KHOfl HOC g* PJP.J.'^Q

TAP CHl

KHOfl HOC g* PJP.J.'^Q

PM'IJiMI'il-^'lhii'i=ir;Tijj;#iJ ISSN: 2354 - 0567

AP DUNG RA DA XUYEN D A T TRONG NGHIEN CLTU DjA C H A T CONG TRiNH, X A Y DLFNG V A G I A O THONG APPLYING GROUND PENETRATING RADAR FOR STUDYING GEOLOGICAL ENGINEERING, CONSTRUCTION AND TRANSPORTATION

vs.y^ Nguyen Thanh Van

• ^ « = ^ ^ £)?/ hoc Cdng ngh$ Sai Gdn Oang Hoai Trung

Og; hoc Khoa hoc Ti/nhien Tp.HCM TLF D a n g Q u o c Thai Dai hoc Cong nghe Sai Gon

T6M TAT

Trong nhd-ng nam gSn day, ra da xuyen d4t hay GPR (Ground Penetrating Radar) dang duac xem la phuxyng phap dia vat ly tdi uv trong khao sat dia chat t§ng nong, kiSm tra va danh gia chat Iwcrng cac cong trinh xay du-ng, giao thong, do ve ban do cong trinh ngim va khao co. De cac thong tin ben du-di m$t dM du-ac thS hien chinh xac tren mat cit ra da xuyen dat, cac bu-ac phan tich v$n tdc va dich chuyen iuon dong vai tro rSt quan trong. Bai bao nay trinh biiy ly thuyit, phuxyng phap tinh toan van toe va diet) chuyen so lieu ra da xuyen dat ma nhom tac gia da nghien cu-u trong thai gian qua. Cac u-ng dung cOa ra da xuyen dat da dem lai nhO-ng kSt qua kha quan va dong gop rSt nhiSu cho s u phat triin ca sa h?

t§ngcua Tp.HCM.

TIP khoa: Ra da xuyen d§t, danh gia chat lu-qrng cong trinh, dich chuyen.

A B S T R A C T

In recent years. Ground Penetrating Radar (GPR) has become the optimum geophysical metl)od for surveying near- surface geology, checking and assessing quality of construction and transportation works, mapping underground utilities and archeology. For GPR sections to show correctly subsurface information, estimating electromagnetic wave velocity and migrating always play a crucial role. This article introduces theory and method for determining velocity and migrating GPR data that we study in some time. GPR applications brought a lot of good results and contributed to the development of trans- portation infrastructures in Ho Chi Minh City.

Keywords: Ground Penetrating Radar, assessmentof quality of construction, migration.

iSSN: 2354 - 0567

TAP CHi

K H o n HOC et p n o T H O

•I.IIIJ.Hl.HJIJU.»MAIimi(.ILI

1 . . C a sir ly thuygt phu'o-ng phap ra da xuyen

1.1. Khai niem

Ra da xuyen dat la p h u a n g phap dia vat ly hien dgi dua tr6n c a s a ly thuyet cua trudng song di$n tCf a dai tan so tCr 10 - 3000 MHz de nghien ciru eau true va dge tinh cua v$t chat tang n6ng ben dual mat dat.

1.2. V$n toe va SLF suy giam cua song di$n

Nguygn ly hogt dpng cua phuang phap ra da xuyen dat d y a tr6n s u Ian truyen song dien tiy trong dat va gh; nh$n nhu-ng tin hieu phan xg cd Ich trong qua trinh s6ng phan xa lai. Trong m6i truang dong nhat v^ d i n g h u a n g , s6ng GPR tuan tiieo h# phuang trinh IVIaxwell [ 1 , 2, 6].

Ti> h$ phuang trinh Maxwell, ta nhan d u a c cac phuang trinh song (hay phuang trinh Helm- holtz) dgng phue:

V^E = j(0[i(a + ja)8)E V^H = ja)|a(a + jcoe)H

dat, y ^ = a + j(3^jffl|i(a+jco8)

Nghiem cua hfe p h u a n g trinh tren doi vo'i song phang dan sac theo ehieu thuan, trong mien thd-i gian:

E ^ ( z , t ) = EoC""^ c o s ( o j t - p z )

H^(z,t) = Hoe""'cos(a>t-pz)

T u do ta tfnh duac*

o: dp dan dien (mS/m);

£• dp dien tham (F/m);

a: h i n g s6 tat dan (dB/m);

y: hang so truyen song.

w: tan s6 goc (rad/s) p: do t u tham (H/m) 3. hang so pha V$n toe tnjyen s6ng dien tCf:

v = — ( m / s )

Tinh v$n toe truyen song b i n g each n^y co the d i n den sai so 16'n do m6i trub-ng dja chat la m6i truang bat dong nhat. Dh k h i c phue dieu n^y, ngoai thuc dja, nguai ta co the tinh vgn toe b i n g eae e^ch sau: s u dyng vat the dS biet dp sau, phuang phap hinh hoc, gian do CMP hogc c^c phuang phap dich chuyen.

