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Application of small non - excavating drill in granite strata crossing construction

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Adopting horizontal directional drilling crossing technology to carry out pipeline crossing construction is an ideal construction method to complete water and electric pipe network construction, communication fiber optic cable laying and other projects under the principle of not damaging the geomorphological state and protecting the environment in urban municipal construction. In recent ten years, horizontal directional drilling crossing technology has been widely used in various industries in China. Crossing construction has gradually expanded from ordinary soil layer to sand layer, gravel layer, gravel layer and rock layer. What follow is construction difficulty is bigger and bigger. This requires that our construction machinery has more functions, and constantly update the construction process, reasonable determination of operating parameters.
 
1. Guiding technology in lithosphere
 
The key to horizontal directional drilling in rock layers is the construction of guide holes, and the quality of the construction of guide holes is the key to the success of the project. There are the following methods for the construction of rock layer guide holes:
 
1.1 fan drilling guidance method
 
This approach is to replace guide plates with three jaw gear cutting bit or a single cone bit, when to change the course of drilling, under a certain interval thrust, on either side of the preset direction within the scope of 30 °, 60 °, fan-shaped drilling, achieve the goal of changing direction. This method is only applicable to the softer rock strata, with high labor intensity and low efficiency.
 
1.2 mud motor with hole bottom
 
Mud motor driven by large displacement mud, mud motor and drill pipe axis Angle is 1.5 ° - 3 ° installation. When the drill pipe and mud motor work at the same time, the drill bit straight drilling; When the drill pipe does not rotate, only provides thrust and direction, mud motor rotation, to achieve the guiding function.
 
Construction method of horizontal rectifying drilling tool
 
Haichuan da construction engineering co., LTD., in cooperation with the trenchless research and development center of the exploration technology research institute of the ministry of land and resources, successfully conducted horizontal directional crossing construction with a 25T small drilling rig in the granite strata through which the communication pipeline of 8X110mm, fuyong street, baoan district, shenzhen passed.
 
2.1 project overview
 
This project is located at chuigang west road, fuyong street office, baoan district, shenzhen, spanning zhengfeng north road with a width of about 40 meters and a crossing length of about 90 meters. 8 x 110 mm Φ communication pipe laying. There are a variety of municipal pipelines, power and communication pipelines on both sides of the road. There is a flood discharge box culvert 8 meters wide and 6 meters deep in the road. Over the past three years, more than ten construction teams have entered the construction of this section of road, all because they could not drill into the granite field.
 
2.2 formation
 
See attached figure 1 for the geological section passing through the construction section. The intersection is made up of hills with granite strata one meter below the surface. The depth is unknown and the length is about 70 meters. It continues over the highway, and then the clay and subclay layers formed by the complete weathering of granite are formed.
 
2.3 construction machines and tools
 
Learn the lessons of previous construction failure, before entering the drilling rig, the matching selection of equipment, conducted a careful study. A typhoon pressure of 1.4mpa is added based on 25T drilling rig. Air compressor of 17m3. Install the lubrication device in the proper place of the delivery pipe and connect it into the high-pressure pipe of the mud pump of the drilling machine through three connections. Adopt the single cylinder water delivery of drilling machine original mud pump, which can not only ensure the lubrication of the impactor in the hole, but also meet the requirements of cooling and dust removal of the probe rod in the hole.
 
Aiming at the characteristics of rock, a high pressure subsurface drilling hammer was selected. Rock is broken by percussion rotary drilling. Under the impact load, rock volume fracture occurs. The impact drill bit exerts an impact force perpendicular to the rock surface. Under this force, the drill bit presses in and breaks the rock. With each impact, the drill bit rotates at an Angle to form a circular drilling hole. Impact crushing is an effective way to break rocks with medium or hard rock under a certain pre-pressure. The required axial pressure in construction is small and the rotary speed of drill pipe is low. At present, drilling RIGS with more than 20 tons on the market can meet the drilling needs.
 
