' I l l KHOA HOC - C 6 N G NGHE
PHAN TiCH ANH HUfiNG COA CHIEO DAI CQC DEN SULAM VIEC COA NEN DAT YEO DOOC GIA CO DANG COC DAT XI MANG
ThS. NGUYEN VI6T HONG KS. T R A N N G Q C H O A TS. TRAN THE TRUYEN Khoa Cong trinh, Tryong OHGTVT
Tom tat: Bai bio niy gdp phan phan tich tfSc tf/lm ling xi> cOa nen ait yeu (Jiron gia c6 bing he cp?
dat-xi mSng khi chieu dii cic CQC thay dSi. M6 hinh phi tuySn dan deo tuyit doi cua dat duxK si> dung trong cac tinh toin bing phufong phap phan tH him h^n vai cic so lieu thiit kS hinh hoc va dja chit cua mot so die in da duK?c ip dung a Viet Nam. Di/a tr&n kit qua tinh team, m^t so khuyen do vi viee Ilia chon chiiu dii CQC dit-xi mSng hop If trong gia c6 nin diy yiu se dugc kiin nghj.
Summary: This article contributes to analyse the behaviour of soft soil improved with cement soil columns with consideration of length variation. Nonlinear elasto-perfectly plastic models of soils are used in calcuiathns by finite element method with geometrical and geotechnicat characteristics given in some typical projects in Vietnam. Based on the obtained results, some recommendations concerning the choice of soli-cement column length will be proposed.
L D A T V A N O i
Hien nay c6 rat nhilu phyang phap xy ly n6n d i t yeu trong xdy dyng, trong do c6 phyong phap tron sau (Deep Mixing Method - DMM) [10] hay con gpi la bi^n phap sy dyng CQC dat-xi mang (CDXM) [9] da va dang dyg'c dp dung rpng rai trong xay dyng cac cong trinh nha cao ting, giao thong, thuy Icxi... Tuy nhien, hau het cdc quy trinh va tieu chuan ve thilt ke he CDXM o" nyoc ta cung nhy tren the gidi [1], [5], [6], [8] chya c6 nhyng de cgp chi tilt den cdc van de ve yng xy cue bg cua COXiVI, den yng xO' cua nen d i t sau gia c6 cung nhy lya chon hop ly so do bo tri he CDXM (chieu ddi coc, ty \Q giya khoang each vd dyang kinh cpc).
Thye te i>ng dung h# CDXM lam nen mong cho cac cang trinh a Viet Nam [2] cho thay, can thiet phai CO cdc phan tich v l trgng thdi yng suat, bien dang, yng xy cue bo nhdm c6 dyac mot kit qua tinh toan thiet ke chinh xdc va hap ly. Noi each khac, cung vai vi$c tinh todn thiet ke theo quy trinh, can thiet phai CO cdc phan tieh tinh toan bang phyang phdp s6 [7]. Nghien cyu lya chpn mpt mo hinh tinh todn hap iy bang phyong phap s l , khpng nhCrng cd the mo ta chinh xae nhIt yng xCf cua nen dat y l u sd dung CBXM, ma con c6 the giCip ddnh gid anh hyang cua cdc thSng s l ca ban cOa CBXM nhy chilu dai cpc, dyang kinh cpc va khoang each giOa cac cpc den yng xi> cua nen dIt sau gia c l mat cdeh d l dang.
Anh hyd'ng cua dyo'ng kinh vd khoang each cpe dat-
DlPSItJi©
xi mdng den yng xO cua ne dat sau gia c6 da diroc cac tdc gid d l cap trong mat s l nghien cyu da cong b l [3], [4]. Bai bao ndy se gop phan phdn tich arh hyd'ng cua chilu ddi CDXM d i n yng xy cua nIn dat yeu thong qua cac tinh todn bang phyang phap phan ti> hyu han [7], [11].
2. M 6 HiNH PHAN TlCH LFNG XCT C O A N^N BAT Y 6 U G I A C 6 CDXM
2.1. Danh gia v l cac m6 hinh phan tich i>ng m cua nIn dat ylu gia cd CXMD
Cdc ma hinh tinh toan Cfng XCP cOa nIn dat yeu gia c6 bang h§ cpc dat-xi mang bdng phyang phdp phan t l hOu han CO t h i phan ra 2 dang chinh la nhcm cac ma hinh quy dpi tyang dyang vd nh6m cdc ma hinh khong quy d l i tyang dyang [3], [4]. Nhom cdc mo hinh quy doi tyang dyang ehi phu hp'p vdi cdc phan tich 6n djnh tang t h i cQa nIn dat, trpng khi nhom khang quy doi tyang eho phep phdn tieh ehi tiet ve dac dilm yng xy rieng biet cua ede cpe dIt-xi mang vd cua nen dat y l u trpng tpng t h i Cmg xO chung oua nIn. M0t trong cdc ma hinh hop 1^ nhIt cd the dung de phan tich anh hydng cac thdng so hinh hpc din yng xCr cua nen dat sau gia c6 Id ma hinh doi xyng trgc [3]. Trong bai bai ndy, ma hinh doi xyng true tilp tgc dyac sCr dung de phan tich anh hydng cua chilu ddi cpc d i n yng xO cua nen flat sau gia cc thong qua cac vi du tinh toan bdng phyang phap phin tu hiiu han.
