For shot-encoded seismic waveform tomography, the restarted L-BFGS algorithm is an effective technique to suppress the crosstalk effect among encoded seismic shots. It restarts the L-BFGS calculation at each iteration segment, consisted of a group of iterations, and re-codes the individual shots randomly not only at the beginning but also at the inside of the iteration segment. Here we simplified this scheme using an invariant shot-encoding within each iteration segment and recoding individual shots only at the beginning of the segment. This simplification did compromise the image quality at the early stage of inversion, as the crosstalk effect appeared on the inversion result of low-frequency data. However, it eventually achieved both the computation efficiency and the good quality for a multi-scale inversion procedure, which inverts seismic data from low-frequency components to high-frequency components in sequence.
The occurrence of geological structure and stratum lithology plays important roles in the seismic stability of complex slopes, which is also the di cult points of engineering construction. Four three-dimensional layered granite slope models with in nite boundary were modeling via nite element method (FEM).Seismic response and deformation characteristics of slopes are systematically studied through timefrequency domain. A frequency-domain analysis method of complex slopes is proposed including modal and spectrum conjoint analysis. Modal analysis can directly display the main vibration modes of slopes.The combination of modal and spectral analysis can clarify the inherent characteristics of slopes, and reveal the interaction mechanism between inherent frequency and dynamic characteristics of slopes. The results illustrate that structural faces have signi cant effects on the propagation characteristics of wave within rock mass, and complex refraction/re ection phenomena occur near these discontinuities, thus to different dynamic response characteristics in the slope. Layered slopes have apparent magni cation effect of slope surface and altitude. Directions of seismic excitation and structural plane types affect the dynamic response of slopes. Horizontal wave mainly affects the middle and upper part of high-steep slope, while vertical wave has obvious in uence on the slope crest. Additionally, Fourier spectral analysis shows that structural planes have ltering effects on the high-frequency waves. Combined with modal analysis, it further explains that high-frequency section of waves mainly triggers local deformation of slopes, while low-frequency component controls their overall deformation. Finally, instability regions and evolution process of different layered slopes were predicted based on time-frequency conjoint analysis.
The influence of seismic waves induced by explosion sources on the dynamic response characteristics of rock slope sites is one of the most important problems affecting engineering construction. To investigate the wave propagation characteristics and attenuation law of seismic waves induced by explosive sources in rock sites from the perspective of time and frequency domains, the high-performance matrix discrete element method (MatDEM) is used to carry out numerical simulation tests on a granite rock medium site. The discrete element model of the high-steep rock slope is established by MatDEM, and the dynamic analysis of the rock medium site is conducted by loading blasting vibration load to generate seismic waves. The results show that the seismic waves in the rock site present characteristics of arc propagation attenuation. The maximum attenuation rate of the dynamic response is the fastest within 0.3 s and 25 m from the explosion source. The slope region can weaken the dynamic response of seismic waves generated by the explosion source. In particular, the high-frequency band (>20 Hz) has an obvious filtering effect. The dynamic response of the P-wave induced by the explosive source is greater than that of the S-wave in the bedrock and surface region. The dynamic amplification effect of the P-wave is greater than that of the S-wave in the slope region. The seismic waves in the slope region show an attenuation effect along the slope surface and have a typical elevation amplification effect inside the slope.
The occurrence of geological structure and stratum lithology plays important roles in the seismic stability of complex slopes, which is also the difficult points of engineering construction. Four three-dimensional layered granite slope models with infinite boundary were modeling via finite element method (FEM). Seismic response and deformation characteristics of slopes are systematically studied through time-frequency domain. A frequency-domain analysis method of complex slopes is proposed including modal and spectrum conjoint analysis. Modal analysis can directly display the main vibration modes of slopes. The combination of modal and spectral analysis can clarify the inherent characteristics of slopes, and reveal the interaction mechanism between inherent frequency and dynamic characteristics of slopes. The results illustrate that structural faces have significant effects on the propagation characteristics of wave within rock mass, and complex refraction/reflection phenomena occur near these discontinuities, thus to different dynamic response characteristics in the slope. Layered slopes have apparent magnification effect of slope surface and altitude. Directions of seismic excitation and structural plane types affect the dynamic response of slopes. Horizontal wave mainly affects the middle and upper part of high-steep slope, while vertical wave has obvious influence on the slope crest. Additionally, Fourier spectral analysis shows that structural planes have filtering effects on the high-frequency waves. Combined with modal analysis, it further explains that high-frequency section of waves mainly triggers local deformation of slopes, while low-frequency component controls their overall deformation. Finally, instability regions and evolution process of different layered slopes were predicted based on time-frequency conjoint analysis.
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