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1 This rticle ppered in journl pulished y Elsevier. The ttched copy is furnished to the uthor for internl non-commercil reserch nd eduction use, including for instruction t the uthors institution nd shring with collegues. Other uses, including reproduction nd distriution, or selling or licensing copies, or posting to personl, institutionl or third prty wesites re prohiited. In most cses uthors re permitted to post their version of the rticle (e.g. in Word or Tex form) to their personl wesite or institutionl repository. Authors requiring further informtion regrding Elsevier s rchiving nd mnuscript policies re encourged to visit:

2 Aville online t Tunnelling nd Underground Spce Technology 23 (28) Tunnelling nd Underground Spce Technology incorporting Trenchless Technology Reserch Evlution of grouting in tunnel lining using impct-echo D.G. Aggelis, T. Shiotni, *, K. Ksi c Reserch Institute of Technology, Toishim Corportion, 5472 Kimgse, Nod, Chi , Jpn Deprtment of Urn Mngement, Grdute School of Engineering, Kyoto University, C , Kyoto-Digku-Ktsur, Nishikyo-Ku, Kyoto , Jpn c Technology Mngement Deprtment, Civil Engineering Hedqurters, Toishim Corportion, 2-Bnchi, Snncho, Chiyod-ku, Tokyo , Jpn Received 1 Octoer 27; received in revised form 7 Decemer 27; ccepted 11 Decemer 27 Aville online 25 Jnury 28 Astrct The shield tunneling method is commonly used for tunnel excvtion. After the excvtion, curved reinforced concrete memers re used to support the surrounding ground/rock nd sel the tunnel. Grouting is performed to provide dhesion etween the concrete memers nd the ground. The ssessment of the grouting qulity y pull-out tests nd core smpling is destructive, time-consuming nd expensive. In the present cse, impct-echo ws pplied s mens of non-destructive nd time-effective evlution. Excittion ws conducted y n impct hmmer on the surfce of severl concrete pltes nd the reflection ws cquired y low frequency ccelerometer. Comined use of time domin chrcteristics, spectrl content nd wvelet trnsform revel the effectiveness of grouting nd indicte tht impct echo is vlule for quick nd relile ssessment of grouting in such cses. Ó 27 Elsevier Ltd. All rights reserved. Keywords: Impct-echo; Non-destructive inspection; Grouting 1. Introduction The shield tunneling method is common method for excvtion of smll dimeter tunnels. Immeditely fter the excvtion y mens of tunnel oring mchine, the surrounding mteril must e supported nd the cross-section of the tunnel secured (Drrg, 1999). For this im, prefricted curved concrete segments re ssemled, nd injection of grout is conducted to fill the void etween the segment nd the excvted surfce. This wy, the surrounding rock mss is supported nd the stresses re conveyed to the reinforced concrete segments. Therefore, it is importnt tht the lining is fully ttched nd no voids exist etween the surrounding ground nd the concrete segment. Although the conditions of the injection re dequtely controlled, there is no confirmtion tht the grout mteril hs filled ll the ville empty volume * Corresponding uthor. Tel.: ; fx: E-mil ddress: shiotni@toshi.kuciv.kyoto-u.c.jp (T. Shiotni). etween the concrete segment nd the ground. Efforts to estimte the grouted volume re sed on the geometry, the permeility of the rock nd the pplied pressure ut in ny cse cnnot supply relile informtion (Brnterger et l., 2). The ssessment of the efficcy of grouting is not trivil (Sud et l., 24). One wy is the core smpling, which of course is destructive nd not representtive of lrge re. The tunnel of this study is 2.3 km long, with dimeter of 5 m. It ws uilt for telecommuniction cles nd sewge pipes. The loction is in the centrl re of Jpn, nd the ground consisted minly of low qulity mudstone. After plcement of the concrete memers nd the injection of grout, the qulity of the filling should e ssessed with non-destructive technique; therefore, impct-echo ws pplied. Impct-echo generlly employs the spectrl nlysis of the response of the memer fter low frequency excittion. Reflections re recorded ccording to the mteril s internl conditions, nd their frequency cn revel informtion out the thickness of the memer, the depth of /$ - see front mtter Ó 27 Elsevier Ltd. All rights reserved. doi:1.116/j.tust

