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Construction measures of over-wet soil in subgrade construction?

What are the main construction measures for over-wet soil in subgrade construction? The following Zhong Da consults the bidding teacher to answer your questions for your reference.

First, the characteristics of over-wet soil

In highway construction, some borrow sites along the line belong to silty moderately weak expansive clay with high plasticity index, liquid limit index and natural water content, low water permeability, strong hygroscopicity and easy instability. The water content must be controlled at about 1 1 ~ 15%, otherwise it is easy to turn over when rolling. The soil is muddy in rainy days and the clay surface is dry in sunny days, but the water content of the soil layer is as high as 30%. Therefore, when this kind of soil is used in subgrade construction, it needs to be stirred, dried, crushed and even mixed with a certain proportion of lime to reduce its water content and improve its compaction characteristics. Therefore, when filling the roadbed, it is necessary to turn over the sun repeatedly, sometimes as many as 5 ~ 6 times, which brings considerable difficulty to the construction and also affects the construction progress.

Second, the wet soil construction measures should be taken

1. Selection and treatment of borrow site Because of the high groundwater level of borrow site in this section, the soil water content is particularly high. In order to reduce the water content of soil, first ditch around the borrow pit for drainage, and then push the soil into piles with bulldozers to dry, so that the earthwork can be directly transported to the subgrade for filling. In order to ensure the normal transportation after the rain, the road into the excavation site should also be carefully trimmed.

2. When filling subgrade, the loose paving thickness should not be greater than 30cm, and each layer should be turned over. Only when the water content of the fill is uniform and the particles meet the specification requirements can it be leveled and rolled to the specified degree of compaction. Qualified road sections should not be placed for a long time, and topsoil should be filled in time to avoid exposure and rain, so as to avoid unnecessary rework.

3. Because of the high natural water content of over-wet soil, its water content will increase after rain, so the optimum water content must be strictly controlled during construction. During construction in high temperature season, the external surface of over-wet soil is easy to dry after exposure, while the internal water content is still high. When the rotary tiller is used to turn over the inner wet soil, the outer soil is also dried and turned into dry soil, and the water content is less than the optimum water content, so it is not easy to press to the specified density, so it should be backfilled. Sun-dried and rolled off-site until the water content is even and more than 2% of the optimal water content, and then backfilled, so that less lime can be added or not, which can not only achieve the specified degree of compaction, but also simplify the construction procedure. When the natural water content of over-wet soil is low in high temperature season, it can be plowed and rolled to the required density with a roller. However, the working face should not be too long, and it should be covered, leveled and rolled to prevent water loss.

4. If the moisture content of the over-wet soil is too large, it can be dug up by the borrow pit, piled up at the edge of the pit for preliminary drying, and then transported to the construction section for paving; Or after digging out from the borrow pit, transport it to one side of the operation section, after preliminary drying, push it to the operation section with bulldozer, crush it 1-2 times with the above machinery, and after leveling, evenly spread all or 2/3 of the specified dosage of external admixture on the ground. Ash mixing, crushing, mixing and initial rolling must be completed within1d.

5. After initial compaction of the soil layer for 24-28 h, spread the remaining 1/3 lime evenly on the soil layer, then turn over the soil, measure the moisture content of the lime soil, level it to 2% of the optimal moisture content, and then roll it with a heavy roller to the specified degree of compaction.

6. In case of rain during construction, it is generally advisable to seize the pressure and seal the lower soil with the upper soil. At the same time, it is necessary to strengthen the drainage function and use rain-proof cloth as a temporary chute on the subgrade slope to prevent the slope from being washed away by heavy rain. For the formed road section, in order to prevent rainwater from infiltrating into the soil foundation, cover it with J tarpaulin before it rains. After the rain stops, open the tarpaulin, recompress it as necessary, re-test the degree of compaction, and then proceed to the next process. This can not only ensure the compactness of subgrade, but also strive for the construction period.

7. For the sections that have been mixed with lime before leveling and rolling, it is advisable to grab the pressure in case of rain and cover them with tarpaulin at the same time. As the road section is rugged, the rainproof cloth should be lifted immediately after the rain stops. Wet soil can be dug up in some places with serious water accumulation, and then mixed with lime soil, and then leveled and rolled until the density is qualified.

