Damage Factor Assessment Hamad&CoweFalls

8/3/2019 Damage Factor Assessment Hamad&CoweFalls

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Damage Factor Assessment through Measuring Direct Response of Asphalt Pavement due

to Heavy Loading

A’arif Hamad, MSc. Candidate

University of Calgary

Department of Civil Engineering-Transportation Specialization

2500 University Drive N.W.

Calgary, Alberta, Canada T2N 1N4

Phone: (403) 220-5970

Fax: (403) 220-7026

Email: [email protected]

Lynne Cowe Falls, Ph.D.

Assistant Professor

University of Calgary

Department of Civil Engineering

2500 University Drive N.W.

Calgary, Alberta, Canada T2N 1N4

Phone: (403) 220-5505

Fax: (403) 220-7026

Email: [email protected]

Word count = 4745+10*200 = 6,745



Hamad, A. and Cowe Falls, L.

ABSTRACT

Road authorities in resource based economies are frequently challenged by the demands of heavy equipmentoperators requiring access to remote sites during sensitive spring thaw conditions. Access to these sites is rarelyalong high volume, structurally engineered pavements and many secondary pavements suffer prematuredeterioration as a result. To overcome this, agencies impose restrictions to overloads that can result in substantialcosts to operators as equipment is broken down and re-assembled onto multiple flatbeds for transportation overprovincial roads. This paper presents the results of a field study of the loads imposed by heavy oilfield cranes (withhydraulic suspensions and super single tires) on thin membrane asphalt pavements in Alberta. Three 50m test roadsections (thin asphalt wearing course, bituminous surface treatment and granular surface) were built andinstrumented for strain at the bottom of the asphalt layer, surface deflection, and subgrade pressures. Temperatureand moisture profiles are also measured.

Field testing involved controlled speed experiments of standard axle configurations and heavy (12,000kg) axlevehicles with and without hydraulic suspensions. The results will be used to evaluate the impact of overloading bythese vehicles and will become part of a long term study to evaluate pavement performance and develop loadequivalency factors.



Hamad, A. and Cowe Falls, L. 1

INTRODUCTION

Road authorities in resource based economies are frequently challenged by the demands of heavy equipmentoperators requiring access to remote sites during sensitive spring thaw conditions. Access to these sites is frequentlyalong low volume, structurally under-designed pavements and consequently many of these pavements sufferpremature deterioration as a result of vehicle overloads. To overcome this, agencies impose restrictions that arebased upon Load Equivalency Factors (LEF) which was initially developed at the AASHTO test road and hasbecome the basis not only for overload permitting, but also for pavement design. Using LEFs, all vehicles using theroad during the design period can be equated to a number of standard axles and the pavement structural thicknessdetermined. LEFs reflect the expected damage imposed on the road by the vehicle, relative to a standard 80kN(18,000 lb) single axle (referred to as the Equivalent Single Axle Load (ESAL)).

Traditionally, pavement engineers have designed the road for standard and/or common vehicle configurations suchas those listed in Table 1. Recently, vehicle manufacturers have begun to design the vehicle to minimize pavementdesign through the use of larger tires, lower tire pressures, central tire inflation, hydraulic suspension systems andnew axle configurations. These changes have altered the vehicle dynamics and a lack of understanding of theimpact of these new mechanical systems (referred to as super singles) on pavement structural behavior means thatexisting Load Equivalency Factors may not be accurate for these vehicles. Extrapolation of the current LEFs foroverload permitting has resulted in increased costs to the operators as agencies require owners of these new vehiclesto ‘break-down’ the vehicle onto multiple flatbeds and/or dollies to meet legal load limits. An indication of the costs

to the operators of this break-down and reassembly was illustrated recently when a Canadian provincial highwayagency allowed a heavy crane (in excess of 48,000kg on four axles) to travel between two sites during the wintermonths without multiple additional dollies. The operator had to move the crane approximately every two weeks fora period of four months and the cost savings were in excess of $200,000 CDN. Incidentally, many of these supersingle axle configurations are built and used extensively in Europe with little reported impact on overall pavementperformance. The argument against super single usage in Canada has centered around the fact that many Canadianroads are thin membrane structures that cannot support heavy loadings. Figure 1 shows sample of these cranes.

