INTELLIGENT PAVEMENTS THROUGH INSTRUMENTATION EARLY RESULTS FOLLOWING AN EXTREME RAINFALL EVENT

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1 INTELLIGENT PAVEMENTS THROUGH INSTRUMENTATION EARLY RESULTS FOLLOWING AN EXTREME RAINFALL EVENT Khaldoon Azawi, ASC Consultants Ltd, New Zealand Prof John Yeaman, University of the Sunshine Coast, Australia Dr Seosamh B. Costello, University of Auckland, New Zealand ABSTRACT The Sunshine Coast Regional Council in Australia recently upgraded a section of Sippy Downs Drive adjacent to the University of the Sunshine Coast campus in late Prior to opening, the pavement was instrumented to monitor temperature under the surface layer, vertical strain in the basecourse and the subbase layers, and moisture in both layers. The instrumented section is a pilot trial to help confirm the final instrumentation setup for a much wider study. The traffic is expected to grow substantially as a new suburb and two major shopping centres are built over the next three years. After the opening of this section a major rainfall event occurred with approximately 480mm of rain over five days in January This paper will discuss the instrumentation setup, the early results of the instrumentation monitoring, and the extreme rainfall event. The intelligence provided in the longer term from the instrumented sections will help refine assumptions in the design and rehabilitation of pavements in such an environment. INTRODUCTION Roads are one of the key contributors to the economic success of developed countries. Queensland has the longest state controlled road network in Australia; about 25% of all Australian state controlled roads valued at approximately $55billion. The main current challenges are: deterioration due to age accelerated deterioration due to the impacts of the recent high rainfall events and cyclonic damage continued usage and traffic growth continued increase in heavy transport, length and axle loading quality of materials. Roads are engineered for a long period, and this includes design, maintenance and renewal considerations. However, the current design assumptions do not account for submerged pavements which occurred recently during a cyclonic occurrence in Queensland where pavements needed repairing immediately after such events. In recent floods almost two thirds of the road network was under water. As a result there is a need to monitor the performance of in-service constructed pavements under these localised conditions. The Sunshine Coast Regional Council (The Council) in Australia recently upgraded a section of Sippy Downs Drive adjacent to the University of the Sunshine Coast (USC) campus in late Prior to opening, the pavement was instrumented to monitor temperature under the surface layer, vertical strain at the top of the basecourse and the subbase layers, and moisture in both layers. The instrumented section is a pilot trial to help confirm the final instrumentation setup for a wider study. The traffic in this area is expected to grow substantially as a new suburb and two major shopping centres are built over the next three years. After the opening of this section a major rainfall event occurred with approximately 480mm of rain over five days (Table 1) in late January ARRB Group Ltd and Authors

2 The instrumentation at the site was installed as part of a final year engineering project and the monitoring of the in service pavement performance will be done as part of a PhD research programme. Aim of the study The aim of the study is to analyse the response of the pavement to the impact of an extreme weather condition on the newly constructed section in Sippy Downs Drive. DESCRIPTION OF TEST SITE The site was upgraded as part of the Sippy Downs Town Centre Master Plan due to the continued growth of the area. It is on the upstream direction from the traffic lights at the intersection and in the outer wheel path of the median lane The location of the test site is shown in Figure 1 at Longitude East; Latitude South and Altitude m. Site Location Sippy Downs Dr University Stringybark Rd University Entrance Sippy Downs Dr University Pavement materials Figure 1: Locality plan schematic. The pavement was constructed to meet the requirement of the approved granular pavement design with 45mm of asphalt surfacing on top of a total pavement thickness of 625mm to be placed on a subgrade with minimum of 3 California Bearing Ratio (CBR). Due to the weak subgrade encountered at the section of the pilot test trial location; there was a need to replace the top 300mm with 40mm nominal size granular fill. Figure 2 shows the pavement design configuration Asphalt Surfacing Gravel Basecourse Gravel Subbase Subgrade Replacement Subgrade Figure 2: Test site pavement cross section (dimensions in mm). ARRB Group Ltd and Authors

