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WHY AND HOW DO YOU DEWATER THE GROUND?

   

DEWATERING GROUNDWATER

Dewatering is the process of removing groundwater or surface water from a construction site using dewatering systems. The process moves water up through wells, wellpoints, or sumps installed in the ground or pumps water from a body of water, ditch, or pit.

WHY IS IT IMPORTANT TO DEWATER IN COSTRUCTION?

Controlling groundwater in a construction project is critical to success. Water intrusion can threaten ground stability.

EXCAVATION SAFETY

Dewatering provides a workable excavation to ensure personnel safety.

CHOOSING THE CORRECT PUMP COMPANY

METHOD 1: WELLPOINT SYSTEMS

Wellpoint Systems are the most commonly used dewatering method.  A properly installed system will pre-drain and stabilize wet soils up to a depth of 17′.  Additional stages can be installed if the excavation is deeper.  The wellpoint system consists of a series of wellpoints usually jetted into place.  Holland Pump can hand-jet, punch, or drill for placing wellpoints.  The tip of the wellpoint will generally be a minimum of six feet below the proposed elevation. The wellpoints are connected to a common header system by a flexible swing joint.  Each swing has a valve to control the flow of water and air into the header.  The header system is connected to a pump to maintain a continuous vacuum.  Atmospheric pressure forces water through the ground, up the wellpoint, into the header system and pump where it is discharged to an approved location.

ADVANTAGES

  • Minimal installation space needed
  • Traditional or sanded wellpoints are suitable for many soil conditions
  • Complicated header geometries are possible
  • Tiered systems possible for deep excavation

 

METHOD 2: SOCK SYSTEMS

Sock Systems are relatively easy. A specialized trencher digs and installs fabric wrapped perforated pipe under the construction area. The drain length is determined by the soil conditions and the water table. In general, drain lengths of 200 to 400 feet and installation depths of up to 18 feet are common.  Multiple runs in parallel can be used.  Individual runs are collected in a common header for connection to a wellpoint pump.  Usually after 2 to 3 days the water table has been lowered enough for initial excavation to begin.  After subsurface construction is completed, pumps and header can be removed from the system allowing the water table to return to normal.  Sock underdrain is capped for future use or abandoned in place.

ADVANTAGES

  • Quick installation with no need for site dewatering prior to trenching
  • Suitable for many soil conditions
  • Minimal disruption to job site both during and after installation
  • Sock installations often provide the most cost effective method of dewatering

 

METHOD 3: DEEP WELL SYSTEMS

Deep Well Systems​​ are used where the excavation depth exceeds the maximum limits for a wellpoint system and a large quantity of water needs to be extracted. They are ideal for keeping water away from construction trench areas enabling work to be carried out in dry and stable conditions. A deep well system would also be used if space is limited as wells can be sited away from the construction area.

ADVANTAGES

  • Drawdown only limited by depth of well and soil stratification
  • Pressure relief can be provided in deep layers
  • Wells can be placed away from working areas
  • Wells are usually installed at spacing which minimizes surface access restrictions

 

INSTALLATION

Holland Pump offers a full installation service for deep well applications.  Our highly experienced team will visit your site and by using soil analysis will advise you on the best solution for your dewatering requirement. We will advise on the depth of each well and also the quantity and positioning to ensure that the excavation remains dry through-out the project cycle. Once the system design has been approved, our specialized drilling team will bore for the well screen to be installed. The well screens are typically 5″ in diameter and joined together to provide the required length. Wells are often surrounded with filter sand to connect soil layers and prevent fines from entering the system. Once the well has been flushed it is ready to have the pump installed. The type and size of pump used will match each application. The pump is carefully lowered into the well where it is safely installed. The depth at which the pump is installed will depend on the final depth of excavation.  The electric cable is taken up the well where it is connected to a power supply via one of our control panels. Each control box is fed from a main supply or generator. Pump discharge is connected to a common discharge main by layflat or pvc discharge pipe.

 

METHOD 4: OPEN SUMPING

Open Sumping Systems or Trash Pump Systems are used where unwanted ponding or pooling water occurs.  It can also be a method to dewater low permeability soils, and where the subgrade is near bedrock or a limestone shelf.

 

ADVANTAGES

  • Pumps are designed to safely pass a 3″ solid without clogging
  • Primes and reprimes automatically
  • Dry run capable
  • Easily relocated to several locations
  • ​Can begin pumping almost instantly

 

METHOD 5: HYDRAULICALLY DRIVEN SUBMERSIBLE PUMP

Since 1978, perceptive contractors have recognized Holland Pump as the premier choice for ruggedly designed and dependable portable submersible pumps. Engineered to pump continuously 24 hours a day under harsh conditions, Holland Submersible Pumps are ideal for high volume, low head applications such as lake dewatering, gravel pits, quarries, control boxes, and various open ditch applications. The power unit is designed to be placed in elevated or dry locations up to 300 feet away from the pump head. Submersible pumps do not require priming because the pump is submersed in the water. 90% of problems with suction lift pumps are in priming and suction elevation – these are all eliminated.

 

METHOD 6: AXIAL FLOW PUMPS

Axial flow units are clear water high volume low head pumps. They include a motor-driven rotor that directs flow along a path parallel to the axis of the pump. The fluid thus travels in a relatively straight direction, from the inlet pipe through the pump to the outlet pipe. Axial flow pumps are best suited for flood control, canal drainage, or agricultural irrigation.

 

APPLICATIONS INCLUDE

  • Flood Control
  • Boat Locks
  • Shrimp Farms
  • Stock Watering
  • Water Treatment
  • Field Flooding
  • River Bypass
  • Field Drying
  • Dry Docks
  • Irrigation
  • Coffer Dams
  • Cooling Ponds
  • Fish Pumping
  • Lake Drainage