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To ensure the stability of broken surrounding rock under the influence of advance abutment pressure and the reliability of support system, the 21104 working face of Hulusu Coal Mine is taken as the research background. By means of theoretical calculation, numerical simulation and field measurement, a mechanical model of the elastic foundation beam for the deformation of the super front roof is established, the influencing factors of the bending deformation of the roof, the leading bearing pressure and the main controlling factors of the concentration coefficient are determined, and the advance grouting anchor cable reinforcement technology for broken surrounding rock is proposed. The results show that the roof elastic modulus only affects the roof deflection above the roadway, and the side elastic modulus controls the overall bending deformation of the roof. The advanced support pressure and concentration coefficient show a rapid increase followed by a slow increase trend with the advancement of the working face, and finally tend to stabilize. There is a 35 m high stress area in the grouting anchor cable reinforcement test face, the anchor cable has a high abundance coefficient, the surrounding rock deformation is low (

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to accurately grasp the evolution laws and distribution characteristics of the overburden cracks in the mining of a single coal seam and coal seam group, physical similar simulation experiments, on-site drilling exploration, theoretical calculations and other methods are used to analyze the characteristics of overburden migration and fracture and the characteristics of mining cracks during coal mining. The research results show that under repeated mining conditions, stratified cracks and longitudinal cracks appear in overlying rocks accompanied by advanced cracks. In forming a structure of “goaf-workface” and “goaf-goaf-workface”, the overburden fissures experienced six dynamic cyclical stages of generation, expansion, closure, re-generation, penetration, and re-closure. The coal seams group forms a “trapezoidal” fissure area during a mining. Under secondary and multiple mining operations, the overburden is affected by the overlying load. The influence of the “cantilever beam” formed by the coal pillars at the boundary of the coal seam and the mining of the lower coal seam makes the fissures on both sides of the working face significantly higher than the middle of the working face, and the overlying rock forms an “M”-shaped fissure distribution pattern. The overburden rock is periodically broken under the influence of mining, and deformation, migration and fracture collapse occur simultaneously in single or multi-rock strata. It can be seen that there is a hard rock layer that controls the upper rock layer and its control rock layer moves and breaks simultaneously in the form of composite beams. According to the fracture characteristics of the overburden rock, a composite rock beam mechanical model based on the failure characteristics of the repeated mining of the Winkler elastic foundation coal seam group is established. The evolution height of the overburden rock fissures calculated from the model is similar to the height measured in the similar simulation experiment and the site, which shows that this model can be used as a basis for calculating the evolution height of overburden cracks in the shallow coal seams group that are repeatedly mined.

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Computational Mechanics / Jisuan Lixue Xuebao is the property of Chinese Journal of Computational Mechanics Editorial Office, Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study the free vibration problem of functionally graded beams for different high-order shear-deformed beam theories, it is assumed that the material properties of the functionally graded beam vary according to the gradient distribution of the volume fraction of the components. The equations of motion of functionally graded beams rested on the Winkler elastic foundation are derived from the principle of Hamiltonian. Based on the basic principle of DQM, the discretization equation for the free vibration of high-order shear deformed beams is presented. The effect of different boundary conditions, foundation coefficient, gradient index and geometric parameters on the free vibration of functionally graded beams are discussed through the numerical results. The study of this problem can provide a theoretical reference to the design and optimization of functionally graded beams. [ABSTRACT FROM AUTHOR]