3 63 D.G. Aggelis et l. / Tunnelling nd Underground Spce Technology 23 (28) defects s well s mteril properties (Snslone nd Streett, 1997; Ohtsu nd Wtne, 22). Specificlly for the tunnel of this cse study, lthough informtion ws collected from the spectrl content, more relile results were otined y chrcteristics of the time domin wveform, comintion of which is used to distinguish etween the fully nd prtilly grouted cses. 2. Mterils nd experimentl method To mke specific clcultions out the expected frequency peks fter the test, except from the geometry of the structure, the mteril properties re essentil. Cores from the surrounding mudstone were smpled t the site nd specimens of grouting mteril were prepred nd tested in the lortory to otin their pulse velocity. The pulse velocity mesurements were conducted with coustic emission resonnt R6 sensors of Physicl Acoustics Corp. (PAC), the pulse genertor ws PAC HV-11 nd the dt cquisition system ws PAC Mistrs 21. The pulse velocities nd densities of the mterils re depicted in Tle 1. The velocity of concrete is close to the highest possile limit for cementitious mteril (Nik nd Mlhotr, 1991) due to the high qulity of mnufcturing nd high integrity conditions (no ccumulted deteriortion) of the metl-reinforced segment. The design strength of concrete ws 42.5 MP nd ccording to the mesured pulse velocity the modulus of elsticity is over 6 GP. The velocity of mudstone indictes low mechnicl properties, (elsticity modulus of the order of 4 GP). The properties of this mteril could not e controlled (since it ws the surrounding mteril t the site) nd the velocity ws mesured to fcilitte the nlysis of the results. Concerning grouting mteril; leving the lest possile numer of voids ws the min trget of grouting. Therefore, the grouting gent should e s liquid nd esy-to-flow s possile nd the engineers t site selected high wter to solid rtio to ensure this condition. The grouting mteril consisted minly of entonite, smller proportion of ssistnt cementitious mteril, ccelertor gent nd wter. The proportions were 2 kg/5 kg/65 lt/85 lt, respectively, for 1 m 3 of the grouting mteril. This led to low pulse velocity, similr to the mudstone (s seen in Tle 1) nd clculted elsticity modulus round 3 GP. In cse lower wter content ws used, higher mechnicl properties nd velocity would e cquired ut possily more voids would e left fter the end of the process; thus it ws compromise etween strength nd flowility, minly sed on the experience of the engineers t site. As seen in Tle 1, the properties of mudstone were slightly higher thn the grout ones. This resulted in similr coustic impednces for the two mterils, mening tht t the interfce etween the two mterils, strong reflection is not expected, s will e discussed lter. According to the mnufcturer, the gel time of grout is 6 12 s, the flow time 8 11 s nd the set time min. In proportion 1/4 with wter, it cquires compressive strength of.6 MP in 1 h nd 1.5 MP t 28 dys. The mudstone t the site hd strength of 4 MP, mesured in lortory on retrieved cylindricl cores of length 1 mm nd dimeter 5 mm. As to the min mesurements t the tunnel site for the evlution of grouting, the excittion ws conducted y n impct hmmer, s seen in Fig. 1. The impct hmmer dimeter ws 25 mm lthough smller dimeters were tested, down to 3 mm. This dimeter ws selected since it resulted in high energy nd clerer signl. Theoreticlly, the mximum frequency excited y steel ll of dimeter 25 mm, is 11.5 khz (Snslone nd Streett, 1997). Hmmering ws repetedly conducted for 1 s resulting in cquisition of 2 individul signls. However, the signl ws strong enough nd stcking did not revel difference in spectrl content from the individul wveforms. The used ccelerometers were Fujicermics SAF51 with flt response up to 3 khz nd the signl ws cquired y TEAC GX-1 system. The smpling rte ws set to the mximum ville vlue of 2 khz. Tle 1 Mteril properties Concrete segment Grouting mteril Mudstone C, wve speed (m/s) q, density (kg/m 3 ) Z (coustic impednce, Fig. 1. Excittion using n impct hmmer of 25 mm ner the MRyl) ccelerometer.

