What are the characteristics of cement mixing pile, and what are the construction processes of cemen

Try: deep cement mixing pile is the use of cement and other materials as curing agent, through special mixing machinery, in the depth of the foundation in the soft soil and the curing agent forced stirring, by the curing agent and soft soil generated by a series of physical and chemical reactions, so that the soft soil hardened into a solidified soil with integrity, water stability and a certain strength of cement reinforced soil, so as to improve the strength of the foundation and increase the deformation modulus.

Deep cement mixing piles can be used to increase the bearing capacity of soft soil foundations, reduce the amount of settlement, and improve the stability of slopes. In order to prevent the deep cement mixing pile from breaking the pile, the inclined pile and the poor lap between the pile and the pile, the pile position error of the cement mixing pile should comply with the provisions of the "Technical Regulations on the Deep Mixing and Reinforcement Method of Soft Soil Foundation" (YBJ225-91).

At present, the maximum reinforcement depth of domestic cement mixing pile can reach 30m

The mixing pile can only drive about 18 meters at most.

Cement mixing pileThe construction process is as follows:

1. Pile lofting.

Before the pile position is lofting, the traverse point and leveling point handed over to the planning measurement unit.

Review and use after confirming that it is correct.

2. Excavate trenches.

According to the construction drawings.

The construction contour line of the cement mixing pile is measured and set up on site as the boundary line of the excavation trench.

3. The pile driver is in place.

The pile driver and the pile driver squad leader will command the pile driver in place, lay the steel plate and roadbed plate under the pile driver, see the situation of the front and back, left and right positions before moving, and find that there are obstacles that should be cleared in time, check the positioning situation after the end of the move, and correct the deviation in time if there is a deviation, and the deviation of the pile position is not more than 50mm.

4. Prepare cement slurry and slurry.

When mixing, water is added first, and then cement is added according to the mix ratio of the laboratory and put into the mixer.

5. Pre-stir and sink.

Cool water to be blended.

After the cycle is normal, start the mixer motor, loosen the crane wire rope, and make the mixer sink along the guide frame to stir and cut the soil.

Common quality problems and prevention measures of cement mixing piles

1. Pass the pile test.

to determine the amount of spraying, the speed of drilling, the lifting speed and the cement slurry pressure in the cement pump.

2. In order to ensure that the construction equipment is at the construction site.

To be able to construct smoothly, it is very important to level the site to the original ditch. Carry out necessary backfilling and leveling.

3. Equipped with corresponding signs, such as construction technical parameters signs, construction responsibility signs, etc. During the construction process, the cement mixing pile adopts a 24-hour shift side station in the whole process, and checks it with the site according to the content of the sign.

4. Before the construction of the cement mixing pile, according to the width of the roadbed and the design parameters, the pile drawing on the canvas in the construction plane is based on the cloth.

The pile diagram releases a large sample of the construction area, and the pile position is lofted according to the design pile spacing in each area.

Cement mixing pile is an effective form of soft foundation treatment, the cement is used as the main agent of the curing agent, and the cement is sprayed into the soil and fully stirred by the mixing pile machine, so that a series of physical and chemical reactions occur between the cement and the soil, so that the soft soil is hardened and the foundation strength is improved. CBI Zhongda Consulting has made the following relevant information for cement mixing piles:

Classify. At present, cement mixing piles are divided into single-shaft, double-shaft and three-shaft mixing piles according to the main construction methods used.

How it works. Cement and soft soil are formed after forced mechanical mixing, which is based on a series of physical and chemical reaction processes between cement and soft soil.

1) Hydrolysis and hydration reaction of cement in soft soil.

Ordinary Portland cement is mainly composed of calcium oxide, silicon dioxide, aluminum oxide, ferric oxide and sulfur trioxide, and these different oxides are composed of different cement minerals. When the cement is fully mixed with the saturated soft soil, the minerals on the surface of the cement particles will soon undergo hydrolysis and hydration reactions with the water in the saturated soft soil to form compounds such as calcium hydroxide, aqueous calcium silicate, aluminate aluminate and calcium iron oxide.

These compounds form a suspended solution that has a cementing effect, and after condensation, it forms the cementing strength of the cement soil. After the calcium sulfate in cement and tricalcium aluminate react with water to form a compound called "cement bacillus", this compound is precipitated in the form of needle-like crystals in a relatively short time, and a large amount of free water in the soft soil is fixed in the form of crystal water.

2) The effect of clay particles with cement hydrates.

When various cement compounds are generated, some hydrates induration themselves, forming a cement-stone skeleton; Some hydrates react with the surrounding clay particles to form new minerals. These effects also include: ion exchange and agglomeration, coagulation, carbonation, etc.

It should be noted that the above is carried out under the condition that the cement and soil are fully mixed in the test chamber. In the actual construction operation, because the construction machinery is cutting and stirring, it is impossible to stir the cement and the soil fully and evenly as in the test room, there are some small soil blocks that have not been crushed in the cement soil, the phenomenon that cement wraps the soil block will appear after mixing the cement (slurry or powder), the large pores between the soil blocks have basically been filled by the particles of cement, so a large number of cement more micro areas have been formed in the cement soil after actual reinforcement, and there is no cement in the inside of the small soil block.

Only after a relatively long period of time, the soil particles in the soil block can gradually change their properties after the infiltration of the surrounding cement hydrolytic compounds. In this way, it is inevitable that the cement stone area with high strength and good water stability and the relatively weak small soil block area before the strength cracking will be produced in the cement soil. This also shows that in the actual construction, the more evenly the cement and soft soil are mixed, the smaller the soil block is crushed, the smaller the discrete strength of the cement-soil structure, the higher its strength, and the closer its unconfined compressive strength is to the indoor test.