Statistics of the leveling results of the Yunlin area in the past 29 years, and the cumulative subsidence statistics drawn every 10 years are shown in Table 3. The table shows that the cumulative change in the Yunlin area in the third stage has decreased, but the decrease is not as large as Changhua The area is obvious, indicating that the Yunlin area must continue to strengthen the control of stratum subsidence. Based on the analysis of the data of the sag monitoring wells, the recent overall compression trend is more obvious in the inland areas than in the coastal areas. Among them, the Xiutan Elementary sag monitoring well has the largest compression trend, with a compression rate of 4.2 cm/year, followed by the Neiliao station. The leveling inspection results of the station, Yuanchang Elementary School, Nanguang Elementary School, Honglun Elementary School, and Yunlin (540 kilometers) area are shown in Figure 2 and Table 1. The related descriptions are as follows:

Statistics of the leveling results of the Yunlin area in the past 29 years, and the cumulative subsidence statistics drawn every 10 years are shown in Table 3. The table shows that the cumulative change in the Yunlin area in the third stage has decreased, but the decrease is not as large as Changhua The area is obvious, indicating that the Yunlin area must continue to strengthen the control of stratum subsidence. Based on the analysis of the data of the sag monitoring wells, the recent overall compression trend is more obvious in the inland areas than in the coastal areas. Among them, the Xiutan Elementary sag monitoring well has the largest compression trend, with a compression rate of 4.2 cm/year, followed by the Neiliao station. The compression rate of sag monitoring wells in Zhan, Yuanchang Elementary School, Nanguang Elementary School, Honglun Elementary School, Shuicanlin Elementary School, and Dongguang Elementary School is between 3.0 and 3.9 cm/year, while the other sag monitoring wells have relatively compressed trends Small, but the development of stratigraphic compression behavior in these locations must continue to be paid attention to in the future

(1)Calculate the leveling results of the Yunlin area in the past 29 years, and draw the cumulative subsidence statistics table every 10 years, as shown in Table 5. The table shows that the cumulative change in the Yunlin area in the third stage has decreased, indicating the prevention of stratum subsidence Results have been achieved, but the reduction has not been as pronounced as in Changhua, indicating that the Yunlin area still needs to continue to strengthen the control of stratum subsidence.

(2)In 2020, the maximum annual subsidence rate in Yunlin area is 5.5 cm/year, and the significant subsidence area is 103.8 square kilometers. The main towns and villages with subsidence rates exceeding 3 cm/year are: Huwei Town, Tuku Town, Yuanchang Township, There are 6 townships including Baozhong Township, Lunbei Township and Dayi Township.

(3)The main subsidence area of ​​Huwei Town is located in the Huwei District of Zhongke and the Huwei High-speed Railway Special Area. The annual average subsidence rate in this area is greater than 3 cm/year; in the Huwei District of Zhongke, the maximum subsidence rate can reach 4.2 cm/year , And the area adjacent to the high-speed rail station, the maximum subsidence rate can reach 3.3 cm/year.

(4)Analyzing the monitoring well data of the 300-meter depression in Guangfu Elementary School, Huwei Town, the area from the surface to the depth of 287 meters has compression behavior, but the main compression range is concentrated in the fourth aquifer (depth of 246-287 meters). Since Guangfu Elementary School is adjacent to the Zhongke Huwei Park, factories have been built one after another, and there are also many farmland pumping activities nearby. Pumping and loading will make the stratum subsidence more obvious. Therefore, in the future, we should pay attention to the water use behavior in this area. In addition, it is also necessary to pay attention to the impact of on-site construction load. .

(5)The subsidence rate of most of the leveling inspection points in Tuku Town is greater than 3 cm/year, and the subsidence in the whole area is significant. Analysis of the monitoring well data of the 300-meter deep subsidence in the Tuku National Middle School in Tuku Town shows that the surface of the area reaches a depth of 294 meters. Compression occurred in the stratum in the middle, but the main compression range was between 228 and 273 meters in depth, belonging to aquifer 3 and aquifer 4; application of GNSS fixed station, leveling survey, deep leveling piles and subsidence The comparison results of the monitoring well data show that the monitoring results of the GNSS fixed station and the leveling survey are consistent, but with the change of time, the amount of subsidence between the two is significantly greater than that of the subsidence monitoring well and the deep leveling pile (the subsidence monitoring well and the deep leveling pile) The monitoring magnitude and trend of deep leveling piles are the same). This phenomenon also shows that there may still be compression in the neighboring areas of the tuku country below the depth of 300 meters.

