I I I I I KHOA HQC - C O N G NGHE
PHAN TiCH Lire KEO TRONG COT DIA KY THUAT
KET HOP Vdl HE CQC GIA ClIdNG DAT YEU DUdi NEN DUdNG DAP
NGUYEN TH! LOAN Khoa Cdng trinh Trudng dai hpc Cdng nghp GTVI Tom tat: Bii bao trinh bay kit qua phin tich lyx) kio trong cot dja ky thuat (dt DKT) dOng chuin cOa Anh BS8006-1:2010. tieu chuin Due EBGEO 2004 vi phuong phip phin tO hihi h^n trong phin mim dia ky thuit Plaxis 3D. Nhung kit qua phin tich khing dinh si^ tin c$y ciJa phucmg phap s6 va nhimg hgn chi cua dc phuang phap trong hai tieu chuin cOa Anh vi St>c. Kit luin cua bai bio ma ra huong nghien cOv tiep theo de xac djnh luc kio trong cit nhim /og/ tri> cic gii thiit lim dem gian hda trong cic tinh toin trud'c diy.
Abstract: This paper presents the analysis results of Geosynthetics tensile using British Standard BSB006-1:2010, the Gennan standard EBGEO 2004 and finite element method in geotechnical software Plaxis 3D, The analytical results confirm the reliability of the numerical method and the limitations of the two standards of English and German. The conclusion of the article opens next reseamh to determine the geogrid tensile in order to exclude the assumptions in the previous methods.
I.DATVANOe
Nguyen tdc chung khi tinh toan Idp cot gia cudng blng cot DKT (vai DKT hoge ludi DKT) la xac djnh lyc kdo vd dp dan ddl phdt sinh trong elt tu dd lya chpn loai cot phii hyp dam bao du cudng dd vd hgn chl dp lun lech cua cpc vd ddt ylu trong gidl han cho phep. Oe tinh lyc keo, hidn taiton tai rdt nhilu quan dilm vd phuang phap tinh dya trdn cdc md hinh tinh vd eac gia thiet khde nhau. Trong so do co the ke tdi ede phuang phap trong tieu ehuIn Anh BS8006:1- 2010 vd Dire EBGEO 2004 la cac phuang phdpchu yeu duyc sd dung. Tuy nhidn, cdc phuang phap da dua ra cdc gia thiet khae nhau nham don glan hda trong tinh toan ddn tdi sy sai khac trong kit qua tinh toan. Npi dung cua bai bao su dgng cdc phuong phdp phuong phap tren va cung vdi phuong phap phan tij' hOu hgn bang phan mim Plaxis 3D de khdo sdt vd phdn tich sy phdt triln lye keo trong ludi DKT vd de xuat cdch tinh phu hop.
2. PHAN TiCH CACH TINH LU'C KEO TRONG LU-ai DKT
Theophuong phap BS8006-1:2010 vd EBGEO2004 thi lyc keo trong cot T va T. gay ra tuong ung do hai thdnh phin lyc la lye thdng dung phan bd trdn Idp cit, dit yeu (B+C) va lyc do hien tupng truyt ngang cua nin dap tren Idp cot (D). Theo hudng vudng gde vdl true tlm dudng (hudng mgt cat ngang) thi lye keo trong cot sd la T = T^+T^, theo hudng song song vdi true tim dudng lyc keo trong cdt ehi la T^ (hinhl). Trong pham vi cua bai toan, tae gia dl vdo phan tich each tinh thdnh phan T do tai trpng thing dung gay ra.
Tj» !J3....-^|
Hinh I.Lyc keo trong luoi DKT De tinh thanh phan T^, theo ca hai phuong phap toan bO lyc thing dung phan bo trdn ludi DKT dupc gid tNel tap trung tgi ddi cot co chieu rdng blng chieu rpng dfrti (hoge mu coc) va sau dd lgi gan dung tdi trpng tgp \iue%
duy nhat vao "syl c^t" d chinh glija rdi c^t (WT). V l nhung gia thilt ndy, eac each tinh nhu vay qud thien ve an todn cho cot vd trdn thyc te lye kdo trdn cMobU rat khac nhau theo phuang song song vd vudng gd^M tnjc tim dudng. Ngoai ra, trong tung phuong phdp 1 ^ ^ cac gia thidt ridng, cae cadi tinh rieng nhu sau: 9 2.1. Phuvng phdp theo tieu chuan Anh BS 8006-1:201l) Tieu chuin bd qua sy lam vide eua ddt ylu, coi toan bg thdnh phan lyc thing dung (B+C) do elt chju. Be xac djnh tal trpng thing ddng nay, tidu chuan dd diiti ra 2 phuang phdp tinh dya vao 2 gia thiet ve voiii cua Marston va Hewlett - Randolph.
