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Construction process: bottom cleaning of foundation pit → inspection of soil quality → layered soil paving and leveling → layered rolling or compaction → inspection of compactness → correction of leveling and compaction
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Construction process standard figure 2.1 cleaning of foundation pit bottom: the holes on the foundation soil or the tree roots, garbage and other debris on the surface of the foundation should be disposed of and cleaned up
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2.2 check the soil material, check the type and particle size of the soil material, check whether there are sundries, whether it meets the design requirements, and whether the water content of the soil material is within the control range; if the water content is too high, measures such as turning over and drying or evenly mixing dry soil can be adopted; if the water content of the filler is too low, measures such as pre watering and wetting can be adopted
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2.3 before layered soil laying, leveling and backfilling, according to the design drawings and acceptance specifications, prepare the construction scheme of the backfill test section, carry out the construction of the test section, and check the backfill quality
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After passing the inspection, the joint acceptance of the test section is carried out to determine the backfill parameters and improve the backfill scheme of the pipe gallery project
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The thickness of each layer of soil and the performance parameters of machines and tools shall be carried out according to the scheme, and the backfill quality shall be tested according to the design and specification requirements
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2.4 when the filling is compacted by layered rolling or ramming compaction, the driving speed shall be controlled, generally not exceeding the following requirements: flat rolling: 2km / h; vibrating roller: 2km / h
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When rolling, the wheel (tamping) tracks shall be overlapped to prevent leakage of compaction or tamping
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When the length width ratio is large, the filling should be carried out in sections
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The joint of each layer shall be made into a slope shape, and the overlapping of grinding tracks shall be about 0.5-1.0 M
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the staggered joint distance between the upper and lower layers shall not be less than 1 m
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When the filling exceeds the surface of the base, the compaction quality of the edge part shall be ensured
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After filling, if the design does not require slope trimming, the width of the filling edge should be 0.5m; if the design requires slope trimming and compaction, the width can be 0.2m
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If the filling cannot be compacted by mechanical construction, it shall be filled by manual pushing and compacted by frog or diesel rammer layer by layer
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2.5 check the compactness of backfill earthwork
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After each layer is compacted, ring knife sampling shall be carried out according to the specification to measure the mass density of dry soil
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After meeting the requirements, the upper layer shall be paved
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2.6 after the correction and leveling acceptance of the filling department is completed, the surface shall be leveled by wire
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Where the elevation exceeds the standard elevation, it shall be leveled according to the line in time; where the elevation is lower than the standard elevation, it shall be leveled and tamped by adding soil
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Each layer is qualified, the test report is complete, the self inspection is qualified, and the joint acceptance is applied
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Prevention and control measures for common quality problems 3.1 foundation pit (groove) backfill settlement 3.1.1 causes (1) backfill without removing the ponding and silt in foundation pit (groove); or backfill with loose soil on both sides of foundation without layered compaction; or loose soil at the edge of groove flows into foundation pit (groove) and is not treated before compaction, so the backfill is soaked by water and causes settlement
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(2) The width of the foundation trench is narrow, and it is backfilled by hand, which does not reach the required compactness
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(3) There are many dry soil blocks in the backfill material, which may cause subsidence due to soaking in water, or cohesive soil, muddy soil and broken turf with high water content are used as soil materials, so the backfill quality is not up to the requirements
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(4) The water bubble method was used to settle the backfill, and the compactness did not meet the requirements
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3.1.2 pre control measures (1) before the foundation pit (trench) is backfilled, the accumulated water in the trench shall be drained, and the silt, loose soil and sundries shall be cleaned up
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If there is groundwater or stagnant water, drainage measures shall be taken
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(2) The backfill soil shall be backfilled and compacted in strict layers
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The thickness of each layer of virtual paving soil shall not be greater than 30cm
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The soil and water content shall meet the requirements
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The compactness of backfill soil shall be sampled and inspected according to the regulations to meet the requirements