S\f suy giam cua song diSn tCr tl le nghich vai ham mij cua hang so t i t dan o.

1.3. He so phan xa va h$ so truyen qua

P-w 1 f

?l rS ^{1 f ^}

^{. •\}

^-n

He so phanxa: R = -

He s6 truyen qua: T = 2 + 1 , J 2ri2

1 2 + 1 1

Vai n,. H;: '3 tong tro ciian thu-c ciJa moi tru-o-ng thLi'nhat va thi> hai.

1 = JUH

^ a +jcos (n)

1.4. Phin biet vit chat dan di$n tot va v$t chat each dien tot

T u phuang trinh Maxwell dang phue:

VxH=:aE + j(oeE

TAP CHi

KHOn HOC & D f l O TIIO

ISSN: 2354-0567

Ta nhSn thiy, mat dp dong toan phan j ^ la tong eae mat dp dong dien d i n J^, = o E va mat dp dbng dien dich la J _ j y j g g , Mat dp dong diSn d i n cho thay s u suy giam nang luang va mat dp dong di6n dich the hien nSng lupng tich trCp trong moi truo'ng

Jc

3c

Vo'i tanG gpi la tang ton hao.

tan 6 « 1: vSt each di6n tot Ltlc nay, he so suy giam a = 0, nghla la trong moi truang c^ch di^n t6t, do Sciu khao sat t u a n g d6i Ian.

tan 6 » 1: vSt d i n dien tot.

LOc nay, he so suy giam o rat Idn, nghTa 1^

trong moi truang d i n dien tot, dp sau khao sat se r i t thap.

2. Djch chuyen dja c h i n

Ve mat toan hpc, djch chuyen dia c h i n la giai bai toan phuang trinh truyen song. Trong thuc tS x u ly s6 lieu, buo'c dich chuyen dirge thuc hien trSn he thong may tinh va p h i n m i m lap trinh, dieu nay doi hoi phai dung cac thuat toan giai tich s6 de xap xi nghiem phuang trinh song, Cfng vai moi dgng thuat toan n h u vay, ta co mpt phuang phap djch chuyen. Co ba truang phai giai tich s&

pho bien nhat d u a c ap dung vao dich chuyen:

cong truang song tan xa - dich chuyen Kirchhoff.

chuyen rmkn b i n g biSn doi Founer - dich chuyen F-K; hg truang - dich chuyen sai phan hipu hgn (F-D) va djch chuyen dai pha n6i suy tuyen tinh (PSPI)[3, 4, 5, 6].

2.1. Phuang phap djch chuyen Kirchhoff Phuang phap nay tien hanh dua vao nguyen ly Huygens - Fresnel va bai toan Kirchhoff cac ranh giai phan xa d u a c xem n h u tgp hpp c^e diem t^n xa, khi song tai kich dong vSo ehung.

chung tra thanh cac tnjng tSm ph^t song cau tiii>

cap, phat ra cac dao dong tcin xa gui ve cac diem khac nhau dpc theo tuyen quan s'at x.

Cac dao dpng song cua cac diem tan xa kii^c nhau (nam trong lat dt dia chat) khi phat then den mat dat, chung giao thoa vo'i nhau va tgo tiianh truo'ng song tong ghi d u a c dpc tuyen quan si\

d u a l dang cac song phan xg, Nhu vay, co the xem cac xung song phan xa ghi d u a c tai diem x, bat kl tren tuyen quan sat la tong cua cac p h i n dong g6p do cac diem t^n xg khac nhau n i m trfen ranh gid'i phan xg song gui ve diem quan sat.

Bai toan Kirchhoff da dupe Sneider (1978) va Scales (1995) giai cho truo'ng the vd huo'ng - s6ng dpc co dgng:

r la khoang each t u Ccic diem quan sat den diem tan xa: r'^ =(x-Xjj f + Z^

e la goc giO'a tia 16 va phuang phap tuyen den mat quan sat v^ P(x, z = 0,t) la truang song do dysqc tren mat d i t .

