Professor Dr.-Ing. Dr.-Ing. E.h. Rudolf Floss
Compaction Technology in
Earthwork, Highway and
Transportation Engineering
Volume 1
Basic Principles of Vibratory Compaction
Compaction of Soil and Rock
Compaction of Asphalt
Professor Dr.-Ing. Dr.-Ing. E.h. Rudolf Floss
Compaction Technology in
Earthwork, Highway and
Transportation Engineering
Volume 1
Basic Principles of Vibratory Compaction
Compaction of Soil and Rock
Professor Dr.-Ing. Dr.-Ing. E.h. Rudolf Floss
Compaction Technology in
Earthwork, Highway and
Transportation Engineering
Professor Dr.-Ing. Dr.-Ing. E.h. Rudolf Floss
Compaction Technology in
Earthwork, Highway and
Transportation Engineering
Volume 1
Basic Principles of Vibratory Compaction
Compaction of Soil and Rock
Compaction of Asphalt
Specialist book of BOMAG GmbH & Co. OHG, Germany, 1st edition 2001 Published by BOMAG GmbH & Co. OHG
Impressum
© BOMAG GmbH & Co. OHG, Germany, all rights reserved Publisher:
BOMAG GmbH & Co. OHG, Boppard Project Management:
Dipl. Ing. H.-J. Kloubert, BOMAG GmbH & Co. OHG, Boppard Prof. Dr.-Ing. Dr.-Ing. E. h. Rudolf Floss, Munich
Layout:
Schray – Grafisches Atelier, Weissach Translation:
Techtrans GmbH, Boppard Print:
Druckerei Seyl & Hohn, Koblenz Publisher‘s notes:
The publication in its entirity is protected by copyright. All details, data, results etc. contained in this book have been reviewed by the project management according to the best of knowledge under utmost care. At the same time, errors
Preface
Mechanical compaction technology with vibratory compaction equipment has reached a high level of development. It has matured to an economical and technically indispensable construction techno-logy used all over the world for the construction of permanently stable and deformation resistant high-ways, transportation routes, earth work, embank-ments and foundations of buildings, bridges, sealing layers and waste disposal sites.
These engineering projects are characterised by increasing output, a strong weighting of economi-cal aspects and high quality demands. Compaction equipment must be powerful, economical and ver-satile in use and contribute to a surface covering quality assurance by means of an immediate work integrated control.
BOMAG has recognised these trends and deve-lopment objectives and already in the eighties tho-roughly investigated compaction processes when using vibratory rollers and the interaction between drum vibration and the soil reaction force changing with increasing compaction.
The push in innovation resulting from this led to the development of automatic measuring and recording systems. With these roller integrated systems the compaction processes can be controlled and opti-mised and provide a surface covering recording of the compaction.
In recent years further research and development activities led to the successful launch of intelligent BOMAG compaction systems such as VARIOMATIC and VARIOCONTROL, which automatically adapt the compaction amplitude to the actual operating conditions. These controlled rollers particularly stand out in terms of compaction performance, depth effect, uniform compaction and suitability for universal use.
Last but not least, the demand for more powerful padfoot rollers for fine grain and rockfill materials, as used on large scale civil engineering projects of the German Railway, led to the development of new padfoot designs.
Systematic fundamental investigations in the Research and Development Centre of BOMAG as well as application oriented investigations on large scale construction sites were the essential prere-quisites for this progress. The author of this first edition of the BOMAG specialist book, University Professor Dr. Ing. Dr. Ing. e.h. Rudolf Floss, has scientifically contributed on these researches and developments over many years.
Purpose and goal of this specialist book is the presentation of the know-how about BOMAG com-paction technology in connection with the scientific state of fundamental knowledge in a comprehen-sive publication. Volume 1 available in German and English and the planned successive volume shall be available for all those who are interested in BOMAG equipment. The experience contained ther-ein shall help civil engineering contractors, autho-rities, and consulting engineers in the planning and execution of compaction tasks in earthwork, Transportation routes and landfill site construction, but shall also provide fundamental knowledge for experts in research and science.
Boppard, March 2001 BOMAG Management
Introduction
Research and development in the field of compac-tion technology concentrates on enhancing the per-formance capacity of machines, on user friendly and environmentally compatible designs and on extending the functional structural range of applica-tion. These improvements, which are achieved in a continuous process, occur temporally parallel with the development of electronic measuring and com-puting technology as well as the use of micro-proc-essor controls.
An important radical change and milestone in this respect is the introduction of automatic measuring and recording systems as well as EDP and GPS based machine controls. These machine integrated systems enable an almost automatic control of compaction work and an optimisation of the use of equipment as well as a surface covering assur-ance of the compaction quality. The application of the construction machine as a “measuring and test-ing unit” and the use of the machine parameters for process control is essential for large area projects, because it is the only way to achieve a uniform placement quality and the reliability of the quality assurance in accordance with the required con-struction progress.
A development leap in control automation of vibra-tory rollers has been in fact achieved by the pos-sibility to combine data of compaction quality and compaction management with DGPS-information (Differential Global Position Systems) about the position of the roller. Further developments aim at the possibility to localise the roller position exactly via a position system suitable for practical applica-tions and to specify, control and record the number of roller passes. The further development of the machine integrated measuring and recording sys-tems as well as the localisation of the roller by means of satellite navigation will also enable the linkage of the position data with the compaction data and the real time presentation in a 3 D-model. Furthermore, poking interfaces for DGM planning software (digital terrain models) are planned, so that the actual position can be compared with the nominal data during the compaction process in a work integrated manner.
The great present and future challenges of engi-neering technology induce BOMAG and the author of this specialist book to communicate, in form of a compendium, the state-of-the-art concerning the optimisation and automation of equipment engi-neering and compaction technology gained by research and investigating to the public and espe-cially to those persons interested in BOMAG com-paction technology.
Volume one of this specialist book is divided into three parts. The first part contains the fundamental principles of vibratory compaction, the characteris-tic equipment technological parameters as well as the design types of and applications for BOMAG vibratory compactors.
The second part deals with the compaction of soil and rock in connection with the operative range of the BOMAG compaction technology in earthwork and embankment construction, describing the soil and rock mechanical principles of compaction and subsequently the recommendations for vibratory equipment with performance data.
The third part contains, in a similar way, experiences and equipment recommendations for the compac-tion of asphalt pavements as applied in highway and transportation engineering and for sealing layers. The appendix contains several conversion tables and reference lists as general assistance for the user of this book.
For the intended sequential volume special sub-jects and special applications for the BOMAG com-paction technology are planned. This includes sub-jects such as the compaction of unbonded and hydraulically bonded base courses and soil-binder mixes in highway and transportation engineering, the compaction of recycling materials, industrial wastes and household refuse, the compaction of cable and pipeline trenches, construction backfills and embankments, as well as the compaction of sanitary landfill constructions and mineral sealing layers. Furthermore, special chapters will deal with fundamental principles and information for the cal-culation of output and costs of compaction work, as well as measuring, testing and recording systems for quality assurance of compaction work.
The author would like to thank BOMAG for the pub-lication of this specialist book, namely Mr. Dipl.-Ing. Hans-Josef Kloubert, who has made a signifi-cant contribution with their engineering knowledge and editorial support. The author would also like to thank BOMAG executives in the research and engi-neering department for the useful discussions. BOMAG and author wish all users of this specialist book many inspirations and beneficial information for their daily work.
