Torn tat: Thwc te cho thiy cd nhleu gidi phip khdc nhau de gia cw&ng cho nin dw&ng dip.
M0( trong nhimg gidi phip m&i trdn thi giai hi^n nay da vi dang s(> di^ng li lifoi dja ky thuit Tuy nhidn, do nhieu nguyen nhin, din nay t^i Vi^t Nam vide ip d^ing gidi phdp twai dja ky thu$t gia cw&ng nin dwdng eon chwa nhiiu. Qua bai bdo niy, ehung toi dwa ra phwang phdp xie djnh dg lun eua nin dw&ng dip trdn dit yiu ed gia cw&ng bing Iwai dja ky thugt, tir dd, kiin nghi giii phdp sw dyng Iw&i dja ky thuit gia cw&ng nin dw&ng dip nhim tao co s& khoa hoc giup ngwai thiit ke, thi cdng cd the dwa Iw&i dia ky thudt vio sO^
diing rgng rai tmng xdy di/ng nin dw&ng fi td a nw&c ta.
TO' khoa: Gia cw&ng nin dip, Iw&i dia ky thuat, nin dat kem on djnh, di lun, dw&ng 6 td.
Abstract: The reality is that there are many different solutions to strengthen the embankment. One of the new solutions in the worid today is using geogrids. However, due to many reasons, so far in Vietnam f/je application of geo-grid reinforced road foundation is quite limited. After studying this article, our team presents solution determine the settlement of the embankment by use geogrids and recommends a solution using geotextile reinforcement road embankment to create a seientifle basis to help designers, it is widely used in automobile road construction in our country.
Keywords: Strengthen embankment, geogrids, soft ground, settlement, automobile road.
1.GI<>I THIEU CHUNG
Trong thiet ke va thl cfing dudng d tfi, vigc gia co dam bao tinh on djnh nen d i p da ddt ra nhiing v i n de nan gial vd cap thilt, Hien nay, tren t h l gidi cfi nhieu phuang phap khde nhau de gia eudng nen dudng dap tren d i t kem I n djnh n h u [1, 3, 4, 6]: gidi phdp d i p be phan dp; tgo tang edt d§m; s u dyng gieng cdt hoac b l e t h i m ; sir dyng vai dta ky thugt...
Cde gidi phdp tren da d u p e s d dyng t u lau nhung trong nhung trudng hpp cy t h l van bOe 10 nhu'ng k h i l m k h u y l t vd nhu'ng han ehe cua nd. MOt trong nhu'ng bien phdp mdi, cfi the mang lgi s u I n djnh cug cdc t u y i n dudng di qua viing d i t kdm on djnh la s d dung ludi dja ky thudt (LDKT).
D l dam bdo cao dO t h i l t k l eiia n i n dudng dap on djnh trong s u i t qud trinh khai thde yeu eau phdi tfnh
XAC DJNH DO LUN CUA NEN DUCJNG DAP CO GI^
CUCiNG BANG L U ( 5 I D I ^
KY THU AT
mm
TS. NGUYEN DUY D O N G TS. L £ V A N CHUNG KS. Yd TitN DUNG Bp mfin Cau dudng San bay Vipn ky thudt Cfing trinh Dudng Hpe vign Ky thugt Quan sy chinh xae ehieu cao phdng lun d l cfi t h l dap rat mOt k h l i lupng v|lt ligu b l sung. Tuc la, trong i trinh t h i l t k l phai d y bdo d u p c chinh xdc v l ag cOa nen dudng Id vigc Idm r i t e i n thilt. Trong bdo ndy, nhfim chung tfii tdp trung vao tfnh toan lun cho n i n d u d n g dap ed gia c u d n g Idp LDKT nh ldm sdng to vai trfi cua nd trong thi edng dudng i tren Idp dat n i n kem on djnh.
2. MQT SO U'U D I ^ M C O A LLFdl D\A K Y THUJ}
LDKT dupe san xuat d i u tien tgi Anh bdi tgp d Tensar International, lam bang chat potypropy polyeste hay bpc bang polyetylen - teretalat [5], i d i n nay, trdn t h l gidt, n h i l u noi r i t ua chupng dung LDKT trong xay d y n g d u d n g fi to, tip do kiem d u y e nhieu ehl phi v l nguyen lieu vd nhan Tang cudng LDKT cho nen d u d n g dap cfi nhirng d i l m sau:
- Tang tfnh on djnh cho n i n d u d n g d i p , tang tuoi efing trinh;
- Lam gidm d u o c dp lun tong the va tgo ra qua I liin d i n g deu eiia Idp d i t dap;
- Thl cfing mOt cdch de dang, gpn nhg va phii vdi n h i l u logt dja hinh;
- Thfch hop vdi mpi logi d i t , da vd cac logi vdt dilng d l d i p nen d u d n g ;
- Dam bao tfnh ben vu'ng vd khfing anh hudni mfit trudng xung quanh.
