KHOA HQC VA CONG NGHE
M O T SO Y K I E N X A C D j N H L U U L U D N G DONG C H A Y L U CHO C O N G T R I N H C A U T R A N L I E N H U P V U N G T A Y B A C
Tom tit:
Thong qua xay dung thanh cdng 4 cdng trinh cau tran lien hgp tren tuyen dudng Pung Banh - Mudng Ldi, tinh Son La. Bai bao tdng ket kinh nghiem va de xuat, kien nghi each xac dinh mot so thdng so trong tinh toan thuy van cdng trinh thudc vung Tay bic.
Abstract:
Through successful implementation of four complex spillway bridge constructions on Pung Banh - Muong Loi route, Son La province. The newspaper article summarizes experience and recommendation on the determination of several parametrics on hydrological calulation for constructions in the Northwest area.
1. BAT VAN BE
Vung Tay bac bao gom cac tinh: Son La, Lai Chau, Dien Bien, Lao Cai, Yen Bai, Phu Thp, thudc day nui Hoang Lien Son co dieu kien tu nhien tuong doi dac biet, do la su phuc tap ve dja hinh, dja chat, su bien ddi nhanh cua dieu kien khi hau theo tung khu vuc.
Trong 10 nam gan day, vung Tay Bac co dieu kien dau tu xay dung co sd ha tang nhung cdn d muc dp han che. He thdng dudng cap huyen chu yeu vin la dudng dat hoac nen dudng cap VI, V. Cac cdng trinh tren tuyen duoc xay dung vTnh cuu nhung qui md d muc tdi thieu.
Vung Tay Bac cd dudng bien gidi vdi hai nude lang gieng la Trung Qud'c va Lao dai 1.200km. De dam bao an ninh qud'c phdng khu vuc bien gidi Nha nude da cd gang tap trung kinh phi de xay dung he thdng dudng giap bien, phan Idn thudc dudng phi tieu chuan phuc vu cho co ddng luc lupng vu trang ket hpp vdi phat trien kinh te dia phuong. Trong thdi gian qua chung ta da xay dung qua nhanh mang dudng vung Tay Bac, nhung chua cd dieu kien rut kinh
TS. NGO HA SON
nghiem trong thiet ke va thi cdng cdng trinh. dac biet la cac cdng trinh thoat nude qua dudng. Qua khao sat cho thay vao mua lu cac cdng trinh thoat nude thudng bj hu hdng nang, nhu: trdi cdng, tac ngam, hu hdng dudng tran v.v... Mot trong nhung nguyen nhan la do viec lua chon giai phap ky thuat va xac djnh luu lupng nude tinh toan cho cdng trinh chua phu hop vdi thuc te. Tim kiem mot md hinh cdng trinh thoat nude qua dudng, xac djnh luu lupng nude tinh toan v.v... phu hpp vdi dieu kien vung Tay Bac la van de cd y nghia thuc tiin.
Thdng qua 4 cdng trinh cau tran lien hpp da dupe xay dung va dua vao khai thac tu nam 2002 tren tuyen dudng Pung Banh - Mudng Ldi, tinh Son La, bai bao tdng ket nhung kinh nghiem va de xuat, kien nghj each xac djnh mdt sd thdng sd trong tinh toan thuy van cdng trinh thudc vung Tay Bac.
2. BIEU KIEN TIT NHIEN VA HIEN TRANG CAC CONG TRiNH THOAT NUOC QUA BU'fJNG VUNG TAY BAC [3]
Vung Tay Bac cd mat cua tat ca cac dang dja hinh vung nui bao gdm nhung dai ddi nui cao, sudn ddc xen ke vdi cac dai thung lung hep, trung chay men theo cac sdng, sudi. Cd't cao dp tuyet ddi tu 820m den 1.500m. Chju anh hudng cua khi hau nhiet ddi gid mua, chia lam hai mua rd ret: mua mua tu thang 5 den thang 10, mua khd tu thang 11 den thang 4 nam sau. Trong nam lupng mua phan bd khdng deu thudng tap trung vao thang 5 den thang 9 chiem tdi 60% lupng mua ca nam. Mua, bao thudng xay ra tu thang 7 den thang 10, lupng mua trung binh 1.500 1.800mm/ nam.