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(3) There shall be no more than 50 mm diameter soil block in the filling material, and there shall be no more dry soil block
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When the next process is urgently needed, 2:8 or 3:7 lime soil should be used for backfilling and compaction
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(4) It is strictly forbidden to backfill earthwork with water sinking method
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3.2.1 causes (1) when only one side of the wall is filled with backfill, or only one side of the wall is pushed and compacted by machinery, the foundation and wall are squeezed and deformed due to the greater lateral pressure of the soil outside the plane
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(2) The strength of the wall concrete does not reach the value of the backfill strength, so the backfill should be carried out
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(3) Temporary pushing soil, stacking materials, equipment or walking heavy machinery on one side of foundation wall cause unilateral stress
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3.2.2 pre control measures (1) both sides of the corridor structure should be backfilled and tamped with soil layer by layer at the same time to make the stress balance
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The height difference of filling soil on both sides shall not exceed 30cm
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(2) After the wall construction is completed, the backfill construction can be carried out after reaching the design strength
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(3) After backfilling, a large amount of soil or materials, equipment, and heavy machinery and equipment should be avoided on one side
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3.3.1 causes (1) the surface soil of the construction site is highly permeable soil
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If this kind of filler is still used in the external wall foundation trench backfill, the surface water will easily erode the foundation and make the foundation sink
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(2) In the foundation trench and nearby parts, there is a soil layer with high permeability
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Without treatment, it forms a water bag to wet the foundation and leads to subsidence
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3.3.2 pre control measures (1) the backfill of outer trench shall be backfilled with clay, loam and other fillers with weak water permeability, or 2:8, 3:7 lime soil
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(2) If there is soil with high permeability in the foundation trench and nearby parts, it shall be excavated or sealed with filler with low permeability to isolate it from the foundation, and proper drainage gradient or blind ditch shall be made on the surface of soil layer with low permeability in the lower layer
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3.4 room backfill subsidence (control center earthwork backfill) 3.4.1 causes (1) fill material contains a lot of organic impurities and large soil blocks, organic matter decay causes fill subsidence
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(2) The filling is not compacted in layers according to the specified thickness, or the bottom is loose, only the surface is compacted, and the compactness is not enough
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(3) There are some weak soil layers in the center of the house, or there are underground pits such as pits, grave pits and ponding pits, which are not treated or found during construction
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After use, the use load increases, resulting in local collapse
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3.4.2 pre control measures (1) properly select backfill materials, carefully control the water content of soil within the optimal range, backfill and tamp in layers in strict accordance with the provisions, and sample the compactness to meet the quality requirements
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(2) Before backfilling, the original natural soft soil layer should be treated to clean up the organic impurities
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(3) When the backfill depth of the building core is larger (> 1.5m), the anti-seepage measures should be taken when the building exterior wall foundation is backfilled, or the waterproof measures such as adding a layer of cement mortar or brushing one degree of asphalt glue should be taken outside the building exterior wall foundation
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(4) For the filling of the room core with large area and high use requirements, the original natural soil should be rolled and compacted by machinery first, and then backfilled
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3.5 filling settlement and frost expansion of steps and flower terrace 3.5.1 causes the backfill under steps and flower terrace is not backfilled and tamped layer by layer, which causes the settlement and deformation after use, resulting in the cracking of concrete cushion
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The surface rainwater seeps into the fill through the cracks, which increases the water content of the fill and even saturates it
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The frost heave is caused under the low temperature in winter, which makes the concrete bulge and the cracks expand, causing a vicious circle, and even the steps are damaged seriously
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3.5.2 pre control measures (1) the backfill under the steps and flower beds should be carefully done, and the backfill should be compacted in layers
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300-600mm thick graded sand and stone are tamped and filled near the concrete cushion of steps and flower terrace to replace earthwork, so as to reduce settlement and eliminate frost heave
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(2) In the concrete cushion of steps and flower terrace with higher requirements and larger area, the Φ 6@300mm Two way steel mesh structure reinforcement to prevent cracking..
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