Inspection points of soil subgrade construction (1)

1, subgrade excavation

(1) Subgrade excavation must be carried out from top to bottom according to the design section. It is forbidden to dig indiscriminately or overbreak, and it is forbidden to dig a pit to borrow soil.

(2) The spoil shall be cleared away in time and shall not be piled up.

(3) When excavating to the top of subgrade, attention should be paid to the reserved height of rolling settlement.

2, subgrade filling

(1) The fill shall conform to the provisions in Table 3-3.

(2) Base treatment: ① When the cross slope of the original ground is not steeper than 1: 5, the base shall be skinned; When the cross slope is steeper than 1: 5, the original ground is dug into steps. The step width should not be less than 1m, and the height of each step should not be more than 30cm. (2) The embankment foundation is cultivated land or loose soil. When the filling height is less than 1.5m, the roots and weeds must be removed. Compaction shall be carried out before filling.

(3) Filling construction inspection:

(1) Fill subgrade must be compacted by layers according to the design section.

② The width of embankment fill should be greater than the design width of each side fill, and the compaction width should not be less than the design width. Finally, cut the slope.

(3) Different kinds of soil must be filled by sections and layers, and mixed filling is not allowed.

(4) The subgrade is located in the area with high underground water level or soft soil, and an isolation layer should be set.

(4) Inspection of backfill soil of bridge and culvert and pipe trench:

(1) The thickness of fill at the top of pipes and culverts must be greater than 30cm before the roller.

(2) The backfill soil around the bridge, pipeline groove, inspection well and rain mouth shall be evenly backfilled and compacted in layers on both sides or around.

(3) The junction of abutment and subgrade shall be filled and compacted by layers, and the virtual thickness of layers shall not be greater than 20cm.

(4) When the buried depth of pipe culvert and rainwater branch pipe structures under the motorway is shallow and the compactness of backfill soil can not reach the specified value, it shall be handled according to the requirements in Table 3-4.

(2) Inspection standard

1, soil subgrade

(1) After compaction, the fill should not be loose, soft, elastic, boiling and uneven.

(2) Where there are soil-changing sections that affect subgrade quality and design requirements, some inspection points shall be selected and dug for inspection.

(3) All kinds of trench backfill shall not contain sludge, humus and its harmful substances.

(4) The subgrade earthwork compaction standard shall comply with the provisions of 3-5 and 3-6.

2. ballast bed

(1) earthwork subgrade must be tested by 12~ 15t roller, and the wheel track shall not be greater than 5mm.

(2) The stone road bed must be tightly caulked, without pits and turquoise.

(3) The dirt road bed shall be free of frost boiling, peeling and water accumulation, and the compaction degree shall not be less than that specified in Table 3-6. At least 3 points shall be detected every 1000m2.

(4) The allowable deviation of subgrade shall comply with the provisions in Table 3-7.

3. Slope and side pit

(1) The soil slope must be smooth, solid and stable, and it is forbidden to stick the slope.

(2) The top line of the side ditch should be neat and straight, the bottom of the ditch should be smooth and the drainage should be smooth.

(3) The allowable deviation of ditches and slopes shall comply with the provisions in Table 3-8.

Inspection points of stone subgrade construction (1)

1, subgrade excavation

(1) Controlled blasting shall be adopted for excavation of pipe trenches and ancillary structures to maintain the integrity of rocks; Weathered rocks should be protected.

(2) After subgrade and foundation pit excavation, according to the design elevation, check the elevation, vertical and horizontal slope and gradient, do a good job of basement maintenance, and remove all broken block stones.

2, subgrade filling

(1) The slope shall be filled with hard and unweathered stones.

(2) The retaining structure should be completed before the rock-filled embankment; The accumulated slopes should be staggered with fillers.

(3) The stones shall be leveled by layers, and shall not be thrown and filled at will.

(4) Embankments with a height of 1.5m below the top surface of subgrade must be filled in layers, arranged manually, compacted, and then filled with pebbles.

(5) Heavy vibratory roller should be selected for the compaction of stone subgrade. The compaction standard of the top surface of the road bed is 12~ 15t roller, and the wheel track shall not be greater than 5mm.

(6) Within the range of 30cm above the pipe top of the pipe trench, fill it with soil and stone below 5cm, pave it with flaky from the top of the trench to 30cm below the top of the road bed, caulk it with fine materials, level it and compact it.

3. Rock subgrade blasting

(1) Blasting parameters should be determined through field tests before they can be formally adopted.

(2) In urban areas and traffic arteries, electric initiation and nonel initiation should be adopted.

(3) Controlled blasting is suitable for stone blasting of various buildings and their equipment and cultural relics in urban roads, and can demolish various masonry and concrete structures.

(4) The primary explosive amount should be determined by experiments.

(2) Inspection standard

(1) The slope must be stable, and turquoise and dangerous stones are strictly prohibited.

(2) Rock fill shall be hard and not easy to be weathered, and shall be rolled by layers with heavy roller or vibratory roller, and the surface shall not be wavy or loose.

(3) The allowable deviation of stone subgrade meets the requirements in Table 3-9.

Special soil subgrade construction 1, miscellaneous fill

(1) When building muck is used for filling soil, it shall not contain unstable substances such as deadwood, and its loss on ignition shall not be greater than 5%, and its maximum particle size shall not be greater than 10cm.

(2) Using waste residue to fill subgrade, testing the stability and applicable particle size of waste residue, and using it after technical appraisal.

(3) Domestic garbage shall not be used as subgrade filler.

(4) Newly-filled muck and slag shall be rolled several times, and then rolled with heavy roller to the required degree of compaction.

2. Saline soil

(1) Saline soil construction should pay attention to the uniformity of salt content.

(2) In arid areas, measures of memory should be decided through experiments according to local climate and hydrological conditions.

(3) The saline soil subgrade should be in the form of embankment. See table 3- 12 for the minimum height from the top surface of subgrade to the groundwater level.

(4) The subgrade shall be laid in layers, and the thickness of each layer of filled soil shall be no more than 20cm for cohesive soil and no more than 30cm for sandy soil.

(5) The compaction of subgrade should adopt heavy compaction standard, and the water content should be strictly controlled during rolling.