| China is a country with abundant water resources.Many important cities are built around rivers.In the process of highway construction,it is inevitable that they will break through weak and broken water-rich strata.The internal pore water pressure of the surrounding rock not only affects the physical and mechanical properties of the surrounding rock,but also further affects the normal construction of the tunnel and even becomes a factor in inducing the collapse of the tunnel face.At present,there are many researches on the stability of the tunnel face,but there are few studies on the stability of the tunnel face of the mining method,especially the study on the stability of the tunnel face excavation in the mining method with watery strata.This obviously does not meet the actual situation in our country.This article takes the example of the Shuiqin tunnel from Bijie to Yunnan Zhenxiong Expressway as an example,and collects laboratory test and numerical simulations of surrounding rock around the tunnel face.The theoretical analysis is carried out and calculates nearly 100 tunnel collapse scenarios and nearly 40 collapse model tests.The study explored the factors that could easily lead to the collapse of the tunnel face and the effect of pore water on the physical properties of the surrounding rock.The main work and achievements are as follows:(1)In the groundwater rich tunnel or the face of the rainy season is prone to instability;The higher the level of surrounding rock,the more likely the instability of the tunnel face is;The larger the excavation span,the easier it is to cause instability of the tunnel face.In addition,the design parameters,supporting opportunity,vibration and other human factors also have a certain impact on the stability of the tunnel face.Local failure is a precursor to the overall instability,and local failure is likely to occur in the lower part of the sidewall.The destruction of the surrounding rock is a progressive destruction,which first occurs in the nude rock area and then extends to the support section.The groundwater mainly changed the mechanical properties of the surrounding rock,softened the weak and fractured surface,and could easily cause the collapse of the tunnel.(2)With the increase of water soaking time,the uniaxial compressive strength and elastic modulus of rock samples all decreased,while Poisson’s ratio showed an upward trend,And the change of Poisson’s ratio is greater than that of uniaxial compressive strength and elastic modulus.(3)For water-rich tunnels,the higher the head height,the greater the surface settlement,the deformation of the tunnel face,and the destruction of the surrounding rock,and the greater the rate of increase.The maximum negative pore pressure appears behind the tunnel face when the initial water level is higher than the tunnel face,and the maximum negative pore pressure appears on the tunnel face when the initial water level is located at the lower part of the tunnel face.In the excavation process,the distribution of pore pressures is roughly funnel-shaped,and this feature is particularly evident with the rise of the water level.Because the surrounding rock has a certain degree of self-stability,when the support is behind 2.5 meters,its value is not much different from that of timely support.However,when the support is behind 5 meters,each value is more than the former two cases,which have a significant increase.With the increase of footage,the surface settlement,the plastic deformation of the face and the deformation of the face of the excavating step are all improved.(4)A formula for determining the parameters of surrounding rock under different saturation is put forward based on the softening coefficient and Hoek-Brown criterion.Based on the strength reduction method,the calculation method of the stability coefficient of the palm surface with different water rich and full water time is derived,and the verification analysis is given by an example. |
