No abstract

No abstract

a b s t r a c tIn this paper, stress behavior of shallow tunnels under simultaneous non-uniform surface traction and symmetric gravity loading was studied using a direct boundary element method (BEM). The existing fullplane elastostatic fundamental solutions to displacement and stress fields were used and implemented in a developed algorithm. The cross-section of the tunnel was considered in circular, square, and horseshoe shapes and the lateral coefficient of the domain was assumed as unit quantity. Double-node procedure of the BEM was applied at the corners to improve the model including sudden traction changes. The results showed that the method used was a powerful tool for modeling underground openings under various external as well as internal loads. Eccentric loads significantly influenced the stress pattern of the surrounding tunnel. The achievements can be practically used in completing and modifying regulations for stability investigation of shallow tunnels.

No abstract

In this paper, the one-dimensional ground response of a near-fault earthquake is compared by two methods. An equivalent linear method based on total stress modeling in frequency domain and a nonlinear method based on effective stress modeling in time domain. DEEPSOIL.V5 software is used based on the latest achievements and various techniques in both solution domains. LNG port project in Assaluyeh, situated south of Iran, is considered as a real liquefiable site. Due to the lack of the real near-fault recorded data at the project site, the simulated method is used in order to create the artificial earthquake. In order to evaluate the real behavior of the site response due to near-fault incident waves, three near-fault acceleration time histories are selected. In addition, the spectrum responses are compared with spectral acceleration schemes being presented by some legitimate codes such as 2800 and UBC97. The study indicates that the pulse in the horizontal component of acceleration perpendicular to the fault plane affects severely the liquefiable ground response of the near-fault earthquake. The results of the nonlinear modeling of the soil with excess pore water pressure build up in time domain are extremely different from those of frequency domain responses established based on the equivalent linear method. In addition, because of the inherent linearity of the equivalent linear analysis leading to spurious resonances in ground responses, the peak ground acceleration in time domain is lower than frequency domain.

No abstract

Two-dimensional site effects caused by cavities under topographical functions can considerably impact the seismic reaction of the ground surface. Due to the complexity of scattering issues by topographical features above subterranean cavity, few studies have been done in this field. In the present study, the seismic response of semisine-shaped canyons above a subterranean cavity (hole) of different dimensions, depths and locations is examined. The medium is assumed to have a linear elastic constitutive behavior exposed to vertically propagating incident SV and P waves. All calculations are performed using the direct boundary element technique in the time domain. It is observed that a cavity below a canyon can considerably change the ground response of the surface in different periodic bands. The seismic interaction between canyon and cavity with respect to various geometrical parameters will lead to different amplification patterns in the center and edge of the canyon. One of the most important results is the increase in amplification of long periods compared with the case of a canyon without cavity. Moreover, parametric research shows the fact that the cavity detail and canyon height, the ratio of cavity to the canyon size and cavity location impact on the seismic amplification of the canyon surface. Finally, spectral amplification coefficients of the canyon surface led by the cavity are reported for different cases of the canyon-cavity interaction.

No abstract