EuroGPR Guidelines Series. The European GPR Association Guidelines for Pavement Structural Surveys

Transcription

1 EurGPR Guidelines Series The Eurpean GPR Assciatin Guidelines fr Pavement Structural Surveys Dcument Reference: GS1601 V1.0 12/04/2016

2 The Eurpean GPR Assciatin Guidelines fr 1 Scpe This dcument relates t Grund Penetrating Radar surveys carried ut n highway r street pavements as well as private rads prviding they are hard standing (nt dirt r gravel rads). It des nt cnsider surveys f airprt pavements as these require special cnsideratin. It cnsiders nly thse surveys perfrmed specifically t ascertain infrmatin directly relating t the pavement itself. It des nt cnsider surveys perfrmed ver pavements t ascertain lcatin f targets beneath the pavement such as buried utilities r archelgically remains as these require special cnsideratin, althugh it is nted that ccasinally such surveys are cmbined. This dcument aims t prvide guidance t EurGPR assciatin members t ensure they undertake GPR surveys n pavements in a safe and respnsible manner. It is nt meant t prvide a specificatin f hw every variatin f pavement GPR survey shuld be perfrmed. EurGPR members are required t cnfrm t any lcal r natinal specificatin fr these surveys that may be already in place. This dcument will als be useful t thse wh have the respnsibility f cmmissining GPR surveys fr pavements and utilising and string the data prduced. 2 The nature f pavement structural surveys Surveys generally fall int tw categries f deliverable, surveys fr pavement cnstructin and surveys fr pavement material cnditin. Often there is verlap between them and they are ften nt mutually exclusive. In many cases GPR surveys f this nature can be carried ut at r clse t trafficspeed whilst maintaining the desired data density. The surveys can als be perfrmed at much slwer speeds within traffic management either using a vehicle r using man-prtable system cnfiguratins, fr example if transverse prfiles are required. 2.1 Pavement cnstructin Pavement cnstructin surveys deal with identificatin f the nature f the pavement cnstructin. They are ccasinally perfrmed t ppulate pavement management systems due t the lack f r unreliable as built recrds n lder and heavily maintained pavements and ften t prvide cnstructin mdelling fr pavement residual structural life assessment. They can als be perfrmed as a quality cntrl measurement f cnstructin t ensure the built pavement matches the design specificatin. The vast majrity f pavement cnstructin surveys using GPR aim t deliver material layer thickness as by their nature, pavements are cnstructed in layers. Hwever, it shuld be nted that GPR detects interfaces between tw cntrasting materials. This means that in rder fr GPR t deliver layer thicknesses the data analyst must have cnfidence that the interface at the tp and the bttm f the layer has been reslved in the GPR recrd. There are reasns why this might nt be pssible, fr example the material layer may be very thin and the GPR f insufficient reslutin t distinguish between the upper and lwer surface f the layer. Or the cntrast between the layer being measured and either the upper r lwer material may be insufficient t cause a strng enugh reflectin at the interface t be visible in the GPR recrd. Therefre GPR surveys f pavement cnstructin shuld generally reprt identified interface depths. Layer thickness can be reprted in the fllwing ntable exceptins: GS1601 V1.0 Page 1 f 8 12/04/2016

