In response to the land subsidence phenomenon in Yunlin and Changhua area due to groundwater overuse, BOHSR has been supervising THSRC to conduct annual monitoring inspections on HSR piers since 2003. Based on the monitoring records in 2014, areas suffering most from this issue currently are Hsichou Township District in Changhua, Huwei Township in Yunlin and the four places crossing Yunlin Country highway 158 and Provincial highway 78. Among the four places with significant subsidence, one of the areas showed less subsidence due to embankment removal of that certain area. However, the remaining three places showed increase in land subsiding. Looking at the differential settlement statistics (angle variables of adjacent piers) which is the major index to measure HSR operational safety in this matter, even the most significant subsiding area at the intersection of HSR route and Provincial highway 78 showed 0.63/1,500. This number showed decrease comparing to 0.76/1,500, which was measured in 2013. Both measurements in 2013 and 2014 were within the allowable value, 1/1,500, indicating that the HSR structure is safe for operation.
To eradicate the land subsidence issue along HSR routes, the Executive Yuan respectively ratified "Speciﬁc Solutions and Action Plans Confronting Land Subsidence in Yunlin and Changhua Areas (the 1st amendment)" in 2013 May and "Golden Agricultural Corridor Project" in 2013 Dec. The projects successfully reduced groundwater usage which effectively slowed down the land subsidence issue in Yunlin and Changhua areas and brought positive impact toward HSR structural and operational safety in that area. BOHSR will continue to monitor the subsiding status of HSR bridge piers and carry out specific emergency measures to ensure HSR operational safety.