chuong 4.PDF

Ngodi ra, thf nghiOm DMT ld thf nghiOm xuyOn li6n tuc, rdt don giAn trong thinghiom vd trong hieu chinh.. 146 rH[UCHIEIT,I OAT gICru TRUdNG VA IJNG DUNG TRONG PHAN TICH NCN MONG... Do d6

Thi nghiem DMT (DilatoMeter Test) ld mQt loai thi nghi€m n6n ngang, c6c kdt

PMT Ngodi ra, thf nghiOm DMT ld thf nghiOm xuyOn li6n tuc, rdt don giAn trong thinghiom vd trong hieu chinh (Thf nghiOm PMT thubng tidn hdnh trong hd khoan sdn,

Flinh 4.1 minh hoa thidt bi DMT: mdng th6p @ ndm tr6n mfri xuy€n phing O

4.1.2 LlcH s0 cOa rHf NGHlf;ru our

Nam 1974, gi6o su S Marchetti (Italia) b6t ddu c6 f tuctng vd thi nghiOm DMT

DMT bit ddu duoc bidt ddn tr6n nhidu nu6c HQi nghi thd gi6i vd DMT lAn ddu ti6n

li ngudi d6ng g6p nhidu cdng srlc nhat dd ph6t tridn thf nghiOm ndy, til d6, c6 t€n goithi nghiOm lh "Marchetti DMT"

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 khi khai sinh ddnhic duoc sir dung r6ng rdi o Vi0t Nam; cdn thi nghi0m CPT mdt gdn 60 ndm (1931 -l9??) Chfng toi hy vong rAng, thf nghiOm DMT sd chi mdt gdn 30 nam (1975 - 20??)

dd tr& nOn thinh hdnh tai nu6c ta

146 rH[UCHIEIT,I OAT gICru TRUdNG VA IJNG

DUNG TRONG PHAN TICH NCN MONG

cHuoNG 4 THfNGHTEM N€N NGANG DMT (DTLATOMETER) 1 4 7

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 khi 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 trong clra

khidn @ hinh 4.1)

Mfri xuy0n duo.c ndi vdi cdn @ Cdn xuy0n ndy thudng c6 cing kfch thudc vh

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 xuyOn DMT, binh khi n6n, hop

didu khidn md th6i.

4 2 1 L M f r i x u y 6 n p h i n g

chi fia|:

Mfri xuyOn phing r6ng 95 mm, ddy 15 mmthm bang th6p khdng gi G6c nhon tai

d gifra mrii xuy€n ld mdt mdng th6p trdn, c6 dulng kfnh 60 mm, ddy tir 0,2 den0,25 mm (thdng thudng l 0,2 mm) Mhng th6p duoc gin tr6n mfri xuydn bang nhfrngbuldng bit quanh vidn cria mlng th6p FDnh 4.3 minh hoa mfri xuy6n sau khi dd th6omdng th6p

4kglcm2) Mat kh6c, mfri xuy€n rdt kho6 (chiu duoc 6p h1c t6i25 tdn) Vdi ddi trong

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 xuyOn sau m6i ldn thi nghi6m Flinh4.5 minh hoa mdu chuydn cdn (adapter) dd srl dung cdn xuyOn l6n hcrn (vi du tronghinh vd ld 50 mm) Th6ng thudng ngudi ta srl dung cdn 36 mm, nhung khi xuy6n & ddsAu l6n, vdi tii trong l6n thi n6ndirng cAn 50 mm

148 THf NGHTEM DAr HIEN TRUdNG VA rlNG DUNG rRONG PHAN TICH NEN M6NG

trlg1

F I

trlco

j

Hinh 4.2 Kich thu6c m0i xuy6n

Hinh 4.3 Mit cua xuy6n khi th6o ming a) mdt ngodi; b) mdt trong

rrd ng

L

d a i 3 , 9 0 + 0 , 0 1 m m

@ dOm nhda c6ch

d i 6 n

o

Hinh 4.4 Bio dudng thieit bi DMT

Nguydn lj hoat ilQng:

Mhng th6p trOn mfri xuY0n hoat

ddng theo nguy€n tic 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

lu6n cd dinh Dia cim ring s6 l)rm thdnh

mach diOn k(n, vd do d6 gdy ra tieng

dudi h)nh 4.6) trong ciic trudng hop stttt:

a) Mdng th6p dinh vdi dia cim fng(lfc ming chua c6 dp luc khf n6n tr{c

cbn thua rip lgc ngang tu nhi€n pn cira

ddt);

b) Khi n6n (gas) ddy tAm ciiamhng th6p @ ra ngodi 1,1 mm; do d6,

lb xo ddy tru th6p O v) cdn pl€xi @ ra

ngodi, g?ty ra su tidp xric gifra m6t cira

tru O v6i dia cim ring Ap h;c dAt l€n

mhng th6p hic nly th p,

@ loa

k6u bip 5p lUc am thanh

Hinh 4.6 Nguydn lf hoqt d6ng cria ming th6p

O Tru

t h e p kh0ng

-Nhu v6y, ngay khi tidp bfp bi t6t (kdt thric dudng dam n6t 6 hinh 4.6), ta doc sd

THINGHIEM DAT HIEN TRUONG VA IJNG DUNG TRONG PHAN TICH NEN MONG

ddt tdc dung vdo ming th6p hic chuydn vi crja ming ld 0 mm

Sau d6, khOng c6 su tidp xfc vd diOn ticp bfp bi t6t Tidp tuc tdng 6p luc khi n6n,

vd ngay khi tiep bip bit ddu k6u lai, ra doc sd doc B, ti d6 tfnh dugc p, (muc b 6 trcn).sau d6, ta phii xi van di giim rip h;c khf n6n ngay, tr6nh dd meng th6p tiep ruc biddy tidp ra ngoii, gAy hu hai ddn ddi v6i ming th6p

Ngoii ra, ta cbn c6 thd doc sd doc C vd 6p luc p, (xem ci{c phdn ticp) khi giim 6p

thf nghi0m PMT, ta phii do thd tich dung dich dd vlo PMT, tir d6 suy ra chuydn vi (c6thd khong chfnh x6c do dung dich bi n6n, do dng dAn dung dich bi n6l, do mdng pMTn6 khdng ddu!!! - So vdi DMT, qu6 trinh di€n dich kdt qui pMT rdt rudrn ri vh k6mchfnh xiic)

Tr€n hop didu khidn (hinh 4.7) c6 hai "d6ng h6 do tip lqc,', ,,diu t.tint dirt u1t lrckhi dait" til binh khi n6n, "ddu ctim tl6n ip ltt: kh{ di,, t6i mfri xuy6n , ,,diu cdm 6rtgxilanh" dd hieu chinh sd doc, van "kltori t'tip", van,'cifp clrdm,,, van ,,xi rtltalh,,,

khi loa kOu)

AA vd LB)- Vun c'ap cham c6 tdc dung dua ddng khf cdp tir binh khf t6i miii xuy6n

C6 hai van xi khi: van xd nhanh (lon) vir van xti chdm (nh6) Ta cdn d1ne ddnvan xri chdm dd doc sd doc C

chay hay khdng- Ndu tidng kou ctra loa gdy kh6 chiu, ta c6 thd chi cdn d;ng dBn tinhi6u vd tit loa b6i mOt c6ng tic loa Tuy nhi0n, nen dDng ci ddn vd loa khi thi nghi€m

1 5 0

cHuoNG 4 THf NGHIeM NEN NGANG DMT (DIIATOMETER) 1 5 1

ddu c5m phu cong tdc loa n0t "Ki6m tra"

van cdpchdm

van xa chdm

ddu cdm

xilanh dd

hi6u chinh

dr/dng d5n kht

di6u chinh 6p ltlc

N u t " K i d mtra"

Hinh 4.7 Sd dd hOP didu khidn

4 2 1 3 B i n h k h i n 6 n

TrOn binh khf n6n thudng c6 van didu chinh 6p luc, dng ddn khi Van didu chinh

3 ddn 4 Mpa, tuy nhi6n v6i dAt r6n hon, 6p h1c c6 thd cao hon Khf n6n 6 trong binh c6thd ln khOng kh( thuong hoac nito Vdi binh 6p h1c ban ddu 15 MPa, cao 0,6 m, ta c6thd ding trong 1 + 2 ngity thf nghi€m (tt 70 + 100 m dAt)

4.2.2 THU THAP So DgC H|FU CH1NH

4.2.2.1 Dlnh nghla AA vi AB

AA vd AB le 6p tuc khicdn c6 dd vuot qua dO crlng

ctra mdng th6p (khOng c6 6p

luc c[ra ddt)

