Results of geodetic and geotechnical monitoring of subsidence for Taiwan High Speed Rail operation

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 multilevel 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.

Land Subsidence in Chiayi, Taiwan, from Compaction Well, Leveling and ALOS/PALSAR: Aquaculture-Induced Relative Sea Level Rise

“…The total mileage of the leveling routes is about 310 km. On average, two neighboring leveling benchmarks are 1.5 km apart and the leveling network covers an area of 1087 km 2 . Over 2007-2011, we annually measured the heights of benchmarks in Figure 3.…”

“…Over 2007-2011, we annually measured the heights of benchmarks in Figure 3. The heights were network-adjusted using the method described in Hwang and Hung (2008) [2]. Using such time-lapsed heights, we determined the rates of vertical displacements at the benchmarks.…”

Groundwater Overexploitation Causing Land Subsidence: Hazard Risk Assessment Using Field Observation and Spatial Modelling

“…Multiple position borehole extensometers which incorporate magnetic markers anchored to the formation borehole have been used effectively to monitor land subsidence caused by groundwater exploitation, especially in China (Hwang et al 2008), since the first application in Poland (Lofgren 1969;Riley 1986). …”

Geostatistical Data Fusion of Multiple Type Observations to Improve Land Subsidence Monitoring Resolution in the Choushui River Fluvial Plain, Taiwan

“…The Water Resources Agency (WRA) and Central Geological Survey (CGS) have conducted long-term hydrologic and geologic studies for aquifer characterization and land subsidence monitoring (CGS 1999;Liu et al 2001). The collection of geodetic data, including precise leveling, GPS, and recently installed compaction monitoring well (CMW), can provide detailed information on the temporal and spatial variations in surface deformation in the CRFP (Liu et al 2004;Hwang et al 2008). However, using precise leveling to monitor a large area regularly is time-consuming and expensive.…”