S6 9 nam 2014
KHOA HOC - C O N G NGHe # # # #
2.2. Mo hinh d6i xijng tri^c
Mo hinh doi xdng tn^c mo ta SM" Idm vipc dong thdi cua CDXM vd phin ddt yeu xung quanh cpc. Khi dd 1 cpc dgi dipn se du'pc tinh toan vdi vung dat xoay tron xung quanh cpc. M6 hinh doi xdng true dac biet phCi hpp vdi vOng dat y l u can gia eo c6 kich thu-dc Idn.
Vi^c tinh todn dipn tich dat y l u Idm viee xung quanh 1 CDXM du'pc tiln hdnh nhu' tren Hinh 1. Hinh tron cua dIt ylu xung quanh CDXM (Hinh lb) du'pc lly CO di^n tich bang hinh vuong tren (Hinh la).
• • •
s s :
(a) (b) Hinh 2. Sa do tinh todn theo md hinh doi xung tmc,
cdc diiu ki0n bidn vd phan bo ung suit 3. P H A N T I C H A N N HU-dNG C O A c H i e u D A I CDXM D^N LPNG XCT CCIA N £ N
3.1. Cac triFong hq'p tinh toan
Nin dIt yeu sd dyng tfnh todn du'pc tham khao cdc so lieu cua mpt so dy" dn thije te da sd dyng CDXM [2]. Vdi myc dich khao sat d l lya chpn du'pc chilu ddi CDXM thieh hpp tdc gid da gid nguyen tit ca cae so llpu cua dy dn vd ehi thay d l i chieu ddi coc vdi cac tru-dng hp'p xem xet:
4- CDXM chu-a vu'pl qua Idp dIt yeu.
+ CDXM bang chieu day Idp dIt y l u , + vd CDXM vu'pl qua tdp dat yeu.
3.2. So lieu tinh todn
Cac tham so eo- ly cua dat vd h§ CDXM dupe lay nhu" trong Bang 1.
Bang 1. Cac dSc trung ca 1^ cua dat yiu, CDXM, dat dip va dat nin
(a) (b) Hinh 1. Sadd quy doi di$n tich anh hu^ng cua dit
yeu xung quanh 1 CDXM Sa do tinh toan vdi cae dieu kien bien du'pc mo td nhu* tren Hinh 2a.
V^t lieu
Oat yeu CBXM D^tdap D^t nen
Mo dun dan hoi E (kPa)
3150 160000 30000 50000
HSs6 Poisson
0,36 0,2 0,3 0,2
Khoi lirong rieng Y (kg/m')
1440 2000 1900 2010
Gocnpi ma sdt
9 0
8,6 30 30 30
dinh don vj c
(kPa) 15 129 0 1000
Gdc tnfang
ndijr
0 0 0 0 Cdc CDXM du-ac thilt k l nhu- sau [2]:
+ Du'dng kinh cpc (D): Tham khdo so lieu cua ho so*
dy dn 0= 0,7m.
+ Khoang each gida cdc cpc (KC) : Tham khdo s6 lieu cua ho sa dy dn K/C=1.4m
+ Chilu ddi cpc (L): thay doi phy thupc vao chilu day Idp dat yeu (cy the d ly trinh nay chieu day Idp dat yeu = 4 m, Idp ddt nen = 5 m). Chpn chilu ddi CDXM lln lu'pl L = 2; 3; 4; 5; 6; 7; 8 m d i khao sdt.
3.3. Mo hinh vat lieu cho dat va hp CXMD Chu'cng trinh Plaxis V8.2 [11] du'pc dung de tinh todn vdi mo hinh dan deo Mohr-Columb du'pc gan cho cdc Idp dIt vd ludt ddn hii tuyIn tinh du'pc gan cho phIn CDXM. Lu-di phIn td hdu han bao gom cdc phIn td tam gide 6 nut. Lien kit gida cdc phan:
CDXM vd dIt nin cung nhu' gida dat y l u , CDXM va dIt dip nin du'dng du'pc gia thiet la lien tuc. Cae dilu kidn bien bao gom cae lien kit ching chuyen vj theo phu'ang ngang d bien trai va bien phai, lien kit chIng chuyen vj theo phu'ang thing ddng d bien du'di. Dilu kipn bien ve tai trpng tdc dung du'pc bieu dien bang eac chuyin vj thing ddng tdc dung len be mat tren cung cua nin dat dip (Hinh 2).
