Your pool is likely lifting due to hydrostatic pressure from groundwater if the surrounding drainage is insufficient. This phenomenon, often called "pool pop-up," occurs when the groundwater beneath and around your pool shell exerts significant upward force, pushing the structure out of the ground.
Understanding Pool Lifting (Pool Pop-Up)
Pool lifting, or "pop-up," is a severe issue where the entire pool shell physically moves or lifts from its original position. This is primarily caused by an imbalance in pressure: the weight of the water inside the pool (or lack thereof) is less than the upward pressure exerted by saturated soil and groundwater outside the pool.
The reference states: "ground water has been known to lift whole pools out of the ground if the surrounding drainage is not sufficient." This highlights the critical role of proper drainage in preventing such an occurrence.
The Role of Groundwater
Groundwater accumulates in the soil surrounding your pool, especially after heavy rainfall or if the water table in your area is naturally high. When the soil becomes saturated, it behaves like a liquid, and the water pressure increases. If this pressure beneath the pool shell becomes greater than the downward force exerted by the pool's weight (and the water within it), the pool will begin to float or "lift."
Impact on Different Pool Types
It's a common misconception that only certain pool types are susceptible to this issue. However, the reference clarifies: "Issues with ground water are not unique to vinyl liners - ground water has been known to lift whole pools out of the ground if the surrounding drainage is not sufficient. Fibreglass style pools and even concrete pool shells have been known to “pop up” or move in severe ground water situations."
This means that various pool constructions are vulnerable:
- Vinyl Liner Pools: Often perceived as most vulnerable, they are indeed susceptible if the liner is drained without proper dewatering.
- Fibreglass Pools: These pre-manufactured shells can easily float if the surrounding earth is saturated and drainage is poor.
- Concrete Pools: Even heavy concrete pools, despite their substantial weight, are not immune and can "pop up" or shift in severe groundwater conditions.
Key Contributing Factor: Insufficient Drainage
The primary reason for groundwater accumulating around your pool and causing it to lift is insufficient or compromised drainage. This can stem from several issues:
- Poor Site Preparation: Inadequate grading or lack of proper backfill materials during installation.
- Clogged Drainage Systems: Perimeter drains, French drains, or sumps designed to collect and redirect groundwater can become blocked with silt or debris.
- High Water Table: Naturally high water tables in certain areas, combined with a lack of a robust dewatering system, can lead to persistent hydrostatic pressure.
- Heavy Rainfall: Extended periods of heavy rain can quickly saturate the ground, overwhelming existing drainage.
Preventative Measures & Solutions
Preventing pool lifting focuses on managing groundwater effectively:
- Ensure Proper Drainage: Implement and maintain effective drainage systems around your pool. This might include:
- Perimeter drains (French drains): Perforated pipes laid in gravel trenches around the pool's perimeter to collect and divert water.
- Sump pumps: Installed in a pit near the pool, these pumps automatically activate to remove accumulated groundwater.
- Never Drain Your Pool Without Caution: If you need to drain your pool, especially a vinyl liner or fiberglass pool, always consult with a pool professional. They will assess the groundwater situation and might recommend dewatering the area around the shell simultaneously to balance the pressure.
- Regular Maintenance: Keep your yard and surrounding areas properly graded so that water flows away from the pool foundation.
- Professional Assessment: If you suspect a high water table or drainage issues, have a qualified pool builder or geotechnical engineer assess your property.
By understanding the critical role of groundwater and ensuring sufficient drainage, you can prevent the damaging and costly issue of your pool lifting out of the ground.
