New Trenchless Technology

  • Time of issue:2017-12-20

New Trenchless Technology

(Summary description)With the development of society, "pipe jacking" as a new type of trenchless technology has been increasingly used in engineering construction.

  • Time of issue:2017-12-20
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With the development of society, "pipe jacking" as a new type of trenchless technology has been increasingly used in engineering construction. It was originally mainly used to lay protective casings across subgrades, to directly lay gravity sewer pipes (sewage pipes), and now it has been promoted to other large-area underground penetration projects that are not conducive to open excavation. It can be said to be more than a new technology. The pioneering work is a leap in thinking. On July 20th, our team visited the new application of this technology-the cross-street passageway at the entrance and exit of Donghu Station II of Guangzhou Rail Transit Line 6, the cross-section is 6 meters * 3 meters, and the length of the pipe jacking is about 62 meters. . The emergence of this new technology has undoubtedly brought a lot of challenges to our investment review.




1. The plan is selected as the best after technical and economic comparison

The construction plan of the project using pipe jacking was finally determined after many comparisons. What it wants to open is the cross-street passage that crosses Donghu Road at the entrance and exit No. II of Donghu Station on Metro Line 6. Its end face is large, the distance is long, and the ground and geological conditions are quite complicated. According to the usual practice, the first idea of ​​adopting the plan of open excavation, but since Donghu Road is connected to the Haiyin Bridge in the south and the inner ring road in the north, it is a main traffic road in the north-south direction of Guangzhou. The open excavation must be carried out without interruption of traffic. ; And the many pipelines under Donghu Road and the sidewalks on both sides (there are drainage pipes, DN1200 socket concrete water supply pipes, 110,000 volt high-voltage cables, a large number of communication pipes and power pipelines, etc.), like a pair of big hands to handle the entire site Even if the migration can be carried out smoothly, it will cost a huge amount of money. In view of many unfavorable factors, the open-cut plan was finally abandoned because it was not approved by the traffic control department. Can underground excavation work? According to the design, the buried depth of the tunnel bottom of the No. 2 entrance and exit tunnel of Donghu Station is only 8m, and the maximum soil covering of the tunnel does not exceed 4m. If you want to dig under such a thin covering with heavy traffic, it is too risky What's more! Besides, the results of geological exploration show that the tunnel crossing is basically a layer of saturated water-saturated silt that is easy to collapse, and the undercut excavation had to be abandoned. So, is there a way to avoid the interruption of traffic and resolve the problems of the upper pipeline? At this time, the pipe jacking has been used in many cases for its simple concept and economic advantages, as well as successful applications in similar projects in Shanghai. Stand out in the program. It does not even need additional treatment for the wall protection and lining, as the tunnel is completed at one time! After further demonstration is feasible, it will be put into practice immediately.

Pipe jacking construction plan

2. The process is simple in actual construction and the effect is obvious

This project adopts closed mechanical tunneling and pipe jacking. The construction principle is to set up launching wells and receiving wells according to the designed scheme along the jacking line, set up a solid back seat in the launching well, hoist the hydraulic jack and the pipe section to be jacked, and connect the lighting, mud pipe, The oil pipes and other pipelines are then slowly jacked in with a hydraulic jack, and a mud sleeve is formed around the pipe section through the grouting system, and the pipe section is allowed to slide in the mud sleeve (to reduce the huge friction between the pipe section and the soil layer). During the process, the direction of the jacking pipe is measured by the laser theodolite, and the jacking is adjusted while the soil excavated by the front cutter head (boring equipment) is discharged, until the prefabricated concrete pipe section is jacked into the receiving well. After the pipe jacking is completed, the inner wall of the pipe is smooth, and no secondary lining is required, and the process is simple. The main equipment used in this project are: 14 main rear-seat jacks (that is, the power facilities of this project), with a stroke of 2500mm, and a total jacking force of 28000KN. The 14 jacks have an independent oil circuit control system. The joint force center of the top device performs auxiliary correction; five groups of front cutter heads (boring equipment), the large cutter head (torque 1568KN-m) in the center and the four small cutter heads (torque 224KN-m) are arranged staggered forward and backward, and There is a stirring rod behind each knife row, which can stir the cut soil. After full stirring, the soil has good plasticity and fluidity, and has good water resistance.

It is understood that since the official launch on June 1 this year, the project has passed through the reinforced end and the undisturbed soil layer successively, and by July 8 it has successfully jacked 41m. During the pipe jacking construction process, parameters such as surface settlement, jacking axis displacement, and channel elevation are controlled within the allowable range of the design and specifications. At present, the daily footage can be guaranteed 3m (2 knots). Such an efficient process can shorten the construction period by at least four months compared with the open cut, and the personnel only need few configuration.

Related scene pictures:




Power equipment: jack



Tunneling equipment: cutter head





Pipe section and pipe section hoisting

Third, the advantages and disadvantages of pipe jacking technology

It is true that as a trenchless technology, pipe jacking does have many advantages when the underground pipeline is complex and the ground environment is difficult to carry out open excavation: 1. No need to damage the road surface to affect traffic; 2. No interference with the upper pipeline, which can be Save the huge cost of pipeline migration; 3. It occupies a small area and will not severely test the tolerance of the citizens like the BRT construction. The intensity is small; 5. The construction speed is faster, which can greatly shorten the construction period and so on. However, there are some shortcomings. For example, the complete set of equipment needs to be customized according to the site conditions, which is quite expensive and has a low reuse rate; the cutter head is expensive and has a short service life (the maximum life of a pair of cutter heads is only 500m), and once during the jacking process It is extremely difficult to replace or repair a damaged cutter head. The so-called extreme must be reversed, and the extreme conditions applicable to the pipe jacking process are also limiting its performance: once the construction site is originally idle, the organizers will never ignore its high mechanical usage fees and choose this process. In view of the above situation, can the equipment be changed to modular assembly and reduce the amortization fee by increasing the number of repeated use of parts?

4. Bringing new challenges to investment review

Unfortunately, due to the relatively small scope of application of this emerging technology of pipe jacking, the current utilization rate is still very low, and it can only be used under unique conditions. Therefore, this "non-mainstream" construction technology has no supporting quota to determine various costs. How to reasonably and accurately determine the project cost of the project using this technology is a difficult problem that the project cost personnel must solve. According to reports, the price of the whole set of equipment is about 16 million yuan. If converted according to the life of the cutter head, it will be amortized about 32,000 yuan per meter of jacking, but this is based on the fact that durable equipment such as hydraulic presses and cutter heads have the same service life. In consideration, the estimate is too conservative, and when most equipment is used repeatedly when the conditions are met, its amortization cost will be lower. Throughout the entire process, the difficulty of the engineering cost analysis is mainly in the pricing of the "hard" parts (after all, the application of new In the construction plan, the workload of skilled workers is relatively reduced, and the proportion of labor costs is relatively low). In-depth understanding of the operation of the entire process and analysis of the consumption of various labor, materials and machines during the construction process will solve the problem of cost evaluation of the pipe jacking project.

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