On the basis of these cost savings an initiative was begun in Alberta to investigate the impact of the new super singlevehicles on typical pavements found throughout the province. This paper presents the results of a field study of theloads imposed by heavy cranes (with hydraulic suspensions and super single tires) on thin membrane asphaltpavements in Alberta. Three 50m test road sections (thin asphalt wearing course, bituminous surface treatment andgranular surface) were built and instrumented for strain at the bottom of the asphalt layer, surface deflection, and

subgrade pressures. Temperature and moisture profiles are also included in the test sections to capture seasonaldifferences. The long-term plan for the test road is to return to the site quarterly over the next five years to recordand assess pavement deterioration and to develop load equivalency factors for the heavy cranes.

BACKGROUND

The use of instrumented test roads is not a new technique in the evaluation of the pavement response and in fact,similar studies to the one underway have been done in Alberta in the past. Christison at al. 1978 studied flexiblepavement response under various axle loads and loading configurations (single axle dual tires loads ranging from 56to 117 kN, single axle single tire load ranging from 9 to 53 kN, tandem axle dual tires load ranging form 95 to 334kN, and single axle single tire load ranging from 71 to 295 kN on self-propelled earthmovers) on two full-depthasphalt pavements structures. The sites were instrumented with strain gauges to measure strains at the bottom of theasphalt concrete layer, pressure cells to measure stress at the top of the subgrade, and deflectometers to measure

total deflection at the pavement surface. The test pavement structures were full-depth asphalt pavements that werestandard in Alberta at the time of the test with 200 mm (7.7 in.) and 280 mm (11 in.) full depth asphalt concrete,respectively, constructed on a 1.2 to 1.5 m common borrow subgrade made of highly plastic soil. The studyconcluded that for the standard 80 kN axle load, the interfacial strains (at the bottom of the asphalt concrete layer)and surface deflections increase with the increase of the pavement age and pavement temperature and decrease withthe increase of the vehicle velocity. Other findings were the agreement of the results for the LEFs values from thistest with performance based factors from the AASHTO test road and theoretical values derived by other researchers.The study also indicated that the damage from one application of a 133.4 kN axle load is equivalent to the damageof one application of the standard load based on the predicted LEFs. Similarly, for the heavy wheel loads of self-propelled earth movers used in the study, LEFs developed from deflection readings were higher in magnitude than




those found by using the flexural distress concept. A comparison between similar axle loads on the single axle loadof the self propelled earthmover and on a tandem axle showed that the LEFs on the tandem axle is less damaging byfactors ranging from six times to 20-30 times depending on the distress criteria (six times for the interfacial strainand 20-30 times for the surface deflection).

Christison 1990 investigated pavement response under heavy multi-axle crane units, similar to those used in thecurrent study, to predict load equivalency factors. The test was conducted on two pavements: a 135 mm asphaltconcrete pavement (ACP) on a 170 mm cement treated base and a 135 mm ACP on a 250 mm granular base layer,respectively. Subgrade conditions for both sites were similar with moisture contents ranging from 20 – 25% onmedium to high plasticity glacial till. Both test sections were instrumented with deflectometers for surface deflectionand strain gauges at the bottom of the ACP layer for measuring tensile strain. Results from this study indicated thatLEFs for these cranes varied from 5.2 to 26.8 depending on test section structure, crane type, traveling speed, andbasis for calculation (strain based or deflection based).

