Non-Destructive Pavement Evaluation to Assess Flood Damage in The City of Calgary

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1 Non-Destructive Pavement Evaluation to Assess Flood Damage in The City of Calgary Venkat Lakkavalli P. Eng., M. Sc. The City of Calgary Alberta, Canada Presented at TAC 2014, Montreal (Karim, M et al. 2014)

2 Overview On June 20, 2013, The City of Calgary witnessed one of the worst floods in its known history. About 100,000 people were evacuated from their residences, 73 communities affected and about 33,600,000 m 2 flooded. State of local emergency was declared for 15 days

3 Bow and Elbow Rivers Historic Flow Peak flow Bow river in Calgary during history floods Hourly increase in water level through bow river during the flow

4 City of Calgary Post Flood Condition

5 Post Flood Sinkholes

6 Flood Impact Impacted all modes of transportation - rail, light rail, roads, sidewalk, pathways etc. Damage to roads right-of-way Pavement washouts Numerous sinkholes Voids underneath pavement & sidewalk Post-Flood Survey Site reconnaissance and post flood photographs Sinkholes identified were filled with concrete/asphalt concrete and mapped in GIS Immediate goal bring back mobility Long term Strategy Assess pavement damage, remedial measures (resiliency/mitigate)

7 Literature Review Related to void detection under pavements using GPR, FWD or other technologies Any information reviewed related only to void detection under Cement Concrete slabs due to temperature effects and did not find information for void detection under asphalt concrete pavements No specific procedures found for correlating FWD deflection data with shallow void detection under flexible pavements

8 Literature Review Calgary Experience June 5, 2007 Intense rainfall caused flooding Caused dramatic damage to 1 km of roadway due to insufficient storm capacity Combined technique of FWD/GPR utilized to determine shallow subsurface voids and structural adequacy Anomalies determined up to 2 m depth

9 Study Methodology Review of background information & literature Visual condition survey post flood Comparison with pre-flood satellite imagery (also LiDAR) Pavement strength testing (FWD) Determination of shallow subsurface voids & moisture (GPR) Analysis of the data collected Determination of expected service life (or loss of life) Finding & rehabilitation strategies

10 Pavement Condition Review Street Roadway Classification From To Year Last Paved IRI (mm/m) Pre Flood PQI 1 Post Flood IRI (mm/m) Macleod Tr. SE Arterial 25 Ave. SE 9 Ave. SE st St. SE Arterial 9 Ave. SE 25 Ave. SE Ave. SE Industrial / Collector 25 Ave. SW Industrial / Collector PQI 1 4 St. SE 6 ST. SE Macleod Tr. 5 St. SW Ave. SW Local 8A St. SW Edison Cr PQI or Pavement Quality Index is a composite index that takes into consideration the vride quality, structural adequacy and visual condition of the pavement. It ranges at a scale of 0 for a completely failed pavement to 10 for a pavement in near perfect condition. 2 Based on latest available survey or assumed value based on the age of the pavement and local experience.

11 Data Collection Falling Weight Deflectometer (FWD) Ground Penetrating Road Radar (GPR) (Moisture evaluation)

12 Data Collection FWD Locations were selected based on the reported severity and subsurface anomalies FWD testing was completed at 10 or 20 m intervals in both wheel paths of each lane * Normalized the three-drop (targeting 40kN) centralized load deflection to 40kN the standard load applied under the tire of one Equivalent Single Axle Load (ESAL) Temperature corrected applied to each normalized deflection from the reported ambient temperature to standard temperature of 20 C as per AASHTO backcalculation procedure It should be noted that there are no specific procedures correlating FWD deflection data with shallow void detection under flexible pavement structures * The FWD testing was conducted over two nights: October 30/31 and October 31/November 1, 2013.

