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Horizontal directional drilling construction scheme for trenchless crossing project(1)

May 16, 2019

Chapter 1 Basis of compilation of horizontal directional drilling

  1. Main basis for compiling construction plan

1) Determine the point location according to the scene investigation

2) Hydrological and geological exploration data of the construction area

3) Relevant technical standards, specifications and procedures (meeting the water supply requirements) : technical specification for horizontal directional drilling pipeline laying (CSTT)

4) Survey of the current situation of the construction site


Chapter 2 Project profile of horizontal directional drilling

  1. Basic project overview

The power pipeline of this project is laid with PE160 pipe diameter (3 holes).In order to ensure the smooth progress of the project, we suggest that the geological conditions of the construction of engineering geological exploration, to provide effective scientific basis, in order to complete the construction task on time with high quality, high standards.According to the site inspection, we have made the following construction plan:

1) According to the topography, hydrology, river course and surrounding geological conditions of the site and the radius of curvature of the crossing pipeline, in order to ensure the backhaul of the power pipeline, the power pipeline is stably buried at the bottom, and the design Angle is -25 and the unearthed Angle is +25.

2) The proposed directional crossing scheme will select the drilling rig placement site according to the specific location of the site to reach the optimal location as the excavation site.A mud storage pit is dug on each side of the excavation and excavation.


Chapter 3 Project characteristics of horizontal directional drilling

  1. The project construction area is complex, increasing the difficulty of management

During the construction, working pits should be built inside the site, and power pipelines should be crossed from underground. The planned length of pipeline drawstring is about 120 meters, and the drawstring distance is relatively long, which requires accurate engineering.Strengthen measurement and control during construction.

The construction requirements of this project are “precise, accurate and fast” :

1) The project management personnel are energetic, young and strong, and the construction personnel are of high quality.

2) High construction requirements, the pursuit of first-class quality.

3) In case of emergencies or non-conformance to the current situation, timely feedback, contact the design, supervision and construction units, and make reasonable response measures quickly.

  1. Traction construction

Adopt trenchless construction plan namely horizontal drilling machine drilling traction pipeline construction method.The project involves a wide range, how to ensure the quality of the project, to ensure the safety of construction is the key aspect of the project control.Horizontal direction drilling method, its main characteristic is, according to preliminary design good route of pipelines drive equipped with wedge drill pipe from the ground, the ground equipment to receive information from the transmitter in underground drill, according to the predetermined direction control bit around underground obstacles to the destination, and then remove bit change the appropriate size and special type of return, to allow in the back of drill pipe at the same time will be expanded to the required diameter drilling, and drilling pipes will need to shop at the same time return back at the entrance.During the whole work, the drilling fluid provided by the special mixing unit is continuously ejected from the drill bit’s orifice to lubricate the drill bit, drill pipe and reinforce the drill passage, so as to improve the work efficiency of the whole project.


Chapter 4 Deployment construction of horizontal directional drilling

Quality completion of the project is the requirement of the construction unit, but also our company’s pursuit.In order to achieve the above objectives, it is necessary to strengthen the strong organizational guarantee system. Our company decides to set up the trenchless crossing engineering project department according to the modern organizational form. Under the unified leadership of the project manager, a mechanized construction team will be set up and a full-time safety officer will be set up on the site.

  1. Construction preparation

1) Construction organization

After undertaking this project, our company has fully summarized the previous experience of our company in the similar construction, combined with the actual situation of this project, we will spare no efforts to organize the team meticulously, adopt feasible management methods and means, and complete the construction task with quality and quantity guaranteed on schedule.

2) Technical preparation

The project manager and project chief engineer shall be responsible for organizing the engineering and technical personnel, and the personnel of each functional department shall carefully read the construction drawing and the specifications, procedures and standards related to the project.Organize the preparation of construction organization design, construction organization design document approved by the examination and approval, immediately sent to the construction department, and organize the operation personnel to read, study, make the construction organization design as their own basis, truly guide the construction function.

  1. A) Selection of directional drilling equipment

According to the site topography and geological conditions, directional drilling through the construction plan, construction technical measures and other factors, comprehensive consideration:

The drilling equipment is constructed with gd380c-l horizontal directional drilling rig, which has a feed and drag force of 38 tons.The directional control system adopts the falcon wireless directional control instrument produced by DCI.Main machinery and equipment are shown in the following table:

List of machinery, equipment and main tools

  1. B) Construction site layout

If the directional drilling passes through the rock and soil, it needs an area of 20 square meters for construction and stacking, among which 20 square meters for drilling machine, mud mixing system, drilling materials and other stacking sites. The rest is used for temporary piling and abandoning of soil for future backfilling.A 0.5 m (width) by 1.2 m (depth) by 4 m (length) mud pit is dug in the pit to serve as a mud purification and treatment tank for the storage of mud and rainwater. A submersible pump is then used to timely discharge the slurry after treatment.The rig operation, materials and mixing system must be constructed with pipe frame to set up rainproof shed, and the operation area shall be enclosed by fencing.

  1. Construction method

1) Directional construction process

The main working procedures of the crossing project are: surveying and setting out, directional drilling and guiding hole construction, pipeline installation and welding, reexpanding and towing pipe and restoration of the original landform (party a shall be responsible for).

