Piping is a phenomenon in which the fine particles in the soil are taken away from the gaps of the coarse particles by the groundwater under the action of seepage, which causes the soil to form a through seepage channel and causes the soil to collapse. Piping destruction generally has a development process, which is a gradual destruction. Piping generally occurs in a certain gradation of non-cohesive soil. The location can be where the seepage escapes or inside the soil. Therefore, it is also called a kind of latent corrosion phenomenon of seepage.

Definition：The phenomenon that soil particles in the dam body or foundation are taken away by seepage is called piping.

It refers to the general term for the two different meanings of "drifting soil" and "underwater erosion" occurring on the flat land in the dike under the condition of high water level during the flood season. This kind of danger is generally called Fansha Gushui in Hubei and Paoquan in Jiangxi.

Harm：When piping occurs, the water surface will turn over. As the upstream water level rises, the duration is prolonged, and the danger continues to worsen. A large amount of water floods and turns sand, destroying the soil skeleton of the embankment and sluice foundations, expanding the pores, and emptying the foundation soil, causing buildings The collapse caused accidents such as dyke bursting, dam collapse, and gate collapse.

Cause:

1. The foundation soil gradation of dams and sluices lacks some non-cohesive soils with intermediate diameters. When the upstream water level rises and the seepage slope at the escape point is greater than the allowable value of the soil, the finer soil particles in the foundation soil are pushed by the seepage. Walk to form a piping.

Piping diagram

2. The foundation soil layer contains a strong water-permeable layer, and the soil layer covered on it is not heavy enough.

3. The engineering anti-seepage or drainage (seepage) facilities are inefficient or damaged, and the non-cohesive soil produces piping. The following two conditions must be met:

1. The diameter of the pores formed by the coarse particles in the soil must be larger than the diameter of the fine particles.

2. Permeability can drive fine particles to move between pores.

Rush protection method：Stopping the back guide, and applying pressure at the same time, reduce the seepage pressure and prevent the seepage from bringing out the sediment.

Filter trap：Build an enclosed well with earth bags around the water hole. The bottom of the well wall is in close contact with the ground. The well is laid with sandstone or firewood filter material according to the requirements of three-layer filtration. Drain pipes are installed at the wellhead to remove the seeping water Lead away to prevent overflow from collapsing the well wall. In case of strong water surge and heavy sand cannot be suppressed, you can fill gravel and block stones to eliminate the water potential, and then pave the filter material according to the filter requirements, pay attention to observation and defense If the filler sinks, continue to fill it until it is stable. This method is suitable for the situation where the foundation soil is better, piping occurs concentratedly, and the danger is more serious.

Water basin：Use soil bags around the piping to form a fenced well. The well shall not be filled with filter media, and the wall of the well shall not leak water. If the area of the danger is large. When the foundation near the danger point is good, an earth embankment can be built to form a reservoir (i.e. Water basin), do not allow seepage water to flow away, and store water to raise the water level in the well (pool) to reduce the frontal water level difference and prevent the development of dangerous situations. This method is suitable for the situation where the frontal water level difference is small and the high water level lasts for a short time. It can also be combined with filter wells.

Filter water pressure immersion table：Coarse sand, stone chips, and gravel are layered on the large piping surface, the bottom is fine and the top is thick, and each layer is 20cm thick to the left, and finally briquette or soil bag. If there is a lack of sand and stone materials, straw and willow can be used to make firewood rows (15-30cm thick), and then block stones or soil bags can be pressed. This method is suitable for situations where the number of piping is large and the scope is large. If piping occurs underwater: Never drain the water before filling. So as not to worsen the danger.

Flow soil is another form of seepage deformation. The forms of seepage deformation generally include piping and flowing soil, contact erosion and contact flowing soil, etc. In the non-cohesive soil, the flowing soil exhibits the simultaneous movement of particle groups, such as springs, sand boiling, and soil tumbling, which are finally held up by seepage; in the cohesive soil, it is manifested as soil uplift, swelling, floating, fracture and other dangerous situations. The method of emergency protection is the same as that of piping.

The development of piping and flowing soil will lead to cracks and subsidence of the embankment body. While rushing to protect the piping, the dyke should be quickly rushed to protect the dangerous situation. The outer side is closed to prevent leakage from the flood along the seam, and the embankment is reinforced and heightened to prevent floods from overflowing.