Effects of Different Sources and Falling Distances on the Dispersion Curve of Surface Waves

• Main Authors: Hui-chi Hsu, 許惠綺
• Other Authors: Yu-min Kang
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/12256471143200567620

碩士 === 逢甲大學 === 土木工程所 === 95 === There are lots of applications in the area of nondestructive testing, and the Spectral Analysis of Surface Waves (SASW) Method plays an important role in shallow seismic exploration both in academic and application areas. Many research studies showed that insufficient energy of source, noise in the field, erroneous phase information in low frequency area may cause the unusual oscillation phenomenon of the dispersion curves. The purpose of this thesis was to study the effects of source type on the dispersion curve for surface waves insitu testing. The field tests of this thesis were conducted on the lawn in front of Feng-Chia University recreation dome. Four kind of sources with different falling heights and hitting conditions were used, including 6 kg hammer, 20 kg falling hammer of the cable, 30 kg free-falling hammer, 100 kg air-pressured hammer. The results of this research showed that: 1. the 30 kg hammer hitting a rubber pad is the best source in the four sources from the ranking information of five research parameters ; 2. with the usage of effective low-cut frequency as the lowest frequency that the signal/noise amplitude ratio exceeds 20, not only the unusual oscillation phenomenon of the dispersion curves can be avoided, but also discrepancy of the error in apparent velocity between each sources can be effectively reduced; 3. as the distance of source increases, the effective low-cut frequency will increase while the effective high-cut frequency will decrease, hence the band width of effective frequency will decrease; 4. since a lower value of the effective low-frequency can be obtained by a higher falling distance, higher source energy will be helpful to produce a lower effective low-cut frequency and a deeper investigation depth of soil stratum can be conducted; 5. a higher value of signal/noise amplitude ratio in extra-low frequency range does not indicate a higher value of the whole frequency spectrum, thus the increase of the signal/noise amplitude ratio in extra-low frequency range is a must for exploring the deeper soil stratum.