3 Pavement instrumentation plan The site was instrumented during construction; all instruments were located under the outer wheel path. The following factors have been considered for the selection of the gauges: availability of equipment at time of design and construction durability and ability to withstand extreme weather conditions(hot and cold) within the region overall cost including installation the local supplier has a good knowledge and will provide technical support with installation, calibration and extended service after installation. The instrumentation included the following. Temperature gauge (temp) The temperature gauge is located 65mm from the pavement surface, in the upper part of the basecourse layer and below the surface layer. One type T thermocouple was installed. Figure 3 shows the thermocouple used to measure the temperature (source - Larson S, Yeaman J, 2012). Moisture gauges Figure 3: Type T thermocouple. Two moisture gauges were installed, the Theta probe ML2X was chosen as the preferred instrument, with a simple circuit that responds to the dielectric properties of the soil which provides the moisture gauge with an accuracy of ±1% and a measurement range of up to 50% volumetric soil moisture content; it provided an ideal measurement tool for this study. The other useful features are the compact size and the use of a four rod arrangement; three located around a central rod which holds the soil closer together when it is drying and/or cracking. Other types considered were the TDR ThetaProbe which had greater power consumption, more complex cabling requirements and slightly less accuracy at ±1.5% compared to the ML2x ThetaProbe. The Aquaflex Soil Moisture and Soil Temperature product was also a viable option although the accuracy was lower and the cost was slightly more. Figure 4 shows the ThetaProbe moisture gauge (source - Larson S, Yeaman J, 2012). Moisture gauge number 1 (Moist#1) Upper moisture gauge, 345mm from top of surface to bottom of sensor, located at the bottom of the basecourse layer and top of the subbase layer. Moisture gauge number 2 (Moist#2) Lower moisture gauge, 670mm from top of surface to bottom of sensor, located at the bottom of the subbase layer and top of the subgrade replacement layer. ARRB Group Ltd and Authors

4 Figure 4: Moisture gauge - ThetaProbe type ML2x. Strain transducer KM series Two strain gauges KM-100A were embedded in the pavement vertically; the upper strain gauge was placed vertically in line with the lower gauge. The KM series strain transducers are designed to measure strain in materials such as concrete and pavement layers. Their extremely low modulus (40N/mm2) and waterproof construction make them ideal for this type of test. The built in thermocouple sensor enabled actual temperature measurement in addition to the strain measurement. The gauges were manufactured by Tokyo Sokki Kenkyujo Co. Ltd; they are well known in the industry and have supplied similar equipment to various international projects. The durability for the Strain Transducers was critical as they are considered the most important piece of equipment. The supplier stated that these gauges are designed to withstand the heavy compaction loads specified in the construction of the pavement. After comparing various models of strain gauges, the strain transducer KM 100mm was chosen. The 100mm long strain gauge was chosen over the longer strain gauges due to the thickness of the basecourse and subbase. Any longer and the strain gauges would be placed in a large portion of the pavement which would alter the results by transferring strain from different parts of the pavement. The turning circles on these strain gauges are also sufficient enough so that they could be placed vertically with ease. Figure 5 shows the dimensions associated with the KM-100A strain transducer are; A 104mm, B 20mm, C 17mm, D 100mm, E 4mm, F M3 Depth 6, and the weight of each strain gauge is 75g. The input/output cable is Ø9mm thick with an area of 0.30mm2, 5- core shielded, and Chloroprene cable with 2m of cable-end free. The strain Transducer KM-100A is able to measure strain and temperature (measured at a different frequency to strain). If required, this will enable temperature to be measured at two different levels within the basecourse and the subbase layers, and compare temperature at the upper level with the type T thermocouples (can be used for redundancy). The product literature advises that for purposes of analysis positive values from the strain gauge represent values in Compression and negative values signify values in Tension. Figure 5 shows one of the installed strain gauges (source - Larson S, Yeaman J, 2012). Figure 5: Strain gauge - KM-100A. ARRB Group Ltd and Authors

