chuong 4.PDF

Y IJMT(DILATOMETER) NENNGANG 4.THINGHIEM CHUONG 145 CHUONG THiNeHTFMtrtEttNGANG DMT(DILAToMETER) 4.1.GrorrHrf;u ' 1t t O U Y E tltY Thi nghiem DMT (DilatoMeter Test) ld mQt loai thi nghi€m n6n ngang, c6c kdt qui thu duo.c til DMT nhidu hcrnvd di{ng tin cAy hon so vdi thf nghiOm n6n ngang PMT Ngodi ra, thf nghiOmDMT ld thf nghiOmxuyOnli6n tuc, rdt don giAn thi nghiom vd hieu chinh (Thf nghiOmPMT thubng tidn hdnh hd khoan sdn, khdng li6n tuc, rdt phfc tap thf nghiCmvh hi6u chinh) Flinh 4.1 minh hoa thidt bi DMT: mdng th6p @ ndm tr6n mfri xuy€n phing O du-o.c n6n ddy ngoii bang til binh n6n O Ket qui ctra thi nghi0m ld c6c 6p sudt po,pr vi p2tuctngtrngv6i chuydnvi cframdng th6pl) 0; l,l vb mm our LlcHs0 cOarHf NGHlf;ru 4.1.2 Nam 1974, gi6o su S Marchetti (Italia) b6t ddu c6 f tuctngvd thi nghiOmDMT thir nghiOm.NAm 1980,thf nghidm Ndm 1975,thi nghiemDMT thd scrdAu ti6n du-o.c DMT bit ddu duoc bidt ddn tr6n nhidu nu6c HQi nghi thd gi6i vd DMT lAn ddu ti6n du-octd chfc vdLondm 1983,vd h6i nghi gdn d0y nhdt lh nam 2001 Gi6o su Marchetti li ngudi d6ng g6p nhidu cdng srlc nhat dd ph6t tridn thf nghiOmndy, til d6, c6 t€n goi "Marchetti DMT" thi nghiOmlh Trong ba rhi nghicni hioh truong manh nhdt vh pnd bidn nhdt tr6n thd gi6i (SPT CPT, DMT), thf nghiem SPT phai mdt gdn 80 nam (1902 -19??)til khai sinh ddn hic duoc sir dung r6ng rdi o Vi0t Nam; cdn thi nghi0m CPT mdt gdn 60 ndm (1931 l9??) Chfng toi hy vong rAng,thf nghiOmDMT sd chi mdt gdn 30 nam (1975 - 20??) dd tr& nOnthinh hdnh tai nu6c ta 10 -TN DH T 146 rH[UCHIEIT,I OATgICruTRUdNG VAIJNGDUNG TRONG PHANTICHNCNMONG Hinh 4.7 Sd dd crja thi nghi6m DMT ) m O i x u y d np h n g ;2 ) m d n gt h p ;3 ) b i n hk h i ; ) ddy crip d6n n6n; S) h6p didu khidn;6) cdn xuv6n: \ cHuoNG4.THfNGHTEM N€NNGANG DMT(DTLATOMETER) 147 4.2.NOrDUNGTHINGHlErupulr 4.2.1,cAc THANH PHANc0a THIdTBI Ffinh 4.1 minh hoa c6c thinh phdn co bin cira thidt bi DMT: Mfri xuy6n phing O, tren d6 c6 gin mhng th6p @; binh n6n (thudng lI nito) @; day c6p d6n khf n6n @, day c6p nly ddn til binh khf n6n, qua h0p didu khidn O, vi d6n tdi phia clra mdng th6p @ C6c6p su6lttrong queitrinh thf nghiOmduo.c tren ddng hd & hqp dieu khidn @ hinh 4.1) Mfri xuy0n duo.cndi vdi cdn @ Cdn xuy0n ndy thudng c6 cing kfch thudc vh dudmgren nhu cdn xuy6n CPT 0e loai cdn c6 culng dOlcrnhon 1000 MPa) V) vAy co cdu gia luc vd cdn xuy€n ctra DMT cfrng li cria CPT Do d6, ndu ta dd c6 ddy dir thiet bi CPT, thi chi cdn chi mdt khoan tidn nh6 dd inua mfri xuyOnDMT, binh n6n, hop didukhidnmd th6i LM f r ixu y6 np h i n g chi fia|: Mfri xuyOnphingr6ng95 mm, ddy 15mm thm bang th6p khdng gi G6c nhon tai mfli xuy6n tir 24 d€n320 d gifra mrii xuy€n ld mdt mdng th6p trdn, c6 dulng kfnh 60 mm, ddy tir 0,2 den 0,25 mm (thdng thudng l 0,2 mm) Mhng th6p duoc gin tr6n mfri xuydn bang nhfrng buldng bit quanh vidn cria mlng th6p FDnh4.3 minh hoa mfri