Khi thf nghi€m, 6p h1ckhi cAn bang vdi 6p luc d0t

vd d0 cfng cira mdng th6p

& c6c vi trf A vd B nhu hinh

4 8

Mdng th6p khi ru nhi6nthi hdi cong ra ngoli Khi dd

Am (hft vdo) t6c dung vdo

mdng th6p (dat trong kh6ng khi) dd cho m)ng th6p & vi trf A - vi trf ridp xric vdi d1a

cim fng AB le 6p sudt khf n6n duong (ddy ra) tiic dung vdo mhng th6p dd cho mhng

th6p o vi trf B - vi trf rru rh6p O tidp xfc vdi dia cim dng

AA vd AB rdt quan rrong, dic bi6t v6i dat ydu (khi md A vd B kh6ng l6n ho-n AA

vd AB nhi6u l6m)

xilanh kh6ng c6 khdng khf (hinh 4.9a);

cta hdp didu khidn Ban dAu trong

o K6o xilanh dOn gdn hot dng, do d6 c6 mOr dp lgc chan kh6ng hrit ming th6pcham vio dia cim ring, ridng bfp bit ddu keu ftinh 4.9b) Gifi xi lanh khoing 5giay dd dn dinh 6p lgc chan kh6ng, sau d6 thn (ddy) xi lanh that tt tt, ngay khitidng bfp vta tit, ta doc sd doc, vf du li -15 kpa, thi aA le tri ruycr ddi cira s6doc, tfc le AA = 15 kPa hinh 4.9c);

h)nh 4.9d):

Hinh 4.8 Doc so doc AA vir AB

vi tri mang l0c khOng dp sudt

' K h o d c d y ' d 6 n g l r o n g

ffiffiffr]' ro\s

152 THf NcHteM DAr HIEN TRuoNc vA rJNc DUNG TRoNG PHAN TfcH NEN MONG

AA vd AB ld 6p luc khi

cdn c6 dd vuot qua dd cfng

cfia ming th6p (kh6ng c6 6p

luc cira dAt)

Khi thi nghi€m, r{p luc

khf cAn bang vdi 6p luc dAt

vd dO cfng c[ra mirng th6p

& c6c vi trf A vi B nhu hinh

4 8

Mdng th6p khi ru nhi6n

thi hdi cong ra ngoli Khi dd

mfri xuy6n & kh0ng khf,

mdng th6p sE ndm & vi tri

gifra A vi B (vi tri"at rest"

-hinh 4.8)

AA le 6p sudt khf n6n

Am (hft vio) tilc dung v)o

mdng th6p (dAt trong kh6ng khf) dd cho mhng th6p 6 vi tri A

cim ring AB le 6p sudt khi n6n ducrng (ddy ra) tdc dung vdo

th6p 6 vi tri B - vi tri rru th6p O tidp xric v6i dia cim ring

AA vd AB rdt quan trong, dac bi6t vdi ddt ydu (khi mi A vd B kh6ng l6n hon aA

o D6ng van kho6 cAp;

xilanh kh0ng c6 kh6ng khf (hinh 4.9a);

K6o xilanh ddn gdn hdt dng, do d6 c6 m6r 6p lqc chan kh6ng hrit mdng th6pcham vio dia cim ring, tidng bfp bit ddu kOu (hinh 4.9b) Gifr xi lanh khoing 5giay dd dn dinh 6p h,rc chfln kh0ng, sau d6 thn (ddy) xi lanh rhar ri tir, ngay khitiOng bfp via tit, ta doc sd doc, vi du li -15 kpa, rhi AA ld rri ruycr ddi cira sddoc, tfc le AA = l5 kPa hinh 4.9c);

Tidp tuc'ddy xi lanh tt tt, ngay khi tidng bfp keu lai (vi trf B), ta doc sd doc ABhinh 4.9d);

Hinh 4.8 Doc sd dgc AA vd AB

tri ti€p xric v6i diath6p dd cho mdng

ctra h6p didu khidn Ban dAu trong

Y! tri meng ldc khong 6p sudt

' K h o 6 c f p f d o n g t r o n g

trinh do AA- AE

ffitrl:il]' (o\s

cHuoNG 4 THf NGHIgM NEN NGANG DMT (DILATOMETER) 1 s 3

Hinh 4.9 Do M vit AB b) Ch6n khong >> AA c) Ch6n kh6ng = 64 d ) A B

bip lai bip li6n tuc drlng bip

Lap lai qu6 trinh nity 2 ddn 3 ldn dd dim bio AA vi AB le chfnh x6c;

