Gp phn o v bn cng trnh ngm th bng phng phpraa xuyn tNGUYN THNH VN, NG HOI TRUNG, L VN ANH CNG, NGUYN VN THUN, V MINH TRITTRNG I HC KHOA HC T NHIN, I HC QUC GIA TP HCMTm tt: Xy dng bn cng trnh ngm cho ton thnh ph l vic lm khng th thiu c ca cc th hin i trn th gii. i vi Tp. H Ch Minh do cc thng tin v cng trnh ngm trc nm 1975 c c sau ngy gii phng t nc khng y v vic thit k ngy cng nhiu cc cng trnh bn di mt t cng nh s thiu nht qun trong vic qun l, nn Tp. HCM ang i mt vi nhiu kh khn khi gii quyt cc bi ton v khng gian ngm. Raa xuyn t l phng php thm d in t kh hiu qu, cho php nh v cc vt th b chn vi trong phm vi vi chc mt tr li. Bi bo ny trnh by kt qu th nghim, kim tra v tm v tr ca mt s cng trnh ngm vi on ng ti Tp. HCM (h thng cp thot nc, cc loi cp, cng rnh,...) bng raa xuyn t, vi mc ch gp phn cng thnh ph tm ra phng php thch hp nht gii quyt vn trn.T kha: Raa xuyn t (GPR), bn , cng trnh ngm, thm d in t, a vt l.CQM xun qu tbo tr cng xy dng14 TH NGHIM & KIM NH XY DNG - S 06 (01/2013) 1. Khi nimRaaxuynt(GPR)hayGeoradarl phng php a vt l hin i s dng snginttrongditnscaot khong10n3000MHznghincu cutrctngnng.Doditnshot ngcaphngphprtcao,nn sukhostnhhnnhiusovicc phngphpavtlkhc. Tuynhin, phngphpnycuimltc khostrtnhanh,phngiiv chnh xc cao.Sng GPR c pht di dng cc xung sngintnhantenpht,lantruyn trong mi trng v phn x li anten thu tccmtranhgiihocccitng cccthngsthunlichophnx sng in t [4]. (Hnh 1)2. Kt qu th nghim2.1. Thit b v thng tin khu vc kho stThitbcsdnglDetectorDuo ca hng IDS () vi hai anten 250 v 700 MHz c mn chn. phn gii ca ant-en 700 MHz khong 20cm. Do anten pht v thu c t c nh nn thit b ny chthuthpdliubngkiukhong cch chung. (Hnh 2 Chng trnh Detector Duo SW km theo mydngthunhndliuthca, v hin th hnh nh c x l s b ngay lc kho st. S liu kho st s c x l tinh bng chng trnh Refex (phn mm dng cho a chn thm d). Khuvckhostcthchintrn mtonngnh TPHCM,nic h thng cng trnh ngm tng i dy c. Kt qu sau khi minh gii s c so snh vi thng tin c cung cp t cc cngtyqunlvhthngcpthot nc,cpinngm,cpquanghoc nhng quan st trn hin trng.Khuvckhostc14tuyno,bao gm 12 tuyn ngang v 2 tuyn dc. Hai tuyn ngang lin tip cch nhau 15m. Hai tuyn dc di khong 150m nhng theo hai hng ngc nhau.Hnh 1. Nguyn l hot ng ca phng php GPRHnh2.KhostGPRtiTP.HCMbngthit b IDS S 06 (01/2013) - TH NGHIM & KIM NH XY DNG 15 2.2. Kt qu kho stMtsginraasaukhicxl bng chng trnh Refex c biu din bn di. Mt ct GPR hnh 3a cho thy ba hypecbol lin tip nhau trong phm vi t 3,5 5m (ba mi tn mu trng). Trn mt ct tuyn hnh 3b v tr 14 16m, v hnh 3c v tr 5 6,5m cng xut hin cc d thng tng t. iu ny gip khng nh c ba ng ng ko di (theo th t l DV3, DV4, DV5) dc khu vc kho st. Tuynhin,ktqunykhngchophp xc nh y l loi ng g. su v v tr ca cc ng ng ny khng ng nht c th do a hnh khng bng phng v s dao ng ca cc anten khi di chuyn. Vntctruynsnginttibavtr trn khng thay i nhiu v bng 0,1m/ns. Sau khi nhp vn tc truyn sng vo chng trnh, ta o c su ca cc dvt,cnkchthcctnhbng phngphpdchchuynKirchhof[4]. Kt qu th hin trn bng 1.Trn hnh 3b, cn xut hin hai hypecbol ti v tr 