Study On The Influence Of Urban Rail Transit Zone Tunnel Excavation On The Adjacent Municipal Bridge Piles Foundation

With the rapid development of economy in our country,modern metropolises are built one by one and the traffic jam problems are becoming more serious.In order to relieve the problem of congestion,the modes such as overpass and viaduct were adopted in many cities.However,following the rapid increase of people’s living standard,traffic congestion worsened owing to the increase in the number of motor vehicle speed is far faster than the speed of the construction of the urban road.As an important transportation tool of modern metropolis,urban rail transit has the characteristics of large quantity,fast speed,economy,environmental protection,security and so on.which can solve most of the traffic flow in a city.The construction of urban rail transit has been urgent in many cities.Up to now,there are 43 cities in China have constructed the subway,and more cities are planning to build urban rail transit.In the process of rail transit construction,various adjacent constructions appear frequently which exist in intervals of shield tunneling through the existing buildings,whose security risks and impact on the structure of a building have become the important link in the process of project implementation.Shield construction is adopted widely in domestic rail transit tunnel now,It has the advantages of high construction safety,fast speed,small effect on surrounding environment and so on,but,as a difficult point in the construction of rail transit,it will be the first time at Lanzhou to realize interval shield tunneling under a municipal bridge,particularly for special stratigraphic structure at Lanzhou.The construction of rail transit in loess area is less,and such research is rare in domestic and international.In the construction process of implementing shield tunnel engineering,in addition to ensure the safety of the tunnel’s own,it is necessary to insure the safety and control the settlement effect in the safe range of existing municipal Bridges.Therefore,under the premise of horizontal spacing of tunnel and municipal bridge pile foundation cannot be adjusted,it becomes a difficult point in design phase that what kind of scheme can be adopted to ensure the safety of the interval tunnel and the existing municipal bridge and the reasonable protection measures are put forward to ensure the safety of the project,which is particularly important for the similar construction projects in the future.In this paper,three schemes are proposed for the research object of project that Rail Transit Line 1 at Lanzhou crossing the small West Lake overpass which are the interval shield tunnel passes through the upper,middle and lower part of the bridge respectively.Analyzing and summarizing the settlement effect of the municipal bridge by the interval shield tunnel and proposing reasonable design scheme by simulating scheme of grouting reinforcement measures.It can provide useful reference for the similar projects in the future.