The mechanical model of first fracturing of main roof considering the support of coal pillars and solid coal as elastic foundation on both sides of stope is established. Using the differential algorithm and the fracture criterion of primary moment, it is found that(1) when the elastic foundation coefficient k is smaller as well as the thickness of main roof h and the elastic modulus E is larger, the initial fracture position of main roof is the lower surface of central region of hanging roof area on weaker coal pillar side. On the contrary, the position is the upper surface of long side area ahead of solid coal on weaker coal pillar side. (2) When the support coefficients km1, km2 and the widths L1, L2 of coal pillars on the two sides of stope change, the primary moments and their positions ahead of coal wall in the central area of main roof and solid coal area are almost unchanged. However, the values and the positions of primary moments of main roof in coal pillars area on the two sides of stope change significantly. (3) When the thickness h and elastic modulus E of main roof are larger and the values of L1, km1, L2 and km2 are smaller, the main roof in coal pillars area on the twosides of stope will not fracture. So the fracturing order of the roof is that the lower surface of central region of hanging roof area on weaker coal pillar side → the upper surface of long-side solid coal area on weaker coal pillar side, and the final fracture form is the type of asymmetric"=-X". On the contrary, the main roof in coal pillars area on the two sides of stope will fracture. Thus the fracturing order is that the upper surface of long-side solid coal area on weaker coal pillar side → the lower surface of central region of hanging roof area on weaker coal pillar side → the upper surface of coal pillar area on stronger coal pillar side → the upper surface of coal pillar area on weaker coal pillar side, and the final fracture form is the type of asymmetric "O-X". However, when L1, km1 are smaller and L2, km2 are larger, only on weaker coal pillar side, the main roof will not fracture, and the final fracture form is the type of asymmetric "U-X". (4) When k, E and h change as well as km1 and km2 keep a certain arbitrary ratio constant with k, the ratio k/E or k/(Eh~3) is unchangeable and the fracture law of main roof is invariant. [ABSTRACT FROM AUTHOR]

The mechanical model of plate structure of main roof with elastic foundation boundary on the two sides of the long side of goaf（ coal pillars） and the short side is established in this study. According to the fracture criterion of primary moment of thin plate and combined with finite difference algorithm for partial differential equation, the influence factors and weight relationships of the fracture of main roof are studied and calculated. It is found that（1） the support coefficients kc1, kc2 and the widths Lc1, Lc2 of coal pillars (c1,c2) can not only obviously affect the values and positions of primary moments on both sides of coal pillar areas, but also obviously affect the values and positions of primary moments of short side region and central region;（2） the larger the values of elastic modulus E and thickness h of main roof are, the larger the distance from the fracture line of the short-side solid coal area under main roof as well as the coal pillar areas to the surface of solid coal will be; when Lc1, Lc2 are larger and kc1, kc2 are smaller, the fracture line of coalpillars and the short-side solid coal area is farther away from the surface of coal pillar and closer to the center of coal pillar;（3） when the thickness h and elastic modulus E of main roof are larger and the values of Lc1, kc1, Lc2 and kc2 are smaller, the main roof in zone c1 and zone c2 of coal pillar area will not fracture and the fracture form is the type of asymmetric "-X";（4） when the values of h,E, L1 and kc1 are smaller and the values of Lc2 and kc2 are larger, the main roof in zone 1 of coal pillar（ weaker） area will not fracture,but the main roof in zone c2 of coal pillar（ stronger） area will fracture, so the final fracture form is the type of asymmetric "C-X";（5） when the support coefficients and the width of coal pillars on both sides of goaf are larger as well as the values of E and h are smaller, the fracture form is the type of asymmetric transverse "O-X"; and（6） when k,E,h,kc1 and kc2 change, and the ratio k/（ Eh3） is unchangeable (the ratio k/kc1 and the ratio k/kc2 are also unchangeable) , the values and positions of primary moments and the position of first fracture are invariant. [ABSTRACT FROM AUTHOR]

Based on the symplectic superposition method proposed in recent years, the bending problems of free-edge rectangular thick plates resting on elastic foundations were analytically solved. The original problem was split into 3 subproblems corresponding to the bending problems of rectangular thick plates with 2 opposite edges slidingly clamped and resting on elastic foundations, which were solved with the symplectic geometry method. The analytic solution of the original problem was then obtained through superposition. Compared to the conventional analytic approaches such as the semi-inverse method, the symplectic superposition method has the advantages of both rationality of the symplectic method and regularity of the superposition method. The solution procedure starts from the basic equations of elasticity, and a rigorous derivation yields the analytic solutions, thus extending the scope of problems to be solved. The present method can serve as an effective analytic approach to complex boundary value problems of high-order partial differential equations in elasticity, as represented by the rectangular plate problems. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In long wall face,by establishing the mechanical model of the thin plate of main roof at a long wall face,one side coal pillar and three sides elastic foundation boundary,and using finite difference method,the paper calculated and studied the distribution characteristics of primary moments and fracture law of main roof.It concludes that the width of the coal pillar Lm and the pillar support coefficient km almost have no influence on the extreme values of primary moments of the long side,short side of the solid coal side and central section,but obviously affect the primary moment of coal pillar side and fracture form of the main roof.Because of the existence of pillar support area,when the thickness h and elastic modulus E of main roof are small and the values of Lm and km are large,the upper surface of main roof in the coal pillar area will not fracture.Under this condition,the fracture sequence of the main roof is that the upper surface of long side advanced coal wall→lower surface of central region or short side advanced coal wall in solid coal side→upper surface in coal pillar area,and the final fracture form is the type of asymmetric “O-X”.When the values of E and h are large,and the values of Lm and km are small,the upper surface of main roof in coal pillar area will not fracture.Under this condition,the fracture sequence of main roof is that the lower surface of central region→upper surface of long side advanced coal wall→upper surface of short side advanced coal wall in solid coal side,and the final fracture form is the type of “U-X”. [ABSTRACT FROM AUTHOR]