Munich, March 2001
Univ. Prof. Dr.-Ing. Dr.-Ing. E.h. Rudolf Floss
Table of Contents
Part 1 Fundamental principles of vibratory compaction
1 Principles of dynamic vibration1.1 Basic vibrations ...7
1.2 Natural and resonance vibrations ...8
1.3 Harmonic and subharmonic vibrations ...9
1.4 Propagation of vibrations ...9
1.5 Dynamic forces and resilient stiffness of the subsoil ...10
2 Vibration and movement performance of the system types 2.1 Vibration exciter systems for vibratory rollers ...11
2.1.1 Vibrator (circular vibrator) ...11
2.1.2 Oscillator ...11
2.1.3 Comparative compaction effect of vibrator and oscillator ...12
2.1.4 BOMAG directed vibration systems ...13
2.2 Parameters of vibration generation ...17
2.3 Static axle load and vibrating mass ...17
2.4 Centrifugal force, frequency, amplitude...17
2.5 Energy transfer...20
3 Design types and applications for BOMAG compaction technology 3.1 Vibratory tampers...23
3.2 Vibratory plates / hydraulic plates ...23
3.3 Hand guided vibratory rollers...25
3.4 Tandem rollers ...26
3.5 Single drum rollers with smooth drum...28
3.6 Single drum rollers with padfoot drum ...30
Table of Contents
Part 2 Compaction of soil and rock in earthwork
1 Soil
1.1 Soil groups under engineering aspects...33
1.2 Earth engineering classification ...38
1.3 Geotechnical suitability of the soil types ...40
1.3.1 Material and engineering properties ...40
1.3.2 Geotechnical suitability for earthwork ...43
1.3.2.1 Clays and silts ...43
1.3.2.2 Sands and gravel...44
1.3.2.3 Mixed particle soils ...45
1.4 Compaction characteristics of the soils...46
1.4.1 Compaction parameters...46
1.4.2 Compaction characteristics...48
1.4.2.1 Functional interrelationship...48
1.4.2.2 Coarse particle soils ...49
1.4.2.3 Fine particle soils...50
1.4.2.4 Mixed particle soils ...51
1.4.3 Relations between compaction and deformation parameters...51
1.4.3.1 Test dependent deformation parameters ...51
1.4.3.2 Soil specific interrelationships ...54
1.4.3.3 Relationships to international soil classifications...56
2 Rock 2.1 Classification of rock (overview)...57
2.1.1 Congealed rock (magmatic rock) ...57
2.1.2 Sedimentary rock ...57
2.1.3 Metamorphic rock ...57
2.2 Description of rock ...58
2.3 Parting plane structure of rock ...58
2.4 Strength and deformation properties of rocks...59
2.5 Suitability of rock...60
2.5.1 Exploitation of rock as filling material...60
2.5.2 Rock classes...60
3 Application and performance of the BOMAG compaction technology
3.1 Applications...64
3.2 Calculation of compaction output...66
3.3 Trial compaction ...68
3.4 Placement and compaction water content ...70
3.5 General equipment and soil specific recommendations ...72
3.6 Special machine specific compaction effects...75
3.6.1 Static smooth drum rollers ...75
3.6.2 Pneumatic tired roller ...76
3.6.3 Smooth drum vibratory roller ...76
3.6.4 Padfoot rollers with and without vibration...76
3.6.5 Single drum rollers with special padfoot drums ...77
3.7 Compaction of marginal zones (slopes, embankment shoulder) ...78
Table of Contents
Part 3 Compaction of asphalt
1 Asphalt pavements in highway and transportation engineering ... 81
2 Bitumen and bituminous binders 2.1 Types and manufacturing...83
2.2 Chemical-physical properties...84
2.3 Tests...85
2.4 Material specific requirements ...87
2.4.1 Paving bitumen ...87
2.4.2 Special bitumens and bituminous binders ...88
3 Asphalt 3.1 Mineral aggregates ...89
3.2 Asphalt for base courses...91
3.3 Asphalt for surfacing ...92
3.3.1 General requirements ...92
3.3.2 Binder coarse asphalt ...94
3.3.3 Asphalt concrete ...95
3.3.4 Stone mastic asphalt...96
3.3.5 Gussasphalt ...97
3.3.6 Asphalt mastic...98
3.3.7 Combined surface - base - courses ...98
3.3.8 Natural asphalt and modified asphalt...98
3.3.9 Asphalts for special construction methods...98
3.4 Asphalt veneer coats ...99
4 Compaction characteristics of asphalt 4.1 Fundamentals ...100
4.2 Tests methods...101
4.2.1 Marshall stability and flow ...101
4.2.2 Compactibility...102
4.3 Influencing factors...103
4.3.1 Composition of mixture ...103
5 Application and performance of BOMAG compaction technology in asphalt engineering
5.1 Planning and fields of application...105
5.2 Influences caused by ambient laying and compaction conditions...107
5.3 Areal output and volumetric output of the machines ...109
5.4 Compaction equipment ...113
5.4.1 Pre-compaction during pavin ...113
5.4.2 Selection criteria ...113
5.4.3 Static smooth drum rollers ...114
5.4.4 Pneumatic-tired rollers ...115
5.4.5 Vibratory rollers...116
5.4.5.1 Effectiveness in asphalt compaction ...116
5.4.5.2 Hand guided vibratory rollers ...116
5.4.5.3 Tandem vibratory rollers...117
5.4.5.4 Combination rollers ...118
5.4.5.5 Plates and tampers ...119
5.4.6 Applicational advantages of the directed vibration system BOMAG VARIOMATIC...119
5.4.7 List of recommendations for the use of BOMAG vibratory rollers ...120
5.5 Basic rules for rolling technique ...122
5.5.1 Rolling pattern...122
5.5.2 Monitoring of quality influences...125
Appendices A 1 Conversion tables...129
A 2 Compaction parameters (soil)...131
A 2 Conversion of compaction parameters...133
A 3 Characteristics of rock...134
A 4 Standards, regulations, guidelines ...135
Literature ...141
1 Principles of dynamic vibration 1.1 Basic vibrations
With their rotating eccentric masses (unbalanced masses) mounted on one or several drive shafts, depending on the system, the vibratory machines designed for vibratory compaction generate uni-form, stable rotary vibrations. These vibrations are transferred to the substrate via contact areas (spe-cial padfeet, plates, roller drum), either flat or linear. They act as dynamic forces in a spatially distributed manner, compact the medium by means of pres-sure and vibration and, with these volume reduc-ing deformations, increase the physical-mechanical stiffness characteristics.
The interaction between vibration exciter and medium to be compacted - e.g. a soil layer - can be schematically presented using a dynamic substitu-tion model.
The basic vibrations of the exciter system normally have harmonic, periodic attributes, (fundamentals Lit. 1, 2, 5, 6):
The temporal change of harmonic vibrations is defined and described by sine or cosine functions (Fig. 2).
The vibration is periodic if it is continuously repeated after a certain period of time. A periodic vibration can be graphically presented as a super-imposition of several sine or cosine oscillations, the frequency of which is a multiple of the basic fre-quency.