2.2. Dich chuyen tan so - s o s o n g (F-K) Phep djch ehuyen goc nghieng trong mien F-K dupe thuc hien theo dh xuat cua Stolt nSm 1978, xuat phat lit p h u a n g trinh s6ng phang, true x n^m ngang, truez h u a n g xu6ng.

Neu s u dung tich phan Fourier 2 chieu doi voi bien X, z cua ham ^ ' ( ' x . z . / ; , thi'

V„rk,,k,.IJ= ]\'i-(x.=.iM~"''"'"dxdz Neu giai han bai toan doi vo'i song phing 6\kv hoa thi pho F-K cua co dang-

fJli,.lc,.l)^'i'Jlc^,ic^.Oje"" ' Do do, bieu thuc de tinh dich chuyen truo'ng

song trong mien F-K co dang'

•

210

ISSN: 2354 - 0567

T A P C H I

KHon HOC St o n o r n o

VJk,.k,.0) = vfJk,.O.a

C6ng thijc (5) la c a s a de tinh dich ehuyen tm'Q'ng song b i n g p h u a n g phap F-K. Sau do, dCing phep bien doi Fourier n g u a c de chuyen ham

^ x z f ^ i ' ^ ; ' * ^ ) trong mien F-K sang mien kh6ng ttiffi gian.

2.3. Phirong phap dich ehuyen sai phan hOv h^n (F-D)

Dieh chuyen sai phan hO-u hgn la phuang phap giai phuang trinh s6ng de hg truang xuong phia dual. No hoan toan giong phuang phap tinh ha truong t u v^ trpng lye b i n g p h u a n g trinh Laplace theo dang: y - ^ =^0' Phuang phap dich chuyen sai phSn hi>u han gom hai b u a c ngogi suy Vci hpi tu truo'ng sdng.

a) L^ thuySt ngoai suy truung song Ly thuyet ngogi suy t r u a n g song d u a c b i t d i u [it gia thuyet du- lieu truo'ng song p{x, z, t) da d u a v^ dang zero offset, d u a c xac dinh trong mien (x, t) va thoa man phuang trinh song vo huang sau,

g"P| 5 V ^ 1 d-p j^^

dx' 6z^ v' dr

O dSy X la bien true ngang cua diem giua, z la ciii^u sSu, t la thcvi gian hai Ian song t m y i n , v la van t6c, k^ la s6 s6ng ngang bieu k i i n va LO la tan so goc Truang song co the bieu d i i n trong mien tan s6 - so song b i n g bl^n doi Fourier hai chi^u:

Gia s i j vSn toe chi thay doi theo do s§u z, v

= v(z), Thay phuang trinh (7) v^o p h u a n g trinh B) Chung ta thu d u p e p h u a n g trinh vi phan thong hifdng sau

Phuang trinh (8) co nghiem giai tich:

Trong do'

^(k^.2 + liz,(>i) = P(K.z.<^)exp(ik^Az)

Nghiem nay v i n dung vo'i v bien thien theo z, dP(k..2.w)

^-m

P(k,.z.t^) (10) mi§n la dgi lupng Az du nho. De ngoai suy truo'ng song xu6ng d u a l doi hoi Az > 0, tuc la k v^ uj se cung dau (bieu thue (10) lay gia trj k^ duang), tuang ung vai song tnjy^n theo chi^u am ciia true L

Phuang trinh (9) ia nghiem cua phuang trinh song mptchiSu sau

ep(k,..

m

F(k,,z,ta) ^{( H )} Day la phuang trinh ngogi suy chinh xac cho van t6e khong doi.

b) H6i tu trwang song

Thuat toan dich chuyen F-D doi hoi khoi lupng tinh toan khong 16 nen n h i i u gia thuyet d u a c s u dung de xap xi phupng trinh song (11) nham giam thieu tho'i gian chay cho may tinh Thuc chat, viec x i p xf t u a n g d u a n g vai lay gan dung bieu thuc c§n bac hai trong phuang trinh (11) (goi la toan t u ngoai suy) theo hai c^ch khai then Taylor (Gazdag, 1980) va khai trien phan s6 lien tyc (Hil- debrand, 1956).

Giai phuang trinh vi phan b i n g phuang phap sai phan huu han chung ta se tim d u a c cac gici tn a duo-i s§u. Cuoi cCing, b i n g each l i y phep tong thuc hi6n cho tat ea gia tri oj thu d u a c hinh anh ben dud'i tai do sau (z + Az)

P(x.z + Az.l = 0) = Y,P(x.: + Az.a) ₍₁₂₎

2.4. Phmyng phap djch chuyen dm pha npi suy tuyen tinh sau cong (PSPl)

Mac du dich ehuyen do'i pha noi suy tuy&n tinh phu thuoc thuat toan ngoai suy n h u dich chuyen F-D, n6 giai bai toan b i n g c^ch xem xet s u thay doi truo'ng van toe.

