Rotary drilling rig is a kind of construction machinery that is developed in recent years and is suitable for hole formation in building foundation engineering. It is widely used in pile foundation construction of railways, highways, bridges, municipal construction, and urban civil buildings. Dry (short spiral) or wet (rotary bucket) and rock formation (core drilling) hole-forming operations. Rotary drilling rigs have good construction quality, outstanding environmental protection features, less dust and mud pollution, flexible and flexible, high construction efficiency, hole formation. Fast and versatile. Rotary drilling rigs are basically adapted to the soil geological conditions in most areas of China, and have a wide range of uses, which can meet the use of high-rise building foundations and bridge construction projects. At present, rotary drilling rigs have been widely used in various bored pile projects.
Application scope of rotary drilling rig:
1. From the perspective of the suitability of the stratum, it is suitable for both cohesive soil, sandy soil and silty soil, as well as artificial backfill soil and stratum containing some pebble and gravel, and weathered rock with low strength.
2. In terms of drilling, both wet and dry drilling can be used.
3. In terms of the type of bored pile, both straight and 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 is not necessary to provide a large working surface to operate, which is unmatched by other bored piles.
5. From an environmental perspective, 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 site requirements. The self-weight of the rotary drilling rig is generally around 70t, but the contact area between the crawler and the ground is about 7.0m², so the required bearing capacity of the foundation is about 100kPa, especially in the filling area. If the surface is not hardened or replaced, the surface water It should be carefully considered in the rich or rainy season construction, otherwise it is very difficult to use the rotary drilling rig to move only the machine, which will seriously waste the advantages of machinery.
2. Poor wall protection. Due to the fast drilling speed of rotary drilling rigs, which are mainly cut by soil, hole wall protection is worse than drilling and punching piles. Especially in the fill and soft soil layers, cavitation and stuck drilling are prone to occur, so we must pay attention to it. In the filling and soft soil, the drilling speed should be controlled, and as many rotations and fewer drillings as possible are required to meet the requirements of the retaining wall. At the same time, the drilling depth should be paid attention to in the soft soil construction. The depth of one drilling should not be too large.
3. Negative pressure is easily generated in the holes in soft soil. The contact surface between the rotary drilling rig drill pipe and the soil is relatively large. If the drilling depth is large in soft soil, the negative pressure is likely to be generated during the lifting of the bucket. It increases the load on the rotary digging machine body and has stability on the hole wall. Adverse effect, easy to reduce the diameter of the hole wall.
4. For fluid clay and loose sandy soil, the mud problem must be solved and carefully selected.