A stationary vibration is a vibration with tempo-rally constant characteristic functions. Temporary vibration processes (transient and dying processes) are transient vibrations, which will either dissi-pate in the course of time or change over to a sta-tionary condition.
Deterministic vibrations are vibrations that do not
occur by chance; their momentary vibration magni-tude can be mathematically exactly described on the basis of the previous course of time. In con-trast to this, random or stochastic vibration
pro-cesses showing irregular variations of time, can
only be described with the help of statistic or proba-bilistic parameters.
Fig. 2 shows a sinusoidal oscillation process as time function of the vibration displacement a‘ = f(t). The sequence of movement of this vibration type is generally characterised by the following definition and mathematical derivations:
f Frequency, reciprocal value of the
vibration period T (duration of period)
f = 1 [Hz = s-1]
ω Radian frequency, number of vibrations in 2 π seconds
ω = 2 π . f = 2π
a Amplitude [mm]
a‘ Vibration displacement: a‘ = a . sin (2 π . f . t) Compactor
Soil
M suspendet machine mass m1 exciter mass
m2 resonant vibrating soil mass r1 machine damping r2 soil damping
k1 resilience value of machine k2 resilience value of soil Fo exciter force
T T
Fundamental principles of vibratory compaction
Part 1
Compactor - soil - substitution model Fig. 1
the natural frequency f multiplied by 2 π is called
natural radian frequency ω0.
If a vibration system possesses several natural fre-quencies (e.g. compaction machine and dynam-ically coupled soil mass), each of these natural frequencies also has its own type of vibration. When exciting such a system with a frequency which is more or less identical with one of the natural fre-quencies, resonance frequencies with high ampli-tudes will occur.
According to the resonance theory (Hertwig 1933, Lit. 1) the optimal compaction effect is obtained in the range of the natural frequency of the system machine - substrate (resonance frequency). Under this condition the substrate responds elastically, similar to a spring, whereby the natural radian
fre-quency ω02 depends in a linear relation on the
spring stiffness C and the total vibrating mass m of the system:
ω02 = c . m
Depending on substrate and machine parameters, the natural frequencies are located in the range between 13 and 27 Hz (800 - 1.600 vibrations/ minute). Investigations reveal that the natural fre-quency of the system drops with increasing nomi-nal amplitude (Lit. 3).
T
Vibration path a‘
Amplitude a
Time t
T
Fig. 2
Sinosoidal vibration process: Path-time-diagram
Vibration speed v and vibration acceleration b are temporal derivations from the vibration displace-ments a‘: Vibration speed: v = da‘ = a (2 π . f) . cos (2 π . f . t) v = v sin (2 π . f . t + π )) v = a . 2 π . f Vibration acceleration: b = dv = a (2 π . f)2 . sin (2 π . f . t) b = b . sin (2 π . f . t + π) b = v . 2 π . f = a (2 π . f)2
Parameters of vibration generation for the system types, Fig. 16.
1.2 Natural and resonance vibrations
Natural vibrations characterise system inherent vibrations, which solely depend on the properties of the system (e.g. the properties of the compaction machine: dimensions, material parameters, contact as well as marginal conditions) and adjust them-selves after a short excitation period independently from the excitation magnitude.
As far as these natural vibrations are characterised by harmonic vibration features, basic terms as in part 1, section 1.1 are used: Each vibration mag-nitude reappears after the system inherent period duration T (duration of natural vibration). The recip-rocal value of the system inherent period duration
T0 is the natural frequency f0 = 1/T0. The value of
dt 2 dt
Part 1
Fig. 3
Change of frequency in connection with amplitude eccentric mass (Machet 1976)
Fundamental principles of vibratory compaction
1.3 Harmonic and subharmonic vibrationsVibration exciters and oscillating masses of the sub-strate to be compacted form a coupled vibration system. During the compaction process the basic vibration of the machine’s exciter system is changed or disturbed by the stiffness of the dynamically cou-pled mass. These changes in the periodic sequence of movement result in harmonic vibrations, which are a multiple of the basic vibration generated by the exciter. The magnitude of these harmonic vibrations increases with progressing compaction or with the stiffness of the substrate and is therefore an indirect measure for the dynamic change in stiffness. This process reaches a limit condition when the machine lifts off the substrate or “jumps” at a very high stiff-ness. In this jump condition so-called subharmonic vibrations, half the size of the basic vibration, occur besides the basic vibrations generated by the exciter. For example, on vibratory rollers used in earthwork with a normal vibration frequency of approx. 30 Hz, the harmonic vibrations reach 60 Hz and the subhar-monic vibrations 15 Hz.
1.4 Propagation of vibrations
In the dynamically coupled strata the introduced vibra-tion energy spreads in form of space waves (com-pression and shearing waves) and surface waves or even as a combination of both wave types (Fig. 4). The magnitude of these wave types depends on the type of vibration exciter and the introduction of the energy. Since the source of excitation for the vibratory compaction of layers described hereunder is located near the surface, the vibrations mainly spread in form of surface waves. Depending on the distance from the source of excitation, these surface waves have higher vibration amplitudes than the space waves.
The transferred vibrations dissipate with increasing distance from the source of excitation. This is caused by the geometric decrease of the amplitudes as a result of the reduction in energy density and by the material damping caused by the frequency depend-ent absorption of vibration energy. Vibrations with higher frequencies are thereby dampened more than vibrations with low frequencies (Lit. 9).
Locally the propagation of vibrations may be consid-erably disturbed or obstructed, e.g. by extreme divi-sion of layers, building density, clefts in the terrain and the interaction of several vibration sources. In case of distinct layer borders with high density differ-ences, existence of groundwater or loads not applied to the ground the propagation of vibration concen-trates along the surface.
Compared with vibrations originating from blasting activities the propagation of waves from vibration exci-tation introduced by vibratory equipment on the sur-face is only of minor significance. However, during the compaction process the fact must be taken into con-sideration that both surface waves as well as space waves have an effect on buildings (pipes, wall and shaft constructions); example Fig. 5.
Fig. 4
1.5 Dynamic forces and resilient stiffness of the subsoil
Forces, which are variable with respect to their effective duration and direction, are known as dynamic forces. If the effective duration of the force is short in relation to the periodic duration of the natural vibration of the system, the force acts as a blow and depends on the size of the impulse. Vibration magnitudes (speed, acceleration, ampli-tude) are measured as function of time by acceler-ation measurements on the compaction machine. From the measured accelerations a force-way-func-tion can be derived by mathematical evaluaforce-way-func-tion of the soil contact force and the integration of the accelerations and presented as a so-called indica-tor diagram. The released energy or power is an
indirect measure for the dynamic stiffness of the subsoil. The increase of the contact force in rela-tion to the respective assigned vibrarela-tion displace-ment corresponds with the modisplace-mentarily achieved dynamic stiffness of the subsoil achieved by com-paction; see T 1, para. 2.5 and Fig. 21.
