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1.5 Further criteria
Existing pipelines, pipes, vegetation as well as other specifics have to be considered, so that
damage or hazards will be avoided. The soil coverage from the tank shoulder (chapter 4)
may not exceed 1.5 m.
2. Installation
2.1 Backfill material at the tank (backfill, bedding; chapter 3)
The backfill material has to be well compactable and permeable to water, allowing close
packing and no damage the surface of the tank. If the backfill material contains sharp or
sharp-edged components, the wall of the tank has to be protected by a sandy coating.
2.1.1 Sand - gravel mixtures (SW and GW to German Institute for Standardization 18196
and ENV 1046) are the most favourable backfilling materials, because they have a grain line
which consists of several grain sizes with only a low amount of fines (fines: under Ø
0,06mm). At the description of the mixtures the first number gives the mesh width
(simplified Ø) of the smallest grain and the second one those of the biggest grain: e.g.,
0/32; 2/16; 2/8; 2/32; 4/16. Which mixtures are available, strongly depends on the
regional gravel plants.
2.1.2 Concrete gravel, or treated concrete rubble, with a particle size of 0/32 mm is
particularly well suited for use in clay/loam soil conditions with ground water and a high
water table. When ground water and a high water table are present, it is particularly
important to ensure good compaction, especially at hard to reach places.
2.1.3 Grit is broken rock of the grain range of 2/32 and basically is suitable as a backfill
material; because of its sharp edges the tank must be protected against damages, e.g., by
a sandy wrapping.
2.1.4 Excavation, sand and gravel mixtures with irregular grain line are suitable as backfill
material only if they fulfill to the criteria under point 2.1.
2.1.5 Soil, loam or other cohesive grounds are not suitable for the backfilling.
2.2 Filling beyond the backfill
Excavated soil or other material can be used if this is stable and permeable.
2.3 Backfilling and compaction methods
2.3.1 The backfilling and compaction methods to be used are described in Section 3
(Installation instructions)
2.3.2 Methods that are not to be used include in particular adding water. Adequate
compaction is not achieved and the mixture of particle sizes combine in such a way that the
compaction is unstable.
2.3.3 Base layer (driveable version)
Range of grain size 2/45 is to be used.
2.4 Pipes
2.4.1 The feed pipe should be laid with a fall to the tank (>1%; installation guide figure
11).
Tubus + ET30-65
DORW2058
18.04.2013
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