Ket qua cac nghien CLPU tiii nghiem xac dmh dac diem ap lyc nu'O'c lo rong (u) - gradien thuy I IPC ban dau (I J cua tram tich loai dat set yeu bao hoa nu'O'c a khu vyc TP Ho Chi Minh va vung dong bang song Mekong
Mai Di Tam ABSTRACT
One of the difficulties that geotechnical experts frequently encounter in construction in soft soil condition is how to calculate and forecast the stability - deformation of works over time, especially the construction works in soft soil of water-saturated clay deposit.
This article is to show the initial research results about the qualitative and quantitative analysis of the variation process of pore water presure (u) and Initial hydraulic gradient (Io) in soft soil of water-saturated clay deposit - as a base for calculating and forecasting the possibility of increasing or reducing the bearing capacity of the soft foundation soils over time to propose an observation solution and forecast the gross settlement of construction works in soft soil impacting effects of current global climate changes - ensuring the effective exploitation in long-term of the project.
TS Mai Di Tam Cong ty CO phan D|a 6c 10 Tong Cong ty Dia oc Sai Gon
I.GlPi thilu Chung
Vin d l du bio khl ning dn djnh - biln dang cOa cdng trinh theo thpi gian, d|c bi|t II nhiing cdng trinh xdy dung trin nin dit trim tich loai sit bio hda nUdc, ddi hdi thdi gian cdng sdc v l chl phf rit tdn klm. d l khic phuc nhiing tdn tai niy. Bdi vilt nhim cdng bd cdc ket qud nghiin cPu bUPc diu v l djnh tinh vd djnh lupng ciia qud trinh bien ddi Ip lUc nuPe 16 rdng (u), gradien thdy Ipc ban dau (1^) cLia dat set yiu no nuPc dUPi nin cdc cdng trinh - lam co sd cho vile tfnh todn, du bio khl nang tdng - giim dp bin cda dit yeu theo thdi gian, d l tp dd d l xuit giii phdp quan trie vl dp bio dd lun tdng hop ciia cflng tnnh xiy dUng trong mfli truPng dit yiu chju Inh hupng cCia sU biln ddi khf hdu todn d u hi|n nay - ddm bdo cho sp khai thdc hilu qui liu ddi ciia dp dn.
Od ben vd biln dgng ciia dit sit bao hda nudc dudi tac di,ing cua tli trpng ngodi cd liln quan rd rit din dfl Im - dd chat (w) hodc dp lUc nude trong cdc Id rdng (u) cua dit. Ol kilm chPng sp phy thuflc cua dp Ipc nudc Id rflng vdo thinh phin (lo) vl trang thdi (1^) ciia dit, tdc gid tiln hlnh hdng iogt cdc thi nghiim tren d c mlu dit cfl ciu true b| phd vd vd khflng bj phi vd, d c mlu dit ndy diu d trang thii bdo hfla nuPc {h| sd bao hda nudc biln ddi trong gidi hgn tP0,98
•i-1.00), d c mlu dit cd trgng thii dd sit khic nhau. Qua thf nghi|m cdn khing dinh vile thay ddi vi tri d c hgt rln trong dit cdng vdi vi|c nin ehdt dit theo thPi gian chju Inh hudng bdi 3 yiu td:
a) Lpc dinh kit ciu cPng C^ ciia dit;
b) Oac tfnh dp nhdt eiia dit (lpc dfnh nhpt TJ va ddc tfnh dfl nhdt cda nudc trong cdc Id rdng ciia dit;
c) MPc dp thodt nudc cOa d c loai dit sit thupng nhd hon d c loai dit khac do dp
rdng cda chting nhd ciing vPi sp ting d$
nhdt cua Pit.
2. Kit qui nghiin ciilb xic Anh tOc dilm cAa ip life nUAc lA rAng (u) cAa tfit sit yiu bio hda nUPc P khu vpc thtaii ph6 hd chl minh v i tiJu vPng sdng me kong mfln nam Vilt Nam
Kit qud nghien cdu thpc nghiem 6isac trinh bdy bing cac bilu, bing sd va do thj.
