Cong trinh Khoa hoc
ANH HUONG CUA CAC THANH PHAN TRU CAU BE CAO DEN XOI cue BO TRU CAU
NGUYEN DANG P H O N G Bd mon Thiiy luc - Thdy viin Tnrdng Dgi ligc Giao thdng Van tdi
Tom tdt: Bdi hdo trinh bdy thi nghiim xoi cue hg Iru cdu be cao trong diiu kiin dong chdy on dmh. xdi nudc Irong Muc dich de ddnh gid anh hudng cua cdc thdnh phdn tru cdu be cao din chiiu sdu hSxdi cue bg. Kel qua cho thdy, khi ^ „ , ^ / h> 2 5 % thi hSxot chi chiu dnh hudng cua nhom CQC; khi H^.„^ / h<0 hi coc la thdng so chinh anh hudng den chieu sdu ho xoi
Summary: Tests on scouring at complex piers carried out under steady clear-water flow conditions are presented. The aim of this article is to evaluate the contribution of complex pier components on the total local scour depth The results showed that when H^„^ / h>25% Ihe scour hole is only influenced by the group piles, while H^,,^ / h<0 ihe scour hole is mostly influenced by the pile cap.
I . D A T V A N D E
Yeu c i u ve mat kmh tfi, dia ky thuat, ket cSu, cac c d n g trinh c^u t h u d n g d u o c thi^t ke tru cSu dang hinh hpc phuc tap. Dang pho biSn nhat ciia tru cSu la than tru dat tren be coc va dudi be la he thong nhom coc (hinh 1) Nghien cuu vS xoi cue bp tru cau phirc tap d u g c nghien cu'u nhieu trong nhirng nam gan day.
Cac nghien cuu tieu bieu ve xoi cue bg tru cSu phuc tap hien nay phai kk dSn la nghien cuu cua Coleman (2005) [4], ciia Sheppard va Renna (2005 va 2010) [6], cua E.V. Richardson va S.R Davis [5], ... T h e o nghien cuu ciia Coleman, chilu sau ho xdi tru c i u p h u c tap la c h i l u saii xoi ciia mpt try cm t u a n g duong, khong phan biet cac thanh phfin ciia tru cau. T h e o nghien ciiu ciia Richardson, c h i l u sau ho xoi la cong tac dung c h i l u sau h 6 xoi cua cac bp phan tru cau, chilu sau ho xoi cua bo phan phia tren la tiln de cho viec tinh c h i l u sau h 6 xoi ciia bg phan phia dudi. Con theo nghien ciru ciia Sheppard, chieu sau ho xoi tru cau be cao la c h i l u sau h6 xoi cua mpt tru c i u dac co d u d n g kinh h'mg t i n g ciia d u o n g kinh t u a n g d u a n g c a c bo phan tru cau. N h u vay, theo nghien cuu ciia cac tac gia, khi cac bg phan tru cSu ngap trong d o n g chay d l u anh hirong den chieu sau h o xoi cue bo tru cau.
Muc dicli cua nghien ciru nay la 46 danh gia anh huong rieng oiia cac thanh ph5n tru c i u be cao dSn chiSu sau h6 xoi cue bo tru e l u be eao. Voi ly do nay, nghien cilu s u d u n g p h u o n g phap cua Sheppard va Renna ( F O O T ) , cua E.V Richardson va S R. Davis ( H E C - 1 8 ) dS so sanh, danh gia va phan tich.
3 6 Tap chi K H O A H O C G I A O t H O N G V A N T A I 8 6 4 7 - 0 8 / 2 0 1 5
II. THI NGHIEM ANH HUONG CAC THANH PHAN TRU CAU BE CAO DfiN HO XOI
2.1. Chuan bj va trinh ty thi nghiem
Thi nghiem ve anh hudng ciia cac thanh phan cua tru cau be cao den chieu sau h6 xoi dugc thuc hien tai Trung tam nghien curu thuy luc thupc vien Khoa hpc Thuy lgi Viet Nam nam 2012.