So 6 n3fn 201®
KHOAHQC-CQNG NGHE IIIII
* Phucmg phap Maiston:
I I M I I I I I Taitr?ngiigoM:(n.
* SO- dung phucmg phip Hewlett vi Randolph:
Dya trdn quan diem v6m dat dang bdn eau cOa Hewlett vd Randolph, higu qua tniyln tdi E chfnh Id phan tai trpng truyen xuong cpc va Id gid trj nhd nhlt trong 2 gid trj E^^ tai dinh vdm va E^p tgi mu cpc tfnh theo cdng thdc:
Cot DKT E^=l- Vdi:
P'c (1)
^v = ^tsYH+fqW^ (2) Trong dd: H - chieu eao dat dap; p'^ - ung suat thang
dung tren mu cpc; y - trpng luong the tieh cua dat dap; to^- tdi trpng ngodi phdn bo trdn dfnh phan nen dap; a - kich thudc mu cpc vudng; o"^ - ung suat thing ddng trung binh d ddy nin dap; f^, f^ - cdc h$ s l ridng phan tdi trpng bdn thdn vd ngogi tdi; C^
- h§ so vdm, toy thuOc vdo sa d l idm vide eOa cpc nhu sau: Trudng hyp epe chong ddng vdo tang dit
'(epetreo) C = 1 . 5 — - 0 . 0 7 . ' "^ a
'Tdi trpng dudng W.^ tren "syi cot" gii>a hai mu cpc la:
J- Khi vdm dit hinh thdnh hodn todn: H > 1.4 (s-a)
w,='y:'"[s--''(p'.K)] (1)
t S -fl
- Khi vom flat chu'a hinh thanh hit: 0.7(s-a) < H <
'1.4 (s-a) , s -a
Trong dd: s - khoang each tu tim epe din tim cpc.
1 - - (A-AB + C) (5)
A =
Hinh 2. Phan bo tai trgng theo ly thuyet vdm dat cua Marston
Dya vdo thd nghidm cong dudi nin dip cao, Marston quan diem vdm dat ed dang idng tai thing ddng vd xay dyng edng thdc tinh ung suit phan bo trdn cpc khi xet bai todn edn bdng gidi hgn tren md hlnh phang 2D (hinh 2). T7 ie giua dng suit trdn mu cpc vd dng suit thing dung trung binh dudi ddy nin dap {p'J(fJ) xdc djnh bdi cdng thue:
2K -2 s-a I
l + j8
(^P + 1) 1+
2K^-2)
l - s i n ( ^ )
n+K- (6)
Lyc W^ ph§n b6 tren cot duoc tfnh theo cong thij'C:
s(t.yH + f(o)
WT - 2 i' 0 - • £ „ , > (3) s —a
Trong do: a - kich thudc mu cpc vudng hoge kich thudc quy dli td mu cpc trdn; s - khodng cdch giua hai cpc lien k l tfnh tu tim cpc; H - chieu eao dat dap;
Y - trpng luyng the tieh cua dat dap; 6p - gdc ddng eua phuong di qua mdp ngodi eua mu cpc ngodi eung vd vai dudng, 9p = 45° - ^''J2•, E - hieu qud truyin tai tgi mu coc; E^.^. - higu qua truyen tai tgi dlnh vdm; E^i^- gid tn nhd hon trong hai gid tri E vd E^.
Lyc keo do tai trpng thing ddng phdn b l frdn cot (T ):
cdng:C =1.95 0.18; Trudng hyp epe ma sdt T W^(s-a) I J_ (4)
2a V 6e trong dd: £ - dp dan ddi eOa ludi DKT.
