s ■
UNITED NATIONS ECONOMIC COMMISSION FOR AFRICA
Conference on Highway Engineering in Africa-Addis Ababa April 1974
organised by
the Economic Commission for Africa with the co-operation of the British and French Governments
PAPER E
THE ROLE AND ORGANISATION OF ROAD LABORATORIES
by
J. P. SERFASS
IngSnieur Civil des Mines Chef de la Division Technique du Service Outre-Mer et Etranger Centre Experimental d'Etudes et de Recherches du Batiment et des Travaux Publics (C.E.B.T.P.)
12, Rue Brandon
7RO15 - PARIS - (France)
This conference paper has been produced through the co-operation of the Overseas Unit of the Transport and Road Research Laboratory, Department of the Environment, the Overseas Development Administration of the Foreign and Commonwealth Office, of Great Britain and Northern Ireland, and the Secretariat d'Etat aux Affairs Etrangeres
Contents 1. , Introduction.
1.1 Scope of activities.
1-2 Nature of the work.
2. The present: required resources and organisation.
2-1 Feasibility studies.
2.1.1 Preliminary phase.
2.1.2 Second phase (A.P.S.).
2.2 Project studies (A.P.D.).
2.3 Description of the resources and organisation.
2.4 Place of geotechnical studies.
2.4.1 Relation between the geotechnical study and the economic study.
2.4.2 Relation between the geotechnical study and the geometric study.
2.4.3 Relation between the geotechnical study and the structures study
2.5 Costs of geotechnical studies for roads.
Control of construction .
3.1 The different types of control.
3-1.1 Control of conformity - control of quality - automatic control.
3*1*2 Control before, during and after construction.
3-2 Role and organisation of a control laboratory.
3.2.1 Nature of the control:importance and position of the laboratory.
3.2.2 Organisation of classical control.
3-2.3 Observations on some important points. Improvement of methods of control.
3.2.4 An essential task: preparation of records of the road*
3-3 Costs of geotechnical control.
4. Observation of the performance of roads and structures.
4.1 Inspection of roads.
B; * ' ' '
4.1.1 Equipment and functioning of an inspection team.
4.1.2 The CEPTB curviameter.
4.2 Inspection of bridges.
5. Studies of general interest.
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6. Adaptation of specifications to local conditions. 15 6.1 Characteristics peculiar to tropical countries. 15
6-2 Participation of the laboratory. 15
6-2.1 Adaptation of standards. 15
6.2-2 Adaptation of operating methods of certain tests. Creation of 16
new, better-adapted tests.
6.3 Need for inter-state co-operation 1°
7. Plan of organisation. '
7.1 Internal organisation. '<
7-2 External relations. *'
8. The future: Principal problems - Current or proposed research. 17
8.1 Road problems in developed countries. IU
8.2 Problems peculiar to tropical countries. iftIO
8.2.1 The adaptation of specifications. lo
8-2.2 Problems related to terrain evaluation and earthworks. 19 8-2.2.1 Research into the mineralogy of clays in tropical soils- 19
8.2.2-2 Research on expansive clays. 19
8.2.2.3 Research on the use of pedological data.
8.2.2.4 Research on erosion and methods of prevention.
8.2.2.5 Establishment of data banks - use of the information. 19 8.2.3 Problems related to construction and the performance of roadmakingi9
materials.
8.2.3-1 General problem of aggregates, sands and fillers. 19
8.2.3.2 Sub-bases and bases. 19
8.2.3.3 Bituminous surfacings 2n
8.2.3.4 Research on difficult or non-traditional materials. 21 8-2.4 Problems related to the general performance of roads 22 8.2.4.1 Analysis of the performance of roads carrying low 22
volumes of traffic.
8.2-4.2 Research on reinforced roads. 22
8.2.5 Problems related to the finished road. 22
Appendix 1. Operations of the laboratory driving feasibility studies.
Appendix 2. List of geotechnical problems at the project study stage.
Page 23 25
THE ROLE AND ORGANISATION OF ROAD LABORATORIES
1. INTRODUCTION
By way of introduction, we wish to define the term 'laboratory1. At first sight it appears very restricted and suggests simply a building from which the results of tests emerge. The description of the scope of activities and of the amount of money spent on roads will show the considerable part which the laboratory plays in the development and maintenance of the infrastructure of a country. In passing it should be mentioned that it is rare for a laboratory to be concerned exclusively with roads. In most cases, its activities are also applied to civil and building engineering.
1-1 Scope of activities
The operations of a road laboratory are multiple:
(a) Special studies for new roads or improvement or strengthening of existing roads. For new roads, geotechnical studies are necessary at all stages, from the feasibility study to the construction of the project.
(b) Control of construction, which must not only be confined to ensuring compliance with the specification but must also be directed to obtaining the best possible quality. These controls lead to the establishment of road standards.
(c) Observation of the performance of roads and road structures, leading t& a policy of maintenance and strengthening.
(d) Studies of general interest, eg. an inventory and mapping of soils and suitable roadmaking materials, and collection and use of data on materials and methods in a particular region.
(e) Preparation of specifications adapted according to the materials available, the climate and the traffic for different regions.
(f) Research into the development of new materials and methods.
(g) The provision of documentation and technical information, and of technical
training.
1.2 Nature of the work
Experimental activities:
Investigations, surveys, boreholes and in-situ tests
Laboratory tests
Full-scale tests
Observation of the performance of roads and structures
Theoretical work:
Participation in the conception of the project:
Choice of road line
Pavement design (including strengthening).
