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Some problems about trenchless directional drilling through construction

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Trenchless laying underground pipeline directional drilling crossing technology refers to the use of drilling means not excavated in the earth's surface, underground pipeline construction technology. Energy, communications and trenchless technology in our country city municipal engineering construction, the application of more and more widely, especially in natural gas, oil, electricity, water, Pipe roof support in such aspects as level precipitation and get very good applications. Environmental protection and short construction period has been recognized by the market. Below small make up of the three major technical problems encountered in the process and we discuss them together.
 
Guidance of hard soil layer, sand layer and pebble layer
 
Navigation bit selection
 
Before choosing a guide bit, one must first understand the geological conditions of surrounding strata. Many construction units do not adopt geological drilling before laying pipes for small directional drilling. They can only accumulate some data in this area for reference for a long time. When understanding is the main soft stratum on the location, then USES the guide board face larger guide bit, to control the navigation direction as soon as possible, when know the construction period is mainly sand, pebbles and hard formation should use duck-billed, small surface area of guide bit and welding on a certain quantity of alloy plate, and welding blade Angle can't too long in order to protect the navigation of bit wear, make it through hard strata, sand and pebble bed.
 
Boot operation skills
 
When guide bit through sand and pebble layer and hard formation, want to change the direction of the trajectory, if geared to jacking, can produce pipe bending and guide bit outlet plug, etc., according to the work experience, and turn head back to the operating method should be adopted, for example to direction up, then the operator shall feed control of jacking force in pipe to be bent, control returned to the hands, with another hand to guide bit bearing between 11-1 direction, to guide bit turn around in this interval, make its slow drilling but the effect is very good, this method must pay attention to the preparation of the mud, special sand and pebble into a hole, The hole wall shall be protected by a large proportion of mud. The hole wall of hard soil layer has a small clearance with the outer diameter of the guide bit. The rock shall be discharged out of the hole in time to prevent the guide bit and drill pipe from being locked.
 
Problems in reaming
 
reducing
 
Soft soil reaming, prone to reducing phenomenon, on the surface: unloading drill pipe, mud hole through drill pipe flow back pressure, hole with reducing phenomenon, at this point, the reamer bit back to pull hard, mechanical load, operation is not carried drilling accident may be produced at the time, at this time of SiZuanShou operation should be adopted when light slow turning, instrument dial, peg operation according to the circumstance, be about to choose solid mud mud division, and protecting the hole pressure balance, keep pore forming.
 
Slumping hole
 
Sand clay layer, sand layer, loose backfill layer reaming easy to collapse hole, drilling, drilling, serious cracks may appear on the road surface subsidence. Solid - phase mud, heavy - gel solid - phase mud wall protection. Can effectively prevent collapse hole. If slumping hole stone accumulation place, only clear the stone may continue to enlarge hole, at this time of SiZuanShou operation method is: gently pull slowly turn, pay close attention to the instrument dial, stay reaming by slumping hole, drill bit, backward to expanding once or many times, until the hole is at normal torque, such as the back of the found a stone in the drill bit will work toward the tail pit to take out the stones can be used.
 
Mud leakage or non - grout
 
In loose backfill soil, underground water level is low, sandy clay, sand bed, the bottom layer of soft soil reaming, mud is not out of the orifice to return, but from the hole leakage, SiZuanShou at this time to properly control the amount of mud pump, mud division will modulation: increases the slurry concentration and viscosity, formed in the hole wall mud leakage resistance of skin, effectively prevent leakage of mud, when crossing the river, mud loss serious can be cement or fly ash are added into the mud to control the leakage.
 
In the process of reaming or towing pipe laying, the common mud seeps out from the hole to the ground. The reasons for mud seepage are as follows: firstly, the residual mud in the hole reaming and pipe laying blocks the drilling hole so much that the mud cannot return from the orifice, and the mud forms a high-pressure surface in the hole and seeps out from the ground; Second, the local layer is loose to leave the mud channel, the mud along its channel seepage ground.
 
In general, mud seepage from the ground has little impact on pipeline laying, but mud seepage should be controlled under certain circumstances. Such as: mud is not allowed to ooze from the houses of residents, not from the downtown seepage, not from fish, shrimp pond seepage, to prevent the leakage of mud measures is to increase the depth of drilling; The second is to change the structure of the drill bit, using vane type, chute type drill bit, as far as possible mud debris into mud; Third, the driller, mud is to control the mud concentration, viscosity, flow rate, increase the mud wall protection, suspension and chip removal ability, so as to form a complete drilling hole, channel mud unimpeded return from the orifice.
 
