TRANSPORT AND ROAD RESEARCH LABORATORY Department of Transport

RESEARCH REPORT 141

LOADING TESTS ON TWO LONG SPAN CORRUGATED

STEEL CULVERTS

by J Temporal and P E Johnson

The views expressed in this report are not necessarily those of the Department of Transport

Ground Engineering Division Structures Group Transport and Road Research Laboratory Crowthorne, Berkshire, RG11 6AU 1988

ISSN 0266-5247

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on I st 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.

CONTENTS

Abstract

1. Introduction

2. The culverts

2.1 Quy Water

2.2 Stone Hill

3. Instrumentation

3.1 Quy Water

3.2 Stone Hill

4. Experimental procedure

4.1 Quy Water

4.2 Stone Hill

4.3 Plate loading tests

5. Results

5.1 Quy Water

5.2 Stone Hill

6. Discussion of results

7. Implications for design

7.1 Crown deflection

7.2 Factors of safety

7.3 Closed invert and arch structures

8. Conclusions

9. Acknowledgements

10. References

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© CROWN COPYRIGHT 1988 Extracts from the text may be reproduced,

except for commercial purposes, provided the source is acknowledged

LOADING TESTS ON TWO LONG SPAN CORRUGATED STEEL CULVERTS

ABSTRACT Two loading tests have been performed on long span culverts using single axle loads up to 455 kN. The culverts were a 9.83 m span horizontal ellipse and a 7.47 m span high-profile arch with depths of cover to the crown of 1.90 m and 0.95 m respectively. Measurements of culvert deflection gave maximum values of 1 mm and 4.25 mm for the two sites with corresponding maximum bending strains of 10 and 170 microstrain: the maximum ring compression strains were 25 and 80 microstrain respectively. The results obtained from the loading tests are discussed in the context of the design methods available for long span corrugated steel culverts.

1 INTRODUCTION

In 1982, the Department of Transport issued a Departmental Standard BD 12/82, which contained a design method for corrugated steel buried structures with spans up to about 7 m (DTp 1982). This standard made use of the results of a series of loading tests to failure on a 4 m span structure performed by the Transport and Road Research Laboratory (TRRL) in 1981 and reported by Temporal et al (1985).

However, spans in excess of 7 m are frequently required to cross watercourses and to form accommodation roads. Over 2000 such structures have been built worldwide and have proved to be an economic alternative to concrete culverts and small bridges. To date, very few long span corrugated steel culverts have been built in the UK and the largest of these has a span of only 11.25 m whereas the largest structures built overseas have spans of about 17 m.

The design method used in BD 12/82 becomes excessively conservative at large spans and as a result a number of alternatives has been considered by DTp. In order to give some assurance of the applicability of these design methods, two loading tests have been performed on culverts with spans of 7.47 and 9.83 m using a single axle loading trailer, the specification of which was similar to that for one axle of the HB load (British Standard 5400: Pt 2: 1978). Both the culverts were buried at low depths of cover to the crown of the structure and axle loads up to 455 kN were applied during the loading tests. This situation is one of the more onerous conditions which has to be considered in design.

2 THE CULVERTS

2.1 QUY WATER This culvert was a 9.83 m span horizontal ellipse which carries a stream known as Quy Water under a dual carriageway section of the A45 Cambridge Northern Bypass. The culvert was constructed in 1978. The structural plates were 7 mm thick with a corrugation of 152.4 x 50.8 ram. The geometry of the culvert is shown in Figure 1 and further details are given in Table 1. Reinforced concrete thrust beams, incorporated into the structure at each of the shoulders, act as longitudinal stiffeners and may also assist compaction of the backfill in these areas.

The culvert was backfilled with a well-graded sand and gravel which had been well compacted. The particle size distribution of the backfill is shown in Figure 2 and the density and moisture content, determined in accordance with Test 14 of BS 1377: 1975, are given in Table 1. The sand and gravel backfill extended to approximately one span of the culvert on each side of the structure and to a depth of 1.53 m over the crown of the structure. A pavement consisting of 210 mm of lean mix concrete overlaid by 160 mm of bituminous-bound material was constructed on top of the backfill: this gave a total depth of cover to the crown of the culvert of 1.90 m.

2.2 STONE HILL This culvert was a 7.47 m span high-profile arch which carries a branch of the Little Avon river under a now redundant section of the old A38 trunk road between Bristol and Gloucester near the village of Stone, Gloucestershire. Again the culvert was constructed in 1978. The structural plates were 6.2 mm thick with a corrugation of 152.4x 50.8 mm. The geometry of the culvert is shown in Figure 3 and further details are given in Table 1. The culvert was constructed on a 600 mm thick reinforced concrete slab which provided a foundation for the base of the arch and also formed a paved invert for the structure. At the base of the arch, the structural plates were located in a steel channel which was cast into the upper face of the base slab, with one bolt per corrugation connecting the plates to the channel. As at Quy Water, reinforced concrete thrust beams were incorporated into the structure at each of the shoulders.

The culvert was backfilled with a well-graded crushed limestone fill which had been compacted to a high density. The particle size distribution is shown in Figure 2 and the density and moisture content are given in Table 1. The crushed limestone backfill

160mm flexible l road surface

210mm lean-mix j concrete

~- Span 9.83m

0 l m L I

Fig. 1 Geometry of Quy Water culvert -- cross section at inst rumentat ion location

T A B L E 1

Details of Culverts and Backfill Materials

Property Quy Water Stone Hill

Culvert profile Manufactures reference no. Span (m) Top radius (m) Depth of cover to crown (m) Plate thickness (ram) Corrugations (mm)

Horizontal ellipse ARMCO 108 E 54

9.83 6.27 1.90 7.0

152.4 x 50.8

High profile arch ARMCO 87 A15-24

7.47 5.03 0.95 6.2

152.4 x 50.8 Moment of Inertia (mm4/mm) Area of Section (mm2/mm) Longitudinal seams (bolts/corrugation) Backfill material In situ bulk density (Mg/m 3) In situ dry density (Mg/m 3) In situ moisture content (percent) *Maximum dry density (Mg/m 3) *Optimum moisture content (percent) In situ dry density Maximum dry density Uniformity coefficient

Sand

2718 8.71

2 and gravel 2.08 1.99 4.7 2.21 7.5

0.90

20

2396 7.75

2 Crushed limestone

2.24 2.15 4.1 2.19 4.0

0.98

26

*determined in accordance with Test 14 of BS 1377: 1975.

