PCCP (prestressed concrete cylinder pipe) hydrostatic test construction method without back wall design under mountain conditions

Abstract

The invention relates to the technical field of pipeline water pressure tests, in particular to a PCCP pipeline water pressure test method without back wall design under mountain conditions. The test construction method comprises the following steps that S1, a test pipe section is selected as a hydraulic test section, and one end of the hydraulic test section is connected with a PCCP pipe in a bell and spigot joint mode; s2, a plug of the test pipe section is calculated and designed according to a plug plate stress thickness calculation formula, and the other end of the hydrostatic test section is plugged with the plug; s3, taking the test pipe section and the soil body around the test pipe section after backfilling as a natural back wall, and checking whether the bearing capacity of the two soil bodies meets the requirements of the back wall or not; s4, mounting test equipment on the test pipe section to construct a test system; and S5, performing water injection, exhaust and boosting tests on the test pipe section, and judging whether the pipeline installation quality is qualified or not according to pressure drop or the water seepage amount. According to the construction method, the water pressure test is carried out in the mode that the rugged topography and the steel bent pipes form the natural back wall, back wall construction is not needed, the construction period is greatly shortened, and the construction cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of pipeline water pressure testing, and in particular to a method for testing a PCCP pipeline water pressure without a back wall design under mountain conditions. Background Art

[0002] Long-distance water pipeline projects are the main form of engineering to solve the contradiction between water supply and demand in water-scarce areas due to their significant advantages such as high water utilization rate, good water quality assurance, and small footprint. In the long-term development process, they have gradually shown the following characteristics: (1) The pipeline water transmission lines are getting longer and longer, and the requirements for engineering adjustment measures and auxiliary valve configuration are getting higher and higher; (2) The working pressure of the pipeline is getting higher and higher, and the pipe pressure has developed from the low pressure of 0.1MPa to 3.0Mpa or even higher; (3) The diameter of the pipeline is generally increasing. For long-distance high-pressure water pipelines, the water pressure test is the last quality assurance process before the project is completed and put into operation, and its technical requirements and construction difficulty are also increasing.

[0003] Water pressure testing has problems such as high cost, long construction period, and low one-time success rate. The main pain points are summarized as follows: First, due to the increase in pipeline pressure and diameter, the reaction force provided by the back wall system increases significantly, which puts higher requirements on the design and construction of the back wall; Second, existing water pressure tests mostly use cast-in-place concrete as the back wall, and the casting, maintenance and demolition of the back wall have a huge impact on the construction period and cost.

[0004] In addition, in the existing pipeline laying process, when the PCCP pipeline passes through the mountains, it is impossible to lay a straight pipe due to geological reasons, and a steel elbow is needed to cross the pipe. However, when conducting a pipeline water pressure test on the pipe crossing the steel elbow, it is not only difficult to build a back wall, but also lacks an effective pipeline water pressure test method. Therefore, it is urgent to solve this problem.

[0005] The above contents are only used to assist in understanding the technical solution of the present invention, and do not constitute an admission that the above contents are the closest prior art. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a PCCP pipeline water pressure test method without a back wall design under mountain conditions. The method uses the undulating terrain and steel curved pipes to form a natural back wall to perform water pressure testing. There is no need for back wall construction, which saves a lot of construction time and reduces construction costs.

[0007] To achieve the above object, the technical solution of the present invention is implemented as follows: a water pressure test method for a PCCP pipeline without a back wall design under mountainous conditions, the test method comprising the following steps:

[0008] S1. Select a test pipe section as the hydraulic test section, and connect one end of the hydraulic test section to the PCCP pipe socket;

[0009] S2. Calculate and design the plug of the test pipe section according to the calculation formula of the plugging plate stress thickness, and seal the other end of the water pressure test section with the plug;

[0010] S3. The test pipe section and the surrounding soil after backfilling serve as a natural back wall, and the allowable resistance formula of the back soil, the back soil force width formula and the back soil layer length formula are used to jointly verify whether the bearing capacity of the two soils meets the back wall requirements;

[0011] S4. After confirming that the bearing capacity of the soil at the two locations meets the back wall requirements, install the test equipment in the test pipe section to build a test system;

[0012] S5. Then, water injection, exhaust and pressure increase tests are carried out on the test pipe section, and the quality of the pipeline installation is judged by the pressure drop or water seepage.

