In response to the land subsidence phenomenon in Changhua, Yunlin and Chiayi areas due to groundwater extraction, since 2003, BOHSR has been supervising THSRC to conduct annual monitoring inspections on HSR piers and report results to central and local governmental authorities for record and reference of land subsident prevention. Based on the monitoring records in 2016, the subsiding values and angle variables in recent three years of the four significant areas in the area have been listed out in the following table. Data showed increase only in Yunlin Station District due to overall subsidence in the area; the pier angle variables of the remaining three places remained stable. According to the records, significant subsiding sections are TK216~TK234 in Huwei and Tuku Township with maximum subsidence value of 5.1 cm at TK218+465 which was less comparing to 6.6cm in 2015. In addition, the subsidence value on the north shore of Puzi River was measured 1.2 cm in 2016, also a decrease comparing to 3.1 cm in 2015. Currently, the angle variables of piers are lower than the allowable value indicating that the HSR structure is safe for operation.
To monitor the land subsidence condition alongside HSR routes and generate response measures, MOTC established the “HSR Alongside Land Subsidence Prevention Ad Hoc Group” in 2008 to provide relevant agencies to help promote a coordination platform for HSR alongside land subsidence prevention and control work. The 1st Ad Hoc Group Meeting in 2017 had been held on July 10. According to the presentation by Water Resources Agency, MOEA, the groundwater level in 2017 is significantly lower, forecasting that the area of significant subsidence may potentially increase this year. The Agency requested the units to take appropriate measures to strengthen the land subsidence prevention and control, and requested THSRC to continuously monitor and clarify the reasons for the differential subsidence issue at Yunlin Station.
BOHSR has continuously monitored the subsiding status of HSR bridge piers since the opening of the system and will be ready carry out specific emergency measures to ensure HSR operational safety.