Tuyen dudng chju anh hudng true tiep bdi cac ddng nude mat la: sudi va cac ddng nude mat tam thdi thudng xuat hien d dudng tu thuy tren sudn nui khi cd mua. Dp ddc theo dudng tu thuy tu dinh nui xudng tuyen dudng phd bie'n tu 25 + 60. Chieu dai dudng tu thuy tu tim dudng len dinh tu 250 + 600m.
Dp ddc ngang tu dudng tu thuy len hai ben phd bien 15 + 45. Qua theo ddi su bien thien cua muc nude sudi cho thay qui luat bien ddi muc nude cac sudi gan
gidng nhau.
Cac cong trinh thoat nuoc qua dtfohg chu yeu vin la cong be tong cot thep (BTCT) va ngam tran lien hpp. Cong BTCT co mat clt ngang hinh trdn dudng kinh 1m, ap dung cho thoat nuoc tren dudng va luu vuc nhd; Cong cd mat clt hinh vudng 1mx1m, 1,5mx1,5m xay da hoc ket hpp tam dan nip BTCT, thudng ap dung cho thoat nude luu vuc Idn. Hu hdng phd bien cua cac loai cdng nay la khi lu ve thudng xuat hien cac canh cay to trdi theo ddng nude gay tic cdng, trdi cdng. Ngam tran lien hpp la su ket hop cua 2 cdng trinh ngam va dudng tran ap dung cho thoat nude luu vuc Idn va ludn xuat hien ddng chay. Cao dp mat ngam cao hon cao dp day long sudi tu 1,5 2,0m vdi so lupng cua ngam 3 + 5 cua, chieu rdng thdng thuy 1,5 + 2,0m; Oudng tran ket cau be tdng xi mang (BTXM) cd chieu dai 30 -=- 50m tuy theo chieu rdng long sudi. Trong qua trinh khai thac cdng trinh, phan ngam thudng hay bi lap bdi bun dat, canh cay v.v...
nen hieu qua khai thac kem. Hinh 1 la anh chup cdng trinh ngam tran lien hop khi mdi xay dung xong va sau 5 nam khai thac. Chinh vi vay ma nhdm thiet ke da lua chon md hinh cau tran lien hpp ap dung cho vung Tay Bac.
a. Khi moi xay dung xong
b. Sau 5 nam khai thac
Hinh 1. Anh chup mot cong trinh ngam tran lien hgp
3. QUI MO CAU TRAN LIEN HOP VA XAC 0|NH LUU LLTCfNG NUOC TINH TOAN QUA CONG TRiNH
4 cau tran lien hop xay dung tren tuyen dudng Pung Banh - Mudng Ldi, tinh Son La duoc thiet ke vdi cac hoat tai: doan xe H13 va X60; doan ngudi 300daN/m2.
Qui md xay dung: 3 cau tran dupe xay dung d phia dau Pung Banh tren cung mdt doan sudi, cd chieu dai dam ban I = 5m; khd cau K = 7m; chieu dai dudng tran b = 50 + 70m phu thupc dia hinh vi tri dat cdng trinh; 1 cau duoc xay dung d phia dau Mudng Ldi cd 2 cua; cau tao gan gidng cac cau tran ben Pung Banh vdi chieu dai dudng tran b = 73m [4, 5].
Theo tai lieu [1] cau, cdng la cdng trinh vTnh cuu cd thdi gian phuc vu tren 100 nam. Oe dam bao cau va cdng lam viec binh thudng trong sud't thdi gian khai thac, can thiet ke theo mdt tan suat lu dupe qui dinh tuy theo tam quan trong cua cdng trinh va cap dudng. Tan suat lu dung cho dudng d td theo Tieu chuan Viet Nam TCVN 4054-2005 vdi dudng cap III - VI cho cau nhd, cdng la 4%, tuc la cu 25 nam cd mot lan xuat hien lu Idn hon hay bing nd. Ban than khai niem ve tan suat lu thiet ke khdng ndi rd nam nao, ngay nao xuat hien lu thiet ke, ma thuc te chi ndi len muc dd quan trong cua cdng trinh thiet ke. Theo Tieu chuan Lien Xd (cu), tan suat lu dung cho dudng d td cap IV VI ddi vdi cdng trinh cau nhd la 1:50, cdng la 1:30. Day la van de het sue quan trong lien quan den xac dinh qui md va giai phap ky thuat cdng trinh thoat nude ngang dudng.