[0013] Preferably, the test pipe section is formed by selecting an elbow whose vertical fluctuation exceeds 11.25° along with the terrain as the two ends of the test pipe section.

[0014] Preferably, the calculation formula for the thickness of the blocking plate in step S2 is:

[0015]

[0016] Where: δ is the load-bearing thickness, mm; P is the design pressure of the plug, MPa; D i is the nominal diameter, mm; σ is the allowable stress of the steel plate at the design temperature, MPa; Ф is the weld coefficient, which is 0.85.

[0017] Preferably, the allowable resistance formula of the back soil in step S3 is:

[0018]

[0019] Where: E P --Passive earth pressure per 1m width, kN / m; γ--gravity density of back soil, kN / m3; c--cohesion of back soil, kN / m2; H--height of back wall, which can be equivalent to the height difference of pipeline, m; h--height from the top of back wall to the ground, which can be equivalent to the height from the top of the highest pipe to the ground, m; Kp--passive earth pressure coefficient, K P =[tg(45°+θ / 2)]2 (θ is the internal friction angle of the back soil, which is 16°), and K is calculated. P =1.76.

[0020] Preferably, the formula for the back soil force width in step S3 is:

[0021] B≥2.0F P / E P

[0022] Where: B is the back soil force width, m; F P It is the force transmitted to the back by the pipe plug, which is equal to the total thrust F of the water pressure test, kN; 2.0 is the safety factor.

[0023] Preferably, the length of the back soil layer described in step S3 is:

[0024] L=(F / B) 1 / 2 +L R ,

[0025] Where: L is the length along the back force direction, m; L R For additional safety length, 0.5m.

[0026] The beneficial effects of the present invention are embodied in:

[0027] The construction method provided by the present invention innovatively proposes to conduct water pressure testing by fully utilizing the undulating terrain and the steel bends to form a natural back wall according to the characteristics of the PCCP pipeline passing through mountainous conditions. Compared with the traditional water pressure test with a back wall, the production and removal of the back wall can be avoided, the construction period required for the back wall production, the labor and material costs required can be shortened, the success rate of the test can be increased, the safety during the test can be improved, and at the same time, by reducing the use of back wall production materials such as concrete, it has a good environmental protection effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a process flow chart of the present invention;

[0029] Figure 2 A schematic diagram of the terrain and pipeline at A0+054 in the implementation of the present invention;

[0030] Figure 3 This is a schematic diagram of the terrain and pipeline at Y5+740 in the implementation of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] Example

[0033] like Figure 1As shown, through the construction method provided by the present invention, the first section of the Chemu River water diversion pipeline construction project (Phase III) in Anning City that has been implemented is taken as an example.

[0034] The implementation process is as follows:

[0035] Selection of test pipe section: Figure 2-3 As shown, the selection principle is to select the areas with greater terrain undulations as the two ends of the test pipe section, select A0+054 as the end and Y5+740 as the other end. This section is 5794m long and is used as the water pressure test section.

[0036] Perform test system calculations:

[0037] Plug design calculation:

[0038] The plug is a welded plug, which has a reserved water injection port / drainage port and exhaust port, and is equipped with a socket or plug. The plug is designed and calculated according to the following method.

[0039] The calculation formula of the thickness of the plugging plate is:

[0040]

[0041] Where: δ is the load-bearing thickness, mm; P is the design pressure of the plug, 1.3 MPa; D i is the nominal diameter, 1400mm; σ is the allowable stress of the steel plate at the design temperature, which is 133MPa; Ф is the weld coefficient, which is 0.85.

[0042] The calculated value is δ=8.1mm. To ensure the safety of the pressure test, the thickness of the plug used in this project is 12mm.

