S U DUIMG PHUDIMG TRIIMH VI PHAIM LIEIM TUC CUA DDIMG IMGAIVI D E GIAI BAI TDAIM HA T H A P MUC IMUDC
IMGAIVI KHI THI COIMG HO IVldlMG S A U
Luong van Anh'
T6MTAT
Khi xay dung cac cong trinh noi chung, cong trinh thuy lgi, thuy dien npi rieng thuong gap truong hpp day hd mong dao sau xuong duoi (MNN); trong trudng hpp do, de thi cong dugc thuan lgi va dam bao chat lugng cong trinh can phai hiit nuoc thao kho ho mong. Viec lua chpn phuong phap ha thap MNN phu thupc vao rat nhieu yeu td tu nhien, thiet bi thi cong va dia chat nen mong cua hd mong; su lua chpn hpp ly se mang lai hieu qua kinh te cao, bao dam thoi gian thi cong, con neu khong thi dan den gia thanh xay dung tang len va co khi din den that bai do viec tieu nuac hd mong gay len. Giai phap thao kho ho mong bang each hiit nuac tir he thdng gilng bd tri xung quanh hd mpng la mpt giai phap uu viet, thuang dugc su dung bao dam chu dong ha thap MNN den dp sau yeu cau, tao gradient tham ngugc, khac phuc dugc cac hien tugng xoi ngam, cat chay, buc nen, lam mat on dinh mai hd mong va can tra viec thi cong mong. Cong tac tieu nuac hd mong can phai tinh toan can nbic de bao dam tiln dp, hieu qua cong viec va ban che tdi da anh huong den moi truong.
Tu khoi: Bdc thodt, gieng quan trdc, hiit nude hoac ep nude, md phong.
LDATVANDE
Phuong phip ha thIp mue nude ngam (MNN) bing gilng II bii toln phiic tap. D l tinh toan thilt k l he thdng gilng mdt cleh chinh xlc, tic gil sii dung phuong trinh vi phan lien tyc eua ddng nglm vdi elc dilu kien ban diu va dilu kien bien cu fhl d l giii cle bii toln nude nglm trong elc ting chiia nude. Viec giii phuong trinh nly dugc thuc hien bing phuong phip sai phan hQu ban. D l giii bii toln ha thap MNN, cin chgn dugc cle thong sd hgp ly, mo phdng so dd tinh toln thich hgp, n h | p cle thong sd dia chit vl thuy van, xlc dinh thong sd gilng, dudng kinh gilng, khoing elch dat elc gilng (vdi gilng don, mdt hang hay nhilu hang), xac dinh cle dilu kien bien khac nhau phu hgp thyc t l vung ven song, ven biln, bai bdi. D l d i m hlo tinh chinh xlc cua md hinh mo phdng bii toln ha thIp MNN, trude h i t cin phli tinh thli cho mot bii toln don giln, rdi tiln h i n h kilm nghiem mo hinh tren co sd ddi chilu k i t q u i tinh toan vdi sd lieu thuc do dd ha thIp MNN thuc t l tai hien tiirdng. Tic gil da su dung phln m l m Modflow, mdt cong eu tin cay; tuy nhien d l bio dim thinh cong ngudi thief k l cin n l m vung ly thuylt v l thuy van nude dudi dat d l mo phdng he thdng mot elch diing din.
ILNOI DUNG VA PHUDNG PHAP
1 Trung lam Quoc gia Nuoc sach va VSMTNT
1. Phuong trinh toln hpc
Phuong trinh tdng quit bilu diln chuyin dong eiia nude nglm ba chilu ed dang:
d dx
d dz
'K
^^'
{K.'-!d
\ dzj -h— d
dy
-1-
dt (1.1)
Trong dd:
Kx, Ky, K^ - He sd thIm theo cac hudng x, y vl z (z II chilu t h i n g diing);
h - Muc nude nglm tai vi tri (x, y, z) d thdi dilm t;
S^- He sd n h l nude don vf G/m);
'^s = Ss(xyz); K x = Kx(x,y,z); Ky = Ky(xyz); K , = Kz(x.y.z)
II elc h i m phy thude vio vi tri khong gian x, y, z.
Xet d i n k h i nang ciia cac ngudn bd sung (R) hay thoat ciia nuoc nglm trong phan, khi dd phuong trinh khong dn dinh ba ehilu qua moi trudng Id rdng khong ddng nhlt va khong ding huong bao hoi.