Phuang trinh (9) trong phan djch chuyen F-D c6 the Viet duo'i dgng'

TAP CHl

KHOfl HOC & p n o TflO

•Liiij.uiniJ<jijjjjaaiim!Bi

ISSN: 2354 - 0567

/'('A,, z + Az, (o; = Pfjt^, z, uje>

Phuang trinh ngogi suy truo'ng sdng (13) eh?

Sp dung duac trong tru6'ng hap van toe v khong thay doi theo phuang ngang. De xet den hu6ng bien thi6n n^y tren thuc te, trud'c h i t ta tach phuang trinh ngoai suy dgng tong quat (9) th^nh hai thanh p h i n :

(14)

(15) p-{z)=Piz)exp(i^Az]

P{z + &2)=P'(z)exp\i{k,--]&z\

Vai v' ^ v{x, z) la mot phep xap xi v6i v(x, z) Phuang trinh (15) khong the tinh to^n true tiep khi v" = v(x, z), do do can phai thyc hign gian tiep thong qua m6t so b u a c

Bub'c 1 Tim hai van tocv^ v^ v^+1 nhu lachan tr6n v^ chan duo'i cua v(x, z). Cac v$n toe nay duac goi la v$n toe tham c h i l u .

Buo'c 2 Thay hai gia tri van toe nSy vao cong thO-c (15), ta d u a c hai hSm song tham chieu trong m i i n F - K , sau do thuc hi6n phep bien doi Fourier nguac, dua ham s6ng ve mi^n (x, w).

H^m s6ng e i n tim se la:

Thuc hi^n c^c buo'c tinh toan tren cho tilrng diem toa do, sau do tinh tong truo'ng sdng theo ui de thu dwgc truo'ng song tai t = 0, cCJng i^ truong song cua eSc doi t u p n g phan xg:

/'(.t,z + Az./ = 0) = ^ P ( . r , z + Az,(o) (17)

Nhu v^y, phep djch ehuyen d6'i pha n^i suy tuyen tinh dS hoan tat vi6c d u a d u a c tin hifeu plian xa trong lat cat c6ng ve dang mat phSn each cua moi truo'ng.

3. U'ng d u n g 3.1. Khao CO hoc

Vo'l dp phan giai cao, phuang ph^p ra da xuy- en dat da d u p e s u dung trong khao co hoc vS dem lai nhung ket qua het sue thuyet phyc.

Hinh la Khu vi/c khao sat va ho dao cho thay b&c tuang thanh a vi tri 5

Wat Pan Sao (Thai Lan), hay con gpi 1^ den soc vol. Phan Ian khu v y c den bj chia c i t vS thupc Pan Sao, n i m ben ngoai buc tud'ng thanh pho quyen sa hO-u c& nhan cho den tSn nam 2007.

Chiang Mai, bao quanh bai hao nuo'c d y p c d i n Khi trung tam nghien ciiu Malaria d u p e xay du'ng, tip thac Huay Kaew. Wat Pan Sao bi ph§ huy trong trung tarn da thu lai nhCVng khu vue nay va tao ehien tranh va d u a c SLP dung nhu khu vue eham thanh trung tam PhSt giao cua Chiang Mai. OiSn

TAP CHl

KHOfl HOC & DflO TflO ISSN. 2354 - 0567

tho' Chanantra Satit Mahathan Baramee Snchaiya Monkol hien tai d u p e xay dyng tren vCing den tho' xua.

Muc dieh viec khao sat cua chiJng toi thuc hien tai den Pan Sao v^o thang 1/2010 n h i m phue vu cong tac khao co, tim k i i m va xac dinh vj tri cOng nhu d6 sau cua cac buc tuo-ng dugc tim thay trong eae ho dao nhung tranh pha hong cac co vat trong qua trinh khai quat di tich nay. Khu v y c

nay da co mot so h6 dao de cung cap thong tin tien nghiem phue vy cho viec khao saL Thiet bi d u a c s u dung la GSSI SIR-20 vai anten 200MHz c6 man chan. cac tuyen khao sat each nhau 1m vo'i hai dang t u y i n c i t vuong g6c tit Bac - Nam va D6ng - Tay. Dinh dang tap tin tai day la •*.dzL VSn t6c truyen sdng dupe tinh b i n g each s u dung cac hyperbol tan xg tren mat c i t GPR. Ket qua van toe trung binh tai khu vue khao sat khoang 0,07 m/ns

