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The power spectrum density and coherence function for slow ground motions are studied for the construction of the large future electron-positron linear collider. Dominant part of the ground motion in the low frequency range (f
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... our experiments, f 0 is about 0.1Hz for the quiet hard rock region, and about 0.01 Hz for the noisy weak ground region. A typical example of the spectra is shown in Fig. 1. In the f < f 0 frequency region, P(f) can be characterized by K/f 2 . This slow ground motion occurring like Brownian motion of rocks becomes dominant at this frequency region. The coefficient K strongly depends on the geology of the site and its value is 2 1 10 ∼ nm 2 /Hz. A large spectrum component around f 0 is ocean swell, but ...
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Unlike the waves associated with ground motion, waves in an ocean environment are predominantly generated by winds, so can be considered as virtually continuously varying phenomena. Irregular wind generated waves in deep water can be characterised by a power spectrum that incorporates a directional spreading term. The frequency-wavelength character...
Citations
... Slow ground motion which frequency components are less than characteristic frequencies of the accelerator has been usually considered as not having serious effect on the machine operation, assuming complete space and time coherence of the ground motion. This assumption, however, not exactly works out for the weak geological structure as shown by relatively large A value of the ATL model [1,2]. The ground motion caused by daily or seasonal variation of the ground temperature, groundwater level variation, atmospheric pressure variation and earth tides have a large correlation length. ...
... The residual part of these variations, however, becomes inelastic component of the ground motion and looses the correlation since the source of the motion is removed. The ground motion spectrum excluded characteristic spectra is empirically given as, 2 2 2 0 ( ) , ( ) ...
The power spectrum density and coherence function on the ground motions have been reported by many authors aiming at the construction of the large future electron- positron linear colliders and next generation accelerators. The transfer function of the ground motion, however, is not exactly clear by these present data. We are developing the study to obtain the transfer function using the distinct ground motion source. In the beginning, our studies started in the granite tunnel which is near the dam site, since the wide frequency band source of the ground motion is available and the geological character is simple.
A slow-ground-motion monitoring system has been developed for J-PARC (Japan Proton Accelerator Research Complex) linac to improve its operational stability. The monitoring system utilizes a hydrostatic leveling system with non-contact water-level sensing, and it has remote water-level control capability. Online calibration has been performed with a remote water-level control and an accuracy of 0.02 mm over the range of 1 mm has been obtained. Characteristic time response of this monitoring system is evaluated based on a hydraulic model. This simple modeling can simulate dynamic fluctuation of a multi-vessel system with various conduit network topologies. We have performed a forced water-level variation test, and confirmed that the modeling shows a reasonable agreement with experiments. The time resolution of this system is confirmed to be around 540 s with a filling tank for remote water feeding. To demonstrate the system performance, the slow ground motion of J-PARC linac has been measured with this monitoring system. A periodic ground movement is observed with this system, which is supposed to be induced by a tide effect. The stability of the accelerator tunnel has some local variation possibly due to the difference of the geological circumstances and the inequality in the foundation constructions.