3. XAC DjNH D O L O N C O A N £ N D A T DU'OC CU'd'NG B A N G l u ' d i OjA K Y THUAT 3.1. Xdy d y n g m o h i n h bai t o a n T r u d c khi thi efing Idp dat dap, ngudi ta thudr mOt Idp vai dja ky thugt (VDKT) len tren Idp d i l kem on djnh. Khi dd, Idp VDKT cd tdc dung nhu ldp Ipc va phan edeh. Sau dd se rai mpt Idp d l mong, khodng 5 cm, ldp ndy ed tac dyng tgo p t r u d c khi trdi ldp LDKT len tren (hinh 1).
S6 9 n
^frmtTTTTF
Hinh 1. SO- dung LDKT gia cw&ng nin dat dip 1 - Nin dip; 2 - Lwai dja ky thuit; 3 - Lap vai dia ky thugt phin each; 4 - Nin dit tt/ nhidn kem Sn dinh idt toan d u p c xay d y n g trdn gta t h i l t Idp LDKT ldp
^DKT va l d p d i t nen kem on dtnh la mOt khoi dan i l l tuyen tfnh dang h u d n g , cfi t h l tfch khdng doi.
"lln hanh tfnh todn ldp LDKT vd VDKT t u o n g t y ihu nhirng ldp d i t vdl cac dgc trung c a - ly rieng.
trong dfi;
E,,Ej,E^,E^ - l l n lupt Id md dun ddi hoi cua Idp LDKT ( k l cd vdt lieu Idm d i y LDKT), Idp d i t d i p , Idp VDKT vd ldp d i t nen, kPa;
h,,h^,h - l l n lupt Id chleu day Idp LDKT, Idp VDKT vd Idp dat nen, m;
0,05 m la chleu day ldp d i t giua Idp LDKT vd VDKT.
Ej d u p c xac djnh nhu quan hd [10]:
E,=E„Jc (3)
vdl k la hd s l xde djnh theo (4):^^^TOT^^-
16pVDKT:Ev.3^v ldp VBKT. E., a ^ .
Hinh 2. Sa do xie djnh iOn Idp ddt nen ed gia cw&ng LDKT
rheo giao s u D u a n g Hpc Hal va Nguyen Quang 3hieu [ 1 , 2, 3], dp lun tong eOng cua nen d i p d u p e cac djnh theo cdng thue:
S^=S,+S^ + S„ + S„ (1)
rong dfi:S„ - la dp lim t i n g cOng eua nen, m;
S, - dp lun tiic thdi x i y ra khi khong thoat n u d c lo fing, m;
^ - dp lim CO k i t xay ra kht thoat mOt p h i n n u d c to fing cung vdi viec gidm dp lyc n u d c l5 rfing, m;
S - 66 lOn gdy ra do c h u y i n vj ngang cCia d i t d u d i ien dap, m;
S,j - dO lun t u b i l n t u o n g ung vdl s u t i l p tyc b i l n Igng sau khi ap lyc n u d e lo rong b i l n m l t , m.
t.2. Xdc djnh dp lun tire thdi
iJen d u d n g bay g i d Id 1 he bao gom 3 ldp vdt lieu:
dp LDKT ben tren; Idp VDKT d giua vd Idp d i t nen
;em on djnh d u d i eiing (kht chua d u p e gia eudng thi l l n d u d n g chi bao gom Idp dat nen kem on djnh),
^d dun ddn hoi ehung eOa hg nen E^^ d u p c nhdm ac gia k i l n nghj xac dinh nhu theo cfing thuc sau tay [9]:
E, Jl, + Ej .0,05 -i-E^h^ + E^Ji hi+0,05 + h^+h
E.I.- (2)
^ = l / ( l -
E^.R ^ )
(4)trong dd:
jU la hg so Poisson Idp vgt lieu Idm d i y ; R id bdn kfnh mat tudi, m;
C la mo dun dan hoi t u o n g d u o n g , kPa, xac djnh theo [10].
N h u vgy, dp lun tuc thdt se id:
S6 9n5m2017
^^''
(5) trong do:/ - he so dnh hudng [1];
y^p - la trpng lupng the tfch ciia idp d i t d i p , kN/m^;
H - c h i l u eao Idp dat d i p , m;
h - e h i l u sau tdp d i t n i n kem I n djnh, m.
Ro rang nhdn thdy, vdl mo dun dan hfii cua hg Idp d i t efi gia cudng bang Idp LDKT ldn han mfi dun dan h l i eiia rieng ldp dat kem I n djnh ddn d i n dO liin tdc thdi cua hd gia eudng giam di dang k l . Mfi dun dan hoi eua ldp LDKT cdng Idn thl dO lun tuc thdi n i n d i t kdm I n djnh cang nhd.