5 Strain gauge number 1 (Strain#1) Upper vertical strain gauge to measure vertical strain at the top of the unbound layer, 115mm from top of surface to centre of sensor, located in the upper part of the basecourse layer and below the surface layer. This gauge was attached to the same conduit as the temperature gauge. Strain gauge number 2 (Strain#2) Lower vertical strain gauge to measure vertical strains at the bottom of the basecourse and the top of the subbase layers. 395mm from top of surface to centre of sensor, located at the top of the subbase layer and below the basecourse layer. Data logger The DataTaker DT82EM Series 3 model was chosen due to its ability to collect data at both high and low frequencies, low solar power usage and wireless data transfer. For all gauges the data is summarised and reported every minute. Figure 6 shows the inside of the data logger box (source - Larson S, Yeaman J, 2012). Figure 6: DataTaker DT82EM Series 3 inside the box. Figure 7 shows the location of equipment within the pavement cross section of the test site in Sippy Downs Drive. 300mm 325mm 300mm 45 Asphalt Surfacing Gravel Basecourse Gravel Subbase Subgrade Replacement Subgrade CBR 3 Temperature 70mm from top of surface to middle of sensor Strain no mm from top of surface to middle of sensor Strain no mm from top of surface to to middle of sensor Moisture no mm from top of surface to bottom of sensor Moisture no mm from top of surface to bottom of sensor Figure 7: Test site - location of equipment within pavement cross section. The instrumentation and pavement construction was completed during December 2012 and the monitoring of the test site started on the 19 th of December ARRB Group Ltd and Authors

6 Calibration of strain data by standard load The gauges were calibrated as per their respective calibration guides provided by the supplier. A further calibration exercise was undertaken on 6 March 2013, the Sunshine Coast Regional Council provided a single axle, dual tyre truck loaded with 8.2 tonnes on the rear axle. Tyres were inflated to 760 KPa. This unit made 10 passes over the test site between the hours of 9:30 am and 10:30 am and again between the hours of 1:30 pm and 2:04pm (hours when the pavement appeared to be generally at the median of the temperature range). The strains were recorded for each pass with the results summarised in Table 1. Table 1: Calibration by standard load Time Strain#1 Strain#2 Moisture#1 Moisture#2 Temperature Remarks Upper Layer Lower Layer Upper Layer Lower Layer Surface Layer 10:06:23-27µε --4µε 18% 19% 27.6 C TEST TRUCK 10:14:25-55 µε -23 µε 18.1% % 27.8 C Truck with Excavator 10:17:32-35 µε -9 µε 18.1% % 27.8 C TEST TRUCK 10:23:25-23 µε -7µε 18.1% 19% 28 C TEST TRUCK 10:30:30-57 µε -20 µε 18.1% % 28.1 C Bus followed by TEST TRUCK 13:30 to 13: µε -305µε 18.03% 19% 33.5 C TEST TRUCK sat on site for 3 minutes 13:36:33-84 µε -53 µε % % 33.7 C TEST TRUCK 13:43:24-82 µε -51 µε 18.03% % 33.9 C TEST TRUCK 14:03:38-81 µε -54 µε 18.04% % 34.4 C TEST TRUCK Upper Layer Strains results indicate an order of: -23 to -30 µε for temperature/moisture content of 27/18 and - 80 to -85 µε for temperature/moisture regime of 35/18. Lower Layer Strains are of the order of -5 to -10 µε for temperature/moisture regime of 27/18 and -50 to -60 for temperature regimes of 35/18. Description of the rainfall event During the Australia Day long weekend a heavy rainfall event occurred as a result of a cyclonic depression that passed over Sippy Downs between 24 th and 28 th January 2013 with total rainfall of approximately 480mm. Table 2 shows the rainfall details throughout the event. Table 2: Rainfall at Sippy Downs during the event Date Day Rainfall (mm) 24th Jan 2013 Thursday 42 25th Jan 2013 Friday 52 26th Jan 2013 Saturday 92 27th Jan 2013 Sunday th Jan 2013 Monday 95 Total 479 It is worthwhile noting that the period from the start of monitoring on the 19 th December 2012 up to the start of the event on 24 th January 2013 was hot and dry without any rain. The following section will discuss the results of the data received from the test site before, during and after the event up to the 28th February RESULTS AND DISCUSSION For the following temperature, moisture and strain data, the graphs on the right side (8,10,12,14 and 16) show the average daily data between 19th December and 28th February 2013 and the graphs on the left (9,11,13,15,17) show the data for three days of the week before, during the event (five days) and three days of the week after the event. The days before and after the event are not consecutive. Data represents one reading at the top of every hour for each day plotted. ARRB Group Ltd and Authors

