According to the foundation survey report of this section, there are partial sections along the line with 0.4-3.5m deep plain fill soil. Due to the evacuation of the plain fill soil structure and the short accumulation period, the design considers removing the plain fill soil and backfilling qualified roadbed fill when the thickness of the plain fill soil is ≤ 0.8m; When 0.8m
When the roadbed is in a pond section, when the roadbed occupies a large pond area and the pond area outside the roadbed area is small, the pond should be abandoned and treated as a dry pond. First, the entire pond should be pumped and drained, and the sludge within the range should be treated. Then, 0.6~1.0m thick coarse gravel should be replaced, and then plain soil should be replaced to the top of the roadbed; Level the outer side of the roadbed with plain soil to the embankment.
When the roadbed occupies a small area of the pond and the pond still has retained value, water should be pumped from the outer side of the slope toe, and the inner side of the roadbed should be dredged and backfilled with coarse debris in layers to the pond ridge; The slope below the constant water level of+0.5 meters is protected with mortar rubble, and the woven bag cofferdam is removed after construction.
Due to the large height difference and steep slope at the embankment of the pond, in order to avoid uneven settlement, steps were excavated to treat the embankment. The width of the steps should not be less than 2 meters, and a 4% inward transverse slope was set. A two-way geogrid was laid in layers, and finally a layer of two-way geogrid was laid at the top of the embankment.
The cross section survey and design of the roadbed should pay attention to:
The height of the up and down sub stations (h) should not be too high or too low, and h=5-6 meters is appropriate;
The second split belt should adopt a lightweight support structure and avoid a gravity type structure, with a slope ratio of n=0.25~0.5 as appropriate;
Thirdly, strengthen the drainage between the upper and lower platforms, especially for the super high road sections that tilt towards the lower platform line;
Fourth, strengthen the safety measures for the middle section of the upper platform line, especially when the upper platform is a downhill section and the middle section is a section outside the curve;
The length of the five point table roadbed should be combined every 2-4km, which is conducive to the connection between the up and down lines;
The width of the median strip should be appropriately widened in the six fill section to reduce support engineering and facilitate the safety and stability of the roadbed.