Problems needing attention in the construction of

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Problems needing attention in the construction of compaction pile composite foundation

1. Experimental problems

in order to test the change of mechanical properties after foundation treatment and provide basis for foundation design, the low-level treatment shall be determined according to the site foundation conditions. Before the commencement of construction, the non-metallic mineral filler for plastics shall be made in the adjacent site or building site, which can generally be considered as the existence of artificial mining The non-metallic mineral material test pile composite foundation with the above defined properties and added to plastic shall be processed and used. The foundation shall be designed after the test data are obtained. The test pile composite foundation can not meet the design requirements, and the treatment scheme should be modified. In practical projects, many projects do not carry out tests in advance, but do experiments on the treated composite foundation. If the test data meet the requirements, it is OK, otherwise it will cause passivity. Remedial measures will be taken to delay the construction period, which is not ideal. In some places, attention should be paid to accumulating data and summarizing the quotation of several typical soft foundation geological products. In addition, with rich construction experience, the test can also be avoided by referring to the data

2. Hole forming problem

there are two kinds of hole forming methods: mechanical hole forming and manual hole forming, which should be determined according to geological conditions, drilling depth and construction conditions. During pore forming, the moisture content of the foundation soil should be 12%~23%: it is difficult to form pores below 12% and the hydrolysis of quicklime blocks does not provide enough water; When it is greater than 23%, it is easy to shrink, or the pile core softens after the pile is completed. Therefore, the soil with lower than the optimal moisture content needs to be moistened with water, and the soil with higher than the optimal moisture content needs to be dried in the air. At least 0.2m thick soil shall be reserved for the foundation pit. After the hole filling, the compacted soil shall be excavated to ensure the compaction effect

3. Compaction problem

the key of compaction pile composite foundation is compaction. How to give full play to the compaction effect, construction is the key. Reasonable filler mix proportion and careful compaction are the premise to ensure construction quality. There are a variety of commonly used filler mix proportions. For example, lime sand pile is quicklime block: medium sand =7:3 (volume ratio), lime sand gravel pile is quicklime block: medium sand: gravel with particle size of 20~40mm =5:2:3 or 6:1.5:2.5, and an appropriate amount of fly ash can also be added to improve the strength of the pile

after the completion of some compaction pile composite foundation, the ground at the top of the pile rises and cracks, or the concrete cushion rises and cracks on the cushion after the completion of the concrete cushion. This is the result of the upward release of part of the expansion force of the compaction pile, which actually weakens the compaction effect of the compaction pile. In order to avoid this energy consumption, it is generally possible to use 3:7 lime soil to compact and seal the top 300mm below the pile top elevation, which can solve this problem. After the completion of the composite foundation of some projects, although the top is also sealed with lime soil, the concrete cushion is not made immediately. As a result, the pile top is still uplifted and the nearby ground is bulging. To avoid this situation, concrete cushion shall be made immediately after the completion of composite foundation. If possible, it is better to make concrete cushion while completing composite foundation

4. Some dry wells, pits, ditches and other treatment problems are encountered.

after the foundation pit is excavated, or after many important factors need to be considered through the drill rod sample test, it is found that there are dry wells, pits, ditches and water tanks filled with miscellaneous soil or miscellaneous fill or plain soil under the building foundation, which must be treated in time. In addition to the method of filling soil for shallow buried depth, compaction piles can be generally used for treatment. According to the local foundation conditions, the pile depth can be the same or different. It is appropriate to use the pile bottom to support the soil, and adjust the pile spacing. The pile spacing can be sparse or dense to achieve the required foundation strength. During treatment, attention shall be paid to make the bearing capacity of the treated local foundation basically consistent with that of the large-area foundation of the building site

5. Quality inspection problems

compaction pile composite foundation is a concealed project. Inspection must be strengthened during construction. The inspection contents include the depth, diameter and perpendicularity of the hole, the compaction quality of the filler in the hole. After the completion of the pile, the dry density of the soil between the piles, the dry density of the pile filler, the foundation bearing capacity, etc. shall be inspected. The inspection methods include excavation sampling test, penetration test, load test, etc

at present, some engineering compaction pile inspection methods are incomplete and the original records are incomplete; After the completion of the pile body, the cushion shall be made as the foundation immediately. The test of the foundation bearing capacity is often carried out after the completion of the main project, or this test is not carried out at all, which makes the bearing capacity of the composite foundation treated with closely packed piles insufficient. It is only after the completion of the main project that it is known that the foundation bearing capacity cannot meet the design requirements, so it is very difficult to carry out the treatment. For those composite foundations that are not checked at all, there may be hidden dangers in fact, so we should pay attention to and strengthen the quality inspection of compacted pile composite foundation

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