①Measurement pay-off

According to the coordinates of the entry point and unearthed point of the construction design drawing, the axis released by the total station instrument shall be 10 meters for each control point. The deviation Angle between left and right of the pipe spooler shall not exceed 20mm, and the error along the spooler shall not exceed 40mm.Meanwhile, the boundary line of the construction site and the excavation boundary line of the foundation groove at the entry point are released.

②Directional drilling

Drilling rig is installed in the grave, and unearthed point on the same axis, control error is less than 100 mm, drill the grave Angle for 25 °.The directional drilling machine is anchored with bolt.Put the main rig in place and connect the ground anchor box, mud system, drill pipe and power source for support, etc.Connect all kinds of hydraulic pipeline, mud pipeline and control cable.After all the equipment is assembled and carefully checked and confirmed, the equipment is put into trial operation: debug the drilling rig system, check whether all the dial indicators are normal, check whether all the operating handles are reset, adjust the direction control system, and store the measurement data in the computer;Debug mud system.

2) Guide hole construction

The construction of guide hole is the key of the whole project. The construction should be strictly according to the track design parameters and horizontal directional drilling pipeline laying engineering technical specifications.The selection of a 125mm guide bit, a 73mm reinforced drill pipe guide hole construction.

①The drilling tool combination of the drilling rig’s guide hole is: guide drill bit + direction controller + drill pipe, the transmitting rod inside the guide drill bit sends the signal to the ground direction controller, so as to grasp the direction and depth at any time.

②In the process of directional crossing construction, at any time according to the data provided by the monitor and the design of the rail change contrast, such as drilling rail change deviation, it is necessary to pull the drill pipe to drill again, or drilling correction in the opposite direction.Control data should be carefully handled during construction and drilling speed should be appropriately controlled.

③Directional drilling drilling curve should be carried out according to the crossing construction specifications and design curve requirements.The longitudinal deviation of the unearthed point along the design axis is no more than 1% of the crossing length and no more than 1m;The lateral deviation shall not be greater than 2% of the crossing length, and shall not be greater than 2m.

3) Reverse reaming

Guide hole, after the completion of the bit, chase installed back to the head are very back to enlarge, considering the through pipe length, cross the length (120 meters) long and complex formation, design finally back to enlarge Φ 400 mm in diameter.

4) Pull back the laying pipe

During drilling, pressure test is carried out by welding the pipe group that is towed back, welding the pull pipe lifting lug on the top of the pipe group welded, then connecting the pipe with the drill pipe in the hole through the joint and the reamer, and connecting the pipe back into the hole filled with mud.

5) Installation of backhaul pipeline

When welding the PE160mm rubber hose work pipe, the pipe should be arranged along the direction of crossing the axis and cannot form a certain Angle with the axis. After the bend of the work pipe, the friction between the rubber pipe and the ground and the groove wall will increase when the pipe is dragged, resulting in the pipeline cannot be dragged.

  1. After the completion of the hole reaming construction, the phi PE160mm working pipe which has passed the inspection and pressure test shall be dragged back into the hole.Carefully check whether the clay bag slide under the pipeline is padded before the backhaul to ensure that the backhaul pipeline is intact.

After the connection of the expanding bit is completed, send the mud to wash, check whether the mud nozzle is normal, and then carry out the backhaul after confirming that it is qualified. Use the backhaul power of the directional drilling machine to drag the drill pipe into the expanded drilling hole, and the backhaul construction should be carried out continuously.

Calculation of drag resistance: friction coefficient is 0.3~0.5.

The calculated drag resistance of pipeline in the process of backhaul: the minimum drag F group of a 300mm working pipe =2 tons, the maximum drag F=5 tons, less than the rig used in the construction of the backhaul force of 28 tons, so it can completely meet the requirements of the crossing work.

In the process of backhaul, slow backhaul should be carried out, and changes in backhaul force should be observed at the same time. If any abnormality is found, it should be stopped immediately, and then the next step can be carried out after finding out the cause.

6) The following measures shall be taken to prevent the corrosion layer from being damaged in the process of backhaul:

①During the pull back process, PE pipe end is welded on a steel plate, and then use the phi 250mm pull back expansion guide, put the nozzle back expansion center, ensure that the nozzle is located in the center of the hole.,

②Before the tube through repeated back expansion, and increase the speed of back expansion, without the detrital material in the hole, make the hole wall surface more smooth, reduce friction resistance, conducive to the work of the pipe back.

③The hole is filled with high quality drilling fluid, to achieve good lubrication, at the same time because the work pipe seal in the thick drilling fluid in suspension, which is beneficial to protect the PE anticorrosive layer.

7) Mud control

The mud mixing system of this drilling rig is adopted for mud mixing. Different mud is adopted for drilling in different strata.Mud meets sand stratum to be given priority to by splash soil mud in drilling, the most basic function of the mud is to maintain the stability of the hole wall, prevent the collapse of the empty wall, cool the drill bit, jet drilling and other functions, the mud is mainly composed of water, high-quality clay (bentonite), is a kind of harmless, meet the requirements of environmental protection mud material.

8) Mud treatment

Construction in accordance with national environmental requirements, do not use toxic and harmful and environmental pollution of raw materials construction.The mud discharged during construction can be discharged only after being treated with precipitation.

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    Wuhan Yichao Technology Equipment Co., Ltd. is a professional supplier of horizontal directional drilling rigs. We are XCMG authorized distributor and has nearly 10 years of trenchless pipeline experience.


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