3.3. Xac djnh do lun co k i t , lun do chuyen vj ngang va do tCr b i l n
T i l n hdnh tfnh dO liin eo k i t , lun do c h u y i n vj ngang va t u b i l n ciia he n i n gta c l LDKT t u a n g t y nhu khi nen chi efi nguyen ldp d i t chua gia e l . Diem khac nhau trong 2 mfi hinh cfi vd khfing cfi gia c u d n g Idp LDKT Id gtd trj ung s u i t nen thang dirng tde dyng vdo eiing mOt d i l m tren dat n i n kem on d[nh khdc nhau, S y khdc nhau cua dng s u i t nay la do tai trpng d i p tdc dyng len n i n d i t trong hai trudng hpp khac nhau. V d i vide s u dyng Idp LDKT, VDKT thl tal trpng
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d i p tae dyng Idn nen dat se nho han nhilu kht khfing s u dung ehiing do ban than Idp LDKT, VDKT khi bj keo edng do tdi trpng eua n i n d i p se sinh ra phan lye c h l n g lal tai trpng dfi.
Khi kfch thude ciia n i n dap Idn hon so vdl ehieu ddy eOa d i t kem on djnh, Ung s u i t t h i n g dirng trong d i t d u y c lay bang ung s u i t d u d i trpng luong eiia dat cfing vdi dp lyc cua nen d i p gdy ra [1]. Ngupe Igt, n l u ehieu ddy Idp d i t kdm I n djnh thl e i n xet tdl s y phdn b l thyc te cua cac ung s u i t .
Gpi q Id tdi trpng d i p , xuyen qua Idp LDKT vd VDKT gia cudng, tdc dyng len dat n i n theo dang hinh c h u nhdt, kN/m^. Yeu c l u bai toan dgt ra Id e i n xdc djnh d u p c gia trj eiia q.
Gpi p' la tai trpng dap tde dyng trye t i l p Idn Idp LDKT trong he nen gia eo theo dgng hinh ehu' nhgt, kN/m^, Phdn iyc xuat hign trong Idp LDKT vd VDKT khi nd bj keo edng do tdi trpng dap gdy ra ta T se phu thuOc vdo md dun b i l n dgng E;^^ eiia ehiing [7, 8]:
(6)
nd hfing, tir dfi, se hgn d u p c che dp lun e l kit, liin do c h u y i n vj ngang vd dp lun do tir b i l n . Khi da xac djnh d u p c dng s u i t ndn t h i n g ddng, d l dang xde dlnh d u o e dO ldn co k i t theo gido i N g u y l n Quang Chieu n h u sau:
trong d o :
^oed Id dp lun khdng n d hdng;
IJ Id hg so dieu chfnh Skempton vd Bjerrum.
DO lun khfing n d hfing la :
(1
T = £jj.(^b''+Q,25S' -b'),kN/m;
p'.[\ + cosfilgip^]
(8) v&i (j) la gbc npi ma sat cua d^t dap.a I"
cos,8 - , ,;
V i ' + 0 , 2 5 . S ' T^i trpng q d u g c tinh theo cong thi>c:
. , (T-p'dtg(j>).cosfitgif, b'-d
Nhif vay, vdi hp nen gia cucmg LBKT, do itng suat n6n thang dung giam di nen giam dup'c dp lijn I<h6ng
iii»i@
l<N/m';
(9)
(10)
1+e H-C,.lg- , m ;
l + e„ c (1
trong d6:
b' - la 1/2 dp rang phSn bp tal trpng hinh c h u nh|it p'> m;
S - la dp IOn tong cpng cua lop dat dap khi khdng gia cud'ng, m;
E^ tinh bang trung binh cOng mo dun bien dang cua lap LDKT (c6 x6t den vat li#u iam d^y cac mat ciJa LBKT), I6p dSt dap 5 cm v4 lop V B K T
Dp rpng vung mep bien can thi^t cua Idp dat d i p d de dam bSo kep c h j t idp LBKT v4 VDKT trong nen la:
^ IM
trong dfi:
^0 la dp r i n g ban dau;
Cj Id ehi so nd;
C^ l a c h i s l nen lun;
o 'p la dp lyc tien c l k i t , kPa;
o\^ Id ap lye eua ede Idp d i t ndm phfa tren, kPa;
<y\^ id ung s u i t ed hieu t h i n g dung d giO'a ldp, kPi Aft la c h i l u day Idp dat thdnh p h i n , m.
DO fun do c h u y i n vj ngang:
S^=- B
- , m ; (1'vdl B la mfit nua chleu rOng day nen dap.
DO ICin do t u bien se Id:
S„--^C^.lg'-.m: (1!
l + Co t trong do:
C „ ia chi so tCi bien.
t la thdi gian tinh bang 1 ngay.
Theo nghien c u u [8], n6u dp lun tong cpng d i t nS kem on djnh khong qua 50 cm, ta cd t h l ap dung ki cau theo hinh 03, vdi Idp LDKT d u p c rai ngay tr«
Idp dSt n^n, d u d i Idp LDKT s§ t r i i 1 idp VBKT nhSi mgc dich ipc va phan c i c h .
