Can You Bury a JoJo Tank? Risks and Proper Installation

What structural modifications are required to install a polyethylene water tank underground?

Modifying a standard tank for burial requires constructing a rigid, load-bearing enclosure that isolates the vessel from all external soil forces. This typically involves pouring a reinforced concrete retaining wall around the tank, leaving a gap of at least 300 millimeters to prevent any contact between the soil and the tank walls. The lid of this vault must be engineered to support the weight of any surface traffic, such as vehicles or heavy footfall, which would otherwise crush the plastic.

One specific example involves using a specialized pea-gravel backfill between the tank and the vault to ensure even distribution of any accidental pressure. The primary exception to this modification is the use of proprietary underground cisterns, which feature thick, ribbed walls specifically engineered to resist earth pressure without an external vault. These units are manufactured with higher-density resins that provide the necessary rigidity for direct burial.

How does the soil pressure surrounding an underground tank affect its long-term integrity?

The continuous lateral force exerted by soil eventually causes fatigue in polyethylene, leading to micro-cracking and eventual catastrophic failure of the tank walls.

• Hydrostatic pressure from groundwater often acts against the tank's exterior, forcing the walls inward when the internal water level drops.
• Soil settlement creates uneven distribution of weight, which leads to stress concentrations at the tank’s base and fittings.
• Thermal expansion cycles cause the tank to shift slightly against the surrounding earth, wearing down the exterior surface over time.
• Moisture infiltration through small cracks accelerates the degradation of the plastic material, shortening the tank's effective lifespan by decades.

What are the specific risks of installing a tank not rated for subterranean use?

Installing a non-rated tank underground invites structural failure because these vessels are designed for hoop stress, which is the tension caused by internal water pressure, rather than the compressive forces of earth. Without the necessary wall thickness or ribbing, the tank will deform under the weight of the backfill. A common example is the "ovaling" of a cylindrical tank, where the circular shape flattens into an ellipse, eventually causing the lid to pop off or the side walls to split open.

The only nuance to this risk is the depth of the burial; even shallow burial of a standard tank is dangerous because the top section remains vulnerable to surface loads. Even if the tank survives the initial installation, the lack of structural integrity means it cannot withstand the shifting nature of wet soil, which acts like a fluid against the tank's exterior.

How can one prevent a buried water tank from floating or shifting due to groundwater levels?

To prevent floating, you must anchor the tank to a heavy concrete base slab using stainless steel straps that are rated for underground corrosion resistance. People often assume that filling a tank with water provides enough weight to keep it anchored, but this is dangerous because you must empty the tank for cleaning or maintenance. Once the tank is empty, the buoyant force of the surrounding groundwater will easily lift it out of the ground, potentially rupturing your plumbing connections and destroying the surrounding landscaping in the process.

What type of backfill material is recommended for installations below ground level?

Use clean, well-draining material like 10-millimeter to 20-millimeter pea gravel for backfilling. This material flows easily around the tank to eliminate voids and does not expand or contract significantly with moisture changes, which helps maintain stable pressure against the tank walls.

How does burial depth influence the accessibility of the tank for cleaning and maintenance?

Greater burial depth significantly increases the difficulty of routine maintenance by requiring expensive risers and specialized equipment to reach the tank's internal components.

• Inspection ports must be extended to the surface, which creates a potential entry point for surface runoff and debris if not sealed correctly.
• Sediment removal becomes a labor-intensive process, often requiring a vacuum truck because standard manual cleaning tools cannot reach the bottom of a deep tank.
• Pump access is complicated by the added depth, as you must make sure the electrical and plumbing lines are protected within a conduit to prevent soil-related damage.
• Structural inspections are nearly impossible once the tank is buried, meaning you will likely only discover leaks after the surrounding soil becomes saturated.

Are there specific regulatory or building codes that govern the burial of plastic water storage vessels?

Yes, local building codes generally mandate that any underground vessel must comply with structural standards such as the SANS 10108 or equivalent regional engineering requirements. These codes typically require that a professional engineer certify the installation design to make sure the tank can withstand the specific soil conditions at your site.

What are the primary differences between vertical above-ground tanks and purpose-built underground cisterns?

Above-ground tanks rely on the weight of the water to maintain their shape, whereas underground cisterns use structural geometry to resist external soil pressure.

Use these thickness values to understand why a standard tank cannot withstand the heavy compressive loads found at typical burial depths.