The Effect of Non-linear Soil Behavior under Vibrating Loads

Seismic vibrators are used to investigate the structure of the subsurface in the framework of soil and gas exploration, also to locate faults and rupture zones in earthquake investigations. Vibrators introduce seismic waves that propagate through the ground and are received by seismic sensors at some distance from the source. This enables interpretation of the sub-soil structure by inverse analysis. To analyze the behavior of the soil below a seismic vibrator, analytical models were developed in the past in which the behavior of the soil is simplified by linear elasticity. This assumption of linear elastic soil model does not describe real soil behaviors. In this research, a seismic vibrator standing on a homogeneous soil is simulated by means of an axisymmetric finite element model with an advanced soil model, i.e. Hardening Soil model with smallstrain stiffness, called HS-small model in which the non-linear, irreversible soil behaviors as well as small-strain stiffness effects below a seismic vibrator are taken into account. The sign and amplitude of displacements of the ground surface in the near field and the far field are observed for a homogeneous sand and homogeneous clay. A comparison between the linear elastic model and the HS-small model in simulation the soil response is made. The response of the sand and clay under delta-pulse load, minimum-phase-wavelet load, chirp load, and harmonic load with different frequencies (5Hz and 50Hz) and amplitudes (10kN/m2 and 20kN/m2) is simulated and evaluated. The influence of stress-strain dependent soil stiffness and porewater on seismic wave velocities is evaluated by means of seismograms.

Subject

seismic
elastic soil model
finite element

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Student theses

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master thesis

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