3 The Eurpean GPR Assciatin Guidelines fr The number f material layers present can be verified by an independent surce f cnstructin infrmatin, such as a cre r an as-built recrd which can be cnfirm the quantity f layers measured by the GPR is the crrect number expected. If layer thickness f nly majr material types is required, fr example asphalt thickness and cncrete thickness. Surveys can als deliver ther infrmatin relating t specific types f pavements, fr example it can deliver the arrangement f rebar in reinfrced cncrete pavements and bridge decks. 2.2 Pavement cnditin GPR can prvide infrmatin relating t the apparent cnditin f a pavement and due t its high prductivity and lw disruptive nature can prvide a useful recnnasance survey t direct mre resurce intensive investigatin. Typical deliverables include apparent material density variatin and viding, and apparent misture variatin. 3 Limitatins f GPR use n Pavements The fllwing is a list f cmmnly held (but nt exhaustive) limitatins regarding the use f GPR n pavements: GPR cannt penetrate metal (e.g. clsely spaced rebar) r ther highly electrically cnductive materials. GPR surveys shuld be avided when it is raining and shuld nt be carried ut when standing water is present n the surface f the pavement. GPR surveys must nt be carried ut n rads treated with de-icing salts in case f significant penetratin f salt water int the pavement materials. 4 Survey Assessment Upn receiving the initial enquiry r request fr survey services, the survey cntractr shuld carry ut an assessment t determine if GPR is a feasible apprach t the client s investigatin requirements. The assessment shuld primarily be based n the likely capability f GPR t meet the investigatin bjectives but shuld als be based n whether anther technique will be mre cst effective, accurate r practical. If the utcme f the assessment is that the likelihd f a GPR survey being successful is lw, the client shuld be infrmed. The way frward frm this pint may be via ne f the fllwing appraches: The survey cntractr can recmmend an alternative technique r perhaps a suite f techniques that may have a better chance f meeting the survey bjectives. The survey cntractr can recmmend a pilt scale trial t reduce risk, if the scale f the whle survey warrants this apprach 5 Survey Specificatin Assuming the decisin t g ahead with a GPR survey is reached, in advance f undertaking a pavement structural survey, the survey cntractr and the client shuld agree a suitable survey GS1601 V1.0 Page 2 f 8 12/04/2016

4 The Eurpean GPR Assciatin Guidelines fr specificatin r strategy which shuld include written evidence f agreement f the fllwing minimum infrmatin: Key survey aims r deliverables Traffic management requirements Site specific health and safety requirements, as a minimum a risk assessment shuld be perfrmed and a methd statement prvided. Agreed wrking hurs (if under traffic management) r wrking time restrictins, e.g. nt during peak traffic. Survey data utputs frmats Definitin f the survey extent(s) and cverage including: Start and end psitins and hw they shuld be identified, typically by sectin/chainage, marker-pst, spatial (GPS) crdinates r ther physical feature. Fr vehicle based surveys, the number and psitin f measurement ffsets required, e.g. wheelpath psitins r measured ffset psitins relative t lane dividers, as well as the number f lanes t be cvered, shuld be agreed. Fr n ft surveys, the number and psitin f all individual prfiles r grid density if a full rthgnal grid is t be used. The in-line GPR measurement interval; fr traffic-speed vehicle based surveys this will mst ften be the minimum spacing achieved by the GPR system in rder t cnfrm t the site definitin f traffic-speed. This may als determine whether r nt the survey can be perfrmed at traffic speed if the spacing required is less than that achievable by the system when perated at lcal site traffic-speed. The type f antenna r range f antennas t be used must be agreed in advance fllwing expert guidance frm the survey cntractr and will depend n the fllwing: The maximum penetratin required frm the GPR data, the survey cntractr shuld prvide realistic estimates f signal penetratin t the client. The minimum desired target size r layer thickness, again the survey cntractr shuld prvide a realistic indicatin f this and guidance t the client. The type f targets and materials under investigatin. The lcal envirnmental cnditins. Hw the velcity calibratin will be perfrmed; if cres are t be used the fllwing shuld be agreed: Wh will be taking them (in sme cases the survey cntractr r client may be als the cring cntractr r it might be a 3 rd party cntractr appinted by the client r survey cntractr) The number f cres available/t be taken. Hw they are lcated (sectin/chainage r GPS) and t what accuracy. GS1601 V1.0 Page 3 f 8 12/04/2016

