Application of pipe jacking technology in sewage treatment project?

Application of pipe jacking technology in sewage treatment project: pipe jacking construction technology has developed rapidly in China in recent years. Pipe jacking construction in municipal engineering can move the working face underground, thus avoiding the influence on ground traffic. As long as the route selection before construction is reasonable and the construction method is proper, the structures will not hinder the normal construction. This paper briefly expounds the pipe jacking construction technology and its application in sewage treatment, and prospects that the pipe jacking method will become more and more mature in the future and can become a common technology in municipal construction. I. Introduction With the improvement of people's awareness of environmental protection, the requirements for sewage treatment in cities are becoming more and more strict, and the sewage interception pipelines for off-site collection system projects of sewage treatment plants have increased greatly. Because the sewage interception pipeline is long and the geological and site conditions are complex, it is impossible to dig and bury the pipeline in the open ditch during construction, and the pipe jacking method can be used as an effective supplement. Our company used this method to construct underground sewage pipes in Daliang, Shunde District, which not only ensured the construction safety, but also did not affect the old houses in the urban area, and achieved the expected results. Second, the pipe jacking method is suitable for construction. When the diameter of sewage pipeline is large (above 600mm), open trench excavation and buried pipe construction cannot be adopted in the construction site, and there is no other building foundation along the pipeline, pipe jacking method can be considered for construction. Third, the principle of pipe jacking construction. The principle of pipe jacking construction is to set working wells and receiving wells along the pipeline according to the designed scheme. Set a solid back seat in the working well, lift the hydraulic jack and the steel pipe or concrete pipe to be jacked, and connect the lighting, mud pipe and oil pipe. Then use hydraulic jack to push in slowly, and form a mud sleeve around the pipe joint through grouting system. The pipeline slides in the mud jacket, and the direction of pipe jacking is measured by laser theodolite when pushing. Four. Pipe jacking 1 construction, working well, receiving well and inspection well construction. According to the geological conditions and site conditions, appropriate supporting methods shall be adopted for excavation, and then the concrete of the bottom plate and wallboard shall be prepared as soon as possible, and the strength of the concrete and soil of the backrest required for pipe jacking shall be checked to determine the thickness of the concrete and steel pad. This is the key to jacking the pipe joint smoothly. 2, hydraulic jack in place, rail installation. 3. Selection and installation of the pipe joint: The pipe joint must undergo a comprehensive inspection, and it is forbidden to use if it is found to have defects in appearance. Wear rubber water stop ring before lifting the pipeline. Hang the pipe joint on the track, place the annular jacking iron, and push it slowly to make the joint butt joint smoothly. If it is found to be damaged, overturned, out of the groove, etc. , you must exit the pipe joint for replacement, adjust the rubber ring and reinstall the butt joint. After the joint is aligned, continue to start the hydraulic jack to jack up the pipe joint. 4. Pipe joint jacking A. The process of jacking is as follows: B. The resistance of jacking is mainly composed of two parts: front resistance and friction around the pipeline. In order to reduce the positive resistance of jacking, the jacking head can be improved into a pointed head. With the increase of pipe jacking distance, the thrust rises rapidly. In order to avoid the damage of pipe joints beyond the compression limit, drag reduction outside the pipe wall is a necessary measure for the smooth completion of the project. During construction, thixotropic mud is injected around the pipe joint to change the dry friction between the pipe joint and the soil into wet friction, thus achieving the purpose of drag reduction. Thixotropic mud is prepared according to the ratio of bentonite: caustic soda: CMC: water = 0.3: 0.2: 0.0 1: 1, and can be used after standing for 24 hours. During construction, thixotropic mud is pressed in from the grouting holes of the nose and the first three pipes through the grouting system to form a mud sleeve with a thickness of about 10mm, so that the pipe jacking can slide in the mud sleeve and reduce friction. According to the pressure gauge and flowmeter, the grouting pressure is about 1. 