7 Temperature data Figure 8 shows the average temperature at the start of the event was 41.2 C; this dropped to 25.6 C at the end of the event on the 28 th and started to stabilise again from the 29 th with temperatures increasing from 29.7 C to 39.5 C seven days after the event. Figure 8: Daily average temperature. Figure 9 shows the drop and stability in temperature during the event and also shows that temperature after the event reverted back to a similar trend to the temperature before the event. Moisture data Figure 9: Hourly temperature (selected days). Upper moisture gauge no. 1 (Moist#1) Figure 10 shows the average moisture at the start of event was 16.8%; this was increased to 19.6% at the end of the event on the 28 th and dropped to 18% seven days after the event. Figure 14 shows the details. Figure 11 shows that the moisture started to increase during the 26 th and 27 th and part of the 28 th, when it started to decrease steadily. ARRB Group Ltd and Authors

8 Figure 10: Moist#1 Daily average moisture. Figure 11: Moist#1 - Hourly moisture (selected days). Lower moisture gauge no. 2 (Moist#2) Figure 12 shows the average moisture at the start of event was 17.9%; this was increased to 19.4% on the 29 th and dropped to 19% on the 4 th of February. Figure 13 shows the moisture started to increase on the 27 th and 28 th of Jan from 17.7% to approximately 19.5% and dropped to 19% on 4 th of Feb. Figure 12: Moist#2 Daily average moisture. ARRB Group Ltd and Authors

9 Strain data Figure 13: Moist#2 - Hourly moisture (selected days). Upper strain gauge no. 1 (Strain#1) Figure 14 shows that the average daily strain is generally in compression but it changed to tension during the storm event. The average daily strain changed from compression on the 24 th to tension on the 25 th and remained in tension during the event up to the 28 th where it reverted back to compression from 29 th of January. Figure 14: Strain#1 Daily average strain. Figure 15 shows in more details how upper strain changed from compression to tension during the storm event and reverted back to compression after the event. Figure 15: Strain#1 Hourly strain (selected days). ARRB Group Ltd and Authors

10 Lower strain gauge no. 2 (Strain#2) Figure 16 shows that the average daily strain fluctuated between compression and tension remained in tension during the event and went back to fluctuation after the event. The average daily strain changed from compression on the 24 th to tension on the 25 th and remained in tension during the event up to the 28 th and after the storm event until the 4 th of February. Figure 16: Strain#2 Daily average strain. Figure 17 shows in more detail how lower strain changed from compression on the 24 th to tension on the 25 th and remained in tension during and after the storm event until the 4 th of February. Strain and temperature Figure 17: Strain#2 Hourly strain (selected days). Figure 18 shows that both strain gauges went from compression to tension when temperature dropped during the event, the upper gauge moved back to compression after the 29 th of Jan while the lower gauge remained in tension longer before going back to compression on the 12 th February Figure 19 shows in more detail how both upper and lower strain changed from tension to compression during the five day event period, while upper strain changed to compression during the five days after the event; the lower strain remained in tension. During the event, the temperature trend continued to drop from 51 C at 4:00pm on 24 th to 26.5 C at 9:00 am on 28 th January. ARRB Group Ltd and Authors

