renal volume significantly differed (P < 0.05). However, no significant differences were observed 3 years later (P > 0.05).Decortication in patients with stage I ADPKD can alleviate back pain symptoms and decrease blood pressure within 1 year, but the long-term efficacy is not ideal. Scr levels can be maintained within normal limits, suggesting that decortication does not lead to deterioration of renal function. For patients with stage II ADPKD, decortication can significantly improve renal function over the short term. However, after 3 years, renal function returns to the preoperative level, and surgical difficulties and complications also increase

Influence of Proteolysis on the Binding Capacity of Flavor Compounds to Myofibrillar Proteins

Proteolysis occurs extensively during postmortem aging, enzymatic tenderization and fermentation of meat products, whereas less is understood regarding how proteolysis affects meat flavor. Myofibrillar proteins (MP) were extracted from beef longissimus dorsi muscle and subsequently treated with three commercial proteases. The effect of proteolysis on the interactions between the treated MP and butyraldehyde, 2-pentanone, octanal and 2-octanone was investigated. The progress of proteolysis increased the degree of hydrolysis (DH) and the surface hydrophobicity but decreased the turbidity and particle size. Fluorescence-quenching analysis results indicated that the enzymatic treatment generally increased the quenching constant (Ksv) between the treated MP and ketones but decreased the Ksv between the treated MP and aldehydes, and the papain treatment changed the Ksv value to a larger degree than treatment with proteinase K and bromelain. The adsorption assay showed that the proteinase K treatment largely increased the adsorption capacity of the MP to octanal (by 15.8&ndash;19.3%), whereas the bromelain treatment significantly reduced the adsorption capacity of the treated MP to butyraldehyde (by 6.0&ndash;7.9%) and 2-pentanone (by 9.7&ndash;11.9%). A correlation analysis demonstrated a strong positive correlation (0.859, p &lt; 0.05) between the DH of the MP and the adsorption ability of the treated MP to octanal. This study highlighted the significant but complex influence of proteolysis on MP binding capacity to flavor compounds