2

90

80

70

• ~ 60 50

c 40 la

i_

~- 30

20 10

0.02 0.1

(ram) tZ3

I~' I I ~ "

I I J/i II I l Y l l .~' I l l l I i !1 V i l l i #

I I 1 . • I I I I ; I I I 1 ~ II 1 .'" ', I II l,'l i !

~'i I , I II l i I II I 20 I I ou~ ~ater I I - - ~ . - - Stone Hill I0

II II i i I IIII II Jo

I0 I00

//,i,m

•

o ~ O ~ O _= _ N o l o _ ~

I' r i! I i ' I! ~o I II II I', 8o I

'::I , I ' ,dl I

, ,, ol [, t i 201-,M I L , ,F I

I I / I IJ.l~t' i ,01 I . . ~ " ~ " r T I I I i t l i l I I I I I I I I

1.0

Pa r t i c l e s i ze (mm)

, CO'" 'EIFNE ' [ SILT I SAND G R A V E L

I 0 0

~0

70

60 50 40 30

Fig. 2 Part icle size d is t r ibu t ion fo r back f i l l mater ia ls

i 20mm flexible l road surface

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i::i:~i:~i::i::i::i::i~:!!i Cover ]il::i::!::i::!:~ :~ii!i!!!!!!~!~!~!~i~iiii~iiiiiiiiiiiiiiii!ii!!iii!!!!!!!!!!ii!!i~iiiiiiii~ii~iii~i~iiiiiiiiii~i~i~i~i~i~i~i~i~i~!~!~i~i~i!!iii!!!~iiiiiiii~iii~iiii

Re~°f°rced !!!!!iiiiiiiiiiiliiiiiiiiiiiiiiiii iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii concrete : : i : : i : : i : : i : : i i ~ i ! i i i i i i i i i i i i i i i i i i i i i i i i }i:i:i:i:

beam !::i::!::!::!::i ::::::::::::::::::::::::::::::::::::::::: ::::::::::::::::::

i:i:;:ii ~ ~ . 1 9 m

!' Maximum span 7.47m '1

0 l m i i

Fig. 3 Geomet ry of Stone Hi l l cu lver t -- cross sect ion at ins t rumenta t ion locat ion

extended to approximately one span of the culvert on each side of the structure and to a depth of 830 mm above the crown of the structure. A pavement consisting of 120 mm of bituminous-bound material was constructed on top of the backfill: this gave a total depth of cover to the crown of the culvert of 0.95 m.

3 INSTRUMENTATION

For the loading tests at both Quy Water and Stone Hill, a single ring of instrumentation was installed circumferential ly within each of the culverts. Instruments were installed to measure vertical deflection of the culverts and strains within the structural plates. The rings of instruments were located so that they were as close as possible to the centre line of the loading trailer. The measuring points wi th in the culverts were spaced at horizontal centres of 900 mm and the loading positions on the carriageways were also 900 mm apart.

The loading trailer consisted of a single axle with four wheels which could be loaded incrementally from an unladen weight of 120 kN up to a maximum weight of 455 kN using concrete blocks as kentledge. The trailer was built in about 1960 to represent one axle of the abnormal (HB) load given in BS 153: 1954. This is similar to the revised HB load given in BS 5400: Part 2: 1978. A full description of the loading trailer is given in Temporal et al (1985). For the tests at Quy Water and Stone Hill, the trailer was towed using an attachment boom and heavy duty tractor unit, which was suff icient ly far away from the loading axle to have little effect on the loading. As the full HB load consists of two axles at a spacing of 1.8 m, the 900 mm spacing of the measuring points and the loading positions was chosen to al low superposition to be used to estimate the deflections and strains likely to be caused by two axles.

3.1 Q U Y WATER In general, the simplest method of accurately measuring the vertical deflection of a culvert is by direct measurement between datum points in the invert and crown sections using dial gauges mounted on st i f f rods. Unfortunately the water level was over 2 m above the invert and pumping was not feasible. As this precluded access to the invert, an optical levelling system was used to measure the vertical deflection of the crown.

Scaffolding was erected within the culvert to provide access to the crown area and a steel measuring tape, graduated in millimetres, was f ixed to lengths of aluminium section and bolted to brackets glued in the culvert crown. An optical level was mounted on a rigid f rame which was anchored into the concrete ring beam at the end of the culvert, some 12 m from

the ring of instruments. It was estimated that with this system, the vertical deflection of the measuring points could be determined to_+0.5 ram. During the loading tests, the concrete ring beam was accurately surveyed to check that no vertical movement occurred.

At each of the measuring positions within the culvert, a pair of vibrating wire strain gauges was attached to the steel plate with adhesive. One gauge was attached to an internal trough and the other to an internal peak: this arrangement allowed both ring compression and bending strains to be determined at each measuring location. A close-up of one of the measuring positions is shown in Plate 1 and a general view of the site is shown in Plate 2. The layout of the measuring and loading positions is shown in Figure 4.

During the loading test, the nearside lane of the eastbound carriageway was closed to traffic so that the combined width of this lane plus a 1 m wide hard strip at the edge of the carriageway was available for the loading trailer, tractor unit and mobile crane. At Quy Water, the culvert was skewed at 15 degrees relative to the carriageway as shown in Figure 5. The overall length of the loading trailer and tractor unit was about 20 m, so that there was insufficient space available to allow the line of loading positions to be in the same vertical plane as the line of measuring positions without closing both lanes of the eastbound carriageway. As this would have caused considerable traffic delays, it was decided that the line of loading positions should be parallel to the carriageway, thus allowing the loading test to be conducted within one lane. It was thought that the fact that the ring of instrumentation and the loading path were not in the same vertical plane was unlikely to have a serious effect on the results of the loading test. However, to minimise any such effect, the loading positions were set out so that for the most critical case, where the loading trailer was on the culvert centreline, the load was directly above the instrumented ring.

3.2 STONE HILL The culvert at Stone Hill was under a section of the old A38 trunk road which no longer carries through traffic. As a result, it was possible to close the road completely without any inconvenience to the public. The culvert carried one branch of the Little Avon river, the rest of the f low passing beneath an adjacent bridge. It was fairly easy in this case to construct small dams on both the upstream and downstream approaches to the culvert. All the flow was then diverted beneath the adjacent bridge and the culvert pumped dry. This revealed that the foundation slab of the culvert was buried beneath about 1.5 m of silty sand which had been washed down by the river.

