GeoRadar Nghien Cuu Sat Lo Song Tien

7/22/2019 GeoRadar Nghien Cuu Sat Lo Song Tien

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34(3), 205-216 Tp chCC KHOA HC VTRIT 9-2012

GP PHN XC NH NGUYN NHN ST LBSNG TIN V SNG SI GN

BNG CC KHO ST A VT L GN MT TL NGC THANH1, NGUYN VN GING2,

E-mail: [email protected] l Ti nguyn Tp. HCM - Vin Khoa hc v Cng nghVit Nam

2Vin Vt la cu - Vin Khoa hc v Cng nghVit Nam

Ngy nhn bi: 15 - 6 - 2012

1. Mu

Qua kt qu nghin cu kho st trong nhngnm gn y trn cc im st l b sng Tin,sng Si Gn, chng ti nhn thy nguyn nhn stlbsng u c im chung lin quan n iukin a hnh, a mo (trng thp, sng un khc),iu kin a cht (vt liu trm tch bn st v ctmn ln bt c chiu dy ln), iu kin a chtthu vn (mc nc ngm dng cao st mt t,

chtriu, p lc thung ca nc trong t),iu kin a cht cng trnh (t c lin kt kintrc yu, thuc loi t c thnh phn trng thi vtnh cht c bit nh c tnh xc bin khi c titrng ng, t d tan r khi c dng chy ln),iu kin dng chy (triu, l, ma,), iu kinkinh tx hi (xy dng tri php ln chim lunglch, sng; tn cao nn qu mc ca cc hot ngdch v theo bsng, khai thc ct qu mc dilng sng). Nhng ni no, v tr no trn onsng m tp trung nhiu iu kin nu trn th bsng ni khng n nh, sbst lm trong nguyn nhn ch yu l tc ng ca con ngilm thay i chdng chy v n nh hai

bn bsng.

Dbo st lt bsng phi da trn c snghin cu quy lut ca dng chy, lng dn vcu trc a cht bsng [9, 13]. Trong phi coicu trc a cht b sng l ni lc v l yu t

bin i theo thi gian vi tc bin i nhanhhay chm tuthuc vo tc ng ca ngoi lc gyra [3, 8, 10]. Nu coi dbo sthay i dng chy,lng dn l di hn th cc nghin cu nh gihin trng cu trc a cht bsng l xp vo d

bo ngn hn. Nu bit c cu trc trm tch gn

mt t bsng mt cch chi tit, ta c th tm rac ngun gc ca chng v gp phn quan trngvo vic dbo khnng st lgp phn thch ngvi bin i kh hu hin nay. Phn ln, cc nghincu t trc n nay u da chyu vo ti liucc l khoan a cht cng trnh v quan st ahnh, a mo trn mt [6, 14]. Bng cch ny,mun t c nhng mt ct cu trc a cht chitit th phi tiu tn nhiu kinh ph v thi gian. khc phc tnh trng ny, chng ti nghin cu

la chn thp cc phng php a vt l o vtrn mt t gii on hin trng cu trc acht b sng. Trong , phi k n cng nghGeoradar (GPR) kt hp vi phng php in ttn s rt thp (VLF), cc phng php in trnh: o su in i xng (VES), o su mt ctin (EP), o nh in, o mt ct in a cc 2D,3D, [16, 19]. Phn tch tng hp cc ti liu ovbng a vt l v a cht a ra nhng mtct cu trc a cht tng nng chi tit vi chnhxc cao. Kt qunghin cu ny gp phn lmsng t cu trc di mt t ng b vi vicxc nh cc ranh gii gia nhng lp trm tch,

cc lng knh cha nc, cc n ct c hnhthnh qua nhiu giai on khc nhau, gp phnquan trng trong vic dbo st lt v lm tincho cc lun im v tch t trm tch vng bsng Tin, bsng Si Gn,...

2. Phng php v thit b

2.1.Phng phpGeoradar

GPR l phng php a vt l ng dng ccnguyn l ca sng in tdi tn srt cao (1-2000MHz) nghin cu cu trc v cc c tnh


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ca vt cht bn di lng t m khng cn phio bi. Thit b pulse EKKO100 [18], thit b

Ramac/GPR [17], thit b Ingegneria Dei Systemi(IDS) Detector Duo [15] l nhng hmy hin inht ang c sdng Vit Nam. Kt qucuicng m thit bGPR a ra l mt ct hin trngcu trc ca vt cht bn di mt t c phngii cao.