Tdc gid rut ra cdc kit ludn sau diy:
+ Gil tri he sd 3 ^ = 1,00 dung vdi sir chuyin t l i trpng P^ hodn todn sang nude d|c dilm nay ed P d c loai dit P trang tnii nhaovldlonhlo.
+Trong d e truPng hop cdn Igi. gia tn he sd ( J ^ < 1,00 ddi vdi cdc logl dit d trang thdi nPa cdng vd cdng th) p,^ tiln gin tdri 0.
+ Ol dat duoc sp dn djnh thpc te ep hit nudc trong d c Id rdng ra khdi Pit nin, iilu hit trong cdc logi dit sit vd a sit d trang thdi bdo hda nuPc. Ip luc nudc Id rdng ciing khflng gidm din 0, md vin cdn giii' Igl vdi tij u#0.
+ I) thuyit cila Gherxevanov - TerzagW (tli trpng ngoii ban diu truyin lufln toin b$
cho nudc trong dit) chl phCi hop trong cac logi dit P trang thdi nhio vd dio nhlo. Cdn ddi vdi cic loai dit P trang thli dio mim din cPng thi t l i trpng ngoii truyin true tilp
Hinh 1 : dc kit quS nghien cilu SU bien ddi ap I A ^ nuiJc lo rong (u) theo thcrt gian {t}. .^
5 2 j n n E W K [ | H x 0 5 . 2 0 1 2
l i n cdt P i t ngay tir thdi diem ban d i u khl dat Ipc tac d u n g . Can chii y d i n d i e diem ndy khi dp bao qud trinh nen c h | t ciia dat n i n dUdl mdng cflng trinh.
Tac gid tap trung n g h i i n ePu t h i n g h i i m d l x i c dinh d i e diem gradien thiiy lUc ban d i u (1^) ddi vdi dat set y i u bao hda nudc d vCing ddng b i n g sdng CPu Long va khu vuc Thdnh phfl Hd Chi (Winh, d l ddnh g i i I n h hudng cCia ( i j d i n q u i trinh cd k i t dat va xem nd n h u m d t y i u t d quan trong de xdc d m h viing hoat ddng v l cd k i t D^ theo d i l u kien (i^ = i^. Qua k i t q u i ciia hdng loat t h i nghiem t r i n cdc m l u d i t Idy t i i n i n cdc cdng trinh thpc t l , da k h i n g dinh dUoc vai trd ciia gradient ban d i u Id: i^ < i^ thi nudc khong thodt ra; khi i^ > i^ thi nUPc bi I p t h o i t ra khdi d i t K i t q u i n g h i i n cPu thuc n g h i i m dUdc trinh bdy tren cdc sd dd, bdng sd, dfl thj.
Tdc gid rut ra cdc k i t ludn quan trpng + Gradien ban d i u cOa P i t cd quan h i phu thudc v i o trang thdi d i t va b i n c h i t nudc trong cdc Id rdng cda d i t (nUdc t p d o , nUdc lien k i t y i u , nudc lien k i t chat)
+ Nudc trong dat lam thay ddi d d am ciia nd. ddng thcti lam thay d d i trang thdi cda dat.
Tiiy theo d p I m ma d i t cd t h i d cac trang thdi cting, nPa cPng, d i o ePng, d i o m i m , d i o c h i y va chdy. K i t q u i t h i nghiem cho thay r i n g : gradient ban dau cda d i t phu thudc vao gidi han d i o 1^ va d d s i t 1^ cda nd. Khi d i t d trang thai chay, d i o c h i y thi cd gradient ban d i u nhd n h i t va ngUpc lai, gradient ban dau ldn nhat khi d i t Strang t h l i cdng.