3.4. Ket qua tinh va nhan xet
Tiln hdnh gid nguyen du'dng kinh, khodng cdeh cac cpc cung nhu- dilu kidn dja chit cua nin dat y l u chi thay doi chilu ddi cpc L vdi cdc gia tn khac nhau g i m L=2,3,4,5,6,7, 8 m d l td do lya chpn du'pc chieu ddi cpc hpp \^.
Dp lun cua ddy nin dip du'pc phan tich theo khoang each tinh td tim cpc nhu' tren Hinh 3.
mmsi
Ill KHOA HOC-CONG NGHE
Hinh 3. DC lOn cua diy nin dip theo khoang cich tinh tCr tim CQC (vol tnfdng hop L= 6 m)
5 -M a. 'Ui
^ ^ ^ ^ ^ ^ B u dai coc (ml J
1
3 4 5 6 U j ^ i '"
Hinh 4. Tvcmg quan vi do lOn cua phin dit yiu vi CDXM khi chieu dii CQC thay dii (Tuvng ung thay
dii ohiiu dii CBXM tir 2 din 8 m)
Quan sdt bieu do trong Hinh 3: khi chieu ddi cpc cdng ddi thi dp lun tong t h i cang giam, tuy nhien do lun tong the khong deu nhau cu the dp lun cua nen dat cd bydc nhay Idn khi chieu dai epcbdt dIu bang chieu ddy Idp dat yeu (tren Hinh 4 ta thay khi chieu dai cpc be han chilu day idp dat yeu thi dp lun ting t h i cua nen dat Id rat ldn=24,2cm, khi chieu ddi coc bang ehilu day lop dat yeu thi dp lun tong the giam
=20cm vd gan nhy khong thay doi cho du cd tang ehilu dai CDXM = 20em). Nhy vay trong moi trydng hap, khang nan chpn chieu dai cOa CDXM vyot qua chieu day lop dat yeu ma ehi chpn chilu ddi cua CDXM toi da d myc ngang bdng Idp dat y l u 4. K^T LUAN
Hien nay d nyde ta viee sCr dung CDXM d l gia co nen dat y l u da trd nen pho biln vd cd xu hydng ngay cang gia tdng. Tuy nhien viee cdc tieu chuan vd quy trinh d nyde ta v l CDXM chya cd nhyng hydng dan eg t h i v l md hinh tinh, phyang phap tinh eung
nhy yng xCr cija CDXM vdi h8 nin lam chp cdc ky sy thilt k l ggp rdt nhilu khd khan. Nghian eCpu trong bai bdp ndy ndy da phan tieh dyac dnh hydng cOa chilu ddi coc d i n sy lam viee eCia nen dat ylu. Ket qua nghidn CLPU nay cd t h i dijng Idm ca sd tham khao cho cae tinh todn nen dat y l u gia e l CBXM bSn cgnh eac tinh toan thiet k l theo cdc quy trinh thilt kl •
TAI U 6 U THAM KHAO
1. BO Giao thdng van tdi (2000),Quy trinh khdo ;'l sdt thilt k l nen dydng a to dip tren dIt y l u ' t 22TCN 262:2000, Ha NOI.
2. H i so thilt k l xi> Vl nen dIt yeu Dy dn Long >';
Thdnh - Dau Giay.
3. Nguyen Vidt Hung, Tian T h i Truyin, VQ Dinh Phgng (2013), Me hinh phdn tich iJng xO' eCla nen dIt y l u gia e l xi mang, TuyIn tap cang trinh khoa hpc - HOi nghj ca hpc toan quic Ian thCp 9.
4. Nguyin Viet HOng, Vu Dinh Phgng (2013), MOt s l anh hydng clia dydng kfnh vd khoang cdeh cpc dat gia c6 xi mang d i n dd lOn cua h^
nen d i t y l u sau gia c6. Tgp chi Cau Dydng Vidt Nam-S6 4, 2013.
5. Quy trinh chau Au ve phyong phdp trOn sau (TC 288 - EU-2003) vd gia o6 dIt yeu (CT97- 0351-EU-97).
6. Quy phgm ky thudt x\s \<i nin mdng, Tieu chuan thanh p h i Thyp'ng Hal DBJOB-40-94.
7. Chu Quec Thang (1997), Phyang phap Phan 10 hu'u hgn, Nha xuat ban Khoa hpc vd ky thuat. Ha NOi.
8. Tieu chuan Nhat ban CDIT (2002).
(Deep Mixing Method, Prineiple, Design and Construction).
9. Vi$n Khoa Hpc ky Thudt xdy dyng (1986), D l tdi Cpe Dat Xi Mang.
10. Masaki Kitazume & Masaaki Terashi, The Deep Mixing IVIethod, CRC Press/Balkema.
11. PLAXIS VERSION 8, Reference Manual.
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