Nng lng pht ra tng ten pht lan truynvo trong lng t, mi trng ng nht chngtip tc i su v suy yu dn, khi gp dthng mi trng bt ng nht s to ra cc sng phnx v c anten thu ghi li cc tn hiu phn xny mt cch lin tc. Chng ta c th tip cnc n ngun gy ra d thng trn c s xcnh gi tr cc i lng vt l ca sng in tnh: vn tc truyn sng (v), bc sng ( ), su thm thu (), h s suy gim (B), inthm (r), tthm (r), dn in (),... Diy l cc i lng c sdng trong GPR [2]c trnh by trongbng 1.

Bng 1. Cc i lng ca sng in t

c dng trong GPR

Struynsng in t

mi trng cdn thp

ngha cabiu thc

=a

=c

r r

Vn tc truyn sngchphthuc vor, r= 1

=2

a

=

1

f

Bc sng phthuc vo vn tc

=1

b

=

2

su lp mtgim khi dntng

B = 20blog10(e) B r

r

= 1636 01, *

Hstt dnkhng phthucvo tn s

S dng GPR mi trng a cht l mitrng c dn in thp, v lin quan ch yun t v lc th tthm c gi trxp x

bng 1. Do cc sng phn x ny c to ra tnhng mt ranh gii trung gian trong mi trngnghin cu bt ng nht nn chng thng linquan n c im trong cu trc a cht nh:ranh gii cc lp trm tch c tnh cht vt l khcnhau, cc khe nt n, cc khi xm thc, cc dvt,... su thm thu ca phng php phthuc vo tn s ca ng ten pht-thu tn hiu v

ph thuc vo tnh cht ca t trong mi mitrng a cht [1, 2]. Cc loi anten thng thngc dng kho st cu trc a cht y ctn s l: 50, 100 v 200 MHz v bc o tngng l 0,5; 0,25 v 0,1m. Trong trng hp ny su kho st c tht c n 30m, 20m v 10m[4, 5].

Mt ct radar l mt bc tranh tng hp phnnh cu trc a cht chi tit lm c s cho cngtc iu tra c bn, nghin cu a cht cu trc,a cht cng trnh, a cht thuvn, a kthutv mi trng [1, 7].

Vi nhim vchnh l nghin cu cu trc acht gn mt t bng cc ti liu a vt l cacng trnh ny nn cc tc gi thc hin vic lymu c trng cho trm tch bsng Tin v sng

Si Gn, ng thi tin hnh phn tch mu theocc tham svt l (xem bng 2). Di y l ktqu ca 18 mu chun c nghin cu kho stti ch v phn tch trong phng th nghim theotiu chun mu a cht ca Cc a cht Ba Lan

ban hnh nm 1998 ti phng th nghim muthuc H Khoa hc v Cng nghAGH (Krakow,Ba Lan). Kt qutrong bng 2l gi trtrung bnhvi sai s


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Ct ht mn, bhn

10 Tn Chu 66,8 14,970 9,97 1 0,095 8,01 2,018 - 2,285

11 Vnh Long 56,5 17,699 9,57 1 0,097 9,67 2,045 - 2,276

12 Thanha 49,9 20,040 11,89 1 0,087 9,82 2,027 - 2,312Ct ht th, kh

13 Tn Chu 616 1,623 3,08 1 0,171 1,56 1,694 49 1,297

14 Vnh Long 793 1,261 2,94 1 0,175 1,24 1,758 41 1,492

15 Thanha 833 1,200 2,75 1 0,181 1,22 1,700 42 1,515

Ct ht th, bhn

16 Tn Chu 167 5,988 23,41 1 0,062 2,09 1,706 - 1,338

17 Vnh Long 171 5,848 24,19 1 0,061 2,01 1,804 - 1,632

18 Thanha 192 5,208 20,05 1 0,067 1,97 1,800 - 1,620

2.2. Phng php VLF

VLF (Very Low Frequency) l mt phngphp a vt l o ghi trng t th cp gy bi

cc vt dn nm bn di mt t khi b tc ngbi trng in t s cp c pht i t nhngi pht sng raio cng sut ln trong di tn st15 n 30 kHz nm ri rc trn thgii [12].

