Root pile is a kind of micro pile made by grouting method, which originated in Italy in the 1950s
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It is usually used for underpinning and reinforcement of foundation, and the diameter of pile is generally less than 1 Φ 100-300 mm
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Generally, the anti floating methods include counterweight concrete, soil anchor, cast-in-place pile and root pile
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The counterweight concrete has large volume and large area, which will cause cracking if it is not properly constructed and maintained; Soil anchor is easy to cause reinforcement leakage or insufficient mortar protection layer due to anchor bar deflection; The construction period of cast-in-place pile is long, the pile diameter and pile spacing are too large, and the cost is high
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In contrast, root pile has the characteristics of short construction period and low cost
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1、 The root pile method is suitable for foundation treatment of silt, muddy soil, cohesive soil, silt, sandy soil, gravel soil and artificial fill
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General construction sequence diagram 2
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Conditions for root pile construction 1
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Allowable deviation of pile plane ± 20mm； The deviation of pile inclination shall not be greater than 1%
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2
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When drilling in the soil layer, the drilling machine can be used to form the hole
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It is better to use clean water or natural mud to protect the wall, or casing can be used
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3
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The reinforcement cage for root pile should be hoisted in the whole length
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When it is hoisted in sections, the length of overlapping weld between sections should not be less than 5 times of the diameter of reinforcement; The single side welding shall not be less than 10 times of the diameter of reinforcement, and the time of lifting and welding shall be shortened during construction; The filling pipe shall be inserted directly to the bottom of the hole
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4
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In order to prevent adjacent pile hole displacement and hole string, measures such as interval construction, intermittent construction or increasing the dosage of accelerator should be adopted in grouting construction
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5
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Permanent casing, casing or other protective measures shall be adopted when the groundwater flow rate is high, which may lead to the erosion of newly poured slurry, mortar or concrete
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3、 The grouting material for root pile should meet the following conditions: 1
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It has good segregation resistance, plasticity, cohesiveness, fluidity and self compaction; 2
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When concrete or mortar is piped or pumped, round aggregate shall be used
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The maximum size of aggregate shall not exceed the minimum value of 15mm, 1 / 4 of the clear distance between longitudinal bars and 1 / 6 of the inner diameter of pumping pipe or underwater pouring pipe
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3
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For underwater pouring concrete, the cement content should not be less than 375 kg / m3, and the water cement ratio should be less than 0.6
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4、 The water cement ratio should not be greater than 0.55
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2
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When grouting through the temporary casing, the placement of reinforcement should be completed before the temporary casing is pulled out, and the grouting pressure should be applied every 2 meters during the casing pulling out process
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3
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When pipe fittings are used as load-bearing components, grouting can be carried out through the bottom; 4
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When using the flower tube grouting, it can be used for multiple grouting in the whole length section through the flower tube, it can also be used for sectional grouting through the flower tube and special valve, or it can be used for step-by-step grouting through the staggered post grouting tube
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5
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Secondary and multiple grouting can only be carried out after the cement slurry injected by the above method has set
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When the grouting pressure specified in the design can not be applied, it should wait until the specified grouting pressure can be applied
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6
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At the end of the grouting process, the grouting pipe should be filled with cement slurry and the grouting pressure should be maintained for a certain period of time
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7
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When the gravel or fine stone filling and grouting process is adopted, the filling material shall be cleaned, and the input amount shall not be less than the calculated pile hole volume 9 times of the grouting pipe, the grouting pipe should be used to clear the hole at the same time
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During one-time grouting, the grouting pressure should be 0.3MPa ~ 1MPa, and the grouting should be stopped until the slurry overflows out of the hole
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The second grouting can be carried out only when the first grouting slurry is initially set, and the cement slurry pressure should be 2MPa ~ 4MPa for the second grouting
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After the grouting pipe is pulled out, gravel should be filled at the top of the pile immediately, and grouting should be supplemented within the range of 1m ~ 2m
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5、 The quality inspection of root pile should meet the requirements
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1
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The compressive strength of pile body should be measured with reserved test block, and the strength of pile body should meet the design requirements
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2
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The vertical bearing capacity of root pile should be tested by load test, and the quality of pile body can be tested by dynamic test
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Graphic reference: Douding construction typesetting editor: Xiaohui technical support: niuhui new media ★ Hubei Tianhao Construction Engineering Co., Ltd.} Larsen steel sheet pile construction, leasing comprehensive service technical exchange & business contact Liu Meng 13707186388 Liu Meng → wechat welcome to add scanning QR code, pay attention to us 。
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