1 ~ 1.2 times of the natural groundwater pressure. In the process of construction, it is necessary to maintain the performance of mud jacket by means of "grouting first, then jacking, jacking while grouting, stopping jacking and filling slurry frequently". C. The control head of the jacking line has a correction section, and the maximum correction angle range can reach up and down1.7 and up and down1.2. The control of jacking line mainly depends on the correct operation and foresight of equipment. In order to push the pipeline according to the elevation and direction required by the design, the vertical rotation of the tool pipe should be continuously measured during the pushing process, and the correction jack should be adjusted according to the measurement feedback results to change the direction of the nose, so as to control the pushing direction and ensure that the pipeline is pushed according to the design axis. Rectification runs through the whole process of jacking construction, and try to correct the deviation in the bud. The direction is measured with a 2 "laser theodolite, and the torsion is measured with a nose goniometer. After calibration, the laser theodolite is firmly fixed at the jack end, and then the reflective glass is installed at the first end of the pipeline, and the measurement results are directly output to the computer controlling the hydraulic jack, which is convenient to operate. Avoid tool pipe deviation when pipe jacking passes through the wall. In the early stage of wall penetration, due to less burial, the tool pipe is supported by only two points, one is the guide rail and the other is the shallow buried soil. The bearing capacity of soil bearing surface is low, which leads to the nose bearing sinking easily. Therefore, when the nose penetrates the wall, the lower part of the wall-penetrating pipe should be supported, and the tool pipe should be pushed quickly to shorten the exposure time of the soil in the wall-penetrating pipe and reduce the potential safety hazard. The deviation of the pipe jacking length within the range of 3-4m is the key to affect the deviation of the whole pipe section, especially when the pipe is out of the wall hole, because of the short length of the pipe section, the heavy weight of the nose, the soil around the hole is easily disturbed and other factors, downward deviation often occurs. At this time, the direction of pipe jacking should be controlled by comprehensively using the nose itself to correct deviation and adjust the center of jack resultant force. D. Mud cuttings transported by mud are discharged from the mud system along with the mud pipe, filtered in the mud pit, and transported out in time. E. the power supply in the tube and the power supply in the lighting tube are mainly used for excavation, rectification, excavation and jacking, and the power supply is 380V. Due to the humid environment in the pipe, safe low-voltage lighting must be used for lighting. Transform into 36V safe voltage lighting. F. Precautions for pipe jacking: pay attention to prevent ground subsidence or uplift: set settlement observation points at regular intervals along pipe jacking construction to monitor ground subsidence during pipe jacking construction. Too much or too little earth is taken from the excavation end face, which will cause ground subsidence or uplift. In order to avoid this adverse effect, the following measures can be taken: control the pressure during grouting and just balance the pressure of the soil above the mud jacket. Strictly control the sealing quality of pipeline joints to prevent leakage. In the position where the buried depth of some pipe joints is shallow and less than 1.5m from the ground, steel plates can be pressed locally along the pipeline, and sandbags can be stacked for loading, so as to prevent thixotropic mud from floating up when the pipe joints are jacked up, which will make the mud sleeve invalid. After the tool pipe is rectified, a gap is formed behind the blade foot, and the surrounding soil will collapse into the gap when the pipe is jacked in, causing the ground to sink. In order to avoid this situation, pipe jacking should be measured in time and corrected frequently to avoid large-angle deviation correction. 5. With the development of English-speaking society, people's awareness of environmental protection has been continuously strengthened, urban planning has become more and more strict, and the greater the urban sewage treatment capacity, the more sewage pipes need to be built. In the past, people were often difficult to dig or cross the river under the control of site conditions, and the laying of sewage pipes was restricted everywhere. With the maturity of pipe jacking method, the above problems can be solved easily, and the layout of sewage pipes can be more and more flexible, which can greatly meet people's requirements for sewage treatment. Pipe jacking construction will become a common technology in municipal engineering construction.