In order to minimise any stiffening effect of the spandrel walls at each end of the culvert, the ring of

4

N e g r~o R666 84 12

Plate 1 Detail of measuring position at Quy Water

Plate 2 General view of site at Quy Water

I I I I I

6 5 4 3 2 ~ 0 Loading positions

0.9m 0.9m =1. ~1. . I . • -1 ~ ~ 1 ~ ,,-1 ~

0 lm i I

Strain gauge pairs and vertical scales at I to

Fig. 4

Embankment slope

Grass verge

\ \

\

Layou t o f ins t rumentat ion and loading posi t ions at Quy Water

\ , \ \ 15° ~ \\

N

Hard strip

N.S. lane

! I I

0 1 2m

\ i t~, Measuring points (in culvert)

\ \ \ Loading positions

\ \ \ , \

\ \ \

Culvert centreline

O.S. lane

Hard strip

Central reserve

f Loading trailer

I

Fig.5 Plan v iew of Quy Water site

instrumentation was installed at the mid-length of the culvert. At this location, a 1 m wide trench was excavated through the silty sand to give access to the foundation slab and along the base of the arch (Plate 3). The trench sides were supported by timber sheets and props: access to the crown section of the culvert was obtained using scaffold towers and staging boards.

Five measuring points were located in the crown section of the culvert, one point at the crown and two points each side of it at 900 mm horizontal centres. At each location, a datum point was fixed to the culvert and a second datum point was fitted directly below in a hole drilled into the foundation slab. Vertical displacements were measured using dial gauges mounted on lengths of aluminium tube and located between the datum points. In addition, the maximum horizontal span was monitored in a similar manner; this system enabled displacements to be measured to an accuracy of about __ 0.02 ram.

A pair of vibrating wire strain gauges was installed at each of the five crown measuring positions with a pair of additional gauges located near each shoulder as shown in Figure 6. The system was the same as the one used at Quy Water. In addition, a pair of strain gauges was installed on each side of the culvert approximately 150 mm above the base of the arch to show whether any stress concentrations

occurred near the connect ion between the base of the arch and the foundat ion slab. The installation of these gauges is shown in Plate 3.

As the whole road could be closed at Stone Hill, the loading posit ions could be set out directly above the ring of instrumentat ion. Eight loading positions, spaced at 900 mm horizontal centres, were marked out down the centreline of the carriageway. The layout of the instrumentat ion and loading posit ions is shown in Figure 6 and a general v iew of the site is shown in Plate 4.

4 E X P E R I M E N T A L P R O C E D U R E

4.1 QUY WATER A set of readings of all the instruments was taken immediately before the loading test to provide a datum from which to analyse the subsequent results. The unladen trailer was then towed to position 0 and all the instruments were read again: the trailer was then moved sequential ly to posit ions 1 to 7 and a set of readings taken at each location. The trailer was then reversed to its start ing posit ion, well away from the culvert, and four kentledge blocks were loaded onto it. Ano ther set of readings was taken wi th the culvert unloaded and subsequent sets of readings taken wi th the trailer at posit ions 0 to 7. The whole

Neg. no. R483/86/6

Plate 3 Ins ta l la t ion of s t ra in gauges near the base o f the arch at S tone Hil l

O I I I I I i I

G F E D C B A Loading posit ions =

0.9m 0 9 m

l m

I

Stra*n gauge pairs at T to "T/TI" and foundat ion 1 and 2 Dial gaugesat } - [ to ~/mr and HorizontaJ 1

Fig. 6 Layout of instrumentation and loading positions at Stone Hill

/

Plate 4 Genera l v i e w o f s i t e a t S t o n e H i l l

Neg. no. R484 86 '6

procedure was subsequently repeated with 8, 12, 16 and 20 kentledge blocks until the total load on the trailer was 455 kN.

During the day of the test, the temperature of the pavement was monitored at a depth of about 50 mm below the surface: this increased from about 14.5°C at 0830 hrs when testing started to about 19.5°C at 1630 hrs when the test was completed. The wheel tracks of the loading trailer were monitored throughout the loading test using a precise level, but no rutting of the pavement was observed. Precise levelling was also used to check that the ring beam at the end of the culvert, on which the deflection measuring system was mounted, did not move during loading. No movement was detected, even at the highest loads used in the test.

4.2 STONE HILL The procedure adopted at Stone Hill was similar to that used at Quy Water. The main difference was that the dial gauges used to monitor culvert deflection were considerably easier to read and more accurate than the levelling technique used at Quy Water. Precise levelling was however used to check that the foundation slab did not move during the test. No movement of either the slab or the base of the arch was detected, even at full load conditions. The temperature of the pavement was monitored in a

similar manner to that used at Quy Water and found to be reasonably constant at about 27°C th roughout the test. This reflects the fact that the test was conducted on a very hot day.

4.3 PLATE L O A D I N G TESTS Tests were performed at both sites to measure the constrained modulus (M*) of the backfil l material around the culverts. A t Quy Water, a shal low trench was dug in the grass verge at the side of the carriageway and at Stone Hill a shal low trench was dug through the pavement until the backfill material was exposed. In both cases the trenches were suff iciently far away from the culvert for this to have negligible effect on the tests. The tests were performed in accordance wi th BS 5930:1981 Chapter 29 using a 300 mm diameter plate. A t Quy Water, the plate was seated onto the careful ly prepared surface of the backfil l using a thin layer of plaster of Paris. A l though this method worked quite well , it was rather t ime consuming and as a result a th in layer of f ine sand was used at Stone Hill to seat the plate.

Loads up to 60 kN were applied to the plate in increments of 10 kN using a hydraul ic cyl inder and hand pump. The load was measured using a calibrated pressure gauge, and reacted by the dead-

Neg. no. R485/86/4

Plate 5 Layou t o f a t yp i ca l p la te l o a d i n g tes t

weight of a suitable piece of construction plant. The deflection of the plate was measured using two dial gauges mounted on a beam, the ends of which were suff ic ient ly far away from the loaded area to be unaffected by the loading. A typical test arrangement is shown in Plate 5.

A t each location, three loading cycles were performed wi th measurements being taken during loading and unloading. A t each load, deflection measurements were taken until the deflection was sensibly constant - - in most cases this took 3 to 4 minutes. Values of the constrained soil modulus (M*) were calculated for each load cycle using the secant modulus between plate pressures of 150 and 350 kN /m 2 and assuming a value of Poisson's ratio of 0.3: this method is consistent with that proposed in a DTp design method currently being developed for long span structures.