The key to the success of construction in the lithosphere is not the problem of drilling but how to control the direction in the lithosphere. After repeated studies, it is decided to use the horizontal rectifying drilling tool developed by the trenchless technology development center of the institute of exploration technology to complete the construction of the guide hole. Horizontal rectifying drill tool is composed of directional control measurement system - pneumatic submersible hammer - inclined rock bit.
 
The shock absorber is designed to ensure the normal operation of the probe rod in the working environment of the submersible hammer. The rock-breaking bit is a ball-tooth bit with an additional bevel. Under the condition of percussion rotary drilling, the drill bit keeps straight direction of drilling, and the guide hole trajectory shows as straight hole drilling; When directional drilling is carried out, swing drilling in the fan in the predetermined direction is carried out.
 
2.4 construction process
 
After the equipment is in place, connect the drill tool with drill bit, drill hammer, rock guide system and drill pipe. The drilling begins at the location of a hole previously constructed. The old drilling hole was drilled by rotary drilling with hard alloy, and the alloy bit was badly worn. Although it was repaired several times, only 70cm was drilled after two working days. The same drill used the original drill, using percussion rotary drilling, only about 7 minutes to drill a drill pipe. The submersible hammer stopped working when the second pipe was drilled. After checking and confirming that there is no abnormality in the ground equipment, the drill tool is pulled out of the hole and the impactor is opened. It is found that rock debris enters the inner cylinder of the submersible hammer and the piston of the hammer is stuck. After field analysis, due to the high water level and large water volume, once the air supply is stopped, the flushing fluid and drilling cuttings will be sucked back into the drill string. In order to ensure the normal operation of the submersible hole hammer, the mud in the working pit shall be drained clean, and the hole shall be re-opened from the top of the original borehole. The pneumatic submersible hole hammer shall work normally and troubleshooting shall be carried out.
 
The drilling machine carried out linear drilling and arc-shaped directional drilling. The drill speed is 10~40r/min, and the feed pressure is controlled around 2~5T. When drilling in the direction of control, fan type swinging drilling is used. The average drilling speed is 7min/m. When drilling 24 drill pipes, the drilling speed is suddenly accelerated, the rotary resistance is decreased, and the feed force is decreased. The formation is analyzed and the rock-oriented drill pipe is put forward. The ordinary earth-oriented drill pipe is replaced and the guide hole is drilled for more than 20 meters.
 
The oriented hole construction, rock drilling length of about 70 m, the deepest 7.9 m, with 15 ° hole construction in rock, namely to bore through rock, Angle is adjusted to 5 °.
 
Construction characteristics of rock layer in percussion rotary drilling
 
Pneumatic drilling with submersible hammer is a kind of percussion rotary air drilling method, which has been widely used in the exploration and mining of solid mineral deposits, well drilling and cast-in-place pile construction for many years. This application in the construction of horizontal directional drilling guide hole has some characteristics:
 
(1) the construction of guide hole adopts the method of percussion rotary drilling. In medium-hard granite, directional control is simple and practical. Each drill pipe (3 m) can be adjusted to 1 ° around;
 
(2) quick slag discharge and clean drilling. For each drill pipe drilled, lift the drill pipe repeatedly and clear the hole with high air flow;
 
(3) compared with rotary drilling, percussion rotary drilling does not require a high speed, generally in the range of 10~60r/min, the normal drilling torque required is small, the drilling pressure required is only about 1/3 of rotary drilling;
 
(4) water and dust should be added when the hole is opened. When drilling below the underground water level, the water inside the hole should be cleaned timely;
 
(5) high drilling efficiency. According to statistics, the pure drilling efficiency in construction is between 10m/h and 20m/h.
 
The practice has proved that the rock stratum guide hole construction can be completely realized by adopting the percussion rotary drilling and the swing direction change, which opens up a new way for the non-excavation construction of difficult strata to be drilled.

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