Jet Pump for Foundation Pit Dewatering

In underground engineering projects, it is often necessary to artificially lower the groundwater level. When open ditch drainage with large-scale excavation is not suitable, well point dewatering is an excellent alternative, including light well points suitable for shallow drawdown and jet well points capable of drawdown depths exceeding 10 to 20 meters.

I. Light Well Point Dewatering

Light well point dewatering uses a jet pump with a supporting centrifugal pump arranged above ground level at the foundation pit (see Figure 1). Each well point pipe is connected to the suction inlet of the jet pump via a common header pipe, and the centrifugal pump circulates clean water. The ultimate suction depth of the jet pump is 10 meters, typically achieving a dewatering depth of approximately 8 meters.

Figure (1) Light Well Point Dewatering System Flow Diagram

1. Centrifugal Pump; 2. Motive Water Pipe; 3. Jet Pump; 4. Suction Header; 5. Discharge Pipe; 6. Well Point Pipe; 7. Circulation Water Tank

Light Well Point Dewatering System Installation and Commissioning

Install the ground-level centrifugal pump, jet pump, water tank, and surface piping. Determine the well point layout, drill holes, sink the well point pipes, and backfill with sand filter material. Test to confirm that the well point pipes are free of air and water leaks before placing the system into operation.

II. Jet Well Point Dewatering

An alternative approach is jet well point dewatering, in which the jet pump is installed inside the jet well pipe (our company has integrated this into a single jet deep well pump unit). The burial depth of each jet deep well pump is determined based on the required dewatering depth (see Figure 2). Typically the suction depth (required dewatering depth) can be approximately 4 to 6 meters below the jet pump position. This type of jet pump generally requires a supporting high-pressure water pump.

Figure (2) Jet Well Point Dewatering System Flow Diagram

(A) Equipment Layout Diagram; (B) Plan Layout Diagram.

1. Circulation Water Tank; 2. Centrifugal Pump; 3. Water Supply Header; 4. Return Water Collection Pipe; 5. Outer Pipe; 6. Inner Pipe; 7. Jet Pump; 8. Filter Pipe

a. Circulation Water Tank; b. Centrifugal Pump; c. Return Water Collection Pipe; d. Water Supply Header; e. Jet Well Point

Jet Well Point Dewatering System Installation and Commissioning

Install the ground-level centrifugal pump, water tank, and surface piping. Determine the well point layout, drill holes, sink the jet well point pipes (jet deep well pumps), and backfill with sand filter material. Test to confirm that the well point pipes are free of air and water leaks before placing the system into operation.

III. Advantages of Jet Pumps for Foundation Pit Dewatering

Whether it is a surface-mounted jet pump or a jet deep well pump, the jet pump contains no moving parts whatsoever, making it well suited for pumping water containing sediment and debris. Compared with mechanical suction pumps, jet pumps offer significantly improved reliability and stability, with long continuous operating cycles.

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