Groundwater is a common challenge encountered during construction projects, particularly in areas with high water tables or near bodies of water. Managing groundwater effectively is crucial to ensure the safety and stability of construction sites. This article explores the strategies and design principles for dewatering systems in construction.
Understanding Groundwater
Groundwater is the water that saturates the subsurface of the ground and fills the spaces between soil particles and rock fractures. It is a common occurrence at varying depths depending on geographical location and hydrogeological conditions.
During construction, encountering high groundwater levels can lead to a range of challenges, including:
- Excavation Stability: High groundwater can undermine the stability of excavations, leading to collapses and safety hazards.
- Foundation Flooding: Water infiltration into foundation excavations can jeopardize the integrity of foundations, footings, and underground structures.
- Trenching and Pipelaying: In projects involving trenching or underground utility installation, groundwater can impede progress and cause soil erosion.
Dewatering Strategies
Dewatering involves the removal of groundwater from construction sites to maintain a safe and dry working environment. Several dewatering strategies are commonly used:
- Wellpoints:
- Wellpoints are small-diameter pipes equipped with screens that are installed in the ground around the construction area.
- Vacuum pumps are used to draw water into the wellpoints, lowering the groundwater table.
- Deep Wells:
- Deep wells, also known as deep-well systems, involve the installation of large-diameter wells that penetrate deeper into the ground.
- Submersible pumps are used to extract water from these wells, effectively lowering the groundwater level.
- Sumping Pits:
- Sumping pits are excavated depressions within the construction area.
- Water naturally collects in these pits and can be pumped out using submersible pumps.
- Horizontal Drains:
- Horizontal drains, often in the form of slotted pipes or geotextile-wrapped drains, are installed horizontally to intercept and collect groundwater.
- Pumps are then used to remove the collected water.
- In addition, this pipe network would be connected to one location where a collection pit is established for dewatering.
Designing an Effective Dewatering System
Designing a dewatering system requires careful consideration of site-specific conditions and project requirements. Key design principles include:
- Hydrogeological Investigation:
- Conduct a thorough hydrogeological investigation to understand the groundwater flow, water table fluctuations, and potential impacts on the construction site.
- In also very important to make sure there won’t be sand boiling. Necessary testing on soils also shall be done.
- Further, rate of the ground water to be discharged shall also be know before starting the excavations.
- Pump Selection:
- Choose appropriate pumps based on the required flow rate, lift height, and discharge capacity.
- Ensure redundancy and backup systems in case of pump failure.
- Discharge Management:
- Plan for the proper disposal of extracted groundwater to prevent environmental impacts or groundwater contamination.
- Comply with local regulations regarding groundwater discharge.
- Monitoring and Control:
- Implement a monitoring system to track groundwater levels and pump performance.
- Adjust the dewatering system as needed to maintain optimal conditions.
- Safety Measures:
- Implement safety measures to protect workers and prevent accidents related to dewatering operations.
- Environmental Considerations:
- Minimize the environmental impact of dewatering by using sedimentation tanks and filtration systems to treat extracted groundwater before discharge.
Consequences of Improper Dewatering
Dewatering is inevitable in some of the construction work due to the availability of the groundwater table close to the ground surface and requirement of excavating below the groundwater table.
When the ground water table is at certain level, the ground and surrounding structures are stable. When the water table is lowered, there will be significant issues.
- Uncontrolled dewatering lowers the Groundwater table in the surrounding area. Thus, the pour water pressure get reduced.
- When there are buildings or any other structures constructed on shallow foundations, reduction in the pour water pressure would cause settlement in the foundations.
- Therefore, it is required to control the lowering of the ground water table. This would eliminate the possible risks.
- Once of the precautions that can be taken is groundwater recharging. We are excavating pits or insert perforated pipe or cylinders in the surrounding area, and they will be filled with the water.
- One of other methods is to continue the shoring unto the bed rock level. So that the movement of the groundwater can be eliminated. This is more commonly done in deep basements.
- However, when we are excavating of shallower depths, it is not practical to continue up to the bed rock level. In such situations, continuation of the shoring as much as possible would minimize the ground water drop as it would be required a longer distance water to travel.
Effective groundwater management and dewatering are essential for the successful and safe execution of construction projects.
A well-designed dewatering system, tailored to the specific site conditions and project requirements, can prevent delays, ensure excavation stability, and safeguard foundations and underground structures.
By understanding the principles of groundwater control and implementing appropriate dewatering strategies, construction professionals can mitigate the challenges posed by high groundwater levels and create a safer and more efficient work environment.