[0043] Natural back wall system verification

[0044] The method provided by the present invention is calculated by taking a pipe section of the water diversion pipeline construction project (Phase III) of Chemuhe Reservoir in Anning City as an example. The pipe material of the pipe section is PCCP pipe, the pipe diameter D=1400mm, the pipeline working pressure P=1.0Mpa, and the test pressure P S =P+0.3Mpa=1.3Mpa, total thrust of water pressure test (force acting on the back wall) F=P S πD 2 / 4=2000kN.

[0045] A0+054 to A0+094 is a steel pipe section, which is socket-connected to the PCCP pipe at A0+094. Therefore, the steel pipe section from A0+054 to A0+094 and the surrounding soil after backfill can be regarded as a natural back wall. Similarly, the steel pipe section from Y5+667 to Y5+740 and the surrounding soil after backfill can be regarded as a natural back wall. The bearing capacity of the soil at both locations needs to be verified.

[0046] Allowable resistance of back soil: When the force transmitted to the back by the pipe plug coincides with the combined force point of the back passive earth pressure, the allowable resistance of the back soil can be calculated as follows:

[0047]

[0048] Where: E P --Passive earth pressure per 1m width, kN / m; γ--gravity density of back soil, take 20.0kN / m3; c--cohesion of back soil, take 30kN / m2; H--height of back wall, which can be equivalent to the height difference of pipeline, take 5.5m at A0+054 and 14.3m at Y5+740; h--height from the top of back wall to the ground, which can be equivalent to the height from the top of the highest pipe to the ground, take 0.6m at A0+054 and 2m at Y5+740; Kp--passive earth pressure coefficient, K P =[tg(45°+θ / 2)]2 (θ is the internal friction angle of the back soil, which is 16°), and K is calculated. P =1.76.

[0049] Calculate A0+054 to get E P =1086.35kN / m, E at Y5+740 P =5744kN / m.

[0050] The calculation formula for the back soil force width is:

[0051] B≥2.0F P / E P

[0052] Where: B is the back soil force width, m; F P It is the force transmitted to the back by the pipe plug, which is equal to the total thrust F of the water pressure test, kN; 2.0 is the safety factor.

[0053] Calculation shows that B≥3.7m at A0+054 and B≥0.7m at Y5+740. Obviously, the width of the back soil at both locations meets the requirements.

[0054] The calculation formula of the back soil layer length is:

[0055] L=(F / B) 1 / 2 +L R ,

[0056] Where: L is the length along the back force direction, m; L R As an additional safety length, 0.5m is taken. The calculation shows that L = 23.7m at A0+054 and L = 54m at Y5+740. Obviously, the length meets the requirements.

[0057] Under mountainous terrain conditions, the working conditions that can pass the above-mentioned water pressure test for the verification of the natural back wall system are very common. Therefore, this method is universal. If this method is adopted, the back wall system that consumes a lot of manpower and material resources to make during conventional water pressure tests can be avoided. The artificially made back wall system is also an unstable factor and weak relief in the entire water pressure test process. The reason for the failure of a large number of water pressure tests is that the back wall system is not strong enough, resulting in the fall of the plug and the inability to stabilize the pressure. The use of this method can perfectly avoid this risk and solve the pain point of the artificial back wall system being difficult to construct firmly, thereby greatly improving the success rate of the water pressure test.

[0058] Test system installation

[0059] Instrument and valve installation: set a DN25 exhaust hole at the top of the upstream plug, install an exhaust tee, install a DN15 pressure gauge on the side, and set a DN80 water injection hole. Set a ball valve on each pipeline and install a small ball valve in front of the pressure gauge.

[0060] The downstream plug vent and pressure gauge are set the same as the upstream. A DN80 drain hole (also used as a water injection hole) is set at the bottom of the downstream pipeline, a tee is installed, and a DN40 pressure hole is set on the side to connect the electric test pump. A ball valve is installed on each pipeline.