Size of culverts and bridges (ie soil mechanics and hydrology foundations of bridges, drainage, slope stability, etc).
Advice on the survey and construction work Helping to draw up satisfactory specifications Helping to develop new techniques
Participation in the road policy of the country Technical training (courses, conferences, etc).
The accomplishment of all these tasks requires a number of disciplines:
Geology, geomorphology, hydrology, pedology, photo interpretation Geotechniques of roads
Soil mechanics and hydrology Road engineering
Strength of materials
Physical mechanical properties of materials In-situ and laboratory testing.
In the remainder of this paper we have avoided giving much detail on laboratory tests and equipment since these are of interest only to specialists. Instead it is intended to describe in a general way the different activities of a laboratory and to show the importance of the benefits they provide, directly or indirectly, to the
economy of the country.
There is some overlap between the subjects in Theme D and those in this paper and this has led to some repetition, but it was thought that this would be useful in some
cases.
2. THE PRESENT: REQUIRED RESOURCES AND ORGANISATION
The problems put to a road laboratory determine the resources and organisation require(
For each of the listed tasks, we will show the contribution that a laboratory can make and give indications of the necessary resources. We will finish by drawing up a scheim for the organisation of a laboratory (both internal organisation and external relation:
The table shown below indicates, for the different phases, the approximate relation between the international method and the French method of carrying out road
studies
International method
Feasibility study —
Preliminary phase
Second phase
Project study
French method
Preliminary study Cor general appraisal)
Brief pre-project study (A.P.S.)
Detailed pre-project study (A.P.D.)
construction study (possibly for certain difficult points)
2.1 Feasibility studies
The aim is to evaluate the cost-benefit of the project to an accuracy oj 20 per cent. From the geotechnical point of view, it is necessary:
To choose the best location taking account of necessary river crossings and topographical features
To determine on broad lines the design of the road and structures.
These two phases usually follow one another immediately.
about
D■1-1 Preliminary phase The techniques used are largely covered in the paper in Theme but a brief summary is given in Appendix 1.
2.1.2 Second phase (A.P.S.) The various operations are listed in Appendix 1 and
comments are given below.
a) Large river crossings often determine the choice of the location of the road
and they are therefore studied first. Plate 1 shows a penetrometer test on a proposed bridge site.
b) The suggested numbers of boreholes and tests are averages and may vary widely
according to the complexity of the terrain.
c) The feasibility study should normally lead to a choice of a location but sometimes it is not precise enough to decide between several alternatives. The choice is then laft to the project stage.
d) It is well known that the geotechnical features can be a determining factor in the feasibility study for the choice of the location of the road and the techniques of construction. What is less well known is the size of the economies that can be obtained by the use of well-conducted geological and geotechnical studies, but it is thought that in many cases the economies are large.
2.2 Project studies (A.P.P.)
The aim is the exact definition of the work to enable a precise estimate of the cost to be made.
A check-list of the problems likely to be encountered is given in Appendix 2.
This form of presentation tends to separate a number of matters which are in fact linked, eg when determining the slopes of cuttings it is necessary to consider at the
same time problems of stability, drainage and erosion (see Plate 2).
Likewise the design of the road depends to a large extent on he properties of the subgrade (bearing capacity and possible settlement or swelling). It is thus
absolutely arbitrary to dissociate subgrade conditions from that of the main.structure
of the road. This is now well established.
In contrast, studies for large bridges, embankments on compressible soils or for tunnels are usually so specialised that they have not been included in this paper. The laboratory, however, may have to find and test materials for concrete for bridges.
2.3 Description of the resources and organisation
In the time available it is not possible to give a full description of the equipment used in the field and in the laboratory, but an indication is given in
Tables 1 and 2 of the sequence:
operations—^resources (personnel and equipment) *■tests—*- reports on the feasibility and project studies.
2.4 Place of geotechnical studies
The necessity and benefit of a complete and detailed geotechnical study is self-evident and it is now rarely omitted (although some tend to under-estimate its importance). On the other hand, insufficient co-operation between different
specialists is encountered, perhaps only in a few cases, but still too often. I believe that one cannot repeat too often that a road project forms a whole and that the economist, the surveyor, the works engineer and the geotechnician must work in direct collaboration.
2.4.1 Relation between the geotechnical study and the economic study. The economist indicates to the geotechnician the level of surveys and the design life of the road.
He must also give him all the useful information on traffic: intensity, predicted rate of growth and the wheel-load spectrum. The latter is often badly known, which leads the geotechnician to demand (with more or less success) wheel-weighing surveys.
Inversely, at the feasibility stage, the geotechnical parameters (quality of the soils, haul distances for roadmaking materials, river-crossing difficulties, etc) must be known with some accuracy for calculating the economies of the project.
Another example of the role played by geotechnology is when the traffic intensity is low enough for a gravel road to be regarded as normal, but when the study shows an absence or insufficiency of suitable materials for construction and maintenance of an unpaved road. One then has to pass straight from a dry- weather road to a paved road.
Another illustration of fee necessity for collaboration is that of large
cuttings with risks of landslides. An ideal slope, with berms, will give absolute safety, but will require a large volume of earthworks. The economist must indicate to what extent local landslides can be accepted, with interruption of traffic and the formation of special maintenance units during the first few years. The volume of earthworks can thus sometimes be greatly reduced.
2.4.2 Relation between the geotechnical study and the geometric study At the time of the feasibility study, the location of the road line must be the.combined work of the technical units. The positions of bridges are fixed either by
constraints or by preference; geotechnology and topography indicates areas to be preferred or avoided.