Hinh 1b. M$t cSt doc tiieo hu6ng 0 - Hint) 1c Mat cat doc theo huvng B - (v

f. Hinh 2a Mat cSt GPR 3D - 1 Hinh l b va 1c cho t h i y mat c i t 2D tai khu vue khao sat theo hai huo'ng Dong Tay va B i c Nam Q\tgc ve b i n g phan mem Matlab. Rat nhi^u di thudng xuat hien r i t ro tren ca hai mat c i t , tuy nhien hinh anh nay khong cho ta t h i y d u a c mpt so dac tinh v4 vj tri va kich t h u a c eua ehung. De chinh xac han, t u d u lieu thu d u a c , chQng toi da tien hanh ghep cac mat c i t 2D thanh mat c i t 3D the hi?n ro han tinh chat cua cac di thuang cung bing phan mem Matlab. CSc d u ligu theo hai huang khao sat d u a c tong hap lai, roi d u a c ve

Hinh 2b Mai cat GPR 3D - 2 thanh m6t mat e i t 3D oho phep quan sat khu vue khao sat theo nhieu h u a n g a tung dp sau khae nhau.

Hinh 2a va 2b la mat cat 3D cua tuyen khao saL cho phep ta quan sat d u a c ben d u a l mat dat theo phuang t h i n g dung hogc phuang ngang nhu trong cac mat c i t 2D Dieu nay giup nguai minh giai dS dang han trong viec xac dinh dac tinh c a c d j thuang.

Nhu v | y , qua s u dung phuang phap ra da xuy- en dat do dac khao co tai Wat Pan Sao, ta nhan

TAP CHi

KHOfl HOC & P f l O TflO

ISSN: 2354-0567

thay rang dO" lieu thu thgp d u p e rat tot de x u ly vS minh giai. S6 lieu thu d u a c theo cac huo'ng khac nhau d i u cho nhipng k i t qua kha dong nhat. Cac mat c i t da cho thay rat nhieu di thuang nhu 6ng nuac, buc tuang thanh, r i cay, kha phu hpp vd-i nh&ng thong tin d u a c nha chCia cung cap truac.

Hau nhu khong tim thay Qitgc eae eo vat bang dat nung, d i i u nay co the do dp phan giai eua thiet bj chua du. Tuy nhien, quan sat mpt s6 hien vat

cd mat tgi Ccic h6 d^o, ta thay rang ehung thu&ng xuat hien a eae vi tri rat gan buc tuang thanh. Do ca hai d i u c6 cung c h i t lieu d i t set nen phuang phap ra da xuyen dat rat kho de phan bigt ro rang Cac ket qua tren day da d u a c kiem chiJng chinh xac nha nhOng khai quat tai khu v y c nay. Niiu vay, phuang phap ra da xuySn dat hoan toan phu hpp khi s u dung de khao sat dja c h i t tang n6ng vai muc dich khao co.

thai

6 dao

Vi tri dat may do

Hinh 3: Kit qua khao co tai Wat Pan Sao

3.2. Djnh vi cap Crng lifc tai toa nha 177 Hai Ba Trwng, quan 3, Tp.HCM

Die lieu dupe thu thap tgi toa nha 177, duang Hai Ba Trung, Quan 3, TP.HCM. Toa nha gom 1 t i n g tret va 12 tang lau vai dien tich mat san 300 m^ Do t h i i u sot trong qua trinh thi cong, nha t h i u muon khoan tat ca cac t i n g de l i p mot ong thong gio t h i n g du'ng mai t u tang tret den san thuang.

Tuy nhien, ho lai khong chac chan vi tri cua cac cap d u ung luc, von la thanh phan r i t quan trong

giup chju tai toan bp cong trinh, mSc du vj tri cua chung da d u p e danh dau ro rang tren mSt san San be tong cua mSi t i n g g6m co mot tam lu'di thep nam each mat san 220 mm, va cac cap Crng luc (ij) = 16 mm, kha nang chju tai 35 tan) c^ch mat san khoang 150 mm.

Trong bai bao nay, ehung toi chi trinh bay ket qua khao sat b i n g ra da xuyen d i t tren t i n g 3, bao g i m 12 tuyen do 7 tuyen doc va 5 tuyen ngang.

