Wellpoint Dewatering in Engineering Groundwater
With the development of social economy, the improvement of modern industrialization and urbanization, and the increase of population, the shortage of urban ground space becomes more and more serious. To take full advantages of limited land, it has been pa
- PDF / 2,576,640 Bytes
- 79 Pages / 439.37 x 666.142 pts Page_size
- 24 Downloads / 164 Views
Wellpoint Dewatering in Engineering Groundwater
With the development of social economy, the improvement of modern industrialization and urbanization, and the increase of population, the shortage of urban ground space becomes more and more serious. To take full advantages of limited land, it has been paid attention on the high-level space and underground space. In recent years, the emergence of a large number of high-rise buildings, and underground projects such as the subway, underground commercial street, underground power plants, and pumping stations are well developed. In the construction of high-rise buildings and underground projects, the deep excavation accounts for a large percentage, which has became a preferred method in construction. However, engineering accidents, which is caused by quicksand, piping, the instability of the pit bottom, or the collapse of the pit wall, have happened almost every year, resulting in inestimable casualties and loss in economy. Such accidents can be prevented by dewatering the groundwater table in advance of excavation. The wellpoint system has been in general use in construction dewatering, which has became the most versatile of pre-drainage methods, being effective in all types of soils. Dewatering wells are set around the foundation pit, deeper than the bottom. When dewatering begins, the water level goes down and forms the cone of depression. The water table should be 0.50–1.00 m lower than pit bottom to keep the soil dry during excavation. Wellpoint dewatering technology has been developed over a hundred years of history. In the early days, only some simple ditches and sumps were set during excavation. Later, the filter wells appeared, and pump was used for water drainage. Practice shows that when the effective diameter d10 is less than 0.10 mm, the time required for dewatering sharply increases; when the d10 is less than 0.05 mm, this simple approach cannot achieve the purpose of dewatering. Later, it was found that a certain vacuum degree around the tube can break through this limit, thus the vacuum wellpoint, also known as light wellpoint, occurred in 1925–1930. Then in 1930s, electroosmosis wellpoint also had been used in dewatering. With the increasing dewatering depth, the multistage wellpoint, ejector wellpoint, and deep wellpoint have been developed. © Tongji University Press, Shanghai and Springer Science+Business Media Singapore 2017 Y. Tang et al., Groundwater Engineering, Springer Natural Hazards, DOI 10.1007/978-981-10-0669-2_5
183
184
5 Wellpoint Dewatering in Engineering Groundwater
Table 5.1 Application for different types of wellpoint Wellpoint types
Hydraulic conductivity (m/day)
Drawdown (m)
One-stage light wellpoint Two-stage light wellpoint Electroosmosis wellpoint Tube wellpoint Ejector wellpoint Deep well pump point
0.10–80.00 0.10–80.00 15.00
In the excavation and construction of deep foundation pit, dewatering with wellpoints to reduce phreatic or confined underground water table has become a necessary engineering measure. Wellpoint dewa
Data Loading...