+ Chieu day cOa vitng hoat dflng (D^^) [vung hoat ddng v l cd ket) ciia dat nen dUdi cflng trinh phu thuflc vao gia t n gradient ban dau (io) ciia P i t n i n . Vi^ng hogt ddng (D^,) xay ra trong pham vi d p sau ma trong vCing dfl cd i, s i ^ . T r l n ranh gidi cda viing s e c d i ^ = i j , .
TO
1 0,75 0,50 0,25 Hlnh 2: Cac ket quS nghien ciju suphu thufic gradien ban dau (1^ vao thanh phan (1) va trang thai (1^) c^a datsetbaohoani/dc
3. Ket q u i n g h i i n cihi budc d i u v l v i l e x i c djnh d c dac diem cPa gradien thuy Ipc ban d i u (i^) cPa d i t s i t yeu bdo hoa nudc P vPng chau thd song CPu Long v l cac t i l u viing thudc 24 khu vpc q u i n - huyen cPa TP Hd Chi Minh
+ H i l n nay ed 2 hudng n g h i i n cdu hien tupng c d k i t ciia d i t set y i u bao hda nudc
s a OO PHAN KHU DIA C H A T C O N G T R I N H KHU V l / C T H A N H P H O H O C H I MINH
trudng hudng ciia cac ly t h u y i t consolidation can cP vho sU b i l n ddi ap luc nUdc 16 rong u (pore - pressure), trudng hudng ciia \^ t h u y i t consolidation can cP v i o sp b i l n ddi do am - dfl chat (W) cCia dat. Chting ta nhan thay trUdng hudng t h P 2 don g i i n hdn v l ]•} t h u y i t va ve sP dung d c thiet bi thi n g h i i m trong phdng va d hien trudng.
+ Gradien ban dau (1^) ciia dat cd quan he phu thudc vao ddc d i l m ciia thanh p h i n { ^ cda dat vd trang thai (1^) ciia d i t va b i n chat nUPc trong d c 16 rflng cOa dat (nUPc tU do, nUdc lien k i t y i u . nudc lien k i t chit). Rd rang nUPc trong dat lam thay doi d d am ciia nfl, dong thdi lam thay ddi trang t h l i cCia dat. Tiiy theo d d am ma d i t c d the 6 trang t h l i cdng, nPa cdng. D i o cPng, d i o m i m , d i o n h l o v l n h l o . K i t q u i thf nghlem c h o t h l y r l n g g r a d i e n t b a n d ^ u ciia dat phu thuoc vdo giPi han d i o (1^) va do set (I j cua nfl, Khl dat d trang thai n h l o , d i o n h l o thi cd
gradient ban d i u be nhat (= 0 - 0,5), v l ngupc lai gradient ban d i u Idn nhat khi dat (= 50) P trang thai cting.
+ Chieu day viing hoat dflng ( D J (viing hoat ddng co k i t t h d 1) ciia dat n i n d U * cflng trinh, phu thudc vao gia t n gradien ban dau ( i j ciia dat nen v l gradien nen ep (i^) do t l i trong ngoai gay ra. Viing hoat ddng D^ chl xdy ra trong pham vi dfl sau md trong viing dd cd: cd 1 a i^. Tren ranh gidi ctia vting s i cfl i^ - i^.
TAI LlEU THAM K H A O
1. Mai Dl T^m - Ngtiidn cihi g\i\ phap Nen - Mong IhSa man cac dieu kien Ky thuat - Kmh t ^ c h o cac loai nha dan dung tis 5 den 7 t^ng xSy dUng tren viing dat yeu co chi^u dSy liJn 6 Mien Nam - Viet Nam - Lu|n in Tien si Ky thuat, Dai hoc Bach Khoa Thanh p h 6 H 6 C h i M i n l i , 1 9 9 8 .
Z. Le Ba Luong, tfnh toan nen nong cong tnnh theo th&i gian, tiU6ng{)ai hoc Bach Khoa Thanh pho Ho ChiMlnh, 1981
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