深井（大口井）井點降水工法.doc

前言
    在深基礎施工中，經常需要降低地下水位，而國內常用的輕型井點，存在一些難以克服的缺點，其性能也是不理想的。輕型井點受吸程限制，如果降水深度超過6m，往往需要設置多級井點，至使抽水設備翻番，挖土量也明顯增加，輕型井點并距很小，土方運輸車輛和施工機械出入不便，而且施工費用也高。1983年，我局在承建引灤入津工程時，大面積的基坑降水，若采用輕型井點，需設置1萬5千口以上井點，保證降水系統的正常運轉是比較困難的。繁重的施工任務促使我們探索降水新技術，經過試驗驗證，決定采用深井井點，全部基坑只需600口井點即可滿足降水要求，降水深度可以超過10m。潛水泵出現故障，只局限于單個的井點，更換也比較方便。深井井點在引灤入津工程中的成功應用，表明其性能優于國內認為先進的噴射井點，該項技術在我局承建的國內外工程中都已得到推廣應用。微透水性土層歷來都是降水的難題，近年來在天津地區采用深井井點降水取得成功，使降水技術又取得了新的進程。
1特點及適用范圍
    1．l特點
    深井井點降水是將潛水泵沉入井管底部，將水排出，故不受吸程限制，一般可根據需要的降水深度確定井深和井距，深井井點管路沒有嚴格的密閉要求，安裝維修都比較方便，而且費用和能耗都較低。
    1．2適用范圍
    深井井點降水適用于滲透系數在10m／ed以上的土層。天津地區的土層滲透系數很小，但有一定數量的透水類層。故也能有效地降低地下水位，但需延長抽水時間，安排基坑開挖應考慮提前降水時間。
2材料
    2．1濾管
采用無砂砼管作濾管。
2．2濾網
宜采用雙層濾網，內層用篩網號2.5－l.24（0.24－40.96孔/cm2，即8－16目）尼龍絲篩網，外層用尼龍或塑料窗紗（約1.6mm孔），濾網也可用雙層棕皮代替。
2．3濾料
宜采用粗砂或3－8mm砂礫混合料，要求濾料級配合理，孔隙率較小。
3施工準備
3．l機具準備
以一臺鉆機配備考慮；
Preface
    In deep foundation construction, it is often necessary to reduce groundwater levels, and domestic common light well, there are some difficult to overcome the shortcomings, the performance is not satisfactory. Light well by the suction limit, if the rainfall depth of more than 6m, often need to set up multi-level wells, pumping equipment to make double the amount of excavation has also increased significantly, from the light well and a small, earth-moving transport vehicles and construction machinery access inconvenience, but construction costs are high. In 1983, the Bureau Luan River to Tianjin in the construction of projects, large areas of the foundation pit, the use of a light well, needs to be set 10 005 1 000 or more wells to ensure the normal operation of precipitation systems is difficult. Heavy precipitation in the construction task prompted us to explore new technology, after experimental verification, decided to use deep well point, all pit only 600 wells can meet the requirement of precipitation and precipitation depth of more than 10m. Submersible pump failure is confined to individual wells, the replacement is relatively easy. Deep well point in Luan River to Tianjin project successful application, show that its performance is superior to the domestic advanced injection wells that point, the technology at home and abroad in the construction of our Bureau projects have been promoted and applied. Micro-porous layer has always been the problem of precipitation in recent years in Tianjin with the success of Deep Well, so precipitation technology has made new progress.
Features and application 1
    1. l Features
    Deep Well Submersible Pump is to sink tube wells the bottom of the water discharge, it is not subject to restrictions on smoking process may generally be required to determine the depth of precipitation from the well depth and well, deep well point pipe is not strictly confined requirements, installation and maintenance are more convenient, and cost and energy consumption is relatively low.
    1.2 Scope
    Deep Well for the permeability of soil in 10m/ed above. Permeability of soil in Tianjin area is small, but there are a number of permeable type layer. It also can effectively reduce the water table, but need to extend the pumping time for the excavation should be considered ahead of time of precipitation.
2 Materials
    2.1 Filter Pipe
Concrete pipe used for non-sand filter tube.
2.2 Filter
Should adopt the double filter, the inner sieve No. 2.5-l.24 (0.24-40.96 holes / cm2, the 8-16 mesh) nylon screen, the outer layer of nylon or plastic window screening (about 1.6mm hole) , the filter can also be used instead of double brown leather.
2.3 filter
Should use sand or 3-8mm gravel mixture, with the reasonable demands filter level, low porosity.
3 construction preparation
3. l machines ready
Drilling rig equipped with a consideration;

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