8. For the road sections crushed by rain and without rain-proof cloth, it is necessary to use tracked vehicles for one-way ploughing after the rain stops, and it is not suitable to directly use rotary cultivators for crushing and drying, because the wet soil adheres to and wraps the rotary knives, and the broken clods form a dense covering layer, which makes it difficult to remove the moisture in the lower soil. With tractors and plows, the clods become larger, and the gaps between clods are also larger, so the air circulates, which is convenient for reducing the water content, so it is necessary to mix.

9. For the "Ninth Five-Year Plan" fill, in order to improve the strength of subgrade and ensure the overall strength and service life of pavement, it needs to be reinforced. The method is: the 80cm thick fill in the Ninth Five-Year Plan is divided into four layers, each layer is 20cm, the first two layers are mixed with 5% lime, and the last two layers are mixed with 8% lime, and the wet soil is treated to improve the strength of subgrade.

Three. Matters needing attention when dealing with wet soil

1. In the construction of over-wet soil, the emphasis should be placed on the continuity of construction procedures, so as to seize the time, make a surprise attack, pay close attention to the weather forecast frequently and try to avoid rain.

2. Lime should be fully digested and sieved before it can be used in the sections treated with lime, but the lime stacking time should not be too long, especially in the absence of covering, the effective calcium and magnesium content is greatly reduced, and the expected effect cannot be achieved after mixing. Lime whose original quality meets the requirements can be reduced to unqualified lime if it is piled up for several months without covering. ? Lime must be fully digested and strictly screened before use, so as to treat subgrade with less insufficiently digested lime. After rolling, the insufficiently digested lime will continue to be digested in the process of rain, resulting in local expansion and bulging, forming a mushroom shape, which affects the strength and smoothness of subgrade.

3. Control of moisture content in over-wet soil. Because the natural water content of over-wet soil is more than 30%, its water content will increase after rain, so the optimum water content should be strictly controlled during construction. During construction in high temperature season, the outer surface of over-wet soil will dry quickly, while the water content of inner soil is still high. When the rotary tiller is used to turn over and roll the inner wet soil, the outer soil also becomes dry soil, and the water content is less than the optimal water content, so it is not easy to press to the specified density. Therefore, before backfilling the subgrade, the soil should be turned over and rolled outside the site until the water content is uniform, about 2% higher than the optimal water content, and then backfilled, so that little or no ash can be mixed, and at the same time, the particle pits formed by clods can be reduced. This can not only achieve the required degree of compaction, but also simplify the construction procedure.

4. Because of the high natural water content of over-wet soil, its water content will increase after rain, so the optimum water content must be strictly controlled during construction. During construction in high temperature season, the external surface of over-wet soil is easy to dry after exposure, while the internal water content is still high. When the rotary tiller is used to turn over the inner wet soil, the outer soil is also dried and turned into dry soil, and the water content is less than the optimum water content, so it is not easy to press to the specified density, so it should be backfilled. Sun-dried and rolled off-site until the water content is even and more than 2% of the optimal water content, and then backfilled, so that less lime can be added or not, which can not only achieve the specified degree of compaction, but also simplify the construction procedure.

5. Due to the high water content of over-wet soil, the filling thickness should be strictly controlled, and the number of over-thin processes will increase, which will not only waste manpower and mechanical shifts, but also affect the construction period. Too thick fill will not turn over the soil, and the rotary tiller is more difficult to crush. Because there is no water loss in the lower soil, even if it is rolled again, it can't meet the requirement of compactness. Repeated rolling with heavy road roller will make the subgrade in a "spring" state, making it unstable and unable to continue construction, and finally it can only be reworked and redone. Therefore, in the construction of over-wet soil, the thickness of subgrade fill should be strictly controlled.

Four. conclusion

Through the construction of over-wet soil subgrade, we have explored and practiced, and found some shallow treatment measures, that is, lime should not be mixed when filling in high temperature and sunny days, but should be preliminarily turned outside the site before entering the subgrade. When the water content is high and the ploughing period is long, the required lime content (5% ~ 10%) can be calculated according to the actual water content, and then the fully digested and screened lime is paved on the filling section. After uniform mixing, the water content can be effectively reduced and the subgrade strength can be improved. After taking the above measures, not only the project progress is accelerated, but also the quality of subgrade construction is guaranteed. The above measures can be used for reference by similar projects in the future. In the future project construction, it is still necessary to constantly find problems, constantly explore and solve problems, ensure the quality of the project, and do excellent projects.

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