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.

Groundwater-related aspects during the development of deep excavations below the water table:A short review

The expected growth of urban areas requires the construction of underground infrastructures,especially for improving transportation and mobility.These new infrastructures are commonly constructed below the water table because they must be deeper than previous underground structures.In addition,many urban areas are located near surface water bodies(i.e.,seas,rivers and/or lakes)that induce a shallow water table.The"cut and cover"method combined with dewatering wells is a frequently used procedure under these conditions for the construction of underground infrastructures.The main concerns of this procedure are related to the stability of the excavation bottom,the behavior of the retaining walls and/or the impacts induced by the dewatering actions.These issues must be evaluated,and new solutions must be proposed to improve its weak points.This paper compiles the main publications focused on the construction of underground infrastructures below the water table and in urban areas by using the cut and cover method combined with pumping.This review reveals that,despite many published studies,more research is needed to address some relevant issues such as:(1)the mitigation of dewatering impacts by using artificial recharge,(2)the adaptation of methods for characterizing retaining walls to be used under heterogeneous conditions,(3)the improvement of the prediction of surface settlements produced by pumping,and(4)the consideration of non-Darcy flows in the design of dewatering systems.