Vibration speed at a foundation [mm/sec]
4
3
2
1
5
200kg-700kg 2t 6t 9t 17t 18t 19tVibratory plates Tandem-vibratory rollers Single drum rollers Compaction equipment
10m distance 5 m distance 2 m distance
Fig. 5
Effects of vibrations generated by vibratory compaction equipment on a hall building
2 Vibration and movement performance of the system types
Overview of the system types (matrix) as in Fig. 6
2.1 Vibration exciter systems for vibratory rollers
The vibration and movement performance of vibra-tory rollers change with increasing stiffness of the soil layers which develops in the course of com-paction. This interaction between the reactive per-formance of the roller and the stiffness of the soil depends on soil specific and machine character-istic influence magnitudes. When weighting these influencing parameters a distinction must be made as to their effect on the compaction process. T
1, para. 2 describes the substantial vibration and
equipment parameters which interact in an accu-mulated way, depending on the type of machine.
Vibratory rollers work with various types of vibration exciters which, depending on design and system produce non-directed or directed rotational vibra-tions by eccentric masses.
2.1.1 Vibrator (circular vibrator)
The exciter system consists of a central drive and exciter shaft with an attached unbalanced mass. The fast rotation of the exciter shaft generates cen-trifugal forces rotating 360° with undirected rota-tion vibrarota-tions. This type of vibrarota-tion exciter is also known under the name single shaft rotation vibrator (Fig. 7).
2.1.2 Oscillator
The exciter system consists of a central drive shaft and two rotating exciter shafts with the same sense of rotation. The unbalanced masses of these toothed belt driven exciter shafts are 180° offset to each other, thereby generating a varying moment around the central axis. This exciter system gen-erates an oscillating, i.e. rotary movement of the drum, whereby the drum is permanently in contact with the soil, without any blows and impact (Fig. 8).
Circular vibrator Directed vibrator
Circular vibrator Oscillator
Directed vibrator
(Variomatic 1) Directed vibrator(Variocontrol)
Fig. 6
Vibration exciter systems
Fig. 7
Circular vibrator
With the oscillation principle, which has previously only been developed for and used in special com-pactors, it is assumed that the oscillatory move-ment of the drum together with the support of the effective axle load introduces a compaction effec-tive shear stress to the surface of the substrate.
2.1.3 Comparative compaction effect of vibrator and oscillator
Figures 9 and 10 show the results of measurements obtained from pressure and acceleration transduc-ers to compare the different performances of vibra-tor and oscillavibra-tor with respect to vertical pressures as well as vertical and horizontal accelerations. Figure 9 clearly shows that the maximum vertical pressures achieved by the vibrator are several times higher than with the oscillator and that the oscillator works statically without losing ground contact. The comparison in Fig. 10 reveals that, due to its princi-ple, the oscillator can only introduce minor vertical accelerations compared with the vibrator. From Fig. 10 the conclusion can be made, that the horizontal accelerations of the oscillator are also of minor sig-nificance in comparison with the vibrator.
Fig. 8 Oscillator system Tooth belt
Fig. 9
Vibrator, vertical pressure distribution Oscillator, vertical pressure distribution
Part 1
Fig. 10
Vibrator, horizontal acceleration Vibrator, vertical acceleration Oscillator, vertical acceleration
Oscillator, horizontal acceleration
The differences shown in the illustrations, which quantitatively only apply for the examined silty gravel, but qualitatively reveal the different compac-tion effects of both systems, can be explained by the fact that the vibrator has the effect of a combi-nation of directed vibrator and oscillator. Since the vibrator applies a higher pressure force the vibrator not only introduces a higher vertical compression, but also a higher shear stress than the oscillator.
2.1.4 BOMAG directed vibration systems
The directed vibration systems from BOMAG unify the advantages of rotary and oscillatory vibrators. With the newly developed directed vibration sys-tems VARIO for vibratory rollers a long striven goal of development and an important technological leap was achieved. These new self-controlling systems automatically detect and adjust the energy required for compaction. These systems are based on the analysis of the interaction between the drum and the stiffness of the material to be compacted. The compaction energy is automatically optimised by using the acceleration signals. This adaptation has the effect that the maximum possible compaction energy is transferred at any time, without the drum changing over to a unfavourable jump operation or causing any overcompaction.
For the compaction of asphalt a directed vibrator, the VARIOMATIC system (Fig. 11), was developed. This system consists of two counter-rotating eccen-tric shafts and generates directed vibrations. The direction of the resulting force can be automatically changed between vertical and horizontal (oscilla-tion), depending on the stiffness of the substrate, by simply offsetting one shaft in relation to the other. Both shafts are synchronised by a pair of gears. The control of the force direction is accommodated by a control circuit. The adjustment of the eccen-trics is accomplished by a hydraulically controlled adjustment cylinder with integrated way measuring system.
Two acceleration transducers pick up the stiffness data of the substrate and transmit these to a pro-grammable logic control (PLC), which then sends signals to the control unit. The exchange of signals is accomplished by a new, high-speed valve tech-nology.
The vertical component of the amplitude (effective amplitude), which is of major importance for the compaction, is automatically reduced before the machine changes to jump operation because of a too high stiffness of the soil or a too high effec-tive amplitude. This not only optimises the energy requirement, but also leads to a material preserving and uniform compaction.
Besides the automatic mode, in which the system controls itself, it is also possible to pre-select a cer-tain direction of vibration. In this case he can select from a choice of 6 vibrating directions between hori-zontal and vertical (Fig. 12).
The higher amplitudes needed for the large vibra-tory rollers used in earthwork led to the develop-ment of the VARIOCONTROL system (Fig. 13). This new exciter system with its vibrating mass of 9000 kg
generates vibration amplitudes of up to 2.5 mm and centrifugal forces of up to 500 kN. Two concen-trically arranged vibrator shafts carry three eccen-tric weights, the two smaller weights near the ends and the large eccentric weight in the middle of the exciter shaft (Fig. 14). The middle eccentric weight rotates in the opposite direction of the outer weights. The resulting centrifugal forces add up to a directed vibration. The effective direction of this directed vibration can be adjusted by turning the complete vibrator unit. Any desired angle position between horizontal and vertical direction of vibra-tion is possible. The control technology is based on the same concept as for the VARIOMATIC system. With increasing compaction the directed vibrator changes automatically from the vertical direction of vibration with high vertical acceleration towards the horizontal direction of vibration with a reduced effective amplitude. The amplitude is continually adapted so that areas with low stiffness are com-pacted with a high effective amplitude and areas with an already high stiffness with an appropriately lower effective amplitude. The offered compaction energy is thereby automatically reduced when the stiffness of the soil becomes too high. This method ensures that high amplitude generated by the vibra-tion system achieves a favourable depth effect already during the first passes and that a premature lid or plate effect can be avoided.
