1、工程简介ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
着中重说明基础工程中的地质概况、地下水概况以及与降水有关的情况，即为什么要降水？ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
2、降水方式方法及采取的措施ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
现场井点布置，采用的设备型号，技术参数等。ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
3、降水工作中应注意的事项ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
在降水施工过程中，技术、质量、安全、环保应注意的事项ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
4、计算书（附后）ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
本节主要讨论轻型井点降水有关计算ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
轻型井点降水计算ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
一、 总涌水量计算ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
1.基坑总涌水量Q（m3/d），即环形井点系统用水量，常按无压完整井井群，ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
用下式计算公式： ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
（2H―s）s ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
Q＝1.366K ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
lgR―lgx0 ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
2.单井井点涌水量q（m3/d）常按无压完整井，按下计算公式：ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
（2H―s）sÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
q＝1.366KÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
lgR―lgrÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
式中：K—土的渗透系数（m/d）；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
H—含水层厚度（m）；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
s—水的降低值（m）；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
R—抽水影响半径（m），由现场抽水试验确定，也可用下式计算：R＝1.95 s√H• KÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
r—井点的半径（m）；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
x0—基坑的假想半径（m，当矩形基坑长宽比小于5时，可化成假想半径x0的圆形井，按下式计算：x0＝√F/πÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
F—基坑井点管所包围的平面面积（m2）；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
π—圆周率，取3.1416；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
二、井点管需要根数ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
井点管需要根数n可按下式计算：ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
QÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
n＝m ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
qÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
式中 q＝65π•d•l 3√ KÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
式中：ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
n—井点管根数；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
m—考虑堵塞等因素的井点备用系数，一般取m＝1.1；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
q—单根井点管的出水量（m3/d）；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
d—滤管直径（m）；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
l—滤管长度（m）；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
三、井点管平均间距ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
井点管平均间距D（m），可按下式计算：ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
2（L＋B）ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
D＝ ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
n－1ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
求出的D应大于15d，并应符合总管接头的间距（一般为80、120、160mm）要求。ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
式中：L—矩形井点系统的长度（m）；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
B—矩形井点系统的宽度（m）；ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
四、例题ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
某工程基坑平面尺寸见图，基坑宽10m，长19m，深4.1m，挖土边坡1：0.5。地下水位－0.6m。根据地质勘察资料，该处地面下0.7m，为杂填土，此层下面有6.6m的细砂层，土的渗透系数K＝5m/d，再往下为不透水的粘土层。现采用轻型井点设备进行人工降低地下水位，机械开挖土方，试对该轻型井点系统进行计算。ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
解：（1）井点系统布置ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
该基坑顶部平面尺寸为14m×23m，布置环状井点，井点管离边坡为0.8m。要求降水深度s＝4.10－0.6＋0.5＝4.0m，因此，用一级轻型井点系统即可满足要求，总管和井点布置在同一水平面上。由井点系统布置处至下面一层不透水粘土层的深度为0.7＋6.6＝7.3m，设井点管长度为7.2m（井管长6m，滤管1.2m，直径0.05m），因此，滤管底距离不透水粘土层只差0.1m，可按无压完整井进行设计和计算。ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
（2）基坑总涌水量计算ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
含水层厚度：H＝7.3－0.6＝6.7 mÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
降水深度：s＝4.1－0.6＋0.5＝4.0mÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
基坑假想半径：由于该基坑长宽比不大于5，所以可化简为一个假想半径为x0的圆井进行计算：ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
x0＝√F/π ＝√（14＋0.8×2）（23＋0.8×2）／3.14 ＝11mÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
抽水影响半径：R＝1.95 s√H• K ＝1.95×4√6.7×5 ＝45.1mÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
基坑总涌水量： ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
（2H―s）s ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
Q＝1.366K ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
lgR―lgx0 ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
（2×6.7―4）×4 ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
＝1.366×5 ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
Lg45.1―lg11 ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
＝419 m3/dÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
（3）计算井点管数量和间距ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
单井出水量：ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
q＝65π•d•l 3√ K ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
＝65 ×3.14 ×0.05×1.2 3√ 5 ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
＝20.9 m3/dÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
井点管数量：ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
Q 419ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
n＝m ＝1.1× ＝22根ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
q 20.9ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
在基坑四角处井点管应加密，如考虑每个角加2根井管，采用的井点管数量为22＋8＝30根。ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
井点管间距平均为：ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
2×（24.6＋15.6） ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
D＝ ＝2.77 m 取2.4mÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
30―1ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
井点管布置时，为让开机械挖土开行路线，宜布置成端部开口（即留3根井管数量距离），因此，实际需要井点管数量为：ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
2×（24.6＋15.6） ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
D＝ ―2≈31.5根ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
2.4 ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
用32根。ÈWm3Ïè!bbs.3c3t.comâä^(ÿ|Z
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