The scope of application of the rotary excavator and the shortcomings in the construction

Rotary drilling machine (English name: Rotary Drilling Rig) is a construction machine that has been developed in recent years and is suitable for hole-forming operations in building foundation projects. It is called "green construction technology". Widely used in the construction of pile foundations such as railways, highways, bridges, municipal construction, and urban civil buildings. With different drilling tools, it is suitable for dry (short spiral), or wet (revolving bucket) and rock (core drilling) hole-forming operations. The excavator has the characteristics of good construction quality, outstanding environmental protection, less dust and mud pollution, flexible maneuverability, high construction efficiency, fast hole formation speed and multi-function. Rotary excavators are basically adapted to the soil geological conditions in most areas of our country, with a wide range of applications, and can meet the needs of high-rise building foundations, bridge construction and other projects. At present, the rotary excavator has been widely used in various bored pile projects.

The scope of application of the rotary excavator:

1. From the suitability of the stratum, it is not only suitable for cohesive soil, sandy soil, silty soil, but also for artificial backfilling soil, stratum containing some pebbles and gravel, and weathered rock with low strength.

2. In terms of drilling methods, either wet drilling or dry drilling can be used.

3. In terms of the types of bored piles, either straight holes or oblique holes can be drilled. The maximum pile diameter can reach 2.5m, and the deepest pile length can reach 100m.

4. In terms of construction space, it can be operated without providing a large working surface, which is unmatched by other bored piles.

5. From an environmental point of view, the construction noise is low, does not pollute the environment, and is suitable for construction areas with high environmental protection requirements.

The disadvantages are as follows:

1. Self-importance, stricter requirements on the venue. The working weight of the rotary excavator is generally about 70t, but the contact area of ​​its crawler with the ground is about 7.0m2, so the required foundation bearing capacity is about 100kPa, especially in the reclaimed area, if the surface is not hardened or replaced, the surface water The construction in rich or rainy season should be carefully considered, otherwise it will be very difficult to use the rotary excavator to construct and only move the machine, which will seriously waste the advantages of the machine.

2. Poor hole wall protection. Due to the fast drilling speed of the rotary excavator, the drilling is mainly based on cutting the soil, and the hole wall protection is worse than the drilling and punching piles. Especially in fills and soft soil layers, hole collapse and stuck drill are prone to occur, so attention should be paid. In filling and soft soil construction, the drilling speed should be controlled, and the drill should be rotated as much as possible to meet the requirements of wall protection. At the same time, the drilling depth should be paid attention to in the construction in soft soil. The drilling depth should not be too large at a time.

3. It is easy to produce negative pressure in the hole in soft soil. The contact surface between the drill barrel of the rotary excavator and the soil is relatively large. If the drilling footage is large in the soft soil, negative pressure is likely to be generated during the lifting process of the drill bucket, which increases the pulling load on the rotary pile body while improving the stability of the hole wall. Adversely, it is easy to form the diameter of the hole wall.

4. For cohesive soil and loose sandy soil in flow plastic state, the mud problem must be solved and selected carefully.