Sebaaly et al. 2003 conducted a study to evaluate the effect of agricultural equipment on the response of low-volumeroads in South Dakota. Four different agricultural vehicles were selected for this study and the tests were done ontwo different types of roads: a gravel pavement with a 100mm crushed aggregate base (CAB) and a blotterpavement with a 212mm CAB. Both pavements are on a silty subgrade. The roads were instrumented with pressurecells in the subgrade and the base layers and with deflection gauges for surface deflection measurements. The testwere conducted quarterly (corresponding to winter, spring, summer, and fall) in order to evaluate the effect of

environmental conditions on the response of the pavements. The research showed that most of the vehicles testedimposed more damage to the roads than the standard 80 kN axle load especially when they are fully loaded orexceeding their legal limit. The LEFs values found from this study ranged from 0.4 to 25.1 depending on the testvehicle type, pavement type, amount of loading (whether it is empty, fully loaded or exceeding the legal limit), andtesting season. It was found that LEFs decrease as the testing season changed in the following order: summer(highest), fall, spring, and winter (lowest). Also found in this study was that the LEFs decreased with the increase of the base course layer thickness.

OBJECTIVE OF THE STUDY

The objective of this study is to study the impact of heavy axle loads on thin membrane flexible pavementstructures. Specifically, the study has several long-term objectives including:1. Update historical data

• Christison data on mag tape

• Load Equivalency Factors• Dynamic loading

• Seasonal factors2. Develop new performance models3. Evaluate new technologies and equipment

• Super singles

• CTI4. Update/validate existing road user regulations

The study and assessment of the effect of these loads are achieved through the construction and instrumentation of atest road and a finite element analysis. The test road is funded by a consortium referred to as the Alberta RoadResearch Initiative, comprised of industry, academia and government.

The test road was built in the County of Leduc - Nisku Industrial Business Park – near to Edmonton InternationalAirport. The Nisku Industrial Business Park is the home of many oilfield servicing companies, serving the NorthernAlberta oil fields and consequently, is resident to many of the large vehicles of interest. Site selection criteria for thetest road included geometric features that enable the testing to be both safe and practical due to the vehicle sizes andspeeds involved in the program and to minimize disruption to other businesses in the area.




DESIGN OF THE TEST ROAD

The test road was designed to capture the Alberta provincial highway and county road standards with construction of three 150 meter sections with a road surface width of 9.0 meters. Three pavement structures: Hot Mix AsphaltConcrete (HMA), Cold Mix Asphalt Concrete (CMA) and Granular Base Course (GBC) were constructed on atangent section of 8th St. The subgrade soil is a heavy plastic clay and the road prism has been constructed using asilty clay borrow material. All of the pavements are constructed on a standard 150 mm prepared subgrade and the

pavement structure for each section is summarized in Table 2 and shown graphically in Figure 2.

INSTRUMENTATION DESIGN

The test road instrumentation was designed to capture a variety of axle widths (from 1.2 m to 2.8 m) and tire sizes(up to 390 mm wide). Instrumentation was also designed to capture a large amount of data at high speeds (up to 60km/hr) and for redundancy / survivability over the duration of the test. Each array is repeated in the inner and outerwheel path and is also duplicated at two of the sites (HMA and CMA). The instrumentation layout in plan view andcross section are shown in Figure 2. The typical array in each of the HMA and CMA sections consists of twopressure cells, six strain transducers, and temperature and moisture profiles. The GBC section does not have straintransducers, however all other elements are measured. The instrumentation is described in the following sections.

Pressure Cells

Pressure cells measuring vertical pressure on the subgrade were installed in the inner and outer wheel paths, 300 mm

below the top of the subgrade (which is 150mm below the prepared subgrade layer). The HMA and CMA sectionshave four pressure cells each (two in each wheel path), while the GBC section has three pressure cells (two placed inthe inner and outer wheel path and one in the centre lane). The centre lane GBC pressure cell was placed to measurethe combined effect of loading in the two wheel paths and to capture the intersection of the pressure cone beneatheach wheel. This arrangement was used only in the GBC section as there is no bound wearing course and it ispossible that it could be the worst case for the vertical pressure development.

