TRANSPORT and ROAD RESEARCH LABORATORY

Department of the Environment

TRRL REPORT LR 525

A DEFLECTION SURVEY TECHNIQUE FOR PAVEMENT EVALUATION IN DEVELOPING COUNTRIES

by

H.R. Smith

Overseas Unit Transport and Road Research Laboratory

Crowthorne, Berkshire 1973

CONTENTS

Abstract

1. Introduction

2. The use of deflection measurements for pavement evaluation

3. Deflection surveys

4. Details of the road sites studied

5. The spacings of the test points investigated

6. Test results

7. Discussion of results

7.1 The 'density' .of testing 7.2 Differences between wheeltracks 7.3 The distribution of the deflection values

8. A suggested deflection survey method for overlay design

9. Conclusions

10. Acknowledgements

11. References

Appendix A Standard Road Research Laboratory method of making deflection beam measurements

Appendix B Classification of road surface conditions

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(~ ) CROWN COPYRIGHT 1973

Extracts from the text may be reproduced provided the source is acknowledged

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on l S t April 1996.

This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

t

? !7

A DEFLECTION SURVEY TECHNIQUE FOR PAVEMENT EVALUATION IN DEVELOPING COUNTRIES

ABSTRACT

The role of deflection beam surveys in the evaluation of flexible pavements is discussed. Deflection studies in Malaysia and Zambia are described from which a suitable survey method for use on tropical roads, for the purpose of designing strengthening overlays or pavement reconstruction, has been developed.

Testing at 100m intervals in both wheel-tracks is recommended with provision for a higher density of testing if the road deflection is variable, if the road surface has areas of visible distress, or if there are occasional very high deflection values.

Deflection values of roads tend to exhibit skewed distributions but it is concludedthat this is not necessarily a significant factor from the point of view of survey analysis for practical overlay design.

1. INTRODUCTION

Many countries in the world are experiencing a rapid growth of road traffic, both in terms of the weights of vehicles and their numbers. As a consequence there is a need to strengthen and improve a large number of existing roads, some of which were originally constructed before the era of the motor vehicle, and others which though built recently were not intended to carry present-day levels of traffic. Other roads that require strengthening include those constructed on the 'stage construction' principle that are designed to be strengthened progressively in several stages as the traffic grows. In many developing countries the stage construction principle has been widely adopted and the surge of road building in these countries in the fifties and early sixties has resulted in the need for a formidable programme of road strengthening in the present decade.

The most common way of strengthening a road is to overlay the existing pavement with bituminous premix. Besides strengthening the road there is an opportunity to improve riding quality and skid resistance if necessary.

Traditionally the thickness of bituminous strengthening overlays has been decided intuitively or by applying empirical pavement design procedures in which the existing pavement layers are assigned notional structural values.

These methods are prone to produce uneconomic designs primarily because they do not take proper account of the residual strength of the existing pavement. Bituminous road materials are relatively expensive thus there is a strong incentive for highway engineers to improve methods of designing strengthening overlays for existing roads. In response to this need there has been growing interest over the last decade in the use of non-destructive methods of evaluating the strength of existing pavements, ranging from wave propagation techniques to simple plate bearing tests.

The most widely used method of pavement evaluation is the measurement of the surface deflection of the pavement under a standard wheel load using a deflection beam. The deflection beam is simple to use and maintain and has strong attractions in many developing countries where more automated equipment such as the deflectograph can involve high operating and maintenance costs. The main disadvantage of the deflection beam for the evaluation of long lengths of road is the slow and laborious procedure that is required to obtain the same density of measurement as can be easily acquired with a deflectograph. In carrying out a deflection survey with hand deflection beams a compromise has to be struck between the number of measurements that are required to obtain a knowledge of the variation in the strength of the pavement from point to point, and the number of requlremer.t~ it is practicable to take.

t.ca c~g:i c: u c" e , , ~ e t..~ l " ~

This Report describes fieldwork in Malaysia and Zambia aimed at developing a satisfactory deflection survey procedure (using hand deflection beams) for evaluating the strength of existing roads.

A survey procedure is recommended and a simple method of analysing deflection survey data for the purpose of designing strengthening overlays is outlined. The approach put forward is suggested as being especially appropriate for evaluating pavements in areas where the operation of electronic equipment for road testing is difficult and expensive.

No attempt is made in this Report to define deflection criteria as such since many papers have been written in recent years on this subject. Deflection criteria for British roads have been discussed in a recent paper by MiUard and Lister 1.

