| As the concern of coal mining continues to turn to the deep area and the west distinct,the geological conditions such as deep high ground stress and weak cemented soft rock in the west are increasing.This brings a great challenge to roadway support and it is obviously difficult to meet the needs of this kind of roadway support.At present,the arch with high bearing capacity has become one of the important ways of supporting soft rock roadway.However,the understanding of the contact relationship between surrounding rock and arch and its mechanical effect is still insufficient,and this leads to the design of the arch support capacity is not fully developed in the field.In view of this key problem,this paper has carried out the following main work.(1)Research on characteristics and evolution process of surrounding rock-arch contact behavior of soft rock roadwayThe measured data of surrounding rock and arch support in soft rock roadway are analyzed,concluding that there is contact behavior between the surrounding rock and the arch,including radial separation and circumferential friction sliding,which has received little attention before.The direct shear test of the surrounding rock-arch contact basic element is carried out in FLAC3D,where the solid element and the interface element are used to simulate the arch and the surrounding rock-arch contact relationship,respectively.The evolution process of radial contact is linear elastic,while that of circular contact is elastic-plastic.Further analysis focused on the effects of contact parameters,where the friction angle parameter shows the significant effect.In addition,the numerical test of the complete contact between the surrounding rock and the arch is carried out.The radial contact stress-radial relative displacement and the circumferential contact stress-circular relative displacement curves are obtained,and the evolution process of radial and circumferential surrounding rock-arch contact is analyzed.Test results indicate that radial and circumferential contact behaviors occur at the same time,where radial contact shows a tendency to be compressed before separation,and radial separation first appears at the arch leg.Although this model can be used to analyze the surrounding rock-arch contact,it is not suitable for actual simulation work because of the cumbersome modeling and difficult data acquisition.(2)Development of the numerical model of the arch considering its own bearing capacity and the contact relationship with the surrounding rockAiming at the defect that the Liner element does not have a yield criterion,FISH language programming is used to embed the yield criterion of the arch section under the combined compressive and bending loads(f(m,n)=1).When the axial force or bending moment of the Liner element reaches the set values,the element yield is determined,and the arch yield is achieved by reducing its elastic modulus.The original model of Liner element,the modified model of Liner element,and the modified model of Beam element were used to simulate the surrounding rock-arch contact behavior.The results show that the original model of Liner element has no yield limit.The modified model of Beam element can describe the mechanical behavior of arch buckling and yielding while it can not express the surrounding rock-arch contact relationship.The modified model of Liner element can not only describe the arch buckling and yielding,and suit for the simulation of the surrounding rock-arch contact relationship,where the radial contact is linear elastic,and the circumferential contact is elastoplastic.(3)Research on numerical simulation of joint support system of arch in soft rock roadwayCombined with typical engineering cases,based on the developed arch failure model and bolt broken model,the numerical test of soft rock roadway arch supporting system is carried out.Firstly,a comparison test is conducted with the original model of Liner element.The results show that the maximum axial force of the arch reaches 9000 kN in the original model of the Liner element and the deformation of roadway is small.The maximum axial force of the arch is only 2875 kN in the modified model of the Liner element with a relatively large roadway deformation and yield failure of support,which could further confirm the effectiveness of the development of the arch model.A comparative test of four different arch types is carried out.The results show that the support capacity order of the four arch frames is SQCC150 8 square CFST>CCC159 8 circular CFST>U36 steel>22b I-beam,where the volume of plastic zone is 72m3,74m3,78m3,83m3,respectively.Comparative tests of 10 models with different in-situ stress levels and lateral pressure coefficients is carried out.The results show that the surrounding rock deformation,the arch failure degree and the broken bolt amount are positively correlated with the level of in-situ stress.The greater the level of vertical in-situ stress is,the larger the amount of roadway deformation and the degree of support failure are.Moreover,with the increase of the lateral pressure coefficient,the damage range of the plastic zone of the roof and floor is lager,and the damage degree of the support is more serious.A comparative test of the effect of the cavity behind the wall of the roadway at different locations is carried out.The results show that the cavity behind the middle wall of the roadway has a greater effect on the stability of the support,which tends to cause the support to become unstable.Among them,the cavity in the roof of the roadway is the most harmful.A comparative test of a circular roadway and a straight-leg semicircular roadway is carried out.The results show that the supporting capacity of the circular roadway is greater than that of the straight-leg semicircle roadway.According to the above conclusions,it is concluded that the yield failure of the arch at the sides of the roadway is the beginning of the overall failure of the joint support system of the arch.Based on this finding,three support suggestions are proposed for the joint support system of the straight leg-semicircular roof roadway arch:?Pay attention to the strength of the supporting members,and the dangerous cross-section can use yielding bolts and CFST arches;?For solving arch buckling,a lock arch bolt can be added to the roadway;?When it is difficult to maintain stable construction conditions,circular roadway support form can take place. |
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