| In the soft soil area,the underground highways and subway tunnels,which are constructed by open-cut method in the core area of the city,have to pass through the dense buildings and the criss-cross pipeline network.The ground condition is the soft soil with low strength,high compressibility and significant rheology.It is very difficult to protect the foundation pits and the surrounding environment.Based on a highway tunnel project in soft soil area of Ningbo,how to reduce the influence of open excavation of urban underground tunnel on neighboring buildings is investigated.And the design and construction measures are analyzed by theoretical and numerical simulation.The main contents and conclusions are as follows:1.Considering that the foundation pit of open-cut tunnel is mostly long and narrow,a comparative analysis on the deformation rules of long and narrow foundation pit and non-long and narrow foundation pit is carried out to obtain the relevant proportional parameters for estimating foundation pit and surrounding deformation based on the measured data.The reuslts show that lateral displacement of the retaining wall of the long and narrow foundation pit is about 1/2 of that of the non-long and narrow foundation pit,while the other rules such as the surface subsidence,the maximum deformation position,and so on,are mostly the same.2.Sensitivity analysis of design parameters,quantitative analysis of the effects of various design measures and cost-effectiveness study on relevant design measures to reduce the impact of open-cut tunnel on surrounding buildings are carried out.The reuslts show that the effect of depth of soil reinforcement and thickness of retaining wall on the maximum settlement and settlement difference of adjacent buildings is more significant,but the effect of fixing ratio and replacement ratio is not obvious.3.The relevant construction measures to reduce the impact of open-cut tunnel on surrounding buildings are analyzed.The reuslts show that the longer the exposed time of foundation pit without support,the larger the horizontal displacement of the retaining wall and the settlement of the building outside the pit;The surface subsidence outside the pit increases outside the pit increases nonlinearly with the decrease of water level.Thus,the exposed time without support or cushion shuold be reudced and the recharge and water-seal measures should be strictly executed.4.Based on the comparison between the calculated results and the measured results of typical sections of open-cut tunnel,the influence law of open-cut tunnel construction on the surrounding building environment is obtained,and the effectiveness of the measures in this paper is verified. |