2. THE USE OF DEFLECTION MEASUREMENTS FOR PAVEMENT EVALUATION

Deflection techniques have been used for evaluating the structural condition of pavements for many years. When A C Benkelman devised the simple deflection beam for measuring surface deflections on the WASHO test road in 19532 he introduced a technique that has become increasingly popular over the years, first with research workers and then with highway engineers responsible for road maintenance and strengthening.

Fifteen years ago the Transport and Road Research Laboratory started to use the deflection beam for monitoring the performance of full-scale road experiments 3 ,4, and a great deal of knowledge of the relation between deflection and performance has now been built up for the principal types of construction used for new main roads in Britain ~.

The principle o f the use of deflection measurements for pavement evaluation is very simple. When a loaded wheel passes over a pavement a small transient vertical depression of the surface of the pavement occurs. The magnitude of the surface depression or 'deflection' is a function of the wheel load, the area of contact between the tyre and the road, the speed of the wheel, and the stress-strain characteristics and thicknesses of the various pavement layers and the subgrade. Thus if a standard wheel load, tyre size, and method o f measurement are adopted, the magnitude of the surface deflection that occurs under the wheel enables comparisons to be made between the stiffness of different pavements and the change in stiffness over ~.time of a particular pavement.

2

Early in the history of the use of deflection measurements to monitor the structural condition of highway pavements it was found that for a particular pavement the magnitude of the transient deflection correlated well with the subsequent 'life' of the pavement 5 ,6, and this has been amply confirmed by the long-term deflection studies in Britain. This fact is of great importance in that it enables predictions to be made about the future traffic carrying capacity of a pavement on the basis of its present deflection characteristics. The measurement of the surface deflection of a pavement under a standard wheel load does not of course measure any absolute properties of the pavement system and in order to be useful it is necessary to know, in broad terms at least, the composition of the pavement layers and properties of the subgrade.

The method of measuring the surface deflection of a pavement with a deflection beam has been described many times. Appendix A summarises the standard TRRL dynamic procedure.

3. DEFLECTION SURVEYS

When a decision has been made to survey the structural condition of a road with deflection beams a compromise has to be found between the number of measurements that are necessary to determine the significant variations in the strength of the pavement from point to point and the number of measurements it is practicable to make.

Different authorities have different ideas as to the number of measurements required. In California 7 measurements are made at 15.2m (50ft) intervals in one wheel track of two lane roads; in Canada 8 ten measurements are made at random chainages in the verge-side wheel tracks of 305m (1000ft) lengths of road which are judged to be typical of longer stretches of road; in Brazil 9 measurements at 50m (164ft) intervals in both wheel tracks are recommended.

In the fieldwork described in this Report a study was made of the effect of varying the number of deflection measurements made from a maximum of 80 per lane per kilometre (128 per mile) to 10 per lane per kilometre (16 per mile) for several types of road construction in Malaysia and Zambia. The effect of choosing the spacing of the measurement points on a random basis as opposed to an equally spaced system was also studied.

4. DETAILS OF THE ROAD SITES STUDIED

Five road sites were studied altogether. The location of the three sites in West Malaysia are shown on the diagram of the main road system given in Fig. 1. The two sites in Zambia were both on the road f rom Kafulafuta to Fisenge.

The sites were chosen to provide a range of different types of construction in different sorts o f terrain. Two of the sites in Malaysia had crushed bases (one of granite and one of limestone) under bitumen macadam surfacing, and the third had a sand-cement base under a bi tumen sand surfacing. The crushed stone bases are typical of most new road construction in Malaysia

The two sites in Zambia had been constructed on top of an old road 3.7m (12ft) wide. The old road was first widened to 6.7m (22ft) by the addition of sub-base material along its edges, the whole width was then covered with a base 150mm (6in) thick of gravel stabilised with 4 per cent o f hydra ted lime. The base was surfaced with a double surface dressing.

:Details o f the sites are given in Table 1.

In each case a 1.61km (one mile) length of road was studied.

3

TABLE 1

Details of the sites surveyed

Location

Site 1 Route 1 121km (75ml) south of Ipoh

Site 2 Route 2 26km (16ml) west of Kuala Lumpur

Site 3 Route 3 152km (94aA ml)

L a n e

tested

Southbound

Slow lane Eastbound

Southbound

Type of construction

75mm (3in) granite bituminous premix BS 1621 base course on 200mm (8in) of granite 'crusher run'

75mm (3in) limestone bituminous, premix BS 1621 base course on 200mm (8 in) limestone 'crusher r u n ~

40mm (1½in) hot sand mix on 200mm (8in) cement stabilised sand

Pavement age in years at time

of testing

Open to cars 2½ years Open to lorries 1 year

3½

1½

south of Kuantan

Site 4 Zambia 18km (1 lml) from Kafulafuta

Site 5 Zambia 25km (15½ml) from Kafulafuta

Towards Fisenge

Towards Fisenge

6.7m (22ft) wide double surface dressing on 150mm (6in) base of lime stabilised gravel Constructed on an old road 3.7m (12ft) wide with extended sub-base to 6.7m (22ft)

6 t o !2

5. THE SPACINGS OF THE TEST POINTS INVESTtGATED

The 1.6km (one mile) length of each test site was marked out in the following ways:-

l) in 64 equally spaced chainages

2) in 64 randomly spaced chainages

3) in 16 equally spaced groups each having four test points 3.05m (10 feet) apart.