Fig. 11 VARIOMATIC 2 Vibratory roller with self-regulating
direction of force and effective amplitude
Fig. 12
VARIOMATIC Control unit
250 200 150 100 50 0 [mm]-4 -3 -2 -1 0 1 2 3 4 5 Bodenkontaktkraft [kN] 250 200 150 100 50 0 [mm]-4 -3 -2 -1 0 1 2 3 4 5 Bodenkontaktkraft [kN] 250 200 150 100 50 0 [mm]-4 -3 -2 -1 0 1 2 3 4 5 Bodenkontaktkraft [kN] 250 200 150 10050 0 [mm]-4 -3 -2 -1 0 1 2 3 4 5 Bodenkontaktkraft [kN] 250 200 150 10050 0 [mm]-4 -3 -2 -1 0 1 2 3 4 5 Bodenkontaktkraft [kN] 250 200 150 100 500 [mm]-4 -3 -2 -1 0 1 2 3 4 5 Bodenkontaktkraft [kN] 250 200 150 10050 0 [mm]-4 -3 -2 -1 0 1 2 3 4 5 Bodenkontaktkraft [kN] 250200150 100 500 [mm]-4 -3 -2 -1 0 1 2 3 4 5 Bodenkontaktkraft [kN] 250 200 150 100 50 0 [mm]-4 -3 -2 -1 0 1 2 3 4 5 Bodenkontaktkraft [kN] 130 120 110 100 90 80 70 60 50 40 30 20 10 0 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 [m] 6th pass 3th pass 1th pass EVIB [MN/m 2] Fig. 15
Dynamic stiffness EVIB
determined with the VARIOCONTROL system on silty gravel
Fig. 14
VARIOCONTROL, design of exciter system
Fig. 13
VARIOCONTROL single drum roller with automatic or selectable amplitude and stiffness control
FB
FZ
m . a
Acceleration measurement and recording of values
Rolling track
Processor
FB
S
E
VIBFB = Ground contact force
s = Vibration path
The angular position of the directed vibrator of the
Axle load, drum (Fstat) = static weight of drum and [kg]
drum frame
Axle load, drum (kg)
Static linear load = [kg/cm]
Drum width (cm)
Vibrating mass (M0) = Drum mass under vibratory motion [kg]
Number of revolutions of eccentric
Frequency (f) = , f = 1/T . n [Hz]
Unit of time
Angular velocity (ω) = 2πf [1/sec]
Unbalanced mass (me) = eccentric mass [kg]
Eccentricity (e) = distance between gravity centre of eccentric and rotation axis [mm]
Eccentric moment (Me) = eccentric mass, Me = me . e [kg . mm]
Centrifugal force (FC) = Fc = me. e ω2 = me. e (2πf)2 [N]
Unbalanced moment(Me)
Theoretical amplitude (a) = [mm]
Vibrating mass (M0)
Total weight
static linear load vibrating
mass amplitude frequency
Amplitude
Vibration path Time for revolution of eccentric
Mo
vement
Vibrating mass Eccentric mass Centre of gravity ofeccentric mass
Eccentricity
Fig. 16
Parameters of vibration generation
Part 1
VARIOCONTROL system can be used for a direct and surface covering determination of the dynamic stiffness of the soil (T 1, para. 2.5 and Fig. 15). For this purpose the ground contact force is determined on the basis of the accelerations measured on the vibrating part of the drum and a force-path-diagram is developed by integration of the acceleration. The ratio of the contact force to the related path of com-pression corresponds with the dynamic stiffness of the soil. The dynamic stiffness provides a physical magnitude as a measure for the compaction status. It can be directly measured and, in comparison with the previously used non-dimensional magnitudes, it is considerably less influenced by machine related parameters (amplitude, frequency, travel speed).
2.2 Parameters of vibration generation
On vibratory rollers the generation of vibrations is characterised by the machine related parameters listed in Fig. 16. In T 1, para. 1 these fundamental values are described in more detail (Lit 7, 8, 10).
2.3 Static axle load and vibrating mass
The statically effective mass consists of the drum axle load (kg). The static linear load is
mathemati-cally determined by the static axle load Fstat, divided
by the drum width (kg/cm). The drum diameter influ-ences the static linear load in as far as a high drum axle load requires an appropriately large diameter. When increasing the static axle load while leaving other influential parameters unchanged, the static and dynamic pressure strain applied to the soil by
the drum increase almost proportionally with the axle load. The penetration depth of this stress or the effective compaction depth increases accordingly.
The vibrating mass M0 contains all vibrating parts
of the machine, such as drum, hydraulics, mass of eccentric and others. The ratio of this vibrating mass to the mass of the suspended and statically effec-tive drum frame influences any compaction effect or the compaction depth. The compaction effect rises with increasing vibrating mass, while other parameters remain comparably constant, because the vibrating mass is dynamically coupled to the sympathetic mass of the soil layers (Lorenz 1934, Lit. 2). The vibrating mass changes with the vibra-tion amplitude generated by the centrifugal force. The increasing vibration amplitude mobilises also less sympathetic mass particles in the soil layers so that the natural frequency of the vibration system drops.
2.4 Centrifugal force, frequency, amplitude
Centrifugal force, frequency and amplitude are fun-damental machine related magnitudes which con-trol the energy transfer during compaction. However, depending on the type and stiffness of the soil their individual influence has different effects and they must therefore be weighted in a differentiated manner.
The centrifugal force FC is generated by the
eccen-tric mass me rotating with a rotary or angular veloc-ity e (revolutions per minute). The gravveloc-ity centre of the eccentric mass is centred at a distance e from the centre of the rotation axis.
Abb. 17
Position of eccentric in connection with the vibration path of the drum
Vertical amplitude
v
The diagram in Fig. 18, Lit. 3, confirms that the influ-ence of the frequency is limited and that there is no interrelationship between the mathematical vibra-tion force and the centrifugal force. Strong irregular impacts, as occurring during jump operation of the drum, may cause overcompaction or result in a decrease of density. During such jumping of the drum excessive vibrations are generated in the drum frame and the rubber damping elements between drum and fame are highly stressed. The variations in frequency only have a limited effect on the vibration force. The energy transferred into the base rises with a comparably constant vibration force and an increasing frequency. For this case the compaction energy VE per volumetric unit can be calculated by approximation (Yoo and Selig, 1980, Lit. 4).
VE = f1 (FIstat) + f2 (a . f)
f1, f2 = values of function,
FI
stat = static linear load (kg/cm),
a = amplitude f = frequency v = rolling speed The centrifugal force increases quadratic with the
angular velocity or the frequency f. The rotation velocity of the eccentric determines the number of revolutions n or the frequency of vibrations f = 1/T . n (frequency in Hz or vibrations per unit of time; see
T 1, para. 1.1). The nominal vibration amplitude a
(mm) depends on the magnitude of the eccentric moment Me (kg . mm)
The drum moves while the eccentric mass is rotat-ing. This movement is 180° out of phase (Fig. 17). The magnitude of the vibration force effecting the substrate is the result of a complicated interaction between drum and substrate. On the one hand, the centrifugal force is a fundamental unit for the calcu-lation of the vibration force, but on the other hand there is no interrelationship between the two mag-nitudes.
The effective vibration force is mainly activated by the vibration amplitude which, however, is not determined by the centrifugal force. However, the centrifugal force controls the vibration intensity (acceleration) of the drum. The centrifugal force can only be used for a direct comparison between var-ious types of rollers if both static mass and fre-quency are identical, because in this case they reveal the relative differences in amplitudes.
Fig. 18
Interrelation between vibration force and frequency (calculation example by Machet 1976)
Ko=5.107 M0=1600 C0=2.105 M1- M0=3400 K1=5.106 M2=1000 C1=9.103 me=1.0 M1-M0 M0 M2 K0 K1 C0 C1
M0 = vibrating mass of machine
(exciter mass) M1 = machine mass
M1-M0 = suspended machine mass
M2 = resonant vibrating soil mass
Me = unbalanced moment
K1 = resilient value of machine
K0 = resilient value of soil
C1 = damping of machine
C0 = damping of soil
Raising the vibration force up into the range of res-onant frequency has not gained practical signifi-cance, since the vibration level of the entire single drum roller increases extremely in such a case, placing extreme stress on roller and operator. Oper-ation with frequencies in a relatively stable fre-quency range slightly above the resonant frefre-quency is generally of advantage for soil and rockfill com-paction, whereby the resonance effect is also uti-lised to a certain extent.
