Under the effect of constant shear stress, the soft soil subgrade will continuously cause slow shear deformation, and also lead to the reduction of shear strength.
What are the construction steps and precautions of impact rolling? For silt and muddy soil, which are referred to as soft soil subgrade in engineering projects, impact rolling shall pay special attention to the characteristics of this kind of subgrade during project construction.
After the “spring” is confirmed, the “spring” layer shall be excavated, and then the gravel shall be backfilled.
Precautions: The construction shall be carried out strictly in the marked area.
Therefore, it takes a long time for the subgrade of soft soil subgrade to achieve positive partial consolidation under its own weight or load.
When the impact rolling passes straight, the “S” route can be used if the crushing effect is not obvious.
Its variation range is about 5~25kPa.
The concrete face slab is less affected in the horizontal direction, and the crushing effect is better.
During the rolling construction, special personnel shall be responsible for observing the buildings along the line to avoid damage.
The driving route of impact rolling construction of impact roller should be rolled in the way of “big bones”.
(4) The water permeability is relatively poor.
The natural undrained shear strength of soft soil subgrade is generally not higher than 20kPa.
B.
Permeability coefficient of soft soil subgrade is generally × 10-5 to i × 10-7 mm/s (i=l, 2…, 9).
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Impact rolling construction steps: A.
After the consolidation settlement is completed, the soft soil subgrade may continue to produce considerable secondary consolidation settlement.
D.
(6) It has very significant rheological property.
A brief description of this kind of subgrade is given in the following section: impact rolling (1) has relatively high moisture content and relatively large void ratio.
The compressibility of soft soil subgrade is between 0.5-1.5MPa-1, sometimes up to 4.5MPa-1, and its compressibility often increases with the increase of liquid limit.
The sensitivity can be used to mark the characteristic of reducing toxicity of soft soil subgrade after a certain vibration.
E.
The speed of rolling construction is about 7~9km/h, and the rolling speed can be increased to 9~12km/h during compaction.
According to the data analysis, the following conclusions can be drawn: the moisture content of soft soil subgrade is generally 35%~80%, and the void ratio is 1~2.
Especially for soft soil subgrade, if it is subject to vibration (vibration, mixing or kneading), its flocculent structural characteristics will change to a certain extent, the strength of the soil will be significantly reduced, and liquidity will also occur.
C.
In case of rainy weather during impact rolling construction, the construction shall be stopped immediately and the area shall be covered to prevent precipitation from seeping into the roadbed.
F.
The sensitivity of soft soil subgrade in the southeast coast of China is about 4~10, which belongs to highly sensitive soil.
After leveling, the ordinary roller shall be used for layered compaction, and then the impact roller shall be used for rolling for a certain number of times to reduce differential settlement.
Therefore, during the subgrade construction, impact rolling is carried out in the order of shoulder, motorway and overtaking lane.
(5) It has a very obvious structure.
Impact rolling construction steps.
During rolling construction, the number of times of impact rolling shall be adjusted quickly according to the crushing conditions on site to reduce excessive crushing or insufficient crushing during construction.
(3) The shear strength is very low.
When the soil quality and subgrade strength of the same section of the road are different, there will be different crushing conditions.
(2) The compressibility is relatively high.
For the construction method of special foundation, if the phenomenon of “spring” occurs in some sections during impact rolling, stop immediately for inspection.
