In the construction of Guangzhou project, we adopted high-density polyethylene hollow wall winding pipe, the maximum diameter of the pipe is DN 1800mm, and the pipe is a flexible joint, which has the characteristics of light weight, no need for concrete foundation of the pipe and shortened construction period. In the construction, according to the characteristics of environmental conditions such as large-diameter pipeline interface stress, easy leakage, high thermal expansion coefficient of HDPE material, easy deformation of new pipe materials such as nozzle, deep trench excavation and abundant groundwater, the construction scheme of internal and external heat shrinkable tape sealing, external fused tape connection sealing, pipeline ground splicing and integral hoisting was adopted, which reduced the influence of groundwater on the interface technology and ensured the construction progress and installation quality.
1. Project overview
Guangzhou installed the drainage pipeline 19780m, and adopted the new domestic HDPE butt drainage pipeline.
The annual rainfall in this area is 1800- 1900mm, with deep trench excavation and abundant groundwater. Drainage measures were taken in the whole construction process.
2.HDPE hollow wall winding pipe
2. 1 HDPE pipeline structure:
High density polyethylene, also known as low pressure polyethylene, is polymerized from ethylene in the presence of catalyst. It can be formed by injection, extrusion, blow molding and other methods. It has good heat resistance and cold resistance, superior mechanical properties to low density polyethylene, good wear resistance and chemical properties, corrosion resistance to various acids, alkalis and salts, and low water absorption and water vapor permeability. The main material used in this construction, the high-density polyethylene drainage pipe, is a structural wall pipe with HDPE as the main raw material and the same or different materials as the auxiliary supporting structure. It is made by hot winding molding process and has a butt nozzle with a maximum diameter of1800 mm.
Due to the large pipeline diameter and complicated geological conditions on site, the supplier has no installation experience to guide.
2.2 Physical test performance of high-density polyethylene pipe is as follows:
Experimental method of serial number item index
1 ring stiffness KN/m2 ≥8 GB/T9647
2 Plate test (40%) does not crack, does not crack, and the damaged two walls do not leave GB/T9647.
3 longitudinal dimension shrinkage% ≤ 3 GB/t667 1.2
4. The inner wall of the test tube is not broken when the drop hammer hits it, and the two walls are not separated GB/T 14 152.
5. The water pressure test will not break or leak GB/T6 1 1 1.
6. There is no leakage in the sealing test of the connection part GB/T6 1 1 1.
Ring stiffness, also called ring bending stiffness, is a measure of pipeline's ability to resist ring deformation, which is determined by experimental method or calculation method, and the unit is N/m2. Generally, the measured value is taken when the diameter is deformed by 3%.
In plate test, continuous load is applied in radial direction. When the deformation of the inner diameter of the sample in the vertical direction is 40% of the original inner diameter, unload it immediately. During the test, the load should not be reduced and the sample should not be broken.
Longitudinal shrinkage rate, also called longitudinal shrinkage rate, is the longitudinal shrinkage rate of pipe samples after oven test at 1 10℃. The linear expansion coefficient of HDPE pipe is relatively large, so this item is taken as the test item of pipe.
The above three tests were carried out on the basis of testing the performance of this new type of drainage pipeline, and the drop weight test and water pressure test are routine inspection items of fluid transportation pipeline.
3. Determination of construction technology
Because the model of HDPE pipeline used in the project is much lower, DN 1600mm pipeline installed in the early stage of the project is taken as the discussion object.
3. Characteristic Analysis of1HDPE Pipe
(1) When manufacturing the pipeline, ensure that the inner diameter of the pipeline, the flat pipe and the butt joint nozzle are fused and connected by electric heating;
② The weight is light, and the hollow wall HDPE pipe is about1/8 of the weight of cement pipe with the same length;
(3) Flexible pipes and interfaces do not need to make concrete foundation.
3.2 Selected installation process
Select the connection technology to ensure the connection strength and tightness of the pipeline, and determine the construction scheme of integral lifting of the ground connection of the pipeline. Connect the pipeline at the edge of the groove, and lift it in place as a whole, so as to reduce the bad construction conditions in the groove and the adverse influence of water and mud on the connection effect. The key point of quality control is the connection and treatment of nozzles.
3.3 Determine the construction process
Ensure that the construction is carried out according to the following procedures: measuring and setting out; Trench excavation; Manufacture of foundation sand cushion; Inspection well production; Pipeline splicing; Pipeline installation; The pipeline is connected with the wellhead; Tube waist pressing; Closed water test; backfill
4. Pipeline installation and construction technology
4. 1 trench excavation
The deepest excavation of the pipe trench is 4m, with poor soil quality and high groundwater level. The pipeline foundation should be tamped and leveled according to the layered combined trench excavation, and a 200mm sand layer should be laid to increase the contact area between the bottom of the pipeline and the foundation, thus protecting the pipeline.
