10. GROUND IMPROVEMENT WORK10.1 General10.1.1ScopeApplies to ground improvement work (surface ground layer improvement and deep ground layer improvement).Notes(1) Surface layer ground improvement is improving the ground using backhoes, stabilizers and other equipment to agitate and mix the earth with cement, lime, and other solidification materials that are added to harden the ground.(2) In deep layer ground improvement, solidification materials are sprayed or injected through pipes inserted into the ground, and the soil is agitated and mixed with the surrounding soil to improve the ground.10.1.2Execution planBefore improving the ground, an execution plan containing the following items shall be submitted to the Engineer for approval.(1) Execution organization (2) Work schedule (3) Testing (4) Execution method Surface layer ground improvement : Scope of execution, execution sequence Deep layer ground improvement : Improvement method, scope of improvement, improvement sequence, improvement speed, interval between steps, measures taken regarding changes to nearby structures(5) Quality control plan (method, criteria, locations, quantities, etc., to confirm the effect of improvement)(6) Machinery and equipment(7) Material used (list of ingredients, mix proportion etc., for solidification material)(8) Other10.2 Ground Improvement Work10.2.1SurveyIf nearby water areas may become affected, the following shall be studied and the results reported prior to improving the ground to preserve the environment and prevent accidents.(1) Purpose of use, status of use, locations, configuration, depth, structure, etc., of wells, public water areas, etc., near the area of improvementWhen specifically noted, the water quality shall be inspected.(2) Names, locations, dimensions, structure, etc., of buried objects within or near the area of improvement10.2.2 Solidification material(1) The quality and quantity of solidification material brought in to the site shall be reported, and the certificate shown in Table 3-1 shall be appended to the report. Table 10-1 Material quality and quantity-related referencesType Reference Issuing Source Timing of ReportsQuality certificate Quality standard Manufacturer Before work begins Inspection results Quantity certificate Delivery statement Manufacturer At each delivery(2) Solidification materials shall be stored in a manner that will protect them from weathering and deterioration.Materials that have become weathered or deteriorated shall be replaced with new materials.10.2.3 Preliminary mix testWhen determining the type and quantity of solidification material to be added for surface layer ground improvement, a laboratory mix shall be tested for the following items. For deep layer ground improvement, the quantity of solidification material to be added may be determined based on the type of soil in the area for improvement and the relationship between the uniaxial compressive strength and the quantity of solidification material added for each type of soil in the existing references.(1) Uniaxial compression test(2) CBR test(3) Hexavalent chromium elution test (if required)(4) Other 10.2.4TestingAs a rule, tests shall be made before the actual work, and the results shall be reported. In the case of small-scale ground improvement or the like, however, the effect may be checked by means of small- scale test performed during the actual work.Testing shall be performed on the same ground as actual execution.10.2.5 Ground improvement work(1) The ground shall be improved carefully for the specified area. In addition, the improvement thickness and depth shall be measured and records of the measurements shall be submitted to the Engineer.(2) When improving the ground in areas adjacent to tracks, structures, etc., the areas shall be monitored to detect changes. In the event of an abnormality, ground improvement shall be halted immediately and a report regarding corrective action shall be submitted to the Engineer for approval.(3) If there is a possibility that conditions will differ significantly from the testing conditions as a result of groundwater or weather, ground improvement shall be halted and the execution method shall be reconsidered.(4) Surface layer ground improvement(i) The delivery quantity, planned use quantity, quantity actually used, remaining quantity, etc., of solidification material shall be managed daily, and a report shall be submitted to the Engineer after the conclusion of the work.(ii) Solidification material shall be mixed thoroughly and surface-compacted in order to obtain the specified improvement effect. (iii) The area that has been improved (area, depth, height of soil-cement column top etc.), the number of times the surface has been compacted, etc., shall be recorded and reported.(iv) The ground shall be compacted evenly by surface compacting each layer until there is no further settling. The standard spread thickness of each surface-compacted layer shall be approximately 30 cm.