Results of geodetic and geotechnical monitoring of subsidence for Taiwan High Speed Rail operation |
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| Authors: | Cheinway Hwang Wei-Chia Hung Chih-Hsi Liu |
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| Institution: | (1) Department of Civil Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu, 300, Taiwan;(2) Energy and Resources Laboratory, Industrial Technology Research Institute, Building 24,195, Sec. 4, Chunghsing Road, Chutung, Hsinchu, Taiwan |
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| Abstract: | Taiwan High Speed Rail (THSR), which began operations in January 2007, passes through an area in Yunlin County where the largest
cumulative subsidence measured during 1992–2006 exceeds 100 cm. Leveling benchmarks, GPS pillars and multi-level monitoring
wells were deployed in this area to collect detailed subsidence data from October 2003 to 2006. Leveling is carried out on
both ground benchmarks and survey bolts attached to THSR columns. Minimum constraint solutions of leveling networks produce
estimated heights accurate to a few mm. Special attention is paid to code smoothing, ionospheric, tropospheric and ocean tidal
loading (OTL) effects, so that height estimates from GPS are optimal. Leveling and GPS-derived height changes are consistent
to 1 cm, and show that from Stations 210 to 240K of TSHR, the subsidence is bowl shaped. Measurements of sediment compaction
in specific depth intervals at three monitoring wells indicate that most of the subsidence is caused by sediment compaction
at depths from 50 to 300 m. The major compaction occurs in the interval 220–300 m and is attributed to ground water withdrawal.
Large angular deflections as determined from subsidence measurements are detected at some columns, but are below the upper
bound (1/1,000) of tolerance specified in the safety code. With the current subsidence and sediment compaction, no significantly
reduced loading capacity of the columns is expected to occur. For a safe THSR operation, subsidence and sediment-compaction
monitoring should be continued, and current ground water withdrawal in Yunlin must be reduced or stopped. |
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| Keywords: | GPS Leveling Monitoring well Subsidence THSR |
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