32 of 49 Construction of Giresun Wastewater Treatment Plant  Tender Dossier Volume 3 Employer’s Requirements  Section 05: Earth Works, Pipe Works and Ground Improvement  5.4 Ground Improvement  5.4.1 General  5.4.2 Soil replacement  5.4.3 Admixture stabilization  The Contractor is required to test several jet grout column sections prior to construction to determine  the geometry and quality of treated material that can be obtained. 5.4.4 Jet grout columns  For assessing the geometry, excavation or coring shall be made. Wet grab samples shall be taken for  strength and permeability testing. If piezometers are installed for later hydraulic conductivity meas- urements, the construction details of the piezometers shall be recorded.  During construction, it shall be monitored and the Contractor is required to note if the grouting param- eters and materials are consistent with the approved test section. The ability to erode the soil with the  jets is an important factor in successful jet grouting. There shall be a continuous flow of spoils to the  ground surface during jetting. If there is no spoil return, it is possible that hydrofracturing is occurring.  The rate of rotation and removal of the grout pipe and the rate of material consumption shall be moni- tored. Method of jet grouting shall be approved by the Engineer.  5_Vol3_d4.3_Section 5 Earth and pipe works_en_GIR_rev6.docx  Method of admixture stabilization shall be approved by the Engineer.  During stabilization of soils with admixtures, the most important observations are the amount of ad- mixture and water mixed into the soil, the amount of mixing performed, and the amount of compaction  effort used on the fill. The moisture content and density of the fill can be determined in the field. The  curing time and conditions should also be recorded. Samples should be taken for laboratory testing.  Admixture stabilization consists of mixing or injecting admixtures such as cement, lime, fly ash or  bentonite into a soil to improve its properties. Admixtures can be used to increase the strength, de- crease the permeability or improve the workability of a soil. Admixtures can fill voids, bind particles,  or break down soil particles and form cement. The general process of admixture stabilization consists  of (1) excavating and breaking up the soil, (2) adding the stabilizer and water, if necessary, (3) mixing  thoroughly, and (4) compacting the soil and allowing it to cure. Method and material or soil replacement shall be approved by the Engineer.  Soil replacement involves excavating the soil that needs to be improved and replacing it. Excavated  soil shall be replaced with compacted granular soil (Sand & gravel) with more suitable properties for  the proposed application. All in-situ verification of ground improvement shall be made by CPT or SPT test after ground im- provement works.  In the selection of ground improvement method, the time limitations of the Contract shall be taken into  consideration. The methods listed in the Employer’s Requirements may be used and all methods are  subject to the approval of the Engineer. Where directed by the Engineer the Contractor shall carry out  a field trial of the proposed treatment to demonstrate that it meets the stated performance criteria.  Any ground treatment proposed by the Contractor to improve the bearing capacity and/or settlement  characteristic of the soil must be supported by a full method statement -including design calculations  and design drawings- with a statement of the minimum performance to be achieved. 