Mang thi nghiem la mang kinh co be rpng lm, cao 1,2m, chieu dai phan thuc hien thi nghiem la 12m. He th6ng thi nghiem la he thong tuSn hoan, gIm mang thi nghiem, he thong kenh din thugng luu, ha luu, be chii'a. Nudc thf nghiem dugc bam tir bl chira qua mang do luu lugng vao kenh dan thugng luu den van dieu tiet thugng luu, vao mang thi nghiem, din van dieu tilt ha luu, kenh ha luu va chay l?i be chira.
Thi nghiem dugc thuc hien vdi luu lugng 401/s, vdi hai chieu sau dong chay 1 Scm va 21 cm (cd luu toe trung binh 0,22m/s va0,19m/s; so Froude tuong ung la 0,126 va 0,092).
Cat trong thi nghiem la cat song Hong lay tai bai cat An Duong, Ha Ngi dugc phan tich thanh phin hat tai Trung tam Thi nghiem Cong trinh, trudng Dai hgc Giao thong Van tai. Kit qua phan tich dugc cho thay phan ldn cat hat co dudng kinh trong pham vi tir 0,1mm den 0,4mm, CO dso = 0,27mm; he so hinh dang hat Oy = 1,29 < 1,30, do do dugc coi la cat hat dlu.
Vdi \o^\ cat nay, luu t6c gidi han khong xoi bang 0,30m/s, nhu vay thi nghiem se thuc hien trong dieu kien xoi nudc trong.
Thi nghiem dugc thuc hien vdi 03 truong hgp: 1) to hgp than try va be cpc, 2) rieng be cgc va 3) rieng than tru.
Sau khi cat trong mang thf nghiem dupc lam phang, tii'ng bo phan try ciu dugc g^n chat vdi mgt bg ga, bg ga nay lai dugc gin chat vdi thanh mang thi nghiem. Bg ga thi nghiem glm mgt thanh thep nSm ngang va mgt thanh thep thang dirng dang hinh hop dirng, phia dudi thanh thep thing dirng c6 g^n mgt ban Mica nim ngang de gan vdi try cau. Lien ket giua hai thanh thep bing mot dng thep hinh hop cd kich thudc trong bang kich thudc ngoai ciia thanh thep thang dirng, thanh thep thang dung gan vdi try se djch chuyen theo phuang thang dung trong ong thep lien ket (hinh 2).
• ' ' ^
Hlnlt 1. Mo hinh tru cdu b^ cao Hinh 2. Lien ket bo phdn Iru cdu irong thi nghie
M
vdi thdnh mdng kinh.
Tap chi KHOA HOC GIAO THONG VAN TAI S6 47 - 08/2015 37
Cong trinh Khoa hgc
Bdn^ I. Kit qud thi nghiem cdc thdnh phdn iru cdu be cao
H^,(cni) I MNIcml ^ TT^Cmin) I h..,.(crn).
Ghi chu: H,;jt - cao do ddy cdc bo phgn so vdi ddy cdt
Sau khi cd djnh bp phan tru cau vao thanh mang kinh bit diu thi nghiem. Ban dau day cac bp phan tru cau dugc dat cao hon day cat mdt khoang 10,5cm va quan sat su djch chuyen cat d -xung quanh try cau. Quan sat sy chuyln dong cua cat trong khoang 15 phiit ma khong thay cat djnh chuyln tiln hanh ha bp phan tru ciu xuong va lai tilp tyc quan sat chuyln dpng ciia cat.
Cu ha dan bg phan thi nghiem nhu vay cho din khi quan sat thiy cat co su djch chuyln co nghTa d vi tri do bit diu chiu anh hudng ciia bp phan try cau thi nghiem va luc nay tiln hanh do luu toe xung quanh bg phan tru ciu va luu tic trong mang thi nghiem. Sau khi do xong luu toe lai tiep tuc ha bp phan tru ciu thi nghiem xudng khoang nhat dinh de cho xoi day cat, sau khi h?
xuong khoang 3 din 4 tiing thi tiln hanh do luu tic. Dirng thi nghiem sau khoang 5 den 6 gid khi xoi ket thiic.
