26 of 49 Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 05: Earth Works, Pipe Works and Ground Improvement  5.3.9.7 Backfilling of pipe trench (supplementing the text "Backfilling and Filling", section 5.2.9)  After excavation of the trench, placing and compacting the bedding, laying the pipe and concreting the  thrust blocks the pipe must be surrounded by fill or concrete (if protection is required). Unless other- wise specified, the space between the sides of the trench and the pipe must be backfilled with the same  material as for the bedding. The material shall be placed and compacted in accordance with the re- quirements of section "5.2.9 Backfilling and Filling". Special care must be taken to backfill on both  sides of the pipe evenly to support the pipe properly and avoid distortion of the pipe. Unless specified  otherwise the pipe surround is continued up to a level 200 mm above the pipe crown. The layers shall  be compacted, in layers not exceeding 100 mm thick after compacting, by small manually maneuvered  compaction plant on each side of the pipe only. Mechanical compaction of the main backfill directly  above the pipe may not be commenced until there is a total depth of cover at least 300 mm above the  top of the pipe. Site test shall be made to prove the effectiveness of the method of compacting at inter- vals instructed by the Engineer.  The trench above the so finished pipe surround shall be filled with fill complying with the require- ments of section "5.2.9 Backfilling and Filling" and shall be compacted flush with ground level ac- cording to the requirements of the section "5.2.9 Backfilling and Filling". Trench supports shall be  gradually withdrawn in accordance with the progress of the fill subject at all times to the provision that  such withdrawal will not prejudice the safety of all works.  In- situ excavated material shall not be allowed as bedding.  Where pipes are surfacing or having less than the required ground cover of 750 mm, pipes shall be  surrounded by concrete grade BS 25. The pipes shall be supported on regularly spaced blocks in ac- cordance with any recommendations from the manufacturer. Plastic pipes to receive concrete bed and  surround shall be closely wrapped in a sheet of plastic (nominal thickness 120   m).  For pipes with flexible joints, compressible filler shall be cut and placed at each pipe joint over the  entire cross section of the concrete.  Concrete shall be poured in a single operation and shall comply with the requirements of Section 6- Concrete Works. Pipes shall be secured against lifting or moving during pouring of concrete.  5.3.9.8 Concrete Bedding and Surrounding  5.3.9.9 Floating, Submerging and Placing of Pipeline Sections  The “float and sink” method or “S” sinking method is the most common installation method for long  PE outfalls. In case the Contractor uses the “float and sink” method for long pipeline sections, the  pipeline shall be floated from the prefabrication area in a single, preassembled length or in sections to  be assembled on site.  The maximum length to be floated and sunk in one piece shall be defined by the Contractor according  to its capability and in order to minimize ship traffic obstruction. Floated sections to be stored offshore  have to be fixed with anchors and have to be marked with surface marker buoys with lights.  The outfall pipeline designed to be buoyant including concrete weighting and the pipe filled with air  and to be strongly negatively buoyant when it is subsequently filled with water. Air shall be main- tained in the pipe by means of a blind flange securely connected to the terminal end of the pipe. The  flange connection shall withstand 2 times the maximum necessary air pressure. The blind flange shall  be fitted with a check valve, a quick connect coupling as inlet for an air compressor hose and an air  valve for air release control. Also, the terminal/air release boat shall be equipped with a diesel driven  air compressor with a hose at least 50% longer that the depth of the end of the outfall to allow refloat- ing and adjustment if necessary.  5_Vol3_d4.3_Section 5 Earth and pipe works_en_GIR_rev6.docx 