238 TUYEN TAP KHOA HOC CONG NGHE 50 NAM... TAP II
TAC DUNG CUATH^M GIAM SONG TRONG CONG TRJNH DE BIEN a TUYEN DE QUAN TRONG
PGS. TS. Nguyin Van Bdn NCS. Hodng Ngoc Tuan
Summary:
INFLUENCE OF WAVE DECOMPRESSED BENCH FOR SEA DIKE IN IMPORTANT DIKE SECTION
Author of this article presents to readers about typhoon and storm situation along the Vietnam coastline. This area is under the influence of regular natural risk which cause serious damage to coastal inhabitants and infrastructure. Simultaneously, this article also introduce the interface complex of wave decompressed bench of sea dike.
The coastal dike section is designed and constructed with wave decompressed bench offer 2 benefits: Increase the stability level of dike; reduce the wave height to 28% - 30%; suggest the best alternative in dike construction.
I.DATVAND^
Nam trong vimg co tan suat bao lan nhit thi gioi, vimg biln Tay Bic Thai Binh Duong nuac ta chju anh huong lan cua bao nhiet doi la gio manh, d6i chieu, mua to va keo dai va kem theo cac thien tai nhu song lan, nuac dang. Do la nhirng thien tai thuang xuyen doi voi nuac ta noi rieng cung nhu nhiiu viing biln tren thi giai noi chung. Con bao ngay 12 va 13 thang 11 nam 1970 d6 bp vao biln Bangladet da lam cho han 20 van nguoi thiet mang, nuoc dang cao din 6 ^ 7 m. Can bao Wanda xay ra nam 1962 da lam dam va hu hai tren 2000 tau lan nho o viing biln lan can Hong Kong.
Ci viing ven biln Viet Nam, trong cac nam 2005 va 2006, bao gay ra song ldn, gio manh va mua dir dpi da lam sat la nhiiu doan de, ke biln, gay thiet hai nang vl nguai va ciia 6 Da Ning, Quang Nam, Thira Thien Hul...
Vai tac dpng ciia gio bao haiig nam, vimg ba biln nuoc ta da bi nhiiu t6n thit
lan. Song nuac ta con ngheo, hau het cac tuyin de biln tir miin Bic den miin Nam chi
dugc thiet ke de chong gio bao cip 7 va cip 8. Nhim giam bat thiet hai do thien tai gay
ra. Dang va Nha nuac ta dang co chii truang nang cip de biln a nhirng vimg quan
trpng de chong dugc bao cap 10. Vi vay, viec nghien cim thilt kl mat cit de biln co
dang mat cat phiic hgp se la mpt npi dung nghien cuu ciia Chuang trinh nang cip de
bien ma cu the la nghien cuu tac dung ciia thim giam song. Trong pham vi bai vilt nay,
chiing toi giai thieu tac dung giam chieu cao song leo ciia thim giam song.
II. K^T QUA NGHIEN CLFU BU-QC OAU DANH GIA TAC DUNG CUA TH^M GIAM SONG
Them giam song la mot giai phap cong trinh giam chiiu cao song leo, ding thoi dimg ve mat on dinh cua than de biln co tac dung nhit dinh. Khi thilt kl de biln theo tai lieu huang din: "Cu6n tieu chuin nganh 14TCN-130-2002" da neu cong thiic tinh cao trinh dinh de:
Zd = Zip + Hnd + Hsi + a Trong do:
Zd - cao trinh dinh de thiet ke (m);
Ztp - myc nuac bien tinh toan (m);
Hnd - chieu eao nuac dang do bao (m);
Hsi - chieu cao song leo (m);
a - tri so gia tang dp cao an toan (m).
Thong thuang mat cat de bien truac day dang mai nghieng nhu hinh 1.
(1)
K [dug 161 Di liam 2 0 "
Vai ilia ky lliu Jt
' ^ ^
Tufeig da xay
W ^ •«; X- « « '^ y^
Hinh 1. M5l cit ngang de bien mai n g h i e n g
^ ^ ^ 1 "
Loai de mai nghieng co nhuge diem la chieu cao song leo len mai de phia bien kha laij, dl khic phuc nhuge dilm nay nguai ta thucmg thiet kl them giam song a mai de phia biln, dang mat cat thiet ke nhu hinh 2.
