Concrete Tank Lining

Concrete tanks frequently leak and deteriorate with age. Old concrete is frequently poor quality and may incorporate river gravel. Over time carbon dioxide permeates the concrete and causes the reinforcement to corrode. The corroding reinforcement expands and causes the overlying concrete cover to spall.

The concrete tank may well still have the strength to resist the hydrostatic pressure to which it is subject but leaks like a sieve. Remedial work is frequently required to the concrete structure to slow the structural deterioration. Much more work is required to restore the watertightness of the tank and slow the leaks and this later work is often fraught with difficulty. The best solution may be to carry out the repair works to slow the structural deterioration and then line he tank with an impermeable liner. The liner is usually hung from a perimeter fixing along the top edge of the tank and is made to measure to fit around the various appurtenances within the tank

If you want a structural assessment of your leaky tank give us a call. We can provide professional assessment services and talk with you about the process for fixing the problem.

Decorative Pond

Decorative ponds are usually free formed and are constructed in a variety of locations. Some are exposed to the public and require special attention and edge fencing. Where fish are contained in the pond the lining material needs to be of a potable standard. Decorative ponds often have features such as rock beds, filter beds and various planting. All these can affect the liner that is placed and need to be considered in the design phase.

Secondary Containment

Gdt Lining Systems have completed complex and detailed secondary containments involving the placement of lining system under and around steel storage tanks, which contain a variety of hazardous and hydrocarbon products. We have worked with jet fuel, diesel, caustic soda. The secondary containment pondage is designed to AS 1940. GDT can offer design and construct services for secondary containment systems or install only. We are more than happy to offer advice.

POND MONITORING

Cleaning A pond using a high pressure nozzle. Flows of 140 litres/sec with a throw of up to 80m can be achieved with a 6” monitor hooked to an 8” pump. Nozzle pressures of 70KPa can be achieved with the right pump and delivery arrangement. Application of force of this magnitude will shake up any pond sediment deposits.

Putting the deposits into suspension is only half the story. The extraction pump system will also need to be engineers specifically for the solids and the delivery arrangement o the point of disposal.

The whole process is dramatic.

LANDFILL LINERS & COVERS

Landfill Liners utilising Geosynthetics

The use of geosynthetics in landfill lining systems is now common. HDPE, Geosynthetic Clay Liners (GCL’s) and geotextiles are commonly used. The purpose of the liner is to separate the leachate produced by the stored waste from the underlying water table. A typical arrangement consists of a GCL in contact with the subgrade of the landfill overlaid by a 1.5mm HDPE followed by a heavy geotextile to give mechanical protection to the HDPE. A drainage layer of gravel or sand is then placed. A lighter geotextile is often provided above the drainage layer to act as a filter between the drainage layer and the stored waste.

Following completion of the landfill the top surface may be sealed with a system of geosynthetics which may include; an LLDPE (Linear Low Density Polyethylene), a geocomposite (Drainage mesh + two layers of geotextile) and a cover soil. The landfill will often produce biogas which needs to be vented or flared. A system of polyethylene pipes may be installed through the waste layers to capture and vent the gas.

The leachate which is drained from the landfill is taken either to holding ponds or a treatment plant. The holding pond is often lined with HDPE and is on some occasions provided with a floating cover in order to prevent the entry and dilution by rainfall.

DAM LINERS & COVERS

Geomembrane Liners for Dams and Ponds

One of the most common geomembrane applications is as a pond liner. Pond liners may be used where:

  • The subgrade conditions do not allow a cut to fill pond to hold water.
  • The subgrade materials are dispersive and this interferes with the end use of the water.
  • Liquids other than pure water are stored and it is required to minimise the escape of the contained liquid. An example of this is sewerage effluent where the entry of small amounts of pollution to subterranean water supplies may have health implications for downstream users.
  • It is required to minimise erosion on the pond embankments. Erosion may be caused by the impact of rain or by the effect of aeration or mixing equipment within the pond. An example of this is the use of lining systems on prawn grow out pond embankments to minimise the entry of suspended sediments into the pond and the associated increased risk of disease and crop loss.

For more information regarding the use of geomembrane applications for pond lining.

Liquids that are contained may be drinking water, industrial process waste such as dunder or mine washings, sewerage or molasses.