xuy6n sau dd th6o mdngth6p Trong thf nghi0m,ta c6 tidn hdnh"hi6uchinh s6 doc cira mhng th6p,v) vAy thi nghiOmDMT rat chinh x6c ci v6i ddt bin nhSo(S, = + kPa, E = 0,4 MPa = 4kglcm2).Mat kh6c, mfri xuy€n rdt kho6 (chiu duoc 6p h1ct6i25 tdn) Vdi ddi ld xe tii 2O tdn, DMT c6 thd xuy€n qua vdi loai d6 mdm, d6 macno vdi S" = 1000 kPa, E = 400 MPa r 4000 kg/cm: Flinh 4.4 minh hoa qu6 trinh bAo dudng mfii xuyOnsau m6i ldn thi nghi6m Flinh 4.5 minh hoa mdu chuydn cdn (adapter)dd srl dung cdn xuyOn l6n hcrn(vi du hinh vd ld 50 mm) Th6ng thudng ngudi ta srl dung cdn 36 mm, nhung xuy6n & dd sAul6n, vdi tii l6n thi n6ndirng cAn50 mm 148 THfNGHTEM DAr HIENTRUdNG VArlNGDUNG rRONGPHANTICHNENM6NG trl g1 F I trl co rrd ng Hinh 4.2 Kich thu6c m0i xuy6n Hinh 4.3 Mit cua xuy6n th6o ming a) mdt ngodi;b) mdt L j T 149 DMT(DII-ATOMETER) NENNGANG cHuoNG4.THINGHIEM Mdu chuy€n cfn G5n Somm l$p thEm t o ddu drjc M2TxSmm Hinh 4.5 Adapter (mdu chuydn cdn) Hinh 4.4 Bio dudng thieitbi DMT Nguydn lj hoat ilQng: Mhng th6p trOn mfri xuY0n hoat ddng theo nguy€ntic giong nhu chu6ng di0n (hinh 4.6) D€m nhua @ dd cdch di€n gifra dia cim rirng (hay dia cim nhAn @) vdi mfri xuy€n th6p Dia cim c gin chat vdi dem @ vh rlng @ du-o lu6n cd dinh Dia cim ring s6 l)rm thdnh mach diOn k(n, vd d6 gdy tieng kOubip (ducrngddm n6t minh hoa & nfra dudi h)nh 4.6) ciic trudng hop stttt: a) Mdng th6p dinh vdi dia cim fng (lfc ming chua c6 dp luc khf n6n tr{c dQng,chng nhu ltic rip luc n6n v6n cbn thua rip lgc ngang tu nhi€n pn cira ddt); b) Khi n6n (gas) ddy tAm ciia mhng th6p @ ngodi 1,1 mm; d6, lb xo ddy tru th6p O v) cdn pl€xi @ ngodi, g?tyra su tidp xric gifra m6t cira tru O v6i dia cim ring Ap h;c dAt l€n mhngth6phic nly th p, O m d n gt h p O Tru thep kh0ng @ d1ac3m fng si O cdn bing thach a n h h o d ct h y t i n h pl6xi (plexiglass) d a i , 0+ , m m @ddy di6n @ dOm nhda c6ch di6n @ loa Io -T_ t" l-tiengkoubiP -lr'" tFr *r0,8): (4.20) Ko=0'6[iKoo'to J S€tthudng,kh6ng xirnlnghoA z tq xlixo /r.sto'41a6 I 's€t lang len, Fr* o.5 0i 4.3 I 7Esfr*-$ n 30 (b) KD 20 KD Hinh4.18.Quan h6 giira Ko vd Ko nhay cam ld: cbn quanh6 hinh 4.19 (Marchetti)cho ddt s6tthudng,khong =O'34 Ko''tu (xem (a'9)) OCR = (0,5 KD)''s6 Phuongtrinh nhy c6 dang tdng qu6t ho6 lh: oCR = (FoKo)''tu d6 Fo= 0,5 v6i ddt s6t thudng; 0o= 0,75 v6i ddt s6t nft ne; 0o= 0,35 vdi ddt s6tnhaYcim' tudi ctra s6t: Tucrngtu v6i phucrngtrinh tim Ko, Lunne cho rang OCR phu thuoc vdi dat s6tdudi 60.000ndm tudi (S"/ o'uo0,8): OCR = 2,7 KDt'tj (4.2r) (4.22) Mayne( l9S7)don giAncho rang: OCR = 0,51KD 4'20' Todn bd c6c quan didm tinh OCR kh6c duo.c t6m'tit hinh (4.23) loo rHf IEXIEIT,I DATHIENTRUONG VAIJNGDUNG TRONG PHANTICHNENMONG 0 -X-Mayne "r - Marchetti +new Lunne(trd) (XR = 0.14Ko' " *-1r.0,*o),",C!, KD Hinh /9 euan h6 gi0a OGR vi Ko 1 l0l Hinh4.20.T6mt5ttinhocR theoDMT Vdi dat cd kdt thuong (OCR = 1), tt phucrngtrinh (4.9) ta