Ndu ddy c6p dan khf dcn mffi xuyen DMT qu6 dii (vii chuc m6t), khi doc AA

vh AB, ta phii chd khoing 15 giay dd 6p luc truydn ddn mdng th6p ;Trudc khi thi nghiOm, th6ng thudng AA = 15 kPa, AB = 40 kPa Neu AA nimngohi khoing 5 + 30 kPa hoac AB nam ngohi khoing 5 + 80 kPa, th) mhng th6pkhdng dat ti€u chudn;

xa (kh6c hon 25 kPa) so vdi AA vh AB trudc khi thi nghi€m' thi mhng th6p niiyd5 rdo, cfr, do d6, ldm giim d0 tin cay cria thi nghi6m Ta cdn thay ngay nhfrngmdng th6p qu6 rio, hodc bi xudc Gi6 tri cudi cilng cira AA vd AB li gi6 tritrung binh tru6c vi sau khi tidn hdnh xuy6n DMT;

Tuy nhien, mdng th6p m6i nguyen (chua thi nghiem ldn nho) cfrng ft tin cdy

dinh Vdi mhng th6p m6i nguy€n, n€n t6c d6ng mdt 6p luc khoAng 500 kPa,sau d6 giim r{p vd 0, crl nhu thd v}ri ldn Ta c6 thd thir nhu vAy trong mdt chAunu6c dd kidm tra xem mdng c6 khi nang ho)n tohn c6ch nudc hay kh6ng

4 2 3 Q U Y T R I N H D g C A , B , C

-4 2 3 L G h u d n b ! t h i n g h i Q m

1 Bit ren cira ddu ciip p-e (c6p pneumatic-electri cal, tfic ld c6p vila d6n khi n6n, vta truydn tfn hiOu diOn) vho mfli xuy6n DMT-

2 Bit ren ctra cdn xuyen thrl nhdt vdo mfri xuyOn, trdnh khong dd crip bi xoin.

3 Ndi Am voi ddt: m6t ddu cira doan c6p "ndi dat" c6m vho gi6c c6m "ddt" nim trOn h6p didu khidn; cbn ddu kia kep vho cdn xuy6n-

a) Vi tri tu nhi6n

kh6ng bip

1 5 4 THINGHICM DAT HIEN TRUONG VA I]NG DUNG TRONG PHAN TICH ruEru U6HE

4 An tay vdo mlng th6p dd kidm tra xem c6 tieng bfp chua

5 Md vun rd nhanh, 96 ray vho c6c ddng hd 6p h,rc vh chinh sd doc v6 0

6 Xric dinh AA vi AB nhu phdn rr€n

7 Cim van didu chinh 6p h,rc vio binh khi n6n (khi tdt ch c6c van rr6n binh khfvAn d6ng), didu chinh ddng hd 6p luc v6 0

8 D6ng chvan khoti cap vd vun cap t'hdm,m6 vun.rti nhanh, ta c6m c6pn6igifra binh khf ndn v6i gi6c c6m cap khf nlm tr0n h6p didu khidn

n6n v) m& vun khod t:up tr€n hdp di6u khidn (vh trong qud trinh thf nghi€m,

4 2 3 2 T h i n g h i 6 m

Thi nghidm DMT dbi hoi hai nhAn cdng: mot ngudi didu khidn h6p didu khidn,mdt ngudi didu khidn h6 gia luc Trinh ru rhf nghiOm nhu sau:

l Tren hop didu khidn: d6ng van t:tfp t:hdm,m6 van xri nhunh (vun xtJ rthanh

vi 6p luc ddt rdc dung lOn ming th6p, trong qu6 trinh ddy xuy€n, s6 c6 tidngbfp li6n tuc vi ddn d6

A

' ' o - o ' - - - ' ' - - Y -

\ l l /

fng), ta phii thao t:ic nhanh:

r Doc ngay sd doc B;

o M& vun xd nhunh ngay, trrinh dd mdng th6p bi r5o;

r D6ng van cdp chAm;

r Ndu cdn doc sddoc C, xem phdn "Sddoc C" dudi dAy;

o Quay lai budc I tr0n day dd xuyOn rhf nghi€m tidp

cHuoNG 4 THI NGHTcM NEN NGANG DMT (DILATOMETER) 1 5 5

Sd iloc C

mb van -rti cham Tidp bip s6 ngirng kOu (vi trf at rest) (tuy nhi0n, dAy chua phAi

ld sd doc C)

