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

Introduction: Small and medium-sized rotary drilling rigs have always had the following technical difficulties when entering the rock: 1. The axial pressure is small; 2. The weight is light; 3. The rock has a large impact on the equipment itself. Due to the insufficient axial pressure of the rotary drilling rig, it is difficult to achieve efficient rock crushing in the form of "jumping crushing". There are two main reasons. The rock is anisotropic, heterogeneous, and discontinuous. The structure and the rock are located deep underground, and the geological conditions are complicated. Second, it is a new challenge for small and medium-sized rotary drilling rigs. It is necessary to ensure the mobility and flexibility of small and medium-sized drilling rigs, and to ensure that their own weight can be To withstand the reaction force of the rock, while ensuring its own safety and stability, this 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 regard. It is constructed on the weathered limestone on the construction site in Sichuan. The hole diameter is φ900mm, and the rock is successfully inserted into the rock 1000mm. The uniaxial compressive strength of the rock Reached 30MPa. The time used was 1.2 hours. A barrel drill is used, which uses the grinding or fatigue damage of the picks, and is equipped with a suitable construction method to completely take out the core.

Rock-in construction: In April 2013, the KR125A rotary drilling rig of Pinghan Heavy Industry was constructed in Chongqing, Sichuan. The geological conditions were moderately weathered limestone, the uniaxial compressive strength was 30MPa, the hole diameter was φ900mm, and the rock-entry requirement was 1000mm, and the cylinder was used. Drill plus picks mainly use the rotation and revolution of the picks in the barrel drill to grind the rock. As shown below.

The pressurization construction method of the drilling rig mainly adopts the “combination of constant pressurization and inching motion”. Constant pressurization is mainly to generate static load, which provides constant pressurizing pressure for the grinding of rocks, and inching pressurization is mainly formed A certain impact on the rock. Due to the uneven hardness of the rock, the rotation speed will change with the load, resulting in a rapid and slow alternation during the drilling process, and also causing a certain impact on the rock, thereby accelerating the cutting action of the rock.

In addition, in the process of drilling, it is necessary to continuously produce fresh water, mainly to lubricate and cool the drill bucket, and reduce the problems caused by the drill bit due to heat.

Removal of the core: When the barrel drill is used to drill to meet the specified requirements, the rock needs to be cut and taken out. Because the small drilling rig is light in weight and small in torque, it cannot directly cut the rock. This requires a special wedge-shaped drill bucket to successfully break the rock using the principle of wedge-shaped pressure. 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. Then use the barrel drill to take out the core.

Analysis of the principle of rock entry: The reason why the KR125A rotary drilling rig can enter the rock is mainly because the rig itself is designed to strictly comply with the European Union’s EN791 safety design standard, and the stability of the rig, as well as the weight of the rig and the flexibility of the rig are fully considered The ratio of the two has achieved excellent results.

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

1. Grinding and crushing section: Under the action of a small axial pressure, the contact pressure generated by the contact between the drill bucket and the rock is significantly less than the limit strength or indentation hardness of the rock. The crushing is performed by friction cutting, and the crushed particles in the second stage are small. The drill bit has a certain amount of wear.

2. Fatigue fracture section: When the pressure load increases to a certain value and the rock’s limit strength or indentation hardness is not reached, the rotating drill bit impacts and contacts with the rock many times, causing the rock to produce micro-cracks. The more micro-cracks, The strength of the rock is reduced a lot. When the strength of the rock is reduced to a certain level, the rock that has been hit by the drill several times will form large particles of rock debris, which will cause fatigue fracture.

3. Leap-forward crushing section: 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 under sufficient axial pressure, the rock will undergo leap-forward crushing. Yuejin's broken particles are relatively large.

The rock crushing mechanism of KR125A into the rock is to use the grinding crushing section and the fatigue crushing section. It solves the problems of small and medium-sized rotary drilling rigs that are light in weight and provide small axial pressure, obtain reasonable values ​​in pressurization and power head speed, while maintaining the advantages of small and medium-sized drilling rigs in terms of mobility. On the issue of core extraction, reasonable construction methods and suitable tools were used to successfully extract the complete core.

Conclusion:

1. Use the rock breaking mechanism, adjust the design of the rotary drilling rig, and equip it with suitable drilling tools, so that it is completely feasible for the rotary drilling rig to enter the rock, and it has been fully demonstrated in practice. The problem that small and medium-sized rotary drilling rigs cannot enter the rock is solved.

2. Drilling in the rock must be equipped with suitable drilling tools, especially for the issue of core removal. Therefore, the research on drilling rig tools is also indispensable, and it will be our future introduction of rotary drilling rigs. A general direction of rock research.

3. The research on the construction method of the rotary drilling rig is indispensable, such as the reasonable distribution of the relationship between the pressure and the speed, and the injection of clean water when entering the rock to cool the drilling tool and increase the lubrication.

4. What is particularly important for small and medium-sized rotary drilling rigs is that due to the limitation of their own weight, under the condition of ensuring stability, the proportional relationship between the drill pipes, drilling tools, masts and the total weight of the drilling rig can be reasonably distributed, and at the same time, small and medium rotary drilling can be used. The drilling rig has the characteristics of flexibility and low fuel consumption.