At Quy Water, the average value of M* was 180 MN/m 2 for the first load cycle tests and 420 MN/m 2 for second and subsequent load cycles. At Stone Hill, the first load cycles gave M * = 110 MN/m 2 and subsequent load cycles gave M* =250 MN/m 2. In general, the values of M* obtained from first load cycle tests would be the ones used in design and back-analysis. However, the results from subsequent load cycles give an indication of how well the plate was seated onto the backfill. Previous experience (Temporal et al 1985) suggests that if the surface of the fill is prepared carefully, the value of M* for subsequent load cycles will be approximately double the value obtained from first load cycle tests. If the surface of the fill is disturbed during preparation, the first load cycle will yield artifically low values of M* and the increase for subsequent load cycles will be considerably greater than 2.

Load position I I I I I I I I 7 6 5 4 3 2 1 0

E

5

,$ "13

O E3

Measuring position

I I I

o l i i

i2 / 1 \ %

I IV

i

I I I

I I I I I v i i

Load at :: 6 :

: 7 :/ i

//3 / /

/ t °

1.0

Fig. 7 Q u y W a t e r : d e f l e c t i o n o f m e a s u r i n g p o i n t s I to V I I for a 455kN load at pos i t ions 0 to 7

10

5 RESULTS Previous load tests on a 4 m span culvert (Temporal et al 1985) confirmed that deflections, ring compression strains and bending strains increase with increasing axle loads. In addition, the largest effects usually occur close to the crown of the structure when the load is in the vicinity of the crown. Preliminary analysis of the data from Quy Water and Stone Hill produced similar results.

5.1 QUY WATER The distribution of deflections around the crown of the culvert is shown in Figure 7 for the maximum axle load of 455 kN. The maximum deflections recorded were approximately 1 ram, which was.

Load posit ion

I I I I I 7 6 5 4 3

considerably less than had been anticipated and only slightly greater than the resolution of the measuring system (0.5 mm). As the deflections were very small, the variation with increasing load shows considerable scatter.

The distribution of ring compression strains for the maximum axle load of 455 kN is shown in Figure 8. The maximum strains recorded were about 25 microstrain* and the distribution showed some asymmetry. When the load was to the right of the crown position, the maximum strain occurred to the

* For steels of the type used in culvert plates, the tensile yield stress is typically in the range 220-300 N / m m 2. Assuming linear elasticity and a Youngs modulus of 205 kN /mm 2, the strain at yield will be in the range 1070-1460 microstrain.

I I I 2 1 0

0 ¢0

o --2 b E v

--4 .c_ ¢O

t- --6 o

O3 t~ E 8 --10

n- --12

--14

--16

.Co --18

O3 ~ - - 2 0 E 0

- 2 2

- - 2 4

- 2 6

Measuring posit ion

I l l

I I I I

I IV

------t------_.._

I I I I vii, I I I I I I

/

Load at

- - 7

°°°°°°°

°°°°°°°° 5 °.°° ° / ° ° s

r \ \ ...................... . . / / \\, ' \ . .~. ~ j . . / _ ~ .

/ / \.\ . / i \ / I i / , , " 2

• ,, t f %% • ~1

-,,, \,,. ,, / t _-'.>....-" 4 , , • \ / ' #

\ \ \v ' i x

\ /

Fig. 8 Q u y Water: d is t r ibu t ion of r ing compress ion strains fo r a 4 5 5 k N load at p o s i t i o n s 0 to 7

11

- 2

E

m L

~ - - 4 0

b E .~_ - 6

.~ - 8

e~

E --10 8

r r

- - 1 2

- - 1 4

- - 1 6

- - 1 8

--20

--22

E O

--24

- - 2 6

100

% •

Load (kN) on G L

200 300 400 500 I I I I

Measuring position

IV

\

• " VI

Fig.9 Q u y Water: ring compression strain against increasing load applied direct ly above the crown

left of the crown and vice versa. Figure 9 shows that the relations between ring compression strain and axle load are approximately linear.

The distribution of bending strains for the maximum axle load of 455 kN is shown in Figure 10: the max imum strains recorded were about 10 microstrain. As expected, sagging bending strains were recorded under the axle load with hogging strains being recorded further away from the point of application of the load. Figure 11 shows that the bending strains general ly increased with increasing load. As with the recorded deflections, the ring compression and bending strains were very small and as a result some of the scatter in the data may be due to errors in the measuring system used.

In order to simpl i fy the data obtained, a series of graphs has been derived which show maximum

values of deflection, ring compression and bending strain recorded for each load increment. These graphs form upper bounds to the experimental data and are shown in Figure 12. They therefore represent worst case loading effects for worst case loads and are analogous to what has to be considered in design. From Figure 12, it can be seen that the maximum combined compressive strain, obtained by summing the maximum values of ring compression and bending strain, would be 35 microstrain at the extremity of the section. This corresponds to a maximum compressive stress of about 7 N /mm 2 or approximately 3 per cent of the minimum tensile yield strength of the steel used. As the ring compression strains were always greater than the bending strains, none of the section would be in tension.

12

10

m m 8

i 4 -~ 2

E "~ 0

~ -2

--4

- 6

.~, - 8

o

--10

Load position

I I I I I 4 3 2 1 0

Measuring position

i v

f i I I I v i i I I I I I I I ' , I I I I

, I

sSS~%

.......... J~-"~" - ~ , , "" 4

' 0

Fig. 10 Quy Water: d is t r ibu t ion o f bending strain fo r a 4 5 5 k N load at pos i t i ons 0 to 7

Load (kN)

0 1 O0 200 300 400 500

10

1 I I I I '

Measuring position

. . . . / ° / I v

4 - / °

" E j ,,

" . . . % % --6 -- • II %°.°

"wJ

- 8 - o I

--10

Fig.11 Quy Water: bending strain against increasing load app l ied d i rec t l y above the crown

13

E

~O

O £3

A

E

¢o

J ~

¢o

o~ L 0 -

E

n"

0.5

1.0 -

10

--2

--4

--6

--8

--10

--12

--14

--16

--18

--20

--22

--24

--26

Load (kN)

100 200 300 400 500 = i ~ i I

Sagging bending strain

Hogging bending strain

Deflection

Ring compression • strain

F ig .12 Q u y Water : upper b o u n d graph o f m a x i m u m strain and de f l ec t i on at any po in t for increasing load a t a n y p o i n t

14

Load position

I I G D

A

E v

8

no

c o C3

V

0 5

I 0 5

15

2 5

3 5

4 5

Measuring position I

iV ~

- .... . . - - " '~. .~--__a"~. , . / . / / ......... : .-~_~ t • - . . # F

t " "" ' - G | H | s # •

,, f , / I t • ~ , . / /

' / " / I ., l I ( D c

.." t ~ I .." to i I """~ / !' , • • "'l ~ !