11 v 12m (DV1 v DV2). Nhng tnhiunycngthyctrncc tuyn cn li nhng khng r rng. (Hnh 3a,Hnh3b,Hnh3c,Hnh4a,Hnh4b, Hnh 5, Hnh 6, Bng 1, Barng2)Hnh4av4blktqucctrat haituyndccchiudikhln. suvkchthccanhngdvtny c tnh tng t nh cc tuyn ngang. Trong phm vi kho st, nhm thc hin phthincchnvtrdonl ng thot nc ct ngang ng. 2.3. Nhn xtKt qu gii on kh tng ng vi cc thngtintinnghim.Hthngcng, cpccungcptrcuxuthin hu ht trn cc tuyn GPR ct ngang. C hai trng hp ngoi l trong kt qu minhgiildvtDV1vDV2chxut hin trn tuyn 8, v pht hin thm hai ng cng thot ct ngang ng (9 so vi7). TnhiuDV1vDV2xuthinrt mtrnhuhtmtctcthdotnh chtincavtliulmvahvng khtngngnnsngintgn nh khng phn x li. su v kch thc ca mt s cng, cp ngmcssailchsovitiliuc cungcp.Phngphpdchchuyn Kirchhofcthchoktqukhngtt nu vn tc truyn sng tnh c khng chnhxc. Tuynhin,sais0,1mivi K hiu Cng trnh ngm su ti nc (m) (mm)DV1 Cp ngm 0,9 200DV2 Thot nc 0,8 1000DV3 Cp vin thng 0,6 200DV4 Cp nc 0,85 400DV5 Cp ngm 0,9 150DV6 Thot nc 0,9 600DV7 - DV14 Thot nc 0,9 500BNG 1. KT QU MINH GII S LIU GPRCQM xun qu tbo tr cng xy dng16 TH NGHIM & KIM NH XY DNG - S 06 (01/2013) su v 0,05m i vi kch thc c th chp nhn c.phngiicaanten250v700MHz khngchophpphnbitccng cptrongcngmtbhocccng ng qu gn nhau.3. Kt lunQuaqutrnhthnghimnhvh thng cng trnh ngm th bng raa xuyn t, nhm tc gi c mt s nhn xt v xut sau:+ Raa xuyn t l phng php a vt ltiucthnhvtngichnh xc cc cng trnh ngm.+ Cn chn c loi anten ph hp vi yu cu v c phn gii v su ca cuc kho st.+ Qu trnh x l v minh gii ti liu cn c nhiu kinh nghim v thng tin c cungcptrctccnvqunlh thng cng trnh ngm.+ Cn thc hin tht sm vic o v li bn cng trnh ngm cho ton thnh ph. + qun l h thng cng trnh ngm mt cch tt nht cn kt hp thm GIS. Tuynhin,saisqulncahthng nh v l mt bi ton kh.Ti liu tham kho[1]DavidJ.Daniels,GroundPenetrating Radar,TheInstitutionofElectricalEngi-neers, UK, (2004).[2]Nguyen Thanh Vanandetal,Investi-gatingsinkholesbygroundpenetrating radar in Ho Chi Minh city, The 6th Interna-tionalConferenceonAppliedGeophys-ics, Thailand, (2012). [3] Nguyn Kim nh, Nguyn Thnh Vn, Trngint,NXBihcQucGia TP.HCM, (2010).[4] Nguyn Thnh Vn v nnk, Xy dng quitrnhvnhnhthitb,thuthp,x l,minhgiisliuraaxuynt xcnhcchngmvmtscng trnh ngm trn a bn TP.HCM, ti S Khoa hc & Cng ngh TP.HCM, (2011).Hnh 3a. Mt ct GPR tuyn 5Hnh 3b. Mt ct GPR tuyn 8Hnh 3c. Mt ct GPR tuyn 10Hnh 4a. Mt ct GPR tuyn 13Hnh 4b. Mt ct GPR tuyn 14Hnh5.Sminhgiihthngcng trnh ngmHnh 6. S h thng cng trnh ngm c cung cp trcK hiu Cng trnh ngm su ti y (m) (mm)1 Cp ngm 1 1,22 Thot nc 1,8 10003 Cp vin thng 1 1,24 Cp nc 1,5 2,5 4005 Cp ngm 1,5 2,26,9 Thot nc 6007,10,11,12 Thot nc 5008 Thot nc 400BNG 2. THNG TIN V H THNG CNG TRNH NGM C CUNG CP TRCRaa xuyn t (GPR) hay Georadar l phng php a vt l hin i s dng sng in t trong di tn s cao t khong 10 n 3000MHz nghin cu cu trc tng nng. Do di tn s hot ng ca phng php rt cao, nn su kho st nh hn nhiu so vi cc phng php a vt l khc. Tuy nhin, phng php ny c u im l tc kho st rt nhanh, phn gii v chnh xc cao. S 06 (01/2013) - TH NGHIM & KIM NH XY DNG 17