(5) Deep layer ground improvement(i) The delivery quantity, planned use quantity, quantity actually used, remaining quantity, etc., of solidification material shall be managed daily, and a report shall be submitted to the Engineer after the conclusion of the work.(ii) During improvement, the depth, verticality, elution quantity of solidification material, r.p.m., etc., in particular shall be monitored continuously.(iii) The positions of soil-cement columns (depth, height of soil-cement column top, etc.), the interval between soil-cement column holes, the soil-cement column hole insertion depth, the soil-cement column diameter, the soil-cement column length, etc., shall be recorded and reported to the Engineer.(iv) In the event of sudden fluctuations in discharge pressure, etc., ground improvement shall be halted immediately and the cause shall be investigated and appropriate action taken. A report shall be submitted to the Engineer regarding the status, cause, and correction method.(v) Charts that has been stamped with the seal of approval of the supervisor prior to the start of work shall be used. When the entire roll has been used up to record the work (without cutting it in the middle), the supervisor shall check the chart (and sign it, etc.) without delay.(vi) As a rule, the autographically recording flow-meter shall not be turned off during the ground improvement process unless this has been approved by the supervisor in advance, and the data shown in Table 3-2 shall be recorded on a chart.Table 10-2 Recording dataType Method of Execution Basic Data Execution DataInjection mixing Date of execution Injection quantityMechanical mixing Injection quantity, digging/lifting speed, depth(vii) The execution manager of the Contractor (principal contractor or subcontractor) shall always sign the charts for all holes.(viii) The execution manager of the Contractor (principal contractor) shall manage each roll of charts. Charts that have been checked (and signed, etc.) by the supervisor shall be noted with the necessary information such as injection quantity, etc., and compiled in an orderly fashion and then re-submitted to the Engineer.(ix) In the injection mixing method, an injection testing shall be performed, and the flow rate, pressure, etc., of the solidification material shall be recorded on the charts. (x) In the injection mixing method for each hole, during the drilling of the previous hole, the number of rods shall be checked and confirmed by means of the remaining length, the hole boring depth.10.2.6 Quality control for solidification materialWhen slurry is used as the solidification material, the specific gravity shall be measured at least once a day to confirm that the conditions determined in the preliminary mix test have been met.10.2.7 Confirmation of effect of ground improvement(1) Surface layer ground improvementFollowing execution, a report with references showing the confirmation results of the effect of improvement shall be submitted to the Engineer without delay. The method of confirmation shall be a standard penetration test, a plate loading test, etc. The frequency shall be one location per 1,000 m2. If the area is less than 1,000 m2, the test shall be performed in at least one location.(2) Deep layer ground improvementFollowing execution, a report with references showing the confirmation results of the effect of improvement shall be submitted to the Engineer without delay. The method of confirmation shall be a uniaxial compression test. The frequency shall be one soil-cement column per 100 soil- cement columns. Each soil-cement column shall be tested three times: once each at the top, middle, and bottom of the column. The test value shall be the average of the values for the three test specimens.If the ground improvement area is small in scale, the slime discharged during the ground improvement process may be used as the test specimen.10.2.8 Check of finishing status(1) Surface layer ground improvementThe finishing status shall be measured and the measurement records submitted and checked by the supervisor. However, in the case of track subgrade improvement, the procedure after execution shall be in accordance with “2-7 Subgrade surface finishing.”(2) Deep layer ground improvementThe finishing status shall be measured and the measurement records submitted and checked by the supervisor.10.2.9 Effect on groundwater, etc.When executing ground improvement, there should be no impact on groundwater or the public water supply, etc. However, if water glass materials are used, perform the procedures described in “4-4-13 Water quality inspection for groundwater, etc.”10.2.10 Environmental measures (preservation)If crops, groundwater, etc., becomes contaminated, the area around the plant shall be covered in sheeting or other appropriate steps taken.10.2.11 Execution recordsThe fol
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