10 of 49 Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 05: Earth Works, Pipe Works and Ground Improvement  If any unsound material occurs in the bottom of any excavation, the Contractor shall remove it and  dispose it all to the satisfaction of the Engineer. Unless otherwise specified or ordered by the Engineer,  the Contractor shall fill the voids so formed with concrete grade C8/10 or with suitable granular mate- rial to the approval of the Engineer.  Unsuitable material shall e.g. include:   Peat, timber and perishable material;   Material susceptible to spontaneous combustion;   Clay with a liquid limit exceeding 80 and having a plasticity index exceeding 55; and   Materials having moisture content greater than the maximum permitted for such materials.  If areas of excavation are not accessible for earthmoving equipment due to limited working space, traf- fic or any other reason, excavation shall be carried out manually.  The Contractor shall make records of the position and extent in excavations of every type of service  and obstruction encountered during the construction of the works, and samples taken and the results of  tests on such samples.  The extent of excavations shall be kept to a minimum practicable for construction of the works, and all  over-excavation shall be filled with suitable material and compacted to the satisfaction of the Engi- neer.  The earth excavation shall be organized taking into consideration the local conditions as the can be  interpreted from the appended soil investigations or supplementary investigations made by the Con- tractor.  Excavation for structures includes removal and disposal of material for all structural excavation.  Should the surface of excavations at foundation level become deteriorated through any cause whatso- ever, then the Contractor shall further excavate all materials, which in the opinion of the Engineer has  become unsuitable, and replace it- at his own expense- with such material and in such manner as the  Engineer shall direct.  5.2.7.2 Excavation for structures  5.2.7.3 Tolerance  Unless otherwise specified no point of the surface of the completed earthwork shall be more than +/-  50 mm from the designed surface. Within the above tolerances, the surface shall have a smooth regular  face all to the satisfaction of the Engineer.  Bed levels of drains shall not be higher, (tolerance 0), or more than 200 mm lower than the correct  level.  5.2.7.4 Slips, falls and excess excavations  The Contractor shall prevent slips and falls of materials from the sides of the excavations and em- bankments.  In the event of slips or falls occurring in the excavations, and where excavations are made in excess of  the specified dimensions, then any unsuitable material that has entered into the excavation is to be re- moved from the excavation, and the additional backfilling that may be required is to be carried out  with selected excavated or imported material and compacted to the approval of the Engineer.  5.2.7.5 Safety of excavation and adjacent structures  The Contractor shall provide support necessary to ensure the stability of the excavation and adjacent  roads and structures. The support may be made with sheet-pile walls, holding walls, open caissons or  5_Vol3_d4.3_Section 5 Earth and pipe works_en_GIR_rev6.docx 