Installation procedure for the JoJo 6000 litre Underground Tank

Underground tank installation is more time consuming and complex compared to the installation of above-ground vertical tanks that can be installed on a firm base/platform or tank stand.  However, there are some situations where an underground tank, such as the JoJo 6000 litre underground water tank, is a better storage solution over JoJo’s vertical water tanks.  JoJo Tanks also manufacture the 6000 litre underground tank in a conservancy tank version as well as a septic tank version.

JoJo Tank’s 6000 litre underground tank is becoming a popular choice for storing rainwater from rainwater harvesting systems as well as for storing water from other sources for a multitude of uses.  It is important to ensure that these excellent JoJo 6000 litre underground water tanks are correctly installed.

1. CHOOSING THE SITE

The location of the underground water tank should be considered carefully.

If possible, try not to install the underground tank:

• in water saturated clay or in a high water table (or an area that is frequently flooded)
• where the depth to bedrock is less than 2.5 m
• in the path of vehicles or heavy equipment
• where underground services are expected (such as telecommunication or electrical cables, water and sewer pipes, gas lines etc.)

The underground tanks will need to be placed on soil with a bearing capacity greater than 120 kPa.

2. EXCAVATION

Note: Take care not to damage any underground services (such as telecommunication or electrical cables, water and sewer pipes, gas lines etc.)

The underground tank is approximately 3.2 m long by 1.9 m wide. Allow between 300 mm to 600 mm on all sides of the tank.

The depth of the excavation will depend on the following conditions:

Soft in-situ soil (fine sand, silt or clay)

• Excavate to a depth of no less than 2.4 m and no more than 2.7 m

No ground water will affect the tank. No traffic will pass over the site (Non-load bearing)

• Excavate to a depth of no less than 2.1 m and no more than 2.7 m

Ground water will affect the tank. Traffic will pass over the site (Load bearing)

• Excavate to a depth of no less than 2.4 m and no more than 2.7 m

Note: If ground water present in the excavation hole, continuously pump the water out during the installation process.

3. BEDDING

The type and thickness of bedding will depend on the following conditions:

Rocks or rocky soils

• Remove all large rocks or loose rocks and objects that could interfere
• Bedding to be minimum 150 mm crusher dust or a coarse sand / gravel mixture (Bedding to be thicker where hollows or uneven areas are levelled out)

Gravel or coarse sand. No ground water will affect the tank (Dry installation)

• Bedding to be 150 mm crusher dust or a coarse sand / gravel mixture
• Stabilise bedding layer with 3 % cement (1½ bag of 50 kg ordinary Portland cement)
• Spread cement evenly and compact, using a mechanical compactor (Do not wet cement, as the natural moisture from the ground will do this over time – if the soil is too dry to form a lump when pressed in your hand, you must add a little bit of water, but make sure the lump still crumbles in your hand when lightly touched)

Soft in-situ soil (fine sand, silt or clay). No ground water will affect the tank (Dry installation)

• Bedding to be 2 layers 150 mm crusher dust or a coarse sand / gravel mixture each
• Stabilise each bedding layer with 3 % cement (1½ bag of 50 kg ordinary Portland cement)
• Spread cement evenly and compact, using a mechanical compactor (Do not wet cement, as the natural moisture from the ground will do this over time – if the soil is too dry to form a lump when pressed in your hand, you must add a little bit of water, but make sure the lump still crumbles in your hand when lightly touched)

Ground water will affect the tank (Wet installation)

• Drainage bedding layer of 150 mm crushed rock (19 mm), use crusher dust or coarse sand to bind, followed by
• Bedding to be 150 mm crusher dust or a coarse sand / gravel mixture
• Stabilise each bedding layer with 3 % cement (1½ bag of 50 kg ordinary Portland cement)
• Spread cement evenly and compact, using a mechanical compactor (Do not wet cement, as the natural moisture from the ground will do this over time – if the soil is too dry to form a lump when pressed in your hand, you must add a little bit of water, but make sure the lump still crumbles in your hand when lightly touched) Place tank carefully.

4. WATER TANK CONNECTION

Connect water tank as per the manufacturer’s specifications.

5. BACKFILL

Note: Fill the underground tank with water before commencing the backfill procedure. This will stabilise the tank and reduce movement. It is essential to do this if there is any groundwater present.

One of the most critical aspects of the installation is proper backfill material. Suitable backfill material shall be coarse river sand or sand / gravel mixture. The sand / gravel mixture shall have no particles larger than 20 mm and at least 50 % of the particles shall be smaller than 5 mm.

Fill around perimeter of tank with suitable backfill material, maximum 150 mm layers. Compact each layer properly before laying the next layer.

Proper compaction means 97 % Mod. AASHTO. For field installations, use a hardwood pick handle (or similar) and drop it from about 300 mm onto the compacted soil. Properly compacted soil should make a ‘ping’ sound when the pick handle is dropped from about 300 mm. If the pick handle makes a dull sound the soil is not yet properly compacted.

6. DRESSING

The dressing over the underground tank will depend on the following conditions:

No ground water will affect the tank. No traffic will pass over the site (Non-load bearing)

• Ensure that the backfill over the tank is no less than 200 mm and no more than 750 mm.
• Shape the soil over the top of the tank to ensure positive drainage.

Ground water will affect the tank

• A compression ballast will be required to prevent the tank from floating when empty, due to hydrostatic lift.
• Pour 2.8 m3 grade 20 Mpa concrete on top of the tank (slump around 80). This will give a ballast of approximately 450 mm thick over the entire area of the tank.

Traffic will pass over the site (Load bearing)

• Where vehicles will drive over the tank, a concrete slab must be poured over the tank. This slab shall be 4.2 m x 2.9 m. The slab shall be minimum 150 mm thick grade 25 MPa concrete, with two layers of Ref. 156 reinforcing mesh.

7. USAGE AND MAINTENANCE

Ensure usage and maintenance of the underground tank in accordance with the manufacturer’s specifications.

JoJo Tanks South Africa offer a wide range of products such as plastic water tanks and chemical tanks to suit every household, business or agricultural need, including silo tanks and silo tank stands as well as other high quality JoJo Tanks products.  See JoJo Tanks’ VERTICAL TANKS, HORIZONTAL TANKS (transporter tanks), STEEL TANK STANDS and OTHER JOJO PRODUCTS and see JoJo Tanks’ NEW 6000 LITRE UNDERGROUND TANKS. Also see our FAQ and WATER TANK PRICES.