What are the classification of cement mixing pile construction methods? What are the common quality problems and preventive measures?

Cement mixing pile is an effective form of soft foundation treatment, which uses cement as the main agent of curing agent. The cement is sprayed into the soil by the mixing pile machine and fully stirred, so that a series of physical and chemical reactions occur between the cement and the soil, which hardens the soft soil and improves the foundation strength. What are the classification of cement mixing pile construction methods? What are the common quality problems and preventive measures?

First, the construction process:

Pile location lofting → drilling rig in place → drilling rig inspection and adjustment → positive circulation drilling to design depth → turning on high-pressure grouting pump → reverse circulation drilling and shotcreting → 0.3m→ below the working datum → drilling to design depth with repeated stirring → reverse circulation drilling and shotcreting to the surface → pile completion → construction of the next pile.

At present, cement mixing piles are divided into uniaxial, biaxial and triaxial mixing piles according to the main construction methods.

Second, the number of spiral drilling holes in uniaxial mixing piles and triaxial mixing piles is different, and the construction methods are different, and their functions are also different:

1, the number of spiral holes is different: uniaxial mixing pile has only one spiral hole, while triaxial mixing pile has three spiral holes at the same time.

2. Different construction methods: single-axis mixing pile can only be constructed downward with one spiral hole, while three-axis mixing pile can be constructed downward with three spiral holes at the same time. The cement is sprayed into the soil by the mixing pile machine and fully stirred, so that a series of physical and chemical reactions occur between the cement and the soil, which hardens the soft soil and improves the foundation strength.

3. Different functions: Triaxial mixing piles play an important role in foundation pit enclosure engineering. One kind is only used for stopping water, without inserting section steel in the middle, and other technologies should be combined if soil retaining is needed; One is that inserting H-beam into mixing pile (commonly known as SMW construction method) can not only stop water but also be used as retaining wall, which is suitable for shallow foundation pit excavation. However, uniaxial mixing pile does not have these functions of triaxial mixing pile.

Three, cement mixing pile quality common fault and preventive measures

1. Determine parameters such as shotcrete quantity, tripping speed, lifting speed and cement slurry pressure in cement pump through pile test.

2, in order to ensure the smooth construction of construction equipment in the construction site, site leveling is very important, for the original ditch pond. Carry out necessary backfilling and leveling.

3, equipped with corresponding signs, such as construction technical parameters, construction responsibility card, etc. In the process of cement mixing pile construction, the whole process of 24-hour shift is adopted, and it is checked with the site according to the contents of the notice board.

4. Before cement mixing pile construction, according to the subgrade width and design parameters, draw a pile bitmap on the construction plane, release the details of the construction area according to the pile bitmap, and release the pile positions in each area according to the designed pile spacing.

5, the specialist is responsible for the cement mixing pile construction, cement mixing pile construction requires 24-hour on-site, construction equipment requirements number, mark the scale line per meter on the main tower, in order to grasp the drilling depth and re-mixing depth.

6. In order to ensure that the verticality of the pile body after construction meets the design or specification requirements, a hanging hammer is hung on the main tower, and the verticality of the main tower is adjusted by the lifting of the drilling rig leg, so as to ensure the verticality of the drill pipe and the pile body.

7, strictly control the speed of drilling and lifting, it is strictly prohibited in the absence of shotcrete drilling or lifting drill pipe.

8. Drill sticking may occur in the construction process, and the method of increasing shotcrete quantity can be adopted to meet the need of re-mixing the whole pile.

9. After a period of construction, the drill bit should be removed to check its size to ensure that the size of the pile can meet the specification requirements, otherwise it will be replaced.

10, and the curing agent of cement mixing pile is cement slurry. In order to prevent the pipe from blocking when spraying concrete, a filter screen should be set at the slurry inlet to prevent caked cement or sundries from entering grouting pump.

1 1, on-site construction technicians and constructors strictly control three parameters, namely shotcrete quantity, lifting speed and pressure, to ensure the quality of cement mixing piles. And make site records, timely organize data, to ensure that the pile spacing and quantity meet the design requirements.

12, 28 days cement mixing pile drilling sampling frequency is 3%. By drilling core samples, whether the grouting and mixing of the pile are uniform, whether the pile is broken and whether the pile length meets the design requirements are detected.

13. The core samples are processed and ground into equal-height samples to obtain unconfined compressive strength. Try to grind three specimens in the upper, middle and lower parts of the core sample, and evaluate the strength of the pile according to the representative values of the three specimens.

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