/ - Tiim Irt tong lii m.ii 30~
— t).iitLim2l)'"
• Vii lpc Thim gi.ini s6iij;
Hinh 2. Dang mSt dt di bi^'n co tlilm giam song
D I tinh chiiu cao song leo len mai nghieng don cua song bien den tir huang
vuong goc dugc tinh theo cong thuc:
240 TUYEN TAP KHOA HOC CONG NGHE 50 NAM... TAP II
HsP
K.KJC
ix
L* > . * i . (2)
+m Trong do:
KA - he s6 nham va xet d i n tinh tham cua mai nghieng dya vao tinh chat cua vat lieu gia co mai de de tra bang (bang D-1);
Kw - he so kinh nghiem dya theo dai lugng W de tra bang (w - toc do gio bao cap thiet ke (m/s); h - do sau nuoc trung binh cua khu vyc truac de (m); g - gia toc trgng truang) (bang D-2);
Kp - he so tinh doi tan suat liiy tich ciia chieu cao song leo, xac dinh theo eac bang CO san (bang D-3).
Song doi vai mai de co them giam song thi chua co cong thiic tinh tryc tiep ma sir dung cong thirc tinh chieu cao song leo len mai nghieng nhung dimg mc thay cho m.
Vai mc theo ket qua nghien cuu truoc day dugc xac dinh theo 3 truang hgp:
a) Trw&ng hop mdi tren vd dw&i them gidm song co ciing dp dde Am = mo - mr = 0
mc = mT(l-4*J—^-*K,)
^ j
v a : K b = 1 + 3 * ^ b) Trw&ng hffp Am > 0 twc Id mD> mr
mc = (mr + 0.3Am*0.1A^m) c) Trw&ng hffp Am < 0 tire la mD< mr
mc = (mr -I- 0.5Am*0.08A^m)
1-4.5 h'w
1 + 3 ^ K,
K,
(4)
(5)
Trong cac cong thiic tren mr, mo la he so mai doc phan tren va duoi thim giam song; hw la dp sau nuac tren them giam song. Khi them giam song a duai myc nuac tinh thi hw lay gia tri duong, khi cao dp them giam song a tren myc nuac tmh thi hw liy gia tri am, |hw| la gia tri tuyet doi; bf la chieu rpng ciia them giam song (m); Ls la chiiu dai song (m).
Phuang phap dp doc tuong duang thich hgp vai diiu kien:
mT=1.0-f4.0; mo = 1 . 5 ^ 3 . 0
h'w b va 11:1=.0.067; - ^ < 0 . 2 5
Theo phong thi nghiem thiiy lyc Delft (Ha Lan) de nghi liy chiiu cao song leo len mai co them giam song bang chieu cao song leo len mai nghieng dan nhan voi 1 va chi ra rang vi tri them giam s6ng khi a Ian can muc nuac tlnh thi tac dung doi vai song leo chi the hien a gia tri mr, con mo khong co anh huang. Song trong truang hgp (a) khi Am = 0 thi neu them giam song cao han hoac thap hon muc nuac tlnh tinh toan |hw| thi gia tri mc tinh doi chi la mot gia tri cho ca hai trudng hop, nhu vay cao trinh them giam song hw cao han myc nuac tinh toan khong co tac dung lam giam theo chieu cao song leo. Van de nay can dupc nghien ciru them va dugc thi nghiem mo hinh thiiy lyc kiem chung. Nhu vay ta thay viec tinh toan chieu cao song leo khi CO them giam song con can lam sang to them.
Tuy vay de nhan biet tac dung cua them giam song khi ap dung thiet ke cho nhirng doan de bien quan trpng, ehiing toi dua ra vi du tinh toan de minh hpa.
Gia sir co mpt doan de bien cap 1 a viing chju song gi6 Ion de chuan bi dau tu xay dyng doan de nay, ta thir thiet ke theo hai truang hgp. Doi vai truang hgp mai de phia bien la mai nghieng, don c6 he so mai m = 3.0, mat mai de dugc bao ve bang tam be tong lat, chieu cao de la 13 m, than de dap bang dat set pha cat dam nen, mai de phia dong c6 ca rgng 2 m dugc trong co. Doi vai truang hgp dieu kien lam viec ciia de dugc thiet ke vai gi6 bao co cuang dp 90 km/gia; dp cao song bien phia truoc de la /?j = 3.25 m va Ls = 18.0 m; dong thai doan de nay co the chong dugc gio bao co cuang do 110 km/gia vai dp cao song bien dat 4.50 m va Ls = 21 m. (+) Dp sau muc nuoc bien phia truoc de la 7.0 m, thir xac dinh chieu cao s6ng leo Hsi cho hai truang hgp CO thim va khong co them giam song; truang hgp c6 them giam song mai de mi = mo = 3.0. Mat mai va them giam song deu dugc bao ve bang tam be tong lat, chpn chiiu rpng thim giam song bf = 6.0 m; cao trinh them hu' = 1.20.