(vi tri A) Ta doc so doc C

Toc dd th{ nghiAm

hctn 30 m, thi c6c khoing thdi gian c6 thd ldu hon chft

phii kh6ng bing c6ch sau: cl6ng vun cdp t:hdm, ndu 6p sudt tren ddng hd giim

c6p bi rd ri

4.2.4.rHi NGHtf u lEu rAN AP LUc Nuoc L6 n6nc (sAr oinnl

Ddi v6i ddt c6 tinh tham k6m (dat dinh), xuyOn DMT sE tao ra 6p luc nudc 16

r6ng dd ^a" Oint tinh thdm vi c6c tharn s6 cd kdt cua dAt dfnh Phu thudc viro tinhthdm, th( nghi€m ri6u rdn 5p lqc nudc 16 r5ng c6 thd mdt vdi phrit, vhi gid, thAm chi cdngdy

phuong ph6p DMT-A (do Marchetti vi Totani dd xudt nAm 1989) duoc mo titrong ASTM 2001 C6c thao t6c nhu sau:

2 Sau d6, cap khf ngay (van cup chdm) (trong khoing 15 giay) dt! doc so doc A

3 Khi doc A, ngay lAp trlc xA khi bang c6ch mb vun xd nhunh, ddng thdi do laithdi gian tren ddng hd bdm giay (Sau khi doc sd doc A, ta khdng cdp khi n6ntidp dd doc s0 doc B)

4 Chd m6t khoing thdi gian dinh trudc (thudng ld 0,5; 1;2; 4;5; 15; 30; phtit)

cHuoNG 4 THf NGHIEM NEN NGANG DMT (DILATOMETER) 1 5 5

Sd doc C

mb vun tti chdm Tidp bip s0 ngimg k6u (vi tri at rest) (tuy nhi€n, ddy chua phii

ld s6 dqc C)

(vi tri A) Ta doc so doc C

Tdc dQ tht nghiim

chdm) phii hqp lf dd doc A sau khoing 15 gidy, doc B sau khi doc A khoang

hon 30 m, thi cdc khoing thdi gian co thtj lAu hon chrit

c6p bi rd ri

Ddi v6i dat c6 tinh tham k6m (dat dinh), xuyOn DMT s6 tao ra dp luc nuoc 16

r6ng dd xiic dinh tfnh thdm vd c6c tham sd cd kdt cua dat dfnh Phu thudc v)ro tinhrhdm, thi nghiem ti€u r6n 6p luc nu6c 16 r6ng c6 thd mdt vii phft, vdi gid, thArn chf ciingdy

trong ASTM 2001 Ci{c thao t6c nhu sau:

1 Du.rg xuy0n lai, ngay lAp trlc b6t ddu ddng hd bdm giAy (t =

0)-2 Sau d6, cdp khi ngay (vun cdp chdm) (trong khoing l5 giay) dd doc so doc A

3 Khi doc A, ngay laptrlc xikhibang cdch mb van xd nhanh, ddng thdi do laithdi gian tr6n ddng hd bdm giay (sau khi doc sd doc A, ta kh6ng cap khi n6ntidp dd doc s6 doc B)

4 Chd m6r khoing thdi gian dinh tru6c (thuong ld 0,5; l:2; 4;5; 15; 30; phrit)

1 5 6 THINGHIEM DAT HIEN TRUONG VA UI.IG DUNG TRONG PHAN TICH NEN MONG

Lap lai cdc bu6c 2 vd 3

cong kh6 16 r€t v6i m6t didm udn rn"* 6 gifra (h)nh 4.17)

ph6p DMT-A, c6 trinh ru nhu phuong ph6p DMT-A, v6i vdi didm kh6c nhau sau:

A

Thf nghi0m DMT-A, c6 thd kh6ng phii hoo vdi s6t cring

cHuoNG 4 THINGHIEM NEN NGANG DMT (D!|-AT0METER) 157

l) tju didm lon nhdt clra DMT ll c6 su

x6o rr6n dat it nhdt (hinh 4.11) vdi thf

nghiOm SPT, CPT, do bd dhy cira thidt bi 16n,

n€n ddt bi xi{o trdn (c6 thd bi n6n chat) nhidu,

x6c-2) Uu didm lon thri hai cta DMT lh n6 c6

d6 chfnh x6c cao nhdt trong cdc thi nghiOm

hiOn truhng Vi du khi khio si{t o ving dat

sau, & hai vi tri khio sdt kd nhau, sd doc N c6 thd thay ddi tir 10 ddn 20, thAm chf 30tuj, thu6c vho ngudi thao tdc vd thidt bi Cbn v6i DMT, sd doc thay d<ii khdng ddng kd(ta goi ld tinh lap lai cao)

