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CAC DAC TRUNG BI^N DANG COA OAT VA Tl/ONG QUAN GIOA OAC TRUNG BÎ N DANG V6l DAC TRUNG VAT LY ThS Do Thj Thu Hien CN Pham Trgng Tinh Khoa XSy dt/ng Ciu dudng Trudng Dai hgc XSy dung Tdm tat TU kit qua[.]
CAC D A C T R U N G BI^N D A N G C O A OAT VA Tl/ONG QUAN GIOA OAC TRUNG BI^N DANG V6l DAC TRUNG VAT LY ThS Do Thj Thu Hien CN Pham Trgng Tinh Khoa XSy dt/ng Ciu dudng Trudng Dai hgc XSy dung Tdm tat: TU kit qua thi nghidm cho thay chi sd nen C^ cht phu thupe vao loai dit, khdng phu thupc vao khoing img suit; he sd quS cd kit OCR cd thi eoi khdng dii ddi vdi mpt loai dat, khdng phu vao dp sSu lay miu 'Vt vay, tSe gia klin nghj ndn sit dung quan he e - Igo, cOng cSe dSc trung tuang itng C^, C, se thuan Igi hgn vide danh giS tinh biin dang ciia dit; ndn sit dung he sd quS ed kit OCR di dSnh giS trang thSi cd kit cua dat Summary: Results of an odometer test shows that compression index C^ depend on the type of soil but not depends on increment of stress; over consolidation ratio OCR is more or less a constant with the type of soil, doesnt depend on a depth of sample I petition for using e-lga plot with correlative compression characteristics C^, C, because this form of plot is convenient for showing stress - strain behavior over a wide range of stresses and such curve usually become more or less straight at large stresses; and petition for using OCR to define the consolidated state of soil I.MdDAU Biin dang cda da't xay rat phdc tap, gdm nhiiu dang vd phy thude vdo nhieu yiu td khdc nhau, ehu yeu sU thay ddi the tich Id rdng vd mdt phin la sU s i p x i p lai vj tri cac hat d i t Do dac diem cda tai trpng edng trinh ldn n i n dat, biin dang eua dat chd y i u la biin dang nen Vdi d i t tinh nen la kha Idn vd hdu qua la edng trinh cd the bj Idn qua mdc dan d i n khdng the sddyng dupc binh thudng, thdm chi pha hoai edng trinh hoac mpt bd phan edng trinh Du bao biin dang cda nen d i t Id mpt cdng vide khd khdn, dd chung ta ein phai nghidn cilu cin than tinh biin dang cda da't CAC D A C T R U N G BIE'N DANG CCiA DAT Oe nghien edu tinh biin dang cda daL ngudi ta tiin hanh thi nghidm bdn nen tai hidn trudng Td k i t qua thi nghidm bdn nen, ngUdi ta xde djnh Mddun bien dang £„: E„ = pblriio3 p: dp lue nen; b; dudng kinh ban ndn trdn hoac canh ban nen vudng; lo: he sd hinh dang bdn nen, ta = 0.79 vdi ban nen trdn, a> = 0.88 vdi bdn nen vudng; S: dp Idn cda bdn nen tuong dng vdi ap luc nen p; m,: he sd biin dang ngang cua dit 82 TAP CHf KHOA HOC CONG NGHS XAY DUNG Sd02-12/2007 Thi nghidm bdn nen phan dnh tUong ddi tdt tinh hinh Idm vide eda nin d i t dudi tde dung cua tai trpng nhung khd dp dung thi nghiem mudn nghidn ci!ru cdc Idp dd't d sau hon Vi vdy, ngudi ta thudng dung thi nghidm nen mpt ehiiu khdng nd ngang phdng thi nghidm d i thay t h i K i t qua thi nghidm nen thudng dupe bieu dien bing dd thi quan he gida dng suit ndn vdi hd sd rdng theo hai dang: - Dang e = f(a) - Dang e = f(lga) 2.1 Dudng cong ndn dang e = f(a) a) Thi nghipm nen miu chi bj b) Thi nghidm nen - dd tii Hinh Dudng cong ndn dang e - f(o) - H$ s6n4n liin a khoang thay ddi dng suit ndn tif a^ d i n oj: Ae a=ACT e - e , = —^ — (72 - o " , Hd sd ndn lun a dupc sd dung Idm dai lupng ddc trung cho