, / ' 1 i - - t

i ' X" "I l

.. /,; / /~ - I I

• t I t° I

I i \ L , ; -\ I ' ",, , •

• i i .1", i . I / , / I

\ " ~ l • t /

# - \ ' , / "/ / \ ,;/, ," ." I \ r

• ~ • I I a \ / i , v

\ / ~ , • I I

I I )'

F i g 13 Stone Hil l : de f lec t ion o f measuring points I I t o V I f o r a 4 5 5 k N load at pos i t ions A t o H

15

--0.5 A "o

E 8

E3

o £3

T

Load (kN)

100 200 300 400 500

I I r I I

ssSS~%, Measuring posi t ion

S S ~ =. . . - I I # , _ _ = t

I \ \ \ ~ v " ' ~ ' - v ,

0.5 t " t ~ ~ % _ _ _ _ , ~ %

\ \ "',

'- \Skk// \ \ ""- \ ",,

,o ,,, \ " - • %

\ , \ ",,,, 111

~ - \ \ \ \

3 m

3.5 --

4 -

4.5

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%

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1

\ I

\ I \

V

IV

Fig.14 Stone Hill: deflection against increasing load applied directly above the crown

16

Load position I I I I I I

C I

A

A - 1 0

=: F-

10

A e -

20 O _~ E v

30

t~

E oo 40

Q:

50

¢z 60 E O

O

T

70

80

Measuring position

I I I I

, I

I IV

I v i i I

i I

Load at

/ ... / " / - ........ / - " /

° . , " w S ....... ... / / . . . . . . . . . . . . . . j - / /°

!'- / l"x/"\ ',, ! I/~ / ',. ; ~ / \ ~ ',. i Y

/ ",, / / i \ \ ",. ; ,,1 - i ",d I," \ \ "d I " / ?',,, !;,; \,',, ,/Vl ' \ , " , I / \~ I l

", ! ;':' " X I # I \ , I I

! # - - " ~ /

V

\

X I X I

X I X I

\ I X l

Fig.15 Stone Hil l : d is t r ibut ion o f ring compression strain fo r a 455kN load at posit ions A to H

17

100 Load (kN)

200 300 400 500 I I I I

A

O b

.c_

P Q. E 8 E

8

~L E O

C)

¥

--10

--20

--30

--40

--50

--60

--70

--80

~ °° o Oo

~ ° ° % o °

' ~ ' ~ % - , o, I , - - I ' ' ' " ' ° % % . i °

% %°

~ . . ~ , . "'-.... ~ . X ~ N Measuring

%~, X ~ " , position \ \ \ ' ~ "..

,,.\ \ , "..v,,

,,.,, X,\, v

"NN "",

\ 'k,

%'~ Ill

|

vI

Fig.16 Stone Hill: compression strain against increasing load applied direct ly above the crown

5.2 S T O N E HILL The distribution of deflection for the maximum axle load of 455 kN is shown in Figure 13. The maximum deflection recorded was 4.25 mm and in general the deflections were largest at the measuring position directly under the loading axle. Figure 14 shows that deflection generally increased with increasing axle load,

The distribution of ring compression strains for the maximum axle load is shown in Figure 15. The maximum ring compression recorded was approximately 80 microstrain but there are no clear trends in the distribution of ring compression. Figure

16 shows that the ring compression strains increased linearly with increasing axle load.

The distribution of bending strains for the maximum axle load is shown in Figure 17. The maximum bending strains recorded were 170 microstrain in the sagging direction and 100 microstrain in the hogging direction. In general, the largest sagging bending strains were recorded directly beneath the axle with hogging strains occurring to each side. Figure 18 shows that the bending strains generally increased in an approximately linear manner with increasing axle loads.

18

Load position

F E D C B A I I I I I I

170 1 1 i ~ I I

II 160 Measuring | | position

150

140 r I I | VII

130L h E t~'.D : !

"L / \ ! \ 1 ~ 8 120

11oL i \ ! \i ~ ;, ,oo t i / \

6O A E "~ 50 8

E 40 .E m

30

g~ 2o

-10

-20

-30

-40

- 5O

g "~ - 6 0 o -r

-70

-80

- 9 0

'1

90 ~ ~e

!\ 'I', : / II ~ / t 8O

l / 1 t ~o I ! \ , , ,, , ~," ,

/s t I /\, / ! , / / \ ' ,

/ i IX , ! ] , ; ; t - ' t , , \ . ! ' , / < , , , ,

I i

I 10 ,., ~ H l

o ¢ I t ,

Ii I ; i i ;

' I I I " I ,, /

I~ " , i l ' v \ / r', ',, \! ' , / / ,' , ,,, / , / , , , , , , , . ,

I I , / ', ! v / , , , l I \ I

, I : ' I 1 ' , 1 ',, , , ,1' " " ! /

V '

-100

Load at

F i g . 1 7 S t o n e H i l l : distr ibut ion of bending strain for a 455kN load at posit ions A to H

19

160

150

140

A 13o

120

110

100

90

80

c ca

E ._c ca L

== ~5

70

60

50

40

30

20

100 200

--3O

--40

o I

- s o

--60

--70

~ 0

--90

I

/ /

/ /

/

Load (kN)

300 I !

400 500

I /IV I

• Measuring position

/ I

/ I

/ ,/

/ /

/ /

/

- /

- / lo i J ' 0 , . - , - ~ V I I

~ , III

- - 2 0 - -

%,. •

• %% - ',~,,

\ \

II %%VI t

Fig.18 Stone Hil l: bending strain against increasing load applied direct ly above crown

20

0 D

.1 "

E . ~ . .2 i

.3

O . E . 4 E

,~ .5 c-

B

.6

Load position

H G F E D C B A I

4 ~ / I I I I Culvert I ~ centreline <<~, j# "" "~ "~

0

.8

¢o

g

8 -3

h=

,..... \

- "% "Ikl ~,,~..'" S S ". -"~ Rinn compreSslon /s,-'1~..__

". "%, . . . . . . . . . . I , ' -t #=6

- 4

- 5

- 6

° ' .

