The builder has to meet with swimming units quite often. How in this case to open ditches, trenches or pits for buildings? How to avoid the destruction of close buildings? We have already met a cunning way to which Siberian builders of bridges resorted to. However, rye flour or other substances close to it by the effects on the floats have only a short -term effect. In addition, this method is applicable only to shallow pits and trenches, therefore it cannot find widespread. The posed questions are easily resolved when it is necessary to build on pseudo -shuts. In this case, it is enough just to take the groundwater, and the drained sands will stop fuel. And what to do in the case when the open pumping of water from the pit into the pseudopli -nuns becomes dangerous to the surrounding structures, when it entails suffusion – the removal of the soil with all the ensuing consequences? For a long time it was not possible to solve this problem. As in many other cases, its decision turned out to be very simple. In 1886. German experts for the first time used a preliminary decrease in the water level in the sands using soil drainage. This method turned out to be quite reliable, it was quickly picked up and used during the construction of the subway in Budapest and Berlin. What is the essence of this method? Let’s make a drill well in the ground. We lower the suction pipe of the pump into it. In order to prevent sand from being delayed in the pump, we will supply its end with a filter of thin copper grid. Now let’s try to download water. If you pump out a certain time, then around the well due to the suction, a decrease in the level of groundwater is formed. It will have the shape of a funnel, as shown in the figure. Geologists called a similar decrease in the level near the well caused by pumping, a depression funnel. Take not one, but two such wells located nearby. Let’s start to pump water from them at the same time. The depression funnels around the well will merge and the level of groundwater between them will decrease. Now let’s try to surround the foundation pit with a number of wells. If you start to pump water from them at the same time, then you can achieve the required decrease in the level inside the site, thus draining the sands within the construction site. This principle is the basis of soil drainage. Soviet scientists and engineers have significantly improved this method. Now at the construction sites of our country, special water supplying devices are widely used – needleofilters. Deep needle -filters created in. TO. Yartsev and p. P. Argunov. They are a pipe with a diameter of 75mm, inside which a different, thinner pipe with a diameter of 50 mm is placed. The lower part of the large pipe is supplied with a filter. The inner pipe at the end is equipped with a rubber ball valve. Water pumping using an needleofilter is carried out as follows: first it is installed in a prepared recess and in a small pipe under pressure (2-3 atmospheres) is supplied with water. Her stream squeezes the ball valve and strokes with force in the ground, producing its erosion. The breed particles then, along with water, are carried up in the forth. The needle -filter under the weight of its own weight, as it were, “falls” into the void formed under it. The whole process of such an immersion to a depth of 8-20 meters takes 5-15 minutes. After that, the inner pipe is connected to the vacuum pump, which creates a vacuum in it. Under the influence of the rarefaction, the water is sucked into the pipe and rises upward. To increase the height and speed of lifting, compressed air is additionally pumped into the outer pipe. Water flows through a pipe to a height of 15-20 meters. Such deep needleofilter installations make it possible to lower the level of groundwater by 10-16 meters. This method is good in the fight against the fueling of pseudo -puppies, but to drain the true swims, it is unsuitable.