5 The Eurpean GPR Assciatin Guidelines fr When the cre data will be available and what frmat it will take. The survey cntractr shuld state what risks there are t the prject. Risks will include cnditins that may prevent the survey frm being effective, may prevent the survey frm being delivered n time r may prevent the survey frm being delivered within budget. Such risks may include but are nt limited t: Weather cnditins, either during the survey r fr a perid befre the survey that may render the survey r certain deliverables unreliable. Surface cntaminatin, fr example winter maintenance de-icing salts r gritting. Staffing and equipment resurce cnflicts. Delays in btaining calibratin data, particularly cre data frm a third party cntractr. Deliverable timescales shuld be agreed. Results f GPR pavement surveys ften feed int ther pavement evaluatin techniques. Delays in delivering GPR data may have a dmin effect dwn the chain and lead t significant delays n a the client s wn prject delivery. The verall cst f the survey, breakdwn f charges and cnditins under which additinal charges may be ccurred. The latter may be included in the survey cntractr s standard terms and cnditins fr undertaking surveys. The frmat and presentatin f the deliverables. 6 Lcatin Referencing Incrrect r inadequate lcatin referencing is ne f the primary causes f errr in GPR surveys n pavements. This errr can be triggered by errrs in matching GPR lcatin t cre lcatins when perfrming calibratins and generally in the reprting f GPR data. The frmer errr is nt always the result f errrs in the GPR but can als cme frm errrs in the cre lcatin measurement, especially if a third party cntractr is invlved. The survey cntractr shuld ensure that every effrt is made t minimise the risk f lcatin referencing errrs. 6.1 Vehicle based lcatin referencing The minimum requirement fr lcatin referencing f traffic-speed data is by elapsed chainage frm reference pints. In rder t achieve this, the survey must utilise at least ne dmeter wheel cnnected t the GPR t cntrl scan rate and prvide chainage measurement. These dmeters are ften built int the wheels f dedicated survey vehicles but can als be additinal wheels that are twed behind the vehicle alng with the GPR system, munted n the wheel nuts f a nne driven wheel r mre recently can be laser distance measurement instruments. S called time based r cntinuus GPR cllectin mdes shuld nt be used fr traffic speed GPR surveys. It is imprtant t ensure that the distance measurement system is crrectly calibrated. The survey cntractr shuld select a suitable site t perfrm a calibratin check. The check shuld be perfrmed weekly r whenever the equipment is used if less frequent than weekly. Fr devices attached t wheels with pneumatic tyres, the tyre pressures shuld be checked regularly and befre the calibratin check. GS1601 V1.0 Page 4 f 8 12/04/2016

6 The Eurpean GPR Assciatin Guidelines fr The mst cmmn methd fr delineating chainage measurement is by manually entered event markers in the GPR data, ften knwn as push-buttn events. This intrduces inherent errr int the GPR data due t nrmal reactin times fr an peratr pressing a buttn ver the required reference pint in a vehicle travelling at traffic-speed. This errr shuld be taken int accunt when reprting GPR with this methd and when perfrming dmeter calibratin checks with this methd. Use f a GPS receiver is recmmended as an additinal methd f relcatin. The traffic-speed capable systems prduced by all EurGPR manufacturers have the capability t use a GPS receiver. Even a lw-cst cnsumer grade GPS unit is useful as an independent check f the wheel dmeter fr highlighting bvius errrs in chainage measurement r marker event placement. If GPS derived spatial crdinates are t be included with the deliverables f the survey, the GPS system used shuld be cnsidered survey grade and be calibrated accrding the manufacturers recmmendatins. 6.2 On ft survey lcatin referencing There are numerus methds f prviding lcatin referencing fr n ft GPR surveys, the survey cntractr shuld ensure that the apprpriate methdlgy is utilised fr the survey applicatin and the client s desired accuracy requirements. 7 Data Quality and Backup The survey cntractr shuld ensure that all cllected data is checked fr apprpriate cntent ideally befre leaving the survey site. This is ften pssible in real-time via the data cllectin system sftware streaming data t the screen in real-time. A simple check f data file sizes can als be an early clue t a malfunctining system. One r mre randm data files frm the data set shuld be pened t check data quality and file crruptin befre leaving site. The cllected data shuld be duplicated t a separate strage media frm the data cllectin system at the end f a data cllectin shift. 8 Data Reprting The results frm a pavement GPR survey shuld be presented in the frmat agreed in the survey specificatin, ultimately it shuld be in a frmat that can be easily understd by the client. The survey cntractr shuld make available the raw and prcessed GPR data fr the client t view if requested. The client is unlikely t have GPR analysis sftware and shuld be advised n a suitable viewing sftware package, which are generally prvided free f charge via GPR manufacturers and third party GPR sftware prviders. Numerical data shuld be prvided in a standard frmat such as Micrsft Excel r ASCII text file. Graphical interpretatin data shuld als be prvided in a standard and pre-agreed frmat, if this is nt pssible r practical, the survey cntractr must prvide suitable viewing sftware as part f their deliverables. A written reprt is nt generally required fr rutine pavement cnstructin surveys but may be required fr pavement cnditin surveys and fr pavement cnstructin surveys if the fllwing circumstances are met: GS1601 V1.0 Page 5 f 8 12/04/2016

