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Introduction to construction method of pipe jacking across highway

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This paper mainly introduces the simple method of pipe jacking construction in combination with many highway crossings in wuqi - yanlian oil pipeline project.
 
The main oil pipeline designed in wuqi - yanlian oil pipeline project starts from the first shibaiwan oil pipeline station and ends at the last yanlian oil pipeline station. The length of the pipeline is 272.49km. The whole line crossed the highway 28 times, crossing the length range of 10 ~ 40m. The design takes into account the principle that most highway traffic cannot be interrupted due to heavy traffic, and the principle that the road surface grade is higher and the road surface is not damaged as far as possible. The highway crossing is designed as pipe jacking crossing, and the protective sleeve is made of reinforced concrete. The inner diameter of the sleeve is 0.8~1 m, and the sleeve has a protective steel pipe ring.
 
Due to the fact that the length of all 28 highway crossings is within 40m, and the geology of all the crossings is loess soil, manual excavation and jacking of reinforced concrete sleeve on one side of the highway are all adopted in the construction. The specific construction method is detailed as follows:
 
1. Introduction to construction methods
 
1) highway pipe jacking crossing method: measure the alignment at the crossing point, select one side to level off a site to dig a working pit, and the other side to be the receiving pit. Install tracks, hydraulic equipment installation in place, lifting concrete pipe, using hydraulic push one thousand catties by casing, each into a certain trip, return DingGang, dig for outbound operators into the casing, and then add in the top iron or casing continue to jacking, circulating operation, until the casing across the roof to the receiving pit, then dismantle equipment, cleaning tube residual soil, undertake other construction.
 
2) pipe jacking through construction machinery and equipment: it mainly includes 1 hoisting machine, 2 sets of sling, 2 sets of track, 1 set of jack, 1 set of hydraulic equipment, 1 set of jacking iron, 1 set of pipe jacking, 6 mining lamps, earth-digging equipment (mainly referring to spade and truck) and 1 cubic meter of wood, etc.
 
3) flow chart of construction process: construction preparation -- survey lay-out -- excavation of foundation pit -- leveling and compaction -- pouring concrete cushion -- guiding line -- installing pipe guide -- hoisting pipe and installing pipe joints -- detection -- jacking -- detection control -- jacking -- advance and retreat -- adding iron jacking -- transporting soil within the pipe -- lifting of waste soil.
 
2. General requirements of construction technology
 
1) according to the control points on both sides of the highway submitted by the design institute. Set up two central axis control piles before and after the proposed pit, so that the front and rear piles can be seen through. And the proposed pipeline in a straight line, and then according to the Central Line control pile to determine the working pit and the receiving pit excavation boundary.
 
2) excavation of working pit and receiving pit: manual or mechanical excavation is adopted. After the foundation pit is dug, the soil at the bottom of the pit shall be leveled and rammed to ensure even soil quality. Four leveling control points shall be measured at the four corners of the working pit, and then concrete bedding shall be poured.
 
3) set up the center line pile of pipe jacking: to the theodolite on the center line control pile, measure the center line to the pit wall, and drive into the wooden pile as the center line pile of the jacking correction sleeve. In addition, two leveling points are temporarily set in the working pit to control the jacking of casing according to the designed elevation and slope.
 
4) guide rail and jack installation: the guide rail is a steel integral guide rail, installed on the concrete cushion, the two main rails of the guide rail must be straight, parallel, and of equal height, its longitudinal slope should be consistent with the pipeline longitudinal slope, the distance between the two guide rails should be between the center of the pipe and the central Angle of the two rails between 70-90. The jack shall be fixed on the bracket and symmetric with the vertical line at the center of the pipe. The vertex position shall be 1/4~1/5 of the pipe.
 
5) crane tube: for reinforced concrete casing pipe (tongue-and-groove), USES the assembly machine assembly, when lifting the ground about 10 cm, should check whether casing of the strapping and firm, mechanical braking performance are in good condition, confirmation of safe lifting, the tube when the pit is strictly prohibited standing person, when the casing is apart from the guide rail is less than 50 cm, operators can work into the pit, casing pending on the guide rail, technician, quality engineer, safety personnel should be testing center line and elevation, slope, and when all the work and correct before construction.
 
