Brief introduction of method
abstract
All piles made of mechanical rotary drilling holes and then pouring concrete or reinforced concrete into the holes are called bored piles. According to the characteristics of hole-forming technology, it can be divided into three categories: positive circulation rotary drilling, reverse circulation rotary drilling and non-circulation spiral drilling, each of which has its own application scope and advantages and disadvantages.
Positive circulation rotary drilling hole-forming technology: suitable for cohesive soil, silt, sandy soil, gravel soil, strongly weathered rock, soft rock and so on. Pile diameter is 500-2200mm. According to different strata, different bits can be used to drill, so as to realize coring-free or coring drilling with high drilling efficiency. The disadvantage is that it is difficult to drill holes in the pebble bed; When the diameter of the borehole is large, it is difficult to protect the borehole wall of the collapsed stratum, and the amount of mud is also large.
Hole-forming technology of reverse circulation rotary drilling;
Suitable for cohesive soil, silt, sandy soil, gravel soil, strongly weathered rock and soft rock, etc. , the pile length is 500-2200mm. Drilling into fine sand, gravel, cohesive soil and silt has high efficiency and fast footage; Clean water can be used for drilling, the water column pressure can keep the hole wall stable, the slag is completely discharged, the hole bottom is clean, the drilling efficiency is high, and the bit consumption is low, which is beneficial to drilling large-diameter deep holes; The disadvantage is that it can pump water from the aquifer and consume a lot of water, especially in the case of water leakage, which is easy to cause hole collapse.
Non-circulating spiral drilling hole-forming technology
It is suitable for filling soil, cohesive soil, silt and sandy soil with medium density above the groundwater level. The pile length is 300-800 mm ... For homogeneous cohesive soil, silt and sandy soil, the drilling efficiency is high, no flushing fluid is used, no mud pollution, low noise and small vibration, and it can be constructed in narrow sites with low cost and less materials. The disadvantage is that it is not suitable for large-grained gravel, boulder and rock construction. Generally, the diameter of pile is small, and the bearing capacity of single pile is low.
mechanism
Although the structural form and construction method of cast-in-place pile are very different from precast pile, there are many similarities in terms of the basic working principle of pile, and its calculation theory and design method are also based on the theory of driven precast pile.
When the settlement of shallow foundation on natural foundation is too large or the stability of foundation cannot meet the building requirements, pile foundation is often used. Pile foundation is usually composed of several piles, the top of which is connected into a whole through the cap, and then the superstructure is built on the cap. The load of the building is transferred to the foundation soil through piles to meet the deformation and stability requirements of the building.
According to the mechanical properties of piles, piles can be divided into two types: end-bearing piles and friction piles;
End-bearing pile: the load of the building is transferred to the hard soil layer or rock stratum through the pile, and most of the load on the pile is borne by the supporting force at the pile end, and the friction of the soil around the pile plays a very small or negligible role.
Friction pile: the load of the building is transferred to the soil around the pile and below the pile end through the pile. Most of the load on the pile is supported by the friction between the pile surface and the soil, and the supporting force at the pile end can be ignored if it is very small.
Advantages and disadvantages:
Advantages:
Wide adaptability, suitable for construction in various strata, large selection range of pile length and diameter, high bearing capacity of single pile, steel saving, cost reduction and low construction noise compared with prefabricated piles, and suitable for construction in urban areas with dense buildings.
Disadvantages:
The construction technology is complex, there are many factors affecting the quality, the construction quality is difficult to control, and a large amount of sewage is sometimes difficult to treat.
The above is the introduction of what bored piles are provided by Zhong Da Consulting for architects. For more knowledge of architectural terminology, please pay attention to the architectural knowledge column of Zhong Da Consulting.
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