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After excavation of tunnels in interbedded surrounding rock, accidents such as rock peeling and arch crown collapse are prone to happen. In response to this issue, we first established an analysis model for the excavation of the interbedded surrounding rock tunnel through theoretical analysis, proposed corresponding failure criteria, and analyzed the reasons for the easy failure of the interbedded tunnel support structure based on the concept of principal stress difference. We also created interfaces in FLAC3D (version 6.0) software to restore the actual interbedded interface, verifying the effectiveness of principal stress difference in analyzing the deformation characteristics of the tunnel. Then, the instability forms of the interbedded surrounding rock tunnel were divided into two types, and effective support methods for the corresponding instability forms were proposed. Finally, based on the analysis results of the study, support was provided for the collapsed tunnel on site. A grouting large pipe shed was put to innovative use to support the tunnel arch waist, stabilizing the surrounding rock that is prone to shear slip and fracture at the upper part of the arch waist. The results indicate that the surrounding rock control effect is good. This study has a good reference value for on-site rapid construction and support design, and is of great significance for the instability prevention and control of interbedded surrounding rock tunnels. [ABSTRACT FROM AUTHOR]

The mining stress formed in the surrounding rock after coal seam mining is the root cause of the damage and fracture of the stope surrounding rock. In order to study the evolution characteristics of mining stress and the fracture process of overlying strata on the mining face, a numerical model was established to simulate the evolution law of stress field and fracture field in the mining process of the working face by taking the 40101 mining face of Gaoliang Coal Mine as an example. The results show that the relationship between rock collapse and failure can be judged by using Mohr-Coulomb criterion to analyze the variation law of the difference between maximum and minimum principal stresses. The correctness of the time-varying evolution of fracture field and stress field in working face mining can be verified by comparing the numerical simulation results with the field measured results.

To study the layout of the short-distance thick underlying coal seam stopping roadway in Yanzishan Mine, a mechanical model of the remaining coal pillars in 4216 and 4218 of No. 4 sides of the overlying coal seam through theoretical calculation, and clarified the transfer law of the principal stress difference of the remaining coal pillars in the floor. The author simulated the distribution characteristics of vertical stress, horizontal stress and difference between principal stresses at different depths of floor by using FLAC3D numerical software, and analyzeds the principal stress difference and the stress reducing area roadway within the reasonable factors that influence of the reasonable inner distance. The results show that the roadway layout should avoid the peakand be in the environment of principal stress difference. When the horizontal distance of the lower coal seam is more than 30 m from the edge of the overlying coal pillar, the vertical stress is close to the original rock stress, the average principal stress difference is less than 1.24 MPa, and the principal stress difference change rate is low. Finally, the mining roadway of the working face of the lower coal seam is arranged with an inner stagger distance of 30 m. The field practice shows that the deformation of the surrounding rock is small under the misspacing, which can ensure the safety and efficient production of the mine.

Every year in Japan, industry and household consumption generate a significant amount of clam shell waste. It has inevitably imposed a negative impact on the national environment and economics. To reduce those effects, this study proposes the reutilisation of abandoned clam shell for ground improvement. An experimental study was conducted to evaluate the shear strength of this new construction material. Soils were mixed with various percentages of clam shells as well as cement. The new soil-clam shellcement samples were tested under the triaxial consolidateddrained tests (CD tests). Test results showed that the addition of clam shell and cement in the soil leads to increase deviatoric stress. Furthermore, shear strength parameters of specimens were quantified in terms of cohesion and frictional resistance. Based on the results of the current study, it was concluded that approximately 9.50% increase of frictional angle can be achieved whilst the cohesion can only be improved by 6%. This new construction material can be used in the future for the base course of unpaved roads in agriculture engineering applications.