Cc vt dn to ra trng th cp thng linquan n i ph hy kin to, t gy a cht,thu knh cha nc, ranh gii trung gian hoc ccthn qung.

Thit bVLF-WADI ng dng cc thnh phnt ca trng sng in tc to ra tcc i

pht cng sut c300 - 1000 kW di tn s rtthp, t 15 n 30 kHz v c truyn i vi

khong cch ln [20]. ng ten ca cc i phtVLF thng l mt dy cp thng ng c dimt vi trm mt. Trng in tpht ra lin tct cc ng ten theo phng nm ngang c dngnhl cc ng trn ng tm.

Sng VLF ti pht lan truyn trong khnggian v i vo lng t. Khi mi trng a cht lng nht, ngha l khng tn ti d thng th ts gia in trng v t trng xp x bng 0.

Nhng khi gp dthng, nht l dthng c intrsut thp (lin quan n cc i cu trc bphhu trong mi trng a cht) th s xut hin

trng th cp c phng thng ng v ngcdu vi trng s cp. Lc t s gia intrng v ttrng skhc 0. V vy, khi quan stng cong o c ta cng c thbit cc thngtin cbn vdthng [12].

Bng cc cng thc ton hc ngi ta chngminh c rng phn thc ca t s gia thnh

phn thng ng trn thnh phn nm ngang catrng in tVLF khi lan truyn qua vt dn xpxbng tangvi l gc nghing gia trc chnhca elip phn cc so vi phng nm ngang: phno ca tsgia thnh phn thng ng trn thnh

phn nm ngang xp x bng tm sai ca e lipphn cc:

Phn thc Hz/Ho(%) 100 tang (tang tnh

theo radianes)Phn o Hz/Ho(%) 100 e (e l tm sai=t s

trc ln/trc b ca Elip)

su thm thu ca sng in t tn s rtthp: p ph thuc vo in tr sut (R) ca mitrng kho st v tn si pht (f) theo cng thc:

f

Rp 500=

R l in tr sut ca mi trng lp ph(m); f l tn si pht (kHz).

Trong trng hp lp t phc chiu dy lnth cng tn hiu thu c sbnh hng cc

b. Trng thsinh pht ra sbao xung quanh bmt ca i tng a cht, trng ny c tho v

phn tch c. WADI tin hnh o ghi cng ca trng v s thay i vpha xung quanh cci dp vtrong t [20].

2.3. Cc phng php in tr

Mi trng a cht ni chung thng l dnin km, v vy phng php GPR trnh by trn pht huy c li thca mnh khi sdng

kho st cu trc a cht gn mt t, nhng ivi cu trc bsng m vt liu lin quan n stv bn th su nghin cu ca GPR bhn ch.nghin cu cc i tng a cht c skhc

bit vin tr sut ca cc loi t trong mitrng v c dn cao th cc phng php intr pht huy c hiu qu s dng. Gi tr cain trsut hay l mc dn in ca t phthuc vo cc yu tnh: thnh phn khong vt, rng v nt n, m, khong ho canc ngm, cu kin trc ni ti, nhit , psut,... Tuthuc vo i tng cn nghin cu m


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ngi ta la chn cc kiu thit bo. Trong iukin c th nhmi trng trm tch b sng th

cc kiu thit bc s dng ph bin nh: osu i xng kiu Schlumberger c su khost n mt vi trm mt khi ta m rng khongcch gia hai cc pht dng n 1000m; o sumt ct in kiu Wenner vi khong cch cc cct2, 5, 10 hoc 20m [3]. o su nh in hoc oin a cc nghin cu phn nng vi chi titcao. Thit bsdng o trong cc phng phpin tr l Terrameter SAS 300C, Terrameter SAS1000, Terrameter SAS 4000 do ABEM sn sut [19]hay SuperSting R/IP do AGI sn xut [16].