Khi tinh toan thuy van cho cdng trinh cau tran lien hpp dua tren so lieu dieu tra khao sat, nhdm thiet ke su dung phuong phap xac dinh luu lupng tinh toan khi cd nhieu nam lien tuc quan trie thuy van Qpo/o. Npi dung chinh cda phuang phap la mdi nam chon mdt lu cd luu luang Idn nhat va thdng ke thanh mdt chudi dai nhieu nam lien tuc; tinh luu luang trung binh:
n
^tb n (D Trong dd:
Q - luu luang Idn nhat cua nam;
n - so nam quan trie lien tuc.
KHOA HOC VA CONG NGHE
Lau lugng thiet ke theo tan suat P°= la QP% duge xac dinh theo cong thuc:
Qp%=Q*-KPfc (2)
Trong do he so Kpo/o la ham phu thupc
(3)
He so bien hoa Cv co y nghTa chi ro do bien hoa cua lu so voi lu trung binh trong chudi thong ke lien tuc va duge xac djnh bang cong thuc:
8
^ - (4) C„ =
Trong do:
8 - sai so quan phuong;
8 = Z ( Q : - QtJ2 (5) He so phi doi xung Cs phan anh dac tinh khdng ddi xung ve cudng dp lu ma he sd Cv chua chi ra duge.
He sd Cs thudng duge xac djnh dua vao cac sd lieu thdng ke thuc te trong nhieu nam.
Trinh tu cac budc xac djnh luu lugng ddng chay lu cho 4 cdng trinh cau tran nhu sau:
1. Chon tan suat lu P;
2. Xac djnh luu lugng ddng chay lu theo Tieu chuan 22TCN - 220-95 cua Bp Giao thdng van tai Viet Nam 'Tinh cac dac trdng ddng chay 10" vdi tan suat ID P;
3. Xac djnh luu lugng ddng chay lu theo so lieu dieu tra lu tai dja phuong va khao sat lu tai hien trudng;
4. So sanh lua chon luu lugng dinh lu tinh toan;
5. Kiem chung dp tin cay cua cac thdng sd lua chon thdng qua sd lieu khao sat lu trong 5 nam khai thac cdng trinh gan day, dac biet la luu lugng trung binh Qt b lam co so du bao luu lugng dinh lu.
Ba cau tran lien hgp dau tuyen thudc xa Pung Banh la: Na Lien, Phieng Ban 1, Phieng Ban 2 bd tri gan nhau tren cung mdt doan sudi, nen luu lugng dinh lu xac djnh tai Na Lien (phia ha luu) lay tuong tu
cho cau tran Phieng Ban 1, Phieng Ban 2. Cau tran lien hgp Ban Ldi thudc xa Mudng Ldi, tinh Lai Chau, cd luu vuc thu nuoc nim tren ranh gidi giua 2 tinh Son La va Lai Chau, each tram khi tugng Sdng Ma (San La) la 52km va each tram khi tugng Oien Bien Phu (Lai Chau) la 56km. Khoang each tu luu vuc den 2 tram khi tugng gan bing nhau, trong khi dd Nha nude chua ban hanh ban do dudng dang trj lugng mua ngay theo tan suat HP %, day la van de rat khd khi tinh toan, thiet ke cdng trinh. Neu chon theo tram khi tugng Oien Bien Phu thi lugng mua ngay ung vdi tan suat P = 10% la H1 0 % = 167mm va khi dd luu lugng dinh lu qua cdng trinh len den Q = 350m3/s, neu lay theo tram khi tugng Sdng Ma la H1 0 %= 97mm khi nay luu lugng dinh lu qua cdng trinh la Q = 85m3/s, chenh nhau 4,12 lan. Rd rang viec lua chgn sd lieu cua tram khi tugng nao se lien quan den qui md xay dung cdng trinh. Nhdm thiet ke ap dung phuang phap ndi suy tuyen tinh, do khoang each tu luu vuc tinh toan den 2 tram gan bing nhau, nen lugng mua ngay ung vdi tan suat P duge tinh bing gia trj trung binh giua 2 tram
do. Cu the: , n
167 + 97 x
Hio% = = 132(mm) (6)
Cac thdng sd tinh toan dac trung dinh lu [2] xem Bang 1.