T H
T N Sliepp
Richar
T N
"S"
Ricliat
T N Shepp
^'^'
T N Sliepp
R ^ h i i r N h 6 m coc
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%
l ) H „
.12 ; wii S'),69 \ N - i
.17
"
62.90 .18
'
49,26
.16 2K.2
3 ) H
im
71.5 25.11
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7 1 H
"
60,5^
.17
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54.') IX.'
Bang 2. Anh B i . , .
,1;, : "
huang cua cdc
T h S n I r u
, = I O ! > m m ; M N ^ 2 i a m m
0 ; 11,11
B.21 i 12.1 18 ; li')
0 ; oil 0,28 \ 11.4
77 i 5VJ
™ = 4 S m m ; M N = 2 1 0 m m 0 ; 11.11
18,85 i 21.4
.15 ; 2J.J 0 ; 11 a
6.19 1 7 0 78 1 51.^
„ , = O m m ; M N = Z I O m m .10 ; Hi,-"
2\.T> ; 2r,,2
56 \ 33.3
„ = - 2 2 , 4 m m ; M \ = 2
13 1 mil 2 7 , M ; 24.f,
8.1 : 4l.r, 0 I 11.11
12,01 ; • 145 76 1 45.1
Omm 0 '. 11.11
22,52 ; 211.4 80 ; i-j-
hdnh ph dn tru cdu bf cao den chiiu sdu
N h 6 m c c c
li„,i 1 ,^
B f c o c
ho xdi
T h S n t r M
( m m )
%
2 ) H „ = l O K m m ; M N = 1 8 0 m m
4 1 76,0.1
.18
urn
S5.'J 2S.'J
0 ; 11,0 11.22 1 I2.~
15 ; /I.4 0
1,29
80 11.11 1.5 5-17
• l l H t „ = - l 5 n i m , M S ^ 1 8 0 m m 49
79,31
19
m
^i.ii 25.3
0 i IIM 23,14 ; 211,7
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9.2'!
83 (HI K3 53,1
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80,29
40
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, 1 ; » «
30,95 ; 23 3
57 ; 31,3 0
21,71
86 11.11
lf.,3 46 >,
S ) H , , . = - 2 1 . 4 m m ; M N = 1 8 0 m m 0
75,26 39
O.ll 55 4 li/l)
41 1 UK, 12.51 ; 24.0 82 ; 411,11
0 27.97
84 0.11 211,6
2.2. Anh hirdng ciia cac thanh phan tru cau den chilu sau hd xoi
De nghien cuu anh hudng ciia cac thanh phin tru ciu be cao din chilu sau hi xoi cue bp
38 Tap chi KHOA HQC GIAO THONG VAN TAI S6 47 - 08/2015
de tai nghien ciru thi nghiem xoi eye bg ciia toan try ciu vdi chieu cao cgc (H^uc) bang I0,5cm;
4,5cm; 0cm, be cpc ngap Yz trong day cat va be cpc bj ngap toan bp trong day cat (thi nghiem toan bg tru ciu da dugc thyc hien nam 2011 d trudng DH Thuy lai), sau do tien hanh thi nghiem vdi tiing thanh phin tru ciu. Khi do chilu sau xoi do cac bg ph^n duac xac dinh nhu sau:
Chieu sau xdi do than tru va be try: theo kit qud thi nghiem, Chieu sail xoi do nhom cpc: /it-nA"m - h^- K-ihon - K^hc
Trong dd: h^, hc.ti,am hc-b^ hc-nhom - chieu sau xdi toan bp tru cau; do than tru; be cgc; nhom cpc gay ra.
Anh hudng ciia cac thanh phan tru cau be cao den chieu sau xoi dugc the hien trong bang 1, 2 vacac hinh 3, hinh 4.
