Characteristics of over wet soil in highway construction, some borrow pits along the line are silty medium weak expansive clay, with high plasticity index, liquid limit index and natural moisture content, low permeability, high hygroscopicity, and easy to lose stability
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The moisture content must be controlled at 11% ~ 15%, otherwise it is easy to turn mud during rolling
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The soil is muddy in rainy days, the clay surface is dry in sunny days, but the soil moisture content is about 30% higher
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Therefore, when this kind of soil is used as subgrade construction, it needs to be mixed, dried, crushed, and even mixed with a certain proportion of lime to reduce its moisture content and improve the compaction characteristics
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Therefore, when the subgrade is filled, it is necessary to turn the sun repeatedly, sometimes up to 5 ~ 6 times, which brings considerable difficulty to the construction and also affects the construction progress
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Measures to be taken in construction of over wet soil 1
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Selection and treatment of soil field Due to the high groundwater level of the soil field in the road section, the soil moisture content is particularly large
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In order to reduce the water content of the soil, first ditch the soil around the pit to drain water, and then push the soil into piles by bulldozer for drying, so that the earthwork can be directly transported to the subgrade for filling
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In order to ensure the normal transportation after the rain, the access road to and from the dump should also be carefully repaired
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2
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The loose paving thickness of filling treatment should not be greater than 30cm, and each layer should be turned and crushed until the water content of filling soil is uniform and the particles meet the specification requirements, then leveling and rolling can be carried out to the specified compactness
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The qualified road sections should not be placed for a long time, and the upper soil should be filled in time to avoid exposure and rain, so as to avoid unnecessary rework
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3 control of water content because the natural water content of over wet soil is high, and it will increase after rain, so the best water content must be strictly controlled during construction
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During construction in high temperature season, the surface of over wet soil is easy to dry after being exposed to the sun, but the water content inside is still very large
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When rotary tiller is used to turn over and crush the inner wet soil, the outer soil is also exposed to the sun and becomes dry again, The water content is less than the optimal water content, so it is not easy to press to the specified compactness
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Therefore, before the backfill is placed on the subgrade, it should be turned over and crushed outside the site until the water content is uniform, and it is about 2% greater than the optimal water content, and then backfilled
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In this way, lime can be added or not, which can not only achieve the specified compactness, but also simplify the construction procedure
.
4
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If the moisture content of the wet soil is too large, it can be excavated from the soil pit, piled up next to the pit for preliminary drying, and then transported to the construction section for paving; Or it can be excavated from the pit and transported to one side of the operation section
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After preliminary drying, it can be pushed to the operation section by bulldozer, crushed by the above-mentioned machinery for 1-2 times, and after leveling, all or 2 / 3 of the prescribed dosage of admixture can be evenly distributed on the working section
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The processes of ash mixing, crushing, mixing and preliminary rolling must be completed within the same day
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5
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After 24-28 hours of initial compaction, the remaining 1 / 3 lime is evenly spread on the soil layer, and then it is turned and mixed
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The water content of lime soil is measured to achieve the best water content ± After leveling, use heavy roller to roll until the specified compactness is reached
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6
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Treatment method in rainy days: if there is rain during construction, it is generally appropriate to use the upper soil to seal the lower soil
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At the same time, it is necessary to strengthen the drainage function, use the waterproof cloth as the temporary chute on the subgrade slope to prevent the slope from being destroyed by the heavy rain
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For the formed road section, in order to prevent the rainwater from seeping into the soil foundation, it is necessary to cover it with the waterproof cloth before the rain, open the waterproof cloth after the rain, carry out the necessary re compaction, and re detect the compactness
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The next process construction can be carried out only after it is qualified
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In this way, not only the compactness of subgrade can be ensured, but also the construction period can be strived for
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For the road section that has been mixed with lime but has not been leveled and rolled, it is necessary to rush to press when it rains
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At the same time, it should be covered with rain proof cloth
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Because the road section is uneven and partially infiltrates into the rain section, the rain proof cloth should be opened immediately after the rain stops, and the local sun should be turned over
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In some places with serious water accumulation, the wet soil can be dug out, and the mixed lime soil can be replaced, and then the leveling and rolling can be carried out, Until the compactness is qualified
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Matters needing attention in the treatment of over wet soil the construction of over wet soil should focus on the continuity of the construction process, seize the time, make surprise, pay attention to the weather forecast frequently, and try to avoid the rain
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For the road section treated with lime, lime should be fully digested and screened before it can be used, but the lime stacking time should not be too long, especially in the case of no covering, the content of effective calcium and magnesium is greatly reduced, and the expected effect can not be achieved after mixing
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The quality of the original lime meeting the requirements can be reduced to substandard lime if it is piled up for several months without covering
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The lime must be fully digested and strictly screened before use, so that the subgrade can be treated with less lime with insufficient digestion
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After rolling and forming, in the process of rain, the lime with insufficient digestion will continue to be digested, which will cause local swelling and swelling, forming mushroom shape, affecting the strength and flatness of the subgrade
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Control of moisture content of over wet soil
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As the natural water content of over wet soil is more than 30%, the water content will increase after rain, so the best water content should be strictly controlled during construction
.
During construction in high temperature season, the surface of over wet soil will be dried quickly, while the water content of inner soil is still large
.
When the rotary tiller is used to turn over the sun and crush the wet soil in the inner layer, the outer layer of the soil will also be dried together and become dry soil
.
The water content is less than the optimal water content, so it is not easy to press to the specified compactness
.
Therefore, before the backfill is placed on the subgrade, it should be turned over the sun and crushed outside the site until the water content is uniform and about 2% greater than the optimal water content, In this way, less or no ash can be added, and at the same time, the granular pockmarked surface formed by soil blocks can be reduced
.
In this way, the specified compactness can be achieved and the construction procedure can be simplified
.
Due to the high natural water content of over wet soil, the water content will increase after rain, so the best water content must be strictly controlled during construction
.
During construction in high temperature season, the surface of over wet soil is easy to dry after being exposed to the sun, but the water content inside is still very large
.
When the rotary tiller is used to turn over and crush the wet soil in the inner layer, the outer layer of soil will also dry together and become dry soil, The water content is less than the optimal water content, so it is not easy to press to the specified compactness
.
Therefore, before the backfill is placed on the subgrade, it should be turned over and crushed outside the site until the water content is uniform, and it is about 2% greater than the optimal water content, and then backfilled
.
In this way, lime can be added or not, which can not only achieve the specified compactness, but also simplify the construction procedure
.
Due to the large water content of the over wet soil, the filling thickness should be strictly controlled, and the over thin process will increase, which will waste labor and machine shift, and also affect the construction period
.
The over thick soil can not be turned through, and the rotary tiller is more difficult to crush
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Because the moisture in the subsoil is not lost, even if it is rolled again, it can not meet the compactness requirements
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When heavy roller is used for repeated rolling, the subgrade will form a “spring” state, so that the subgrade can not be stable and the construction can not be continued, and finally it can only be reworked
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Therefore, the subgrade filling thickness should be strictly controlled in the construction of over wet soil
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