PUMP, LOWER, GROUNDWATER

24/09/2020

In some big cities like HCMC. Ho Chi Minh City, there is a rapid construction speed. In those constructions there are basement construction buildings. During the construction of the tunnel, it is necessary to drain the underground water level hole below the construction part. Designing a reasonable drying system will reduce costs and ensure safety for the project.

When constructing foundation pits and foundation works, it is often necessary to dig the ground below the groundwater level, especially for high-rise buildings, the foundation is very deep, the number of underground floors is quite large. During construction, if groundwater seeps into the foundation pit, causing the foundation pit to be flooded, it will lower the strength of the ground soil, increase the compressibility, and the building will settle too much, or increase the weight stress. the soil itself, causing additional settlement of the foundation, which will directly affect the safety of the construction. Therefore, when constructing the foundation pit, it is necessary to take measures to lower the groundwater level and actively drain water so that the foundation is constructed in a dry state.

When applying water lowering and drainage measures, the following factors must be taken into account:

(1) Soil type and permeability coefficient .

(2) The core requires lowering the water level and the groundwater level, usually the groundwater level must be lowered to the bottom of the foundation pit 0.5 - 1.0m.

(3) Use any form to keep the foundation pit wall, especially the deep foundation pit.

(4) Large or small foundation pit area

Currently, there are two types of measures to lower the groundwater level : one is to lower the water on the surface, the other is to lower the water by wells. The name of the measure to lower the water level and the scope of its application is shown in the following table:

Name	Appropriate conditions
Surface drainage	Crushed rock, coarse sand, soil with small water permeability.
Point well	Powdered sand, clay powder, permeability coefficient 0.1-5m/day, relatively high groundwater level, point well with a depth of 3-6m; second grade point well, the depth of lowering the water level is 6 - 9m; multiple levels up to 12m.
Spray point well	The sandy soil has a permeability coefficient of 0.1 - 50 m/day, the excavation depth is greater than 6m, the water depth of the well can be up to 20m or more.
Pipe point well	The coarse sand and gravel layer of the aquifer is relatively coarse, the permeability coefficient is relatively large, the water volume is quite large, the water depth is from 3 to 15m.
Deep point	The permeability coefficient is quite large, the amount of groundwater is high.
Permeation point well	Above the soil there is an upper layer of standing water or aquifer and below it is an aquifer that does not contain water, or a relatively stable immersion or pressurized aquifer.
Permeable point well	Saturated clay soil, especially silt or silty soil, has a very small permeability coefficient, less than 0.1 m/day