4.2 Pipeline ground splicing
4.2. 1 interface connection mode
HDPE hollow wall winding pipe, the inside and outside of the pipe joint are bonded and sealed with heat shrinkable tape, and the outside is connected with fused fixing tape to ensure the tightness and sufficient connection strength of the joint.
Grounding splicing
Place the pipeline along the trench on the flat side of the trench and cut the corresponding length according to the distance between two wells. The pipe can be cut with a woodworking saw, and the end of the pipe can be planed with a woodworking plane. Dig a 300mm deep operation pit under the pipe joint, which is 200mm wider than the electrothermal melting bandwidth.
Heat shrinkable tape connection
Horizontal and aligned pipes. The pipelines shall be horizontally aligned, the relative deviation of the center lines of the two pipelines shall be no more than 7mm, and the butt joint clearance shall be no more than10 mm. ..
① Prepare steam heating devices: liquefied steam tank, rubber hose and spray gun.
(2) The pipe joint shall be wiped clean, and there shall be no mud, sand and dust within 800mm of the pipe end.
(3) uniformly heating the pipeline connection part to 80-90 DEG C by using a gas spray gun.
(4) Heat and melt the adhesive surface of the fixing tape and stick it on the upper part of the pipeline, that is, the butt joint should be above the middle part of the pipeline.
⑤ Heat the rubber surface of the shrink belt slightly to remove moisture and soften the rubber. The triangular tip of the contraction zone is bonded and compacted at 2/3 positions. It is required to add a fixing belt from the bottom of the pipeline along the middle circumference, and at the same time heat the rubber surface to strengthen the adhesion of rubber. One end of the shrink band is added into a triangle to increase the contact area between the shrink band and the pipeline.
⑥ When it is heated to the other tip of the tip fixing piece, it should be sealed with sealant tape to reinforce the end of the contraction tape.
⑦ After heating, a small amount of glue should overflow from the edge of the fixing belt. If this effect cannot be achieved, heating should be continued.
The operation method of the inner wall heat shrinkable belt is the same as the above steps.
4.2.4 Fused fixing belt connection
① 50kW generator is used as power supply, and the power supply cable is 10 mm2(dn 1200 and above is12mm).
(2) Wipe the pipe joint clean, and there shall be no dirt, sand and moisture within 500mm of the pipe end. If there are water drops and moisture, wipe it with cotton cloth first, and then dry it with a gas spray gun.
(3) Surround the fused belt around the pipeline connection position, including one end of the connecting line, and the center line of the belt is perpendicular to the center line of the pipeline, and shall not deviate from the interface 10 mm. ..
④ Fix the fused belt on the pipeline with nylon buckle (used above DN900) or steel buckle. At the same time, insert the PE rod into the head near the inner end of the electrofusion belt, insert the pipe diameter above DN450 into 90- 100mm, and insert the pipe diameter below DN400 into 50mm, and try to narrow the gap at this position when fastening. The purpose of inserting PE rod is to ensure that the end of electrothermal shrinkage belt is sealed tightly and plays a role in filling.
⑤ Set the heating time according to the ambient temperature.
⑥ Select gear and current.
Diameter gear current range welding machine
200 ~ 400 1 (small) 12 ~ 16
PE-2004X
450 ~ 600 1 (small) 16 ~ 25
600 ~ 1000 2 (large) 20~35
1 100~2000 ; 26~40 PE-2002
⑦ The hot-melt welding machine is electrified and heated.
⑧ After welding, cut off the power supply, remove the output clamp, check the clearance between the belt periphery and the pipe, and then clamp 1/4 to 1/2 turns.
Pet-name ruby cooling above 20℃ 15 ~ 20 minutes, cooling below 20℃ 10 ~ 15 minutes, and then loosen the buckle.
Attending about 10 ~ 15 hours after the completion of welding, the welding position is completely cooled and solidified, and the movable pipeline will affect the welding quality during the welding process or before it is completely cooled.
4.3 pipeline hoisting in place
DN1400 mm ~ DN1800 mm pipeline, connect four 6m-long pipelines at a time, and hoist them in place with two cranes. When hoisting, nylon slings should be used to reinforce the lifting points to prevent the pipeline from breaking. The weight of the 24m DN 1800mmHDPE pipeline is about 2.5t, and the lifting capacity and boom of the crane can meet the hoisting requirements.
