Trench constraction

The width of the trench should be assigned of condition for convenience of assembly work.

The bottom of the trench should be aligned and released from rocks and boulders should not have frozen sections. It may be necessary to strengthen the bottom of the trench in very loose soils. In inclined to shift ground, and in case of danger of soil leaching trench bottom should be reinforced by layer of geotextile material for the separation of the soil from the pipe.

Pillow under the pipe should be settled for all types of soils. For these purposes we should use sand or gravel (maximum grain size 20 mm), thickness of which must be at least 10 and not more than 15 cm. The cushion under the pipes should not be thickened with the exception of plots for 2 meters to manhole or to the wall of the well from the side of incoming pipe. Pillow should be carefully aligned.. When laying pipes must be fitted in areas of pit connections (Fig. 1).

installation of PVC pipes
Fig. 1. Pits in the bottom of the trench under the compound

Soil taken in the preparation of the trench bottom can be used for the primary pipe dusting/sprinkled on the condition that there are no stones (maximum size of - 20 mm, some stones up to 60 mm can be left in the ground). If the soil is assumed to condense and sprinkled, it must be suitable for such an operation. If the removed soil is not suitable for the pipe dusting/sprinkled, it is necessary to use sand or gravel with a size of 22 mm or fractions of crushed stone to the size of fractions 4-22 mm. 

Primary pipes should be sprinkled over the entire width trench to a height of at least 0.15 m from the top of the pipe. Soil compaction at pipes sprinkling where required, must be done with thick layers of 0.15-0.20 m. The first layer should not exceed half the diameter of the pipe and shall not exceed 0.20 m.

The second layer is poured to the top of the pipe and its thickness should not exceed 0,20 m. Ramming of soil directly above the pipe is unacceptable. 

Backfill of the trench can be done by the soil taken out of it , provided that the size of the largest boulders in it does not exceed 300 mm. The size of the stones, however, should not exceed 60 mm, where a layer of protective tubes and sprinkled at least 0.3 m from its top.

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Developer: O. Protchenko.