Today, we will compare rotary drilling rigs with commonly used impact and rotary drilling rigs in the past, and give some suggestions on how to choose hole-forming machinery in pile foundation construction for your reference!
The following is an analysis and comparison between the three most common drilling rigs currently, impact drilling rigs, rotary drilling rigs, and rotary drilling rigs.
1. Analysis of impact drilling rigs
Impact drilling rigs are a kind of hole-forming machinery that takes both hard and soft drilling into consideration, and are suitable for almost all geological conditions, from clay soil and sandy soil to gravel layers, pebbles, boulders, soft rock, and hard rock. Impact drilling rigs are particularly suitable for drilling holes for rock-embedded piles in mountainous hills. When the surface layer is soft soil, the surface soil can be replaced to stabilize the drilling rig.
The impact drill can also be assembled by itself according to the actual conditions of the construction site and is easy to operate. In terms of the structure and operating procedures of the drilling rig, impact drills are superior to rotary and rotary drilling rigs. If you only consider the geological conditions and do not consider the project progress or economic benefits, impact drills can be used. In terms of hole formation speed, in specific geology, impact drilling rigs are inferior to rotary and rotary drilling rigs. Comparing the cost per linear meter of single-hole drilling, impact drilling rigs are the highest, rotary drilling rigs are the lowest, and rotary drilling rigs are in between.
2. Analysis of rotary drilling rigs
Rotary drilling rigs, whether they are positive circulation or partial circulation, are suitable for clay soil, soil layers containing a small amount of gravel and pebbles, and soft rock. They are not suitable for large pebble layers and hard rock layers. Among them, the positive circulation drilling rig is also suitable for silt sand and fine, medium, and coarse sand layers. When a reverse circulation drilling rig drills in a sand layer, if the mud conditioning index is insufficient or the drilling speed is too fast, it may cause a hole collapse accident.
The rotary drilling rig is particularly suitable for drilling friction piles in plains with thick inland alluvial layers and coastal tidal flats. From the perspective of hole-forming speed, the rotary drilling rig is faster than the impact drilling rig but not as good as the rotary drilling rig. From the perspective of project cost analysis, the rotary drilling rig is the most economical and cheapest of the three drilling rigs.
3. Shortcomings of impact and rotary drilling rigs
Based on the above, the common characteristics of impact drills and rotary drills are that the equipment is cheap and easy to operate. After decades of market selection, it has become the mainstream machine for pile foundation drilling. However, with the progress and development of society, some shortcomings that are difficult to overcome are gradually exposed:
Pollute the environment, not environmentally friendly
Mud is required for wall protection and suspended particle slag removal, but mud causes environmental pollution to the site and surrounding environment, and cannot meet the requirements of environmental protection and civilized construction that are increasingly valued by contemporary society.
Circulating mud and settling out slag requires a mud tank, which requires a larger construction site.
Slow hole-forming speed
According to normal construction quality requirements and general geological and stratigraphic conditions, a rotary drilling rig drills about 8-10m per day, while the percussion drilling speed is slower.
Poor adaptability
In addition to the strong adaptability of impact drills, rotary drills cannot deal with harder formations other than strongly weathered layers.
Both impact drills and rotary drills can only drill vertical holes, not oblique holes.
The degree of automation is low, the labor intensity of operators is high, and the working environment is poor. The degree of automation of impact drills and rotary drills is not high. They are basically operated in the open air. The working environment of workers is harsh, which is no longer in line with the trend of humanization and high automation in today’s society.
4. Analysis of rotary drilling rigs
Environmental protection and health
Dry hole formation will not cause pollution to the site and surrounding environment. Even when static mud is used to form holes, rotary drilling rigs cause less pollution to the site than the pollution caused by impact drilling rigs and rotary drilling rigs.
Fast hole-forming speed
In general formations, the hole-forming speed of a rotary drilling rig is 4-6 times that of an ordinary drilling rig. It is estimated that in general strata and bridge piles within 30 meters in length, and in accordance with normal quality control requirements for pile foundation drilling, it takes about 24 to 36 hours for a rotary drilling rig to drill a qualified pile foundation. With a skilled rotary drilling rig operator and a technician to guide the drilling, it only takes 6 to 9 hours to complete the hole for the pile foundation. In this regard, rotary drilling rigs have obvious advantages.
Strong adaptability
Rotary drilling rigs can be equipped with different drill bits. Common rotary drilling bits include spiral drill bits and rotary buckets. In addition, there are barrel core drill bits, bottom expansion drill bits, impact drill bits, and impact drill bits for different geological conditions. They can be used for sand Drilling holes in different strata such as layers, soil layers, and rock layers.
The rotary drilling rig can move by itself on crawler tracks, and the positioning before drilling is very accurate and convenient. Rotary drilling rigs not only drill vertical piles but also drill inclined piles.