The randomly spaced chainages were obtained by choosing numbers from a table of random numbers, a different table being used for each site.

The figure of 64 points per 1.6km (one mile) or approximately one every 25m was chosen as being the maximum practicable for general survey work. The superimposition of the three test patterns, however, meant that in practice measurements were made at approximately 12m intervals and a very complete picture was obtained of the variation in deflection over the length of the sites.

4

At each chainage a deflection measurement was taken in both the verge side and offside wheeltracks of one lane except in Zambia where previous work had shown that deflections in the offside wheeltrack gave the greatest variability and therefore further testing was confined to this wheeltrack.

6. TEST RESULTS

The individual measurements are plotted against chainage for each site in Figs 2-5.

The readings are summarised in Table 2 in the form of the mean, median and standard deviations for each wheeltrack. The results for lower densities of testing are also shown, the random chainages for each density of testing were respectively the first 64, 32, 16 and 8 numbers selected from the tables of random numbers.

The deflections obtained from equal numbers of evenly and randomly spaced test points were compared for four densities of testing in each wheeltrack. Table 3 gives details of the comparisons between mean deflections and the variance of deflections using standard statistical tests, where significant differences were found. There were no significant differences found in any other comparison between equally spaced and randomly spaced deflections at equal densities of testing.

Similar comparisons were made between 64, 32 and 16 evenly spaced deflections and 16, 8 and 4 evenly spaced groups of deflections. Table 4 gives details of the comparisons where a significant difference was found.

7. DISCUSSION OF RESULTS

It is concluded from the results that random spaced test points have a serious limitation in that relatively long lengths of pavement were left untested and other lengths were heavily tested for reasons which were in no way related to the condition of the road structure. The results do not show any consistent advantages in using randomly spaced test points.

It might be expected that the use of evenly spaced measurement points might introduce some bias in the deflection results and the explanation why it does not is probably due to the tendency for the strength of a nominally uniform pavement to vary randomly along its length. This means that deflection measurements made at regular longitudinal spacings are nevertheless a 'random sample' of the deflection characteristics of a particular length o f road.

On the basis 0f these results it is considered preferable to use equally spaced measurement points for deflection surveys since this pattern has practical advantages in simplifying and standardising the marking out of road sites.

Although testing in groups would give more accurate average values over short lengths of road it would leave long lengths untested and yet involve a similar mount of work as would testing at single equally spaced chainages.

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Comparison between means and variances of deflections and of groups of deflections measured at evenly spaced chainages

Site No.

3

Number of deflections on 1.6km (one mile)

64 and 8 groups

64 and 4 groups

32 and 8 groups

32 and 4 groups

64 and 4 groups

32 and 4 groups

16 and 4 groups

64 and 4 groups

16 and 4 groups

Wheeltrack

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Offside

Offside

Offside

Offside

Offside

Significant differences and level of significance

Variance of groups of deflections larger at 1% and 2.5% levels respectively.

Variance of groups of deflections larger at 2.5% level.

Variance of groups of deflections larger at 5% level.

Variance of groups of deflections larger at 5% level.

Variance of single deflections larger at 5% level.

Variance of single deflections larger at 5% level.

Variance of single deflections larger at 5% level.

Variance of single deflections larger at 5% level.

Variance of single deflections larger at 5% level.

II

TABLE 5

Per cent change f rom the mean deflection of the measurements made at 25m (82½ft) intervals

S i t e N o .

2

Wheeltrack

Per cent change from the mean deflection of the measurements made at 25m (82½ feet)

intervals and the mean deflection of the measurements made at intervals of:-

50m (165ft) I 100m (330ft) I 200m (660ft)

Verge-side Offside

'Ve rge Offside

Verge Offside

Offside

Offside

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- 1 ½

0

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- 3

0

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+ 4 + ½

+ 17½ - 2

+ 4

+ 3½

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+ 1 1

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+ 26 + 7½

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Per cent change from the variance o f the measurements made at 25m (82½ft) intervals

Site No.