When deciding on the road line, the planner must know the geotechnical information concerning crossing points, areas to avoid (ie unstable, unusable or erodable) and rock spurs which will have a higher bearing strength. Account also
fl
has to be taken of the distance of the road line from deposits of roadmaking materials and, sometimes, sources of water.
To fix the longitudinal profile the surveyor needs to know:
In cut: The soil profile, with the bearing capacity of the different layer$, areas to avoid (rock, erodable soil etc) and the position of the
water-table.
On fill: The minimum height to avoid saturation and capillary action in areas that are flooded or contain a water-table and the maximum permissible height on compressible soil.
The determination of the transverse profile also depends on the geotechnic results;
Side slopes as a function of the stability and erodability
Cross-section of the road as a function of drainage condition and surface water flow (type and width of the shoulders and of the pavement,
impermeability and sensitivity to water of the different materials).
Type, section and slope of the ditches, drains, etc.
Typical cross-sections are shown in Fig 1.
For example, in the case of roads on expansive clays, the optimum transvers profile is mainly determined by geotechnical considerations (creation of a zone equilibrium water content, wide paved shoulders to avoid cracks, etc).
Conversely, the geotechnician needs to know as early as possible the suggested road line, even a provisional line, in order to best define the pattern of bore holes (position and depth).
This shows that it is the planner and the geotechnologist who together determine the following:
Volume of different types of earthworks in relation to the location, gradients of slopes and width of formation.
Movement of soils (possible re-use, required borrow pits).
Quantities and haul distances of different roadmaking materials.
Drainage networks
Protection of slopes, etc.
These items enable the cost of the investment to be calculated.
Lastly, the maintenance and strengthening programme for the roads is necessary to determine the costs of maintenance.
2.4.3 Relation between the geotechnical study and the structures study The type of
structure is also governed by the type of foundation. The structures engineer and and the geotechnician develop the final plans by the following steps:
Superstructure—"-stresses transmitted to the soil under different loads—*
deformations for comparison with those acceptable in the superstructure.
2.5 Costs of geotechnical studies for roads
The ranges of costs for almost all the studies are as follows:
Feasibility: 800-4000 F.F./km (approx £130-640 per mile) Project: 1200-8000 F.F./km (approx £190-1300 per mile)
These ranges are very wide. The lower limits correspond to very easy conditic homogeneous terrain, presence of suitable materials, no difficulties with transport an£ accomodation. The higher values refer to the more complex terrains, with
3. CONTROL OF CONSTRUCTION
3.1 The different types of control
In several western countries, much consideration has been given to the problem of control in road construction and different types of control have been examined.
3.1.1. Control of conformity - control of quality - automatic control.
a) Control of conformity is limited to establishing that the results obtained
satisfy the specification.
b) Control of quality is much more ambitious and aims at achieving the best possible quality. But how does one define the quality of a road?
A report by Leger (French Symposium on the Control of Quality of Road Construction, Paris, November 1972) considers that the quality of a road is shown by:
Lasting riding comfort and safety for the road user.
Minimising the cost of road transport for everyone.
This report distinguishes between:
quality criteria directly linked to the quality of the finished road or of any layer, and some of which are of direct interest to the user
(eg. surface irregularity and skidding resistance).
indicators of quality which enable the road technician to predict at an intermediate stage the performance of the road; these are mostly not of direct interest to the user (eg. deflection and state of compaction).
Controls must be directed not- only to criteria and indicators of quality but also to the methods which at the time of construction combine in the achievement of this quality. This implies good knowledge of the behaviour of a road and its inter mediate and long-term performance. However, further research is required on this
subject.
The optimisation of road transport costs (ie. costs of construction, maintenance and vehicle operation) depends on the choice of standards for roads, which is the
subject of Theme F.
c) Automatic control may be used by the contractor to ensure that the work
is carried out to specification.
3.1.2. Control before, during and after construction a) Classical method: control after construction.
This method of control is effected by measuring certain physical or mechanical properties of the materials used: fill, subgrade, pavement layers, concrete etc.
b) New method: control before and during construction.
Control after construction is still the method used in most African countries.
However, roadworks are becoming larger and methods of construction more rapid. The results with this method of control are often not available for some time and the delays can cause problems. Also, to be representative a large number of tests is
required.
Furthermore, control after construction has an inherent fault: it can only show any defects afterwards, and it is always difficult to go back and correct them, It is therefore strongly recommended that the before and during methods of control
should be developed- These control methods are based on:
the conformity and quality of the various materials: soils, aggregates, fillers, bituminous binders, hydraulic binders etc.
the choice of equipment most suitable for the work or the best use
available equipment. f the
the perfecting of the construction techniques by carrying out physical and mechanical tests on specimens at the start of the work. Then in the following section it is verified that the construction is conforming to the standards set by the tests.
This method of control has the advantage of not delaying the work, and required corrections being made immediately. It requires, however, the presence of supervisors with a good knowledge of current construction practice.
After construction control tests are still used, but at low frequency, for doubtful cases shown by borehole results, and especially to improve knowledge.
• 2 Role and organisation of a control laboratory
3t2.1. Nature ofthe control: importance and position of the laboratory. The control
should not be limited to confirming that the results obtained meet the specification.It should be constructive and aim at achieving the best possible results. The import ance of the laboratory in achieving this is fundamental: it controls the quality of the materials and products used, their manufacture and placing and, lastly, the finished
road.
