深井（大口井）井點(diǎn)降水工法.doc

前言
    在深基礎(chǔ)施工中，經(jīng)常需要降低地下水位，而國內(nèi)常用的輕型井點(diǎn)，存在一些難以克服的缺點(diǎn)，其性能也是不理想的。輕型井點(diǎn)受吸程限制，如果降水深度超過6m，往往需要設(shè)置多級(jí)井點(diǎn)，至使抽水設(shè)備翻番，挖土量也明顯增加，輕型井點(diǎn)并距很小，土方運(yùn)輸車輛和施工機(jī)械出入不便，而且施工費(fèi)用也高。1983年，我局在承建引灤入津工程時(shí)，大面積的基坑降水，若采用輕型井點(diǎn)，需設(shè)置1萬5千口以上井點(diǎn)，保證降水系統(tǒng)的正常運(yùn)轉(zhuǎn)是比較困難的。繁重的施工任務(wù)促使我們探索降水新技術(shù)，經(jīng)過試驗(yàn)驗(yàn)證，決定采用深井井點(diǎn)，全部基坑只需600口井點(diǎn)即可滿足降水要求，降水深度可以超過10m。潛水泵出現(xiàn)故障，只局限于單個(gè)的井點(diǎn)，更換也比較方便。深井井點(diǎn)在引灤入津工程中的成功應(yīng)用，表明其性能優(yōu)于國內(nèi)認(rèn)為先進(jìn)的噴射井點(diǎn)，該項(xiàng)技術(shù)在我局承建的國內(nèi)外工程中都已得到推廣應(yīng)用。微透水性土層歷來都是降水的難題，近年來在天津地區(qū)采用深井井點(diǎn)降水取得成功，使降水技術(shù)又取得了新的進(jìn)程。
1特點(diǎn)及適用范圍
    1．l特點(diǎn)
    深井井點(diǎn)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(jù)需要的降水深度確定井深和井距，深井井點(diǎn)管路沒有嚴(yán)格的密閉要求，安裝維修都比較方便，而且費(fèi)用和能耗都較低。
    1．2適用范圍
    深井井點(diǎn)降水適用于滲透系數(shù)在10m／ed以上的土層。天津地區(qū)的土層滲透系數(shù)很小，但有一定數(shù)量的透水類層。故也能有效地降低地下水位，但需延長(zhǎng)抽水時(shí)間，安排基坑開挖應(yīng)考慮提前降水時(shí)間。
2材料
    2．1濾管
采用無砂砼管作濾管。
2．2濾網(wǎng)
宜采用雙層濾網(wǎng)，內(nèi)層用篩網(wǎng)號(hào)2.5－l.24（0.24－40.96孔/cm2，即8－16目）尼龍絲篩網(wǎng)，外層用尼龍或塑料窗紗（約1.6mm孔），濾網(wǎng)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(jí)配合理，孔隙率較小。
3施工準(zhǔn)備
3．l機(jī)具準(zhǔn)備
以一臺(tái)鉆機(jī)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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