6) jacking: casing jacking includes excavation, jacking, measurement, deviation correction and other procedures. Jacking should be carried out slowly and gradually. The construction staff should always master the center line, slope and elevation of the guide rail. If there is any deviation, stop jacking immediately and continue jacking after correction. After casing into the soil, cutting soil top-down hierarchical excavation, lower part of tube 135 ° range limit of digging. The excess at the top of the pipe shall not be greater than 1.5cm, and the pipe shall not exceed 50cm in front of the casing. The earthwork excavated shall be transported out of the pipe in time. When jacking, the casing should be prevented from rotating. When jacking is stopped temporarily, the horn mouth of the casing head should be cut into the soil layer. Pipe jacking should be carried out continuously. If the casing is in front of obstacles or the rear support is seriously deformed and the jacking iron is distorted, the pipe position deviation is larger than the specified range and the correction is invalid, jacking shall be suspended and timely handled. After the casing jacking into the receiving pit, the lower part of the casing and pipe end shall be provided with pillows or poured with concrete. The length of both ends of the casing exposed in the working pit shall be greater than 50cm.
 
3. Technical and safety measures:
 
1) before the commencement of construction, firstly conduct comprehensive education for all the workers who participate in the construction, make a comprehensive technical disclosure for each shift group, so that the workers really understand the process flow and understand the operation procedures and methods of various machinery. Secondly, the construction equipment used for a comprehensive inspection, no fault can be used. Finally, to each shift group undertakes safe production confesses, implement safe responsibility to every worker, raise the consciousness of safe production of the worker, undertake strictly according to operating regulation, each place sets full-time safe officer 1 person, inspect every working procedure at any time in the construction.
 
2) this project is all constructed on both sides of the highway. During the construction, safety signs shall be set up within 50m from each side of the pipe jacking axis to draw a safety warning line.
 
3) excavate pipe jacking working pits on both sides of the highway, slope relief shall be carried out according to the soil condition, and support shall be provided when necessary, so that the working pits shall be safe enough. The pit is 6 m long, 5.5 m wide, depth to be decided according to the design line elevation, dug earth accumulation point must be outside of 3 m from the pit wall, and left shoulder to 3 m, set on the top of the control of thickness according to the design of the soil, but must be below is apart from the top of the road is not less than 1.2 m, is apart from the road below the groove surface not less than 1 m. A water retaining wall shall be provided outside the working pit to prevent rainwater from entering.
 
4) the specific requirements of the back wall at the rear support of the jack in the pit are as follows: (1) the back wall table and to be straight, flat, and perpendicular to the axis of the jacking pipe, in order to avoid eccentric compression. (2) in the back wall to take the corresponding support measures, such as close to the soil wall with the technique and pad, in order to bear the greater recoiling force, to avoid the back wall uneven or insufficient strength and tilt phenomenon. (3) back wall pad should have enough stiffness, when the jack reaction force, should be compressed deformation small, when the reaction force is cancelled, should be able to restore the base wood in place, in order to give full play to the effective stroke of the jack. (4) back wall pad to have enough strength, in the jacking can withstand the hydraulic jack most people reaction force and not destroy.
 
5) when hoisting casing, it is strictly prohibited to stay under the crane arm and within the radius of rotation, and to stand in the working pit.
 
6) the jacking force position of the jack shall be above the pipe bottom of the jacking pipe, the diameter of the jacking pipe shall be 1/4 ~ 1/5, plastic material cushion shall be used between the jacking iron and the end face of the jacking pipe, the center line of the longitudinal jacking iron must be parallel to the center line of the jacking pipe, and perpendicular to the transverse jacking iron. In the process of pipe jacking, personnel on both sides of the jacking iron shall not stay, but the center line and elevation of the pipe shall be checked at any time with theodolite and level, and any deviation shall be corrected at any time, and the deviation shall be corrected by excavation correction method or forced correction method. When jacking, if obstacles occur that cannot be jacked in, jacking should be stopped immediately and the reason can be found out before proceeding.
 
