How to effectively control the groundwater level in the construction of water conservancy projects

Control scheme of groundwater level in the construction of water conservancy projects:

In order to make the water conservancy project have safe and reliable good construction conditions, ensure the normal operation of existing hydraulic buildings, effectively protect the natural environment, and prevent the harm caused by groundwater, in the process of survey, design and construction, it is necessary to take corresponding measures and countermeasures according to the specific situation to effectively control the groundwater. According to its basic principle, it can usually be divided into three types of control methods: construction diversion, foundation pit drainage, and artificial interception of seepage leakage.

1.Construction diversion.

In the construction of rivers and canals, first build cofferdams to protect foundation pits in the upstream and downstream of foundation pits, and discharge upstream water by means of temporary drainage buildings or deep trenches, which is the first step of groundwater level control. It must be done well and carefully. The cofferdam should be made of local materials, built with sandy loam and loam, pay attention not to mix tree roots, wooden sticks, ice cubes, frozen soil blocks in the middle, and the parts on both sides of the back of the canal should be tamped to prevent leakage, and the effect is better if geotextiles and plastic films can be used.

The top width of the soil solid weir is generally not less than 2m, if it is used for traffic, the top width should be determined according to the road requirements, and the slope of the cofferdam should meet the stability requirements, and a section of 1:2 is appropriate. When filling in water, the slope should be gentle, and the slope should be 1:

or 1:3. When arranging the cofferdam, the upstream and downstream cofferdams should be kept at a certain distance from the edge of the foundation pit, and the distance should be determined according to the stability of the foundation pit slope and the layout requirements of the construction site.

2.Foundation pit drainage.

After the upstream and downstream cofferdams are built, as long as there is water in the foundation pit, the water in the foundation pit should be discharged first. Generally, according to the amount of stagnant water, the water pump can be discharged several times. Ming-style drainage is suitable for the excavation of new and old foundations, and it is usually arranged in the foundation pit to arrange the drainage ditch to facilitate the soil on both sides.

When the foundation is narrow, the main drainage ditch should be located on the upstream side. A number of drainage branch ditches are set perpendicular to the main drainage ditch. The seepage water branch ditch flows into the dry ditch, and then flows into the collection well or reservoir located outside the foundation range, and then pumps out of the cofferdam.

The water pump for drainage is appropriately selected according to the water volume and head, and a certain number of standby pumps should be prepared considering that the pump may fail. The water pump can be submersible pump and centrifugal pump, we generally use electric power mud mixed flow pump, this pump is convenient, fast and adaptable.

3.Artificial interception of seepage precipitation.

In the soil is sand or sandy loam, the scale of the work is not large, the control range is small, the excavation foundation depth is shallow, and the groundwater level drops below the bottom surface of the foundation pit to ensure the construction of the project, and the earth well point method is adopted at this time. The specific method is: every well point is laid around the foundation pit, each well point is connected with a water collection pipe, and the water collection pipe is connected with the pump.

The wells can be more or less, and the outer wells can also be connected with tees and five-way pipes, and pumped in several groups. The well pipe at the well point is inch) plastic pipe, and the pipe is inserted into the well by the method of pressurized water downhole plastic pipe. The lower end of the pipe is a flower tube, which is wrapped with brown skin or fine window screen, and the gap between the well wall and the well pipe is filled with coarse sand and other filter materials.

The diesel engine or electric motor is equipped with a 5cm (2-inch) water pump, each pump is connected to 5 well points with a reducer joint, and 2-3 water pumps can be controlled at the same time.

The groundwater level is controlled below the critical depth, the salt accumulation of soil is weakened, and the effect of precipitation and irrigation on soil salt leaching is strengthened, so the soil salinity gradually decreases. Controlling the groundwater level is a huge project, and it is difficult to do it by pumping groundwater alone, but it will achieve an economically feasible purpose by using multiple ways and methods in a comprehensive manner.

1) Build a good surface drainage system. Through the construction of drainage ditches, the surface runoff can be smoothed, the formation of stagnant water can be avoided, and the seepage of surface water into the recharge groundwater can be reduced.

2) Promote water-saving irrigation technology. At present, the irrigation of the Yellow River is mostly carried out in the form of flood irrigation, so that part of the irrigation water seeps into the ground, and the other part of the evaporation zone is concurrent, and the proportion of water used for crop growth is small, and in the long run, infiltration into the ground and evaporation will directly or indirectly aggravate the process of soil salt accumulation. Therefore, the promotion of water-saving irrigation technology is not only of significance for saving water resources, but also has positive significance for soil improvement.

3) Development and utilization of shallow groundwater and brackish water. Except for the southern part of Guangrao County, the degree of development and utilization of groundwater in the area is very low, but there is a certain range of shallow fresh water and brackish water distributed in the area, which can be used as irrigation water in the dry season. It is also necessary to formulate policies to encourage the development and utilization of shallow groundwater, so that water injection for oilfield exploitation and water injection for industrial cooling and air conditioning can be used for shallow groundwater.