7 The Eurpean GPR Assciatin Guidelines fr Cnditins arse (either anticipated r therwise) that significantly affected the utcme f the survey. In which case the reprt shuld clearly reassess the effectiveness f the survey. The utcme f the survey required a great deal f subjective interpretatin; fr example, the number f cres was nt sufficient fr the cnstructin variability r the GPR did nt seem t agree with a significant prprtin f the calibratin data prvided. The client is relatively unfamiliar with GPR. 9 The Survey Cntractr s Obligatins The survey cntractr is generally bliged t cnduct their business in an ethical manner and respect the reputatin f the GPR industry as well as their wn. 9.1 Lcal GPR regulatins The survey cntractr must be aware f any lcal r natinal regulatry cntrl ver GPR where they will be perating. They must cmply with any regulatins at all times when perating. The cntractr may cnsult the EurGPR website r cntact the EurGPR cmmittee directly fr the latest infrmatin relating t lcal r natinal regulatins. 9.2 Prject Management The cntractr shuld have effective prject management plicies in place. Thrughut the cntractr, the cntractr shuld infrm the client f the prgress f the survey and any changes t the risks agreed in the specificatin stage. 9.3 Mis-selling The cntractr must be realistic in its sales and marketing activities and specifically nt ver prmise n GPR capabilities. If the client has requested a slutin that has nt been prven by the cntractr, the cntractr shuld seek input frm the industry in the frm f reviewing previus wrk. Alternatively the cntractr shuld ffer a survey trial where key bjectives can be reviewed befre cmmitment is made t a larger survey r a breakut clause included in the larger survey if it becmes apparent the survey is less effective than riginally anticipated. 10 Definitins Deliverable: The interpretatin f a data set delivered t the survey client. As Built Recrds, pavement cnstructin recrds that detail the riginal pavement cnstructin and any changes made t the cnstructin thereafter. Chainage, a distance measured alng an imaginary line crrespnding t the centre f the rad. Event Markers are digital marks placed in the data t recrd the psitin f key survey pints n the site relative t the data. Lcatin Referencing, a system f determining the psitin f a GPR measurement relative t ther measurements r t an external frame f reference such as spatial crdinates. Man-Prtable System, GPR system pulled r pushed by hand using a suitable trlley r skid plate and handle arrangement. GS1601 V1.0 Page 6 f 8 12/04/2016

8 The Eurpean GPR Assciatin Guidelines fr Odmeter Wheel, an instrument that measures/recrds distance travelled by a vehicle Pavemen,: bund surfaced rad r highway Rebar, a steel bar r mesh f steel wires used as a tensin device in reinfrced cncrete t strengthen the cncrete. Residual structural life, The calculated remaining structural life f a pavement Scheme, A defined prject t investigate the cnstructin and/r cnditin f a sectin f sectins f rad pavement and define maintenance needs. Sectin, Delineated sectin f highway (ranging in length) allwing reference in a pavement management system. Traffic-speed, the minimum speed required n a given highway t negate the lcal requirements fr traffic management. Wheelpath, a lngitudinal measurement ffset defined relative t the lane centreline. Lcal definitins vary. GS1601 V1.0 Page 7 f 8 12/04/2016

9 The Eurpean GPR Assciatin Guidelines fr Versin Histry Ver. N. Descriptin Drafted By Apprved By Publicatin Date V1.0 Cmmittee reviewed draft fr publicatin Adam Ck Cmmittee 12/04/2016 GS1601 V1.0 Page 8 f 8 12/04/2016