Effect Of Soft Layer Research Articles

A study on surface wave dispersion due to the effect of soft layer in layered media

Surface wave techniques are widely used as non-invasive method for geotechnical site characterization. Field surface wave data are collected and analyzed using different processing techniques to generate the dispersion curves, which are further used to extract the shear wave velocity profile by inverse problem solution. Characteristics of a dispersion curve depend on the subsurface layering information of a vertically heterogeneous medium. Sometimes soft layer can be found between two stiff layers in the vertically heterogeneous media, and it can affect the wave propagation dramatically. Now most of the surface wave techniques use the fundamental mode Rayleigh wave propagation during the inversion, but this may not be the actual scenario when a soft layer is present in a vertically layered medium. This paper presents a detailed and comprehensive study using finite element method to examine the effect of soft layers which sometimes get trapped between two high velocity layers. Determination of the presence of a soft layer is quite important for proper mechanical characterization of a soil deposit. Present analysis shows that the thickness and position of the trapped soft layer highly influence the dispersion of Rayleigh waves while the higher modes also contribute in the resulting wave propagation.

Effect of soft layer on seismic response of subway station in layered stratum

The seismic behavior of subway and highway tunnel has been an important topic followed the seismic damages of several structures in recent large earthquakes. Soft layer is often encountered in engineering site, and it is often located with normal strata. There have been limited literatures concerned on seismic performance of subway station with the presence of soft layer. Flac3D is employed to investigate the effect of soft layer on seismic response of subway station structure in earthquake. The effect of soft layer locating below subway station is firstly studied. Then the seismic response of subway station against location of soft layer is further investigated. The relative displacement, acceleration and safety factor of secondary lining, and internal force of central column are highlighted. It is found from numerical results that effects of the two cases are similar when soft layer locates below or above subway station and both beneficial for improving the safety of subway station compared with the case without soft layer. The case when soft layer locates below subway station is more preferable than the case above. It is also found that in the case when soft layer is within the range of subway station, it will greatly amplify the acceleration and internal force of secondary lining, especially for the part that is close to soft layer, and the influence degree gradually decreases with the increase of relative distance to soft layer. As a result, soft layer is generally beneficial for improving stability of subway station, but it should be avoided to be located within the range of subway station to ensure the stability of subway station.