Study On Limited Discharge Of Tunnel Groundwater Based On Vegetation Protection

The rapid development of the transport sector in China in recent years has resulted in the widening of the road network and the need to traverse hydrogeologically complex mountainous areas,where high water pressure water-rich rock formations are inevitably encountered.In the past,in order to reduce the water pressure outside the lining and to improve the durability of the tunnel,groundwater treatment measures were more often adopted in the construction of mountain tunnels,which were mainly drainage based.This reduces the potential safety risks and protects the ecological environment of the tunnel site.In this paper,the relationship between groundwater depth and typical vegetation growth was investigated using a home-made experimental device to determine the appropriate depth of groundwater for typical vegetation growth.The disturbance of groundwater system by different drainage control modes,different drainage restriction modes,different rainfall recharge amounts,different grouting ranges and permeability coefficients in mountainous tunnels were investigated,and the recommended discharge values for mountainous tunnels based on vegetation protection were proposed from the perspective of vegetation protection:(1)The relationship between groundwater depth and plant growth was found that vegetation growth was affected by both groundwater depth and soil water content,and that different groundwater depths and soil water content had different effects on plant growth control.When the soil water content is less than 15%,the groundwater depth plays a major role in controlling vegetation growth,and the smaller the groundwater depth,the less the vegetation will be affected by drought stress and wilt.(2)Using the Longzangshan No.1 Tunnel as a background,combined with the typical vegetation growth groundwater depth of burial obtained from the test,through numerical simulation software to establish the mountain tunnel construction phase seepage model,analysis of the tunnel construction process on the groundwater system of the scope of disturbance and changes in the amount of water influx,tunnel construction will have a large impact on the seepage field,the groundwater level is difficult to restore,consider the rainfall infiltration on the tunnel construction period and operation of the seepage field influence law and rainfall recharge on the groundwater system recharge range depth.(3)Study the groundwater in the full blockage,full discharge,limited discharge and other different prevention and drainage mode on the tunnel construction phase of groundwater influx change law,groundwater level drop depth change law and groundwater system disturbance range changes,analysis of different prevention and drainage mode on the tunnel operation phase of the seepage flow field influence law.(4)To investigate the law of influence of grouting reinforcement measures on the seepage field during tunnel construction,and to analyse the changes of disturbance range,changes of groundwater drop depth and groundwater level recovery on the groundwater system by different grouting ranges and different grouting permeability coefficients,as well as the control effect on tunnel discharge.Combining the current limited discharge standards with the hydrogeology and rainfall recharge conditions of the tunnel site area,a reference discharge value for mountain tunnels based on vegetation protection is proposed from the perspective of vegetation protection.