In response to the land subsidence phenomenon in Yunlin/ Changhua area due to groundwater overuse, BOHSR has been supervising THSRC to conduct annual monitoring inspections on HSR piers since 2003. Annual inspection results have all been submitted to central and local authorities as reference for land subsidence prevention measures. In accordance to 2013 Leveling Survey Evaluation Report conducted by THSRC, amongst the 4 most severe subsidence sections (see table 1), all have showed subsidence deceleration besides HSR Yuanchang section and Tuku section.
Currently, the area along HSR suffering the most from land subsidence is the intersecting section (see figure 1) of HSR and Provincial Highway 78. Although its accumulated maximum subsidence depth has reached 78.6cm, the seriousness has declined through these years. To resolve this issue, THSRC has finished a two-phase preventive strengthening improvement measure on this certain area by the end of 2011 and currently HSR operation is free from safety concerns. Moreover, to diminish the pressure from the embankment of Provincial Highway 78 against the HSR bridge pier which may further increase subsidence of the pier, the Executive Yuan held a project sitting to instruct Directorate General of Highways, MOTC to execute Provincial Highway 78 Embankment Elimination and Viaduct Construction which is scheduled to reach completion before 2015 Chinese New Year Holidays. During the construction period, Directorate General of Highways and BOHSR will continue to monitor the subsiding condition of HSR piers to ensure HSR structure stability and operation safety.
To eradicate the land subsidence issue along HSR, 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 reduced groundwater usage which effectively resolved 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 the operational safety of HSR operation.