Strain Gauges

Strain gauges at the interface between the asphalt concrete layer and the granular base course layer were placed forthe HMA and CMA sections. The distribution for the strain gauges for the HMA and CMA sections was designed tosuit the characteristics of a range of vehicle dimensions the tested vehicles. For redundancy, should any of thegauges deteriorate over the test duration, the arrays were duplicated at each site. Each array consists of six straingauges, as seen in Figure 2, with the gauges distributed over three horizontal lines that have different transversal

spacing forming a trapezoidal shape. The different widths allow for a variety of vehicle axle sizes and can measuretracking of multiple axles and/or dollies as they traverse the site. In each section two orientation were used for thestrain gauges (along and perpendicular to the travel direction) in order to capture both the longitudinal andtransversal strain at the asphalt interface.

Linear Strain Transducers (LSCTs)

Measuring vertical strain or deflection is problematic for pavement researchers as most installations requireplacement of a deflectometer in the pavement after construction. Placement of the deflectometers usually requiresdrilling of the pavement which was felt to be inappropriate for this test road as the introduction of a corehole on athin membrane pavement introduces a discontinuity and a site for crack propagation. This was overcome by theconstruction of a surface deflectometers beam, similar in principle to the deflectometer beam attached to a FallingWeight Deflectometer. Four Linear Strain Transducers (LSCTs) were attached to a 3 m steel beam that was placedon the centrelane of the pavement and was used to capture the surface deflection due to loading as the vehicles creptover the site. Vertical clearance over the beam was very tight for the large crane in the study and it was decided to

not use the deflectometers beam during the higher speed tests.

Data Acquisition System (DAS)

The Data Acquisition System (DAS) was comprised of a 32 channel data acquisition unit and dedicated computercapable of capturing and recording the dynamic readings with 500 Hz frequency. This enabled differentiation of each axle of the vehicles even at 60 km/hr. The system was duplicated and synchronized at the HMA and CMAsections; however, one of the sites had to run on AC power which produced some noise in the signal.




Environmental Conditions Measurements Devices

Temperature and moisture profiles were installed at all sections to measure the surrounding environmentalconditions during the tests. Thermocouples wires were fixed on stakes at six levels (100, 200, 300, 400, 600, and1000mm) and placed strategically on each site to capture the temperature profile throughout the pavement layers.Also, moisture profiles are measured at the same levels for the temperature around the strain gauge arrays for allsections to measure in-situ moisture in the pavement layers. The moisture is measured by insertion of a probe that

has multiple sensors into an installed sleeve at the time of measurement with a stand-alone portable meter.Temperature and moisture readings were not collected dynamically during the test, as it was felt they would notchange in the relatively short time that the test is completed per cycle.

CONSTRUCTION OF THE TEST ROAD

The construction of the test road was completed by the end of May 2005. The instrumentation work wasimplemented in between and after the construction stages. The placement of the pressure cells and the temperaturethermocouples was done prior to placement of the granular base course and the strain gauges and thermocoupleswere placed after. The final step of the construction was done by placing the asphalt concrete layers. The remainingitems for the instrumentation were the installation of the moisture sleeves and the preliminary test of all the devicesto make sure that they were working properly prior to the vehicle testing. Extreme care was taken by the Universityof Calgary team to ensure proper and accurate installation of devices and a fourth order survey was completed forlocation referencing of the devices. The work of Timm D.H et al. 2004 served as a general guide for the

instrumentation installation procedures. Under the supervision of the University of Calgary lead investigator, thesame care was taken by the construction crew to ensure that no direct loading was done by the constructionequipment on the instrumentation array in order not to minimize possible damage. Checks for the devices were donecontinuously during and after all stages that to check for survivability.

TESTING PROGRAM

The test plan that is decided for this test road will help in studying the effect of the heavy loading compared to thestandard axle loading in conjunction with the following variables:

• Changes in the seasonal conditions.

• Different pavement structures.

• Different traveling speeds.