Hand-dug mechanical pipe jacking construction scheme (excerpt) Because there are many kinds of pipe jacking in this project, this scheme takes D2000mmF three-level reinforced concrete pipe with a large number of single items as an example to prepare the construction scheme, and we draw up the hand-dug mechanical pipe jacking construction.

3. 1 hand-dug neck pipe construction technology

3. 1. 1 jacking force calculation and back design

This project is to thicken the wallboard as the back wall of the jack.

L back structure and resistance calculation

As the supporting structure of the jack, the back should have enough strength and grace, and the compression deformation should be uniform.

So calculate the strength and stability. This project adopts a combined steel structure backrest, which is convenient for installation and should meet the following requirements: the height of the center of gravity of the jack should not be less than 1/3 of the height of the backrest.

Jacking force calculation

Theoretical calculation of thrust: (calculated in φ 2000mm)

F=F 1 f2

Where f refers to the total thrust.

F 1- head-on resistance F2- jacking resistance

F 1 =π/4×D2×P(d— pipe outer diameter 2.5m P— earth pressure control)

P=Ko×γ×Ho

Where ko- static earth pressure coefficient is generally 0.55.

Ho refers to the thickness from the ground to the center of the roadheader, with a maximum value of 6m.

γ —— wet weight of soil, taking 1.9t/m3.

p = 0.55× 1.9×7 = 7.3 1t/m2

f 1 = 3. 14/4×2.5×2×8 = 3 1.4t

F2=πD×f×L

Where, the average comprehensive frictional resistance (average mud content according to jacking distance) of F- 1 pipe outer surface is 0.8t/m2.

D —— The outer diameter of the pipe is 2.5m.

L-top distance, the maximum value is 100m.

F2 = 3. 14×2.5×0.8× 100 = 428t .

Therefore, the total thrust f = 31.4+428 = 459.4t. After comparing the total thrust, the maximum jacking thrust that the working well can bear and the axial allowable thrust of the pipeline, the minimum value is taken as the total thrust of the oil cylinder. The maximum allowable jacking force of the working well (2000mm pipe jacking) is 800t, the axial allowable thrust of the pipeline is 700t, and two (or four, depending on the actual situation on site) 300t(3000KN) oil cylinders are selected as the main jacking force cylinders. The jacking force of each cylinder is controlled below 250t, which can be controlled by the pressure of the oil pump. The total thrust of the jack is 500t t, so we can meet the requirements without adding additional jacking system.

L inverse calculation

The back is compressed by the jacking force, and the compression direction is consistent with the jacking force direction. When the jacking stops, the jacking force disappears and the compression deformation disappears. This elastic deformation is normal, and the back should not be damaged during pipe jacking, resulting in impermissible compression deformation.

The back is not allowed to be pressed unevenly up and down or left and right. Otherwise, the jack is located at the back of the remaining surface, resulting in jacking deviation. In order to ensure the jacking quality and construction conditions, it is necessary to calculate the strength and stiffness of the back during construction.

Calculation formula of force on rear backrest

Among them:

R- reaction force of total thrust (generally greater than the thrust of 1.2- 1.6)

A- coefficient (take 1.5-2.5), here take 2.

B- The width (m) of the rear seat wall here is 4m.

γ-bulk density of soil (kN /M3)

H—— the height of the rear seat wall (m), which is 4.5m here.

Kp- passive earth pressure coefficient

C- soil cohesion (kPa) is generally 10.

H—— the height (m) from the ground to the soil at the top of the back seat wall, which is 5m here.

According to the above formula, the jacketed circular working well can bear 159 1.5T jacking force > 500T actual jacking force. It can completely meet the requirements.

3.2. Selection of main equipment

Jack-up equipment mainly includes jack, high-pressure oil pump, jack-up iron, tool pipe and equipment transported out of the ground.

