The main objectives of improving the seismic performance of water supply pipelines are two: one is to ensure the water transmission capacity, to prevent a large area of water pressure loss, in order to be able to supply water to fire and critical facilities in an emergency; The second is to minimize the damage of the pipeline to facilitate quick repair. In other words, when faced with earthquake disasters, a water supply system should have a higher adaptability.
Preventing water main breaks is essential to maintaining the normal operation of the water supply system. The PE4710 (equivalent to PE100) piping system has the lowest probability of rupture and leakage of any water pipe, helping to achieve all of the above objectives.
Wave propagation and permanent ground deformation are the main causes of buried pipeline damage. Due to the existence of axial force and bending stress, the ground movement leads to axial and bending strains in the pipeline. Materials with high rigidity (high allowable stress) generally have a limited ability to deform. The ductile materials represented by polyethylene (PE) (low allowable stress) have good deformation ability and toughness.
The seismic ability of pipeline system is reflected by its adaptability to surface strain. Seismic shaking or seismic wave propagation can cause strain in the ground enough to damage even the most vulnerable pipes. Fault cracking, landslides, soil change to mud and the resulting settlement and/or lateral spreading, ground subsidence and uplift may cause greater ground strain, resulting in damage to large areas of buried pipelines. Table B-1 lists ground strain data observed around the world due to permanent ground deformation.
Table B-1 Observed ground strain due to permanent ground deformation
The required range of ground strain for pipelines is between 0.05% and 4.5%. In a 2008 report by the American Electric Power Research Institute, the strain capacity measurements of the PE4710 material were given. At 50°F (10 ° C) temperature, the average tensile yield strain of PE4710 pipe is 9.9%, while the average ultimate tensile strain is 206%. The polyethylene pipe will move in response to ground motion, rather than resisting loads that could cause rigid or brittle pipes to break. In most seismic events, the welded (welded) high density polyethylene (HDPE) pipe will bend, but will not break or separate (non-seal connection), thus maintaining a normal water supply. It should be noted that all connections of PE pipes with other structures, ancillary facilities and components may be subject to higher differential loads. The connection of these parts should be carefully planned and designed to reduce the risk of rupture.
The tensile yield strain of the PE4710 pipe is approximately twice that of the ground strain caused by the observed maximum magnitude, and the ultimate strain of PE4710 is more than 40 times that of the peak ground strain. The performance obtained by theoretical calculation is consistent with the use of polyethylene pipeline in earthquake. The welded HDPE water supply line performed well in the earthquake. Table B-2 gives partial observations of past earthquakes in Japan (Omuro and Himono, 2018).
Table B-2 Data observed during past earthquakes in Japan
The seismic performance of pipelines should be evaluated, including toughness, axial strain capacity, allowable bending radius, joint strength, stability and existing pipeline condition. A large number of seismic experience shows that HDPE water supply main pipelines in accordance with ASTM pipe series standards can maintain normal operation under most seismic load conditions. When the seismic performance requirements of the water supply main pipe are high, the use of welded HDPE pipes should be considered, because the seismic performance of HDPE pipes is more reliable, and they can adapt to the different strains of the ground generated by earthquakes and maintain normal operation.
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Post time: Mar-06-2025