Anh hudng ciia cac thanh phan try cau dugc so sanh vdi phuong phap ciia Sheppard, Richarson & Davis (bang 2 va hinh 3).
Hinh 3. Anh hudng cua cdc thdnh phdn tru cdu din chiiu sdu hd xdi theo thi nghiem
Hcoc = losmm; MN = 210mm = 105mm; MN = IBOmm
l l I 10'
-III -ll
H}nli 4. So sanh anh huang cua cac thanh phdn tru cdu be cao den chieu sdu ho xd
Tap chi KHOA HOC GIAO THONG VAN TAI S6 47 - 08/2015 39
Cong trinh Khoa hgc
III. B i \ H LUA.N KETQUATHi ^(;iiIEIVI 3.1. Ve rieng ket qua Ihi nghiem
- Trudng hgp thi nghiem t l hgp be cgc vdi than try: Khi ha day be cgc din each day cat 2cm (Hc^ = 2cm) quan sat thay bit dau co cat chuyln dgng (bat diu anh hudng den xdi).
- Trudng hgp thi nghiem rieng be cgc ciing cho ket qua tuang ty thi nghiem to hgp than tru va be cpc.
- Trudng hop thir 3, khi thi nghiem rieng than try: Khi cao dp day than try so vdi day cat 1,5cm (Htoc = 1,5cm) quan sat thay cat bit diu chuyln dpng.
Nhir vay:
- Trong trudng hgp H^oc ^ 4,5cm (H,gc/h > 25%), than tru va be cpc khdng anh hudng din chieu sau hd xdi, chieu sau ho xoi chi anh hudng ciia nhdm cpc.
- Be cpc chi anh hudng den chieu sau ho xoi thi nghiem khi Hc^c < 0 (trudng hgp be cpc dat tren day cat va be cpc bj lap mpt phan trong day cat). Trong trudng hgp nay, anh hudng ciia be cpc den chieu sau \6i len den tren 80%, tham chi khi be cpc bj lap Y2 trong day cat chieu sau ho xoi chi chiu anh hudng ciia be cpc.
3.2. Su Siiiih ket qua thi nghiem vol mot so cong thiic
So sanh ket qua thi nghiem vdi ket qua tinh theo mot so cong thiic pho bien ve dy doan xoi eye bp tru cau be cao hien nay cho thay:
- Ket qua thi nghiem tuang doi nho so vdi ket qua tinh theo cac cdng thiic kiem tra. Dac biet tinh toan theo phuang phap cua Richardson cho ket qua tinh toan Idn hon kit qua thi nghiem tir 3,1 lan khi H^oc- 105mm den 6,1 lan khi be cgc lap '/z trong day cat.
- Anh hudng rieng cua cac thanh phan tru cau den ho xoi cung rit khac nhau:
1. Than tru:
- Ket qua thi nghiem chi ra than try hau nhu khdng anh hudng den chilu sau hd xoi. Theo phuang phap ciia Sheppard than tru anh hudng tuang dii nho din hi xoi (ldn nhit la 20,6% khi be cgc ngap Vi trong cat). Trong khi do, phuang phap ciia Richardson than try anh hudng rat Idn din chieu sau hi xoi (tir 39,7% khi be cpc ngap '/a trong cat den 59,7% khi Hcpc^l 05mm).
- Khi chieu cao cpc thay doi anh hudng ciia than try din chieu sau xdi cung khac nhau, tlieo kit qua thi nghiem va phuang phap tinh cua Sheppard khi chieu cao cpc cang nhd than tru cang anh hudng nhilu din chilu sau ho xoi; nhung vdi phuang phap ciia Richardson khi H^^ cang nho anh huong ciia than tru cung nho theo.