The field testing plan includes five series of tests that will be performed around the year. These five series represent

late spring, summer, fall, winter, and early spring seasons. The late spring series was performed in June 2005and therest will be followed for the rest of 2005 and 2006. Each series of tests will include testing heavy cranes withdifferent axle configurations and different speeds. A standard 80 kN truck will also be tested in each series for acomparison purposes. The testing plan for each series of tests is presented in Table 3. In the spring 2005 test, an 8 –wheel tandem axle configuration was included in the test as this is most common, legal axle configuration in theprovince. Subsequent tests may not include this vehicle and other configurations, (in particular, heavier cranesand/or more axle cranes) may be substituted. Also, the number of passes may not be included in subsequent tests asthe initial analysis may indicate only a few speeds may be necessary to characterize pavement response.As can be seen in Table 3, the equipment passed over the test site at selected varying speeds from creep to 60 km/hrat intervals of 5 kilometers per hour, initially and then 10 km/hr. Each speed was repeated five times for statisticalsignificance and the vehicles traversed the section in alternating directions (south bound, north bound, south bound,north bound, south bound) to reduce any impact of the pavement transitions on the results. Vehicle dynamics as aresult of discontinuities at the edge of the pavement and at the HMA/CMA transition may skew the results andtraveling in two directions will capture this and allow for statistical averaging.Before commencement of the test run, the standard vehicle passed over the site five times to calibrate the sensorsand establish a baseline. In between each speed interval, the standard vehicle again passed over the site again to re-establish the datum and to track any deterioration that was occurring as a result of the test. At the end of the tests, thestandard vehicle repeated the initial 60 km/hr pass as a further calibration mechanism.Four vehicles were used in the initial test: a standard 80 kN single axle picker truck, an 8-wheel tandem 17,000kgaxle, a 48,000 kg Speirings Crane operating on 8 wheels/ four axles and the same vehicle operating on 14 wheels/ seven axles. Each vehicle was weighed on site by Alberta Infrastructure and Transportation Inspection Servicesusing a portable weigh scale system and the standard 80 kN and 8-wheel tandem vehicles were checked again at anearby permanent weigh scale. Table 4 summarizes the axle weights for each vehicle.




PRELIMINARY FIELD TEST RESULTS

This section presents preliminary results of some of the data that are collected from the field test that is performedon June 26, 2005. There was some noise associated with some of the data collected and these data were excludedand will be presented in the future. As mentioned in the testing program, four types of vehicles were tested fordifferent speeds ranging from very low speed (creep speed) until a 60 km/hr. the results presented below are relatedto three types of vehicles and these are, Standard 18 kip truck, heavy crane with four axle configuration, and thesame heavy crane with seven axle configuration, referred to as ST18, CR01, and CR02 respectively, and for a speedof 60 km/hr.

Strains at the Interface between the Asphalt Layer and the Granular Base Course

Longitudinal Strains

Table 5 presents a summary of the mean, plus one standard deviation, longitudinal strains under both wheel pathsfor the HMA and CMA sections. As expected, all vehicles generated a tensile strain in the longitudinal direction(i.e., in the direction of travel). The strains recorded for the CMA section were found to be considerably higher thanfor the HMA section due to the difference in the pavement strength (material and thickness). For example, for bothtypes of cranes the strains were around 65% higher on the CMA section compared to the HMA section (the strainsrecorded for the ST18 truck however showed very high magnitudes for the CMA section compared to the HMAsection.) The CMA results however, could be highly affected by the noise on the signal and therefore need furtherreview. The maximum amount of total strain was recorded under the wheel paths as expected, and then the strainamount decreases gradually away from the wheel paths as recorded by the internal lines of strain gauges. For bothtypes of cranes CR01 and CR02, the percentage of decrease in the HMA section was higher than the CMA section.In general a decrease of around 85% was noticed for the HMA section compared to around 65% for the CMAsection. Figure 3 shows a typical strain profile under the Speiring crane (four axle configuration) and for three straingauges, the highest peaks are for the strain gauge that is located under the wheel path. The comparison of strainsbetween the cranes on different axles configuration however, showed slight difference (strains for the CR01 werearound 10% higher than for the CR02 crane). These strains and after several tests will be used to asses the damagethat these cranes cause to the pavement compared to the standard axle load through predicting a series of LoadEquivalency Factors (LEFs) for each type of loading and according to the vehicle’s other characteristics.