4 D.G. Aggelis et l. / Tunnelling nd Underground Spce Technology 23 (28) Fig. 2 shows the cross-section of the tunnel. The reinforced concrete segments, used to support the mudstone, hd thickness of 225 mm. They cn e considered rches of 68.5 of circle with externl dimeter of 545 mm (see Fig. 2). Five full scle segments nd smller one were used to sel the cross-section, consisting ring. To sel the whole length of the tunnel, severl thousnds of consecutive rings were plced, while the width of the segment (nd the ring) ws 12 mm. The grouting ws performed t ech one out of two consecutive rings from hole in the center of top segment. Using the excvtion dimeter (5.6 m) s well s the estimted empty volume etween the concrete segment nd mudstone, the sufficient quntity of grouting mteril ws clculted. Due to uncertinties relted to this estimtion the ctully injected grout volume exceeded this vlue y 3%, while the existence of grouting mteril ws visully oserved from the next holes. The mximum injection pressure ws 35 MP. However, lthough the pressure of the injection nd the volume of injection mteril cn e dequtely controlled, there is no confirmtion tht the grout mteril hs filled ll the ville empty volume etween the concrete segment nd the ground. The pulse velocity in concrete segment ws determined y through-the-thickness mesurement, resulting in 5 m/s, s stted erlier. Considering the mjor frequency nd this pulse velocity, the wvelength in concrete is clculted to 5 mm, eing much longer thn the dimeter of the reinforcement rs of 13 nd 16 mm in the segment, nd therefore strong interction is not expected. 3. Wve propgtion ckground Since the mteril properties were derived, more specific clcultions cn e conducted, concerning the expected frequencies of the test. After excittion t n impct point, the wve propgtes through the thickness of the segment, until it reches the opposite surfce (see Fig. 3). At the Injection point Concrete segments o Fig. 2. Cross-section of the concrete ring, consisting of six segments. (the dimensions re in mm). Mudstone Void Grout Wek reflection Strong reflection 225 mm Concrete segment Impct point Fig. 3. Reflections ccording to the internl geometry () fully-filled cse, () prtilly filled cse.

5 632 D.G. Aggelis et l. / Tunnelling nd Underground Spce Technology 23 (28) interfce etween the concrete segment nd entonite prt of wve energy is reflected ck. This is ecuse the coustic impednce of stiff concrete is much higher thn the one of entonite (12.5 MRyl nd 1.97 MRyl, respectively) s seen in Tle 1. The reflection coefficient is given y (Snslone nd Crino, 1991): R ¼ Z 2 Z 1 ð1þ Z 2 þ Z 1 where Z 1 nd Z 2 re the coustic impednces of the first nd second mteril (in this cse concrete nd entonite, respectively). It is noted tht the impednce Z, is the product of density nd pulse velocity of medium (Snslone nd Crino, 1991). At the interfce of concrete nd entonite, the reflection coefficient is quite high, R =.727, showing tht the reflected wve will hve mplitude pproximtely 73% of the incident wve (the negtive sign shows tht the phse of the wve is reversed, ut this will not e discussed in this pper). Considering the P-wve velocity of 5 m/s nd the thickness of 225 mm, it is esily clculted tht the time period necessry for the pulse to trvel through the thickness nd ckwrds is 9 ls, which inversed, corresponds to 11 khz. The curvture of the segments ws comprtively smll nd, lterntively, the following expression cn e used (Snslone nd Streett, 1997): f ¼ :96 C ð2þ 2 T where T is the thickness nd C the pulse velocity. This leds to frequency of pproximtely 1.6 khz. Thus, in ny cse, strong pek in the received fst Fourier trnsform (FFT) is expected ove 1 khz. Besides the energy tht is reflected y the concrete grout interfce, there is n mount of energy tht enters in grout. This prt of energy propgtes through the thickness of grout until it reches the next oundry. In cse the grouting is complete, the grouting mteril will e in direct contct with the mudstone (see Fig. 3). As mentioned erlier, the impednces of these two mterils re very close nd therefore, the reflection coefficient will e very low (R =.9). In order reflection to e cler, coefficient of more thn.24 is necessry (Snslone nd Streett, 1997). Therefore, lmost ll the energy will propgte into the mudstone wy from the receiver. This mens tht only one mjor frequency pek t pproximtely 