Numerical parametric study of countermeasures to alleviate basement excavation effects on an existing tunnel

In this study, an extensive numerical parametric study is conducted in sand to investigate the effectiveness of countermeasures (i.e., methods used to alleviate tunnel deformation) to reduce tunnel response due to overlying basement excavation. Centrifuge test results were adopted to calibrate soil parameters and numerical modeling procedures. It is found that the maximum heave and tensile strains (i.e., transverse and longitudinal) of tunnel decrease as an increase in the wall penetration depth. But the reduction in the maximum heave and tensile strains of tunnel is less than 20% when the wall penetration depth is increased by three times. Using a 2 m thick diaphragm wall to replace a sheet pile wall, the maximum transverse tensile strain of tunnel is reduced by up to 27%. The maximum heave and longitudinal tensile strain of tunnel decrease as an increase in the thickness of tunnel lining. However, a slight increase in the thickness of tunnel lining causes an increase in the maximum transverse tensile strain of tunnel. By further increasing the lining thickness, the maximum transverse tensile strain starts to decrease. In terms of the maximum transverse tensile strain of tunnel, a slight increase in the lining thickness may even cause adverse effects on existing tunnels.