The above are common problems in complex strata. The key to this link is that the driller and the mud engineer should communicate in time and adopt reasonable operation methods and effective mud allocation to complete this process smoothly.
 
Problems in the drawing tube
 
Main problems in pipe drawing include:
 
1. Equipment failure reasons, delay in the best time to pull the pipe, so that the mud chip in the hole precipitate and cause pipe hugging.
 
2. In complex strata, there is no corresponding mud wall protection and chip removal causes for pipe deformation and pipe hugging.
 
3, laid pipe quality causes the pipe deformation broken pipe.
 
Preventive measures for pipe sticking, pipe holding, pipe deformation and pipe breaking
 
The fluidity and pressure balance of the mud in the hole
 
A. To prevent underpressure balance from causing insufficient internal support pressure and reducing diameter, and to prevent formation softening and reducing diameter caused by balanced water loss, mud debris cannot be discharged normally, and the pressure of mud in the hole should be controlled at A value that is relatively balanced with the ground stress in the depth of the hole. Objectively speaking, this is very difficult to achieve. However, through comprehensive analysis, reasonable design and strict construction operation, the degree of imbalance is minimized. The static pressure of mud is mainly controlled by adjusting the mud weight. Generally, it should be slightly less than the weight required by the balanced ground pressure, in order to prepare for the superposition of the circulating dynamic pressure. The slurry pit at the orifice is necessary to maintain the pressure balance, through which the slurry inside the hole can be maintained with a certain basic hydrostatic head.
 
B, use strong cement slurry system is the key to control easily slumping hole, reducing, first choose high quality mixing clay, exchangeable cation number, the more water molecules between easy to enter the cell, clay hydration expansion, good dispersibility, can attract more cations at the same time, so the "active", ability to accept processing, package by the hydration of the membrane, is built pulp quality drop water loss of clay, and also to add the right amount of water loss, such as Na - CMC, sodium methyl cellulose, hydrolysis polypropylene fine HPAN, LG vegetable gum, etc.
 
C. Improve the lubrication of mud, as an auxiliary measure to reduce the increase of friction resistance of pull pipe caused by pipe hugging, and improve the lubrication of mud is an important technology of trenchless pipe laying. When the pipe hugging stress is certain, the friction resistance between pipe and hole wall should be reduced. The main reason is to reduce the friction coefficient of the contact surface between them. Suitable amount of polypropylene amine can be added to the mud, which has the properties of lifting adhesion, reducing water loss and lubricating. Site site, also use laundry powder as lubricant and can decompose debris particles. In a word, a complete, clean and lubricated hole wall is the key to successful pipe drawing.
 
Mechanical operation and management:
 
Caused by pressure imbalance and filtration softening reducing, slumping hole degree is increasing with the increase of time, so the trenchless construction should be done in a quick, compact, continuous for the principle, try to steal a march on chip formation creep in, mud precipitation, mud water loss caused by slumping hole, reducing tube are increased before laying pipelines, the optimization design site operation procedures, completes the high efficiency of each process cohesion is very important, SiZuanShou operation is to control the pull and push speed; Avoid too fast piston effect, damage the hole wall. For this reason, before the construction should also do a good job of spare parts, maintenance preparation and other work, once in the use of equipment and other faults, should be repaired as soon as possible, select high-quality pipe, pay special attention to its steel, tensile strength.
 
In a word, all aspects of the problem should be considered before pulling the pipe, in order to pull the pipe quickly, compact, continuous completion of pipe laying construction. The author has many years of on-site construction experience, and always pay special attention to the following ten think, just for reference.
 
First, the performance of the equipment, the existing situation to think about;
 
Second, the hole is clean, complete, lubrication (see the hole torque table) to think about the situation;
 
Three is to think about the quality of pipe, welding situation;
 
Fourthly, whether it is reasonable to think about the combination of tube-pulling bit;
 
Five is to the pipe head structure, connection ability to think about the situation;
 
Six is the mud discharge, slurry cleaning equipment to think about the situation;
 
Seven is to the position of personnel to think about;
 
Eight is to municipal administration, supervision personnel whether to think about the scene;
 
Nine is to environmental protection departments, whether the surrounding masses to think about interference;
 
Ten is the possibility of card, embrace, break the pipe and other emergency measures to think about.

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