(6)The distribution map of the detection points in Yuanchang Township, the maximum subsidence rate is 5.5 cm/year; analysis of the monitoring well data of 300 meters deep subsidence in Yuanchang Township Kecuo Elementary School, the area is between the surface and the depth of 298 meters Compression occurred in all stratums, but the main compression range covers a depth of 147 to 292 meters, belonging to aquifer 2 to aquifer 4.

(7)The main subsidence area of ​​Baozhong Township is located at the junction of Baozhong Township and Tuku Town. The subsidence rate in the year 109 increased slightly to 3.7 cm/year compared with last year, in line with the compression history of the Longyan National Small Subsidence Monitoring Well relative to the bottom of the well. The line graph shows that the main compression range of the stratum is concentrated between the depths of 107 to 149 and 202 to 227 meters, which belong to the aquifer 2 to 4 aquifer.

(8)The main subsidence area of ​​Sihu Township is located in the area between Mingde Elementary School in the center of the township and Nanguang Elementary School on the south side. In 107, a 300-meter-deep stratum subsidence monitoring well was set up in Nanguang Elementary School. According to the data of the depression monitoring well, The main compression occurred between 0 and 54 meters, indicating that the stratum subsidence in this area should be mainly related to shallow water use.

(9)The main subsidence area of ​​Dayi Township is located on the west side of the township and bordering Tuku Town and Huwei Town. The maximum subsidence rate is 3.4 cm/year. At present, 1 continuous GNSS observation station and 1 continuous GNSS observation station have been set up in Jiuzhuang Elementary School in this area. Monitoring wells for land traps to facilitate cross-comparison and analysis of follow-up results.

(10) The main sources of compression in the Huwei Park and the Yunlin Station area of ​​the high-speed railway (Huwei area) in the near future are mainly the depth range of the deeper aquifer 4, and the depth range of the shallow aquifer 1 also has a partial contribution.

(1)Analysis of subsidence in Yunlin area from May 2019 to May 2020

Analyze the average subsidence rate in Yunlin area from 2019 to 2020, and the results are shown in Figure 3-108. As shown in Figure 3-108, the villages and towns with a subsidence rate of more than 3 cm/year in Yunlin County this year include: Huwei Town, Tuku Town, Yuanchang Township, Baozhong Township, Lunbei Township and Dayi Township, etc. In villages and towns, the maximum annual subsidence rate is 5.5 cm/year, and the significant subsidence area is 103.8 square kilometers.

The map showing the average subsidence rate from 2018 to 2019 and 2019 to 2020 (Figure 3-109) shows that the main subsidence areas in the Yunlin area have been concentrated in inland towns (Huwei Town, Tuku Town, Yuanchang Township, Baozhong) in recent years. Township, Lunbei Township and Dayi Township), and the subsidence areas in coastal areas are mainly in Sihu Township, Kouhu Township and Taixi Township; analysis of the results of various inspection points in key subsidence areas in inland and coastal areas (Table 3-20) , And explain according to the detection results of each area.

(2)Analysis of cumulative subsidence from 1992 to 2002, 2002 to 2011 and 2011 to 2020 in Yunlin area

(A)Cumulative change in Yunlin area from 1991 to 2000

Analyze the cumulative change of Yunlin area from 1991 to 2000 as shown in Figure 3-124. During the above period, the Yunlin area is mainly composed of the coastal Mailiao Township, Taixi Township, and the inland Huwei Town, Tuku Town, Yuanchang Township and Baotou Township. Zhongxiang is the main sinking center. Before 2000, the area of ​​significant subsidence in Yunlin was mostly over 360 square kilometers, and the maximum amount of subsidence reached 783 square kilometers. The maximum accumulated subsidence during the above period reached 93.4 cm, which mainly occurred in Mailiao Township.