11 khz is expected for the fully grouted cse. If the grouting is not complete, void will e present etween entonite nd mudstone, s depicted in Fig. 3. Since ir hs negligile impednce, the reflection will e strong (R = 1). The resulting frequency in the spectrum will depend on the propgtion time through the entonite (grouting) lyer nd therefore, its thickness. For exmple, for entonite lyer thickness of 7 mm, the propgtion time would e pproximtely 85 ls (considering its pulse velocity of 165 m/s). In ddition to the 9 ls through concrete, this leds to n expected frequency pek t 5.5 khz. Therefore, second lower frequency pek should rise in the spectrum, indicting the void etween the grout nd the surrounding mudstone. 4. Results Before pplying the method to rings throughout the ctul structure, mesurements were conducted under controlled conditions on severl positions ner the entrnce of the tunnel. There re different cses simulted nmely complete nd prtil grouting, s cn e seen in Fig. 4. Fig. 4 shows the detil of the prtil cse with the grout lyer of out 7 mm Spectrl content Fig. 5 shows typicl fst Fourier trnsforms (FFT) of totlly filled nd prtilly filled cses. The FFT of fully filled, exhiits single pek just ove 1 khz, corresponding to the thickness of the segment, s explined erlier. In Fig. 4. () Different filling cses simulted t the entrnce of the tunnel, () detil of prtil filling cse.

6 D.G. Aggelis et l. / Tunnelling nd Underground Spce Technology 23 (28) Mgnitude Fully filled Prtilly filled Mgnitude Fully filled Prtilly filled Frequency (khz) Frequency (khz) Fig. 5. FFT of different filling cses. () Distinguishle cses, () not distinguishle cses. the cse of prtil filling, except the high frequency, nother cler pek is seen t round 6 khz. However, not ll cses could e distinguished esily. In Fig. 5 two other indictive cses re presented. Concerning the fullyfilled position, smll frequency pek t 5 khz cn e oserved. This pek could cst dout if the filling ws not visully confirmed. On the other hnd, the cse of prtil filling in Fig. 5 exhiits gin similr smll pek t low frequencies. Therefore, the existence of this pek should not e the unique criterion for chrcteriztion, since it cn e oserved in oth fully nd prtilly grouted conditions. It could e the result of the reflection due to void or the reflection etween grout nd mudstone in the fully-filled cse (even though theoreticlly it is expected to e wek ccording to the coustic impednce vlues, s mentioned ove). A powerful wy to visulize the response is the use of wvelets, which cn offer vlule informtion. Wvelet trnsformtion is mens of conducting frequency nlysis in loclized prt of signl. Therefore, it is possile to identify the time within wveform when ech frequency component is ctive (s opposed to the Fourier trnsform tht gives informtion out the frequency content of the whole signl s n entity). The wvelet trnsform (WT) works y reking the signl into shifted nd scled versions of the originl wvelet (fst decying mthemticl function) (Misiti et l., 1996). To hndle suitly ny signl, different originl ( mother ) wvelet functions cn e used. In the specific cse, the softwre used y the uthors (AGU-Vllen Wvelet) employs the Gor Wvelet, which hs proven very useful for nlysis of ultrsonic nd coustic emission signls (Hmstd, 25). The results show tht it is dequte for the nlysis, since it helps the identifiction of different cses, while possily numer of other mother wvelets would produce similr results. In Fig. 6 nd one cn see the wvelet trnsform of wveforms corresponding to fully filled condition. The mjor prt of energy is concentrted efore 2 ls nd lmost no energy is depicted fter 5 ls. For the cse of prtil grouting though (see Fig. 6c nd d), the energy is noticele until out 8 ls. Additionlly, distinct energy component t 5 khz is more evident, surviving up to pproximtely 4 ls (especilly in Fig. 6c), corresponding to the lower pek of the FFT discussed erlier. Visul oservtion cn serve the purpose of rough chrcteriztion; however, there is not decisive difference etween the filled nd not filled cses, since the low frequency component cn e seen in oth helthy nd prtil conditions (see Fig. 6 nd d). The visul inspection of wvelet trnsformtion cn distinguish etween some extreme cses, ut Frequency (khz) c d Mx Min Fig. 6. Wvelet trnsforms of responses from: () nd () fully filled, (c) nd (d) prtilly filled position.