Ap dung cdng thuc:
Qp = Ap-cp-Hp-F., (m3/s) (7)
- Chieu dai binh quan sudn ddc luu vuc:
I000F
b. = (8)
Dac trung dja mao cua sudn ddc:
b0'6
(9) Xac djnh dac trung dja mao thuy van cua long sdng:
1000Z
vl/4 mll)i\F"\<p.H p W j Ket qua tinh luu lugng dinh lu xem Bang 2.
(10)
Bang 1. Cac thdng so tinh toan dac trung dinh lu
TT Thong so Ky
hieu Cau tran Na*
Lien Cau tran Ban Ldi 1 Dien tich luu vuc (km2) F 42 33 2 Chieu dai long suoi chinh (km) L 15 2 3 Tong chieu dai long suoi nhanh (km) li 30 12 4 Do doc long suoi chu (%o) li 15 15 5 Dp doc sudn ddc (%o) ls 300 300 6 Luong mua ngay ung voi tan suat 10% (mm) Pio% 97 132 7 Dat cap III
8 He so dong chay lu <P 0,55 0,55 9 He so nham sudn ddc ms 0,15 0,15 10 He sd nham long sudi m. 7 7 11 Dien tich hd ao trong luu vuc = 0 5, 1 1
Bang 2. Ket qua tinh luu luqng dinh lu qua cau tran
TT Thong so Ky
hieu Cau tran Na Lien
Cau tran Ban Loi 1 Chieu dai binh quan sudn ddc luu vuc (m) bs 526 1,309,5 2 Dac trung dja mao cua sudn ddc *s 10,5 16,1 3 Tir <j>s tra bang ta duoc xs (phut) 92 146,5 4 Dac trung dja mao thuy van long sudi 125,9 16,6 5 He sd tuy thugc vao dac trung dia mao Ap 0,020 0,067 6 Tinh luu lugng nuoc Ion nhat ung vdi tan suat
P = 10% cua lu xay ra tren sudi (m3/s) QP 45,5 160,3
Xac djnh luu lugng dong chay lu dua tren sd lieu dieu tra hien trudng: trong 50 nam, tuong ung tan suat P = 2%, luu lugng dinh lu cao nhat nam 1975 la Q2o/o = 42,1 m3/s tai ban Na Lien va Q2„/o = 243,0m3/s tai Ban Ldi. Nhung de xac djnh luu lugng dinh lu cao nhat irng vdi tan suat P = 10%, ta ap dung cdng thirc tinh thdng qua quan he Qt b va Q2 %:
Q,b = ^ (11 a) va Q,,„ = Q,bKl0% = Q2% (11 b)
Trong dd:
K2 % - he so phu thudc he so bien hoa Cv va he sd lech Cs. Viec xac djnh 2 he sd phu thudc nay cung gap khd khan bdi chua cd sd lieu dieu tra cho tirng con sudi cu the. Nhung nghien ciru cua GS. TSKH Nguyln Xuan True [1] mdi chi de cap den cac sudi cd luu vuc thu nude Idn ciia vung Tay bac, nhung xet ve ban chat thi viec van dung cac sudi tuong duong va da cd so lieu dieu tra khi xac djnh 2 he so Cv, Cs cd the chap nhan duge, vi mire dp bie'n hoa cua lu so vdi lu trung Wnh va dac tinh phi ddi xung ve cudng dp lu theo thdi gian cua cac ddng sudi viing Tay bac la tuong ddi gidng nhau. Nhdm thiet ke chgn sudi tai ban Na Lien va sudi d Ban Ldi tuong duong sudi Nam Rom (Dien Bien) va cd gia trj Cv = 0,65 va Cs = 1,95, tra bang ta duge K2o/o = 2,845 va K10o/o = 1,815 thay cac gia trj nay vao cdng thuc (11b) ta tinh duge luu lugng ddng chay lu tai cau tran Na Lien Q1 0 % = 26,9 (m3) va tai cau tran Ban Ldi Q10% = 155,0 (m3);
So sanh luu lugng dinh lu duge tinh theo Tieu chuan 22TCN - 220-95 vdi luu lugng dinh lu dua tren sd lieu dieu tra hien trudng cho thay luu lugng dinh lu tinh theo tieu chuan Idn hon, de dam bao an toan cho cdng trinh chon luu lugng dinh lu tinh theo tieu chuan.
