Technical Advantages And Common Problems of Rotary Drilling Rigs in Bored Pile Construction

Introduction of advantages of rotary drilling rig

The hole formation of rotary drilling rig is firstly to break up the rock and soil through the slewing of the barrel drill bit with a flap at the bottom and load it into the drill bit directly, and then the drill bit will be raised out of the hole by the lifting device of the drilling rig and the telescopic drilling rod to unload the soil, and so on and so forth, continuously taking soil/unloading the soil until drilling to the depth of the design. For well-bonded rock and soil layers, dry or clear water drilling process can be adopted. In loose and collapsible formations, the mud shield drilling process must be used. Compared with traditional percussion drilling rig and rotary drilling rig, rotary drilling rig has the following advantages:

1, can be multi-purpose, to realize a variety of drilling methods, in the case of the host remains unchanged, rotary drilling rig can be used with a short auger or bucket to adapt to the requirements of different strata of the hole.

2, advanced equipment performance, high degree of automation, low labor intensity: rotary drilling rig for crawler-type fully hydraulic self-propelled drilling rig, the use of a full set of hydraulic systems, and is equipped with advanced computer operating system, the degree of automation is high, the construction site can be moved by themselves, self-erecting mast, mobile, convenient and fast to the hole position. Adopting telescopic drilling rods saves manpower and time for adding and connecting drilling rods, less auxiliary time and high time utilization rate.

3、High drilling efficiency: the rotary drilling rig can be configured with different drilling bits according to the stratum, in the cohesive soil layer can use the long drill pipe to speed up the drilling speed; for the stratum with large content of sand and pebbles, it can use the short drill pipe, configure the mud shielding wall, and control the drilling speed; for the strata containing lone stone, drifting stone and harder rock can be exchanged for the long and short auger bits to deal with it, and then switch to the pipe to continue the drilling after it is loosened.

4, good pile quality: rotary drilling on the ground disturbance is small, the hole wall mud skin is thin, the formation of the hole wall for the rough type, is conducive to increase the pile side friction resistance, to ensure that the pile foundation design bearing capacity. The bottom of the hole slag is less, easy to clear the hole, can improve the pile end bearing capacity.

5, small environmental pollution: rotary drilling mud used only for positive and negative circulation drilling 1/10 ~ 1/20, so the construction site is more neat, the pollution caused by the environment is small, while rotary drilling vibration is small, low noise. However, the rotary drilling rig is subject to greater constraints of the geological conditions of the strata, in the hard rock layer, denser pebbles and gravel, isolated stone layer, the drilling becomes more difficult, but can be equipped with a cylinder core bit for hard rock layer, pebble layer with a grain size of more than 100mm, the diameter of the drifting stone layer of more than 200mm, punching and grasping cone bit, as well as auger drill bit to overcome the difficulties brought about by the strata.

Construction preparation

1, slurry configuration: rotary drilling rig on the ground disturbance is small, usually only with the wall stabilizing fluid can be constructed. In a certain distance from the mouth of the hole dug and set up a mud pool and circulating ditch, and the use of water and bentonite to prepare wall stabilizer, strengthen the test, choose the best ratio, strengthen the quality control, the specific gravity of the mud is controlled at 1.1 ~ 1.3 When drilling into the sand layer and other easily collapsed sections, depending on the situation, the stabilizer to add clay, increase the consistency of the mud, to improve the ability of the mud to protect the wall.

2. Drill bit reserve: increase the reserve of common drill bit and spiral drill bit according to the construction needs.

Common problems and treatment measures in construction

1, card buried drilling tool card buried drilling tool is rotary drilling construction is the most likely to occur, but also more harmful accidents, so in the construction process must take proactive measures to prevent, once the accident, to take effective measures to deal with it in a timely manner. The main reasons for the occurrence and preventive measures are:

1 The looser sand pebble layer or flowing sand layer, the hole wall is prone to large-scale collapse and cause buried drilling. When drilling to this formation, countermeasures should be formulated in advance and the mud specific gravity should be adjusted.

2 clay layer is too deep for one time, the hole wall is easy to shrink and cause jammed drilling. In this kind of stratum drilling should control the amount of one advance, such as drilling in the depth of 15m or less, it is best to drill no deeper than 40cm at one time.

3 Due to mechanical accidents, the drill bit stays at the bottom of the hole for too long, resulting in too much slag around the drill bit cylinder wall or shrinkage of the hole wall, which leads to stuck drilling. Therefore, we should pay attention to the timely maintenance and repair of the drilling rig itself, and at the same time, we should adjust the mud performance so that the bottom of the hole will be less slag in a certain period of time.

 2, the collapse of the hole is mainly due to the drilling process does not use mud, or use very little mud, wall protection effect is poor. In order to prevent the collapse of the hole, the drilling process should keep the water level in the hole appropriately higher than the groundwater level, control the specific gravity of the mud, and pay attention to controlling the lifting speed of the drilling bucket.

3, slurry leakage slurry leakage accident is mainly related to the groundwater level and the performance of the mud, such as the occurrence of large fissure leakage, backfill should be used to deal with; leakage of slurry is not too serious should be adjusted to the performance of the mud, the formation of the mud skin should be sufficient toughness; can be infiltrated into the mud in the appropriate amount of cement, stirred evenly after use.

4, not into the main reason: the drill bit is slipped by the clay paste or drilling process encountered drifting stones, hard pebble layer, bedrock, and so on. Preventive measures: when slippage occurs, adjust the angle of the bucket teeth to 60°, put stones into the hole, change the auger bit or cut-off bit and other methods to deal with. If encountering drifting stones, hard pebble layer, bedrock, etc., replace or remodel the drill bit, rearranging the angle, shape, and arrangement direction of the tool or switching to full cut-off teeth rotary drilling bucket.

5、Dropping the drill bit, drill bit base plate The connection between the drill pipe and the drill bit is not strong or the local joint of the drill bit is not securely welded to the body of the drill bit, or the strength of the wear pin is not enough, etc. may cause the drill bit to fall off. Insufficient strength of the connecting shaft of the drill bit base plate, shear damage of the bolts connecting the drill bit base plate, and poor welding of the connecting shaft of the drill bit base plate to the bushing may cause the drill bit base plate to fall off. Pay attention to the inspection of these parts during construction. If the drill bit is dislodged, it can be salvaged with a cylinder drill.

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