3. Kt qukho st

3.1. Thtrn Tn Chu - An Giang

Khu vc xi l b th trn Tn Chu tnh AnGiang, nm pha bhu sng Tin. Thi gian gny hin tng xi l b sng Tin th trn TnChu xy ra v xy ra lin tc vi tc cngngy cng mnh v phm vi cng cng ngy cngmrng thm vi chiu di khong 2500m v tc xi l trung bnh hng nm l 6m/nm (trcnm 2000) gy nhiu thit hi cvngi v caci. c im st lbkhu vc ny l thng haiti ba nm mi st lmt ln v st lthng xyra vo nhng thng cui ma lu ma kh [10].

Mc tiu ca kho st a vt l nhm xc nhhin trng cu to ng bsng Tin thtrn Tn

Chu, khoanh vng cc i xung yu, xutphng n chnh tr.

Trn ton on ng bsng Tin trc cngUBND huyn Tn Chu tin hnh o GPR, VLFv mt ct in.

Hnh 1 l cnh s dng ng ten 50 MHz cathit b Pulse Ekko 100 kho st ti b sngtuyn trc cng UBND huyn Tn Chu vi bco l 0,5m nhm nghin cu n su 45m [5].dtheo di cc mt ct cu trc ca ctuyn odi 1200m chng ti ct ra lm 3 on tuyncng vi kt quminh gii a cht v c trnh

by trn cc hnh 2 v bng 2 cho on tuynTchau1; hnh 3v bng 3cho on tuyn Tchau2;hnh 4v bng 4cho on tuyn Tchau3.

Hnh 1. Kho st bsng Tin ti Tn Chu bng GPR

Hnh 2. Mt ct cu trc theo ti liu Georadar tuyn Tchau1 (cc k hiu bng sc ch gii trong bng 3)


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Bng 3. Kt quminh gii tuyn TChau1

K hiu lp Vn tc, (m/ns) thm in, () dn, (mS/m) suy gim, (dB/m) Gii on

1 0,100 9,000 0,700 0,383 Nn ng

2 0,130 5,325 3,750 2,665 Ct hn hp

3 0,120 6,250 4,000 2,624 Ct ht nh

III 0,080 14,063 5,250 2,296 Ct ht nhln st

4a 0,070 18,367 8,000 3,061 Bn ln ct ht nh

IV 0,052 36,000 9,000 2,460 Nc bn ln mn thc vt

5a 0,059 19,464 11,500 4,275 Bn ln st

5b 0,065 21,302 12,000 4,264 Bn ln st nho

V 0,062 23,413 11,000 3,728 St do nho + bn

6 0,080 14,063 14,000 6,123 St

VI 0,075 16,000 13,000 5,330 St + bn


Bng 4. Kt quminh gii Tuyn TChau2


1 0,110 7,438 0,800 0,481 Nn ng

2 0,132 5,165 4,000 2,886 Ct hn hp3 0,117 6,575 4,150 2,654 Ct ht nh

III 0,075 16,000 5,500 2,255 Ct ht nhln st

4a 0,065 21,302 8,175 2,905 Bn ln ct ht nh

4b 0,060 26,754 10,000 3,171 Nc bn ln ct ht nh


5a 0,057 20,049 11,000 4,029 Bn ln st

5b 0,065 21,302 13,000 4,619 Bn ln st nho

V 0,062 23,413 10,500 3,559 St do nho + bn

6 0,080 14,063 15,000 6,560 St

VI 0,075 16,000 12,800 5,248 St + bn


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Bng 5. Kt quminh gii Tuyn TChau3


1 0,097 9,5653 0,900 0,4772 Nn ng t

I 0,090 11,1111 7,000 3,4440 Ct hn hp bo ho nc

3 0,130 5,3254 4,000 2,8427 Ct ht nh

III 0,075 16,0000 5,250 2,1525 Ct ht nhln st

4a 0,069 25,0000 9,000 2,9520 Bn ln ct ht nh


5a 0,057 27,7008 12,000 3,7392 Bn ln st

6 0,082 13,3849 17,000 7,6205 St

Kt quo VLF ton tuyn Tn Chu di 3500mbng thit bVLF-Wadi c trnh by trn hnh 5.

Hnh 5.ng cong phn thc (--) v phn o (o o) VLF

tuyn Tn Chu cc mc su 10, 20, 30, 40 v 50m

y, vi mc ch nghin cu s hin dinca d thng VLF lin quan n hin trng cutrc a cht ng bsng cc su t10mn 20m c cc khi cu trc c phn bit bngdn in ca chng. Tsu 30 n 50m, cu

trc ca tuyn c phn chia r rt lm hai phn.Phn u n 2000 m l mt khi kh ng nht v

phn sau t2000m n 3500m l mt khi c dn cao hn hn.