Fig. 19
Influence of the frequency on the compaction amplitude
The optimal effect of vibratory rollers is normally achieved in the frequency range between 25 and 50 Hz (1.500 - 3.000 vibrations per minute). Through-out this entire frequency range both compaction and depth effect are not achieved to such a great extent by the frequency, but mainly by the size of the amplitude and the axle load of the drum (Fig. 19). This influence is apparent with all types of material, however, in dependence on their compo-sition very coarse particle or stony materials as well as cohesive-plastic materials require a high roller mass for an efficient compaction, as far as this is permitted by the shearing strength of these materials. High amplitudes transfer more compac-tion energy deep into the layer to be compacted, but achieve only a minor compaction effect in the upper zone of the layer. Low amplitudes produce only a slight compaction deep inside the layer, but transfer more compaction energy into the zone near the surface.
The material specific properties of the substrate thereby cause different reactions to the
compac-tion energy introduced by the vibratory roller. From practical experience the following exemplary values can be used:
• Compaction of soil layers with a relatively high lift height or a large soil volume as well as stony mate-rial: optimal amplitudes ranging from 1.5 to 2.0 mm and optimal frequencies ranging from 25 to 30 Hz (1.500 - 1.800 vibrations / minute). Compare with inherent natural frequencies of soil types acc. to table 1 (Lit. 1, 2).
Soil type Natural frequency Hz Upm Fine sand ~24 * ~ 1440 Non-uniform sand ~27 * ~ 1620 Medium sand, uniform ~24 * ~ 1440 Medium sand, uniform ~33 ** ~ 1980 Sand, moist ~24 ** ~ 1440 Sand, dry ~22 ** ~ 1320 Sand/gravel ~24-29 ** ~ 1440-1740 Loam, solid ~25-29 ** ~ 1500-1740 Loam, lose ~21-23 ** ~ 1260-1380 Clay, moist ~22 * ~ 1320 Clay, dry ~28 * ~ 1620 Lime, banked ~30 * ~ 1800 Mottled sandstone ~34 * ~ 2040 *H. Lorenz / **F. Fischer
Tabelle 1: Charakteristische Werte für bodenspezifi-sche Eigenfrequenzen (Lorenz, Fibodenspezifi-scher)
• Compaction of unbonded base courses: favour-ably in the above mentioned frequency and ampli-tude range, because of the high required degree of compaction.
• Compaction of asphalt layers as well as bonded and stabilised base courses, optimal amplitudes ranging from 0.2 - 0.9 mm and favourable frequen-cies ranging from 35 - 60 Hz (2.100 - 3.600 vibra-tions / minute).
The rolling speed of the vibratory roller, the increase of which results in a higher area output, has a sig-nificant influence on the compaction effect. The number of vibration impacts decreases with increasing rolling speed, so that more passes are required to achieve the same compaction effect. Within the normal rolling speed range and with a constant lift height the transferred energy is almost proportional to the ratio between the number of passes and the rolling speed.
When doubling the rolling speed, the number of roller passes should also be approximately dou-bled accordingly. Generally recommended rolling speeds are 1 to 2.5 km/h on rockfill material and clayey soils and 2 to 4 km/h on non-cohesive soils. For asphalt compaction rolling speeds of 2 to 4 km/h have proved most favourable for thick layers or stiff mixtures and 2 to 6 km/h for thin layers or soft mixtures.
2.5 Energy transfer
Energy transfer in the contact area of the vibrating drum as well as vibration and movement perform-ance of the rollers are substantially influenced by the reaction force and the dynamic stiffness of the layers to be compacted.
During the vertical movement of the drums the static weight forces, the spring and damping forces of the rubber buffers, the centrifugal forces, the inertial forces and the contact force are effective, as shown in Fig. 20.
Fig. 20
Vertically directed equilibrium of forces of the vibrating drum
The contact force contains the dynamic reaction forces of the base. Entering the contact force over the vibration path results in a force-path-diagram as shown in Fig. 21, in which the movement phases of compaction become apparent (example, Lit. 7, 8).
Part 1
The indicator diagram shows the ground contact force during compaction. The roller temporarily loses ground contact. During this phase of compac-tion the amplitude increases from 1.6 mm to almost 2.5 mm and the soil contact force to almost three times the static drum axle load. Due to the low soil stiffness and the low resonance influence of the static drum axle load both ground contact force and amplitude comply with the theoretical values at the beginning of the compaction process.
The indicator diagram enables an examination of energy transfer and soil stiffness. The hysteresis area between compression and expansion cycle shows the measurement for the energy transfer into the substrate. The area below the expansion curve reflects reactions to the drum. The inclination of the
compression curve ∆FB / ∆x is used to determine
the resilient stiffness of the base.
Fig. 22 shows measured indicator diagrams for amplitudes of various sizes (Lit. 7, 8). If the roller is used with various amplitudes, the energy trans-fer changes in accordance with the diagram. As shown in the diagram, the maximum reaction force increases in a degressive way with increasing amplitude. It clearly shows that a most favourable nominal amplitude exists for any drum axle load and that a higher static linear load in combination with a given amplitude also increases the reaction force of the base. The vibrating mass can only fully transfer the vibration intensity to the substrate, if the static axle load is fully applied to the substrate as a pre-load.
On base layers with a low stiffness the vibratory roller will not lose ground contact when vibrating with a low nominal amplitude and if the maximum contact force does not exceed two times the axle load (Fig. 22).
When continuing to increase the amplitude or the stiffness of the substrate, the roller can no longer fully transfer its movement. Its dynamic resting posi-tion moves up, so that it jumps up with each revo-lution of the exciter shaft when certain limit values are exceeded. In this jumping condition a frequency proportion is generated, which is half or an integer
Fig. 21
Exchange of energy between roller/soil and dynamic resilient stiffness of the soil
Compression and expansion phase during the compaction process
Presentation of the soil contact force in dependence of the vibration path of the roller drum (vertical compo-nent) in the indicator diagram (Kröber 1988)
Fig. 22
Indicator diagram for increasing compaction and different amplitudes (example)
multiple of the originally shown vibration frequency. This operating condition remains stable and repro-ducible under steady conditions.
With a further increase of the vibration amplitude or the stiffness of the substrate the roller becomes unstable and starts to tumble. Under this operating condition non-periodic vibration movements develop around the longitudinal axis of the drum with fre-quencies depending on the natural frequency of the vibration system (frame / vibrating mass).
3 Design types and applications for BOMAG compaction technology (Lit. 24 to 28)
3.1 Vibratory tamper
Vibratory tampers cause an impact compaction. The engine of the vibratory tamper drives a crank drive with conrod, which is clamped between two pressure springs. The vertical movement of the drive shaft results in a movement against the spring force. After a revolution the tamper plate lifts off the base and hits back after a 180 rotation of the crank drive. (Fig. 23 and 24)
Typical weights from 50 to approx. 100 kg. Fre-quency range approx. between 9 and 11 Hz (540 to 660 blows per minute).