Phuong trinh (1.1) d l giii bai toan nude nglm trong dilu kien khong dn dinh cho ting chiia khong ddng nhlt vl di hudng.
2. Phuong phip giii
Giii phuong trinh (1-1) bing phuong phap gin dung sai phan bun ban hay phan chia khong gian
lien tuc thanh cac 6 khong gian hay con ggi la qui trinh rdi rac hoa. Bing each nly dua phuong trinh dao ham rieng vl mdt he phucmg trinh tuyln tinh. Sd lugng phuong trinh trong he bing sd cac 6 ludi chia
X, y, z, t. Tren co sd can bing 6 luoi (i, j, k) va cac ngudn theo budc thdi gian f^,.! den t^,, ta cd duge he phuong trinh sai phan tdng quit sau:
cCi+i/2i.j,k (K*
, , , + h - , J + CR,,^,„,.,(h
I^.j,.hn,.+Q,,,. :SS,j,,(ArjACiAVJ
/2 {K,.k-}
h'
•h;:^,,)+cc,_,,,^,,(h;!,^,-
-K,0 + c\,u.u2(K,..^
K,..) +
'.,j.k ) + (1.2)
• ' . J . k i.J.k
Trong dd:
CR, CC, CV - Do din thtiy luc tuong ting voi phuong X, y, z;
P - Ltm lugng trao ddi don vi (L^T^ ciia he thdng phu thugc vio myc thiiy Ip h;
Q - Luu lugng (JJD^) eua he thdng trao ddi voi ben ngoli;
AtjAC.AVk - Tuong ling vdi khoing chia sai phan theo phuong x, y, z.
Myc thuy Ip tai thdi dilm bit dau tinh toln h™';. vdi tit cl cle thong sd cua mo hinh tai nui i, j, k diu da bilt. Biy gil tri myc thiiy Ip tai thdi diem t„
chua bilt. Phuong trinh khong thi giii mdt elch
Bai diu linh loan cho bucfc IhcM gian m+1 Ket Ihilc linh loan cho huoic lh6i gian m
Nc'u dao dong I K'- h"' I nho hcfn gia Iri chenh !cch cho phep Ihl qua Irinh linh loan duoc coi la hoan tai o day
rieng biet duge vi trong phuong trinh cd 7 In sd.
Phuong trinh ed the vilt eho tfmg phan td the tich trong he thdng (n phan td fhl tich). Vi thi cd fhl giii dugc he phuong trinh gdm n phuong trinh vdi n In sd. He phuong trinh tren dugc giii bing phuong phip lap, tiln hanh chia nhd khoing thdi gian (t^_i, tn,), kit qua nhan dugc II Idi giii gin dung cua he phuong trinh (1.2). Khi thdi gian tang len thi h se thay ddi. Khi h dat dugc sy dn dinh (chenh lech h tinh dugc giira 2 budc thdi gian kl can nhau se nhd hon mdt gil tri cho phip) thi muc nude dat dugc sy can bing ddng vl tai day kit thuc qui trinh tinh toln.
Cao trinh muc nuac tinh duoc cho buoc thdi gian m+1
^ ^ //////////
//////////,' - '/' /,'>
'Y
/ h -
m
^Bat dau tinh loan cho bu6c Ihcti gian m Ket thuc linh loan cho buc'rc Ihfn gian m Cao trinh muc nu6c linh duga cho bu6c thoi gian m
Hinh 1. Sor dd giai hi phuong trinh sai phln 3. Dilu kif n bi6n trong mo hinh Modflow
- Bii toln thIm dn dinh eua cac ting chiia nude, MNN dn dinh.
- Luu lugng bom cua gilng ung voi MNN ha dn dinh.
- Bii toln khong gian 3 chilu (3D) gioi han khoing each cac gilng II dii nhd.
- Dilu kien bien loai 1 la ap luc da dugc xlc dinh trudc, h=const.
- Dieu kien bien loai 2 II lun lugng dugc xle dinh trudc Q=const.
- Dilu kien bien loai 3 II ltm lugng tren bien phu thugc vio sy thay ddi ciia ap luc, Q=f(AH) (cdn ggi II bien hdn hgp).
Trong tu nhien nhirng bien nly duge mo phdng II song, biln, kenh tholt, mach Id, tudng chin, dl gdc, bdc tholt hoi nude, thIm xuyen. Id khoan hut nude hoac ep nude... Nhtmg trong bii toln nly chi ha tiilp
MNN trong thoi ky thi cong (thoi gian thi cong hd mdng rlt ngan vl vio mua kho) do do lugng nuoe bdc hoi, lugng nude mua nglm xudng II bd qua.
