| The construction of traffic tunnels in China is in a period of rapid development.The disaster of dangerous rock collapse is significantly affected by the structural characteristics of rock mass and construction process.It has the main characteristics of“strong structure,strong concealment,strong sudden,wide distribution,great difficulty in exploration and unclear means of prevention and control".Due to the extremely complex construction environment and the lack of effective methods for prevention and control of disaster,the collapse of dangerous rocks has become a major problem restricting the construction of underground engineering.As dangerous rock is a block system composed of the developed structural plane and the excavation face,its motion form is mainly the shearing motion of dangerous rocks along the structural plane,which leads to the failure of anchor in deep rock mass anchoring engineering,such as shear failure,pull failure,distortion failure or breaking away from anchorage.At present,the anchoring problem of dangerous rock has not been solved,and the anchor cannot make a good function.Therefore,the anchoring mechanism of dangerous rocks must be analyzed to guide the anchoring design of dangerous rocks in tunnels.In this paper,the anchoring mechanism of dangerous rocks in tunnels is studied.Based on the Laohushan Tunnel in Jinan,the anchoring characteristics under different anchoring numbers,different arrangement modes and different anchor angles are systematically studied by means of case studies,laboratory tests and numerical simulation.The effects of various factors on the shear strength and deformation characteristics of the anchorage are analyzed.And the anchoring strength characteristics in large-scale tunnel are analyzed.The main research results are as follows:(1)Through the statistical analysis of a large number of cases,the failure modes of dangerous rocks in tunnels are summarized and classified.The three failure modes are falling,sliding and overturning of dangerous rocks,and the mechanical characteristics of anchor are analyzed.The failure modes of anchor are compression-shear failure,tension-shear failure and tensile failure respectively.A simplified mechanical model of anchor unit for dangerous rocks is proposed.(2)Based on the simplified mechanical model of tunnel dangerous rock anchorage unit,laboratory tests and numerical simulations were carried out on three kinds of jointed rock specimens with different failure modes of compression-shear,tension-shear and tension.The action mechanism of bolt on the anchorage strength of jointed rock mass was studied,and the influence law of tunnel dangerous rock anchorage parameters on the anchorage strength are analyzed.It is found that the number of bolts,the arrangement of bolts and the anchorage angle have great influence on the anchorage strength of dangerous rocks.The strength of anchorage increases with the increase of the number of anchors.The same number of anchors arranged in the vertical shear direction has better shear resistance,and the anchorage angle has different optimal angles under different action forms.(3)Taking the Laohushan Tunnel as the research object,the failure modes of collapsed dangerous rocks in Laohushan Tunnel are analyzed.Based on the results of laboratory tests and numerical simulation,large-scale simulation is carried out for different failure modes dangerous rocks of Laohushan Tunnel.Aiming at the dangerous rocks of falling instability,one-sided sliding instability and two-sided sliding instability,the anchorage scheme of dangerous rocks in tunnel is designed from the angle of anchor force and failure form.The anchorage strength and deformation characteristics of dangerous rocks in tunnel surrounding rock are analyzed,and the optimal anchorage scheme is selected and the optimal anchorage design is put forward.It provides effective theoretical basis and suggestions for anchorage scheme of dangerous rocks for Laohushan Tunnel,and plays a guiding role in engineering construction. |
PDF Full Text Request