- " ' . . , . . . . ' " %----'~r~zon"~a t (~el 0~''

i °o e°'e ° i °°°°"°" I

I

Fig.19 Stone Hill: bending and ring compression strain at the base of the arch and horizontal deformation for a 455kN load at positions A to H :

At Stone Hill, additional measurements of deflection and strains were made near the base of the arch just above the foundation slab, see Figure 6. The deflections and strains recorded for an axle load of 455 kN are shown in Figure 19. The maximum recorded change in the horizontal span of the culvert was just over 0.5 mm and the maximum ring compression and bending strains were approximately 6 and 4 microstrain respectively. These data show that the horizontal deflection is a factor of about 10 smaller than the maximum deflection measured at the crown whilst the ring compression and bending strains at the base of the arch are 1/12 and 1/40 of the maximum values measured at the crown respectively.

The data obtained at Stone Hill have been simplified in a similar manner to that used for Quy Water by deriving upper bound graphs of deflection, ring compression and bending strains, which are shown in Figure 20. By combining together the maximum recorded values of ring compression and bending strains, the maximum possible compressive and tensile strains in the extremities of the section can be estimated. The values obtained are 250 microstrain in compression and 90 microstrain in tension, which

correspond to compressive and tensile stresses of about 50 and 18 N / m m 2. These represent approximately 23 and 8 per cent respectively of the minimum yield strength of the steel used.

6 DISCUSSION OF RESULTS

In recent years, a number of field studies of long span flexible culverts has been conducted. Several papers were contained in a recent Transportation Research Record (Transportation Research Board 1985) and a review of earlier work was performed by Selig et al (1979). These studies have included closed invert structures and arches on concrete foundations. Tests have been conducted at both high and low depths of cover and some of the structures studied have incorporated special features such as circumferential crown stiffening beams and load relieving slabs.

Prior to the loading tests at Quy Water and Stone Hill, predictions were made of the deflections likely to be obtained under live loading with an axle weight of about 450 kN. Estimates based on earlier tests on

21

0

200 I

1 6 0

Load (kN)

100 200 300 400 500

I I I I ' T

120

Sagging bending strain

80

A

E E

=0

" 0

0 E3

0 D

1 - -

2 -

3 -

4 - -

5 -

J E

o .R 40 -- E

.S

~ o e-i

7 °

E - -40 - o ° Ring compression strain

r r

- -80

- -120

- -160

--200

Hogging bending strain

D e f l / e c t i o n ~

Fig.20 Stone Hill: upper bound graph of maximum strain and deflection at any point for increasing load at any point

22

a 4 m span culvert (Temporal et al, 1985) suggested that crown deflections of about 5 and 10 mm would occur at Quy Water and Stone Hill respectively. An assessment of previous tests by Selig and Calabrese (1975), Kay and Flint (1982) and Bakht (1985) suggested that the deflections would be somewhat smaller than these values, but the situation was complicated by the fact that some of these tests had been performed on culverts with special features which increased the overall stiffness of the soi l-- culvert system. A further complication was that the magnitude and configuration of the live loads used were different to those used in the present work.

The maximum deflection measured at Quy Water was about 1 mm for an axle load of 455 kN with the maximum ring compression and bending strains of about 25 and 10 microstrain respectively. At Stone Hill, the maximum deflection was 4.25 mm and the maximum ring compression and bending strains were 80 and 170 microstrain respectively.

The differences between the anticipated and actual deflections may be due, at least in part, to two main factors. The first is that at Quy Water, where the grading of the backfill was quite coarse, the constrained soil modulus was about twice the value normally anticipated for a well graded and well compacted granular fill. The second factor is that the estimated deflections did not take into account the stiffening effect of the pavement. This was particularly large at Quy Water where the pavement consisted of 210 mm of lean mix concrete overlaid by 160 mm of bituminous-bound material. To give an indication of the stiffening effect of the pavement at Quy Water, a plate loading test was performed on the road surface using the same method as that used to determine the constrained modulus of the backfill. This gave a constrained modulus in excess of 600 MN/m 2 which is over three times greater than the modulus obtained for the backfill material. Although this test is not particularly useful in terms of pavement design, it does give an indication of the large contribution made to the overall stiffness of the system by the pavement. At Stone Hill, where the pavement was of a lighter construction, the effect of the pavement on deflections would have been somewhat smaller. The effect of pavement stiffness on the performance of corrugated steel culverts will be the subject of future work.

The relatively low values of ring compression and bending strains recorded at both sites are reasonably consistent with the low deflections recorded. The data obtained in the previous loading tests conducted at Newport (Temporal et al, 1985) showed that when the deflection of the crown was about 1 ram, the ring compression and bending strains were between 10 and 50 microstrain. When the deflection of the crown was about 5 mm, the ring compression and bending strains had increased to between 100 and 150 microstrain.

The variations of deflection and strain with increasing axle loads at both sites were in general linear and the residual values recorded at the end of each loading test were very small, indicating that superposition of the strain and deflection data is justified. This is similar to the behaviour found for low crown pressures at Newport, but at larger deflections and strains the Newport data increased exponentially wi th increasing axle loads.

7 IMPLICATIONS FOR DESIGN

The existing design method for corrugated steel buried structures (Department of Transport 1982) covers culverts having spans of up to about 7 m. Above this size, the buckling criterion used in the design becomes excessively conservative. This is due in part to the fact that the buckling criterion used (Meyerhof and Baikie, 1963) was developed from small scale model tests and partly because the maximum value of constrained soil modulus (M*) allowed in the design is 33 M N / m 2. At Quy Water and Stone Hill, the average values of M* from first load cycle plate bearing tests were 180 and 110 MN/m 2 respectively. Even when these values are used in the design method, back-analysis yields factors of safety against buckling of 1.8 for Quy Water and 1.5 for Stone Hill. Both these values are lower than a lumped factor of safety of 1.96, the value obtained by aggregating all the partial factors of safety in the design method. In view of the small deflections and strains measured at both sites, it would seem very unlikely that the factor of safety due to buckling is as low as the values given above. Unfortunately, as neither structure could be tested to failure, it is impossible to say with any certainty what the factor of safety was at the maximum axle load used in the test.

In order to al low structures with spans between 7 and 13 m to be used in DTp schemes, considerable effort has been made to develop a design method for such structures. A review of existing design methods used in other countries was undertaken, with particular emphasis being placed on the Ontario Highway Bridge Design Code for Soil-Steel Structures (Ministry of Transportation and Communications 1983) and the AASHTO method, a review of which is given by Selig (1985). Unfortunately, the former method only covers structures up to 8 m in span and the latter does not contain a buckling criterion for long span structures although such a check is included for smaller structures.