11 Figure 19 shows the temperature readings for the five days after the event are slightly lower than those for the five days before the event. The upper strain changed from compression to tension as temperature decreased and reverted back to compression as temperature increases. The upper strain reading for the five days after the event are slightly lower than those for the five days before the event, this shows that the lower temperature readings after the event might have an impact on the upper strain Strain#1. Figure 18: Strain and Temp Daily average. Strain and moisture Figure 19: Strain and Temp Hourly. Figure 20 shows the upper moisture (Moist#1) increased more rapidly during the event and also has a higher level of moisture drop after the event when compared with the lower moisture (Moist#2). The lower gauge shows a more steady increase in moisture content during the event and steady loss after the event. The upper strain (Strain#1) changed to tension as the moisture increased during the event and reverted back to compression as the upper moisture (Moist#1) started to drop after the event. The lower strain (Strain#2) changed to tension as the moisture increased during the event and remained in tension as the lower moisture was held steady even after the 4 th of Feb. Figure 20 shows the upper moisture increased from 16.6% at 9:00 am on 24 th January to 19.2% at 9:00 am on 28 th January. Figure 26 shows the upper moisture decreased during the five days after the event but remained lower than the upper moisture during the five days before the event. ARRB Group Ltd and Authors

12 Figure 20: Strain and Moisture Daily average. Figure 21 shows the upper strain changed from compression to tension as the upper moisture increased and reverted back to compression as moisture decreases. Figure 21 also shows the upper strain reading for the five days after the event are consistently lower than those for the five days before the event, this show that the lower readings of Moist#1 after the event might have an impact on the upper strain Strain#1. Figure 22 shows the lower strain fluctuated between tension and compression, changed from compression to tension during the event and remained in tension the five days after the event. The steady increase in lower moisture during the event and the steady loss after the event had little impact on the lower strain trend. Figure 21: Strain and Moist#1 Hourly. Figure 22: Strain and Moist#2 Hourly. ARRB Group Ltd and Authors

13 Moisture and temperature Figure 23 shows that the upper and lower moisture content increased with the drop in temperature. The upper moisture showed higher and more rapid increase when the temperature dropped. The lower moisture gauge showed steady increase in moisture and retained higher moisture content even with increased temperature after the event. Figure 23: Moisture and Temperature Daily average. Strain as a function of temperature Figure 24 shows that that the upper strain changed from tension to compression when temperature increased above 33 C. The lower strain changed from tension to compression when temperature reached 39.5 C and above. The upper strain shows high correlation (R 2 =0.87) with temperature compared to the lower strain which is relatively low (R 2 =0.32). Figure 24: Strain as a function of Temperature. Strain as a function of moisture Figure 25 shows strain as a function of upper moisture Moist#1, it shows very low correlation for both upper and lower strains. The upper strain changed from compression to tension as moisture increased above 18% while the lower strain changed from compression to tension when moisture increased above 15%. Figure 26 shows strain as a function of the lower moisture Moist#2, it also shows very low correlation for both upper and lower strains. The upper strain mainly remains in compression as moisture increases while lower strain mainly remains in tension when moisture increases above 18%. ARRB Group Ltd and Authors

14 Figure 25: Strain as a function of (Moist#1). Figure 26: Strain as a function of (Moist#2). Figure 27 shows strain as a function of the difference in moisture (Δ Moisture = Lower Moisture (Moist#2) Upper Moisture (Moist#1)). Both strains showing low correlation with Δ Moisture. The upper strain changed from tension to compression when Δ Moisture increased above 0.5% while the lower strain changed from tension to compression when Δ Moisture increased above 4%. Figure 27: Strain as a function of Δ Moisture. ARRB Group Ltd and Authors