Transverse strains

The transverse strains that are generated on the direction perpendicular to the direction of travel indicate that thepavement is in both tension and compression depending on location in the lane. The data showed that for all thevehicles and for all the sections, tensile strains were generated under the wheel paths however, the area between thetwo axles was frequently in compression for both types of the cranes. The pattern was not clear however for thestandard 18 kip truck. Table 6 shows this distribution for the transverse strain for the HMA section. Because of thenoise in the signal for the CMA section no analysis is available at this time. It was found also that the magnitude forthe transverse tensile strain is less than the longitudinal tensile strain at a percent that depends mainly on the vehicletype and to a lesser degree to the axle sequence. In general the CR01 crane generated transverse strains that wereapprox. 75-80 % of the value of the longitudinal strains, while for CR02 the difference is in the 55-75% range. Thisis probably due to the distribution of the vehicle weight onto more axles in the CR02 crane. This effect for theincreased number of axles was not clear in the case for the longitudinal strain (differences were approx. 10 %) whichmay be related to the effect of the direction of travel on the amount of strains when the pavement is subject underboth the axle weight and the dynamic action of the wheel movement. It was also noted that the amount of the tensile

transverse strain under the outer wheel path is higher than that under the inner wheel path. Again here the vehicletype is a controlling factor. For CR01 strains under the outer wheel path were found to be 35-50% higher than underthe inner wheel path, while for CR02 crane the increase was less at 15-30 %. The range in both cases is related to theaxle sequence. This increase under the outer wheel path could be highly related to the edge effect of the pavementwhere less support is available under the outer wheel compared to the inner wheel. This may suggest in the futureproviding extra width from the outer wheel path to the edge or stronger shoulder structure in case a minimizing tothese strains is required. The compressive strains that were generated between the outer and inner wheel pathshowever were more uniform in their distribution. Two things were consistent; first, compressive strain increaseswith the distance from the wheel path and second, compressive strains that are generated by CR01 crane are higherthan those by CR02 and both are higher than ST18 vehicle.




Vertical pressure in the subgrade layer

Results for the pressure cells readings in the subgrade layer for the HMA section for three types of vehicles for the60 km/hr speed are presented in Table 5. It is clear that the vertical stresses are higher for both cranes than for thestandard truck. Vertical stresses measured under CR01 crane were 90-155% higher than for the ST18 truck, whilefor the CR02 crane, vertical stresses were 35-110% higher than for the ST18 depending on the axle number.Between the two cranes, vertical stresses measured under CR01 crane were 40-55% higher than for CR02 for the

corresponded axle. This could be attributed to the load distribution change when adding three axles to carry the sameload. Further analysis will be done for the other speeds and other pavement section to show the complete effect of the heavy cranes on the vertical stresses measured in the subgrade layer. Figure 4 shows typical vertical stressprofile under the axle loading of Speiring crane (with the four axles’ configuration).

CONCLUSIONS AND SUGGESTED FUTURE WORK

The results that are presented in this paper represent only the first run of a long series; in addition to that the datathat are collected are only three weeks old. Based on that what we presented here is a very preliminary result andtherefore no clear conclusions could be drawn since no detailed analysis was done and therefore all the conclusionswill be made when the complete data will be collected and analyzed. As for the future works, this test road could beadopted to perform more studies making use of the instrumentation design that made. Below are some ideas newstudies.

• Studying the edge effect on the pavement response, making use of the strain gauges array design.

• Including the tire characteristics to the variables in the testing program such as tire size, tire type, tirepressure …etc.

• Investigating the effect of any future work to the test road by comparing current results with the new ones.




REFERENCES

1. Christison, J.T., Anderson, K.O., and Shields, B.P. In Situ Measurements of Strains and Deflections in a Full-Depth Asphaltic Concrete Pavement. Proceeding-Association of Asphalt Pavement Technologies, Vol.47,Minneapolis, Minn., 1978, pp.398-433.

2. Christison, J.T. Predicted Load Equivalency Factors for Two Multi-Axle Cranes. A report for MotorTransport Services, Alberta Transportation, 1990.