(B)The cumulative change in Yunlin area from 2001 to 2010

Analyze the cumulative changes in the Yunlin area from 2001 to 2010 as shown in Figure 3-125. During the above period, the inland Huwei Town, Tuku Town, Yuanchang Township and Baozhong Township were the main subsidence centers in the Yunlin area. The civil structure of the railway is completed, and the high-speed railway is passing through the most severe subsidence center, so the subsidence of the ground will have an impact on the structure of the high-speed railway. During this period, it can be seen that the prevention and control of stratum subsidence began to take effect gradually, and the subsidence of coastal areas gradually slowed down. The position of stratum subsidence in inland areas was maintained in the central fan area, but the subsidence rate increased from the maximum of 12.2 cm (2002 to 2003). It dropped to 6.8 cm (2010-2021), and the area of ​​significant subsidence dropped from 703 square kilometers (2002-2003) to 397.6 square kilometers. During this period, the maximum accumulated subsidence reached 84.1 cm, which mainly occurred in Tuku Town.

(C)Cumulative changes in Yunlin area from 2011 to 2020

Analyze the cumulative changes in the Yunlin area from 2011 to 2020 as shown in Figure 3-126. During the above period, the inland Huwei Town, Tuku Town, Yuanchang Township and Baozhong Township were the main subsidence centers in Yunlin area. Subsidence conditions were also found in Hu Township and Dayi Township. During this period, the prevention and control of stratum subsidence has achieved specific results. The area of ​​significant subsidence has been maintained at 100-300 square kilometers during most of the period from 2011 to 2020. However, in 2014, 2015, 2017 and 2018, these 4 areas The annual water conditions are not good, so the area of ​​significant subsidence increased to more than 300 square kilometers. During the period from 2011 to 2020, the maximum accumulated subsidence reached 62.2 cm, which mainly occurred in Tuku Town.

Observed from the entire area, the main subsidence area is west of Zhongshan Expressway in Yunlin County, and relatively stable area is east of Zhongshan Expressway. This phenomenon is related to geological conditions and pumping phenomena. In terms of the boundary, the fan center and fan tail of the Zhuoshui River alluvial fan are mainly contained. The soil is rich in compressible soil (such as silt and clay). In addition, the main pumping wells in the Yunlin area are concentrated in the fan center and fan tail area. Among them, the fan center is the most, which has caused a lot of subsidence in the inland areas of Yunlin in recent years.

(3)Analysis of cumulative subsidence in Yunlin area from 1985 to 2020

Yunlin County is located in the southern half of the Zhuoshui River alluvial fan, and is one of the important agricultural counties in the province. In the 1970s, due to poor prices of agricultural products and poor returns, coupled with the lure of high profits from the aquaculture industry, a large number of agricultural land in coastal areas was changed to aquaculture. Fisheries. However, the aquaculture industry must rely on a large amount of fresh water to keep the fish ponds clean. Under the situation of lack of surface water in coastal areas, the aquaculture industry turns to pumping groundwater, and then the groundwater is pumped excessively, which causes the occurrence of stratum subsidence.

Based on the leveling results data from 1985 to 2020, the cumulative subsidence of Yunlin from 1985 to 20209 is drawn as shown in Figure 3-127. The figure shows that the early Yunlin area had two subsidence centers from 1985 to 2000, and one was located near Jinhu Lake. The other is located near Taixi Mosquito Port. At that time, the coastal area was mainly fish farming area. After 1996, the center of Yunlin subsidence gradually moved inland. After 1999, the center of subsidence was concentrated in Baozhong Township, Tuku Town, and Huwei Town. With Yuanchang Township; historical analysis data shows that the subsidence center of Yunlin area is gradually shifting from the coast to the inland (Lu et al., 2016). Overall assessment of the total subsidence of the Yunlin area in the past 20 years, the inland area has exceeded 180 cm of subsidence, and the high-speed railway is passing through the most severe subsidence area (Figure 3-128)

In addition, according to the monitoring data of the high-speed railway company, there is no obvious subsidence along the high-speed railway line in the Yunlin area in the Xiluo area. After entering the Huwei area, the subsidence is rapid, and the Tuku and Yuanchang areas are the largest subsidence areas. Analysis of the area of ​​subsidence in Yunlin area from 1992 to 2020 is shown in Table 3-28, and the figure of cumulative subsidence is shown in Figure 3-128.