Hinh anh toa nha va sa do t u y i n khao sat duoc

ISSN; 2354 - 0567

TAP CHf

KHOfl HOC & PflO TflO

•i.iiij.uii.ii,^jy.iJMJ.iiij.iju.i

i j b ) "

Hinh 1.- (a) Toa nha 177, duung Hai Ba Trimg, Quan 3, Tp HCM a (b) So-t36 cac tuyen khao sat bang ra da xuyen 6at

Hinh 6 la mat cat ra da xuyen dat cua cac tuyen 1, 2, 4 va 12, thu nhan bai may Detector Duo (hang IDS - t ) v6i anten co man c h i n , t i n so 700 MHz.

Trong mgt cat t u y l n 1 (hinh 6a), cac thanh thep va cap ung luc co the d u p e phan biet kha d§ dang nha vao s u khac biet ve dp sau. Cac hy- perbol xuat hipn deu dgn dpc theo t u y i n khao sat tai vi tri 3,7 ns la tin hieu phan xa t u cac thanh thep ben trong san be tong Hai hyperpol tgi (x = 1 m; t = 2,7 ns) va (x = 1,4 m; t = 1,7 ns) triing vai vet danh dau vi tri cap tren mat san la vi tri cac cap d y ung lue. Oe xac djnh van t6c truyen song trong be tong, ehung toi s u dung thuat toan djch chuyen Stolt ket hpp gian do entropy cue tieu (gia trj entropy cang nho the hien dp nhieu loan cua anh cang it) [7, 8]. Day la k i t qua mai cua nhom

nghien cu'u d u a vao ehuan XCP ly anh tin hieu so.

Hinh 5 the hien gian &b entropy cua mat cat djch ehuyen vai vgn toe thay doi t u 0,06 m/ns d i n 0,20 m/ns. De dang nhan t h i y mat c i t djch ehuyen vai van toe 0,119 m/ns dgt gia tri entropy cue tieu Day CLJng ehinh la van t6c vRMS den dinh cua cac cap d u ung luc.

Do san be tong kha dong nhat nen van toe tren d u a c ap dung chung cho tat ca eae mat c i t . Dp sau cua cac thanh thep, cap ung luc A l va A2 Ian luat la 220mm, 160mm va 100mm. Dp sau eua eae thanh thep va cap (tng luc A l kha hap ly, tuy nhien dp sau A2 lai khac nhieu so vai thong tin tien nghiem. Ket qua t u a n g t y cung dupe ghi nhan tren t u y i n 2, 12 (Hinh 6b, d), 6 va 7 Cac tin hieu cap ung luc A3, A4 va A5 xuat hien tren tuyen 3, 4 (Hinh 6c) va 5 co cung dp sau 160mm.

Hinh 5. Gian do entropy

TAP CHi . _ _

K H o n HOC & p n o T B O

•I.IIIJ.UII.il.UIJ.IJJ.WJ.IIIJ.Iil.1.1 ISSN: 2354 - 0567

DiSTWiCE rUcTER; EiSTiWCE [UtTSRl • 1 STANCE lUETERJ

Hinh 6: Mat cit ra da xuyen dat: (aj tuyen 1. (b) tuyen 2; (c) tuyen 4; (d) tuyen 12

Ket qua cuoi cung cho thay trong khu vu'c khac cua toa nha nay, k i t qua khao sat hoan toan nay, c6 nam cap d u ung lu'C va chung deu khong dang lin cay va da d u p e kiem chii'ng bang each di qua vi tri d u ki^n cua ong thong khi (hinh 7). khoan san be tong.

Chung toi cung da tien hanh khao sat cac tang

Hinh 7 Sa do minh giai cap O-vg lu'c tang 3

3.3. Ho phun iu-a tai dwiyng Binh Lgi- Quan Binh Thanh-TP. Ho Chi Minh

Theo phan anh cua nguai dan ngay 28 thang 10 nam 2013, khu vue duang Binh Lai xuat hipn ho phun lua gay nguy hiem cho nguai dan sinh song trong khu vue va nguai di lai. Do vgy, S a KHCN Tp.HCM da k i t hap vai cac ca quan khao sat tien hanh dieu tra, tim hieu nguyen nhan nhim dua ra giai phap khic phue. Ngay 29 thang 10 nam 2013, Trung tam Dieh vu Phan tich Thi ng- hiem TP Ho Chi Minh da tiln hanh lay m§u dit va khi de phan tich. Cung luc do. Bo mon Vat ly Dia cau tien hanh SLP dung thiet bj Detector Duo cua

hang IDS (Y) de thu thgp so lieu GPR trong khu vue. S a do tuyen do dupe bieu dien theo hinh 8b, bao gom 12 tuyen do tren toan bp hem 234 duo'ng Binh Lai, quan Binh Thgnh (xung quanh vi tri ho phun lua). So lieu do dge dupe xu ly bang phan m4m "Xac djnh van toe truyen song dien tip" do nhom nghien cu-u thuc hign de tinh kich thu6c va dp sau cac cong trinh ngam. T u do, thanh Igp ban do he thong cong trinh ngam tgi khu vue khao sal nham phue vy cho cong tac dieu tra nguyen nhan gay ra ho phun lua.