4.4 Pipeline connection in groove
The pipe connection in the trench is the same as the above-mentioned ground connection, but the difference is that attention should be paid to the timely removal of groundwater, and mud and water are strictly prohibited from entering the interface. The water level at the bottom of the pipeline should be kept below 300mm. After the tank bottom is leveled, lay 200mm thick medium sand or coarse sand, and tamp it with vibration rammer. Above 800mm at the top of the pipe, it shall be rolled by layers with a roller.
4.5 Connection between pipeline and well
In every process of pipeline construction, inspection wells should be prepared first, and the installation position of pipelines should be reserved. After the pipeline is in place, find the center line and elevation, wrap the pipeline 100mm wide with semi-dry asbestos cement and oil hemp, tamp it with a chisel hammer, and smooth the remaining pipelines with C30 cement mortar.
4.6 Trench backfill
The linear expansion coefficient of HDPE is about 56× 10-6/℃, which is about five times that of steel. When the temperature difference is large, the connection parts that are not completely cooled and fixed are easy to be stressed due to thermal expansion and contraction, which affects the connection effect. After the pipeline installation, backfill and press the waist as soon as possible, spread grass curtains on the pipeline before and after the connection to avoid direct sunlight, water it during the day and reduce the change of pipeline length. Another function of pipe waist pressure is that the drainage pipeline is light and has poor anti-floating performance, so it is necessary to avoid floating the pipeline when the groundwater level rises too high.
The connection of the last interface of the pipeline section between inspection wells should be carried out in the morning or evening, and the appearance quality of the pipeline joint and the joint between the pipeline and the inspection well should be checked according to the construction requirements, and backfilled to 2/3 of the external diameter of the pipeline, and the backfilling should be carried out according to the design drawings.
5. Operation quality
Before the closed water test, the middle and lower parts of pipe joints must be backfilled and compacted in time. As a flexible pipeline, cantilever structure will cause huge radial deformation to the pipeline, which should be avoided in the experiment. The drainage system installed in this project has passed the closed water test, and the pipeline leakage is lower than the specification requirements. At present, the pipeline runs well.
6. Some experiences
In Guangzhou project, the performance of HDPE hollow wall drainage pipe was fully utilized, and the construction technology and flow were reasonably arranged, which overcame various unfavorable construction environments and factors:
No.: Description of pipeline performance, structure and application
For 1 flat pipe, electric welding is adopted to reduce the adverse effects of water, mud and sand on the connection effect.
2. Light integral hoisting speeds up the progress.
3 Flexible pipes and interfaces do not need to be made of concrete foundation. Only one interface is left in the pipe section between two inspection wells to be connected in the groove.
4 new technology: internal and external heat shrinkable tape, and electric fused tape to strengthen the seal.
HDPE pipe is a flexible pipe, which has no obvious difference from the requirements of rigid pipe construction for backfill soil. However, for rigid pipes, they are usually regarded as independent load-bearing structures and must bear all internal and external pressures in strength; Flexible pipe is a system bearing structure of "interaction between pipeline and fill", that is, between pipeline and fill. Due to the coordination of forces, the backfill soil of HDPE pipe and the pipe body form a load-bearing structure of the system, and the density of backfill soil in the chest cavity is greater than 85%, that is, the two-way pressure and force coordination between the pipe and the backfill soil make them combine into an efficient whole structure, and the density of backfill soil in the chest cavity is required to be greater than 85%. In the construction, considering the compactness of the cushion at the bottom of the pipe and the backfill in the pipe box, the backfill is required to be compacted to the specified compactness, that is, the construction is carried out according to the design or specification standards, which determines the bearing capacity of the "pipe-soil" system and the radial deformation rate of the pipeline, and can ensure the safe operation of the project, which is particularly important for the construction of large-diameter pipelines. For small-diameter pipelines, the construction is much easier, and the influence of backfill density on the pipeline is not considered. During the drainage of temporary passage in site construction, DN400mm pipeline 12m was used, without any foundation treatment and backfill soil was not compacted. When the buried depth is 400 mm, the heavy engineering vehicle can remain intact.
HDPE pipeline has not been imported from abroad since 1990s, and its structural forms and connection modes are various. What is mentioned in this paper is a pipeline with simple production process, low manufacturing cost and easy popularization. The service life of HDPE pipe is 50 years, which is more than twice that of cement pipe, greatly reducing the life cycle cost. Therefore, HDPE pipe will be widely used in all kinds of water transmission and drainage construction.
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