دانلود رایگان مقاله انگلیسی یک رویکرد برای پیش بینی حرکات زیرزمینی لرزه ای در خاک اشباع لایه ای تحت آب های سطحی - الزویر 2018

ABSTRACT

Simulation of multi-support (i.e. spatially variable) seismic underground motions in sea areas plays a significant role in the seismic analysis of cross-sea structures such as cross-sea bridges or subsea tunnels. However, existing approaches for predicting multi-support seismic motions mainly focus on the dry site soils without overlying surface water. This paper proposes an approach for predicting multi-support seismic underground motions in layered saturated half space under surface water, subjected to oblique incident P waves. The transfer function in saturated soil under surface water, as the theoretical basis of the subsequent numerical simulation, is first derived based on wave propagation theory and the calculated reflection coefficients of P wave–induced P1, P2, SV waves in saturated soils. The derived transfer function is further employed to deduce and obtain the underground (sub-seabed) power spectral density function and response spectrum function. The two obtained functions, combined with the additional cross-coherence function, are subsequently employed to construct the cross power spectral density matrix and thus to simulate multi-support seismic underground motions. The solutions are validated against the target power spectral density, target response spectrum and target cross-coherence functions. A parametric analysis is presented where the effects of the soil thickness, the incident angle and the overlying water depth are investigated. Results show that the soil thickness, incident angle and overlying water depth have significant influences on the amplitude of transfer functions, which further affect the ratios between seismic ground and underground motions.

Concluding remarks

This paper focuses on the investigation for predicting multi-support seismic underground (sub-seabed) motions in the layered saturated soil overlain by surface water for oblique incident P waves. This aims at providing a feasible approach for simulating the multi-support seismic underground motions required for the seismic analysis of large-span structures (e.g. cross-sea bridges and sub-seabed tunnels) located at the layered saturated soil with overlying surface water. The main works are summarized as follows:

(1) The transfer functions of the layered saturated soil with overlying surface water are derived and obtained. The obtained transfer function is the key theoretical basis of the subsequent numerical simulation of multi-support seismic underground motions.

(2) The underground PSD function and underground response spectrum function are further deduced by employing the derived transfer function. Based on the two derived underground theoretical models and the additional cross-coherence function, the crossPSD matrix is constructed and the multi-support seismic underground motions are further generated. Meanwhile, the simulated results are validated against the target PSD, target response spectrum and target cross-coherence function.

(3) The effects of soil thickness, incident angle and overlying water depth on the simulated seismic motions are investigated, and results show that the ratio of ground (soil-water interface) and underground motions (i.e. the amplitude of transfer function) has a decreasing tendency with the soil thickness or incident angle increasing, but it increases with the overlying water depth increasing.