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目前,大口井的施工广泛应用排水沉井法。该法往往把井内水位抽降得很低,井内外的水位相差较大,当大口井的重量或配重跟不上时,井外四周的土层经常产生严重的坍陷,上部的土层(一般为粘土)沉陷入下部,破坏了原来含水层的结构,特别是遇到细粉砂时还会产生严重的流砂和涌砂,影响大口井的质量,大大地降低井的单位涌水量,严重时要降低50～70％。为了克服该种方法的缺点,我们采用抽筒套管法施工。其施工要点为:
At present, drainage caisson is widely used in the construction of large wells. This method often depresses the water level in the well to a very low level. There is a large difference between the water level inside and outside the well. When the weight or weight of the large well does not keep up, the surrounding soil around the well often produces serious depressions. The upper soil layer ( It is usually clay) sinking into the lower part, destroying the structure of the original aquifer, especially when it encounters fine silt, it will also produce serious sand and sand influx, affecting the quality of large wells, and greatly reducing the unit’s water inflow. When you want to reduce 50 to 70%. In order to overcome the shortcomings of this method, we use the canister method. The construction points are: