1、工程简介Gz4|4<bbs.3c3t.com ÝR©¾Ã
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？Gz4|4<bbs.3c3t.com ÝR©¾Ã
2、降水方式方法及采取的措施Gz4|4<bbs.3c3t.com ÝR©¾Ã
现场井点布置，采用的设备型号，技术参数等。Gz4|4<bbs.3c3t.com ÝR©¾Ã
3、降水工作中应注意的事项Gz4|4<bbs.3c3t.com ÝR©¾Ã
在降水施工过程中，技术、质量、安全、环保应注意的事项Gz4|4<bbs.3c3t.com ÝR©¾Ã
4、计算书（附后）Gz4|4<bbs.3c3t.com ÝR©¾Ã
本节主要讨论轻型井点降水有关计算Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
轻型井点降水计算Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
一、 总涌水量计算Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
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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，Gz4|4<bbs.3c3t.com ÝR©¾Ã
用下式计算公式： Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
（2H―s）s Gz4|4<bbs.3c3t.com ÝR©¾Ã
Q＝1.366K Gz4|4<bbs.3c3t.com ÝR©¾Ã
lgR―lgx0 Gz4|4<bbs.3c3t.com ÝR©¾Ã
2.单井井点涌水量q（m3/d）常按无压完整井，按下计算公式：Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
（2H―s）sGz4|4<bbs.3c3t.com ÝR©¾Ã
q＝1.366KGz4|4<bbs.3c3t.com ÝR©¾Ã
lgR―lgrGz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
式中：K—土的渗透系数（m/d）；Gz4|4<bbs.3c3t.com ÝR©¾Ã
H—含水层厚度（m）；Gz4|4<bbs.3c3t.com ÝR©¾Ã
s—水的降低值（m）；Gz4|4<bbs.3c3t.com ÝR©¾Ã
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• KGz4|4<bbs.3c3t.com ÝR©¾Ã
r—井点的半径（m）；Gz4|4<bbs.3c3t.com ÝR©¾Ã
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/πGz4|4<bbs.3c3t.com ÝR©¾Ã
F—基坑井点管所包围的平面面积（m2）；Gz4|4<bbs.3c3t.com ÝR©¾Ã
π—圆周率，取3.1416；Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
二、井点管需要根数Gz4|4<bbs.3c3t.com ÝR©¾Ã
井点管需要根数n可按下式计算：Gz4|4<bbs.3c3t.com ÝR©¾Ã
QGz4|4<bbs.3c3t.com ÝR©¾Ã
n＝m Gz4|4<bbs.3c3t.com ÝR©¾Ã
qGz4|4<bbs.3c3t.com ÝR©¾Ã
式中 q＝65π•d•l 3√ KGz4|4<bbs.3c3t.com ÝR©¾Ã
式中：Gz4|4<bbs.3c3t.com ÝR©¾Ã
n—井点管根数；Gz4|4<bbs.3c3t.com ÝR©¾Ã
m—考虑堵塞等因素的井点备用系数，一般取m＝1.1；Gz4|4<bbs.3c3t.com ÝR©¾Ã
q—单根井点管的出水量（m3/d）；Gz4|4<bbs.3c3t.com ÝR©¾Ã
d—滤管直径（m）；Gz4|4<bbs.3c3t.com ÝR©¾Ã
l—滤管长度（m）；Gz4|4<bbs.3c3t.com ÝR©¾Ã
三、井点管平均间距Gz4|4<bbs.3c3t.com ÝR©¾Ã
井点管平均间距D（m），可按下式计算：Gz4|4<bbs.3c3t.com ÝR©¾Ã
2（L＋B）Gz4|4<bbs.3c3t.com ÝR©¾Ã
D＝ Gz4|4<bbs.3c3t.com ÝR©¾Ã
n－1Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
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。Gz4|4<bbs.3c3t.com ÝR©¾Ã
式中：L—矩形井点系统的长度（m）；Gz4|4<bbs.3c3t.com ÝR©¾Ã
B—矩形井点系统的宽度（m）；Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
四、例题Gz4|4<bbs.3c3t.com ÝR©¾Ã
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。Gz4|4<bbs.3c3t.com ÝR©¾Ã
解：（1）井点系统布置Gz4|4<bbs.3c3t.com ÝR©¾Ã
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。Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
（2）基坑总涌水量计算Gz4|4<bbs.3c3t.com ÝR©¾Ã
含水层厚度：H＝7.3－0.6＝6.7 mGz4|4<bbs.3c3t.com ÝR©¾Ã
降水深度：s＝4.1－0.6＋0.5＝4.0mGz4|4<bbs.3c3t.com ÝR©¾Ã
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：Gz4|4<bbs.3c3t.com ÝR©¾Ã
x0＝√F/π ＝√（14＋0.8×2）（23＋0.8×2）／3.14 ＝11mGz4|4<bbs.3c3t.com ÝR©¾Ã
抽水影响半径：R＝1.95 s√H• K ＝1.95×4√6.7×5 ＝45.1mGz4|4<bbs.3c3t.com ÝR©¾Ã
基坑总涌水量： Gz4|4<bbs.3c3t.com ÝR©¾Ã
（2H―s）s Gz4|4<bbs.3c3t.com ÝR©¾Ã
Q＝1.366K Gz4|4<bbs.3c3t.com ÝR©¾Ã
lgR―lgx0 Gz4|4<bbs.3c3t.com ÝR©¾Ã
（2×6.7―4）×4 Gz4|4<bbs.3c3t.com ÝR©¾Ã
＝1.366×5 Gz4|4<bbs.3c3t.com ÝR©¾Ã
Lg45.1―lg11 Gz4|4<bbs.3c3t.com ÝR©¾Ã
＝419 m3/dGz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
（3）计算井点管数量和间距Gz4|4<bbs.3c3t.com ÝR©¾Ã
单井出水量：Gz4|4<bbs.3c3t.com ÝR©¾Ã
q＝65π•d•l 3√ K Gz4|4<bbs.3c3t.com ÝR©¾Ã
＝65 ×3.14 ×0.05×1.2 3√ 5 Gz4|4<bbs.3c3t.com ÝR©¾Ã
＝20.9 m3/dGz4|4<bbs.3c3t.com ÝR©¾Ã
井点管数量：Gz4|4<bbs.3c3t.com ÝR©¾Ã
Q 419Gz4|4<bbs.3c3t.com ÝR©¾Ã
n＝m ＝1.1× ＝22根Gz4|4<bbs.3c3t.com ÝR©¾Ã
q 20.9Gz4|4<bbs.3c3t.com ÝR©¾Ã
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。Gz4|4<bbs.3c3t.com ÝR©¾Ã
井点管间距平均为：Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
2×（24.6＋15.6） Gz4|4<bbs.3c3t.com ÝR©¾Ã
D＝ ＝2.77 m 取2.4mGz4|4<bbs.3c3t.com ÝR©¾Ã
30―1Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
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：Gz4|4<bbs.3c3t.com ÝR©¾Ã
Gz4|4<bbs.3c3t.com ÝR©¾Ã
2×（24.6＋15.6） Gz4|4<bbs.3c3t.com ÝR©¾Ã
D＝ ―2≈31.5根Gz4|4<bbs.3c3t.com ÝR©¾Ã
2.4 Gz4|4<bbs.3c3t.com ÝR©¾Ã
用32根。Gz4|4<bbs.3c3t.com ÝR©¾Ã
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