4.3　Sand and Gravel Fills

4.3.1　The materials of sand and gravel fills shall meet the following requirements：

1　Well-graded sand and gravel should be used，of which the maximum particle size should not be greater than 50mm and the clay size particle content shall not be greater than 5%；

2　If fine sand is used，gravel shall be added into fine sand and mixed as per the design requirements；

3　Organic matters such as grass roots and wastes shall be removed from sand and gravel material，and the organic content shall not be greater than 5%.

4.3.2　The construction of sand and gravel fills shall meet the following requirements：

1　Before the construction，the technical parameters such as lift thickness，construction method，vibration times and vibrator power shall be determined through trial construction on site.

2　During section construction，the sections shall be overlapped with slope，and the overlap loaction for each lift shall be staggered by 0.5m-1.0m，and the overlapping zone shall be compacted to dense.

3　Where soft soils occur below the foundation base，a 150mm-300mm fine sand layer or a layer of geotextile shall be placed at the top of the existing soil layer.

4　During construction by lifts，the construction of next lift shall proceed only after the inspection of compaction coefficient of the present lift is passed.

4.3.3　The construction quality of sand and gravel fill subgrade should be inspected with cutting ring method，penetration method，plate loading method or field direct shear test，and shall comply with the provisions in Article 4.2.6 of this code.