The optimum design of deep-coal pillar width at the gob-side entry is the key to control surrounding rocks. Existing studies on this issue are based on the distribution law of mining abutment pressure without considering the principal stress difference distribution, which is related to the shear failure of surrounding rock. This study aimed to optimize the design of deep-coal pillar width at gob-side entry based on the distribution law of the principal stress difference. With FLAC 3D numerical simulation, the distribution characteristics of principal stress difference in the side mining stress field of the deep mining face and the distribution laws of the principal stress difference of the surrounding rock at the gob-side entry under different coal pillar width were explored. According to the distribution characteristics of the principal stress difference, the coal and rock mass on the goaf side in the deep mining face could be divided into three zones, i.e., decreasing, increasing and stable zones. Results show that the principal stress differences of the deep surrounding rock on the roof, floor, and coal wall rib at the gob-side entry present a single-peak curve distribution under different coal pillar width. However, the principal stress difference of the surrounding rock on the coal pillar rib displays a single-peak curve when the coal pillar width is less than or equal to 8 m, but a double-peak curve appears when the coal pillar width is greater than 8 m. The peak value of the shallow surrounding rock is obviously smaller than that of the deep surrounding rock. The width of the coal pillar of the gob-side entry in 11030-tunnel was optimized according to the theoretical calculation. This work provides a novel idea and method for the arrangement of deep coal pillars of gob-side entry.

Highlights • A mathematical model based on co-injection molding is proposed. • Rolie–Poly constitutive equation is used to describe viscoelastic flows. • "V" shape pattern in injection molding is successfully predicted. • Molecular orientation, extension and deformation of polystyrenes are shown. • Velocity, molecular weight are main factors that affecting the "V" shape pattern. Abstract The feature of the flow front for polystyrene melts in injection molding is investigated in detail in this article. To explore the generation and evolution processes of "V"-shape pattern in the skin areas for polymer melt, a mathematical model based on the co-injection molding is proposed in which the evolution of material line is traced by level set method, and viscoelastic behavior of polystyrenes is described by Rolie–Poly constitutive equation; the molecular orientation, extension and deformation of polystyrenes are also studied in this article. The capabilities of Rolie–Poly constitutive equation is validated by simulating the principal stress difference(PSD) for both an entry-exit slit flow and a cross-slot geometry for polystyrenes melt; then the mold filling process has been analyzed by finite volume method to solve the continuity, momentum, constitutive equation together with level set equation. The numerical results for the evolution processes of "V"-shape pattern shows good agreement with available numerical results and experiments results obtained by injection machine. Furthermore, three main factors that include inlet velocity, molecular weight of polymer and temperature that affecting the formation and form of "V"-shape pattern were discussed, and molecular conformation of polystyrenes melt are also presented. [ABSTRACT FROM AUTHOR]

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The flow behavior of polystyrenes is investigated numerically for a cross-slot geometry using Rolie-Poly model with finite extensibility, and governing equations for the polystyrene melts are solved by finite volume method with domain extension technique on the collocated grid. The effect of molecular weight, flow rate, and two kinds of Weissenberg numbers on the principal stress difference (PSD) profiles are discussed detailedly. The microstructures of polymer melts, including molecular orientation, extension, and deformation, are also investigated and presented in this paper. We found that the orientation of Weissenberg number is the major factor affecting the PSD profiles and the performance of the Rolie-Poly model has been improved greatly by introducing finite extensibility at high extension rate. The numerical results are consistent with the available experiment results, which demonstrate the capabilities of single-mode Rolie-Poly model with finite extensibility to simulate the flow behavior of polystyrenes and the numerical method developed in this paper. [ABSTRACT FROM AUTHOR]