ISSN: 2354 - 0567

KHon HOC & pno r n o

no Pin N i.u.\

1.6/ 1.7 1.17 [.11 I J M I.J

(b)

Hinh 8 (a) Da ra da xuyen dat tai ho phun iOa; (b) Sa do tuyin khao sat

\ OPEN ~ | [ RESET 1

CftLCULATE|

[ CLOSE ] VELOCITY Imlns]

0 . 0 7

Xmax [ m ] « 5 . 5 7 T n ) a * [ n i ] - J 1 2 0

Xo tmj = T O £ M I -

JO.7

i»

m^ fssnm

^ 3 f ^1 r -^- ' \J '

AMPLITUDE + 456558 A M P L I T U D E . -425734 V E L O C I T t [ i i i / n s l = 7e+«)7 DEPTH [ m ] = 101S

OBJECTS S i a [m] I 0 330183

OPEN [ C A L C U L A T E ! VELOCITY [ m ( i « l Ifman [ m ] - [ 5 . 5 7 X a [ . n 3 = j o . 7 0.076 Tma« [«]-|l20

/ \

6 10 IS

A M P L I T U D E * A M P L I T U D E - VELOCITY [m/ns] =

DEPTH [m] = OBJECT'S SEE l m | [

49072a 1 -465361 7G»Hia7 1 102 0 57439

TAP CHI

KHon HOC & pno THO

•i.iiij.un.ii.mj.ijj.ij.iiu.iii.1.1

ISSN: 2354 - 0567 0

AMPLITUDE * AMPLITUDE - VELOCITY (mfns] =

DEPTH [m] - OBJECT'S SIZE |m|

4B3237 -466439 e e ^ 0 7 1.16 0 366S45

Hinh 9 Ket qua dich chuyen tuyen T11 vai cac van toe: a) v = 0,070 m/ns, b) v=- 0,076 m/ns;

c) v = 0.080 m/ns

Thuc hien x u ly so lieu GPR trdn cac tuyen ngang, nhom nghien ci>u xac dinh d u a c vj tri ba di vat hai duong cap dien ngam gan v\ tri ho phun lua va mot duang 6ng cap n u a c a phia d6i dien.

Trong cac hinh 9a, b va c, eae hyperbol tai vi tri x = 0,7m, t = 29ns co bien do Ian va phan cue nguac chLPng to ong lam bSng kim loai. Dung phuang phap dich ehuyen F - D vdi cac van too khae nhau, ta d^ dang thay r§ng gia tn bien do tin hieu cue dai khi van t6e v = 0,076m/ns. Trong truang hap nay, chung toi da s u dyng nguyen tSc n l u dieh ehuyen vo'i van t6c chinh xac thi tin hieu se hoi tu tot nhat, d i n den bien dp dgt gia tn 16'n n h ^ t Day la gia trj van t6c truyen song trung binh tai dinh di vat (Vrms) V a i van t6e tren, ta tinh d u a c duang kinh cua ong khoang 0,27m, sau 1,5m vai sai s6 nho han 10%.

Tuang ty. I&n luat xet cac hyperbol tai vi tri X = 4,8m, t = 18ns va x = 5,4m, t = 20ns v^ thuc hien cac buac nhu tren, chung toi xae dinh van toe truygn song la v = 0,075m/ns vai gia trj bien do dat cue dai 70386. T u do, tinh d u a c dp sau cua dj vat Ian luat la 0,6m va 1m.

Thuc hien qua trinh x u ly s6 lieu tren cac tuySn doc, tuyen ngang va thong tin tien nghiem, nhom

nghien cuu da xac dinh d u a c he thong cdng trinh ng^m nhu hinh 10.