7 634 D.G. Aggelis et l. / Tunnelling nd Underground Spce Technology 23 (28) it is not dequte for relile quntifiction purposes. Therefore, other fetures were studied to led to more roust chrcteriztion scheme. These fetures come from the time domin nd, lthough they re not commonly exmined in impct-echo testing, they led to more powerful chrcteriztion thn frequency fetures in this cse Time domin informtion Fig. 7 shows typicl wveforms otined for fully nd prtilly filled positions. For the cse of full grouting, the wveform consists of one single urst tht decys smoothly. Almost ll the energy rrives efore the 5 ls, while no threshold crossings (see horizontl dsh-dot line) re oserved fterwrds (except numer of smll highfrequency cycles which re etter depicted in Fig. 7 nd will e discussed lter). This is resonle since the reflection from concrete grout interfce is the only strong one, nd the energy propgting through the grout will never e reflected ck, due to the similrity of grout nd mudstone, s explined erlier. For the cse of prtil filling though (see gin Fig. 7), the decy is not smooth, presumly due to the rrivl of the lte reflection expected t round 17 ls. Additionlly, even fter 5 ls, some low frequency oscilltions re oserved. To quntify this trend, the numer of threshold crossings or simply counts in coustic emission terminology (Shiotni et l., 23) is exmined. It is resonle tht the threshold voltge is of prmount importnce for such descriptor. In Fig. 8, one cn see the numer of counts for threshold equl to 1% of the mximum voltge for ech wveform. The positions 1 5 correspond to full grouting, while 6 11 to prtil, s simulted in the entrnce of the tunnel (see Fig. 4). It is seen tht most of the fully grouted positions exhiit lower counts thn prtil; however, this does not hold for ll the cses since position 5, lthough considered fully grouted, exhiits the highest numer of crossings. If the threshold is set to 1%, only lrger oscilltions re counted nd the results re depicted in Fig. 8. It is ovious tht this threshold provides etter discrimintion, lthough there is some overlp concerning the numer of 6 counts tht is common for filled nd unfilled positions. The results re improved if one considers the counts of the lter prt of the wveform. As seen in Fig. 7, the filled cse exhiits significnt energy up to out 5 ls, while for the prtil cse, the energy expnds up to 8 ls. Therefore, in Fig. 8c one cn see the counts fter 5 ls. In this cse chrcteriztion is much esier, since there is no overlp; the fully-filled cses exhiit or 1 count, while the prtil exhiit t lest 3 or more. As stted erlier, nd seen in Fig. 7, the wveforms of fully grouted positions exhiit numerous low-voltge, highfrequency oscilltions fter the initil urst. These cn e exmined y suitly low threshold of.1%. This seems to e nother lso powerful descriptor, since the full cses exhiit numerous low, high-frequency counts compred to the prtil (see Fig. 8d). It should e mentioned tht understnding of wve propgtion is not lwys esy in complex structure like the one t hnd. In this cse the origin of the low-energy, high-frequency oscilltions seen t the lst prt of the wveform cnnot e confirmed. Presumly, it is connected with interction of the wve with the metl reinforcement of the segments even though their dimeter is smller thn the mjor wvelength. In ny cse the certin fct is tht they re oserved in gret numers only in the fully-filled cses. Therefore, they could e used s stndlone fetures or in comintion with others to led to relile chrcteriztion, when individul fetures re not powerful enough. Although the numer of dt is limited nd, in this cse, only one of the fetures could result in successful chrcteriztion, the comintion of different fetures in multidimensionl nlysis provides highlighted results. In Fig. 9, the 11 reference cses re depicted in three dimensionl grph with xes: totl counts with threshold 1% of the mximum, counts fter 5 ls with the sme threshold nd counts fter 5 ls with the low threshold of.1%. It is ovious tht the results form two clerly seprted clusters. This could e the first step of pttern recognition pproch if the prolem of chrcteriztion is difficult nd one single descriptor is not powerful enough. Fully filled Prtilly filled Fig. 7. () Wveforms from different filling cses with threshold 1% of the mximum, () the wveforms mgnified fter 5 ls, with threshold.1%.