In terms of the surrounding rock control problems in kilometer depth gob-side entry driving,the No.2122 haulage roadway in Xing-dong coal mine is investigated. The principal stress difference and plastic zone are studied in the process of buried depth from 550 m to 1 250 m with FLAC3D. Analysis result shows that: ① the principal stress differences of roof and integrated coal beside the roadway firstly increase and then decrease, finally tend to be stable from shallow part to deep one, while one of coal pillar displays a symmetrical distribution shape of mountain peak; ② the principal stress differences of roof and integrated coal beside the roadway in the shallow parts have less sensibility than that at the middle and deep parts with the increase of buried depth; ③ the tension shear failure zones display a sector and expands to the depth, the area of which in the gob-side is a little bigger than that around roadway; ④ the principal stress difference peak value in the integrated coal is obviously higher than the one in the coal pillar due to high stress in the depth and failed pillar by the principal stress difference in a long time. Based on above analysis, a high pre-tension and powerful supporting system are proposed to control the deep roadway of gob-side entry driving. Combined with the result of numerical simulation to determine key parameters, the field practice shows the supporting system proposed have achieved an effective control of surrounding rock at gob-side entry driving in deep mining with 5 m width coal pillar. [ABSTRACT FROM AUTHOR]

Abstract: The Mounigou tunnel crosses complex geological strata, mostly with surrounding rock of poor quality with an IV or V classification. Failure in the form of collapses or squeezing deformation occurred many times during the tunnel construction. Especially, in the soft and hard rock contact zone of phyllite and meta-sandstone, the deformation failure was most obvious. This paper uses the FLAC-3D modeling analytical software to establish a 3D-numerical model, on the basis of a field tracing survey and laboratory tests to analyze the stress and strain changes before and after excavation of the tunnel. After excavation there are obvious stress concentrations and differentiations near the interface of the soft-and-hard rock stratum. Stress transfers and concentrates towards the hard rock stratum while in the soft rock zone stress release could be observed to some degree. The range of plastic deformation is obviously larger in the soft rock zone than in the hard rock zone. Both differences in principal stress and principal stress ratio increase after excavation. The amplification of the difference in principal stress is larger than the augmentation of the principal stress ratio. Moreover these principal stress amplifications are smaller in the soft rock zone than in the hard rock zone. The difference in principal stress amplifications between the soft and hard rock zones, together with the fact that soft rock strength is far lower than that of hard rock, causes local “relatively high geostress” effects in the soft rock. It is the main controlling factor of the large deformation of soft rock in the tunnel. It is concluded that the large deformation in the soft and hard rock contact zone in combination with the surrounding rock deformation failure in the Mounigou tunnel and the damage of the supporting structure, belongs to the type of soft rock plastic-squeezing failure. [Copyright &y& Elsevier]

l The evolution of stress field in Cylindrical Blasting with bottom initiation is investigated using caustic method. l The stress field of cylindrical charge with bottom initiation shows a non-uniform stress distribution with remarkable zoning characteristics. l Along the blast hole axis, the stress field of the blast hole increases gradually from the initiation end to the non-initiation end in the side area. l Compared with the side area, the stress field at blast hole ends are weaker, and the stress field at the initiating end is weaker than that at the non-initiating end. The dynamic caustic method and numerical simulation method were used to study explosive stress field of cylindrical blasting with bottom initiation. The explosive stress distribution of cylindrical blast holes with bottom initiation was not uniform, and can be divided into side areas with stronger stress and end areas with weaker stress with notable end effects. In the side areas, the explosive stress field at the initiating end increased, and the stress was high at the initial stage after initiation. However, the stress field at the non-initiating end was the strongest with the explosive detonation wave propagating from initiating end to non- initiating end. Differences in the principal stress difference near the blast hole were significant. The explosive stress field in the initiating end was weaker than that in the non-initiating end. Caustic spots increased and maximum principal stress directions is consistent with crack propagation direction when cracks propagated near circular holes. According to the simulation results, the Mises stress wave has a "conical" distribution. The Mises stress attenuation coefficient in the vertical direction, the axial direction, and the oblique direction increased at initiating end. The Mises stress attenuation coefficient in vertical direction, oblique direction, the axial direction increased at non-initiating end. [ABSTRACT FROM AUTHOR]