Vai yeu ciu thilt k l nhu tren ap dung cac cong thiic tinh chieu cao song leo Hsi neu tren de tinh.
Hi/ =
^^^4^*Vf?
4\+m'
Vai vat lieu gia c6 mai de bing tam be tong lat nen KA = 0.90, con Kir tinh cho hai dieu kien:
, w 90 000 /
Cuang do gio bao thiet ke - ^ = ^^^^^^/V9.8*6.0 = 3.258
^ • '' V ^ 3600
242 TUYEN TAP KHOA HOC CONG NGHE 50 NAM... TAP II
Cuang do gio bao kilm tra ^ = ^^°'°^'^/V9.8*6.0 = 3.98
V ^ 3600
Tir bang D-2 ta duge:
Kwtk= 1.235; Kwki= 1.28
Gia tri Kp tra bang D-3 khi bilt hjt.
Truang hop thilt kl ^ - = -^ = 0.464 > 0.3 nen Kp = 1.76 h 7.0
Truang hap kilm tra —^ = — = 0.643 > 0.3 nen Kp = 1.86 h 7.0
Dem cac gia tri da tim dugc thay vao cong thuc (2) tinh ra chieu cao song leo tren mai nghieng dan m = 3.0 va gia co tam be tong la:
0.90*1.235*1.76
HSLik ••
HSLik =
Vl + 9 0.90*1.28*1.86
-J\ + 9
cV3.25*18 = 4 . 7 3
m
xV4.50*21 = 6 . 5 9 m
Neu doan de tren dugc thiet ke co them giam song eiing ap dung cong thiie (2) nhung thay m = mc.
Vai mr = mo = 3.0 tire la Am = 0 ta ap dung bieu thiic tinh mc:
1 - 4 . 0 ^ L. K,
Dem cac gia tri da biet mt, bf, hw da biet de tinh ra mc.
Truang hgp thiet ke:
mc = 3.0| 1 - 4 . 0 — 1 x 2 . 0 = 4.40 K b = 1 +
Truang hgp kiem tra:
3*6 = 2
,1.20
mc = 3.0| 1 - 4 . 0 - ^ 1x1.857 = 4.297
K b = l + I — I = 1.857
Vai gia tri mctk va men da tinh dugc dua vao cong thirc (2) tinh ra chieu cao s6ng leo khi CO them giam song.
0.90*1.235*1.76 HSLtk =
Vl + 4.4- ;V3.25*18 = 3 . 3 2 m HSL.k^'^^:iMm.4^J^X =A.12m
V1 +4.297'
Dem ket qua tinh toan tren so sanh ta thay:
Truong hgp Thl§t k§
Kiem tra
Mai nghieng don 4.73 m 6.59 m
Co thSm giam song 3.32 m 4.72 m
Giam AHsl (m) 1.41 1.87
% giam 29.80 28.37
III. KiT LUAN
Qua nghien ciru ciia chiing toi cho thay, trong ciing dieu kien gi6 bao Ion gay song a viing bien nuac ta thi sir dung them giam song de thiet ke mai ngoai de bien co the giam chieu cao song leo irng voi gio bao cap 9 ~ 10 la khoang 1.40 m -;- 1.87 m, cao dp song leo giam gan 29%.
Nhu vay, img dung them giam song la mot giai phap cong trinh co hieu qua giam chieu cao song leo khi ta can nang cap de bien.
TAI LIEU THAM KHAO [1]. Tieu chuin nganh: 14TCN 130 - 2002.
[2]. Khi tugng thiiy van viing biln Viet Nam. Do Trung tam Khi tugng thiiy van bien bien soan, 1988.
[3]. Dpng luc hpc cira song ven biln (tilng Trung Quoc). Nha xuat ban Thiiy lgi - Dien lyc Trung Quoc, 1992.
