Standard type of trench prepared for mounting the GRP pipes is illustrated shematically below. GRP pipes are manufactured in SN2500, 5000 and 10000 N/m2 stiffness categories and offer alternative types for mounting depending on the loads, (live loads, backfill loads, etc) In general the bedding material is preferred to be the same material being used for the initial backfill. h = D/2 (max.300 mm), b= D/4 (min. 150 mm)

The initial deflection limit of GRP pipes installed underground is, %3 for pressure pipes DN≥300 mm and %6 for gravity pipes DN≥300 mm

Water Control

İt is always good practice to remove water from a trench before laying and backfilling pipe. Well points, deep wells, geotextiles, perforated underdrains or stone blankets of sufficient thickness should be used to remove and control water in trench. Groundwater should be below the bottom of the cut at all times to prevent the washout from behind sheeting or sloughing of exposed trench walls. To preclude loss of soil support, dewatering methods should be employed for minimizing the removal of fines and the creation of voids within in situ materials. Suitable graded materials should be used for foundation layers to transport running water to sump pits or other drains.

Concrete encasement and Floatation

The concrete must be poured in stages allowing sufficient time between layers for the cement to set and no longer exert buoyant forces. The maximum lift heights are shown in the table below.

During pouring the concrete, or in order to prevent floatation, the pipe must be restrained against movement. This is usually done by strapping over the pipe to a base slab or other anchors. The straps are flat with a minimum of 25 mm width and strong enough to withstand the floatation forces.

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