Effect of geofoam as cover material in cut and cover tunnels on the seismic response of ground surface

In recent years,special attention has been given to the effects of underground spaces and structures on the seismic response of adjacent ground.Nevertheless,to the best of the authors′knowledge,no method has yet been considered to reduce these effects in technical literature.The present study aims to investigate the role of geofoam as the cover material in cut and cover tunnels on the seismic response of the ground surface.For this purpose,a numerical study was performed using FLAC 2D,a finite difference software,and verified against previous studies.The effects of parameters such as the geofoam type,thickness of the geofoam blocks and interfaces between the blocks,on the ground surface amplification pattern were investigated.Parametric studies demonstrate that the geofoam has a strong potential to attenuate the seismic horizontal movements of the ground surface.As the thickness of the geofoam blocks is decreased,its attenuation ability is increased.It was also determined that the interface between the geofoam blocks plays a key role in the attenuation of the aboveground seismic responses.Based on the results,it was concluded that geofoam is a proper material to attenuate seismic amplifications at the ground surface,induced by underground tunnels.

Optimization of confined aquifer dewatering for long-deep excavation using simulation–optimization method

The confined aquifer dewatering for long-deep excavations usually encounters challenges due to complicated geotechnical conditions,large excavation sizes,and high hydraulic pressures.To propose the most efficient scheme of confined aquifer dewatering for long-deep excavations,dewatering optimizations were performed using the simulation–optimization method.An open cut tunnel of the Jiangyin-Jingjiang Yangtze River Tunnel Project was taken as an example.The methods of finite element and linear programming(LP)were combined to optimize the dewatering process.A three-dimensional finite element model was developed.After simulating the pumping tests,hydraulic conductivity was inverted.Then,necessary parameters in the LP method were determined by simulating dewatering with each pumping well,and various LP models were developed based on some important influence factors such as dewatering sequence,considered pumping wells,and pumping rate limitation.Finally,the optimal pumping rates were solved and applied to the numerical model,with induced drawdown and ground settlement computed for comparison.The results indicate that the optimization can significantly reduce the required wells in the original design.Dewatering in the deepest zone exhibits the highest efficiency for long-deep excavations with gradually varying depths.For the dewatering sequence from the shallowest to the deepest zone,more pumping wells are required but less energy is consumed.Higher quantity and more advantageous locations of pumping wells in the LP model usually result in lower total pumping rate,drawdown,and ground settlement.If more pumping wells are considered in the deepest zone,pumping rate limitation of single well will only slightly increase the total pumping rate,number of required pumping wells,drawdown,and ground settlement.