Cu the: chon luu lugng dinh lu tinh toan Q1 0 % = 45,5m3/s cho tinh toan, thiet ke cau tran lien hgp Na Lien, Phieng Ban 1 va Phieng Ban 2; chgn luu lugng dinh lu tinh toan QWA = 160,3m3/s cho tinh toan, thiet ke cau tran lien hgp Ban Ldi.
4. XAC 0|NH LUU LUONG NUOC QUA CAU VA QUA DUONG TRAN
Xac djnh luu lugng nude qua cau la mdt van de mdi khi ket hgp cdng trinh cau vdi dudng tran, vi lien quan den qui md xay dung, chat lugng khai thac cdng trinh. Nhdm de tai chgn luu lugng trung binh Qt b lam luu lugng nude qua cau. Ve ban chat toan hoc thi luu lugng trung binh Q,b chinh la ky vong toaritipc la mdt trong nhung dac trung so ciia ham thdng ke ndi len ban chat cda ddi tugng nghien ciru. Xac suat xuat hien luu lugng dinh lu vugt qua luu lugng trung binh la khdng Idn, tuy nhien can can cu vao thuc te khai
KHOA HOC VA CONG NGHE
thac cong trinh trong nhieu nam de danh gia hieu qua cda giai phap. Luu luong trung binh tinh cho cau dua tren Q1 0 % theo cdng thuc (13b) ket qua tinh xem Bang 3:
Bang 3. Luu luqng nuac qua cau, dudng tran
TT Thong so
Cau tran lien hgp
TT Thong so
Lien Na Ban 1 Luu luong tinh toan Q10% , (m3/s) 45,5 160,3 Loi 2 Luu luong trung binh de xac djnh khau do cau, (m3/s) 25,1 88,3 3 Luu luong de xac chieu dai duong tran (m3/s) 20,4 72,0
g - gia toe roi tu do (9,81 m/s^).
Ket qua tinh kha nang thoat nude qua cau xem Bang 4.
Kiem toan kha nang thoat nude qua dudng tran:
dua vao cdng thuc dap tran dinh rdng [1]:
3
Qt r = an gmbV2^H0^ (13)
Trong dd:
Qt r - luu lupng nude qua tran;
an g - he so triet giam do ha luu bj ngap, phu thudc ti so Kn = hr/Hn = 0,8 tra bang ta duoc an g = 1;
hn - chieu sau ngap d ha luu tinh tu mep dudng tran (0,48m);
m - he sd luu luong khi dap chay theo che dp tu do (0,32);
b - chieu dai dudng tran;
- Ket qua tinh kha nang thoat nude qua dudng tran xem Bang 4.
Bang 4. Kha nang thoat nuoc qua cau va dudng tran
TT Thong sd Ky
hieu
Cau tran lien Ky hup
hieu
Na Lien Ban Loi 1 Tiet dien cau 4,4x3,0 5,4x3,5 2 So luang cua thoat nude 1 2 3 Chieu dai dudng tran (m) b 67,1 73 4 Kha nang thoat nude qua cau (m3/s) Qc 39,83 93,43 5 Luu luong nude qua tran (m3/s) Qtr 64,63 70
5. KIEM TOAN LUU LUONG NUQC SAU 5 NAM DUA CONG TRiNH VAO KHAI THAC (2002 - 2006)
Trong 5 nam dua cdng trinh vao khai thac thi mua lu nam 2004 la Idn nhat, tuong ung tan suat xuat hien P = 20%:
- Cau tran lien hpp Na Lien nude dang den sat day ban mat cau, tuc la luu lupng dinh lu dat bang luu lupng thoat nude tinh toan cho cau Qc = 39,83m3/s.
Kiem toan lai gia trj cda Qt b: Q = Q»L = = 28,45m3 (14)
K 1 4 Dua tren ket qua tinh toan cu the cho 2 cau tran
lien hop ndi tren cho thay ti le giua luu luang nude tinh toan qua cau vdi qua dudng tran la K = 1,23.
Ket qua nay dang quan tam va can duac kiem nghiem trong thuc te.