2

3

4

5

Wheeltrack

Verge Offside

Per cent change from the variance of measurements made at 25m (82½ft) intervals and the variance of

measurements made at intervals of:-

50m (165ft) [ 100m (330ft)

+ 76" + 25

Verge Offside

Verge Offside

Offside

Offside

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+ 7 + 25

- 6

- 2 5

+ 13

+ 54 + 44

+ 56 + 7

- 1 3

- 8 + 12

200m (660ft)

+ 195 + 71

+ 51 + 56

+ 36 + .31

- 3 3

+ 17

12

7.1 The 'density' of testing

The requirement of a deflection survey procedure is that sufficient indication of the variability of pavement strength should be obtained with a minimum of testing.

Continous testing at a rate of 40 equally spaced chainages per kilometre (64 per mile) involves a considerable amount of work and if a similar indication of variability can be obtained with a smaller sample this is obviously preferable.

The differences between different densities of testing at equally spaced chainages are shown in Tables 2, 4 and 5.

As would be expected the more variable the deflection readings over the 1.6 kilometre (one mile) lengths the larger is the number of tests that are required to give a reasonable assessment o f the deflection characteristics of the road.

Using standard statistical tests to compare the mean and variance of 64 equally spaced deflections with 32, 16 and 8 equally spaced deflections for each wheel track on each site showed a significant difference in the variance at the 1 per cent level between 64 and 8 deflections on the verge side wheel track of site 1. There were no other significant differences. However, it can be seen f rom Tables 5 and 6 that as the spacing of the measurement points increases the means and variances of the deflections for each wheel track tend to diverge from the values obtained with the closely spaced measurements. The difference between the results of the 25m spaced measurements and the 50m spaced measurements is small, (less than 5% change in the mean and less than 25% change in the variance), but the difference between the results of the 50m and 100m spacings is more appreciable and becomes marked at the 200m spacing.

If an arbitrary level of divergence of 5 per cent in the mean and 25 per cent in the variance is taken as being the maximum acceptable it follows that measurements at approximately 100m intervals are necessary, but that closer spaced measurements may be required for roads that are highly variable. A system of survey based on this arbitrary level of acceptable divergence was applied to the detailed deflection data of each of the sites and it was found that no significant area of weakness would go undetected if measurements were made at 100m intervals provided that:-

1) additional tests were made on areas of obvious visible distress;

2) additional tests were made to delineate the extent o f excessively weak areas, as indicated by the measurement of a 'high' deflection value (the definition of a 'high' value will vary according to the type of construction but will be of the order o f two times the deflection which is associated with long pavement life, i.e. 10 million standard 8200kg (18 0001b) axles);

3) additional tests were made when the variability of the deflections recorded at the 100m spacings exceeded a certain value.

Condition 3) above was first expressed in terms of the standard deviation o f a group of ten adjacent deflections along the road, but it has been found that a simpler expression of variability suffices as is described later.

13

7.2 Differences between wheeltracks

Many authorities find that the verge side wheeltracks of the roads they test have consistently higher deflections than the offside wheeltrack and as a result only the verge side wheeltracks are tested. This was not the case on the road in Zambia, probably because the recently widened part of the pavement was stronger and more uniform than that part overlying the old road.

The comparison between the deflection measurements on the two wheeltracks for each of the sites in Malaysia is summarised in Table 7.

The results of the testing on the three Malaysian sites show differences in the deflections between the wheeltracks which warrant the simultaneous testing of both wheeltracks.

On site 1 the mean and median deflections of the verge side wheeltrack were lower than those of the offside wheeltrack and some 914m (300Oft) of the offside wheeltrack had consistently larger deflections, however the verge side deflections were much more variable and where failure had occurred it was in a more advanced stage in the verge side wheeltrack.

The variance, mean and median deflections of the verge side wheeltrack of site 2 were higher than those of the offside wheeltrack.

The offside wheeltrack of site 3 had higher mean and median deflections than the verge side wheeltrack due mainly to the construction of the road. The base of site 3 was constructed in two halves and the offside wheeltrack is nearer to the centre-line construction joint than the verge-side wheeltrack is to the verge, this has resulted in generally higher deflections being measured in the offside wheeltrack.

It is suggested therefore that tests should be made in both wheeltracks unless there is a considerable volume of previous experience of the deflection characteristics of roads in the same terrain conditions which justifies testing in one wheeltrack only.

7.3 The distribution of the deflection values

The deflection values measured on the different sites are plotted in histogram form in Fig. 6. For this purpose the measurements at bo th the random and the equally spaced test points have been used. The class interval for the histogrammes have been calculated from the formula 1°.