7) measurement and deviation correction: the measurement shall be timely and accurate to ensure that the pipe joints are located on the designed pipe axis. When the first pipe is located on the guide rail, timely test, meet the requirements for jacking. At the beginning, each pipe jacking of 30cm must be measured once. After entering the normal jacking operation, each pipe jacking of 100cm should be measured at least once. Each measurement shall be based on the position of the front end of the pipe. If the deviation is found and the deviation is less than 20mm, it shall be gradually corrected by increasing or decreasing the amount of soil excavated at different parts in the construction. If the deviation is too large, log or square wood top can be used on the pipe wall on one side of the pipe deviating from the center, and the other end is installed on the soil in front of the pipe with wood board. After the support is stable, it is conducive to the jacks to apply force to the pipe, so that the pipe can be corrected.
 
8) when manual excavation is carried out in the pipe, the construction principle of "dig first, then top, and then top" shall be adhered to. No excavation shall be carried out from the bottom to the top. Each tunneling shall be no more than 50mm. The outer wall of pipe jacking shall be close to the soil surface without any gaps. The earthwork in the pipe should be excavated and transported with it to ensure the air flow in the pipe. Earth-moving personnel in the pipe must be equipped with mining lamps and safety protective equipment.
 
9) the connection between casing and casing shall be strict. The length of outer steel casing shall be 200mm, and the outer diameter of steel casing and casing shall be the same. In the construction of reinforced concrete pipe roof, the interface of the concrete pipe is connected by flexible tongue-and-groove. When the pipe joint does not enter the soil layer, the outer side of the interface is padded with asphalt oil hemp. Leave a 20mm gap on the outside of the nozzle, and the hole of the pipe joint after jacking should be 10-15mm. The surface of reinforced concrete pipe joints shall be smooth, smooth, without trachoma and bubbles. At the end of pipe jacking, the inner clearance of pipe joint joint shall be sealed and filled with asbestos cement.
 
Technical characteristics of pipe jacking
 
Pipe jacking technology is a kind of construction method for laying pipelines. Pipe jacking construction method has the following advantages for laying pipelines:
 
(1) pipe jacking construction is a kind of pipe jacking and laying technology. Without digging the ground, it can cross roads, railways, canals and even under buildings. It is a safe and effective construction method for environmental protection.
 
(2) the pipe jacking construction does not excavate the ground, the upper soil layer of the pipeline is laid without disturbance, the pipe joint end of the pipeline is not easy to produce segment-difference deformation, and its pipe life is also greater than that of the pipe buried by excavation method.
 
(3) the performance of pipe jacking machinery is more and more suitable for all kinds of soil, the scope of pipe jacking construction is gradually expanding, and pipe jacking is especially suitable for the trenchless laying of small and medium-sized pipe diameter pipelines.
 
5. Main matters needing attention in pipe jacking construction
 
1) engineering geology and hydrogeological conditions: the soil layer changes frequently along the pipeline, so it is necessary to understand the change of the soil layer before pipe jacking construction: in addition, for the backfilled land segment, it needs to be strengthened in advance to prevent excessive subsidence of the surface after pipe jacking construction.
 
2) detection and protection: toxic gas pipe jacking construction formation usually by silt layer, decomposing plant and animal experience form of poisonous gas in underground aggregate, harm workers' health and life, so there are people in the case of pipe jacking operation, need to regularly monitor tube poisonous gas content, the ventilation device.
 
6 the conclusion
 
In the construction of the project, the pipeline crossing the road happens from time to time. It is a basic principle of engineering construction to adopt efficient and high-quality construction methods to reduce the cost of engineering construction. The construction practice shows that the pipe jacking method is feasible and effective in the construction of pipeline crossing the highway. On the one hand, it can effectively protect the environment; on the other hand, it does not interrupt the highway traffic and damage the road surface during the construction; and the construction time is less than that of digging the buried pipe of the highway, which can guarantee the construction period and save investment. We can foresee the continuous improvement of construction equipment with the development of pipe jacking construction technology. The pipeline laying technology in the future will be supported by pipe jacking technology, which is bound to be extended and applied in relevant industries. Therefore, it is necessary and imperative to increase the popularization of pipe jacking construction technology.

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