|
e . ~Y ~. wt e ~ ~h; e ~ t ®~' S ECG
<br />~~e, 6-rb'-sS
<br />;uency components of the Fourier spectrum of
<br />tearly wtth the mass (the force amplitude con-
<br />tnce. and the contac[ time the remaining I/3).
<br />of displacements and sibratlons induced on the
<br />.lance from the source point grow rouohly in
<br />nt
<br />pact velocities, the time variation of the contact
<br />?r In shape (Fig. 6). 1[ Follows that. to a first
<br />of the Fourier transform of the contact Force
<br />t i;, linearly with the mass: also, the frequency
<br />with the reciprocal of the contact penod, in
<br />t [ht CUbC rOQI Jt [he maSS.
<br />gut during the sabbatical stay of the first two
<br />:DEX, the Center for Experimental Research
<br />thlic \1'orks, r\'ladrid. Spain. The writers would
<br />General of Scien[ific and Technical Researh
<br />Education and $cience, and the senior admin-
<br />support.
<br />n of low frequency Rayleigh waves for flit sptaral
<br />td."' Php thasis. Untvtrstn~ of ~hchi:an. Ann Ar•
<br />elution for flit Green's function (or dynamic loads
<br />R3/-!?. Dept. of Civ. Engrg.. \IIT. Cambridge.
<br />[ion of rigid fooling," PhD [htsis. Univtrsdy of
<br />11972). `Impulsa response functions for elastic
<br />'t. of Civ. Engro„ Rue Univ., Houston. Te.x.
<br />ratz
<br />~Ourna~ o~ ~{rc~'rt;cu-l E^y~'~+-~'~ i V-120
<br />~ARLl" DEl'F.CTION OF ROC1+ CIO\'E~IEN"1' N'IT11 TIME
<br />DO>IAIN REFLEC-fO~IE"fRS
<br />6. Charlrs H. D~r~ding.' >lemhrr, ASCF..
<br />and pri~Chiu Huang.' :bsncine \lrmher, aSCE
<br />AsSrnaer: Remora a^enuon :. -time Jen: _in rcncaomctn ITDRi +ys0.`m
<br />~LmONLLLLei the ell _'e:'~en+'~i JI ~-'=~•relrle nn,c::on nc Lrt c.uk Jetc i:Un tit fOCw
<br />ma+emcnt Dunn_ nc L' to+un¢ r-^~~rmd hac TDR dna ,,arc Nl:.tcJ to .hrnr
<br />Jei,~rmauon abo,t :~ lon_ vll e_•.n: opcratirr. m~n_ a onriW non he r.•cen the
<br />,ienamrc rciltcu.rn c,•emaa nt an.::ncu Ja~~: m_n„n t+t.thliohed th;.•u±h lahn.
<br />t.vorvmmurement> 41-5.mr;-.`:u Wng.,r.:: ~I cn.nialTpR erhle'., :, arowtd
<br />Imo the roc'.: ma++ u'n.,..; flit h>n.__:, JI cndhm,'~ n__ ~q•c~:~oon anJ anaeheJ to the
<br />~W,rxround~pu6i m~ m.:ru mint TPR dat.i '.+--- then rt momly .icd de~J to ic:
<br />J.ul•. M an opcr.rtor ., ,x ~iri lnt m n. l,yr.p. aeon ,.; TDR men.r ~.r. ch.inee~
<br />uuh lone" r!I-ies hw:•n ,hoar.: :n.rt Ine:d i::_ :n.rnec+"crc Jeta_::.I I~mr Ju,>
<br />bclurc aurh:~: eub+ian:~ oGarr..l .,tin minin::~.n ~t ill ^~ ni 1'_Ul Ill .r :+ 5mtc
<br />;ha minim .. '+ movn_ b,,,anl :.`...:ole at .i :. ,: of IJ m.ln. a ,. ar niod uuC r. al
<br />h t, pea~:J to rt Lrc_::•~r prm^.a .nc+..rtn o.+:r C:IOrmanon c;.r-,.
<br />INTRODUCTION
<br />This paper summan_e; rexlLs of a re:.l-time, remo[ely controlled time
<br />domain retlectomttn ITDR) monnoring ~ rogram to demonstrate the ef-
<br />fectivtness of remote pelting for early de[taion of rock-mas deformation.
<br />Pre~inus work IBauer el al. 199! I demon>t-.ated the frustration of n:anuall}'
<br />polled systemx when a eritical three ~ycek's North of data were not collected
<br />while the rock mass fulled. Add,uon of a communication interface w the
<br />TDR cable tesrer be Tekvoni.x has now' made it posstble to remotely optratt
<br />and poll TDR instruments cia rnodem. Su:h modem accts will now' allow
<br />remote polling at sclll, and aliminates the r,ttd for local human interaction.
<br />which leads to the loss of da[a reported h} Bauer.
<br />TDR is an eltc[rical pulse tesnne technique. original)}' developed to locate
<br />diseontinuines in po~~tr transmisseon cables. which has bolo modified to
<br />' monitor deformanon of a coaxial :able grouted into a rock mass, as shown
<br />in Fig, t(n) (Dow~ding et al. 1958. 1989). As shown in Fig. llh). rock-mass
<br />' motementi deform the grouted .-able, which locally chanties cable capaci-
<br />tanct and the reflected wavefom of the ~ohagt pulse. Ultimately large
<br />shearing deformations sever the cable and shorten the rttleutd signature
<br />a5 shown by the decrensin? length of the ~unatures in Fig. !(b). ey mea-
<br />suring change In these reflection slgnatures~ it is possible to monitor both
<br />local extension and local sheanm_. Furthermore, the sign. length, and am-
<br />plitude of the individual reflection pulses define the location. type, and
<br />secentc, respectively, of every cable defortnue.
<br />Two programs. NUTS.A and NUh1OD )Huang zt al. 199:), have en-
<br />hanced the remote monitoring caoabifitles o[ TDR sys[ems. and are dis-
<br />' cussed in detail in the section entitled "Appendix I. Ins[rumen[ation." NUTSA
<br />'Prot., Dtpt. of Civ. Ecerg., North'•~ts[trn l~niv., Evanston. IL 60'_03.
<br />'Post Doctoral Fellow. Dept. of Cr•. Engrg . ~bnhwestern Untv.. Evanston. IL
<br />60203, q:
<br />' Nom. Discussioe open until January I, 19 To errand the dovng da[t one
<br />month. a writan rtqutst must be iced with the ASCE }tanager o[ Iournals. Tht
<br />manuscript for this paps: was submitred for rt~itw and possible publics[ion on
<br />t Febrvarv '_3. 199:. This pace is pare of the Juurnai of Geutechnicat Engineering,
<br />Vol. Ill], Ho. S. August. 199a. u~ASCE. ISSN O'3b9aln:9a~000S-V 1 ~~S'_.00 + 5.25
<br />t par page. Paper Vo. 56R1.
<br />tat3
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