Range Class interval =

1 + 3.322 logN

Where N = Number of readings

Values o f skewness calculated f rom the first and third quartiles as proposed by Bowley n are also shown

skewness = q 2 - q l

q2 + ql

where ql = first quartile

q2 = second quartile

Bowley suggests a value of 0.1 indicates moderate skewness and a value of 0.3 indicates marked skewness.

14

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I t can be seen that depending on the condition of the pavement, the distribution of deflection values can be very skewed, the weaker pavements tending to have a longer 'tail ' of high values.

This characteristic of 'skewness' is not normally taken into account in the analysis of deflection survey results 12. It is usually assumed that the deflection values of roads or visually assessed representative sections o f roads have a 'normal ' distribution and standard deviations of deflection survey values are calculated on this basis. It is then assumed that the mean deflection plus two standard deviations of a set of deflection survey results will embrace 97.5% of all the deflection values of the whole pavement.

It is clear that because of skewed distributions the evaluation of the deflection characteristics of pavements may often be a good deal less precise than is commonly supposed. However, it is not proposed that it is necessary to make special allowance for skewness in extrapolating from the results of a deflection survey "sample' to the deflection characteristics o f the whole pavement. This would imply that the whole deflection survey process has a precision which in reality it does not have and the method adopted of dividing the road into sections for overlay design tends to reduce the skewness in any one section.

16

8. A SUGGESTED DEFLECTION SURVEY METHOD FOR OVERLAY DESIGN

For a deflection survey method to be practical the manual labour content o f the survey must be kept to a minimum. This can be done by making maximum use of visual evidence of the pavement surface condition.

It is suggested that the following deflection measurements are made in both wheeltracks of the slow lane on dual carriageways and in both lanes of two-lane carriageways; this latter recommendation could be modified with further practical experience.

I. tests on a basic pattern of ten equally spaced tests per kilometre.

2. additional tests on any area showing surface distress.

3. if any measurement exceeds a predetermined value, which is related to established deflection criteria for the type of pavement concerned, the extent o f the area involved should be delineated by additional tests.

. additional tests should be made when the variability o f the above measurements exceed a certain value.

The deflections used both to check variability and to design the overlay should be the largest reading from either wheeltrack at each chainage.

A simple and adequate check on variability can be made in the following way. Ten consecutive measured deflection values are considered as a group and their mean value is calculated (for this purpose all the deflection values at the regular 100m spacings are used but only the maximum reading is taken from any one area tested on account of its surface distress or large deflection). If the largest and smallest values of the group differ from the mean by more than one-third of the mean then four additional tests should be made, each test being made midway between the test points which registered the largest and smallest deflections and their immediate adjacent test points. I f any of these four measurements would reduce the distance between test points to less than 10m (say 30ft) then the extra measurement need not be carried out.

The process is then repeated on another group of ten consecutive deflection values which is formed by taking into the previous group the next deflection value along the road, whilst omitting the first deflection value from the previous group. The process is repeated as each new deflection measurement is made so that a running check on variability is maintained.

This survey method was applied to the field results obtained on the five sites and it was found that no significant area of pavement weakness remained undetected. Using this method a team consisting o f a supervisor, three technicians, two drivers and five labourers equipped with one truck and two deflection beams should be able to cover up to 5 kilometres (3 miles) of two-lane road in a day.

After all measurements have been made it is convenient to plot for each lane the max imum deflection (corrected for temperature effect) and the largest pavement surface condition ratings for each cross-section ,against chainage along the road site. Any area showing exceptional weakness which may require reconstruction or special treatment is delineated. The remainder of the road is then divided into sections by inspection in such a way as to minimise variation in deflections within each section. The minimum length o f a section should be compatible with the method of resurfacing that it is intended to employ. It is unlikely that the thickness of a machine laid surfacing would be varied over lengths less than about 200m (660 feet). I f the deflection values are very high, implying that base reconstruction is required then short lengths of pavement can be considered separately since normally hand labour '(assisted by machine) would be used for such an operation.

17

The final stage is to design the overlay for each section of the road "and to determine those areas which merit further investigation. On those areas of pavement where deflections are very high or failure has occurred inspection holes should be dug and a careful note of drainage conditions made.

I f it is assumed that the distribution of deflections is normal then only 2.5 per cent of the pavement would be expected to have a deflection in excess of the sample mean plus twice the standard deviation of the sample. The survey method proposed will tend to separate out the very high deflections on areas warranting special t reatment or reconstruction and so reduce the effect of skewness, thus the distribution of deflections in each selected section should not be far removed from a normal distribution.

