Xiaobian inquires through the architectural knowledge column of the encyclopedia website of the construction industry-Construction Network, and the basic situation is as follows:
Xiaobian takes the subgrade widening construction scheme as an example, and the basic situation of subgrade widening in construction enterprises is as follows:
After years of opening to traffic, the subgrade settlement is basically completed, and the subgrade widening section is due to the difference between the old and new subgrade. Secondly, the design optimization and construction quality of highway subgrade widening must be strengthened to minimize the settlement and ensure the quality of highway.
The construction scheme of subgrade widening mainly includes: (1) construction preparation; (2) foundation treatment; (3) subgrade widening; (4) reinforcement measures and other contents, among which the contents of subgrade widening reinforcement measures are as follows:
(1) laying geo-products
Geogrid has the characteristics of high tensile strength, low elongation and difficult deformation, and it is fully connected with soil, greatly increasing the connection with soil. Laying in the widened road section can increase the combination of the old and new subgrade, increase the shear capacity of the joint, and prevent the settlement of the new subgrade from damaging the old subgrade, thus achieving the effect of stabilizing the uneven settlement of the old and new subgrade.
The geogrid can be set according to the height of road fill. When the subgrade filling is less than 1.5m, three layers can be set at the bottom; When the height of fill is 1.5m~8m(1m), three layers are set at the bottom and top of subgrade respectively; When the height of filled soil is more than 8m(1m), three layers shall be set at the bottom and top of subgrade, and three layers shall be set at the middle platform, in which the bottom layer shall be laid after the basement is leveled and rolled, and one layer shall be laid for every two layers of filled soil, and the upper layer shall be laid at the top and bottom of upper road bed and one layer at the bottom of lower road bed. The laying width of geogrid shall be based on the widened width, but the laying width of new and old subgrade shall not be less than 1.5m. If conditions permit, 6 cm ~ 12 steel bars can be used for anchorage and grouting, and the steel bars will cross the soil layers of the old and new subgrade, which will play a positive role in shear resistance. Steel-plastic two-way geogrid can be given priority, but its elongation should be less than 4% and its tensile strength should be greater than 45kN/m, and the anchorage spacing and lap width are the same as those of ordinary construction.
(II) Impact compaction
The settlement of subgrade body is mainly related to the compactness of subgrade itself, so that it can be closely combined to form a whole, and the settlement of subgrade body and foundation can be minimized, so as to reduce the settlement of subgrade and reduce or avoid the occurrence of longitudinal cracks at the junction of new and old subgrade. Therefore, the impact rolling (tamping) method can be selected to reinforce the subgrade. Impact rolling construction can improve the compaction degree of widened subgrade, make the old and new subgrade well combined into a whole, increase its ultimate resistance, minimize the settlement of subgrade body and reduce its sedimentation coefficient; Impact rolling can also avoid the weak sliding layer at the joint due to insufficient rolling.
It is very difficult to achieve the compaction degree of 96% in subgrade construction by mechanical compaction. According to the construction experience in Meihe Expressway and Guangdong-Jiangxi Expressway, the compaction degree can reach 98% by using impact compaction. At present, the blue roller (dynamic compaction machine) which is widely used in highways in our province and has mature construction technology. During mechanical operation, the tractor drives the compactor wheel to roll, and the non-circular curve of the compactor wheel profile exerts a comprehensive effect of kneading, rolling and impact on the surface, so that the soil can be compacted from the upper part to the lower part with the transmission of pressure waves.
before the construction, select representative sections to carry out tests, and summarize the walking speed, influence depth, settlement and number of walking articles of the machinery. The past experience is as follows: it is appropriate to use 25t to fill the subgrade with a depth of 1.m(4 floors) for 5 ~ 7 times, and the effect of filling is also obvious; By using impact roller to make up the pressure of subgrade, the compactness of subgrade is improved, the settlement of subgrade is accelerated, the time of natural settlement of subgrade is shortened to the maximum extent, and the settlement deformation of subgrade is effectively reduced, which plays a good role in the combination of new and old subgrade.
(3) Cross-year construction
In order to reduce the settlement of widened subgrade, cross-year construction of subgrade should be done as much as possible to make subgrade experience rainy season; After the subgrade is completed, the traffic should be opened as much as possible, and some measures should be taken on the road to make the vehicles drive at the widened place as much as possible, increase the driving load and minimize the settlement.
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