8 D.G. Aggelis et l. / Tunnelling nd Underground Spce Technology 23 (28) Totl counts (thr=1%)_ Totl counts (thr=1%)_ Position numer Position numer c Lte counts (thr=1%)_ d Lte counts (thr=.1%)_ Position numer Position numer Fig. 8. Numer of () counts for threshold 1% of mximum voltge, () counts for threshold 1% of mximum voltge, (c) counts fter 5 ls for threshold 1%, (d) counts fter 5 ls for threshold.1% (positions 1 5 correspond to full filling nd 6 11 to prtil filling) Other time domin fetures Another descriptor tht seems chrcteristic is the wveform centrl time (or the centroid of the rectified wveform), which hs een studied in other cses (Aggelis nd Philippidis, 24). As cn e seen in the exmples of Fig. 1, the filled positions exhiit single urst followed y smll cycles. For the prtil cses though, the urst lsts longer, while more, strong oscilltions follow, trnslting the centroid of the signl to lter times. For ny of the intct positions, the centrl time is elow 5 ls, while for ll the prtilly filled cses it is higher thn 55 ls, s cn e seen in Fig. 1. An dditionl feture tht could e used to quntify the lter rrivls is the ccumulted mplitude of the wveform points. This is clculted y ddition of the solute mplitude of ech wveform point to the previous (Kruger, 25; Shiotni nd Aggelis, 27). In Fig. 11 one cn see the ccumulted mplitude curve of the wveforms for the different reference positions. For ll the curves of fully-filled positions, more thn 75% of the totl energy is received efore 5 ls. On the contrry, for the cses of prtil filling, t the time of 5 ls, the energy is less thn 7% of the totl (see Fig. 11), since, s stted erlier, some energy components rrive lter. This prmeter is depicted in Fig. 11 for different positions nd cn lso e used to chrcterize the filling since no overlp etween the full nd prtil cses is oserved. 5. Further considertions Fig. 9. Three dimensionl representtion of different clusters. The min wve propgtion issues nd fetures tht cn help the chrcteriztion were mentioned in the previous section. After selection of the ove fetures, mesurements on 1 rings were conducted. For ech ring, eight positions were tested, s depicted in Fig. 2. The results were stisfctory for lmost the sum of the points. Troulesome results were found only for position #2 in specific rings. This is resonle since the fresh grout tends to fill the lower prts due to grvity, nd therefore, position #5

9 636 D.G. Aggelis et l. / Tunnelling nd Underground Spce Technology 23 (28) Fully grouted Prtilly grouted Centrl Position numer Fig. 1. () Rectified wveforms for different grouting cses, () centrl wveform time for different testing points (positions 1 5 correspond to full filling nd 6 11 to prtil filling). Cumultive energy Complete filling Prtil filling Cumultive energy 9% 8% 7% 6% % Position numer Fig. 11. () Normlized cumultive energy for different testing points, () normlized cumultive energy t the time of 5 ls (positions 1 5 correspond to full filling nd 6 11 to prtil filling). exhiited the est ehvior (low numer of lte counts nd centrl time, fst increse of ccumulted energy). Since top positions exhiit higher possiility for troulesome grouting, it cn e suggested tht two or three points on the roof of ech ring cn e trgeted, nd if time llows, mesurements cn e conducted in denser pttern nd for more rings. The ove descriptors cn distinguish etween completely nd not completely grouted spots. The determintion of the entonite lyer thickness in prtil filling is much more difficult tsk. Estimtion could e done, sed on the frequency of the low pek of the spectrum. For exmple, frequency of 4 khz should correspond to grouting lyer thickness of 12 mm, while frequency of 7 khz would indicte grouting of 4 mm. However, chrcteriztion sed on the low frequency pek is not relile, s stted erlier. In ny cse, the crucil question concerns the dhesion etween entonite nd the surrounding ground. If the grouting is not full, no dhesion cn e developed, since there is no contct etween the mterils. Therefore, even if the empty pocket is just few millimeters or severl centimeters the sme lck of dhesion will e the result nd more ccurte chrcteriztion would not offer