In 1970, KI6ppel and Glock published the results of an experimental and theoretical study of the load carrying capacity of corrugated steel culverts. This report contained a design method which was subsequently extended to cover structures with spans up to 13 m by Glock (1973). The method models the soil-culvert system in the fol lowing ways:

23

(i) as an elastically supported two hinge upper arch wi th a lower section consisting of a bend resistant partial ly embedded polygonal beam: for this configuration the failure mode is a single wave buckle.

(ii) as an elastically supported three hinge upper arch with a lower section consisting of an elastically f ixed sprocket chain: for this configuration the failure mode is a mult i -wave buckle.

In addition to the buckling criteria, Glock's method also checks for yielding of the culvert wall, for adequate strength of the longitudinal bolted seams and for soil failure under live loading near the crown of the structure. The elastic modulus of the backfill material is taken into account by considering the relative stiffness of the corrugated steel section and the backfill. The design method has been used successfully on a number of long span culvert installations in Europe and has been modified and extended for use under UK conditions by Stirling Maynard and Partners (1979, 1984), who have also used it to analyse the loading test to failure by Temporal et al (1985). The method predicted that soil failure would occur at a depth of cover of 0.47 m under live loading, whereas the culvert at Newport actually failed at 0.36 m cover. A draft Department of Transport Departmental Standard based on Glock's design method is currently being prepared.

In order to give further indications of the applicabil ity of Glock's method, it has been used to back-analyse the results obtained from the loading tests at Quy Water and Stone Hill. The measured values of constrained soil modulus (M*) of 180 M N / m 2 at Quy Water and 110 M N / m 2 at Stone Hill have been used throughout this back-analysis.

7.1 C R O W N DEFLECTION Values of maximum crown deflection have been obtained using the method given in Glock (1973) and modified by Stirling Maynard and Partners (1984). The deflections have been calculated for the axle geometry used in the loading tests with a total load of 455 kN. The deflections due to dead loading, which are relatively small, have been subtracted from the calculated deflections to give an estimate of the deflection due to live load only. The values obtained for maximum crown deflection were 0.7 mm for Quy Water and 5.0 mm for Stone Hill. These values are extremely close to the measured values of 1.00 mm and 4.25 mm respectively.

Crown deflection is the only aspect of the back- analysis where a direct comparison can be made between actual and predicted performance of the culverts. As the method by which deflection is calculated is critically dependent on the results of the buckling analysis, this suggests--by inference-- that the factors of safety against buckling wil l also be realistic for both the structures tested.

7.2 FACTORS OF SAFETY Factors of safety against wall yielding, seam failure, buckling and soil failure have been calculated using the method given in the draft DTp Departmental Standard for long span corrugated steel culverts. As mentioned in Section 7, this method is based on the work of Glock (1973) as subsequently modified by Stirling Maynard and Partners (1979, 1984). For both culverts, the back-analyis has been performed for the live load configuration used in the tests with a total load of 455 kN. This has been combined with the dead load corresponding to the actual depths of cover to the crown of the culverts. The factors of safety derived from the back-analysis are given below with the minimum values required by the design method in parentheses.

(i) Quy Water

Minimum factor of safety against wall yielding = 3.4 (2.0) Minimum factor of safety against seam failure = 3.4 (2.0) Minimum factor of safety against buckling = 8.5 (2.0) Minimum factor of safety against soil failure = 4.1 (2.0)

(ii) Stone Hill

Minimum factor of safety against wall yielding = 2.7 (2.0) Minimum factor of safety against seam failure = 2.0 (2.0) Minimum factor of safety against buckling = 3.1 (2.0) Minimum factor of safety against soil failure =0.75 (2.0)

All the factors of safety obtained for the structures at Quy Water and Stone Hill are adequate, with the exception of the value obtained for soil failure at Stone Hill. However, the draft DTp design method which makes no allowance for the stiffness of the pavement layers, also assumes an angle of internal friction (~p) of 35 degrees: for the type of backfill used and the in situ density obtained (see Table 1), a more appropriate value of + would be approximately 45 degrees. When such a value is used the factor of safety against soil failure rises to an acceptable value of about 2.5. The factor of safety also rises dramatically with increasing depth of cover to the crown of the structure. At Stone Hill, the depth of cover was 0.95 m, but a lower limit of 1.5 m is likely to be imposed in the DTp Standard currently in preparation. With this restriction, it is unlikely that soil failure will be a problem, because the factor of safety would rise to 2.3 with a value of + of 35 degrees.

The extremely good agreement between the actual and predicted crown deflections (see Section 7.1) has already indicated that the factors of safety against buckling are realistic for both structures. To

24

some extent this is borne out by the extremely small strains measured at Quy Water where the calculated safety factor against buckling was 8.5 and by the somewhat larger strains measured at Stone Hill where the calculated safety factor was 3.1.

The factors of safety for wall yielding and seam strength calculated by the draft DTp design method are all reasonably similar to the values obtained from simple ring compression models (White and Layer, 1960). Considerable reliance has been placed on such methods over several decades (Selig, 1985) and they have worked well in most situations. Unfortunately, it is difficult to relate the ring compression and bending strains measured in the tests to the factors of safety obtained from the design method without testing the structures to failure. However, the maximum possible live load stresses, calculated from the recorded strains, were 7 N/mm 2 at Quy Water and 50 N/mm 2 at Stone Hill (see Sections 5.1 and 5.2). These can be compared with the maximum stresses of 35 N/mm 2 and 67 N/ram 2 obtained for Quy Water and Stone Hill respectively using the wall yield criteria in the design method with the live load used in the tests. This suggests that the design method is conservative.

7.3 CLOSED INVERT AND ARCH STRUCTU RES

The design method developed by Glock (1973) does not distinguish between closed invert structures like the one at Quy Water and arch structures on concrete foundations like the one at Stone Hill. Measurements of ring compression and bending strain near the base of the arch at Stone Hill showed that these were considerably smaller than the corresponding effects near the crown of the structure. This suggests that load concentration effects in the base of the arch near the connection with a rigid foundation slab are unlikely to occur. Similar behaviour for arches has been observed by Lefebvre et al (1976), Selig et al (1979) and Kay and Flint (1982). Experiments on closed invert structures have also shown that the measured strains in the lower sections of the structure are smaller than those occurring near the crown (Beal 1982; Temporal et al 1985). For both closed invert structures and arches, this effect can be explained by considering the shedding of load from the culvert wall into the backfill by interface friction. The fact that no load concentration effects were observed near the base of the arch at Stone Hill suggests that closed invert and arch structures behave in a similar manner under live load conditions.