The subgrade that is to receive the liner requires careful preparation. The subgrade preparation is required to meet the specification of the liner manufacturers. Failure to meet these requirements may result in the invalidation of the any offered guarantees. Typically the embankments are required to be regular and free from sharp or large rocks. Material placed in contact with the liner is required to be less than 10mm in size. Where granular material forms the subgrade it is usual to place a geotextile under layer. The geotextile used is usually a needle punched, non-woven material with a weight of not less than 250gms/m2.

Where ponds are to be constructed in areas where there is vertical gas movement through the subgrade of the pond then it is required to provide a subgrade venting system to prevent gas collecting below the liner. Vertical gas movement may be produced by the movement of the water table over a seasonal or diurnal period or by the degrading of vegetation matter at depth. The venting system usually consists of a full geotextile layer underlayed by a herringbone system of slotted pipe or slot drain wrapped in geotextile. The venting system may fulfill a dual roll. The system can double up as a leak detection system and can also be used to monitor the level of the ground water before the level of the contained liquid is reduced to minimum levels.

Lining materials for ponds include HDPE, Polypropylene, Elvaloys and PVC.

The most widely used lining systems are HDPE,
which is produced in various thicknesses and textures. HDPE is delivered in 7m rolls weighing approximately 1.6 tonnes. The material is unrolled and welded on site with wedge and extrusion welding equipment.

Lining systems are anchored at the perimeter of the pond by either burying the upper edge or by fixing the perimeter to a concrete anchor beam.

CHANNEL LINING SYSTEMS

Geomembrane Liners for Canals

The transport of water from the source to the point of use has been a problem to man since the beginning of time. Canal systems have been used widely for this purpose since the times of the Romans and before. Engineers have tried almost everything to line their water conveyance canals including clay, bricks, concrete spray on chemicals and geomembranes.

The use of geomembranes as a liner for new canal systems and as part of a retrofitting operation is well documented. Many standards are being developed for the use of geomembranes specifically as a liner for canal systems. GDT has extensive experience with lining systems in general and has worked with a wide range of liner materials including Elvaloy (Modified PVCs), Polypropylene laminates, heavy PVC laminates, HDPE and polyurethane. GDT is also able to arrange installation & testing of membranes.

To learn more about some of the main elements to note when using a geomembrane application, please click on the following link: basic consideration for geomembrane lining systems

LOW COST WATER STORAGE

In-ground Floating Roof Water Storage

In-ground floating roof water storages are now a genuine alternative to steel water tanks when considering larger installations

Floating roof structures have advantages over steel tanks:

  • Where a large volume of water is to be stored.
  • Where ample land is available for the storage.
  • Where it is desired to prevent exposure of the stored water to the environment and to eliminate evaporation.
  • Where an off peak storage is required and it is desired to minimise pump and delivery line size and expense.
  • Where it is required to construct a large capacity storage in a short period of time.
  • Where it is required to use the floating roof structure as part of a lined catchment to collect rainfall.
  • Where the required location of the reservoir is remote and transport of structural steel plate and members will be a high cost.

The construction costs of an inground floating roof reservoirs dramatically reduces, as the stored volume and the depth of the storage increases

The development of high strength, UV resistant, polymer materials used in the construction of floating roof storage’s has progressed rapidly in the last 10 years. A wide variety of polypropylene, elvaloy and polyethylene sheet is available with tensile strengths up to 8000kg/m width. Materials typically come with a manufacturers 20 year guarantee against UV degradation.

Click here for more information on the stages followed during an installation of a floating cover.

INDUSTRIAL WASTE & MINING

Geomembrane and Geosynthetic Liners for Mining Applications

The use of geosynthetic liners in mining applications has been an established science for 40 years. Specifically HDPE has been used extensively as the lining medium for Heap Leach Pads and lining of Tailings Dams. Other geosynthetic applications have included Evaporation Ponds for the reduction of liquid waste. The complexity of the lining system for a particular application depends on the nature of the material being stored or treated.

 

MOLASSES STORAGE

Geomembrane Liner for In-ground Molasses Storage

GDT has constructed a large number of in-ground molasses storages around Queensland in the last 15 years. The largest of which has the capacity to hold up to 37,000 tonnes of molasses. The excavation for this molasses storage is approximately 140m long, 140m wide and 11m deep. All excavation work undertaken by GDT is performed in accordance with AS3798-1990. As a result of GDT’s experience with Molasses Storages construction, they have become specialised in the requirements to make such a project successful. For an overview of this process click on the following link Molasses Storage Construction Elements.