[0061] Selection and installation of pressurizing equipment and pressure gauge: The pressure gauge consists of a main gauge and a check gauge, which are installed at both ends of the test pipe section and connected with a pressure gauge buffer tube. Combined with the test pressure of the pressure test section, the pressure gauge range is 0-2.5Mpa, and the accuracy is 0.25. For easy reading, the nominal diameter of the case is not less than 150mm, and the pressure gauge is calibrated before use. When connecting the pressure gauge, exhaust the air in the branch pipe to prevent the pressure gauge pointer from frequently fluctuating and damaging the pressure gauge during pressure increase. According to the pressure of the pressure test section, the pressure equipment should select a D12-25X10 horizontal multi-stage centrifugal pump with a head of not less than 200m.

[0062] Test process

[0063] Water injection: Water injection is divided into two stages. The first is non-pressure water injection. Two water injection pumps are used as water injection equipment to inject water from the reserved water injection holes at both ends. The water injection speed should be slowed down as much as possible so that all the air in the pipeline can be discharged to prevent air hammer or water hammer effect in the pipe. When the downstream water injection port cannot inject water, close the low point water injection port until the upstream water injection port cannot inject water without pressure. Then there is pressurized water injection. A pressure pump is installed to perform step-by-step pressure injection. The water in the pipeline is filled by pressurizing, adding water, and exhausting air at the same time. The pressure should not be higher than the working pressure when the water is filled.

[0064] Exhaust: Open the upstream and downstream exhaust valves during the water injection process, and close the exhaust valves after the pressurized water injection is completed.

[0065] Pipeline immersion: After the test pipe section is filled with water, it should be immersed for 72 hours in accordance with the specifications. After immersion, compensate for the water loss in the pipe section, check whether there are any leaks at the connections of each equipment and the pipe section to be tested. The test should be carried out after all inspections are clear of hidden dangers.

[0066] Gradual pressure testing: After all preparatory work and other matters are normal, the pressure is increased. An electric pressure test pump is used for pressure increasing. The pressure should be increased slowly and steadily, and it is generally increased to the test pressure in 3-5 times.

[0067] Pre-test: first slowly increase the pressure to 1.9Mpa of the test pressure and stabilize it for 30 minutes. If there is a pressure drop during this period, water can be injected to supplement the pressure, but it must not be higher than the test pressure; check whether there is any leakage or damage at the pipeline joints and accessories; if there is any leakage or damage, stop the pressure test in time, find out the cause and take corresponding measures before retesting the pressure.

[0068] Main test: Stop water injection and pressure replenishment, and stabilize for 15 minutes; when the pressure drop does not exceed 0.03MPa after 15 minutes, reduce the test pressure to the working pressure of 1.0Mpa and maintain constant pressure for 30 minutes.

[0069] When the pipeline is pressurized, the gas in the pipeline should be discharged. During the pressure-raising process, if the needle of the spring pressure gauge is found to be swinging and unstable, and the pressure is rising slowly, the air should be re-aired before increasing the pressure again. The pressure should be increased in stages, and the back, piers, pipe body and interfaces should be checked for abnormalities after each stage before continuing to increase the pressure. During the water pressure test, it is strictly forbidden to stand on the back support and both ends of the pipeline. During the water pressure test, it is strictly forbidden to repair defects. In case of defects, they should be marked and repaired after the pressure is released.

[0070] Test result determination: According to the Code for Construction and Acceptance of Water Supply and Drainage Pipeline Engineering (GB 50268-2008), one or both of the allowable pressure drop value and the allowable water seepage value can be selected as the final basis for determining whether the test is qualified.

[0071] The pressure drop value and water seepage are jointly determined: when the pressure reaches the test pressure, the pressure is stabilized for 15 minutes. If there is no pressure drop after 15 minutes, the pressure value is reduced to the design working pressure and maintained at a constant pressure for 30 minutes. The pressure value rise and fall and the appearance of the test pipe section are inspected, such as:

[0072] (1) The PCCP pipeline is considered qualified if the pressure drop is less than 0.03 MPa and there is no leakage.

[0073] (2) The spiral welded steel pipe is judged to be qualified if there is no pressure drop and no water seepage.