An optimal compaction is normally achieved at fre-quencies around 10 Hz (600 blows per minute) with an amplitude range from 60 to 80 mm. Vibratory tampers are most suitable for applications in con-fined and difficult to access work areas, where only light compaction equipment can be used or rela-tively high and non-uniform layer thicknesses are required. Vibratory tampers are used for compac-tion of cohesive soils, mixed soils and gravely soils. For applications in narrow trenches, e.g. pipeline or cable trenches, vibratory tampers can be fitted with special small tamper plates.
Fig. 24
Design and equipment of the vibratory tamper
3.2 Vibratory plates/hydraulic plates
Vibratory plates normally work with frequencies between 55 and 90 Hz (3300 to 4500 revolutions per minute). The generated centrifugal forces are in the range between 25 and 86 KN (2.5 to 8.6 t). Machines are available up to weight of 700 kg. In comparison with vibratory tampers the compac-tion performance of the plates widens their appli-cational versatility. Depending on the soil type the depth effect of a vibratory plate may be as favoura-ble as the depth effect of large vibratory rollers. The dimensions of the plates and especially the work-ing width can be adapted to various applications. Due to the development of quiet machines and a more efficient vibration insulation of the guide han-dles the latest vibratory plates are much easier to manoeuvre than older types.
Vibratory plates are self-propelled or self moving (Fig. 25). A differentiation is made between plates which move only to one direction (Fig. 26) and plates with special controls to reverse the travel direction (Fig. 27).
Fig. 23
Movement sequence of vibratory tampers
Fig. 25
Movement sequence of vibratory plates
One-directional plates are equipped with only one exciter shaft. The amplitude depends on the mag-nitude of the unbalanced mass, the mass ratio between eccentric and vibrating parts as well as their centre of gravity. The maximum working speed, a design parameter for the development of such a machine, depends on the position of the exciter shaft and the position of the centre of gravity of the entire plate as well as on the ration of weight and centrifugal force.
This enables also the working speed in forward direction. This working principle is applied to narrow plates with low weight.
Fig. 27
Design and equipment of the vibratory plate (controllable in forward and reverse)
BOMAG plates with reversible working direction use two exciter shafts with double directed vibration. The two exciter shafts with their eccentric masses work in opposed position, whereby the direction of the forces generated by the centrifugal force also change. This enables reversing of the travel direc-tion from forward to the opposite direcdirec-tion during compaction. Furthermore, this allows for a control-led change of the working speed and therefore also of the intensity of compaction per pass. Heavy vibra-tory plates work with an operating weight of more than 120 kg according to this principle. The reversal of the working direction enhances the guidance of the machine and eases work. Heavier plates are equipped with electric starters for easier starting of the diesel engines.
Another rationalisation of compaction work is achieved by coupling hand guided BOMAG vibra-tory plates with a high total weight. This coupling enables forward and backward movement as well as turning on the spot. This application enhances power and mobility during compaction, e.g. in foun-dation excavations and backfills around buildings as well as adjacent foundation objects. Heavy revers-ible plates are also used for compaction work in trenches. For these applications the ventilation and filter systems must be specially adapted, the drive system must be well protected and sufficient lateral
Fig. 26
Design and equipment of the vibratory plate (controllable in forward direction)
machines are additionally equipped with dirt deflec-tors and fixed installations for lifting.
A new development is the steerable hydraulic plate with a vibrator system similar to the reversible mechanical vibratory plates. Similar to the reversible mechanical plates the steerable hydraulic plates are equipped with two counter rotating exciter shafts which are both fitted with an eccentric weight. The main differences of the steerable hydraulic plate are the hydraulically driven exciter unit and the rear exciter shaft. This shaft is designed in a way that the parts of the split eccentric weight can be offset to each other. This generates a torque that enables the operator to control the machine with-out a steering handle, i.e. withwith-out direct contact to the machine, via a remote control. With this working principle the machine does not only move forward and backward, but can also be steered to right and left.
Fig. 28
Working principle of the hydrostatically controlled vibratory plate
Besides their possible use for standard applica-tions, hydrostatic vibratory plates with remote con-trol (Fig. 28) are available for difficult work areas, such as deep trenches. These systems with cable, infrared or radio remote control relieve the machine operator and contribute to safe work in unsupported trenches.
3.3 Hand guided vibratory rollers
Hand guided vibratory rollers are available in single drum version or as tandem rollers (Fig. 29 and 30). Both types are self-propelled with reversible travel direction.
The operator controls and steers the machines by means of a steering rod. Compared with plates and tampers the mobility of these rollers enhances the compaction work. These rollers are used for soil as well as asphalt compaction and most frequently for small area repair and patch work.
Design and equipment of the hand-guided
single drum vibratory roller Fig. 29
Design and equipment of the hand-guided
double drum vibratory roller Fig. 30
Single drum rollers work with weights of 160 to 460 kg, high frequencies of 70 to 77 Hz (4200 to 4630 revolutions per minute) and amplitudes between 0.4 and 0.5 mm.
Hand guided tandem rollers have two drums of identical size with relatively small diameter. Each
drum is fitted with its own eccentric shaft. Both drums are driven, are connected by a rigid frame and are mechanically controlled by pulling or press-ing the steerpress-ing handle. Tandem rollers are also available with hydraulic controls, which reduces the controlling effort.
Depending on the state of technology hand guided tandem rollers are available with mechanical travel and vibration systems as well as with hydraulic drive and hydrostatic vibration systems. The hydro-statically driven system offers smoother response when changing the travel direction, which is of spe-cial advantage when compacting asphalt.
The machines work to their optimum when used on small work areas, for the compaction of soil and, if equipped with a water sprinkler system, on asphalt. The rollers have a very favourable centre of gravity and therefore develop high traction force on uneven ground. Special designs are available for use on trenches and on slopes.
3.4 Tandem rollers
Tandem rollers have two drums of identical diam-eter, each equipped with a exciter shaft. These machines are powered by an air cooled diesel engine. Travel and vibration systems are hydrauli-cally driven. Single lever control and infinite speed regulation enable jerk-free acceleration and decel-eration.
Tandem rollers are available with hydrostatic artic-ulated steering, heavier versions alternatively with hydrostatic pivot steering. A differentiation is made between light and heavy tandem rollers.
Light tandem rollers
The use of light tandem rollers enhances the area output of the compaction process, because these rollers are have a higher mobility, are faster and more manoeuvrable than hand guided rollers. These roller types were developed for the compaction of asphalt and are therefore equipped with water sprinkler systems. They can, however, also be used for soil compaction.
Light tandem rollers vary in the range between 1.5 and 4.5 t with working widths from 800 to 1380 mm (Fig. 31).
The most suitable working width can be chosen to match the site conditions. The static linear loads span from 8 to 15 kg/cm.
Theses machines are generally designed with double drum vibration and double drum drive and normally work with one frequency. By experience the machines in the range from 3 to 4.5 t have sufficient power to be used behind a paver with
an output of 500 to 800 m2
222
per hour on surface
courses or 300 to 400 m2
2
per hour on base courses, depending on the asphalt mixture. They are there-fore specially recommended for this type of appli-cation. Apart from this there is another type of application for these small self-propelled tandem rollers, which are available in different designs and successfully used.
