With the deepening development of urban modernization, the underground pipelines (such as sewage pipes, water pipes, gas pipes, heat pipes, power cables and communication cables) will become more and more dense, forming a huge underground pipe network system. Since all pipelines have a limited life span, they will inevitably be damaged due to various reasons when they are used for a certain number of years.
At the same time, with the rapid development of the city's modernization, the pipelines laid in past cannot meet the needs of modern cities development. These pipelines that have reached their service life and cannot meet the needs must be repaired or replaced. In situ trenchless rehabilitation technology of engineering pipelines refers takes the old pipeline to be replaced as the guide, and pulls or pushes the new pipe into the pipeline while breaking it.
The pipe burst method is a generally recognized method of non-excavation inline replacement of pipes, aiming to replace some pipelines of old, unqualified oil and gas, water supply and drainage projects. The process uses new pipes of equal or over-diameter to replace old pipes online. When there are fewer branches of the old pipeline to be replaced or the old pipeline is structurally damaged or needs to increase its bearing capacity, the blasting process will obtain higher economic benefits. The pipe burst method is the most economical way to expand the existing pipeline. This method can reduce the damage to the sidewalk and the interference to the traffic, thus reducing the social cost caused by the laying of the pipeline.
The pipe burst method was first developed in the United Kingdom in the 1970s, when D.J. Ryan and others joined with the British Gas Company to replace the small diameter (75mm and 100mm) cast iron natural gas main pipelines (Howell 1995). It uses a pneumatic cone-shaped blasting head to complete the pipe replacement through reciprocating impact. This method was patented in the UK in 1981 and in the US in 1986. However, the original patent expired in 2005, and the law got a new development and applied for related patents. The method was first used to replace cast iron natural gas pipelines. It was later used to replace tap water and sewage pipelines. By 1985, the method had be further developed and could replace the MDPE sewage pipe with an outer diameter of 400mm. The length of pipeline replacement in the United States using this method is increasing at a rate of 20% every year, most of which are sewage pipelines.
The pipe burst method first requires a cone-shaped tool (pipe burst head) to be loaded into the old pipe. The pipe burst head breaks the old pipe into fragments and squeezes it into the surrounding soil. At the same time, the new pipe is pulled in behind the blasting head. The rear diameter of the burst head should be larger than the inner diameter of the old pipe to break the old pipe, and should be slightly larger than the outer diameter of the new pipe, so as to reduce the friction resistance of the new pipe when pulling in. The end of the burst head is connected with the new pipe drawn in, and the front end is connected with steel wire or special drill pipe. The detonating head and new pipe enter from the starting pit, while the pulling wire rope or drill pipe is connected to the bursting pipe head through the receiving pit and the pulling force is exerted. Another function of the wire rope or drill pipe is to guide the pipe burst head so that it does not deviate from the route of the old pipe. The specially designed bursting head can also reduce the influence of downward drift or deviation from the pipeline during the pulling in process of the new pipe.
For pipeline repair or replacement, the traditional methods include excavating the ground, digging out the pipeline, laying the pipe section again, connecting the branch pipe and restoring the ground. However, one of the advantages of the pipe burst method is that it can maintain or even increase the flow cross-section of the gravity pipeline, and the increasing range can be reached to 100%.
The pipe burst method can be used for a wide range of pipe diameters and various formation conditions. Typical pipe diameters range from 50 mm to 750 mm, although larger diameter pipes can also be replaced in situ by pipe burst method. The burst method is generally used for the replacement of equal diameter pipe or increased diameter pipe. The larger diameter construction (up to 3 times the diameter) has been successfully carried out, but it needs more pull back force and may cause large surface displacement. Different sites and stratum conditions may be encountered during each pipe burst operation. Consequently, it is very important to investigate the surrounding environment, pipeline depth and soil conditions in detail. It is also important to determine the minimum buried depth of the overlying soil layer (based on the original pipe diameter, original excavation conditions, or possible expansion) to avoid the uplift of the surface and sidewalks. When encountering conditions such as expansive soil layers, pipelines that have been repaired with flexible materials, pipeline collapse and adjacent underground pipeline facilities, it is often unfavorable for pipe burst construction. In all applications of the blasting method, it is necessary to understand the soil conditions, the location of surrounding structures and facilities, and the impact of the blasting method under these circumstances.
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