Groundwater in Beijing has been excessively exploited in a long time,
causing the groundwater level continued to declining and land subsidence
areas expanding, which restrained the economic and social sustainable
development. Long years of study show good time-space corresponding
relationship between groundwater level and land subsidence. To providing
scientific basis for the following land subsidence prevention and treatment,
quantitative research between groundwater level and settlement is necessary.
Multi-linear regression models are set up by long series factual monitoring
data about layered water table and settlement in the Tianzhu monitoring
station. The results show that: layered settlement is closely related to
water table, water level variation and amplitude, especially the water table.
Finally, according to the threshold value in the land subsidence prevention
and control plan of China (45, 30, 25 mm), the minimum allowable layered
water level in this region while settlement achieving the threshold value is
calculated between
Beijing suffered successive droughts since 1999, the precipitation decreased 19 % in recent 12 years. The groundwater has been over exploited in order to ensure the safety of water supply for the capital, the average groundwater depth in Beijing plain decreased from 11.9 m (1998) to 24.3 m (2012), with an average annual decline of 0.89 m, which resulted in intensified development of ground subsidence. In the future, the contradiction between supply and demand of water resources is difficult to solve, the land subsidence will be in sustained and rapid development (Yang et al., 2010).
Years of research shows that, the main causes of land subsidence in Beijing plain is groundwater overexploitation. The characteristic of land subsidence development is closely related to the intensity and depth of groundwater exploitation. The speed and magnitude of the groundwater level change directly affect the speed and amount of ground subsidence.
The relationship between groundwater level and land subsidence in Beijing
plain has the following characteristics: on the plane, the range and
distribution of land subsidence and groundwater depression are similar. The
groundwater depression area has been expanding continuously from 1971, now
the area is more than 1000 km
In vertical, through the comparison regional land subsidence trend, layered water level and settlement, there is a good consistency between groundwater level variety and land subsidence trend. The periodic change of the settlement rate is consistent with the seasonal fluctuation of groundwater level (Yang et al., 2013) (Fig. 2).
Layer water level and settlement in Tianzhu station.
Results of multiple regression analysis.
Groundwater depression in 2010 and accumulated settlement from 1955 to 2010.
According to the sediment regulation of the quaternary stratum, the underground water layer structure, exploitation utilization of groundwater and other factors, the aquifer in Beijing area can be divided into four groups: the first aquifer group, mainly phreatic water and confined water whose buried depth is less than 50 m shallow; the bottom boundary depth of second aquifer group is 80–120 m, while the third aquifer group is 150–180 m and the fourth one is 300 m.
F3–7 (64.5–82.3 m) settlement with the water level elevation of D3–4 in Tianzhu station.
The first phase project of Land Subsidence Monitoring Network and Warning System in Beijing has been built in 2004, three land subsidence monitoring stations were set up. There are marked and layered bedrock standard group, groundwater level and pore water pressure monitoring wells in every station (Table 1). Monitoring data of layered water table and settlement in long time series provide a solid basis on the further research between them.
For further identification of the intrinsic relationship between the two,
multi-linear regression models are set up by long series factual monitoring
data about layered water table and settlement in the Tianzhu monitoring
station based on quarterly average water table, water level variation and
amplitude (Eq. 1).
The minimum permissible level of groundwater in different control of settlement velocity.
The calculated, actual and optimized value of F3–3.
The calculated, actual and optimized value of F3–4.
The calculated, actual and optimized value of F3–6.
The calculated, actual and optimized value of F3–8.
The correlation coefficient of
The analysis results show that (Table 2), in addition to
D3–6/F3–10 monitoring layer, the correlation coefficients of the other layers
are greater than 0.8, the ground ettlement has highly positive correlation
with the above factors (Dong, 2006; Hao et al., 2011).
F0.05 (1, 28)
The coefficient of quarterly average water table variable
According to the annual control targets of land subsidence in Beijing, the threshold values are set as 45, 30, 25 mm.The layered control target of F3–3, F3–4, F3–6 and F3–8 are calculeted by the historical data of settlement.The minimum allowable layered water level in this region while settlement achieving the threshold value can be calculated (Table 3).
Ground subsidence has high degree correlation with the groundwater level
in Beijing plain area. On the plane, the range and distribution of land
subsidence and groundwater depression are similar. In vertical, there is
good consistency between groundwater level variety and land subsidence trend. The ground settlement has highly positive correlation with the average
water table, variation and amplitude. Quarterly average water table has
the strongest impact on accumulated settlement.
According to the threshold value in the land subsidence prevention and
control plan of China (40, 30, 25 mm),the minimum allowable layered
water level in this region while settlement achieving the threshold value is
calculated between