Back Issues 11-20

THE MAJOR CAUSE FOR THE DESTRUCTION OF THE GANGWEIGOU CREEK FLOODWAY 

Tse-Shan Hsu
President, Institute of Mitigation for Earthquake Shear Banding Disasters Professor, Department of Civil Engineering, Feng-Chia University Taiwan, R.O.C.
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Ming-Tuo Chen
Ph.D. Program for Civil Engineering, Water Resources Engineering, and Infrastructure Planning, Feng-Chia University, Taiwan, R.O.C. 

Shey-En Chiu
Water Resources Agency, Ministry of Economic Affairs Taiwan, R.O.C. 

Abstract 

At present, all hydraulic structure design codes have not fortified the main effect of tec- tonic earthquakes. Therefore, although the designs provided by the technicians have fully met the requirements of the code, the hydraulic structures after completion will still have localized piping failure problems under shear banding effect. In view of this, the authors of this paper have conducted an in-depth study of the piping failure induced landslides in Gangweigou River Floodway in Tainan, Taiwan. The results of the study reveal that be- cause the piping failure mechanism proposed by Terzaghi is based on the steady-state groundwater seepage flow with mass conservation, after it was adopted by the techni- cians, most of them were unable to obtain results consistent with actual piping failures; and actual piping failures only occur locally in the shear bands, where the degree of brit- tle fracture of the soil stratum increases with the increase in the amount of shear banding, so soil particles will flow out along the pipelines formed by the pore space in the shear band. Therefore, the condition of initiating piping failure is redefined as the bottom ve- locity of particles in the shear band being greater than or equal to the critical bottom ve- locity of the particles. Finally, it is suggested that the shear banding effect and the new piping failure mechanism proposed by the authors should be incorporated into the hydraulic structure design specifications, so as to ensure that the design provided by the technician is safe and the major cause of the disasters provided by the investigator is cor- rect in the future. The results of the study reveal the following. (1) Because the piping failure mechanism proposed by Terzaghi, the father of soil mechanics, is based on the steady-state groundwater seepage flow with mass conservation, after it was adopted by the technicians, most of them were unable to obtain results consistent with actual piping failures. (2) Piping failures only occur locally in the shear bands, where the degree of brittle fracture of the soil stratum increases with the increase in the amount of shear band- ing, so soil particles will flow out along the pipelines formed by the pore space in the shear band. Therefore, the condition of initiating piping failure is redefined. Finally, it is suggested that the shear banding effect and the new piping failure mechanism proposed by the authors should be incorporated into the hydraulic structure design specifications, so as to ensure that the design provided by the technician is safe and the major cause of the disasters provided by the investigator is correct in the future. 

Keywords: hydraulic structures, shear banding, piping failure, bottom velocity. 

Attachments:

1102 Final.pdf

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