3. Sebaaly, P.E., Siddharthan, R., and Huft, D. Impact of Heavy Vehicles on Low-Volume Roads. InTransportation Research Records: Journal of the Transportation Research Board, No.1819, TRB, NationalResearch Council, Washington, D.C., 2003, pp228-235.

4. Timm, D.H., Priest, A.L., and McEwan, T.V. Design and Instrumentation of the Structural pavementExperiment at the NCAT Test Track. National Center for Asphalt Technology NCAT, Auburn University,NCAT Report 04-01, 2004.

5. Transportation Association of Canada (TAC). Pavement Design and Management Guide. Ottawa, 1997.




LIST OF TABLES AND FIGURES

TABLE 1 Common Axle Configurations Found on Canadian Roads (TAC 1997) TABLE 2 Pavement Structure for the Different Sections in the Test Road TABLE 3 Testing Sequence TABLE 4 Test Vehicle Weights and Specifications TABLE 5 Longitudinal Interfacial Tensile Strains1 and Vertical Stress2 on Top of the Subgrade Layer Recorded

Directly Under the Wheels Path for the Tested Vehicles (Speed = 60 km/hr) TABLE 6 Distribution of the Transversal Strains Within the Array for the HMA Section/All Vehicles

FIGURE 1 Sample crane. FIGURE 2 The test road layout . FIGURE 3 Typical longitudinal strain profile under Speiring crane, HMA section, speed 60km/hr. FIGURE 4 Typical vertical stress profile under Speiring crane, HMA section, speed 60km/hr.




TABLE 1 Common Axle Configurations Found on Canadian Roads (TAC 1997)

Axle Tonnes Kips

Steering 5.50 12.1

Single 9.10 20.1

Tandem 17.00 37.5

Tridem1 21.00 46.3

23.00 50.724.00 52.9

Combinations

5 Axle Tractor Semi-Trailer 39.5 87.1

6 Axle Tractor Semi-Trailer 46.5 102.5

A Train Double 53.5 117.9

B Train Double 62.5 137.8

C Train Double 53.5 117.9

1 The three weights relate to different axle spacings.




TABLE 2 Pavement Structure for the Different Sections in the Test Road

Pavement Layers Description

Test SectionAsphalt Concrete HotMix

Asphalt Concrete ColdMix

Granular Base Course Prepared Subgrade

HMA

Hot mix asphalt concrete.

Total thickness is 110mm. constructed in twolifts. First lift is 50 mmand second lift (surface)is 60 mm. Maximumaggregate size is ½ in.Asphalt binder is 200-300A. Tack coat on thefirst lift is SS1.

N/A

¾ in. Maximum crushed

compacted granular basecourse. Thickness is 50mm. primed with MC30.

CMA N/A

Cold mix asphaltconcrete. Total thicknessis 50 mm. Maximumaggregate size is ½ in.Asphalt binder is 200-300A. Prime coat on thecompacted granular baseis MC30.

¾ in. Maximum crushedcompacted granular basecourse. Thickness is 50mm. primed with MC30

GBC N/A N/A

¾ in. Maximum crushedcompacted granular basecourse. Thickness is 50mm. primed with MC30.

Prepared Silty Clay.Thickness is 150 mm.scarified and compacte



Hamad, A. and Cowe Falls, L 12.

TABLE 3 Testing Sequence

Load Repetition No.

1 2 3 4 5

Standard 18kip @ 60 km/hr

Standard 8 wheel Tandem (17,000kg) @ 60 km/hr

Creep Standard 18 kip

Creep Crane

Standard 18kip

5km/hr Crane

Standard 18kip

10 km/hr Crane

Standard 18kip

15 km/hr Crane

Standard 18kip

20 km/hr Crane

Standard 18kip

30 km/hr Crane

Standard 18kip

40 km/hr Crane

Standard 18kip

50 km/hr Crane

Standard 18kip

60 km/hr Crane 4 axle configuration

Standard 18kip

60 km/hr Crane 7 axle configuration

Standard 18kip



Hamad, A. and Cowe Falls, L 13.

