Abstract: Rotary drilling rig into the rock has long been a major problem in our construction, especially for small and medium-sized rotary drilling rig into the rock is difficult. The rotary drilling rig KR125A of Jiangsu Pinghan Heavy Industry was constructed on the medium weathered limestone layer in Sichuan, with a hole diameter of φ900mm, successfully entering the rock of 1000mm, and taking out the core completely. It reflects the high reliability of KR125A and solves the problem of entering the rock.

Introduction: Small and medium-sized rotary drilling rigs have the following technical difficulties in entering the rock: 1. The axial pressure is small; 2. Its own weight is light; 3. The rock has a large impact on the equipment itself. Due to the lack of axial pressure of rotary drilling rigs, it is difficult to realize the form of efficient "leap-forward crushing" of broken rocks. There are mainly two reasons. The rock is an anisotropic, heterogeneous and discontinuous structure, and the rock is located in the deep underground with complex geological conditions. Second, it is a new challenge for small and medium-sized rotary drilling rigs, which not only ensure the mobility and flexibility of small and medium-sized drilling rigs, it is also necessary to ensure that its own weight can withstand the reaction force of the rock, while ensuring its own safety and stability, which seems to be a challenge for small and medium-sized drilling rigs. The design of the drilling rig, as well as the appropriate construction methods, have put forward a new requirement for the designers. The small and medium-sized rotary drilling rig KR125A produced by Jiangsu Pinghan Heavy Industry has made a major breakthrough in this respect. It was constructed on weathered limestone at the construction site in Sichuan, with a hole diameter of φ900mm, successfully entering the rock of 1000mm, and the uniaxial compressive strength of the rock reached 30MPa. The time used was 1.2 hours. The use of a barrel drill, the use of cutting teeth grinding or fatigue damage, and then equipped with a suitable method to remove the core integrity.

Rock entry construction: in April 2013, the KR125A rotary drilling rig of Pinghan heavy industry was constructed in Chongqing, Sichuan province. the geological condition is medium weathered limestone, the uniaxial compressive strength is 30MPa, the hole diameter is φ900mm, and the rock entry is required to be 1000mm. the barrel drill and the pick are used, mainly using the rotation and revolution of the pick in the barrel drill to grind the rock. as shown in the following figure.

The pressure construction method of the drilling rig mainly adopts the "combination of constant pressure and inching". Constant pressure mainly generates static load, which provides constant pressure for rock grinding, and inching pressure mainly forms certain impact on rock. Due to the uneven hardness of the rock, the speed will change with the load, resulting in the process of drilling in the alternating situation, but also caused a certain impact on the rock, so as to accelerate the cutting of the rock.

In addition, in the process of drilling, it is necessary to continuously add clean water, mainly to lubricate and cool the drilling bucket, and reduce the problems caused by the heating of the drill bit.

Core removal: When the specified requirements are met by drilling with a barrel drill, the rock needs to be cut off and removed. Because the small drilling rig itself is light in weight and small in torque, the rock cannot be cut off directly, which requires a special wedge-shaped drilling bucket, using the principle of wedge-shaped pressure to successfully break the rock. As shown in the figure below, insert the wedge into the gap between the core and the hole wall, and then apply pressure (using the impact force of the drill pipe) to successfully break the core. The core is then taken out with a barrel drill.

Analysis of the principle of rock entry: The reason why KR125A rotary drilling rig can enter the rock is mainly due to the strict compliance of the European Union's EN791 safety design standards, and the full consideration of the stability of the drilling rig, as well as the weight of the drilling rig and the flexibility of the drilling rig itself ratio, and achieved excellent results.

KR125A fully considers the three stages of rock crushing mechanism: grinding crushing section, fatigue crushing section and leap forward crushing section.

1. Grinding and crushing section: under the action of small shaft pressure, the contact pressure generated by the contact between the drilling bucket and the rock is significantly less than the limited strength or press-in hardness of the rock. The crushing is by friction cutting, the crushing particles in the secondary stage are small, and the drill bit has certain wear.

2. Fatigue crushing section: when the pressure load increases to a certain value and the limited strength or indentation hardness of the rock is still not reached, the rotating drill bit makes impact contact with the rock for many times, causing micro cracks in the rock. the more micro cracks, the more the strength of the rock decreases. when the strength of the rock decreases to a certain extent, the rock impacted by the drill bit for many times will form large particles of rock debris, thus the formation of fatigue broken.

3. Leap crushing section: Under the action of sufficient axial pressure, when the contact pressure between the drill bit and the rock is greater than or equal to the limit strength or indentation hardness of the rock, the rock will be broken. The particles broken by Yuejin are relatively large.

The rock crushing mechanism of KR125A into rock is to use grinding crushing section and fatigue crushing section. It solves the problem of small and medium-sized rotary drilling rig's own light weight and small shaft pressure, obtains reasonable value in pressure and power head speed, and can maintain the flexible advantage of small and medium-sized drilling rig. In the problem of taking out the core, using reasonable construction methods and appropriate tools, the complete core is successfully taken out.

Conclusion:

1. The use of rock crushing mechanism, adjust the design of the rotary drilling rig, equipped with appropriate drilling tools, so that the rotary drilling rig into the rock is completely feasible, and has been fully demonstrated in practice. The problem that small and medium-sized rotary drilling rigs cannot enter the rock is solved.

2. In the rock drilling, must be equipped with appropriate drilling tools, especially to take out the core of this problem, must be equipped with appropriate tools, so in the drilling tool research is also essential, and will be our future rotary drilling rig into the rock of a big direction.

3. It is essential to study the construction method of rotary drilling rig, such as reasonably distributing the relationship between pressure and rotating speed, adding clear water to cool the drilling tool and increasing lubrication when entering rock.

4. It is particularly important for small and medium-sized rotary drilling rigs because of their own weight constraints, in the case of ensuring stability, a reasonable distribution of drill pipe, drilling tools, mast and the proportion of the total weight of the rig, while playing a small and medium-sized rotary drilling rig flexible low fuel consumption characteristics.