Dua vao ket qua thu nhSn tCf ra da xuyen flat, S a Khoa hpc v^ Cong nghe, S a Canh sat Ph6ng chay chOa chay TP.HCM da quyet djnh khai qugt xung quanh "ho phun liia". Thong tin t u viec ph^n tich m i u kh6ng khi cung n h u khao sat b§ng ra da xuyen d^t da gop p h i n xac dinh nguyen nhan vu chay tren d u a n g Binh Lai. Doi dieu tra phat hi$n ben d u a l mat d u a n g co nhieu day c^p b\ chay, bi du't, Chung to day la tai nan lien quan d^n su c6 dien. S a Khoa hpc va Cong nghg cho bietc^c day Ccip nay eo the da bj dap trong qua trinh (JSo duang lap dat c6ng cap nuac. Sau do duffi anh huang cua trieu c u a n g lam phat sinh hien tu'ong phong ho quang dien, cung cap mpt nguon nhiS' I6n gay chay va no eye bo Ben cgnh do, thong qua ket qua phan tich mau khi trong ho phat hien khi metan vai n6ng dp cao bat thucyng (0,2 - 2,0%). Do do khong loai t r u kha nang day chlnh la nguyen nhan gay ra hien t u a n g phun ICpa sau vu no.

ISSN: 2354 - 0567

TAP CHi

KHon HOC & pno rno

n.iiij.uii.n,jjy.ijj.ij.iiij,M

NH.A S6 236 VI TRI HO SLT PH.\T LIA

NHA SO 234

Hinh 10: KSt qua khao sat tren tuySn duang Binh Lai

4. Ket luan

Ra da xuyen d i t co nhieu ung dung rong rai, cd the giai quyet d u a c nhi^u thuc trang ma nuo'c ta dang doi mat nhu danh gia chat lupng eae cdng trinh giao thong, xay dung, dia c h i t cong trinh, khao s^t mdi truang, tim ki^m eae khoang san c6 ich, qui hoach khong gian ngam tai eae thanh pho 16'n va do tim bom min.

Ket qua xac dinh van t6c truyen song dien t u b^ng phan mem do nhom nghien c u u xay dung duac dua tren ngon n g u lap trinh IVlatlab cho k^t qua kha ehinh xac. Cac giai han dich chuyen dua tren gian do cue tieu entropy va cue dai nang

luang hoi tu deu nhan dwac ket qua hap 1^ Ngoai ra, doi vai cac khao sat e i n do chinh xac cao nhu khao CO, mat e i t ra da xuyen dat e i n duac bieu diSn duo'i dgng 3D de tang cuang s u chfnh xac cho qua trinh minh giai. Di§u nay hoan toan co the lap trinh b i n g eae ngon ngu' thong dung, khong e i n s u dung cac p h i n m i m thuang mai r i t d i t tien.

Can luu y la viec x u ly GPR thuang phai doi mat vai nhiSu t u nhieu nguon khi s u dung anten khao sat t i n so cao trong thanh pho va khu dan eu. Do do de eo d u a c cac k§t qua mong muon thi kinh nghiem giai doan dong mot vai tro r i t quan trpng.

Tai lieu tham khao

1. Nguyen Kim Dinh, NguySn Th^nh Van (2010), Truang Dien TCr, NXB Dai hoc Qudc Gia Tp. HCM.

2. Nguyen Thanh VSn, NguySn Van Giang (2013), Ra da xuyen dk: Phirang phap va Lfng dung, NXB D?i hoc QuSc Gia Tp HCM

3. NguySn Thinh Vin va nhom nghien cCru (2011), Xay du-ng qui trinh van hanh thiSt bi, thu thap, xu- /y, minh giai s6 lieu rada xuyen dit dS xac dinh cac hd ngkm va mot s6 cong trinh ngim tren dia ban thanh pho HCM, So Khoa hoc va Cong ngh§ TP HCM

TAP CHl

KHon HOC & p n o i n o

ISSN: 2354 - 0567

4. YImatz 0, 1987: Seismic Data Processing, chapter 3 Society of Exploration Geophysics.

5. Van NT, Giang N.V, CuongLV.A , Trung D H., TrietV.M, 2012 Kirchhoff migration for specifying velocity model in ground penetrating radar method. International conference on Ground Penetrating Radar (GPR). pp 419-424, Shanghai, China.

6 Giang N.V., Van NT., Trung D.H, Jarzyna J, Zietek J., Sylwia-Suchon T, 2012: investigation of sinkholes on the roads by GPR. Application to HCM city Vietnam. International conference on Ground Penetrating Radar (GPR), pp. 443-447, Shanghai, China

7 Fiores-Tapia D., Pistohus S., 2010 An Entropy-Based Propagation Speed Estimation t\4ethod for Near-Field Subsurface Radar Imaging. EURASIP Journal on Advances in Signal Processing, volume 2010, Article ID 636458, 13 pages.

8. Zhou H., Wan X, Lt W., Jiang Y, 2011: Combining F-K Filter with Minimum Entropy Stolt Migration Algorithm for Subsurface Object Imaging and Background Permittivity Estimation. Procedia Engi- neering, Volume 23, pp. 636-641