4. So dd khdi chay phan m l m Modflow a. Cdch chia phdn tie
• Ludi phan tii' hinh tam gilc vuong vl hinh chu nhaf - Kich thuoc phan tii chu nhat 0,5 m x 0,5 m va canh tam gilc vuong II 0,5 m.
c. Sa do khdi chay phdn mem Modflow nhu sau:
Xay dtmg mo hinh mo ph(')ng nen, dia chat Ihiiy van (Kx, Ky, Kz, MNN, nguon bd sung nude,,,)
khu vuc xay dung cong trinh bang cac phan lu khdi trong khong gian
Dal cac gieng (vi Iri, chieu sau) len mo hinh, nhap luu lutmg hut nude don \ i cua mot gieng,
thoi gian hut nui'tc cua he thdnt: gieng
Dal cac gieng quan trac (vi Iri. chieu sau) len mo hinh, nhap muc nut'tc ban dau trong moi gieng.
t Dung
•
Ding
In ket qua dang sd lieu va dd hoa
A
Hinh 2. So do khdi chay phln mlm 5. Bii toln thuc t l
Kit qui tinh toan sii dyng mo hinh ha thIp MNN bing he thdng gilng va sii dyng phln mem Modflow cho hai cong ti-inh cdng Van Cdc v l cdng Hiep Thuan phu hgp voi kit qua thi cong ti-en cong tiirdng da ha thap dugc MNN d l thi cong dugc phln be tong mong cdng, khIng dinh lai do fin c | y ciia mo hinh ha thIp MNN bing he thdng gilng cua hd mdng va phln mem Modflow co the su' dung de tinh toan.
Kit qua tinh toan cua cdng Hiep Thuan bang phln mlm Modflow ven kich thuoc hd mong nhu tren, he sd thIm 9x10"^ c m / s , voi dieu kien II ngudn nuoc nglm dugc bd sung ngudn nuoe mat tu song, chilu dai dng lgc la 1,5 m, cho ta kit q u i sd gieng cin bd tri la 204 gieng va khoang each giua cle gilng la 2,0 m, duong kinh gieng la DUO mm. Khi he fhdng gieng hut nuoc lien tyc 4 ngay thi MNN d giQa hd mdng dn dinh d cao trmh -1,8 m thIp hon day mong 0,6 m. Kit q u i nay hoan toan phu hgp voi thyc te ma don vi thi cong da ha fhip MNN cua hd mong d l dd dugc be tong mong cdng.
Hinh 3. Cdng Hi§p Thu§n - Mat bang bd tri gilng ha thIp MNN
.M31 d.-il 1i/(thi^n
Hinh 4. Cdng Hi6p Thuan - Mat elt ngang hd mdng cdng Hifp ThuSn
U •'
VtUH^miUitlmiu
Hinh 5. Cdng Hi6p ThuIn - MNN xung quanh hd mdng ha thIp sau khi hiit li^n tuc 4 ngly
H e a d vs.Timo
Hinh 6. Cdng Hi6p Thu§n - Dudng quan h$ MNN b gitra hd mdng theo thdi gian
TT 1 2 3 4 5 6 7
Bing 1. So sinh kit qui tinh toln elc thdng sd thilt k l ha MNN cdng Hi6p Thuan
TTiong s(i Kha nang hut nuoc ciia mot gieng q Cao do MNN ha thap a day ho mong Dp sau ha MNN trong gieng S Do sau ha gieng H
Luu lucnig chav vao ho mong Q So luong gieng n
Khoang each giua cac gieng 1
Don vi mVngd
m m m m'/ngd
cai m
Theo thuc te hien truong
62,97 2,55 8,35 13,35 5,000 100,0 4,00
Tinh theo Modflow 29,9
1,8 6,66 13,35 5,885 204,0 2,00 5. Tinh toln cho nhilu bii toln ling vdi elc hS sd
tham khIc nhau, elch bd tri v l dilu ki6n bi6n khIc nhau
TTr4i
^ ^ ^
=§
= ^ ! 1 IT 7]'•'•°\^^-^ ' !•* ' • ' "Tr^T^Nfr"^
liL
M l , M ^ [ / I
liAiir 'jia
Hinh 7. Mat bang hd mdng gia thilt bo tri gilng tinh toln ha thIp MNN
Hmh 8. Mat cat dgc hd mdng bd tri gilng tinh toln ha thIp MNN
Hinh 9. MNN ha thIp xung quanh hd mdng sau 4 ngly bom lifen tuc
Hinh 10. Mat cat ngang qua tim hd mdng
Hinh 11. Mat cat doe qua tim hd mdng
-,
-3 J
, . , _ .