2.2. Phu'Ong phdp theo tidu chuan Di>c EBGEO 2004
Phuang phdp nay tinh cho nen ddp trdn he mong cpc ching. Phuang phdp dya trdn thf nghidm ciJa Zaeske 2001 cd ke tdi hogt dOng phin dit dudi cot thdng qua hg so nen k^. Vdm dat hinh thdnh trong Idp dap dupc gid djnh dgng hinh chdm cau, giong nhu goi '^ eua Hewlett vd Randolph (1988). Dilm khae eua EBGEO 2004 la vdm chda rat nhieu mgt vdm cong phfa trong. Mgt vdm trdn cung cd bdn kfnh
jl So 6 nam 2016
mm
I I I I I KHQA HQC - C O N G NGHE
0.5Sj nhOng m^t vom ben trong c6 ban kinh Ion hon 0.5Sj cho d i n vo cung v6l mai vom thip nhat (Id i5o^n thang sat mat ciJa dat yeu phia dtf^i).
O'ng suat thing du'ng 6* giOa chdm cau tgi diem thip nhat (tr§n mgt cOa nen dat yeu), o"^ du'p'c xac djnh theo cong thili'c:
Traong hp'p b6 tri dgng \uii\ chO nhgt,
= A.-.(y+^).
-(.\+HlJ^y'
(9)
,. , (.s.-df , sl + 2ds,-d'
I O 2
2sl
(10)
trong do: d - d u d n g kfnh mu cpc hoge d u d n g kinh quy doi d = y 4^4^ / n v d i A^ - dien tfch mu cpc; K - hg so dp l y c dat bj dOng, Kp = tan^(45° + q)/2); H - c h i l u cao d i t dap; H^ - chieu cao v d m dat, H^ = sJ 2 v d i H
> s y 2 vd H^ = H v d i H < sJ2; y - k h l i l u y n g ridng eIJa dat ddp; (0^ - tdi trpng ngodi.
A, =—si bt 2 '
A = —s s
1 8 0 '
180
(11)
(12)
trong do: J^, J^ - m d dun d g dan ddi cOa c i t DKT theo p h u a n g x vd y; s^, s^ - khodng each giua hai cpc theo p h u a n g x vd y.
L y e keo do tdi trpng t h i n g d u n g T phy thuOc vao dp dan dai v d m d dun dO dan dai cua cot vd dupc tin!) theo cdng t h d c :
\ = £JYG (13) Trong do dO ddn ddi etra d u y c n h d todn d l (Hinfi 4),
£ phy thuOc vdo l y e phdn b l F trdn ddi d t rpng a = 0 . 5 d V ^ , dO ddi L „ = s - a, m d dun dO ddn ddi cua c^
D K T J v d dat y l u d u a l Idp e l t thdng qua hg so nen k^ vd l y e phdn b l trdn e l t :
trong dd: F, cdng t h d c 1 1 . V d i hd s l n i n k^:
Wj.=^^ (14)
l y c tap trung tren cot, xde djnh tiieo
(15)
trong d d : k^ - h# so n i n ; E^ - m o dun dan hoi cua d nen; t^ - c h i l u day Idp d i t y l u .
Lircri chii nhSt
Hinh 3. Lyc thing dung phin bo tren c6t T d d n g s u i t a\^ d vung didn tich A^ tinh d u o e l y e tdp tnjng F t u o n g u n g tdc dung len e l t , tOy thuOe vdo h u d n g eua c i t vd edeh bo t r i l u d i cpc (Hinh 3)
xde dinh F n h u sau: Hinh 4. Toin do tra dg gian dii lan nhit trin cit
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KHOA HQC-CONG NGHE I I I I I 3. PHAN TiCH LI/C KgO TRgN C 6 T 0 K T VA BlNH
LUAN
Si> dung phu-ong phap tieu chuan Anh BS 8006:1- 2010, Phu'Ong phSp ciJa Diic EBGEO 2004 va phin mem Plaxis 3D phan tich bSi toSn nhu' mo ta a (Hinh 5). Chieu cao dip H = 6m: khodng each cpc s = 1.8m; kich thwoc mu cgc a = 0.6m: trpng luwng the tich cIJa dat dap Y„ = 19 kN/m^, gdc n6i ma sat cua a l t dip (p„ = 30°; Cpc va mu cpc ci5 E = 30 GPa, V = 0,15, Y = 24.5 kN/m^; ngogi tai quy doi 0)^=
60 kPa, mo dun dO dan ddi cua c6t J =1000 kN/m va J = 2000kN/m, khong ke toi cao h§ s6 rieng phin.
