Research On Optimization Of Waterproof And Drainage Measures For Tunnels In High-altitude Seasonally Frozen Areas Based On Temperature Field

Seasonally frozen soil accounts for about 53% of China land area,and is widely distributed in northern and northwestern China and the Qinghai-Tibet Plateau.With the rapid construction of infrastructure projects represented by traffic engineering in my country,the number of tunnels passing through the seasonally frozen area has increased rapidly,and the problem of frost damage has often occurred,which seriously affects the normal traffic operation and tunnel driving safety,and brings huge renovation costs.To this end,the basic conditions,main controlling factors and damage degree of tunnel freezing damage should be clarified,the temporal and spatial distribution of the temperature field of tunnels in seasonally frozen areas should be identified,and the water-proof and drainage measures should be reasonably optimized to reduce the occurrence of tunnel freezing damages in seasonally frozen areas.significant.Based on the Guanjiaoshan Tunnel of Xicha Highway,this paper used literature research,field monitoring,numerical simulation and mathematical statistics to find out the basic conditions,main controlling factors and damage degree of tunnel freezing damage.The temporal and spatial distribution law of the tunnel temperature field in the seasonally frozen area was analyzed.The influence law of multiple influencing factors on the minimum water temperature of the central ditch under the condition of heat-fluid-solid coupling was studied.Sensitivity analysis of each influencing factor,and used multiple regression linear analysis was carried out.The optimal solution of the embedment depth of the central ditch was obtained.Finally,a new waterproof and drainage form to solve the problem of poor drainage of the waterproof and drainage system was proposed and its water passing capacity was verified.The main research results are as follows:(1)Through the investigation of literature and typical cases,it is clear that groundwater occurrence and negative temperature environment are the root causes of tunnel freezing damage.Most of the occurrence of freezing damage in tunnels in my country is due to the failure of waterproof and drainage measures,causing water to freeze behind the lining or inside the drainage system.;(2)Through the analysis of on-site long-term monitoring data,the wind speed,wind direction and air temperature conditions in the tunnel site area were obtained.And according to the analysis of the air temperature in the tunnel,the analysis of the ground temperature and the water temperature of the central ditch,the distribution law of the temperature field during the construction period of the tunnel in the seasonal frozen area is obtained;(3)Combined with the actual project,the "air-lining-surrounding rock" heat-fluid-solid coupling three-dimensional numerical calculation model of the tunnel in the seasonally frozen area was established,and the temporal and spatial distribution of the temperature field during the operation period of the tunnel in the seasonally-frozen area was obtained.On this basis,a simplified model of water temperature calculation in the central water ditch is established,and the validity of the simplified model water temperature calculation is verified;(4)The single factor circulation method was used to study the variation law of the minimum water temperature in the central ditch with various influencing factors.The results showed that the slope of the ditch,the buried depth of the ditch,the initial water temperature,the water depth of the ditch and the temperature of the coldest month had an effect on the minimum water temperature of the central ditch.The effects are all positively correlated.The sensitivity ranking of factors affecting the minimum water temperature in the central ditch based on grey correlation is: ditch buried depth > coldest month temperature > ditch water depth > initial water temperature > ditch slope;(5)Based on multiple linear regression analysis,a statistical model between the minimum water temperature of the central ditch and various influencing factors was established,and the approximate calculation expression of the minimum water temperature of the central ditch was obtained.The optimal solution for the embedment depth of the central ditch is further obtained by taking the minimum water temperature of the central ditch > 0℃ as the control standard;(6)Combining with the basic conditions of freezing damage-poor drainage and the effect of water depth on the minimum water temperature of the central ditch,a new waterproof and drainage form to improve the water-passing capacity of the tunnel’s waterproofing and drainage system is proposed and its water-passing capacity is tested.The results show that:This form of waterproof and drainage structure can significantly prevent the accumulation of water behind the lining due to poor drainage,increase the water collection capacity of the central water ditch per unit time,and effectively avoid the occurrence of frost damage in the waterproof and drainage interior.