\
"
" — " • ' • " -
T,rr-> ld.iv5.1 J O
Hinh 12. Dudng quan h6 MNN b giiia hd mdng theo thdi gian ^ u d n g tr6n II MNN cua bin than hd mdng, dudng dudi II MNN dugc bd sung eho hd
mdng) III. NHAN XET KET QUA TINH TOAN
Tinh toln cho cac tru'ong hop sii dyng gilng thudng ha thap MNN (vdi nIn co he sd thIm 1cm) nhlm tim ra khoang each gitra eac gilng, chilu sau ha gilng. Tir do xay dyng cac bieu dd quan he giQa do sau ha gilng H vl lun lutmg gieng q (H~q) va quan he giua khoang each gieng L va do sau ha gieng H (L~H), xlc dinh thdi gian bom d l MNN dn dinh. Vdi hd mdng sau, cd he sd thIm ldn cin phai bd tri hai, ba h i n g d l tim ra khoing each dat giua cac hang gieng vl do ha thap MNN cua hd mdng.
Giai elc bai toan v6i cac trudng hgp thay ddi khoing elch giua hai gieng bin k l , chilu sau ha gilng, he sd tham,... de tim ra chieu sau ha gieng II tdi uu; ddng thdi cung cin xac dinh voi he sd tham bing bao nhieu thi nen sii dyng phuong phap ha thIp MNN b i n g gieng thudng, khi nIo thi su dung cac bien phip ha thap MNN khac.
Tinh toan trudng hgp voi hd mdng gin song (cd ngudn nuoc bd sung chay vao hd mdng) de bd tri gilng phu hgp nhlm tieu nuoc hd mong dat yeu clu.
Bai toan
1
2
3
4
5 Tr/
hop a.l a.2 a.3 a.4 a.5 a.6 a.7 b.l b.2 cl
C.2
a.l a.2 b.l b.2 a.l a.2 b.l b.2 a.l
a.2
b.l
b.2
a b
So hang gi6ng
2 2 2 2 3
3
3
3
1 1
Bing 2. T6ng hgrp c l e trudng hgp tin KC giira
cac hang gikg (m)
7,0 7,0
•
4,5
4,5
4,5
4,5 So gikg 84 84 84 84 84 84 84 84 98 112 112 66 66 78 78 152 152 177 177 183
183
183 183
66 66
So hang
cir
1 1 I 1
KC giira cac hang cir(m)
6,0 6,0 6,0 6,0
He so tham K (cm/s)
5^10"' 5x10-' 5x10"*
5x10"' 5x10"' 5x10"' 5x10"' 5x10"' 5x10 ••
5x10"' 5x10"'' 5x10"' 5x10"' 5x10"' 5x10"' 5x10"' 5x10^
5x10"' 5x10"' 5x10"'
5x10"'
5x10"'
5x10"'
5x10"' 5x10"'
1 toln c i c Chieu/
dai ong loc 1 (m)
1,5 1.5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1.5 1,5 1,5 1,5 1.5 1,5 1,5 1,5 1.5 1,5 1,5
1,5
1,5 1.5
1,5 1,5
th6ng s6 gilng thudrng Do sau
ha gieng H(m)
14,5 14.5 14.5 14,5 14,5 14,5 10,6 14,5 10.6 10,6 14,5 14,5 10.6 14,5 10.6 14,5 10.6 14,5 10,6 14,5
10,6
14,5
10,6
14,5 14.5
KCgiira Cac gieng
a(m) 2.56 2.56 2,56 2,56 2,56 2.56 2.56 2,56 2.3 1.9 1,9 2.5 2.5 2.1 2,1 a,=2,8
a„=2,3 a|=2,8 a„=2.3 ar2.6 a„=2,4 ai=2.6 a„=2.4 a,=2.7 aj=3,0
a„=3;5 ar2,5 ap=2.9
a„=3,8 a,=2,3 ag=3,l
a„=4.1 a,=2,l aj,=3.3
a„=4.3 2,9 1,7 3,6 2.1
Doha thap So
(m) 4.6 5.8
Ghi chii
Su dung gieng kim hay phuang phap ha thap MNN khac
5.98 7,21 6.37 7.63 8,40 7.30 5.61 8,10 6,72 9.2 7.6 9,9 7,8 11,8
8,6
11.8
8,6
7,2 7,8
H.trong 60.