Finally, we would mention the desirable position for the laboratory. On some roadworks the control laboratory is paid for (in whole or in part) by the contractor.
There are even cases where it is accepted that the contractor's laboratory is in charge of control. We think that this position is unsound: to place the laboratory even partially, under the contractor is to make it both judge and jury. The best solution is to attach the laboratory to the engineer in charge of the work, who pays for it direct. Where the laboratory comes under the contractor, the cost will be included in his tender and in the long run it will be the engineer in charge who bears
the cost.
-• Organisation of classical control. It is not intended here to describe in detail the methods of classical control or to give details of tests and materials.
Anyone interested will find much qualitative and quantitative information on tests and materials in Technical Note No. 18 of the Service Outre-Mer et Etraneer of the
C.E.B.T.P. B
The size and organisation of a geotechnical control team is a function of the size and complexity of the work, of the dispersion of the site laboratories, of the
rate of progress of the construction, etc.
For a road of medium size, ie
concentrated geographically (construction in a single length or in 1 lengths very close together)
with little earthworks (of the order of 10 000m^/km)
not containing large bridges
the necessary permanent geotechnical personnel would be:
1. technical assistant (head of control laboratory)
2. qualified technicians
k. technicians 4. labourers
Also it is important that a geotechnical engineer should make periodical visits to the site for the technical control of the laboratory and to assist the engineer in charge
of all the control work,
For large bridges, a special laboratory team should be provided for the control of foundations, concrete, steel, etc. Also, when a large volume of stabilised or bituminous materials are being used, special control should be set up.
The geotechnical control team must, of course, work in close liaison with other teams (topographic, administrative, construction, etc.) A suggested scheme is shown
in Fig 2.
The site laboratory is limited to simple and rapid tests. More sophisticated tests (hydaulic binders, bituminous binders, stabilised materials) should be carried
out in a central laboratory.
3.2.3. Observations on some important points. Improvement of methods of control.
a) A complete and well-designed study is a prime factor in the good progress and control of road construction. The efficiency of the control can be greatly improved by using before and during construction methods.
b) Before construction control. This must be carried out on all the materials
and products as follows:
natural materials at the place of extraction (borrow pit or quarry)
gravels and crushed rock at the place of production
hydraulic binders, bituminous binders and all other products on delivery
to the site.
With regard to equipment, for two reasons it is difficult in Africa to follow
European practice exactly:
First, there is not generally a great variety of equipment for a given operation.
It is not realistic to specify a particular type of mixing plant or compactor which does not exist in the country. However, at least one can prohibit the use of unsuitable
equipment.
Secondly, if the responsibility for the quality of construction is left to the contractor, the results and the methods cannot both be specified.
c) Control during construction. This method of control requires a great amount of effort, especially for two types of operations:
mixing (in situ or in a central plant)
compaction.
i) Control of mixing.
For in situ mixing the problem is not too critical. The operations of spreading mixing being relatively simple, their control does not require highly specialised
and
personnel. Test specimens are frequently used.
However, control for central mixing requires highly skilled personnel, who are very scarce in practice. We think that a serious effort should be made to provide technical training for this.
ii) Control of compaction.
This problem is extremely important: it concerns all the works (earthworks, base and surfacing). In view of the output of modern compactors, any delay caused by control can have a large effect on tie progress of the work.
The classical method of control after construction in which the apparent specific gravity is measured by means of a densitometer, sand replacement test or by taking cores of undisturbed samples is becoming more and more outmoded, at least
for routine control.
There are several methods of improving control techniques:
i) The use of gamma-densimeters for non-destructive and rapid tests.
Unfortunately this apparatus gives a wide variation in the results, which increases as the size of the aggregate increases. Precise calibration of the apparatus ia there fore required and its use is limited to materials with very uniform properties (in practice, to centrally-mixed material). Moreover, they measure the apparent density and it is therefore necessary to measure the moisture content at the same time to obtain the dry density. As the measurement of moisture content by neutronic diffusion probes has not yet been fully developed, it is always necessary to take specimens.
ii) In some cases it is possible to check a finished layer by measuring deformation under load. However, as plate-bearing tests take a long time, they are used only in special circumstances, eg. with very large material. The optical
deflectometer and the Benkelman beam give measurements that are clearly better. The greatest interest is now in tie use of equipment with a large output: the lacroix deflectograph and the CEBTP curviometer. But it must be remembered that part of the deformability of the supporting layers is always included, and this must be known and
not too variable with temperature and time,
iii) The preceding methods apply in the same way to methods of control after construction. The really important improvement is the change to control during construction: this is based on the carrying out of tests which permit the choice of he best equipment or the best use of the available equipment and, above all, <
decision on the methods of compaction (maximum delays, number of passes, weight of compactor, temperature for bituminous materials, etc.). For materials watered in place, test specimens are often necessary to adjust the moisture content, but the
tests can be very rapid.
3.2.4. An essential task: preparation of records of the road,
construction should lead to the production of two documents: The control of r
i) A report describing the methods used, emphasising the difficulties
encountered and the methods used to overcome them.
ii) A record of the road, giving all the geometric and geotechnical
details of the constructed road.
These records are extremely valuable in the future for the observation of the performance and for maintenance. Their production is still far from systematic and a considerable amount of information is thus lost. We hope that Administrations everywhere will recognise this problem and make provision for its finance, which is,
after all, very modest. | '
3.3 Costs of geotechnical control
In the great majority of cases, the cost of geotechnical control is 1-2 per cent of the total cost of the works.