Kt quo mt ct in tuyn Tn Chu ctrnh by trn cc hnh 6, hnh 7 v hnh 8 diy. Nhn vo cc mt ct ny chng ta thy cdn in ca cc khi vt cht khc nhau v ni

bt ln l cc khi ct th c dn in yu v cckhi st th ngc li.

Trn c s kt qu kho st bng Georadar,VLF v mt ct in cho thy cu to a cht cang b sng ti Tn Chu c s bt ng nhtcao. S xen k gia cc khi ct ht mn v cckhi st kiu thu knh u l nhng cu trc yucho nn mng ng b. nhng chct ht mn,ngm nc nu c ca thng vi lng sng v ditc dng ca p lc nc th dgy ra st l. ycng l nhng c s cn phi da vo trong khitin hnh cng tc dbo st lbsng y.

Nguyn nhn xi l b sng on ThngPhc- Tn Chu, theo cc nghin cu cng b


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Hnh 6. Mt ct a in tuyn Tn Chu 1-1



[9, 10 ] l do lng dn sng y c to bi mtim nt gp khc vi gc khong 120 . imnt gp khc ny lm cho nhng c lao, cn ct

nh ring r, ri rc lng sng pha thng lusau nhiu nm dch chuyn xung hlu bgili,

to thnh mt bi bi rng ln (c lao Mang C -hay cn gi l cn lit s) nm pha bhu i dinvi b sng Thng Phc. Mt khc, khu vcThng Phc, b sng, lng sng c cu to

bi cc lp st pha ct, bn st pha, bn ct pha vlp ct ht nh, cng chc rt thp, dbindng.

Do c im ca on bv sng Tn Chu l:(1) Lng sng un cong gp, thu hp, dng chy t

btchy vung gc sang bhu; (2) Hsi ccb rt su- hn 40m v (3) Thng h lu l ccon phn lch khng n nh, nn cn bo v

ngay khu vc th trn Tn Chu bng vic xydng k b sng theo phng php truyn thng.

Hnh 9di y l bk ang c thi cng ti bsng Tn Chu.

Hnh 9. Xy dng bk ti bsng Tn Chu

3.2. Bk thnh phVnh Long

Mc tiu ca kho st bng GPR nhm xc

nh hin trng cu trc a cht, khoanh vngnhng vtr xung yu ang c nguy cph vktcu v lm st ln trn mt k Vnh Long. Khu vck Vnh Long l bhu sng Tin qua thnh phVnh Long ko di t cu Vnh Long n khchsn Cu Long. Cc tuyn o c thc hin tstchn cu Vnh Long dc theo mt k cnh cngvin, bn v n khch sn Cu Long vi tngchiu di 750m. Hnh 10 di y l on uca k Vnh Long ang c o bng PulseEKKO 100.


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Hnh 10.on u ca k Vnh Long ang c o bng

Pulse EKKO 100

Mt ct GPR ca tuyn b k di 400m.

phc v cho vic minh gii a cht theo ti liuGPR chng ti chia tuyn o ra lm cc on

tuyn ngn (100m) v y trnh by on tuynthnht c chiu di 100m (hnh 11).

Cn lu rng, trong minh gii cu trc t tiliu Georadar th cc tham s vt l ng vai trquan trng, trong c bit l vn tc truyn sngin tc trng cho mi trng kho st. xcnh tham svt l ny, tin hnh o theo kiuim su chung (CMP) [7]. Tgin sng CMPvi ng ten 100MHz, khong cch hai ng ten l1m v bc dch chuyn l 0,25m, ta c th xcnh c vn tc sng t y l: 0,12m/ns. Gitr ny c s dng xy dng nhng mt ctcu trc theo ti liu GPR.

Hnh 11. Mt ct GPR on 1 tuyn bk Vnh Long

Hnh 12 l mt ct cu trc on u tuyn(100m) bk Vnh Long theo ti liu Georadar. Tgin sng radar, p dng chng trnh minh giiWinEKKO pro. chng ta chia ra c 4 lp vtcht phn b trn ton tuyn t trn xung di

nhsau:Lp th nht xut hin trn ton tuyn c b

dy trung bnh 1,5m. Vt liu trn mt ca lp nyl lp b tng mng v bn di l lp t p k.