H. ngoai 92 H.trong 60.
H. ngoai 92 H.trong 65.
H. ngoai 97 H.trong 65.
H.ngoai 97 H.trong 63, H. giira 62.
H. ngoai 58 H.trong 66.
H, giua 64, H. ngoai 53 H.trong 72.
H, giira 60, H. ngoai 50 H.trong 80.
H, giira 56, H. ngoai 47 Phia song Phia song
S ( m ) 16 14 12 10
/ / /
^
<:^
—-—
= ^
• ^
—^
/
^
/A
r /I
/
Ul Ul
<=b.1 0 - 3 0 - 1 —
L ( m )
K=5.1 -K=5 1 3-^
' ^ 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 3 q (m3/h)
Hinh 13. Quan hi giiia dd
ha thIp MNN S(m) vl luu lugmg gilng q(m^/h)
10 12 14 16 S i m )
Hinh 14. Quan h6 gitia khoing
cleh gilng L(m) vl dd sau ha thIp MNN S(m)
IV. KET LUAm
1. Viec lua chgn phuong phip ha thap MNN phu thugc vao rlt nhilu ylu td tu nhien, thilt bi thi cong va dia chit nIn mong ciia hd mdng. Lua chgn hgp ly se mang lai hieu qua kinh t l cao, bio d i m thoi gian thi cong, con n l u khong thi din den gil thinh xay dung fang len va co khi din d i n thit bai viec tieu nuoc hd mdng.
2. Dl tinh toan thilt k l he thdng gilng mot elch chinh xlc, da sii dung phuong trinh vi phan lien tuc ciia ddng nglm vdi cac dilu kien ban diu va dilu kien bien cu fhl d l giii cac bii toan nuoc nglm trong cle ting chua nude. Viec giii phuong trinh nay dugc thuc hien bing phuong phap sai phan hun ban.
3. Dl giii bii toan ha fhIp MNN, c i n chgn dugc cac thong sd hgp ly, mo phdng so dd tinh toan thich hgp, nhap cic thong sd dia chit v l thuy van, xac dinh kit cau gilng, dudng kinh gilng, khoing each dat cac gilng (voi gilng don, mot h i n g hay nhilu hing).
4. Dl dim bio tinh chinh xlc ciia mo hinh mo phdng bai toln ha thIp MNN, trudc h i t cin phli tinh thir cho mot bii toan don gian, rdi tien h i n h kilm nghiem mo hinh tren co sd ddi chilu k i t q u i tinh toln vdi sd lieu thuc do do ha thap MNN thuc t l tai hien trudng.
5. Da giii bai toln voi nhilu trudng hgp khIc nhau vl cac thong sd cua he thdng gilng tren co sd su dung he phuong trinh vi phan lien tiic ciia ddng nglm, phan tich chuyin dong cua nude nglm theo bai toan khong gian 3 chilu, sii dung phuong phip sai phan hiru han; ddng thdi da tinh toan luu lugng nude nglm chly vio hd mdng vdi dong tham dn dinh, khong dn dinh, ting chua ddng nhlt, khong dong nhlt, co ap va khong Ip. Viec xem x l t kha day du cac ylu td nhu vay lam cho do chinh xlc ciia tinh toan cao hon vl tin cay hon so vdi phuong phip phan tich theo bai toan phang truyen thdng.
6. Dl xult dugc pham vi su' dung thich hgp cho cle phuong phap ha thIp MNN. Dd la, vdi hd mdng cd he sd thIm nhd hon 10"'' c m / s thi nen su dung gilng kim d l ha thIp MNN, voi he sd tham tii lO'^ -^
10-^ cm/s thi nen su dung gilng thudng, voi he sd tham lon hon lO^ c m / s thi phli sii dung cic bien phap ha thIp MNN khIc.
7. D l xuat dugc mot sd each bd tri gilng. Ddi vdi hd mong sau va he sd tham lon, cd t h i bd ti-i 2, 3 hoac nhilu hon sd h i n g gilng. Tinh dugc dd sau dat
gilng, khoing each giira cac gieng trong mot hang, khoang cich giira cic hang gieng vl do ha thIp MNN cua tung h i n g gieng. Ddi voi hd mdng cd ngudn nude bd sung cho nuoc nglm, hoac hd mdng cd cac bien thIm khIc nhau trong cung hd mdng, thi bd tri gilng bd sung phu hgp voi he sd thIm d bien dd.