10
km OBSERVATION OF THE PERFORMANCE OF ROADS AND STRUCTURES
This task is a natural complement to the survey and control work. It leads t The improvement of knowledge (eg- for the choice of road structures and
their dimensions).
The drawing up of a rational maintenance policy.
An optimum programme for strengthening.
*+-1 Inspection of roads
The rapid development of the African road networks, particularly of paved
roads, raises (or will soon raise) serious problems of maintenance and strengthening.
The necessity for inspection of road networks is already appreciated in developed countries and it will soon be appreciated everywhere.
The role of the geotechnician in safeguarding the infracture is:
- to establish and keep up-to-date the road records, adding maintenance and strengthening operations, for the whole road network.
- to carry out clearly defined observations on the roads.
^•1*1 Equipment and functioning of an inspection team As well as examining the
condition of the road, the inspection team should be able to carry out up-to-date
tests:
- deflection measurements
- surface irregularity measurements - the taking of undisturbed samples.
Measurements of skidding resistance are still unusual in Africa, a) Deflection measurements (and radius of curvature).
The most widely used pieces of equipment are the Benkelman beam and the
optical deflectometer.
For the larger networks, equipment with a large output,is necessary. The Lacroix deflectograph is already being used in Algeria, Tunisia, Ivory Coast and Madagascar. The CEBTP curviameter has been used in Zaire and will soon be used in other countries; because of its importance it will be dealt with in a separate
section.
Deflection studies are made when the road is in its worst condition, ie the end of the rainy season. The analysis of the results is usually done
systematically by a computer.
b) Surface irregularity measurements.
at
To measure the depressions and irregularities of the transverse profile, the straight edge is still used, but the use of the transverse - profilograph
is becoming very wide-spread.
For the longitudinal profile, either the French viagraphe or the English
multi-wheeled profilometer is used.
Pieces of equipment measuring the dynamic response of a vehicle (the TRRL bump integrator and the LCPC longitudinal profile analyser (A.P.L.) have been used in several countries - only occasionally up to now, but because of their
simplicity their use will undoubtedly become more general.
c) Measurements of skidding resistance.
The use of complicated equipment (SCRIM or the stradographe) is limited at present to exceptional cases. However, some simple tests are available, eg. the
TRRL pendulum, the sand patch test (TRRL) and the drainometer- d) Evaluation of the condition of the road.
A very precise description is first made of the visible condition of the road: deformation, different types of cracks, stripping, bleeding, condition of
the drainage, etc.
Whenever possible, a quantitative assessment should be2made of the defects:
deformations (see above), length of cracks per unit area (m ), percentage of
surface stripping, etc.
These measurements and observations enable an assessment to be made of the general condition of the road, but it is also essential:
to check the thickness of the different layers,
to ascertain the properties of the different materials at the time of inspection.
The effective quality of the roadmaking materials derives in the first place from the way in which they have been obtained and placed. (This emphasises the need for precise records of the roads.) Their properties are then altered either by ageing or by fatigue. It is thus necessary to extract specimens from the road -
a light drill is recommended.
e) Frequency of the measurements
Normally, on primary networks, deflection measurements are made annually on sections typical of all those in the road. However, as described in Theme B, special studies should be made on sections requiring strengthening.
ifr.1.2 The CEPTB curviameter The curviameter (see Plate 3) has been developed to measure automatically and semi-continuously:
- the maximum deflection
- the radius of curvature of the deformation at the position of the maximum
deflection.
12
The measuring apparatus is mounted on a lorry the rear axles of which can be loaded to any value up to 13 tonnes. A special track (see Plate k), the un winding of which is synchronous with the movement of the vehicle, places on the road, 2 m in front of the axle, a sensor which detects movements on the road when the wheels approach the measurement point, and then moves on.
The signal emitted by the sensor is automatically received by an integrator.
Besides the signal itself, which is visible on an oscilloscope, the operator has a recording giving for each point the maximum deflection, d, and the radius of
curvature, fi.
The speed of the readings can be regulated to coincide with the scale of a road plan so that the results can be immediately marked on the plan.
The interval between measurements is 11.5 m and the basic speed is 20 km/h.
The apparatus can operate on curves down to to m radius.
The range of deflection measurements is from 25 x 10~2 mm to *fO0 x 10~2 mm
and radius of curvature can be measured up to 1000 m.
This is thus an apparatus of very high output, operating at a practical road
speed.
The curviameter can measure precisely low values of deflection, which are normal on modern roads, or can be used for the control of earthworks where the deflections are high.
Inspection of bridges
This requires very specialised disciplines:
- measurements of deformations and stresses under load (fleximeters, vibrating wire gauges, strain gauges, etc.)
- assessment of corrosion
- examination of the condition of the paintwork.
We cannot say more about this in this paper except to stress the importance of this role of the laboratory.
5- STUDIES OF GENERAL INTEREST
These are essentially studies requiring the same disciplines and the same equipment as particular studies. Some examples are as follows:
a) Studies concerning a country or a region Preparation of geotechnical maps
of the types of soils
of the resources of roadmaking materials of the different types of foundation.
Inventory of quarries with a general study of the aggregates. Such studies have been carried out in Senegal and in the region of Abidjan.
b) Studies concerning materials
- Laterite soils (Studies by CEBTP, I$ron Associates and Building and Road Research Institute, Ghana)
- Use of fine soils for roadworks (Secretariat d'Etat aux Affaires Etrangeres and CEBTP).
c) Studies concerning a technique
- stabilisation with cement, lime, bitumen, etc.