(1) jack

Jack is the main equipment for pipe jacking, and each working well in this project is planned to be equipped with four 300-ton hydraulic jacks.

The layout of jack working pit adopts four combinations, and all the acting points of jacking force and the reaction point of pipe wall should be on the same axis to prevent jacking force deviation caused by jacking time couple. According to the construction experience, when there is a gap between the upper pipe wall and the soil wall of the pipeline for earthwork excavation and mechanical transportation, the center of gravity of the jack should be at 1/4~ 1/5 of the vertical diameter of the pipeline.

(2) High pressure oil pump

The motor drives the oil pump to work. The hydraulic oil pump with rated nuclear power of 3 1.5Mpa is selected and enters the jacks through the distributor and control valve. The oil inlet pipe of each jack is connected in parallel to ensure the output and stroke of each jack piston are consistent.

(3) Jacking iron

Jacking iron is a device for transmitting and dispersing jacking force. It is required to withstand jacking pressure without deformation and be easy to move.

According to the different position of the top iron, it can be divided into three types: horizontal top iron, horizontal top iron and U-shaped top iron.

(4) Other equipment

A movable working platform is arranged on the working pit. The platform adopts No.30 I-beam, and is paved with 15× 15cm square timber. A sliding platform is installed at the wellhead of the working pit for pipe running and excavation. Set a lifting frame on the working platform and install an electric hoist, the lifting weight of which should be greater than the weight of the pipe.

3.3 Selection of Vertical Transportation Mode

The vertical transportation of working pit ground, earthwork, pipeline and pipe jacking equipment adopts simple gantry and hoist (electric hoist), and I-beam is set as the ground working platform. The lower pipe is lifted by truck crane.

3.4. Selection of jacking equipment

According to the calculation of jacking force and the actual situation, this project adopts piston double-acting hydraulic jack with working jacking force of 300 tons. Jack in a single row. When jacking, the focus position is between 1/2 and 1/3 of the total height of the pipeline. The jacking force is transmitted between the jack and the pipeline through the jacking iron. The top iron is welded with section steel to form the force transmission of various structures. According to the different placement position and force transfer function, the horizontal iron and vertical iron are combined together.

3.5, pipe digging and jacking before

3.5. 1, digging in front of the pipeline

Pipeline excavation is an important operation to control the direction and elevation of the top of pipeline interface and reduce deviation, and it is also the key to ensure the quality of the top and the installation of structures on the pipeline.

3.5.2, pipe

Before excavation, the pipeline shall be laid and the following work shall be completed:

First, check the pipeline

Before running the pipe, the pipe shall be visually inspected, mainly for damage and longitudinal cracks; The end face should be straight; There are no pits and bubbles in the pipe wall, and the pipe wall should be smooth. Only after passing the inspection can the pipe be hoisted to the guide rail of the working pit by lifting equipment.

B, check the lifting equipment

Lifting equipment must be inspected and tested to ensure safety and reliability before it can be lowered. It is forbidden to stand in the working pit when running the pipe. When the distance from the guide rail is less than 50㎝, the operator can work.

C, pipeline in place

In the first section, put the pipeline on the guide rail, measure the elevation of the center and bottom of the pipeline at both ends before and after installation, and jack it up only after it is qualified. As a tool pipe, the accuracy of pipe jacking direction and elevation is the key to ensure the quality of the whole pipe jacking. Therefore, this work must be taken seriously.

3.6, pipe length control before digging

Usually arrange a person to dig. In order to speed up the progress of the project, two people in each class take turns to excavate.

Earthwork in the pipe can be transported by battery car or manual hopper car.

Earthwork is transported vertically in the working pit by electric hoist.

Generally, the soil quality is good, and the excavation can exceed 30 ~ 50 ㎝. Under the railway track, it shall not exceed 10㎝ outside the pipe end and 30㎝ outside the track, and shall comply with the regulations of the management unit.