Some authorities recommend an overlay design deflection of the mean plus twice the standard deviation of a sample of readings. It is felt that in developing countries it is not appropriate to go to the expense of such a high degree of certainty which might lead to the expensive over-design of large areas of pavement. Use of the proposed survey method in'conjunction with a design deflection of the mean plus 1.0 or 1.5 standard deviations for the section is recommended.

Examples of the survey and analysis procedure described above are illustrated in Figs 7 and 8, in which the overlay design is based on the mean plus one standard deviation.

The deflection survey should be carried out at the time of year when the pavement is at its weakest, in the tropics this is usually after the rainy season when the subgrade is at its wettest.

I t is of considerable value in analysing survey data to have information on the deflection history of the pavement but initially readings at two points in time, say twelve months apart, will indicate the rate of change of deflections which may indicate priority of treatment for some roads.

In interpreting deflection survey data it is necessary to have a broad knowledge of the pavement structure and the subgrade. Trial pits dug in the old pavement at one kilometre (say ½ mile) intervals should be sufficient for this purpose. At the same time attention should be given to the improvement of drainage conditions along the road. Drainage improvements should preferably be completed at least one year b.efore carrying out an overlay design survey so that the full benefits of the improvements may be realised before pavement strengthening is undertaken.

9. CONCLUSIONS

.

.

.

A deflection survey procedure for overlay design is proposed on the basis of the detailed evaluation of five road sites (3 in West Malaysia and 2 in Zambia).

Testing at 100m intervals in both wheeltracks is recommended, with provision for a higher density of testing if the road deflection is variable, if the road has areas of visible distress, or if there are occasional very high deflection values.

Deflection values o f roads tend to exhibit skewed distributions as opposed to normal distributions but this is not necessarily a significant factor from the point of view of survey analysis for practical overlay

design.

18

10. ACKNOWLEDGEMENTS

The author is indebted to Tan Sri Haji Yusoff bin Haji Ibrahim, PSM JMN SMK BSc(Eng) MIE(M), formerly the Malaysian Director General of Public Works and to many of his staff for their support and practical assistance.

The deflection investigations in Zambia were made with the co-operation of the Zambian Ministry of Transport and Communications and in particular Mr. F. Sharratt, Director of Roads, and Mr. J. Kiln. The work was conducted by Messrs A B Baker, M N Daniel and D Ramharry of the Overseas Unit of the Transport and Road Research Laboratory.

11. REFERENCES

.

.

.

.

.

.

7.

.

.

10.

MILLARD, R S and N W LISTER. The assessment of maintenance for road pavements. Proc Instn Civ Engrs 1971,48 (Feb). The Institution of Civil Engineers, 1971.

HIGHWAY RESEARCH BOARD. The WASHO Road Test Part 1. Design Construction and testing procedures, Highway Research Board Special Report No. 18, Washington, 1953.

LEE, A R and D CRONEY. British full-scale pavement design experiments. Proc Int Conf Struc Design of Asphalt Pavements, at Univ Michigan, Ann Arbor, USA 1962. Ann Arbor 1963 (University of Michigan).

SALT, G F. Recent full-scale flexible pavement design experiments in Britain. Proc 2nd Int Conf Struc Design of Asphalt Pavements at Univ Michigan, Ann Arbor, USA 1967, Ann Arbor 1968 (University of Michigan).

HIGHWAY RESEARCH BOARD. The AASHO Road Test. Report 7. Summary Report. Highway Research Board Special Report No. 61G Washington 1962.

HVEEM, F N. Pavement deflections and fatigue failures. Highway Research Board Bulletin No. 114. Highway Research Board, Washington 1955.

ZUBE, E and R BRIDGES. The use of pavement deflections in asphalt pavement overlay design. Proc Int Conf Structural Design Asphalt Pavements at Univ Michigan. Ann Arbor USA 1962 Ann Arbor 1963 (University of Michigan).

CANADIAN GOOD ROADS ASSOCIATION. A guide to the structural design of flexible and rigid pavements in Canada. Canadian Good Roads Associati~on Pavement Design and Evaluation Committee. Ottawa 1965 (Canadian Good Roads Association).

HIGHWAY RESEARCH BOARD. Evaluation of pavements by deflection studies for maintenance purposes. Highway Research Record 129, Washington 1966.

STURGES, H A. The choice of a class interval. Journal of the American Statistical Association, March 1926.

1 9

11.

12.

MILLS, F C. Measures of skewness. Chapter 5 Statistical methods London 1955. (Pitman).