Kiem toan kha nang thoat nude qua cau va qua dudng tran sau khi xay dung xong cong trinh la can thiet, vi thiet ke cau va dudng tran dua tren cau tao djnh hinh, dja hinh khu vuc xay dung va hinh dang mat cat ngang long sudi, de tren ca sa dd danh gia phuang an, giai phap ky thuat de xuat.
Kiem toan kha nang thoat nude qua cau: xet trudng hap cau lam viec d che do ha luu cau bj ngap, day la trudng hap bat lai nhat. Ap dung cdng thuc:
Qc =e\|/Qd V
/2g(Hn + H0- hs) (12) Trong dd:
Qc - kha nang thoat nude qua cau;
e - he sd thu hep ddng chay (0,65);
vj/ - he sd van tdc (0,85);
cjd - tiet dien cau;
Hn - chieu cao dap nen dudng (3,92m);
H0 - chieu cao cdt nude tinh tu mep nen dudng phia thuang luu (0,6m);
hs - chieu sau nude chay luc tu nhien tai long sudi a ha luu dudng tran, lay bang cdt dinh cau;
Trong do: K20% duoc xac dinh d Phu luc 1 [1], vdi Cv = 0,65; Cs = 3CV; K2 0% = 1A chon tuong ung vdi sudi Nam Rd'm. Cho thay luu lugng dinh lu trung binh la 28,45m3 so vdi tinh toan ly thuyet Qt b = 25,1 m3/s (Bang 3) Idn hon 1,13 lan.
- Cau tran lien hgp Ban Ldi nude dang each day ban mat cau 0,65m. Mat cat ngang chu vi udt cd kich thudc 5,4m x 2,85m x 2 cua thoat nude, luu lugng
nude qua cau thuc te luc nay la:
Q fu c = 0,65.0,85.5,4.2,85.2.72.9,8^ (15) Ah la chenh cao dp ddng chay giua thugng luu va ha luu cua cau, An = 0,5m, thay gia tri cua h vao cdng thuc tren ta tinh duge:
Qfuc = 53,24m3/s (16)
Kiem toan lai gia trj cua luu lugng nude trung binh
Q,b' O 53 24
Q V 2 0 ° b J J i iH TO 3 /
lb = = =3 8 m / S H7\
K™„ 1 4 1?
l v 20% 1
Luu lugng trung binh Qt b = 38m3 so vdi tinh toan ly thuyet Ql b = 88,3m3/s nhd thua 2,3 lan, nhu vay viec chon kich thudc cau chua hgp ly, thien ve an toan.
Qua khao sat 4 cdng trinh cau tran lien hgp ndi tren cho thay:
- Cdng trinh an toan sau 5 mua lu, trong dd mua lu nam 2004 theo danh gia cua nhan dan dia phuang la Idn, tuy chua bang lu lich su nam 1975. Cdng trinh ben vung, dam bao khai thac thudng xuyen, hieu qua;
- Kiem toan tri so luu lugng trung binh Qtb giua thuc te vdi tinh toan ly thuyet tai cau tran lien hgp Na Lien Idn han 1,13 lan, tai cau tran lien hgp Ban Ldi nhd hon 2,3 lan. Sai sd tuang ddi Idn ve luu lugng trung binh giua ly thuyet tinh toan vdi quan sat thuc te tai cau tran lien hgp Ban Ldi, cd the do chu ky quan sat chua du Idn; lay he so Cv, Cs cua sudi Nam Rd'm vao sudi Kia la sudi bd tri cau tran lien hgp Ban Ldi chua phu hgp, van de nay can duge tiep tuc nghien cuu.
- Odng thai ddng chay lu anh hudng khdng nhieu den mat cat ngang ddng chay va hinh dang dudng bd;
- Cho phep khang dinh su phu hgp cua md hinh cau tran lien hgp ndi tren, kien nghi ap dung cho cac tuyen dudng cap VI -=- V hoac dudng phi tieu chuan vung Tay Bac va can duge nghien cuu nhan rdng.