8. Ddi vdi ngudi thilt k l thi viec lya chgn cong nghe ha thap MNN phai khao sat chinh xac, dly dii cac budc, tinh toan so sinh hieu q u i ky thuat voi su hd trg tinh toln ha thap MNN b i n g phln m l m Modflow hoac cle phln m l m khIc. Khi lira chgn cong nghe ha thIp MNN cin kilm nghiem lai cac thong sd thilt k l thong qua thi nghiem hien trudng d l dilu chinh lai thilt ke cho phu hgp.
9. Ddi vdi cle don vi thuc hien can chii trgng va can nhIc ky viec van dung phuong phip ha thap MNN hgp ly khi xay dung elc cong trmh tren nIn cd he sd tham ldn, xdi nglm a hd mdng se gdp phln dim bio chit lugng cong trinh vl gilm gia thinh xay dung. Co fhl su dung cir chdng tham hoac tudng chin kit hgp ha thIp MNN d l bio ve mii hd mdng, giup giam dien tich tieu nude ciia hd mdng vl khdi lugng dio mdng vl lam ban c h i dugc khdi lugng sat Id cua mai hd mdng do lugng nude dang len va ha xudng trong hd mdng nhanh.
TAI UEU THAM KHAO
[1] Luong Van Anh (2004). Nghien cuu lua chgn so dd hgp ly tinh toln luu lugng cin bom khdi hd mdng khi xay dung cong trinh. Luan van Thac si Ky thuat.
[2] Le Xuan Roanh, Luong Van Anh (2004). Mot sd kit q u i tinh toan vl ha thIp MNN bing gieng dilm tai cong ti-inh cdng Van Cdc-HI Tay cu. Tap chi Nong nghiep va Phat triln nong thon, sd 12.
[3] Luong Van Anh (2009). Xay dung mo hinh mo phdng ciia qua trinh tinh toan ha thIp MNN bing he thdng gilng. Tap chi Nong nghiep va Phlt ti-iln nong thon, sd 4.
[4] Luong Van Anh (2009). Tinh toln ha thIp mirc nude nglm ciia hd mdng bing he thdng gilng.
Tap chi Khoa hgc Ky thuat Thuy loi vl Moi tiirdng, sd 25.
[5] Nguyin Thu Hiln, Hd Viet Hung, Trinh Minh Thu (2007). Phlt triln vl quin ly tai nguyen nude ngam. N h l xult bin Gilo due.
[6] Nguyin Hdng Du'c (2000), Co sd dia chat profgram for estimating parameters of a transient cong trinh vl dia chat thuy van cong trinh, Nha xuat three-dimensional ground-'water flow equations, bin Xay dung HI Noi, USGS, Water-Resources Invesfgations Report 90-
[7] FETTER C. W. Dia chat thuy van ung dung, '^^^8, 43p.
tap 1 va tap 2 (Ngudi dich: Nguyin Uyen va Pham [10] Komkow, L. F. and J. D. Bredehoehf (1978).
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USING THE CONTINUOUSLY DIFFERENTTAL EQUATION OF UNDERGROUND WATER FLOW TO SOLVE THE PROBLEM FOR GROUND-WATER FALLING IN EXCAVATION OF
DEEP FOUNDATION PTT
Luong Van Anh Summarry
The foundation pit bottom is often excavated below the underground water level in construction works in general, hydraulic works in particular. In these cases, the water falling for dry foundation is necessary for the quality and convenient construction of works. The water falling work is implemented by methods that depending on the geological condition, size of foundation pit, excavation method, influence to adjacent works and others. Therefore, the calculation should be careful to meet the construction progress, effect of work, minimum of environmental impact. The method of water pumping-out from surrounding wells is optimal for selecting with advantages as: water level is actively fallen below the pit bottom; hydraulic gradient is generated opposite to the dip direction of foundation pit slope: controls the flowing of sand, the collapse of foundation pit roof; convenientiy for construction. Therefore, the calculation should be careful to meet the construction progress, effect of work, minimum of environmental impact.
Keywords: Evaporation, monitoring well, water pumping-out or compressing, emulation.
Ngudi phan bi6n: GS.TS. Ngo Tri Vilng