Lp th hai cng phn b trn ton tuyn cb dy 2m vi vt liu l st pha ct ht nhngm nc.

Lp thba c bdy 8m v cng phn brngkhp ctuyn. Vt liu chyu ca lp ny l bnst v bin phn xca sng radar y rt nh.

Lp thtl lp su nht trn mt ct cu trcphn b rng khp trn ton tuyn c bin casng phn x nh lin quan n vt cht l ctht mn.

Trong mt ct cu trc cn xc nh c vtrca 4 dthng lin quan n cu to hng hc v1 i cu to xung yu. Cc vtr dthng ny c

bin sng phn x khc bit hn vi bin sng phn xba lp bn trn. i xung yu nmon u ca tuyn o v su ngay trn mtca lp th3 v di y ca lp th2.

Hin trng cu to ca k c bt ng nht songkhng ln v cng cha gy ra mt an ton cho k.Do cu to ng bk nm ngay st ng nhaca thnh phnn khnng trin khai cc phng


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php mt ct in rt kh thi cng v mt ct VLFbnhiu rt mnh, nn vtr cc dthng trn mt

ct GPR c kim chng bng cc l khoan

a cht cng trnh vi mc tng ng rt cao.Cquan chqun bk da vo kt qukho

st bng GPR thc hin duy tu bk.

Hnh 12. Mt ct cu trc on 1 tuyn bk Vnh Long theo ti liu GPR

3.3. Kho st st l b sng Si Gn, bn oThanha

Tnh trng st l b sng Si Gn, bn oThanh a gy ra thit hi vngi v ti sn rtnhiu. Tuy nhin, phm vi st lxy ra trn tngim v vn cn mang tnh bc xc cho chnhquyn thnh ph cng nh ngi dn sinh sng. c nhiu cng trnh nghin cu v c imthy vn cng nh dng chy v sn nh cang b [13]. Kho st nh gi hin trng cutrc ng bbng cc phng php a vt l gnmt t c thc hin y trong sut thigian gn y. Trong khun kh bi bo ny, tptrung gii thiu kt quca mt im kho st stl sn tenis L Hong bng t hp phng phpGPR v mt ct in a cc. Ti y, thc hin3 tuyn kho st song song vi ng bsng vi di 60 v khong cch tuyn l 15m. Tuynkho st c thc hin cch mp nc sng 3m ltuyn 1 nm ngay trn sn tenis vi chiu di l 60m c trch gii thiu di y (hnh 13). ycng cn phi ch rng, cho n thi im khost th sn tenis ny b l mt 20m trong thigian 4 tun trc . Kt quo mt ct a in

bng thit b Terrameter SAS 1000 [19] vikhong cch gia cc in cc l 2m cho ta cutrc theo dng phn lp ngang 5 lp c kch thcv gi trin trsut trong bng 6.

Bng 6.a tng theo ti liu a in sn tenisL Hong

a tngsu

(m)in trsut

(Ohm.m)Thnh phn thch hc

Lp 1 0-2,5 20-28 t p

Lp 2 2,5-7 10-20 St, bn, ct ht mn

Lp 3 6-15 8-10 Bt st, ct ht mn-trung

Lp 4 15-30 10-35 Bt ct, ct ht trung

Lp 5 30-40 35-80 St ct, Ct ht th

Hnh 13.o GPR theo tuyn 1 dc bsng ti sn tenis

L Hong bng thit bPulse Ekko 100 vi tn sng ten

100 MHz

Theo kt qu kho st bng GPR trn tuyn1(hnh 14) cho thy sbc tranh bt ng nht inhnh bng cc khi vt cht khc nhau m tri hn


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c l ct bo ha nc v ct st, bt st xen knhau. Trong , ng knht phi ni n vai tr

ca n ct ngm nc (hnh 15). Khi ngoi snc bao phbng bn t v cc loi cy nhdanc th nhng khi ct di su c ginguyn, nhng khi ci to sn lra cc khict v di tc ng ca ngoi lc nhdng chy,sng v, thy triu ln xung cng nhsthay i

thng xuyn ca dng chy s lm cho khi cttr thnh ct chy theo dng nc to ra nhng

kiu hm ch khc nhau v gy st l ng bsng. Kt qukho st ti sn tenis ny dbosst l trong thi gian ngn l 40 m tnh tmpnc. n nay ng bny c gia c ccmng su 28m v v tr 50m tnh t mp nc(hnh 13).