- bituminous surfacings: mixing, placing, performance.
These general studies would be greatly facilitated by the establishment of data banks. The paper in Theme D emphasises this for terrain evaluation, but we think this should be extended to other subjects. This implies international action and co-operation between states. This is one of the reasons for holding the present Conference and we hope that the discussion will define a number of subjects for action at the regional or continental level-
6. ADAPTATION OF SPECIFICATIONS TO LOCAL CONDITIONS 6.1 Characteristics peculiar to tropical countries
The transfer pure and simple of standards and specifications used in European countries is not possible because of the large differences between them and African countries.
The characteristics peculiar to roads in tropical and desert regions are essentially due to three factors:
a) the climate, which determines the natural environment.
b) The geology, which determines the resources of roadmaking material*.
c) The traffic, which determines the level of geometric and pavement design.
Examples of unrealistic specifications are relatively frequent. The most pressing problems concern:
Materials
Particle size distribution of crusher-run material.
Quality of aggregates for surface dressing, bituminous surfacings and stabilised bases.
Quality of sand for sand-bitumen as for concrete.
Construction
Possibility of mixing in situ.
Adjustment of optimum moisture content for compaction (in very wet regions).
This list is not exhaustive.
Generally, the most frequent fault is the retention of standards suitable for materials typical of temperate climates and higher volumes of traffic than occur in practice. This leads either to higher costs than necessary or to enormous
difficulties on the site when the contractor is in the impossible position of trying to comply with certain clauses of the contract.
6.2 Participation of the laboratory
i•2.1 Adaptation of standards. This is developed from the control and observations on sites and from general studies on particular materials and techniques whose performance is known to be reasonably good. The role of the geotechnician is thus fundamental.
This should lead to:
- Directives, such as those of the SETRA and the LCPC in France.
- The adaptation of pavement design methods to local conditions. An important stage has been passed with the construction method produced by the CEBTP.
To go further, one can envisage manuals on structures for African countries.
- The adaptation of general specifications or special specifications (Cahiers des Prescriptions Communes (C.P.C.) et Spftciales (C.P.S.)).
6.2.2 Adaptation of operating methods of certain tests. Creation of new, better- adapted tests. The test methods used are almost entirely European or American.
The adaptation particularly concerns bituminous materials and stabilised materials
(cement, lime and bitumen). However, climatic conditions (temperature and humidity)
affect the performance of these materials. For example, tests at 18°C for bituminous materials and at 20°G for soil-cements are hardly applicable to African conditions.Moreover, the test methods sometimes differ from one laboratory to another so that comparison of the results is difficult. The test methods for soil-cement and sand bitumen, in particular, are many, different laboratories having more or less modified or improved them. A striking example is the Hubbard-Field test, for which at least 15 different methods exist. A strenuous effort on standardisation is required.
Among the new tests are:
test for liability to erosion (the LNTPB of Madagascar has proposed a method of test),
test for liability to weathering (under tropical climates).
6.3 Need for inter-state co-operation
If they were only at a national level, standardisation attempts would still lead to a wide diversity of specifications, whereas certain problems are identical in
neighbouring countries (the same climate, the same types of soil, similar traffic).
The value of co-operation is obvious: it would enable the maximum use to be made of
the experience gained in any one place.
We would therefore like to see this co-operation evolve, first at a regional level and then at a continental level.
7- PLAN OF ORGANISATION 7.1 Internal organisation
We have drawn up two schemes (see Figs 3 and k)i one for general organisation and one for technical services. This represents one possible organisation of a large laboratory. Others, however, may be adapted to local conditions.
In laboratories with a small staff and few activities, there may be fusion!or absence
of some sections. In practice, no laboratory can employ all the specialists. To
different degrees, the technical support of a competent organisation is indispensable to all laboratories, all the more so as it is a link between laboratories of different
countries and communicates the experience of each.
In this scheme, for the sake of clarity, we have not detailed organisations for soil mechanics and construction materials sections.
_ We have listed appropriate resources for the different road sections: reconnaissance equipment, site laboratories, inspection team, and resources common to all sections.
It is difficult to establish detailed relations between common resources and those of the different sections. In practice, a good study or control team can call upon the
resources of a central laboratory.
Such an organisation must be very flexible and adaptable to what is required;
African laboratories must recruit personnel with wide knowledge rather than specialist
starr.
7-2 External relations
To act with the maximum efficiency, the laboratory must be well integrated with the economic and administrative sectors. Laboratories are generally public or semi-public bodies, usually under the Ministry of Public Works. Whatever their status, their financial independence is a measure of their flexibility of working. In particular, it enables them to extend their activities to all features of roads, civil engineering and building. The field of work of the laboratory is very wide.
Authorities
First: the Ministry of Public Works and connected bodies: Roads, Aerodromes, Ports.
Town Planning, Railways.
Ministry of Agriculture: Directorate of Hydrology and rural amenities, Ministry of Industry, etc.
Then: Local authorities, Planning Department, Firms.
Besides its normal duties, the laboratory acts as adviser, produces reports, participates in standards committees and co-operates in research with universities and technical colleges. It also gives technical training to groups from Administrations and
ilrma by means of courses, training periods and visits.