15 SUMMARY AND CONCLUSIONS Sippy Downs Dr pavement instrumentation was completed in late December An extreme weather event in late January 2013 provided an early opportunity to access the performance of the instrumented pavement while under water, assess the monitored parameters and their interrelations. The average daily temperature dropped from 42 C to 25 C at the end of the event and started to stabilise again from the 29 th with temperature increasing from 29.7 C to 39.5 C seven days after the event. The average daily upper strain (Strain#1) changed from compression on the 24 th to tension on the 25 th and remained in tension during the event up to the 28 th where it reverted back to compression from 29 th of Jan. The temperature readings for the five days after the event are slightly lower than those for the five days before the event. The upper strain changed from compression to tension as temperature decreased and reverted back to compression as temperature increases. The upper strain reading for the five days after the event are slightly lower than those for the five days before the event, this shows that the lower temperature readings after the event might have an impact on the upper strain Strain#1. The upper moisture (Moist#1) increased during the event and decreased during the five days after the event but remained lower than those during the five days before the event. The upper strain (Strain#1) changed from compression to tension as the Moist#1 increased and reverted back to compression as moisture decreased. Strain#1 readings for the five days after the event are consistently lower than those for the five days before the event, this shows that the lower readings of Moist#1 after the event might have an impact on the Strain#1 Strain#1 shows high correlation (R 2 =0.87) with temperature and relatively low correlation with upper moisture (Moist#1), lower moisture (Moist#2) and Δ Moisture. The average daily lower strain (Strain#2) fluctuated between compression and tension, remained in tension during the event and went back to fluctuation after the event. The lower strain (Strain#2) fluctuated between tension and compression, changed from compression to tension during the event and remains in tension five days after the event. The steady increase in Moist#2 during the event and the steady loss after the event had little impact on the lower strain trend. Strain#2 shows low correlation with temperature, upper moisture (Moist#1), lower moisture (Moist#2) and Δ Moisture. The event shows that there is a need to have a better understating of the environmental impact on the pavement, in this case the temperature, moisture and strain. The longer term continuous monitoring of the pavement will provide further evaluation of the environmental influence on the pavement strains. This system was initially installed to test the efficacy of the approach rather than the efficiency of the outcomes. A matter of concern was the longevity of the equipment under operational conditions. The extreme weather event and the calibration of the site using standard axle repetitions were sufficient to comfort us to proceed with the trial. Therefore the equipment was upgraded to include full climatic information and traffic data in form of counts, speed and classification. Photographs of vehicles exceeding 180 microstrain are acquired for future analysis. As a result of the analysis to date the Council decided to instrument two or three more sites including an unbound granular pavement, warm asphalt pavement and the extension of Sippy Downs Drive. Final year engineering student is instrumenting a lean mix concrete base ARRB Group Ltd and Authors

16 and full depth asphalt section on the Bruce Highway in association with Transport and Main Roads, Queensland. All this data will be gathered by the author in the hypothesis and testing components of the research programme. REFERENCES Year Four Engineering Project, Larson S, Yeaman J, Investigation of Pavement Deterioration through Pavement Instrumentation within South East Queensland, Instrumentation Data sheets, Pacific Data Systems Pty Ltd, AUTHOR BIOGRAPHIES Khaldoon Azawi is an Auckland based Asset Management Engineer working mainly in the management and maintenance of transport and infrastructure assets. He has worked in consultant, contractor and client secondment roles and has a particular strength in road asset management and pavement modelling, network management and forward work programming, contract and project management. He holds the degree of Master of Technology (Pavement) from Deakin University. Khaldoon is also a Chartered Professional Engineer (CPEng), International Professional Engineer (IntPE) and a Member of the Institution of Professional Engineers New Zealand (IPENZ). Dr John Yeaman is Professor of Civil Engineering Construction, USC. He has over 40 years experience in assisting road organisations and governments across the world in the management of their road networks. His main fields of expertise include design, implementation and operation of road management information systems, assistance of road authorities in planning and programming road maintenance and improvement programmes under constrained budget situations. John has occupied the position of Director, Deputy Team Leader or Team Leader on several internationally recognised projects as well as occupying key expert positions in multi-disciplinary teams. Dr Seosamh Costello is a Senior Lecturer in the Department of Civil and Environmental Engineering at the University of Auckland and past Associate Dean in the Faculty of Engineering. Seosamh s research focus is in asset management, in particular transportation assets, and he has published widely in the area. He received his MSc (Eng), in International Highway Engineering, and PhD from the University of Birmingham in the UK. He is also a Chartered Engineer (CEng) with the Institution of Engineers of Ireland. Copyright Licence Agreement The Author allows ARRB Group Ltd to publish the work/s submitted for the 26th ARRB Conference, granting ARRB the non-exclusive right to: publish the work in printed format publish the work in electronic format publish the work online. The Author retains the right to use their work, illustrations (line art, photographs, figures, plates) and research data in their own future works The Author warrants that they are entitled to deal with the Intellectual Property Rights in the works submitted, including clearing all third party intellectual property rights and obtaining formal permission from their respective institutions or employers before submission, where necessary. ARRB Group Ltd and Authors