Hinh 2. Anh chup cau tran lsla Lien (2006)
Hinh 3. Anh chup cau tran Ban Loi (2006) 6. KET LUAN, KIEN NGHj
Bai bao mang tinh tdng ket kinh nghiem thuc tiin xay dung cdng trinh cau tran lien hgp vung Tay Bac, va da giai quyet mot sd ndi dung chinh nhu sau: Ida chon tan suat lu P = 10%, xuat phat tir nhu cau, kinh nghiem thuc te khi xay dung cdng trinh cau tran lien hgp. Day la van de quan trong lien quan den qui md cdng trinh va vdn dau tu; xac djnh lugng mua ngay cho luu vuc thu nude thudc vung Tay Bic bing phuang phap ndi suy tuyen tinh theo khoang each tu cac tram khi tugng, day la phuang phap tinh gan dung trong dieu kien nude ta chua nghien cuu va ban hanh ban dd dudng ding trj lugng mua ngay HPo/o; phuang an phan luu lugng ddng chaykdG ddi vai cau la luu lugng trung binh, luu lugng cdn lai tinh cho dudng
KHOA HQC VA CONG NGHE
tran qua thuc te khai thac 4 cau tran lien hpp cho thay phuong an nay la hop ly, vua dam bao khai thac duong tdt, vua phu hop vdi kha nang dau tu kinh phi;
xac dinh he KP%, he so nay phu thudc vao tan suat xuat hien lu P va he so bie'n hoa Cv, he so phi ddi xung Cs, hai he so nay duoc xac djnh dua tren quan trac thdng ke nhieu nam cho tirng ddng sudi cu the.
Tuy nhien cac sudi d vung Tay Bac cung tuan theo qui luat ddng chay ciia cac sudi cd luu vuc thu nude Idn, nhu: muc dp bie'n ddng ciia ddng chay; tinh ddi xung cua cac dinh lu theo chu ky nam v.v... do vay, chiing tdi kien nghi van dung cac sudi cd luu vuc tuong irng d viing Tay Bac da cd sd lieu dieu tra thdng ke de xac dinh gia tri he sd Cv, Cs. Qua kiem toan cho thay sai sd nay cd the chap nhan dupe.
Nhung can tiep tuc nghien cuu dua tren thdng ke nhim de du bao luu lupng dinh lu.
Dua tren ket qua quan trac thuy van nhieu nam lien tuc, la mdt trong nhirng phuong phap thudng hay su dung va cd dd tin cay cao, khi xac djnh luu luong dinh lu tinh toan theo tan suat, day la phuong phap thudng duoc ap dung de ddi chung vdi«cac phuong phap mang tinh ly thuyet. Nhdm thiet ke da su dung phUOng phap nay d 2 ndi dung: xac djnh luu lupng
ddng chay lu tinh toan khi cd ket qua quan trac dinh lu cao nhat trong 50 nam va du bao luu luong dinh lu trung binh Qt b dua tren ket qua quan trac trong 5 nam lien tuc sau khi xay dung xong cdng trinh. Ket qua dat dupe vdi dp tin cay chua cao, can tiep tuc nghien ciru theo hudng thdng ke hien trudng •
TAI LIEU THAM KHAO
[1]. Nguyen Xuan True. Thiet ke dudng d to, cdng trinh vupt song. Tap 3. Nxb Giao due. Nam 2000.
[2]. Tieu chuan nganh 22TCN - 220-95.
[3]. Trung tam Ky thuat cac cdng trinh dac biet. Ho so khao sat phuc vu budc thiet ke ky thuat, cac ban ve thi cdng. Ha Ndi, nam 2001.
[4]. Trung tam Ky thuat cac cdng trinh dac biet. Ho so thiet ke ky thuat, cac ban ve thi cdng. Ha Npi, nam 2001.
[5]. Cau ban be tdng cd't thep md nhe be tdng.
Thiet ke dien hinh 531-11-02. Ha Ndi, nam 1985.
* Hoc vien Ky thuat Quan su
PHIEU DAT MUA
T A P C H I C A U D U 6 N G V I E T N A M Ten co quan (ca nhan) dat mua:
Dja chi nhan tap chi:
Oien thoai:
Oat tap chi moi thang: cudn, ke tCr thang nam 2009 den het thang nam 2009
So tien: x 18.000d/cu6'n x thang =
Thanh tien: BangchQ:
Ngay thang nam Thu truang dan vj (hoac ca nhan)
Phieu dat gui ve: KVt§n- d 6 n9 d i'u
Tap chi Cau duong Viet Nam Tang 7 - toa nha PMU1 308 Minh Khai - Ha Npi