8. THE FUTURE: PRINCIPAL PROBLEMS - CURRENT OR PROPOSED RESEARCH
Among the problems tackled by road geotechnicians are those found almost everywhere in the world and those confined to tropical countries. The first are the object of research in developed countries and are generally complicated and very expensive.1 For African laboratories the best solution is to keep up-to-date with this research and, when the time comes, to adapt the results to local conditions.
The second set of problems can only be solved in place and presents such a large field of activities that the researchers will be fully stretched.
Most road research throughout the world ie concerned with roads for heavy traffic (several thousands of vehicles per day). Traffic at this level i. *•£»*«*> °££
in Africa around large towns, but the lengths of road involved are still short.Road traffic in Africa will continue to grow rapidly but, in the short and medium ^rms, the important problems are concerned with roads carrying low and medium volumes of traffic.
8.1 Road problems in developed countries The principal needs at present are:
a) Faster construction of earthworks and their construction in wet weather;
b) The constraints of line and of urbanism require more and more frequent crossings
of areas of poor soil (compressible soils), increase in the volume of earth works (large embankments and cuttings) and structures (tunnels and viaductsJ.c) Strengthening, often urgent, of old roads.
d) Construction of new roads for very heavy traffic.
e) Obtaining the best conditions of riding comfort and safety in the completed
road.
This explains why the main effects have been directed towards:
a) Stabilisation of soils with lime.
b) Construction of embankments on compressible soils.
- Piled foundations
- Stability and protection of slopes of large embankments.
- Road tunnels.
c) Development of rapid methods of inspection.
d) Analysis of the behaviour of roads under heavy traffic (theoretical studies and methods of measurement).
- Construction with complicated materials (gravel stabilised with cement, lime or bitumen, with particular regard to the quality of the aggregate;.
- Study of the properties of materials for design purposes, particularly:
Study of bituminous materials (visco-elasticity) to improve their resistance to fatigue and rutting.
Study of rigid materials to prevent or reduce cracking and facilitate
construction.
e) Research to improve surface riding quality and skidding resistance.
8.2 Problems peculiar to tropical countries
8 2 1 The adaptation of specifications. As mentioned earlier, many current standards and specifications need to be better adapted to local conditions. In many cases, this requires a considerable amount of work in collecting the results of research.
These specifications should be standardised for similar climatic conditions and
categories of traffic.
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3.2.2 Problems related to terrain evaluation and earthworks. The development of reconnaissance methods using aerial photograph, radar and geophysical techniques are dealt with in Theme D.
3-2.2.1 Research into the mineralogy of clays in tropical soils. Certain eilty or clay soils behave abnormally, ie not in accordance with the usual geotechnical identi fication properties: particle size distribution and Attenberg limits. For example, this happens with the weathered soils of the Hauts Plateaux of Madagascar - no doubt due to the presence of different clays.
From a mineralogical study, one could predict the behaviour of these soils in the presence of water (compaction, bearing strength, swelling) and whether they were
suitable for stabilisation.
3.2.2.2 Research on expansive clays. The construction of roads on expansivte clays is always very difficult. A mineralogical study is useful for predicting their behaviour from cycles of expansion and contraction and, above all, for determining methods of stabilising these clays (eg with lime).
Observation of experimental sections would increase knowledge on the movement of Water in these soils and give an indication of the best methods of attaining moisture
sontent equilibrium under roads. Research into this has already been undertaken in torocco, Senegal and Madagascar.
5.2.2.3 Research on the use of pedological data. Geotechnicians frequently consult pedological maps, but generally obtain few useful data. Little work has been done to relate the geotechnical and pedological properties of soil (except in the caee of laterites). Such work would lead to better use of this mass of information, and co-operative action with pedologists is required.
8.2.2.4 Research on erosion and methods of prevention. Many tropical soils are
very erodable. The research required is in three parts:
i) Development of a simple test for determining liability to erosion, ii) Classification of soils according to erodability.
iii) Determination, for different soils, of the best methods of protection: side
slopes, berms, stabilisation, vegetation, etc.
Research work has already been carried out in Madagascar, Gabon, etc. Also, request has been submitted to the P.N.TJ.D. for multi-national research.
8.2.2.5 Establishment of data banks - use of the information. This subject has
been dealt with in Theme D.
8.2.3- Problems related to construction and the performance of roadmakinK materials.
8.2.3-1 General problem of aggregates, sands and fillers. A review of the available
resources in each country will lead to:
Their optimum use;
The drawing up of realistic specifications, not only for the aggregates, but also for gravels, bituminous mixtures, surface dressings and concrete.
The economic importance of this action is considerable and it is logical to give it top priority.
..2.3-2 Sub-bases and bases
a) Dry compaction
In arid regions, boring for water and the transport of water can be very expensive
However, in certain conditions, powdery materials can be compacted dry (by vibration).
Tests at the Laboratoire dee Ponts et Chaussees in Bouen in France have already given useful results. The research is contimuing into the construction of roads in desert countries.
b) Lime stabilisation
The research must investigate the action of lime on tropically weathered clay with the aim of defining:
The types of materials capable of being stabilised.
Specifications for stabilised materials.
Directives for construction.
Specification for the lime to be used.
The last point is essential: the frequent absence of good quality lime has been the principal obstacle to the development of this technique. Recently, on the Port Berge - Antsohihy road in Madagascar, excellent results were obtained in the sub-base with silty clays stabilised with lime.
c) Cement stabilisation
The improvement of clayey lateritic gravels with cement is current practice and gives good results. Stabilisation of crushed gravels with cement is generally satis factory.