The high degree of automation, low labor intensity for operators, and a comfortable working environment
The rotary drilling rig is a product that integrates high power, full hydraulic pressure, electromechanical integration, and comfortable operation (humanization). It is the crystallization of contemporary high technology and embodies the centralized unity of humanization, intelligence, and high efficiency.
Analysis of the shortcomings of rotary drilling rigs and misunderstandings in use
Disadvantages: Rotary drilling rigs will also be restricted by various conditions such as the geological conditions of the stratum where they are being constructed, the machine’s own factors, human factors such as the operator, etc., resulting in some situations that are currently difficult to deal with, and are mainly not suitable for hard strata. In the initial stage of using a rotary drilling rig, blind superstition or lack of understanding of the rotary drilling rig can easily lead to misunderstandings and misunderstandings, which directly affect the use of the rotary drilling rig.
Rotary drilling rigs are also restricted by the geological conditions of the formation. Drilling becomes more difficult in hard rock layers, denser pebbles, and boulder layers. If the drill bit is not replaced, accidents are prone to occur. Although barrel core drill bits, impact drill bits, and impact cone drill bits can be equipped for hard rock layers, pebble layers with particle diameters exceeding 100 mm, and boulder formations with diameters greater than 200 mm, their actual efficiency and effect are comparable to those of traditional impact drills. However, the effect is still not ideal.
Misunderstanding analysis: When using a rotary drilling rig to form holes, common pile foundation construction accidents such as hole collapse and diameter shrinkage will occur just like other drilling rigs. The causes include subjective and objective reasons. Human factors and defects in the current mechanical equipment design coexist. . The construction technology of rotary drilling rigs depends on different strata and different methods. If you cannot have an objective understanding of the rotary drilling rig and have a deep understanding of the local geological conditions, it will be difficult to avoid accidents.
When encountering easily collapsible strata, high-quality static mud is used to build walls, and the technical requirements of slow advance and multiple sweeps of previous drilling rigs should also be strictly followed. We cannot just focus on the advantages of rotary drilling rig drilling progress and economic benefits, and ignore the quality of the mud retaining wall and the number of hole sweeps, leaving hidden dangers for pile foundation hole formation and pile foundation filling. When the rotary drilling rig passes through the expansive soil layer, it should also strengthen the hole scanning to prevent the occurrence of diameter reduction.
Strictly control the lifting speed of the lifting bucket during the hole-forming process. During the drilling process of the rotary drilling rig, the drilling speed should be strictly controlled to avoid excessive drilling scale. If the drilling rig raises and lowers the drill bucket too fast, the mud between the outer wall of the drill bucket and the hole wall will wash away the hole wall. In addition, a large negative pressure will be generated in the lower part of the drill bucket, causing necking and collapse of the hole wall. When the drill bucket is operating in a silt layer or sub-sand soil layer, its lifting speed should be slower. When necessary, for special weak formations, limit the drilling time of drilling operations, and do not blindly pursue drilling speed. After measuring and mastering the best scientific hole formation time by testing 3-4 piles, we can then standardize and guide the normal construction of the rotary drilling rig.
Structural problems with drill bits and other equipment supporting drilling rigs. When using double-door bottom-opening rotary buckets produced by some manufacturers, the lifting force of the rotary bucket increases significantly, forming a piston effect, which can easily cause collapse and shrinkage holes.
When the rotary bucket is lifted, a large negative pressure is generated below, causing the lifting resistance to increase and the hole wall to shrink and collapse. This reason has led to the policy of prohibiting the use of rotary drilling rigs in some coastal areas with soft foundations. Fortunately, through technological improvements, diversion grooves are welded on the side walls to facilitate the diversion of mud and reduce the negative pressure in the pile holes. can solve this problem. At the same time, the chassis is welded with side teeth to control the distance between the rotary bucket and the tooltip to prevent the rotary bucket from damaging the hole wall when it lifts, lowers, and rotates.
Construction organization of cast-in-place pile foundation after hole formation
From the formation of holes to the completion of pouring a pile foundation, it requires the organization and cooperation of steelwork teams, concrete work teams, transportation vehicles, pouring work teams, etc. Rotary drilling rigs can form holes quickly. If the pile foundation that has formed holes cannot be poured in time due to factors such as untimely processing of the steel cage, poor organization, or mechanical failure and is left idle for a long time, accidents such as hole collapse may occur
5. Summary
When selecting hole-forming machinery in pile foundation construction, many factors need to be considered. When choosing a hole-forming machine, first consider the geological conditions of the formation. According to the geological histogram, the hole-forming machinery is selected in a targeted manner. Secondly, factors such as the economic cost, construction period, environmental protection, and civilized construction of drilling holes by drilling rigs should be considered.
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