CANADIAN GOOD ROADS ASSOCIATION. Pavement Evaluation Studies in Canada. Special Committee on Pavement Design and Evaluation Canadian Good Roads Association. Int Conf Struc Design of Asphalt Pavements, at Univ Michigan, Ann Arbor, USA 1962. Ann Arbor 1963 (University of Michigan).

20

APPENDIX A

STANDARD ROAD RESEARCH LABORATORY METHOD OF MAKING DEFLECTION BEAM MEASUREMENTS

.

.

.

.

.

.

.

8.

.

Load a 5-ton lorry (or similar) fitted with twin rear wheels to give a load of 6,350kg (140001b) on the rear axle. (i.e. 3175kg or 70001b on each pair of twin rear wheels.)

Inflate the rear tyres to 585 kN/m 2 (8511b/sq in). Recommend Tyre size 7 50 x 20 with spacing of 45ram (1¾ inches).

Mark a point on the road at which the deflection is to be measured, and position the lorry so that the rear wheels are 1¼ m (4ft) behind the marked point.

Insert the deflection beam between the twin rear wheels until its point rests on the marked point of the road. If required insert a second beam in a similar way between the other pair of twin rear wheels.

It is helpful in positioning the lorry and aligning the beams parallel to the lorry axis if a pointer is fLxed to the lorry 1¼m (4ft) in front of each pair of twin rear wheels.

Check the beam pivot arms for free movement, adjust the footscrews if necessary, and zero the dial gauges whilst tapping the beam gently with a small spanner.

Record the dial gauge reading. (Either zero or some small positive or negative reading.)

Drive the lorry slowly forward and whilst gently tapping the beam note the maximum dial gauge readings and the final readings when the lorry wheels have moved 3m (1 Oft) or more clear of the tips of the beams.

For each beam calculate the deflection of the road surface by adding the difference between the first and maximum dial gauge readings to the difference between the maximum and final gauge readings.

21

APPENDIX B

CLASSIFICATION OF ROAD SURFACE CONDITION

Transverse deformation under a 2m (6.5ft) long straightedge

Classification Index

D 1

D 2

D 3

D 4

Deformation

(regarded as 'failed' in UK)

D 5

(suggested failure criteria for main roads in Malaysia)

Less than lOmm (3/8in)

lOmm (3/8in) to 15ram (9/,16in)

15mm (9/16in) to 20mm (13/16in)

20mm (13/16in) to 25mm (lin)

Greater than 25mm (1 in)

Degree of cracking (visible cracks)

Classification Index

C 1

C 2

C 3

C 4

C 5

Crack length/unit area

Nil

Not greater than 1 m/m 2

Greater than 1 m/m 2 but not greater than 2m/m 2

Greater than 2m/m 2 but not greater than 5m/m 2

Greater than 5m/m 2 (ravelling & potholing imminent, immediate maintenance required)

2 2

5

100 102 I

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Pave~nent] 8 0 i nves t - I . !~la'r.ion I 180

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Fig. 7 EXAMI

Mean * (1 x s tandard deviot ion)(mm xlO "2)

Thickness of ove r lay requ i red (mm)

to reduce d e f l e c t i o n to 75 x lO-2mm

See append ix B t A s r e q u i r e d to ach ieve

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1 1 1 1 1 1 1 1

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1

21 1 1 1 1 1 1 1 1 1 1 1

t PGY@, 150 15761124 75 24 29 25 47

Inv. : 157 ~ 47

Req'd ~ 9 0 = 0 Reco~ - s t r uc t

49 42 80

402 9 5 0 1019 1257 1609 Chainage (m)

v~ ,,10 1 v 2 v ~ v 4

l l l | l l ~ ~ 76 mi le post "`5 f rom Ipoh

J n~g ¥ ~3

' l ow po in t '

LE OF OVERLAY DEFLECTION SURVEY SITE 1 ~3

R O U T E 2. BATU T I G A

East bound mi le 15116 100mm bi tumen macadam over 2 5 0 m m c rushed s tone Dual c a r r i a g e w a y

Verge Off I s ide side

Basac 100 m • • chainages

Extra points 0 o

o ? . o @ - 1

0"5

m

ID 2~ O -

I Bas is f o r o v e r l a y des ign

/ " ) o • I l

I o

I

0

• 0 0 •

O0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 (m) I I I I I I I I I I I I 0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0 3 5 0 0 4 0 0 0 4 5 0 0 5 0 0 0 5 5 0 0 ( f t )

each weak area Max. d e f l e c t i o n at

Chainage (m) o (~

Extra tests on distressed areos(rnmxlO ~ NONE

Chainage ( m ) 1

Ext ra tes ts def lect ions • 1ram (mm x10-21 NON E Max. de f l ec t i on f rom (mm x10-2] 1

