Eun-Seok Bang

Evaluation of Various Downhole Data Reduction Methods for Obtaining Reliable V S Profiles

The downhole method has been widely used to measure in situ shear wave velocity profiles for the seismic response analysis of geotechnical sites. To analyze the downhole data, the direct and interval methods are mostly used in practice. In this study, the modified interval method based on a straight ray path and the inversion method based on Snells Law ray path were introduced to improve the quality of the wave velocity profiles evaluated by the downhole seismic method. Various synthesized wave velocity profile models were developed to perform the parametric study and the arrival times were determined by a forward modeling scheme based on Snells Law. By comparing the velocity profiles obtained by four different data reduction methods with actual velocity profiles, the accuracy and limitation of various data reduction methods were assessed. The direct method was difficult for evaluating the detailed velocity profiles, and the interval method was found to provide severe errors, particularly when a stiff layer is located beneath the soft layer. The modified interval method provides reliable results, except when a strong soft-to-stiff contrast exists. Snells Law ray path method provides the most reliable velocity profiles. Finally, in situ downhole seismic tests were performed at three sites, and the importance of considering the ray path in the data reduction was emphasized by comparing the reduced shear wave velocity profiles with crosshole and standard penetration test results.

Development of Site Classification System and Modification of Design Response Spectra considering Geotechnical Site Characteristics in Korea (III) - Modification of Desing Response Specra

In the companion paper (II, Development of Site Classification System), new size classification system based on site periods was recommended for legions of shallow bedrock depth in Korea. Despite the site classification method was improved, the response spectrum would be required to be modified by adjusting the integration interval to calculate the site coefficients because the response spectra did not match well the average spectral accelerations obtained by site response analyses in the range of long periods. In this paper, new response spectra for each site categories were determined by adjusting the integration interval of long period site coefficient second. It matched well the average spectral accelerations and new response spectrum, and it was also improved compared to the current she classification system.

Construction of Precise Digital Terrain Model for Nonmetal Open-pit Mine by Using Unmanned Aerial Photograph

We have verified applicability of UAV(Unmanned Aerial Vehicle) photogrammetry to a mining engineering. The test mine is a smectite mine located at Gyeongju city in Gyeongnam province, Koera. 448 photos over area of were taken with overlapped manner using Cannon Mark VI equipped to multicopter DJI S1000, which were processed with AgiSoft Photoscan software to generate orthophoto and DEM model of the study area. photogrammetry data with 10 cm resolution were generated using 6 ground control positions, which were exported to the 3D geological modeling software to make a topographic surface object. Monitoring of amount of ore production and landsliding could be done with less than 1 hours photographing as well as low cost. A direct link between UAV photogrammetry and 3D geological modeling technology might increase productivity of a mine due to appling the topographical surface change immediately according to the mining operation.

Development of Site Classification System and Modification of Design Response Spectra considering Geotechnical Site Characteristics in Korea (I) - Problem Statements of the Current Seismic Design Code

Site response analyses were peformed based on equivalent linear technique using the shear wave velocity profiles of 162 sites collected around the Korean Peninsula. The she characteristics, particularly the shear wave velocities and the depth to bedrock, are compared to those in the western United States. The site coefficients of short period and the long period obtained from this study were significantly different compared to 1997 Uniform Building Code (1997 UBC). underestimated the motion in shot period ranges and overestimated the motion in mid period ranges in Korean seismic guideline. It is found that the existing Korean seismic design code were is required to be modified considering geological site conditions in Korea for the reliable estimation of sue amplification. Problems of the current seismic design code were dicussed in this paper and the development of site classification method and modification of desing response spectra were discussed in the companion papers(II-Development of Site Classification System and III-Modification of Dosing Response Specra).

Development of Site Classification System and Modification of Design Response Spectra considering Geotechnical Site Characteristics in Korea (II) - Development of Site Classification System

In the companion paper (I-Problem Statements of the Current Seismic Design Code), the current Korean seismic design code is required to be modified considering site characteristics in Korea for the reliable estimation of site amplification. In this paper, three site classification methods based on the mean shear wave velocity of the top 30m , fundamental site periods and bedrock depth were investigated and compared with each other to determine the best classification system. Not enough of a difference in the standard deviation of site coefficients to determine the best system, and neither is the difference between the average spectral accelerations and the design response spectrum of each system. However, the amplification range of RRS values based on were definitely concentrated on a narrow band than other classification system. It means that sites which have a similar behavior during earthquake will be classified as the same site category at the site classification system based on . The regression curves between site coefficients and described the effect of soil non linearity well as the rock shaking intensity increases than the current method based on . Furthermore, it is unambiguous to determine sue category based on when the site investigation is performed to shallower depth less than 30m, whereas the current is usually calculated fallaciously by extrapolating the of bedrock to 30m. From the results of this study, new site classification system based on was recommended for legions of shallow bedrock depth in Korea.