8 CONCLUSIONS

Load tests were conducted at Quy Water on a 9.83 m span horizontal elliptical culvert with 1.90 m of cover over the crown and at Stone Hill on a

7.47 m span high profile arch with 0.95 m of cover. In both cases the load was applied using a single axle trailer with a maximum axle load of 455 kN.

The maximum deflections observed during the loading tests were 1 mm for Quy Water and 4.25 mm for Stone Hill. These values are in excellent agreement with the values given by a design method based on the work of Glock (1973) which predicted deflections of 0.7 mm and 5.0 mm respectively. As the design method calculates deflections from a buckling analysis, this suggests that the predicted factors of safety against buckling of 8.5 for Quy Water and 3.1 for Stone Hill are realistic.

The maximum values of bending strain measured during load testing were approximately 10 microstrain at Quy Water and 170 microstrain at Stone Hill. These values are reasonably consistent with the factors of safety against buckling obtained from the back-analysis of the culverts.

The maximum values of ring compression strain measured during the load tests were 25 microstrain at Quy Water and 80 microstrain at Stone Hill. These values appear to be consistent with the factors of safety against wall yielding and seam failure obtained using the draft DTp design method for long span culverts. The measured strains are also consistent with values obtained using simple ring compression theory (White and Layer, 1960).

Measurements taken close to the base of the arch at Stone Hill show no evidence of load concentration effects near the connection with the rigid foundation slab. This suggests that the assumption made by Glock (1973) to treat arches and closed invert structures in the same manner is justified for live load conditions.

9 A C K N O W L E D G E M E N T S

The authors would like to thank Mr A J Hudson of Cambridgeshire County Council and Mr J Bent- Marshall of Gloucestershire County Council for allowing these tests to be performed at Quy Water and Stone Hill respectively. They would also like to thank the staff of the two county councils for their help and cooperation during the load tests. Some of the soil testing and plate bearing tests were conducted by Northamptonshire County Council and the authors would like to thank Mr S Biczysko and his staff for their assistance.

The authors are indebted to Mr B E F Hunnibell of Asset International Ltd for his help in setting up these experiments. They are also particularly grateful to Mr P Beveridge of Stirling Maynard and Partners for the considerable effort he has put into helping with the interpretation of the data in the context of the design methods available.

25

The work described in this Report forms part of the research programme of the Ground Engineering Division (Division Head: Dr M P O'Reilly) of the Structures Group of TRRL. The Laboratory research team consisted at various times of G H Alderman, A R Eusden, P E Johnson, R A Snowdon, J Temporal and G R A Watts.

10 REFERENCES

BAKHT B (1985). Live load response of a soil-steel structure with a relieving slab. Transportation Research Record 1008 pp 1-7. Transportation Research Board, Washington.

BEAL D B (1982). Field tests of long-span aluminium culvert. Journal o f the Geotechnical Engineering Division, Proc ASCE, Vol 108 No GT6 pp 873-889.

BRITISH STANDARDS INSTITUTION (1954). Specification for steel girder bridges: Part 3A. British Standard BS 153 British Standards Institution, London.

BRITISH STANDARDS INSTITUTION (1975). Methods of test for soils for civil engineering purposes. British Standard BS 1377. British Standards Institution, London.

BRITISH STANDARDS INSTITUTION (1978). Steel, concrete and composite bridges: Part 2. Specification for loads. British Standard BS 5400. British Standards Institution, London.

BRITISH STANDARDS INSTITUTION (1981). Code of practice for site investigations. British Standard BS 5930. British Standards Institution, London.

DEPARTMENT OF TRANSPORT (1982). Corrugated steel buried structures. Departmental Standard BD 12/82. Department of Transport, London.

GLOCK D (1973). Superspan. Unpublished report to Armco, Darmstadt.

KAY J N and FLINT R C L (1982). Heavy-vehicle loading of arch structures of corrugated metal and soil. Transportation Research Record 878 pp 34-36. Transportation Research Board, Washington.

KL(~PPEL K and GLOCK D (1970). Theoretische und experimentelle Untersuchungen zu den Traglastproblemen biegeweicher, in die Erde eingebetteter Rohre. Veroffentlichung des Institutes fur Statik und Stahlbau der Technischen Hochschule Darmstadt, Heft 10.

LEFEBVRE G, LALIBERTE M, LEFEBVRE L M, LAFLEUR J and FISHER C L (1976). Measurement of soil arching above a large diameter flexible culvert. Can Geotech J Vol 13 pp 58-71.

MEYERHOF G G and BAIKIE L D (1963). Strength of steel culvert sheets bearing against compacted sand backfill. Highway Research Record 30 pp 1-19. National Research Council, Washington.

MINISTRY OF TRANSPORTATION AND COMMUNICATIONS (1983). Ontario highway bridge design code. Section 12 soil-steel structures. Downsview, Ontario.

SELIG E T and CALABRESE S J (1975). Performance of a large corrugated steel culvert. Transportation Research Record 548 pp 62-76. Transportation Research Board, Washington.

SELIG E T, LOCKHART C W and LAUTENSLEGER R W (1979). Measured performance of Newtown Creek culvert. Journal of the Geotechnical Engineering Division, Proc ASCE, Vol 105 No GT9 pp 1067-1087.

SELIG E T (1985). Review of specifications for buried corrugated metal conduit installations. Transportation Research Record 1008 pp 15-21. Transportation Research Board, Washington.

STIRLING MAYNARD and PARTNERS (1979). The design of Armco multi-plate superspan structures. Unpublished report to Armco Ltd.

STIRLING MAYNARD and PARTNERS (1984). The design of Armco multi-plate superspan structures with worked examples. Unpublished report to Armco Ltd.

TEMPORAL J, BARRATT D A and HUNNIBELL B E F (1985). Loading tests on an Armco pipe arch culvert. Department of Transport, TRRL Report RR32. Transport and Road Research Laboratory, Crowthorne.

TRANSPORTATION RESEARCH BOARD (1985). Culverts: analysis of soil-culvert interaction and design. Transportation Research Record 1008. Transportation Research Board, Washington.

WHITE H L and LAYER J P (1960). The corrugated metal conduit as a compression ring. Highway Research Board Vol 39 pp 389-397.

Printed in the United Kingdom for Her Majesty's Stationery Office Dd8222700 5/88 G426 10170

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