6
1:
W l = a^Vml
T 9
19kIVm3 IkPa
H
r;
f
' „ , , , d „ . ^ T>14.7kWm3 c - S 6 k P .
J \
e) Theo phuang phdp phin tu huu hgn Su dyng phin mem d\a ky thudt Plaxis 3D md phdng, phdn tfeh khdng gian bdi todn Vz nin dudng dip vdi sy Idm vide phoi hap cpc vd ludi DKT (Hinh 6),epc lam vigc theo so do cpc ching. Cdc md hinh vgt li^u sd dyng nhu sau:
- Dat su dyng md hinh dan h l i - ddo ly tudng Mohr - Coulomb bao gom 5 thdng so: E, v cho dgc tfnh ddn hoi; C, cp cho dac tfnh ddo vd tp Id gdc gian nd.
- Cpc su dung md hinh dam cpc "embeded beam"
vdi eac thdng so E - md dun ddn hoi epe, kfeh thudc cpc (mgt eat, chilu ddi).
- Ludi DKT duoe md hinh hda Id logi vat lieu ddn ddo. Day Id loai vat iigu hodn todn khdng ehju nen ma eh! chju keo. Cae phuong trinh bieu thj sy iam vi$e cCia c i t nhu sau:
T„, = Je, vdT^,
Hinh 5. So do bii toin phin tich
Kit qud tinh:
a) Phuong phdp tidu chuan BS8006:1-2010 - Vdm dat Hewlett va Randolph:
= J£, (14)
frong dd: T , T [kN] - lyc keo theo phuong vudng gdc (phudng x) va song song (phuong y) vdi tim dudng; J [kN/m] - md dun dO dan ddi cua d t DKT;
s,, e^ [%] - dp dan ddi tuong d l i cOa c i t theo phuong X vd y trdn 1 m ddi.
J (kN/m)
1000 2000
Hieu qua truydn tai tgi dinh vom Kp
2.998 2.998
A 0.198 0.198
B 0.283 0.283
C 0.189 0.189
E^
0.706 0.706
Hieu qua truyen tai tgi mu cpc
P
1.544 1.644
E„, 0.607 0.607
W,(kN/m) 138.475 138.475
E(%) 0.19 0.11
(kN^m) 189.796 219.701 - Vom dat theo Marston:
J(kN/m) 1000 2000
H§ s6 vom Cc 19.32 19.32
c f . 174 174
P'c 649.48 649.48
W , (kN/m) 37.83 37.83
E(%) 0.07 0.04
T „ (kN/m) 69.68 84.23 b) Theo EBGEO2004
J(kN/m)
1000 2000
cToz (kN/m=)
87.45 87.45
Hv(m)
1.275 1.275
a ' c d (kN/m=)
666.180 866.180
P(kN)
311.825 311.825
Fx(kN)
141.498 141.498
F/(a.J)
0.236 0.118
k,L\
J 2.448 1.224
E(%)
0.045 0.033
(kN/m)
45.0 66.0
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iixi@
ttMMB KHOA HOC - CONG NGHE
Hinh 6. Md hlnh s6 bai toan phan tich bing phin mem PiaxisSD
Khoang each tfnh ti> t'm du&ng (m) b) Theo phi/cng song song
Hinh 7. Biiu do iyv kio theo phuong vudng gdc va song vol tim duong
Kit qud phdn tich cho phep tinh duac lyc keo tren cot theo ca phuong vudng gdc vdl tnjc tim dudng (T^,) va phuang song song vdi tryc tlm dudng (T^J.
Bilu d l phdn bo lyc keo tren cot theo hudng mat eat ngang tgi ehinh giua rdi elt trong pham vi hai epe nhu (Hinh 7).
