What are the precautions for backfilling in winter?

After freezing, the soil becomes a hard clod, which cannot be compacted or compacted during backfilling. After thawing, the hard clods are easy to collapse, which leads to the backfill area sinking greatly. The more frozen soil blocks are contained in the backfill soil, the greater the scope and depth of collapse, leading to serious engineering quality accidents. Therefore, when using frozen soil as backfill, we should pay attention to the following problems. The following is the main content of winter backfill matters needing attention brought by Zhong Da Consulting for reference.

(1) When backfilling earthwork in winter, the thickness of each layer of soil should be reduced by 20%~25% compared with that at normal temperature, and the reserved settlement should be appropriately increased.

(2) A certain number of frozen soil blocks can be used as backfill soil for large-area backfill soil and fill soil of flat ground in pavement subgrade and sidewalk, but the particle size of frozen soil blocks shall not be greater than 150mm, and its content (by volume) shall not exceed 30% of all backfilled earthwork. When backfilling, frozen soil blocks should be spread separately, not piled up centrally, and compacted by layers.

(3) Before backfilling construction in winter, the ice and snow and thermal insulation materials on the basement should be removed.

(4) Within the surface layer of1000 mm fill slope, soil containing frozen blocks shall not be used for filling. The whole upper part of the filled soil shall be backfilled with unfrozen or breathable backfill soil, and its thickness shall meet the design requirements. The upper part of the slope is usually the aproll position of the building. We often see the phenomenon of aproll fracture, one of the reasons is that frozen blocks are backfilled, and it is easy to backfill soil containing frozen blocks during aproll construction. Attention must be paid during construction.

(5) Because the backfilled soil particles are frozen in winter, the form of expression is firm; when the temperature gets warmer, the soil particles are warm and the form of expression is loose. If the frozen soil particles accumulate too much, the backfill will be soft in a large area, and will sink once it turns to warm state. Therefore, the height of backfill earthwork in winter should not be too large. Even if soil without frozen blocks is used for backfilling, it can be used in production when it is expected that the backfilling in winter may exceed the requirements in the table.

Only when backfilling with stones, sand without frozen blocks (excluding fine silt) and gravel soil, the backfilling height is not limited by Table 1- 15.

(6) Outdoor foundation trench (pit) or pipe trench can be backfilled with soil containing part of frozen soil, but the particle size of frozen soil should not be greater than 150mm, and the content should not exceed 15% of all backfilled soil, and it should be evenly distributed and cannot be placed centrally. Within 500mm above the bottom of the trench, backfill with frozen soil is not allowed.

(7) Indoor foundation pit (pit) or pipe trench shall not be backfilled with frozen soil. At the same time, backfill construction should be carried out continuously and compacted. When artificial compaction is used, the thickness of each layer of soil should not be greater than 200mm, and the compaction thickness should be 100~ 150mm.

Earthwork backfilled under the indoor ground cushion shall not contain frozen soil, and shall be compacted in time. After the completion of filling, anti-freezing measures should be taken before the construction of ground cushion.

(8) When backfilling temporarily unused pipelines and their sites during the freezing period, the content and particle size of frozen soil blocks are not limited, but they should be properly handled after melting.

(9) In order to obtain more frozen soil backfill, the excavated accumulation place should be strictly insulated before winter, and when backfilling is needed in winter, the soil with a certain heat inside should be dug out for backfilling.

(10) When preparing the construction scheme, the balance between excavation and filling should be considered. For example, the thawed soil dug from pit A is filled into pit B as backfill soil, which is quickly compacted and effective protection measures are implemented.

(1 1) appropriately and systematically reduce the amount of backfill soil in winter, and backfill it after the weather gets warmer, which needs to be arranged in detail in the production plan.

(12) In order to ensure the quality of backfill soil in winter, some important engineering projects can use graded sand and gravel backfill when necessary.

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