Theoretical analysis on the deformation characteristics of coal wall in a longwall top coal caving face

Against the background of analyzing coal wall stability in 14101 fully mechanized longwall top coal caving face in Majialiang coal mine,based on the torque equilibrium of the coal wall,shield support and the roof strata,an elastic mechanics model was established to calculate the stress applied on the coal wall.The displacement method was used to obtain the stress and deformation distributions of the coal wall.This study also researched the influence of support resistance,protective pressure to the coal wall,fracture position of the main roof and mining height on the coal wall deformation.The following conclusions are drawn:(1) The shorter the distance from the longwall face,the greater the vertical compressive stress and horizontal tensile stress borne by the coal wall.The coal wall is prone to failure in the form of compressive-shear and tension;(2) With increasing support resistance,the revolution angle of the main roof decreases linearly.As the support resistance and protective force supplied by the face guard increases,the maximum deformation of the coal wall decreases linearly;(3) As the face approaches the fracture position of the main roof,coal wall horizontal deformation increases significantly,and the coal wall is prone to instability;and(4) The best mining height of 14101 longwall face is 3.0 m.

Effect of Wall Deformation on Dewatering-Induced Ground Surface Settlement

In practice,dewatering for pressure relief is commonly undertaken during ongoing excavation to secure bottom stability against basal upheaval.Simultaneously,through unloading,wall deflection is obviously observed.Noticing that both cause soil deformations,this research is to study the effect of wall deformation on dewateringinduced settlement.A coupled numerical analysis of finite-difference software is employed to model Shanghai soft soils under multi-aquifer-aquitard systems(MAASs)by analyzing the results in association with an empirical approach.Consequently,through gradual force reduction,shear strength at soil-wall interface is significantly diminished.As wall deformation increases instantaneously upon lower loading,wall surface becomes deformedly bending;this condition causes the challenge to workability of shear strength.Moreover,wall deformation caused by unloading affects dewatering-induced settlement substantially.Under smaller loading,large wall deflection is observed;soil plane of failure caused by both sliding and compression occurs along slip curve,with weaker shear-strength soils at rD=0.4 and stronger shear-strength soils between rD=0.4 and rD=0.65,where rD is the distance from the wall that is normalized by the depth measured from ground surface.During dewatering,stronger soils tend to drag weaker soils upward to reduce large differential settlements caused by additional compression.Consequently,settlement becomes larger at rD=0.4 and smaller at rD=0.65.Remarkably,at rD>2.3,both settlement curves that result from numerical analysis and empirical method show overlapping;this indicates that the unloading effect on dewatering-induced settlement at rD>2.3 is insignificant.Furthermore,as wall reaches maximum allowable wall deflection by 67%applied force,additional compression caused by dewatering after loading remains smaller than that under 70%applied force,contributing to smaller dewatering-induced settlement.

Behavior of Vortex-Induced Vibration of A Circular Cylinder Near A Deformable Wall with Two Degrees of Freedom in Steady Flow

The behavior of vortex-induced vibration of a two-degree-of-freedom cylinder near a deformable wall in steady flow is investigated experimentally. The typical phenomenon of the two-degree-of-freedom cylinder＇s VIV is discussed. The influences of initial gap between the cylinder and the wall on the dynamic responses of the cylinder are analyzed. The comparison is made about dynamic responses of the cylinder with one and two degrees of freedom. Experimental results show that the vibration of the cylinder near a deformable wall with a small value of initial gap-to-diameter ratios can generally be divided into two phases. The initial gap-to-diameter ratios have a noticeable influence on the occurrence of transverse vibration. The transverse maximum amplitude of the cylinder with two degrees of freedom is larger than that of the cylinder with one degree of freedom under the condition with the same values of other parameters. However, the vibration frequency of the cylinder for the two degrees of freedom case is smaller than that for the one degree of freedom case at the same value of Vr number

Seismic earth pressures on flexible cantilever retaining walls with deformable inclusions

