Background/Purpose. This three-dimensional finite element study observed the stress distribution characteristics of 12 types of dental implants and their surrounding bone tissues with various structured abutments, implant threads, and healing methods under different amounts of concentrated loading. Materials and Methods. A three-dimensional geometrical model of a dental implant and its surrounding bone tissue was created; the model simulated a screw applied with a preload of 200 N or a torque of 0.2 N·m and a prosthetic crown applied with a vertical or an inclined force of 100 N. The Von Mises stress was evaluated on the 12 types of dental implants and their surrounding bone tissues. Results. Under the same loading force, the stress influence on the implant threads was not significant; however, the stress influence on the cancellous bone was obvious. The stress applied to the abutment, cortical bone, and cancellous bone by the inclined force applied to the crown was larger than the stress applied by the vertical force to the crown, and the abutment stress of the nonsubmerged healing implant system was higher than that of the submerged healing implant system. Conclusion. A dental implant system characterised by a straight abutment, rectangle tooth, and nonsubmerged healing may provide minimum value for the implant-bone interface.
a b s t r a c tField investigations of high stress soft rock deformations show that the high stress soft rock roadway can slide with large deformation. Severe extrusion and floor heave can also be subsequently observed. The supported roadway can be locally damaged or completely fail, where the floor has a large deformation and/or is seriously damaged. The factors inducing large deformation of surrounding rocks in deep roadway are rock strengths, structure face cutting types, stress states, stress release, support patterns, and construction methods. Based on the deformation characteristics of high stress soft rock roadway, a comprehensive support scheme is proposed. The overall support technology of "step-by-step and joint, hierarchical reinforcement" for roadway is presented, and the anchor cable and bolt parameters to check the design methods are also given. Finally, the proposed comprehensive support method "bolt þ metal mesh þ U-steel arch þ shortcrete þ grouting and cable" is used in the extension section of east main haulage roadway at À850 m level of Qujiang coal mine. The 173-day monitoring results show that the average convergence of sidewalls reaches 208 mm, and the average relative convergence of roof and floor reaches 448 mm, suggesting that this kind of support technology for controlling large deformation of high stress soft surrounding rock roadway is effective.
SUMMARYIn order to examine the effect of the spatial variation of ground motion on the response of an indeterminate structure, the stochastic responses of a two-span beam to spatially varying support excitations are analysed. A space-time earthquake ground motion model that accounts for both coherency decay and seismic wave propagation is used to specify the support motions, and the results are compared with those for various simplified excitations that are commonly used in practice. The response is computed through a linear random vibration approach with the structure being modelled by finite elements. The results of the study indicate that, even for moderate lengths, the effect of the spatial variation of ground motion can be significant. The assumption of fully coherent support motions (same excitations at all supports or delayed excitations allowing only for wave propagation) may be overconservative for some beams and unconservative for others.
In order to reveal the failure mechanism of the deep roadway under mining-induced pressure in coal mine, the boundary equations for the plastic zone around the deep roadway were deduced, and then the evolution laws for morphology of the plastic zone and the relationship between the morphological indexes and the stability of surrounding rock were discussed. The results show that, for the deep roadway, the effect of mining on the plastic zone is more sensitive than that on the shallow one. Even if the changes of mining influence are small, they may also cause extremely serious plastic failure of surrounding rock masses, leading to the sudden instability of the roadway. When the plastic wings of the plastic zone are approximately perpendicular to the roof, floor, or sidewall, the large deformation and failure of the deep roadway are very likely to occur. Compared with the index of the uniformity coefficient, the irregular shape coefficient can be used to better characterize the differences in the plastic zone morphology. Finally, a case study was provided to apply the principles for the formation and extension of a butterfly-shaped plastic zone.
In order to clarify the influence of anchor bolts on the supporting effect of the layered weak roof and surrounding rock of nonlayered roof with good integrity, the mechanical model of the roadway with nonlayered homogeneous roof and layered weak roof was established using FLAC3D. The distribution characteristics of the stress field and the displacement field of the bolt support are analyzed, and the supporting effect of the bolt on the roof of two types of roadways is studied. The research results show that when the original rock stress is not considered, the bolt support shows obvious tensile, compressive stress areas and positive and negative displacement areas in the surrounding rock of the roof of the roadway; when the original rock stress is taken into account, the tensile and compressive stress zones and the positive and negative displacement zones of the anchor support in the surrounding rock of the roof plate disappear obviously. The effect of the bolt support on the stress field and plastic area of the surrounding rock of the two types of roadway roof is not obvious. However, it has a significant effect on suppressing discontinuous deformation such as delamination and sliding between layered roof rocks. The delamination phenomenon between rock layers disappeared obviously, and the range of each numerical curve of the displacement field of the surrounding rock in the anchoring area was significantly reduced. However, the effect of the anchor support on continuous deformation control such as elastoplastic deformation of roof rock of nonlayered roadway is very limited. There is almost no change in the displacement field curve in the depth of the roof-surrounding rock. Only the shallow surrounding rock displacement field curve range has decreased.
Based on the analysis of the monitoring data of surface displacement and internal multipoint displacement of coal pillars near three inclined strata roadways, which have similar burial depth and different surrounding rock conditions in a coal mine in the east China, the coal pillars' stress change was combined with discontinuous numerical simulation software to simulate the deformation process of one of the roadways. Field monitoring data and numerical simulation results show that when this working face roadway is dug, the coal pillar enters plastic state after being affected by multiple mining influence, but it can still maintain the basic stability of the roadway and control coal pillar deformation under the current widely used supporting method. With the shortening of the distance between the monitoring area and the working face, the vertical and horizontal stress in the coal pillar increase gradually, but the maximum value of the vertical stress decreases by 1.4 MPa, and deformation amount and velocity of the coal pillar show the characteristics of nonlinear rapid increase. The shape of the vertical stress core area in the coal pillar changed from oval to rectangle, and the width of the core area increased, and it moved 1 m to the goaf side. In the process of coal pillar deformation, there is no zero displacement surface within the monitoring range of 6 m. K E Y W O R D Scoal pillar deformation, ground control, numerical simulation, stress concentration | 545 WU et al.
Taking a deep-mine horizontal roadway in inclined strata as our research object, the true triaxial simulation technique was used to establish a model of the inclined strata and carry out high-stress triaxial loading experiments. The experimental results show that the deformation of surrounding rock in the roadway presents heterogeneous deformation characteristics in time and space: the deformation of the surrounding rock at different positions of the roadway occurs at different times. In the process of deformation of the surrounding rock, deformation and failure occur at the floor of the roadway first, followed by the lower shoulder-angle of the roadway, and finally the rest of the roadway. The deformation amount in the various areas is different. The floor heave deformation of the roadway floor is the greatest and shows obvious left-right asymmetry. The deformation of the higher side is greater than that of the lower side. The model disassembly shows that the development of cracks in the surrounding rock is characterized by more cracks on the higher side and fewer cracks on the lower side but shows larger cracks across the width. The experimental results of high-stress deformation of the surrounding rock are helpful in the design of supports, the reinforcement scheme, and the parameter optimization of roadways in high-stress-inclined rock, and to improve the stability control of deep high-stress roadways.
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