c6 Ko = (vd d6, Ko= 0,54) Di6u ndy dd duoc nhidu t6c gihchLnrgminh b6ng thuc nghi0m Vi du nhu, Totani vd cQng su (1997) dd tien hinh xem x6t mot mi{i d6c bi truot 16 tu nhiOn.Tai mar trudr, ddt s6t dd bi xrio tr6n, bi mdt su ximdng ho6, gid ho6, , d6, dat s6t tai mat truot duoc coi l) dat cd kdt thudng (NC) Thf nghi€mDMT cho thdy,tai vilng mar trud tren mrii ddc bang dat qu6 cd kdt, K o = ( h i n h4 ) (DMrhz Hinh 4.21 Ko o t?i met trrrdt vdi ddt s6t bi ximang ho6, gii ho6, c6tcphuong trinh tfnh Ko vd ocR rrgn ld kh6ng phDhqp V6i ddt s6tco k6t thudng nhungbi ximang hoii, th) Ko c6 thd tD ddn Do d6, F* phucrngtrinh (4.g) c6 rhd lon hon, vf du nhu ti 2,5 ddn 3,0 vdi ddt kh6ng bi ximdng ho6, bidu dd KD cho ddt qu6 cd kdt (oc) s6 gi6m theo dd sAu,cbn cho ddt cd kdt thudng(NC) thi Ko= (tuong iu bidu dd OCR a f,lnt l.l4) Ndu dat qu6 cd kdt (oc) m) bidu dd KD khong gi6m theo chidu sau thi chring t6 dt't s6t bi xim[ng ho6 vdi dat s6t quri cd kOtnriTn6, thi bidu dd KD thudng c6 dang dao d6ng, dfch dic 4-4.5.2.D6nh gi6 h6 sd Kovi oGR cfra d61c6t dr,ra tr6n k6t qui DMT vdi ddt cdt, vi0c xdc dinh ocR vi Ko ld cuc k,,kh6 khan Hon nfra,lai kh6ng c6 ti6u chudnnio dd so sdnhvi dat c6t kh6ng thd ldy mdu nguyendangdd thf nghi€mxric dinh OCR phdng du-o c (thf nghi€m oedometer) DMT(DII-ATOMETER) NENNGANG cHuoNG4.THINGHleM 167 Nhiiiu tdc gih (Jendeby-1992,Baldi-l988,Jamiolkowski-1995,Marchetti-2O0O) cho rang,c5 thd x6c dinh mdt cdchdinh tinh nhu sau: ' ' Ndu Mort/ = + 10 thi OCR = l; Ndu Mort/ 9"= 12 + 24 th\ OCR >1' d6 Mor, - modun kh6ng n6 hOngsuy tt thf nghiem DMT; q" - sfc kh6ng xuy€n mfli tt thf nghiOmCPT' (o'no= C6 thd giii thich nhan x6t tren nhu sau: V6i ddt qu6 cd kdt, 6p lgc ngang Ko 6'uo) ting l€n; Do bAn chat n6n ngang cira thf nghiem DMT, Mot, ting l€n kh6 nhidu, rrong d6 q tang rdt it Nhu vAy ddt cdng qu6 cd kdt thi Mo", / q" cdng cao' T6m lai, DMT nhAnbidt tdt hon su qu6 cd kdt (OCR) so v6i CPT' x6c dinh dua Ta dd bidt, Marchetridd xudt dd thi hinh 2.40,trong d6 K0 du-o.c tr€n q., q.DUa trdn dd thi cfia Marchetti,Schmertmann(1982-1992)dC xuAt phucrng ph6pt(nh tinh lap x6c dinh Ko vh 9' qua Ko vd q.: Kn= + K , ,+ ( 2- K D X l - s i n q ' ) - 7 ( l - s i n < p ' ) ' (4.24) Trong d6, q' ll g6c ma s6t hlru hi€u, duoc tfnh llp cing v6i Ko bang c6ng thrlc cira Michell vd Durgunoglu (tuctngtu phuctngphfp Marchetti & hinh 2'40) vir bang phucrngtrinh (4.24) Marchetti,saud6ld Baldi (1936)d5 dcrngiin ho6 phuongph6pcua Schmertmann thdnhphuongtrinh sau: Ko= 0,376 + 0,095Ko- € q./o'uo t r o n gd (4.2s) € = 0 7l d a td i p ) ddn 0,0046(ddt nguY€nthd) Kulhawy, Mayne (1990) trich d6n ld: Phucrngtrinh tuong tu ctraMarchetti du-o.c Kn= 0,359+ 0,07lKD- 0,00093q,lc',o (4.26) Tuy nhiOn, Ko vd OCR cho ddt cilt kh6ng c6 dQ chinh x6c cao, hon nfra, c6c phuongtrinh tr6n ddu phii dua v)o m6t thdng sOthrl ba: hodc q" (thi nghiOmCPT gdn thi nghiOmDMT) hodc