[0074] Determination of allowable water seepage: When the pressure pipeline uses the allowable water seepage as the final qualification determination basis,

[0075] (1) The measured water seepage of PCCP pipeline should be less than or equal to:

[0076] (2) The measured water seepage of spiral welded steel pipe should be less than or equal to: 0.05 1400≈1.871 (L / min·km)

[0077] Gradual pressure relief and drainage: After the test is completed, the pipeline is slowly depressurized through the drain port, and the pressure relief speed is controlled to be no more than 0.1MPa / min. After the pressure relief is completed, the test water is discharged into the designated drainage area using a water pump. During the drainage process, the exhaust valve on the test pressure pipeline should be opened to release water and reduce pressure to prevent the pipeline from being vacuumed.

[0078] The cost, construction period and success rate of the method provided by the present invention are compared with those of the traditional back wall system, as shown in the following table:

[0079] Comparison table of cost, construction period and success rate with traditional back wall system

[0080]

[0081] It can be seen from the above table that the method provided by the present invention can not only save construction time, but also reduce test costs and improve the success rate of the test, and has a strong prospect for application and promotion.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. The PCCP pipeline water pressure test method without back wall design under mountainous conditions is characterized by: The test method comprises the following steps: S1. Select a test pipe section as the hydraulic test section, and connect one end of the hydraulic test section to the PCCP pipe socket; S2. Calculate and design the plug of the test pipe section according to the calculation formula of the plugging plate stress thickness, and seal the other end of the water pressure test section with the plug; S3. The test pipe section and the surrounding soil after backfilling serve as a natural back wall, and the allowable resistance formula of the back soil, the back soil force width formula and the back soil layer length formula are used to jointly verify whether the bearing capacity of the two soils meets the back wall requirements; S4. After confirming that the bearing capacity of the soil at the two locations meets the back wall requirements, install the test equipment in the test pipe section to build a test system; S5. Then, water injection, exhaust and pressure increase tests are carried out on the test pipe section, and the quality of the pipeline installation is judged by the pressure drop or water seepage.

2. The method for hydraulic testing of PCCP pipelines without back wall design under mountainous conditions according to claim 1 is characterized in that: The test pipe section is selected at an elbow whose vertical fluctuation exceeds 11.25° along with the terrain as the two ends of the test pipe section.

3. The PCCP pipeline water pressure test method without back wall design under mountainous conditions according to claim 2 is characterized in that: The calculation formula for the thickness of the blocking plate in step S2 is: Where: δ is the load-bearing thickness, mm; P is the design pressure of the plug, MPa; D i is the nominal diameter, mm; σ is the allowable stress of the steel plate at the design temperature, MPa; Ф is the weld coefficient, which is taken as 0.

85.

4. The PCCP pipeline water pressure test method without back wall design under mountain conditions according to claim 3 is characterized in that: The allowable resistance formula of the back soil in step S3 is: Where: E P --Passive earth pressure per 1m width, kN / m; γ--gravity density of back soil, kN / m3; c--cohesion of back soil, kN / m2; H--height of back wall, which can be equivalent to the height difference of pipeline, m; h--height from the top of back wall to the ground, which can be equivalent to the height from the top of the highest pipe to the ground, m; Kp--passive earth pressure coefficient, K P =[tg(45°+θ / 2)]2 (θ is the internal friction angle of the back soil, which is 16°), and K is calculated. P =1.

76.

5. The PCCP pipeline water pressure test method without back wall design under mountain conditions according to claim 4 is characterized in that: The formula for the back soil force width in step S3 is: B≥2.0F P / AND P Where: B is the back soil force width, m; F P It is the force transmitted to the back by the pipe plug, which is equal to the total thrust F of the water pressure test, kN; 2.0 is the safety factor.

6. The PCCP pipeline water pressure test method without back wall design under mountain conditions according to claim 5 is characterized in that: The back soil layer length described in step S3 is: L=(F / B) 1 / 2 +L R , Where: L is the length along the back force direction, m; L R As an additional safety length, take 0.5m.

Images