Under the condition of filling coal mining, a thin plate mechanics model of main roof on elastic foundation with elastic foundation boundary was established. According to the difference theory and the fracture principle of primary bending moment, the effects of the elastic foundation coefficient k b of filling body, the thickness h and elastic modulus E of the main roof and the elastic foundation coefficient km of boundary on the primary bending moment and fracture regularity of the main roof were studied. It is concluded that when the kf increases, the absolute maximum principal bending moment of the short side and long side ahead of the coal wall and the filling area Mh ,Md and Ma all decrease , while the Mo decreases most, and the distance b of Mb ahead of (he coal wall increases. When E or h decreases, the b and the Mo,Mh and Md all decrease. When the km decreases, the b decreases, while the Mb ,Md and Mo increase. In the filling area,the principal bending moment of main roof has differentiation phenomenon. The larger the kf ,or the smaller the h and ft, the maximum principal bending moment of the filling area is gradually transferred to the surrounding area. The principal bending moment in the non-midpoint region is more than Mo. The km has little effect on the differentiation phenomenon. Under the filling conditions, when the principal bending moments of main roof is greater than the ultimate moment of main roof, the initial fracture position is the upper surface of the long side leading coal wall or the middle lower surface of main roof. When the kf is small, the filling rate is low and the overlying load is large, there are three types of main roof fracture sequence;① upper surface of long side→upper surface of short side→dower surface of the middle; ② upper surface of long side→dower surface of the middle→nipper surface of short side; ③ lower surface of the middle→supper surface of long side→supper surface of short side. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

By establishing the basic roof mechanical model of elastic thin plate at elastic foundation boundary and using the finite difference method of partial differential equation，this paper researched the effect of the step length，elastic foundation coefficient，basic roof thickness and elastic modulus on the basic roof main bending moment and fracture positions.It is concluded that with the increase of basic roof thickness or elastic modulus，the maximum main bending moment Mz of the middle roof section increases，and the absolute maximum main bending moment Mc，Md of roof long side and short side decrease；with the step length increasing，the Mz，Mc and Md increase，while the growth rate of the Mz is smaller；and when the elastic foundation coefficient increases，the Mz decreases，while the Mc and Md increase. According to the breaking criterion of the main bending moment，when the step distance or elastic foundation coefficient is small，the middle of basic roof fractures first，whereas the roof long side ahead of the coal wall breaks first；if the basic roof thickness or elastic modulus is small，the long side breaks ahead of the coal wall，whereas the central fractures first.The greater the basic roof thickness or elastic modulus，the farther the pre-breaking distance of main roof；the greater the elastic foundation coefficient or step distance，the smaller pre-breaking distance of main roof.There are three types of basic roof breaking sequence：① long side-middle-short side；② long side-short side-middle；③ middle-long side-short side. [ABSTRACT FROM AUTHOR]

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The close form exact solutions of free vibrations of thin orthotropic rectangular plates on the Pasternak elastic foundation or the elastic foundation with two parameters are solved by means of separation of variables method. It is noteworthy that the exact solutions for the plates with boundary conditions CCCC, SCCC and SSCC ( S denotes simple support, and C denotes clamp) were considered impossible to be solved. In separation of variables method, the general formulation of the natural mode and the relationship among the two spatial eigenvalues and the temporal eigenvalue are directly obtained from the governing differential equation, and the coefficients of the exact eigenfunctions and the exact eigenvalue equations are determined on the basis of boundary conditions. The numerical results agree well with those in literature and FEM, this validates the correctness of the present method. [ABSTRACT FROM AUTHOR]