comprtively lrge enefit. A compliction in the interprettion of dt would rise if insted of possile void etween entonite nd mudstone, the cvity ws filled with wter. This could hppen in certin loctions where there is underground wter flow. Considering the density nd sound velocity in wter (1 kg/m 3 nd 15 m/s, respectively), its coustic impednce is of the sme order with entonite, s well s mudstone. Therefore, reflection would not e oserved nd this cse could e mistken for fully grouted cse. Considering the thickness of the segment, higher frequency excittion is supposed to revel more ccurte informtion (Snslone nd Streett, 1997). However, ppliction of smller dimeters of impct hmmer, led to reduced energy nd therefore, nlysis of otined fetures did not result in relile chrcteriztion. It is lso mentioned tht the ove presented fetures served well the purpose of the specific monitoring. It is suggested tht these fetures could e used (individully or comined if necessry) to chrcterize similr cses. However, the clculted or expected vlues for ech descriptor (e.g. frequency pek or numer of threshold crossings) which were used to distinguish complete from troulesome grouting, should e modified ccording to the geometry nd the mteril properties in cse y cse sis fter reference mesurements for ny different ppliction. 6. Conclusions In the present pper, the impct-echo method is used to investigte the filling etween the tunnel lining nd the sur-

10 D.G. Aggelis et l. / Tunnelling nd Underground Spce Technology 23 (28) rounding mudstone. Troulesome grouting is indicted y strong reflection from the existent void which leds to distinctive pek in the Fourier spectrum. Wvelet trnsformtion of the received signl is powerful wy to visulize the energy content in reltion to time nd its frequency content. However, time domin chrcteristics, like the numer of threshold crossings, or the dely of mjor energy rrivls seem more powerful to distinguish etween fully or not fully grouted cses. It is concluded tht the impct-echo technique cn e used s non-destructive evlution method since it is time nd cost effective nd hs the ility to exmine unlimited numer of positions, s opposed to trditionl core drilling. References Aggelis, D.G., Philippidis, T.P., 24. Ultrsonic wve dispersion nd ttenution in fresh mortr. NDT & E Interntionl 37 (8), AGU-Vllen Wvelet, R , Brnterger, M., Stille, H., Eriksson, M., 2. Controlling grout spreding in tunnel grouting nlyses nd developments of the GIN-method. Tunnelling nd Underground Spce Technology 15 (4), Drrg, A.A., Ground stiliztion for tunnel construction in mixed-fce conditions. Tunnelling nd Underground Spce Technology 14 (3), Hmstd M.A., 25. An Illustrted Overview of the Use nd Vlue of Wvelet Trnsformtion to Acoustic Emission Technology, AGU- Vllen Wvelet R , User s Guide. Kruger, M., 25. Scnning impct-echo techniques for crck depth determintion. Otto-Grf-Journl 16, Misiti M., Misiti Y., Oppenheim G., Poggi J., Mtl Wvelet Toolox User s Guide. Nik, T.R., Mlhotr, V.M., The ultrsonic pulse velocity method. In: Mlhotr, V.M., Crino, N.J. (Eds.), CRC Hndook on Nondestructive Testing of Concrete. CRC Press, Florid, pp Ohtsu, M., Wtne, T., 22. Stck imging of spectrl mplitudes sed on impct-echo for flw detection. NDT& E Interntionl 35 (3), Snslone, M.J., Crino, N., Stress wve propgtion methods. In: Mlhotr, V.M., Crino, N.J. (Eds.), CRC Hndook on Nondestructive Testing of Concrete. CRC Press, Florid, p Snslone, M.J., Streett, W.B., Impct-Echo Nondestructive Evlution of Concrete nd Msonry. Bullrier Press, Ithc, NY. Shiotni, T., Aggelis, D.G., 27. Determintion of surfce crck depth nd repir effectiveness using Ryleigh wves. In: Crpinteri, A., Gmrov, P., Ferro, G., Plizzri, G. (Eds.), Frcture Mechnics of Concrete nd Concrete Structures Design, Assessment nd Retrofitting of RC Structures. Tylor & Frncis, London, UK, pp Shiotni, T., Bisschop, J., Vn Mier, J.G.M., 23. Temporl nd sptil development of drying shrinkge crcking in cement-sed mterils. Engineering Frcture Mechnics 7 (12), Sud, T., Tt, A., Kwkmi, J., Suzuki, T., 24. Development of n impct sound dignosis system for tunnel concrete lining. Tunnelling nd Underground Spce Technology 19,