Heavy tandem rollers
Heavy tandem rollers with operating weights between 6 and 12 t are used for the compaction of asphalt surface courses, asphalt binder courses, asphalt base courses and unbound base courses. They normally work with two amplitudes or two fre-quencies for an optimal compaction of different lift heights.
VARIOMATIC tandem rollers with the new directed vibration system described in T 1, para. 2.1.4 allow for an automatic adaptation of the effective ampli-tude to the material to be compacted.
Heavy tandem rollers are equipped with vibration automatic, a system which switches the vibration off when stopping the machine or when changing the travel direction, thereby avoiding transverse depres-sion and unevenness in the asphalt course. Heavy tandem rollers are available with spit and non-split drums. Split drums reduce the risk of shov-ing and crackshov-ing when compactshov-ing in tight curves. Depending on the design one must differentiate between tandem rollers with articulated steering and pivot steering, which enable different modes of steering (Fig. 32).
Design and equipment of a light,
articulated tandem roller Fig. 31
Heavy, pivot-steered tandem roller
with split drums Fig. 32 Combination rollers
The combination roller is a combination of pneu-matic-tired roller and vibratory roller (Fig. 33). The combination combines the advantages of the vibrating drum with the benefits of rubber tires, which have a kneading effect and seal the asphalt surface.
One axle of the combination rollers consists of a smooth drum, the other axle carries smooth rubber tires.
These rollers are also powered by air cooled diesel engines which drive the hydrostatic travel and vibra-tion systems. The rubber tires are driven in pairs by two hydraulic motors, ensuring adaptation of the left and right hand wheel pairs to the rolling speed differential when driving around curves.
Single lever control, hydrostatic power steering as well as vibration automatic ensure simple and safe operation of the large combination rollers.
Articulated combination roller with smooth drum and four rubber tires Fig. 33
3.5 Single drum rollers with smooth drum
Single drum rollers are self-propelled compactors with a front drum and rear tires (Fig. 34). These roller types are specially designed for soil compac-tion, where high tractive power and gradability is required besides excellent compaction work. Front frame with drum and rear frame are con-nected by a central oscillating articulated joint. The rear frame carries diesel engine, drive elements and operator’s stand. The infinitely controllable travel systems works hydrostatically via the rear wheels. Single drum rollers are normally equipped with drum drive. The vibration drive also works hydro-statically. Single lever control and hydrostatic power steering enable simple operation. Depending on the tire tread the single drum rollers achieve a grad-ability of up to 45%. For even higher gradgrad-ability the single drum rollers can be equipped with a stronger drum drive and an anti-spin-control (ASC). With these features the rollers can be used for gradients of up to 55%. Depending on soil or rock material the single drum rollers are used with smooth drums or with padfoot drum.
Smooth drums can be used on most soil types, from rockfill to cohesive soils. The single drum roll-ers are generally equipped with all-weather tires, which ensure favourable traction and gradability under most soil conditions. The operating weights stretch from 2 to 25 t. The heavy single drum roll-ers are normally available with 2 amplitudes and 2 frequencies for thick and thin layers (Fig. 34). In order to withstand extreme loads, e.g. during the compaction of rockfill, the drum must be of high strength and durability.
A long striven goal of research and development and a remarkable leap in technology was achieved especially with the newly developed VARIO vibra-tor exciters. These innovative self-controlling sys-tems detect the energy requirement and regulate the system automatically;see T 1, para. 2.1.4.
Design and equipment of a single drum roller
with one vibrating drum Abb. 34
Attachment of vibratory plates:
The attachment of hydraulically driven vibratory plates to the single drum vibratory roller extents the range of applications and rationalises compaction work. The depth effect of the single drum roller is thereby combined with the favourable surface effect of the plate, thereby achieving a higher compaction output with less passes.
With this combination the single drum roller com-pacts with the front drum and the vibratory plates attached to the rear at the same time (Fig. 35). The vibratory plates are driven by an additional
hydrau-lic pump on the single drum roller and work with an adjustable frequency of 32 to 50 Hz and a centrifu-gal force of max. 50 kN.
Single drum vibratory roller with hydrostatically
driven vibratory plates attached Fig. 35
Another possible application is the efficient soil compaction in highway and transportation engineer-ing, urban foundation and civil engineering projects or such projects under confined spatial conditions. This work requires compact and extremely manoeu-vrable single drum rollers in the 7 t - class, which can be optimally adapted to the permanently chang-ing fillchang-ing material while considerably reducchang-ing the vibration stress for nearby buildings at the same time. The use of the VARIOCONTROL system is therefore also recommended for these compact single drum rollers.
3.6 Single drum rollers with padfoot drum
Padfoot drums are designed for the compaction of cohesive soils and mixed particle soils with a rela-tively high water content. The imprints of the pad-feet contribute to a reduction of the water content. They are also used for the compaction of rockfill, in order to reduce the air void content and to crush large particles. As an adaptation to very moist, slip-pery soil conditions single drum rollers with padfoot drums are equipped with extremely profiled tires, similar to tractors, as a measure to enhance the traction power. These single drum rollers need a highly durable drive system. From the present point of view separate drives of drum and wheels should be standard.
BOMAG padfoot rollers are equipped with special teeth (Fig. 36). With their shape and in combination with vibration they should achieve a kneading and impact or crushing effect together with a favourable depth effect:
- Pyramid teeth (high studs, small contact areas, extremely steep flanks) for intensive kneading and compaction of cohesive soils,
- Triangular teeth for crushing of hard rock by means of high tip pressure and splitting forces, - Triangular teeth with cutters in between for the splitting and crushing of brittle rock, whereby the cutters in between also prevent jamming of parti cles between the teeth (Fig. 37).
Single drum vibratory rollers with with special teeth
Fig. 36 BW 225 with 120 triangular teeth and additional wear resistant tips, H = 200 mm
BW 225 with 100 pyramid teeth, H = 150 mm BW 225 with 150 standard teeth, H = 100 mm
BW 225 with 100 triangular teeth and cutters in between, H = 200 mm
Crushing of claystone by special padfoot roller drum with triangular teeth and cutters in between
Fig. 37
The latest BOMAG class of heavy single drum vibratory rollers (BW 225, 18 t drum axle load, 80 kg / cm static linear load) is a special development for the compaction of rockfill material, extremely stony cohesive soils as well as high lift heights. After compaction the teeth leave a structured sur-face (Fig. 38). In these impressions water can col-lect, which increases the water content of the soil when a new layer is placed. On the other hand the structure enlarges the surface of the soil, so that it can dry out more quickly during dry periods or by wind. In most cases it may be necessary to follow the padfoot roller with a smooth drum roller after a short period of time, in order to seal the open tex-ture
Compaction work with a single drum roller
equipped with a padfoot drum Fig. 38
Especially suitable are single drum rollers with an anti-spin-control to achieve the favourable tractive power in a controlled manner. These systems are of highest significance for an economical compaction when a high gradability of the machine is required (Fig. 39). Furthermore, this system enables safe operation on inclined areas.
High gradability during compaction work
due to the anti-slip system Fig. 39