2. Be cpc:
- Theo kit qua thi nghiem, be coc bit diu anh hudng din chilu sau xoi khi each day cat 2cm (H,oe = 2cm), be cpc cang xuong thip anh hudng cang ldn. Khi be cpc each day 1 cm chieu sau xoi la 1.3cm (h^o,/h = 6.5%), khi be cgc dl sat day chieu sau xoi tang len la 3cm (h,n,/h * 15%). Anh hudng ciia be cgc den chieu sau xdi chiem tir 0% khi H„^> 4,5cm den tren 80% khi 4 0 Tap chi KHOA HOC GIAO THONG VAN TAI S6 47 - 08/2015
be cpc de sat day cat.
- Vdi kit qua tinh toan theo cac phuang phap khi be cpc cang xuong thap anh hudng ciia be cgc cang tang (theo Sheppard tir 12,1 % din 24,6%; con theo Richardson tang tir 11,4% den 41,6%).
3. Nhom cpc:
- Theo ket qua thi nghiem, nhom cpc anh hudng rat ldn den chieu sau hi xoi, dac biet khi chieu cao cgc Idn hon 0. Khi chieu cao cpc cang nho thi anh hudng cang giam (Hcgo = 0 thi anh hudng ciia nhom cpc den ho xoi chi con dudi 20%).
- Doi vdi phuang phap ciia Sheppard, anh hudng ciia nhom cpc den chieu sau ho xoi tuang doi Idn (trung binh xap xi 70%). Nhung theo phuong phap cua Richardson thi anh hudng cua nhom cpc den chieu sau ho xoi nhd di rat nhieu (khoang 23%).
IV. KET LUAN
Tir ket qua thi nghiem cua nghien cuu, khi U^^ > 4,5cm (Hcoc/h>25%)) than tru va be cgc khong anh hudng den chieu sau ho xoi, chieu sau ho xoi chi anh hudng cua nhom coc; khi Hcot
< 0 (trudng hgp be cgc dat tren day cat va be coc bi lap mot phan trong day cat) anh hudng ciia be cgc den chieu sau xoi len den tren 80%, tham chi khi be cpc bj lap ¥2 trong day cat thi chieu sau ho xoi chi chiu anh hudng ciia' be cpc.
Til' ket qua nghien ciiu tren tac gia da kien nghi khi dy doan xoi cue bg tru cau be cao nen chia thanh hai trudng hgp:
1. Trudng hpp 1: khi Hcgi/h ^ 25%i, xoi cue bp try cau chi chiu anh hudng ciia nhom coc, khong chiu anh hudng ciia than tru va be cpc.
2. Trudng hop 2: khi Hcpc/h < 25%i, xoi cue bg tru cau chiu anh hudng ciia nhom cpc va be cpc.
Ngay nh^n b^i lin diu: 4/S/2015 Ngay nhan bai siia: 2/6/2015 Ngay chap nhan dang bai: 11/6/2015
Tai lieu ttiani khiiu
[1]. Trdn Dinh Nghien: "X(3i 16 6 c6ng trinh cau" Nha xuat ban XSy dyng - Ha Noi 2008.
[2], Trdn Dinh Nghien: "Nghien ciru x6i cue bo d nhom cpc ciia try c^u bS cao" De tai NCKH cap Bo GiioducvaDaotao201l -2013.
[3]. Nguyen Ddng Phong: "Danh gia cac phuong phap du doan xoi cue bo try cau be cao" Tap chi KH Giao thong Van tai - sl 32-nam 2010
[4]. Coleman, S E • "Clearwater Local Scour at Complex Piers" Journal of HydiBulic Engineering / April 2005.
[5]. Richarson, E. V,. and Davis. S R.: "Evaluating Scour At Bridges - Fourth Edition" U.S. Department of Transportation - FHWA, May 2001.
[6]. Sheppard. D M.. and Renna, R.: "Bridge Scour Manual" Florida Department of Transportation - May 2005*
Phan bien: Tran Dinh Nghien; Tong Anh Tuan
Tap chi KHOA HOC GIAO THONG VAN T A i S 6 4 7 - 0 8 / 2 0 1 5 41
