Rotary drilling rig is a kind of pile machinery used for hole-forming operation of building foundation engineering. It has the advantages of fast construction speed, good hole-forming quality, low environmental pollution, flexible and convenient operation, high safety performance and strong applicability. It has become the main hole-forming equipment for bored pile construction, but the construction of rotary drilling rig also has certain defects, mainly reflected in the following six aspects:

1, the initial investment is relatively large.

At present, the price of domestic rotary digging pile machine on the market is millions of yuan, and the one-time investment of self-purchased equipment is relatively large.

2. The rig is self-important and has strict requirements on the site.

The working weight of the rotary pile machine is generally tens of tons. However, due to the small contact area between the crawler and the ground, the bearing capacity of the foundation is required to be about 100kPa. Especially in the filling area, if the ground surface is not hardened or replaced, the surface water is abundant or the construction in rainy season should be carefully considered and protective measures should be taken. Otherwise, it is very difficult to use the rotary pile machine to move, seriously waste mechanical advantages and there are great risks.

3. The hole wall protection is poor.

Due to the fast drilling speed of the rotary pile machine, the drilling mainly depends on cutting soil, and the wall protection of the hole wall is worse than that of drilling and punching piles. Especially in the fill and soft soil layer, collapse and shrinkage prone to occur, to give attention. The drilling speed shall be controlled in the construction of filling soil and soft soil, and the drilling speed shall be changed as much as possible to meet the requirements of wall protection. At the same time, the drilling footage shall be paid attention to in the construction of soft soil, and the drilling depth at one time shall not be too large.

4, need other mechanical cooperation operation.

Due to the structural characteristics of the rotary pile digging machine, the installation of the reinforcement cage and the pouring of concrete cannot be completed by itself after the hole is formed, and other hoisting machinery must cooperate, and the spoil generated in the hole digging process must be excavated and transported by other earth moving machinery.

5. The content of pores in soft soil is easy to produce negative pressure.

The contact surface between the drilling tool of the rotary pile machine and the soil body is relatively large, if the drilling footage is large in the soft soil, the lifting process of the drilling bucket is easy to produce negative pressure, which has an adverse effect on the stability of the hole wall while increasing the load on the rotary pile machine body, and is easy to form the hole wall shrinkage and collapse.

6, the construction process of short-term investment increased.

Due to the fast construction speed of the rotary pile machine, the short-term need to invest in the material cost is relatively large, the construction unit should be combined with the operation of the project funds, the project duration and the relevant conditions agreed in the contract for comprehensive consideration and selection.