In this study, the results of 1-g shaking table tests performed on small-scale flexible cantilever wallmodels retaining composite backfill made of a deformable geofoam inclusion and granular cohesionlessmaterial were presented. Two different polystyrene materials were utilized as deformable inclusions.Lateral dynamic earth pressures and wall displacements at different elevations of the retaining wallmodel were monitored during the tests. The earth pressures and displacements of the retaining wallswith deformable inclusions were compared with those of the models without geofoam inclusions.Comparisons indicated that geofoam panels of low stiffness installed against the retaining wall modelaffect displacement and dynamic lateral pressure profile along the wall height. Depending on the inclusioncharacteristics and the wall flexibility, up to 50% reduction in dynamic earth pressures wasobserved. The efficiency of load and displacement reduction decreased as the flexibility ratio of the wallmodel increased. On the other hand, dynamic load reduction efficiency of the deformable inclusionincreased as the amplitude and frequency ratio of the seismic excitation increased. Relative flexibility ofthe deformable layer （the thickness and the elastic stiffness of the polystyrene material） played animportant role in the amount of load reduction. Dynamic earth pressure coefficients were compared withthose calculated with an analytical approach. Pressure coefficients calculated with this method werefound to be in good agreement with the results of the tests performed on the wall model having lowflexibility ratio. It was observed that deformable inclusions reduce residual wall stresses observed at theend of seismic excitation thus contributing to the post-earthquake stability of the retaining wall. Thegraphs presented within this paper regarding the dynamic earth pressure coefficients versus the wallflexibility and inclusion characteristics may serve for the seismic design of full-scale retaining walls withdeformable polystyrene inclusions. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Study on gob-side entry retaining in fully-mechanized longwall with top-coal caving and its application

Based on the engineering background of gob-side entry retaining in fully-mechanized longwall with top coal caving(GER-FLTC) on N2105 working face of Yuwu coal mine, by adopting the methods of theoretical analysis and numerical calculation, the control techniques of surrounding rocks in GER-FLTC working face are studied in this paper. The two main difficulties of stability of surrounding rocks at gob-side retained entry in fully-mechanized longwall working face are the stability control of top coal and control of large deformation of GER-FLTC working face. Interaction mechanical model between roofing and roadside backfilling in GER-FLTC is established and the equations for the calculation of roof-cutting resistance of roadside backfilling are derived. Results of numerical calculation show that the damage zones of top coal can be categorized into the delaminating zone of top coal above the backfilling, tensile damage zone of top coal above the retained roadway and shear damage zone of the upper rib of the solid coal. Stability control of top coal is the critical part to success of GER-FLTC. With consideration of large deformation of surrounding rocks of gob-side retained entry in fully-mechanized longwall, the support technique of‘‘roofing control and wall strengthening'' is proposed where high strength and highly prestressed anchor rods and diagonal tensile anchor cables support are used for top coal, high strength and highly prestressed yielding anchor rod support is used for solid coal and roadside prestressed load-carrying backfilling is constructed by high-water material, in order to maintain the integrity of the top coal, transfer load, high resistance yielding load-carrying of solid coal, roof-cutting of roadside backfilling and support,and to achieve GER-FLTC. Results from this study are successfully applied in engineering practice.

State-of-the-art review of soft computing applications in underground excavations

Soft computing techniques are becoming even more popular and particularly amenable to model the complex behaviors of most geotechnical engineering systems since they have demonstrated superior predictive capacity,compared to the traditional methods.This paper presents an overview of some soft computing techniques as well as their applications in underground excavations.A case study is adopted to compare the predictive performances of soft computing techniques including eXtreme Gradient Boosting(XGBoost),Multivariate Adaptive Regression Splines(MARS),Artificial Neural Networks(ANN),and Support Vector Machine(SVM) in estimating the maximum lateral wall deflection induced by braced excavation.This study also discusses the merits and the limitations of some soft computing techniques,compared with the conventional approaches available.

Chest complications in autologous breast reconstruction

Complications from autologous free flap reconstruction of the breast can present with both common surgical complications and unique complications at the chest recipient site.This review covers complications at the chest recipient site,including chest wall deformity,chronic pain,mastectomy skin flap necrosis,infection,pyoderma gangrenosum,bleeding complications,pneumothorax,chyle leak,and positive internal mammary lymph node metastasis.

In-vitro experimental study on the fluid-structure interaction in an image-based flexible model with a lateral cerebral aneurysm

Aiming to experimentally investigate the effect of aspect ratio(AR)of image-based aneurysm on wall deformation oscillation under different pulsatile flow conditions with considering the fluid-structure interaction.In this study,three silicon aneurysm models with different AR(0.8,1.0,and 1.2)were constructed.It was found that the detected wall deformation oscillation of patient-specific aneurysm increased with pulsatile inflow frequency increases,which was greater and more obvious oscillation than that in the ideal lateral aneurysm.In addition,the maximum amplitude of wall deformations oscillation of the aneurysm at the dome during the systolic phase decrease and the oscillation of wall deformation become obvious as AR increases.These results could provide more knowledge about the effect of AR and pulsatile flow on the wall deformation of aneurysm and will be helpful for understanding the aneurysm rupture risk.