4.4　Flyash Fill

4.4.1　For flyash filling materials，GradeⅢand above flyash shall be selected and the particle size should be 0.001mm-2.0mm；household waste and other organic matters are strictly forbidden；and the flyash filling materials shall meet the requirements of building materials concerning radioactive safety.

4.4.2　The flyash fill construction shall meet the following requirements：

1　During construction，the flyash shall be spread and compacted in lifts，and the spreading thickness should be 200mm-300mm；where road roller is used，the spreading thickness should be 300mm-400mm，and isolation measures with protection against erosion should be arranged all around；

2　The water content in construction should be controlled within±4% of optimum water content；coarse ash shall be placed at bottom layer with water content a little lower than optimum water content；

3　The cushion of small-area foundation pit or trench may be manually spread in lifts and compacted to dense by vibration（tamping）；the vibration（tamping）plate shall overlap 1/2-1/3；the compaction shall proceed from both sides or four sides to the center；the tamping passes shall be no less than 3.Large-area cushion shall be spread with bulldozer by prerolling 2 passes first and then rolling with road roller；the pressure rollers overlap 1/2-1/3 wheel width during construction，and the rolling compaction shall proceed 4 passes-6 passes；

4　The flyash should be spread and compacted in the same day and the minimum temperature for construction should not be below 0℃；

5　After each lift is compacted and inspected，the upper layer shall be spread immediately and vehicles shall be strictly forbidden to travel on it；immediately upon completion of flyash fill，a concrete cushion course shall be poured or a 300mm-500mm layer of soil shall be covered to seal the fill.

4.4.3　The construction of flyash fill shall not be conducted through hydraulic fill method；dewatering and drainage measures shall be taken for construction below groundwater level，and the construction shall not be conducted under saturated or flooded condition.If soft soils occur below the fill，coarse sand or dry blast furnace slag with a thickness of about 200mm should be spread and filled first.

4.4.4　During construction of flyash fill，the lift thickness，number of rolling passes，construction water content，degree of rolling compaction in overlapping area，compaction coefficient and others shall be inspected and shall meet the provisions specified in Article 4.2.6 of this code.