Hnh 14. Mt ct GPR tuyn 1 sn tenis L Hong bng ng ten 100 MHz

Nhchng ta bit, ton bmt ct a cht

c on sng Si Gn qua khu vc Thanh a ccu to bi trm tch tui Holocen gia - mun.Thnh phn thch hc gm bn st, bn st, bntrn giu hu c, cc lin kt kin trc yu.

Nhvy, on sng Si Gn vi su trungbnh 12m nm gn trong cu to t yu trm tchHolocen, y sng c ni khot vo lp ct trungmn ln bt. Chdng chy phc tp, hai chiutheo nhp thy triu. y sng c nhiu vng su,xoy, d to nhng hm ch sn b, gp cccu to ct chy h sn th hin tng st l

ng bl thng xuyn xy ra. Mt khc, on

sng vng nghin cu c c im nc ngm lncao ngang mt t v c quan hthulc trc tipvi dng chy sng. Chbn nht triu to iukin cho mc nc sng nng ln v h xung 2ln trong ngy, iu ny hnh thnh p lc thung tc dng trong t hai bn bgp phn thcy qu trnh st l, trt mt s v tr c iukin a cht khng n nh.

4. Mt snhn xt v kin ngh

c im ca vt liu trm tch bsng Tin vsng Si Gn l mm, do v bo ho nc phn

Hnh 15. Mt ct cu trc tuyn 1sn tenis L Hong theo sliu

GPR v mt ct in.

Ch gii: (1)=t p, (2)= St,bn, ct ht mn, (3)= Ct ht mn-

trung ln bt st, (4)= Ct ht trung

ln bt ct, (5)= Ct ht th, st ct


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di m thnh phn bao gm t bi, t st, ctht mn n ht trung, bn, tn tch thc vt. Cc

loi vt liu ny nu bo ho nc th chngthng c dn in cao, phn brt phc tp vthng l mt hn hp trong tng lp cu trc.Chnh v thm thp cc phng php a vt lnh GPR, VLF v mt ct in c th c sdng kho st i tng ny c hiu qu.

St lbsng Tin ti Tn Chu - An Giang,bk Vnh Long v bsng Si Gn ti bn oThanh a- thnh phHCh Minh u c ngungc lin quan n dng chy, lng sng v cu tong b. V vy, nghin cu cu to ng b

bng a vt l nhm nh gi hin trng cu trc

a cht chng ta phi thc hin cc tuyn kho stdc tng on ng b v nn b tr song songvi nhau. Tt ccc tuyn ny phi c o bngmt loi kch thc thit b lm iu kin so snhnh gi ngun gy st l. Ti mi on tuyno cn phi xc nh vn tc truyn sng in tc trng cho mi trng a cht khi sdngcng nghGeoradar, bi v phi ch n tnh rta phng y. Mt khc phi s dng t hpcc phng php bng vic o mt ct in vVLF trong iu kin cho php nhm xc nh dn in ca mi trng cc lp cu trc v tngchnh xc ca kt qukho st.

Cc s liu kho st bng GPR, VLF, mt ctin c xl, phn tch, minh gii thp to ra nhng mt ct cu trc hin trng ng btrn tng on tuyn sng Tin v sng Si Gn,lm csnh gi ngun gy st l, gp phn d

bo st lbsng cng nhxut cc gii phpchnh tr, gim thiu thit hi.

TI LIU DN

[1] Davis J.L., Annan A.P., 1989: Groundpenetrating radar for high resolution mapping of soiland rock stratigraphy. Geophysical Prospecting,37(5), p.531-551.

[2] David J. Daniels, 2004: Groundpenetrating Radar - 2 nd edition. The Institution ofElectrical Engineers, London, pp.726.

[3] N.V. Giang, J. Zietek, N.B. Duan, J.Karczewski, T. Golebowski, 2005: Study ofgeological sedimentary structures of Mekong river

banks by GPR: Forecasting avulsion-prone zones.Acta Geophysica Polonica, vol. 53,2,pp.167-181.