TABLE 4 Test Vehicle Weights and Specifications

VehicleTireSpecifications

Axle 1 Axle 2 Axle 3 Axle 4 Total

Standard 80 kNMichelinXZEM/275/80R22.5

4,980 7,800 - - 13,140

8 WheelTandem

MichelinXDEM/275/80R22.5

5,160 12290 17,040 - 34,490

Speiring Crane

GoodyearOmnitrack MSS 445/75R22.5Inflationpressure 90psi

11,700 12,400 10,650 9,200 43,950




TABLE 5 Longitudinal Interfacial Tensile Strains1

and Vertical Stress2

on Top of the Subgrade Layer Recorded Dire

the Tested Vehicles (Speed = 60 km/hr)

Axle # for the tested vehicle

1 2 3 4 5 Tested Vehicle

Test

RoadSection3

Standard18 kipTruck (ST18)

Longitudinal interfacial strains

HMA334(379)

1053(1362)4

1051(1345)

1031(1361)

1049(1392)

-

Speiring Crane -Four Axle Configuration (CR01)

CMA1057(1704)

1703(2238)

1806(2380)

1677(2110)

1792(2309)

-

HMA334(379)

923(1164)

938(1170)

932(1177)

914(1157)

86(1

Speiring Crane -Seven Axle Configuration (CR02)

CMA1057

(1704)

1732

(2261)

1832

(2273)

1844

(2343)

1951

(2347)

17

(2

Vertical stress on top of the subgrade layer

Speiring Crane -Four Axle Configuration (CR01) 9.5 18.0 23.3 24.3 23.1 -

Speiring Crane -Seven Axle Configuration (CR02)

HMA

9.5 12.8 14.9 16.5 15.3 15

1 Average+ 1S.D. (mm/mm x 10 -6)2 Average+ 1 S.D. (kPa)3 HMA=Hot Mix Asphalt, CMA= Cold Mix Asphalt4 Values between ( ) are for total strains




TABLE 6 Distribution of the Transversal Strains Within the Array for the HMA Section/All Vehicles

O1 Strain Gauges Array I1

O2 Travel Direction I2

O3 I3

Vehicle Type Axle # O1* O2 O3 I3 I2 I1

ST18 2 C C/T T C C/T T

1 T T C C C T

2 T T C C C T

3 T T C C C T

SpeiringCrane -FourAxleConfiguration(CR01)

4 T T C C C T

1 T T C C C T

2 T T C C C T

3 T T C C C T

4 T T C C C T

5 T T C C C T

6 T T C C C T

SpeiringCrane -SevenAxleConfiguration(CR02)

7 T T C C C T

* O1, O2, and O3 refer to the strain gauges on the side of the outer wheel path, while the I1, I2, and I3 refer to theside of the inner wheel path




FIGURE 1 Sample crane.




FIGURE 2 The test road layout .

PLAN VIEW Centre line

Strain Transducer

Moisture Gauge

1000mm1000mm

390mm

Temperature Profile

D.A.S

CROSS-SECTION VIEW

Hot Mix Asphalt 110 mm

Granular Base Course 300 mm

Subgrade Prep 150 mm

1000mm1000mm

Pressure Gauge

150 mm

Cold Mix Asphalt50 mm

GBC – 50 mm




Longitudinal Interfacial Strain (H-CR01-1-60-P05)

-0.0004

-0.0002

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0 0.2 0.4 0.6 0.8

Time (Seconds)

S t r a i n

( m

m

/ m

m

x

E - 0 6 )

ACP 1SLO1 018

ACP 1SLO2 030

ACP 1SLO3 011

FIGURE 3 Typical longitudinal strain profile under Speiring crane, HMA section, speed 60km/hr.

Axle1 Axle2 Axle3




Vertical Stress in the Subgrade (H-CR01-1-60-P05)

0

5

10

15

20

25

30

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Time (Seconds)

V e r t i c a l S t r e s s

( k P a )

ACP 2PO 310

FIGURE 4 Typical vertical stress profile under Speiring crane, HMA section, speed 60km/hr.

Axle1 Axle2 Axle3

Damage Factor Assessment Hamad&CoweFalls

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