13 FWD Benchmark for Analysis Benchmark established based on roadway classification, serviceability and design ESALs of the roads segments evaluated Deflections <500 µm insignificant Deflections between µm exhibiting a structural deficiency <50 mm Deflections between µm exhibiting a structural deficiency of 50 mm Deflections >1000 µm representative of a weakened pavement structure exhibiting structural overlays > 50 mm

14 Data Collection GPR Road Radar TM System It is a hybrid ground penetrating radar system optimized for non-destructive substructure investigations A high-resolution air-launch radar system (2.5 GHz) provides unambiguous resolution of structural layers as thin as 40 mm A second surface-coupled array radar system (1.1 GHz), maintained in contact with the road surface, provides signal velocity (dielectric) measurements for structural layers up to 1.5 m below surface Boundary between dissimilar materials produce horizontal multi-colored bands

15 Data Collection - GPR The radar surveys at a longitudinal sampling interval of 0.09 m (3.5 in) This resulted in over 1,000 samples per 100 m surveyed The surveys were conducted in each wheelpath of each travel lane of the roadway Based on the intensity measured at the ACP/Base boundary, five anomaly severity levels were established: Unclassified (i.e. no indication of abnormality ) Wet Low severity anomaly Medium severity anomaly High severity anomaly

16 GPR Data Localized Area of Study (Macleod Trail SE) Radar Imagery with Anomalies Wet and Low Severity Raw data location Plan View with Highlighted Section

17 Assessment of Flood - Road Segment

18 Summary of Sections Showing Anomalies Roadway From To Lane* Length MacLeod Tr. MacLeod Tr. MacLeod Tr. S. of 17 Ave S. of 14 Ave S. of 14 Ave N of 15 Ave N of 13 Ave N of 12 Ave 1 & 2 3 & 4 MacLeod Tr. 11 Ave 10 Ave All 4 1 Street SE N of 11 Ave S of 11 Ave 1 All m 170 m 210 m 120 m 40 m 1 Street SE 14 Ave 13 Ave 1 & 2 90 m 1 Street SE N of 13 Ave S of 18 Ave 11 Ave SE E of 5 St W of 5 St both 90 m 25 Ave SW 2 St E of 2 St both 25 Ave SW Bridge 38 Ave SW 7 St Erlton Road E of Elbow Dr 4 EB both 250 m 100 m 160 m 260 m *Lane number starting from left to right in the travel direction Anomalies by Severity from Road Radar TM Unclassified, wet, low severity Unclassified, wet, low severity Unclassified, wet, low severity Unclassified, wet, low severity Unclassified, wet, low severity Unclassified, low severity Unclassified, wet, low severity Unclassified, wet, low severity, and medium severity Unclassified, wet, low severity Unclassified, wet, low severity Unclassified, wet, low severity No of Deflection FWD tests Range Ave + 2SD µm 346 µm µm 546 µm µm 722 µm µm 673 µm µm 409 µm µm 181 µm µm 432 µm µm 326 µm µm 607 µm µm 260 µm µm 633 µm Summary no discernible pattern or correlation of the reported anomalies and FWD no discernible pattern of correlation of the reported anomalies and FWD no discernible pattern of correlation of the reported anomalies and FWD no discernible pattern of correlation of the reported anomalies and FWD no discernible pattern of correlation of the reported anomalies and FWD no discernible pattern of correlation of the reported anomalies and FWD no discernible pattern of correlation of the reported anomalies and FWD no discernible pattern of correlation of the reported anomalies and FWD no discernible pattern of correlation of the reported anomalies and FWD no discernible pattern of correlation of the reported anomalies and FWD no discernible pattern of correlation of the reported anomalies and FWD

19 Findings FWD testing was completed on selected sites with the expectation that a shallow void in the pavement structure or subgrade below the asphalt concrete layer and bridged by the asphalt concrete layer, would have resulted in a significant measured surface deflection when tested with the FWD The GPR - Road RadarTM was used to provide a continuous survey of both wheel paths of each lane for each of the five project. This allowed for use of NDT to identify potential anomalies in the pavement structure and subgrade to about 1.5m below the pavement surface There was no discernible correlation between Road Radar TM reported anomaly severity levels and surface deflection as measured by the FWD However, with the exception of a few isolated locations, the measured deflections were considered to be negligible or very low Flood caused reduction of service lives by up to 50-70% Road roughness (IRI) reached the trigger point, where pre-flood IRI was very good

20 Treatments Road reconstruction was carried out where damage was beyond repair Road rehabilitation consisted of partial reconstruction and localized deep base repairs Sinkholes and settlements were treated by excavating and backfilling up to 2 m deep Repairs started in 2013, still going on

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