3.6. 1, Overexcavation control around the pipeline

At the top where soil settlement is not allowed (if there are important buildings or other pipelines on it), overbreak is not allowed around the pipeline.

In general, the pipe jacking section is allowed to be overbreak above 1.5㎝, and it is not allowed to be overbreak below 135, and the pipe wall must be consistent with the soil foundation surface.

3.7, jacking

The main jacking adopts two 300t/hydraulic jacks. At the beginning of jack-up, slowly, and then jack-up at normal speed after the contact parts are closed.

When the oil pressure suddenly rises, jack-up should be stopped, and the jack-up can be continued only after checking the reason. When returning the pick, the oil pressure should not be too high and the speed should not be too fast.

The excavated earthwork should be transported out in time and jacked in time, so that the jacking force is limited to a small range.

3.8 Installation tool expansion ring

In order to facilitate the guidance, an inner expansion ring should be installed at the interface of the first few sections of jacked pipes, and the expansion ring and the pipe wall should be fastened into a rigid body through a back wedge or an adjusting bolt. The expansion ring must be aligned with the interface gap. Firmly installed, check and adjust at any time during jacking.

3.9 Measurement and Calibration

I. Measurement

When jacking the first section pipe (tool pipe) and rectifying the deviation, the measuring interval shall not exceed 300㎜ to ensure the correct position of buried pipe; Notify the pipeline in writing to jacking normally after burying, and the measuring interval shall not exceed 1000㎜.

Center measurement: the jacking length is within 600㎜, which can be measured by hanging the ball and pulling the wire. It is required to increase the distance between the two vertical balls as much as possible, and measure the center deviation of the front end of the first pipe with a level. More than 600㎜ jacking is measured by theodolite.

Elevation measurement: according to the leveling points and elevations set in the working pits (two), measure the elevation of the inner bottom of the pipe at the front end of the first pipe with a level gauge and a special elevation ruler to master the direction of the first pipe. After measurement, it should be closed with another leveling point in the working pit.

Laser measurement: install the laser theodolite in the working pit and adjust it according to the designed slope and direction of the pipeline. At the same time, install signs in the pipeline. When the jacking pipeline is in line with the design position, the laser spot will hit the center of the signboard, indicating that there is no deviation in jacking quality, otherwise it should be corrected according to the deviation.

After total jacking, the center position and elevation shall be measured at the joints of each pipe joint. If there is a mistake, it is necessary to measure the height difference of the mistake.

B, correction (rectification)

The rectification of pipe jacking is carried out step by step. After the error is formed, the jacking pipe cannot be corrected in place immediately, but it should be corrected slowly to make the pipe gradually in place, and hard adjustment cannot be corrected violently to prevent the opposite result. Commonly used methods are as follows:

Overexcavation rectification method: when the deviation is 10 ~ 20mm, this method can be adopted, that is, appropriate overbreak is carried out on the opposite side of the deviation, but no overbreak is carried out, even a ridge is left on the deviation surface, which forms resistance, so that the pipeline is biased towards the overbreak surface with less resistance during jacking and gradually returns to the design position.

Jack correction method: the method is basically the same as that of the top wood correction method, except that the pipe is slowly displaced and corrected with a small jack on the top wood.

3. Auxiliary design of auxiliary pipeline in10 pipeline

The auxiliary pipes in the pipe are installed on the inner wall of the pipe and fixed on the pipe wall in an orderly manner with steel frames.

A, ventilation facilities:

Due to the long jacking distance and deep burial of the pipeline, the air in the pipeline is not fresh, and harmful gases will be produced in the soil, so it is necessary to set up a gas supply system. The ventilation facility is to use a diesel air compressor to input compressed air into the air filter, then enter the air storage tank, pass through the air pressure regulating valve, deliver the compressed air to the front end of the pipeline, and exhaust the air at the front end of the pipeline for air circulation.

B, power supply layout:

In the process of pipe jacking, the main power sources are power and lighting.

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