The precursor phenomenon of subgrade boiling is

The precursor phenomenon of subgrade boiling is ().

A. Cracking and bumpy driving

B. Road surface water accumulation

C. There are cracks on the road surface

D. Slope collapse

A: A.

Subgrade boiling is a common phenomenon in northern China. It refers to high groundwater level, poor drainage, poor soil quality and excessive water content, which leads to wet and soft subgrade and decreased strength. Under the repeated action of driving, the subgrade appears elastic soft, crack and silt.

Prevention and cure method

1. Drainage of ditches. The road surface is often in a wet state, which makes the subgrade soft and begins to boil. In order to eliminate surface water accumulation, horizontal ditches should be excavated on the shoulder in time, with a width of 30 ~ 40 cm and a spacing of about 5 m. The depth of the ditches is lower than that of the pavement base and higher than the bottom of the ditches. In areas with serious potholes, in addition to horizontal ditches, small longitudinal blind ditches or seepage wells should be built along the edge of roads.

2. turn over the soil. Dig out the mud and mud on the subgrade and replace it with 40~

60cm thick sandy soil or broken (gravel) stone should be compacted in layers and then paved again. For the severely boiled part, all soft soil shall be excavated, filled with gravel with good water stability, and compacted by layers.

3. Eliminate road water. Repair the road surface grooves and potholes on the shoulder in time to make it smooth and free of deposits and snow, and eliminate surface water as soon as possible.

4. Replace the aggregate. Mud is dug out in the mud-turning section and replaced with granular materials such as gravel, bricks or slag, which are leveled and then rolled to traffic. Or dig out the silt and fill it with dry soil with good water stability, and then spread and flatten the granular materials before opening to traffic for rolling.

5. Set up sand piles. When the subgrade is boiling, a circular or rectangular seepage well can be dug in the driveway, with a general diameter or side length of 30~50cm. Pump the water out of the well and deepen the water margin until it is below the frozen layer. When seepage stops, coarse sand or gravel can be filled to form sand piles, and the spacing and number of piles can be determined according to the boiling degree. Usually, the influence area of a sand pile is 6 ~ 60.

6. Wood and branches can be used to keep the traffic smooth on the expressway with less traffic and less heavy vehicles. After the boiling stops and the subgrade is stable, the firewood raft should be dismantled in time to restore the subgrade to its original state.

7. In the section with serious boiling, heavy vehicles should be controlled to pass or allowed to bypass.