[4] Nguyen Van Giang, 1999:. Detectionfractures and defects in the dyke by GroundPenetrating Radar. Proceeding of the NCST ofVietnam,vol.11 (2), pp.95-101.

[5] Nguyn Vn Ging, 2000: Kh nng pdng raa xuyn t trong a k thut v mitrng Vit Nam. Tp ch a cht, s 257 (3-4/2000), tr.23-32.

[6] Nguyn Vn Ging, L Ngc Thanh, 2004:Khnng sdng thp cc phng php a vtl trong nghin cu cu trc a cht gn mt tti cc tnh pha Nam.Tuyn tp Bo co HNKHnghin cu cbn, Tp. HCM 20/12/2004, tr.71-79.

[7] Nguyen Van Giang, 2004: Geotechnicaland Engineering Application of GPR in Vietnam.Procceedings of International Conference onGround Penetrating Radar, 21-24 June 2004, Delf,the Netherland.

[8] N.V. Giang, L.N. Thanh, J.Zietek,J.Moscicki, 2008: Characteristics of sedimentarystructure of Mekong and Saigon river banks bygeophysical and geological data. Poster

presentation at the Near-surface 2008 EAGEconference, September 14-17, 2008, Krakow,Poland.

[9] L Mnh Hng. inh Cng Sn, 2002:Xi lbsng Cu Long v gii php phng trnhcho cc khu vc trng im. NXB Nng Nghip,Tp. HCh Minh, 196tr.

[10]L Mnh Hng, Nguyn Tun Long, 2001:Thc trng st l b sng Cu Long. Tc. Hotng Khoa hc, thng 10/2001. BKHCNMT.

[11]Keller G.V., 1993: Electrical andelectromagnetic methods in areas of complexgeology. Journal of Applied Geophysics, 29,181-192.

[12]McNeill J.D., Labson V.F., 1989:Geological mapping using VLF radio fields.Investigations in Geophysics N.3. SEG.

[13]Hunh Ngc Sang, Nguyn vn Thnh,Thim Quc Tun, 2003: Bn vnguyn nhn stl khu vc Thanh a Tp. H Ch Minh. Tc Phttrin KHCN, tp 6, s3+4/2003, tr.43-50.

[14]L.N. Thanh, N.V. Ging, N.S. Nhn, 2008:c im cu trc bsng Tin (khu vc Sa c)theo ti liu a vt l-a cht. Tc. Cc Khoa hcvTri t, T.30, 1, tr.84-90.


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[15] IDS Detector Duo Technical ManualInstruction, 2010 Pisa, Italy.

[16] Ramac/GPR instrument manual instruction,2004, Mala Sweden.

[17] Sensors & Software, 1996:PulseEKKO100RUN, Users Guide, Version 1.2.Technical Manual 25.

[18] SuperSting R1/IP User InstructionManual, 2010. Advanced Geosciences Inc. (AGI),

USA.[19] Terrameter SAS1000 Resistivity, IP & SP,

2006. Manual Instruction ABEM, Sweden.

[20] VLF WADI instrument manualintroduction,1995. ABEM Sweden.

SUMMARY

Enhancement to source determination for Tien and Saigon rivers banks avulsion-prone zones

by near-surface geophysical investigations

The paper presents complex geophysical techniques as well as Ground Penetrating Radar (GPR), Very Low

Frequency electromagnetic method (VLF), resistivity methods for investigating near-surface geological structure of riverbanks to localize interfaces and weakness zones which are related to the source of Tien and Saigon rivers banks

avulsion-prone zones. The field techniques and results of complex geophysical investigations on Tan Chau-Tien river

banks, Vinh Long embankment and Saigon river banks in Thanh Da were presented for assessment of landslide by

present river banks structure for short time forecasting. The near-surface geological cross-sections which were

established by geophysical data are proved effectiveness by some engineering wells in site. The result of investigations

is scientific based for Tien and Saigon river banks landslide forecast and maintenance/regulation to preventing hazards.

The near-surface geophysical methods are good tools for delineating fracture zones, saturated, weakness zones in

subsurface structures of river banks to landslide forecast in near future.

Documents

GeoRadar Nghien Cuu Sat Lo Song Tien