tinh biin dang eda dat Dat ed hd sd ndn cdng Idn thi kha ndng Idn cua dd't edng Idn (tinh bien dang cdng eao) vd ngupc lai Oo dudng cong ndn dang e - f(o) khdng phai Id mdt dudng thing, md cd dang mpt dudng cong, ndn ddi vdi mdt lo^i dit hp s6 nin a khdng phai li hing so mi phu thupc vao khoang thay d6i Cmg suit Au, vio diem bat dau cua lirgng ting iiy,a = f (dUt,CT„Aa) - Mddun bien dang E„ xdc dmh theo cdng thdc: E„ = k E„ k: hd sd hidu chinh Id'y phu thudc he sd rong ban dau Oo; E„: mddun ndn cda da't xdc ^ n h td thi nghiem nen mdt chiiu khdng nd ngang m„ - 2MI -fo -^ A m vdi p = - m; hd sd biin dang ngang, \i^ phy thudc vdo loai dit; TAP CHf KHOA HOC C O N G N G H $ XAY DUNG m,: he sd nen the tich; sd 02-12/2007 83 2.2 Oudng cong nen dang e = f(lga): OUcing cong nen nguyen thdy Igbi) '9fe) igf) Igfcj) a) Thi nghiem ndn miu chi bj b) Thi nghidm ndn - dd tai Hinh Dudng eong ndn dang e=f (Igo) oac trung biin dang eda dd't dupc bieu thj bang dp dde cda dudng cong ndn gpi Id chisd nin Cc xac djnh theo bieu thdc sau: lg(CT,)-lg(CT,) C^ khdng phu thudc vio khoang thay d6i iing suit mi chi phg thupc vio loai dit Terzaghi vd Peck (1948) de nghj xdc djnh ehl sd nen C^: + Vdi miu dat c h i bj: C^ = 0,007(W„h -10%) + Vdi mau d i t nguydn dang: C^ = 0,009(W„h -10%) Trong dd: W^^ Id dp am gidi han nhao, tinh bing phin trdm Kit qua nen lai khdi phuc dan trang thai trudc dd theo dudng cong ndn lai cd dd ddc nhd hon Cc rat nhiiu dupe gpi Id chis6nin lal C^ Vdi mlu da't d sau h ndo dd da't d trang thdi tu nhidn, phdn td dat tai dp sdu h chju tac dung cda trpng lupng ban thdn cac Idp dd't d bdn trdn Ung suit ndn theo phuong dimg (dng suat Idp phd) a, = Y,t,h Trong dd, y^,: trpng lupng ridng trung binh cua dd't trdn dp sdu h Khi mau dupe lay khdi dd't, img suit giam xud'ng bang 0, dat da trai qua qua trinh dd tai Idm cho mau bj nd Khi a < a „ dUdng eong nen Ide Id dUdng eong nen lai vdi dp ddc C, Khi a > a „ dUdng eong nen din trd lai dudng eong nen nguydn thdy vdi dp ddc C^ (Hinh 3) Oiim giao cda hai doan thing tuong dng vdi iimg suit nen tdi da qud khd md mau ttmg trii qua gpi Id dng suit tiin ed k i t o^ Tuy vdo loai dat md iJfng suit o^ cd t h i bing hode khac img suit a, Co hpe da't phdn bidt cdc trang thai cd k i t cua dat theo quan hd gida a^ vd a,: + a,, = o,; d i t cd k i t binh thudng (dd't NC: Normally - Consolidated) + Oj > a,: dat qud cd k i t (dd't OC: Over - Consolidated) + Ce < a,: dat chua cd k i t (dat UC: Under - Consolidated) - Ode diim biin dang eda ttmg loai d i t ndi trdn khac thudc vdo trang thai cd k i t cda dd't, dd dd ldn eua n i n chiu tai cQng khde Vide xde djnh c^ Id c i n thiit 84 TAP CHf KHOA HOC C O N G N G H $ XAY DUNG sd 02-12/2007 Oudng cong nen sda ddi JK Oudng cong thi nghiem igC) Hinh Dudng cong ndn dat thuc ti Xdc djnh a^: Trdn dUdng cong nen thi nghidm e = f(lgCT), keo ddi hai doan thing gap tai diim F Ung vdi hoanh dp a^ Nhan xdt: Ung suit tiin ed k i t o^ vd dng suit Idp phd o, phu thudc vdo dp sdu Id'y mau, dd g i n ddng cd the coi ty sd giiJfa a^ vdi o, khdng phu thudc vdo dp sdu liy mau, khdng ddi cho mdt Idp dd't cr OCR= —^ OCR: hd sd qud cd kit (Over Consolidation Ratio) vd dupe dung Idm dac trUng cho trang thdi cd kit cda dd't Oit OC cd OCR >1 Dat NC ed OCR = Da't UC cd OCR