Su dung gia tri ldn nhdl dd phdn tich:
Tm'&ng hpp J = 1000 kN/m J = 2000 kN/m
T„, (kN/m) 46.54 63.534
T„(kN/m) 24.791 26.551 Doi chieu cac ket qua tinh theo cac Phu'Ong phap nhU" bilu do trang sau:
Nhgn thly k i t qua tinh theo cong thu'c de xuat du-pc x§y dyng tCr phyong phap phan tO hOu han silr dung phan plaxis 3D va su' di,jng cac ham hoi so voi cac Phu'Ong phap doi chilu cd moi typng quan nhu* sau:
So vol vol ket qua phan tfch tare tlep bang phIn mem Plaxis, dp l#ch khoang 3% den 7%. So vS phyong phap cua Birc EBGEO 2004 thi khi J = lOOOkN/m, dp lech khong dang k l va khIJ = 2OO0 kN/m thi dp ISch khoSng 8%. So vdi tiSu chuan anh BS 8006 thl CO sif khac biet rat ion, dac bipt neu tinli theo phuong ph4p Hewllet sy khac bi$t ISn din 2 toi 3 lln.
mm
S66nKHOAHQC-CONGNGH$ I I I I I
_ 250 . | 200 1 150
? 100 1^ 50
.S 0
m: i
•^ >
cK?'
-NO'#
N*?"'.V
1J = 1000 kN/m
• J = 2000 kN/m
H/nh 8. B/du do dii chiiu /yc /fdo fheo phuong vudng gdc vdf fruc tim dudng (T^J
4. K £ T L U A N
Theo cdc each tinh frong hai tidu chuin cua Anh BS 8006:1-2010 vd Birc EBGEO 2004, cdc kit qud phdn tfch lyc keo tren cot rat khae nhau. Sy khde bigt ed the gidi thfch do nhung gid thiet ve kich thude vdm dat tu dd xac djnh lyc truyin vdo cit. Ngoai ra, theo phuang phdp cua Anh, phan dat yeu dudi cot coi nhu khdng tham gia chju tdi, chfnh vl vgy cot coi nhu chiu toan bp tai trpng do vdy lye kdo trdn elt cd kit qud Idn hon.
Lyc kdo do tdi trpng thang ddng T^ theo kit qud phan tieh so blng phan mem Plaxis 3D gin sdt vdi kit qud sd dyng phuong EBGEO 2004, dieu nay ehdng td sy tin c§y cDa phuong phdp Tidu chuan EBGEO 2004. Tuy nhidn todn d l cOa EBGEO 2004 khdng eho phdp tfnh todn duac tnfdng hyp dyng nhieu Idp ludi vd su dung Idp vdt ligu ddm giua cdc Idp iudi khae nhau eung nhu trong mOt so trudng hyp khdng tra duoe kit qua do dp gian dai toi da trdn todn do chi Id 6%, Bdn canh dd, phdn tich bang phin mim Plaxis 3D cdn cho phdp tinh duyc lyc kdo theo phuang song song vdi true tim dudng (T^^), gid trj ndy duyc gia thiet Id bang lye kdo theo phuang vuflng gdc d cae tieu ehuan Anh vd Due. Chfnh vl vdy hudng nghidn euu tilp theo cua tdc gid tilp id
tye sd dung phan mem Plaxis de khdo sdt, phdn tfch tim quy lugt phdt triln lyc kdo trong ludi DKT nham toi da ke tdi eae yeu tc anh hudng tdi lyc kdo trong ludi va tim ra moi tuong quan giua ed thdng so ndy vdi iyc keo trdn cot •
T A I L I ? U T H A M K H A O
" [1 ] Nguyin Thj Loan, Phin tich s6 sy iim viic cgc kit /Jpp voi luon dia ky thuit gia cu&ng dit yiu trin md hinh thyc nghigm zaeske 2001, tgp ehf GTVT so dge bidt thang 10 - 2015.
[2] Synwaf Satibi PhD thesis (2009). Numerical Analysis and Design criteria of embankments on floating pile, Stuttgart University in Gennany.
[3] British Standard BS8006-1:2010, Code of Practice for Strengthened/ Reinforced Soils and Other Fills. British Standard Institution, London.
[4] H.G Kempfert, "German recommendations for reinforced embankments on pile - semilar elements". Institute os Geotechnique University of Kassel- Germany.
[5] Plaxis 3D-2012 manual.
I S6 6 nam 2016