0 0 0 0 0 0 0 0 0 0 0 0 ~ ~ o~ ~ ~ ~ ~- q" I/3 ~0 0 CO , ~ ~ ~ ~ ~ ~ ~ ~

5 6 G 4 5 8 lOOm in te rva ls (mmxlO "2} 41 48 33 5 6 6 9 4 8 79 G8 76 20 9 4 6 6 76 9G 6 2

Mean of groups of t en (mm x l O -2] I ! 5 4 5 9 61 6 5 6 9 6 8 6 9 6 7 6 6

÷1/3X (mmxlO -2} I 72 7 9 81 " 8 7 9 2 91 9 2 9 0 8 8

' ~. -1/3~ ( m m x10-2} I 36 39 4 0 4 4 4 6 4 5 4 6 4 5 4 4

Ext ra tes t s if x>-~ ÷1/3X (mmxlO-21 51 6 6 i 36 6 6 74 71

Ex t ra tes t s if X<Y.-113:~ ( m m x l O "2} 58 36

Chainage ( m )

~Vergel c I Surface isidelD 2 condi t ion Ioff i c I

ra t ing t Is ide J D 1

Def lec t ions used fo r over lay (mmxlO-21 desicjn

Mean * (1 x standard dev ia t ion )(mmxlO'21

Thickness of over lay requ i red (mm)

to reduce def lec t ions to 5 0 x 1 ( ] 2 m m t

See append ix B As r e q u i r e d to ach ieve

1~ des i red des ign l i fe

Cu t t i ngs

E m b a n k m e n t s

Mile pos ts

v Heights I

in I I me t res

I I ~I 1 1 1 I I 1 I I I 1 I 1 1 1 1 I 1 I I I

1 2 2 2 4 2 . 2 2 5 i ! , 2 2 1 2 3 5 5 4 2 2 2 2 1 1 2 !

'!1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

1 2 1 1 1 1 i 1 1 2 ~2 1 1 2 1 2 2 2 2 2 1 1 1 1

41 48 33 5 6 G9 4 8 51 79 GG 6 8 7G ~58 20 3G 94 GG 6G 7G 74 9G 71 5G G4 5 8 G2

5 7 5 ~ 9 7 5 - 1 3 7 5 1710

Ch_ nagea'i (m) 1 5 m i l e pos t

1 f r o m 16 mi le " / ' ~ ~ l,

• z~lO post from 1 Kua,o Lumpur Kuola L u m p u r ' , r y A 3 1 t i / I I I I i l I I i J l i ~ d ~ I I I l l

~ . ~ . ~ "~ ,, ?TTTTTT TT?T VYTTTTIST V $~ STTTTIT ?V$?I$~YVYVTVVVTTTTTYSTTT?V~?T

• z~lO v 12 i A1 Z~I

! Fig.B. EXAMPLE OF OVERLAY DEFLECT ON SURVEY SITE 2

(1733) Dd891796 4,000 12/72 HPLtd , So ' ton G1915 PRINTED IN ENGLAND

ABSTRACT

A deflection survey technique for pavement evaluation in developing countries: H R SMITH: Department of the Environment, TRRL Report LR 525: Crowthorne, 1973 (Transport and Road Research Laboratory). The role of deflection beam surveys in the evaluation of flexible pavements is discussed. Deflection studies in Malaysia and Zambia are described from which a suitable survey method for use on tropical roads, for the purpose of designing strengthen- ing overlays or pavement reconstruction, has been developed.

Testing at 100 m intervals in both wheel-tracks is recommended with provision for a higher density of testing if the road deflection is variable, if the road surface has areas of visible distress, or if there are occasional very high deflection values.

Deflection values of roads tend to exhibit skewed distributions but it is concluded that this is not necessarily a significant factor from the point of view of survey analysis for practical overlay design.

ABSTRACT

A deflection survey technique for pavement evaluation in developing countries: H R SMITH: Department of the Environment, TRRL Report LR 525: Crowthorne, 1973 (Transport and Road Research Laboratory). The role of deflection beam surveys in the evaluation of flexible pavements is discussed. Deflection studies in Malaysia and Zambia are described from which a suitable survey method for use on tropical roads, for the purpose of designing strengthen- ing overlays or pavement reconstruction, has been developed.

Testing at 100 m intervals in both wheel-tracks is r ecommended with provision for a higher density of testing if the road deflection is variable, if the road surface has areas of visible distress, or if there are occasional very high deflection values.

Deflection values of roads tend to exhibit skewed distributions but it is concluded that this is not necessarily a significant factor from the point of view of survey analysis for practical overlay design.