Stabilisation of fine soils has given good results in wet regions (eg Bonoua - Aboisso road, Ivory Coast), whereas serious failures have occurred in arid region
(eg Gueoul - Louga road, Senegal - Chad),
Failures are usually due to the nature of the treated soil, to the subgrade support
or to the drainage (RN 4 - Port Berge road in Madagascar).
The cements used are nearly always CPA 325 which is currently produced in African cement works. In road stabilisation, this cement sets too quickly, giving the material considerable rigidity and leading to shrinkage and cracking. It is very desirable that
for road construction one should use a less 'sensitive' cement obtained either by
limiting the fineness of grinding or by mixing the cement with an inert filler (A cement of class 150 - 250 would be suitable).
Research on soil-cement should be directed to the following objectives:
Standardisation of test procedures, according to the climatic conditions, both for road improvements and for stabilisation.
Study of the cracking of soil-cement and means of reducing it (including cracking due to thermal stresses).
Specifications for stabilised materials and instructions for laying them.
Specifications for more suitable cements.
d) Bituminous stabilisation
Very satisfactory results have been obtained with slightly clayey sands stabilised with a soft bitumen (M'Bour - Kaolack road in Senegal, Port Bouet - Grand Bassam road in Ivory Coast, Ambilobe - Ambanja road in Madagascar). The important quality of these materials is their flexibility. However, it is impossible to generalise without caution, since the method of construction is always critical.
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Research should be directed towards:
Standardisation of the test procedures, according to the climatic conditions.
Determination of the most suitable binders for different types of soil.
Specifications for stabilised materials and methods of laying them.
Stabilisation with other products
products have been tried in the past without great success (eg sodium . at Gassi Touil in Algeria). Others are periodically put forward by the
manufacturers, usually as miracle workers. Obviously their use on a large scale requires
previous research work with test sections. ! requiree
8.2.3-3 Bituminous surfacings
a) Research on the aging of bituminous binders
In desert or arid regions, the action of the climate (strong sunlight large 1™?™^ temperature) leads to rapid aging of bituminous binders. Research using accelerated aging tests could determing the least sensitive binders and means of
improving their performance.
b) Research on the action of adhesion agents
Development of the use of hard bitumens for coated materials
Bitu"en\currently
There is little experience on this subject, so that it is impossible to know the long-term performance of any agent supported by the manufacturer. Research would at
ofaanyeroadworksleCtiOn tO ** "*** °f 6atlsfactory a*ents 'or the particular conditions
c)
4 are often too soft (80/100, sometimes 60/70,) having regard
-J. The desirable use of harder bitumens presupposes previoustesta in sufficient numbers to determine the performance of the coated materials,
8*2-3.^ Research on difficult or non-traditional materials a) Stabilisation of dune sand
Two methods appear possible:
i) Stabilisation with a mixture of cement and emulsion: the results from the
Nouakchott - Rosso road in Mauritania were not very conclusive, the materials
£?! ;y^e^Ving-,aS \sand-cement' raPid «id subject to cracking. However,
this method should not be rejected; more intensive research is required for
better adaptation to the local conditions.
il) Coating with hard bitumen: The results obtained in France were encouraging -
"* on/™?8 Wrth M alluvial filler *»<* ooatlng with very hard bitumen
or 20/30). It is intended to construct a test section in Mauritania.
b) Use of lateritic concretions (pisoliths) in surfacing
a«.jT?El.F; %* 5 I uCfn y?"8 th66e concretions *a™ been satisfactory i
Senegal (Dien Road) and in Mali (Segou - Bla - San road). This method of treatment is worthy of more general study (for low volumes of traffic).
c) Use of shells
been used in bases and in surfacings in the form of surface dressings land
1 (near Saint Louis and Ziguinchor)L - Akjoujt roads).
d) Use of gypsum
This problem is of most concern in the Sahara (Algeria, Mauritania).
e) Use of coral
Coral occurs in different forms, the geotechnical properties of which have not yet
been determined (Indian Ocean).f) Use of volcanic products
This includes pozzolanas, ashes and lavas. The countries concerned are Cameroon,
Zaire, Madagascar, Tanzania, etc.
8.2.4 Problems related to the general performance of roads.
^^">" "f ™»ds carrying low volumes of traffic. Roads
rarrvine low volumes oi trainc are ibdo j.««=^ -~ * 7 - aachh *.«art tpKt
o77e^ heavy axle loads or natural aging. Pavement design based on the AASHO road test,
generally leads to excessive thicknesses.
This is why it is.necessary to use a pave^design ^T^^^SSS^
countries (CEBTP). This method requires to De
conditions as a function of the subgrade soils perhaps by producing a catalogue of structures
The future performance of the road can be predicted from indicators of its
the by considering other parameters (radius of curvature, vi methods, etc).Some interesting research has already been carried out in the Laboratoire Public
d'Essfis et d'Lude^in Morocco (Mariotti). The work is well worth extending and
completing with full-scale test sections.
1.2-5
rftlflted to the finished road. This is dealt with in Theme F.
9. CONCLUSIONS
We hope that this paper has amply demonstrated two things:
the term 'laboratory* is too narrow and that one cannot separate
from its natural extension into interpretation and advice
on applications.
b) That seotechnology - to employ a very broad term - plays a considerable
economic role\ Laboratories contribute widely to the optimisation of road investments I; the interests of all, ie in the construction of -economic'
roads in all senses of the word.
Lastly, hope that in the field of research and of the standardisation of
^freselt Conference will lead to a number of co-operative actions and will
source of new progress in road techniques in Africa.
the
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