Before starting of earth works there is to stake out all underground lines, which are in the vicinity or cross the excavation routing. Crossing and concurrency with engineering communications and service pipelines must be in accordance with ČSN 73 6005.
Execution of actual earth works abides by ČSN 73 3050. The excavations must be done in such a width to result in a sufficient space for subsequent working procedures, in the first instance welding, coupling installation, compaction of backfills etc.
In case of presence of low ground water level it is necessary to drain off the excavation bottom permanently in the level under the sand bedding.
Bedding depth is selected in the project in term of economic execution of earth works in respect to existing engineering communications and service pipelines. That all in consideration of observance of required parameters for bedding of pre-insulated pipeline distribution systems. Minimum covering layer above the top of the slip conduit may not be less than 500 mm. The covering earth layer must meet the common load of 9 kg/sq. cm. In case of non-fulfilment of this condition, it is necessary to use e.g. concrete bearing plates, steel protection pipe and the like. In case of big burial depths, i.e. below 2,500 mm and more, it is necessary to consider the static load of the slip conduit that no damage occurs. The common burial depth is from 800 up to 1,200 mm below ground - relating to the protection pipe top.
The supporting layer in minimum height 100 mm according to protection pipe diameter up to 200 mm is performed with sand of fineness 0 - 8 mm with compaction rate 0.8. This compacted subbase will be done to levelling bedding height of pre-insulated pipeline. The side spacing of the protection pipes must be at least 150 mm, the same is valid for the spacing of the protection pipe and excavation walls.
The pipeline backfill is carried out with sand again with the same compaction rate. This layer reaches 150 mm above the protection pipe top after compaction. On this a warning foil is set.
The final covering is made in accordance with the project documentation.