3) Trong qud trinh cd kdt tham ba chitiu, tfnh tham theo phuong ngang (Cn vd kn)c6 thd sai khdc nhidu so v6i tinh thdm theo phudng dung (C, vi k', ld cdc thdng s6 md

ra rhubng x6c dinh duoc trong phdng) Sir dung DMT, ta c6 thd phdn dor{n kh6 chinhxdc Cn vd kn

4) Tinh qu6 co ket cua ddt rdt quan trong Tinh qu6 co ket cua ddt the hi€n quaOCR v) Ku Trong khi d6, vi6c thi nghi€m trong phbng thudng lhm mAu ddt mdt mOt

thi dat @ (c6 hO sd 6p luc ngang tinh K,, vi fng suat ngang o'n l6n hon) sE c6 dd lfn

Hinh 4.12 Anh tru6ng cria 5p luc ngang (on=Koo!"o) den do l0n

qui, kd ci vi6c xdc dinh muc nudc ngdm th6ng qua sd doc C (neu c6 mdt lop ddt rdinam du6i muc nudc ngdm - mUc 4.4.3.1)-

Nhuoc didm cila thi nghiAm DMT ld:

1) Ndn ddt ldm viec chtr ydu theo phuong dung, trong khi thi nghiOm DMT n6ndAt theo phuong ngang

1 5 8 THINGHIEM OAT HIEN TRUONG VA ITNG DUNG TRONG PHAN TICH HEI.I It,IoruC

4.4.UAC riNH CAC CNi TIEU CO LY DUA TREN XEr OUA DMT

Do dd cting cfia mlng th6p (AA vi AB), vd do sd doc ban ddu trOn ddng h6 Z, md

ta phii hi6u chinh 6p h.rc nhu sau:

( 4 1 ) (4.2) (4.3)

Thdng thuong 2,,,r= 0; z* chi khr{c 0 trong rrudng hap sau: ddng hd dd doc AA v)

AB (goi li ddng hd A) khdc v6i ddng hd lfc doc A vi B (gqi ld ddng hd AB); khi d6,

Zr ld hi€u sd gifra sd doc trdn ddng hd A ldc 6p lqc khf le 0 vd sd doc rr€n ddng hd AB

v A n b a n g 0 '

Lfc chuydn vi bang 0, p, ti 16 v6i 6p lgc dia tinh theo phuong ngang (ung sudt

Lru y rang' po > ono vh Pr ) op (hay po) b6i vi, dD bi x6o tr6n rat (t dudi mfri xuy€nDMT m6ng (1,5 cm), cdu rrric ddt vAn c6 su thay ddi

BAng 4- l t6m tit nhlrng tham sd thu duoc rir rhf nghiem DMT Trong d6, ta phiiixiic dinh ba th6ng sd quan trong Io, Ko, vh Eo tru6c (goi lh chi sd DMT) sau d6, c6c

Trong bdng 4.1, ta ciin luu j:

th6i b'inh thudng (trudc khi thf nghidm DMT);

b i e h dang khong no

d a n g c6 no hOr ,

6 hinh 4.13\:

Trong phuong trinh (4 lz), tn"^ld thdi gian rai didm udn trOn dd thi A-log(t) cria

v) bin chdt do "i{p luc-bidn dang" crja DMT, c6ng thfc tinh M, K^ vd ocRduoc cho ld c6 d0 tin cAy cao nhdt, sau d6 li ddn S,,

p = 1 , 0 5 ( A - Z * * AA) - 0,05(8 -ZM- LB)

P I = B - Z M A B

P z = C - Z * + A A

h6ng) bang phuong trinh (4.14), sau d6, m6dun bidn

) r r 2E= I -3 1 - u tut = BM r (0,5 + 0,g) M;

cHuoNG 4 THI NGHTEM NEN NGANG DMT (DTLATOMETER) 1 5 9

Bdng 4.7 Bing t6m tit nh0ng tharn sd trt DMT

y (khdi lugng ricng)

th6ng thudng Kn= (K-/1,5)o'4t- 0,6 (4.8) OeR Rc) (he s0 qu6 cd kdt);