Limit Support Pressure Of Tunnel Face And Ground Settlement Analysis In Rock-soil Interface Composite Formations

Studies concerning the shield tunnel support pressure and the ground settlements induced by tunneling construction under the condition of rock-soil interface(RSI)composite formations(Tang et al.,2016)are rare,and the existing efforts are only confined their scope in certain special condition like half-rock and half-soil interface,without taking into account the changing ratio of rock and soil part on the interface of tunnel excavation.Given the present research status,this paper is dominantly at solving the following two aspects of the issue:(1)Stability analysis of the tunnel face in the context of rock-soil interface composite formations: A three dimensional sliding model(3D LS-M model)is built based on the proposed RSI angle,which would changing accordingly with respect to different RSI compostite formations.The limit supporting pressure was deduced and then expressed as a formula which would take account of three influence numbers including Nc,N? and Ns,which representing the influence exerted by soil cohension,soil weight and surface charge,respectively.By detailed discuss and analysis,as well as necessary examination via numerical simulation,the study shows that: the proposed 3D LS-M model is morphologically similar to the practical collapse shape of the tunnel face,and can reflect well the pattern of changing support pressure of the excavation face due to different RSI angle.In certain RSI angle,the limit support pressure of the tunnel face will increase hyperbolically with the increase of the friction angle of soil,and decrease linearly with respect to the increase the the cohension of soil.The correlation between the limit support pressure of the tunnel face and the RSI angle?the strength parameters and the burried depth is also recognized.Consequently,good uniformity and accuracy is showed when comparing with the published results.(2)The ground settlement induced by the tunnel construction in the RSI composiste formations: the forecast formula of the ground settlement was deduced based on the ground loss,which incorporate the physical gap of shield machine,grouting filling effect,and tunneling eccentric ratio into consideration.Detailed quantitive analysis,based on Zhu-Ji intercity subway project,was conducted in order to explore the influence of these three parameters on the ground settlement,and then the changing pattern of gound settlement with respect to the grouting effects?eccentricity of shield tunnel and physical gap of shield machine was obtained.With other conditions remain unchanged,the ground settlement will increase with the RSI angle,and the shape of ground settlement will change from initial gentle curve to overt basin shape,as a result,the settlement trough width decreases hyperbolically.At last,the influence of supporting pressure on the tunnel face is revisited by numerical anaylsis in the context of different RSI ratio,several results and proposals are then presented.