Soil compacting apparatus

A soil compactor has (1) an apparatus preceding it to measure characteristics of the soil significant to the compaction operation, and/or (2) an apparatus following it to measure characteristics of the soil after compaction. The soil compactor has one or more controls over the compaction operation. The controls are operated in accordance with the measurement indications of said apparatus.

BACKGROUND AND SUMMARY OF THE INVENTION 
The invention relates to soil compacting apparatus in which one or more 
operational characteristics such as the rotational speed of the exciter, 
the unbalance, the direction of force or the traveling velocity may be 
varied and which has measuring means and adjusting means for varying the 
operational characteristics, which adjusting means may be influenced in 
accordance with the signal delivered by said measuring means. 
Soil compacting apparatus, in particular apparatus in which the soil is 
compacted by vibrations, such as plate vibrators and rollers with 
vibrating barrels are frequently provided with systems, known in the prior 
art, by means of which the kind, magnitude and duration of the effects 
produced by the apparatus on the soil which is to be compacted may be 
adjusted either in steps or continuously; for example, such systems may 
vary the velocity at which the apparatus is driven or pulled over the soil 
which is to be compacted or they may vary to the magnitude of the 
centrifugal force exerted by such apparatus. The said force may be altered 
in compacting apparatus with unbalance excitation by means of the 
unbalance, the excitation rate being retained, and it may also be varied 
together with the rotational speed of the exciter; it is also possible to 
vary the unbalance and rotational speed of the exciter relative to each 
other so that a new vibrator frequency is obtained with the same vibration 
intensity. In addition to varying the aforementioned two characteristics 
it is also possible to vary the principal direction of the centrifugal 
force of a working part, either by pivoting the exciter or by phase 
displacement between the rotors in the case of exciters with two or more 
mass force generators. The phase relationships of the vibrations of soil 
compacting apparatus with a plurality of working parts may also be varied, 
for example in a first setting to produce a simultaneous maximum action on 
the soil or in a second setting to produce an alternating effect. 
Experience has shown that the kind of soil compacting apparatus, which may 
be adjusted in the manner described hereinabove, do not provide optimum 
compacting results on all soils if the previously mentioned operating 
parameters are fixedly defined, but that instead it is advantageous for a 
high vibration frequency to be applied to one soil while a low centrifugal 
force is more advantageous for another soil and a sliding rather than 
pressing stress is more advantageous for yet another soil. Manufacturers 
of dynamic soil compacting apparatus therefore provide adjusting means of 
the kind mentioned heretofore to provide a wider range of applications for 
such apparatus and to render them universally usable. 
In practice there are however substantial difficulties which militate 
against the envisaged technical progress being achieved. The first and 
basic reason is due to the fact that the relationships between the action 
produced by the compacting apparatus on the soil and the displacement 
phenomena which occur as the result of such action are substantially 
unknown: according to the prior art, the user is not yet in a position to 
optimize the vibrator frequency of the apparatus in accordance with 
accessible soil properties such as particle distribution and water content 
based on experience or in terms of a mathematical formula. 
A further reason is due to the relationship between the vibration 
technological characteristics of the soil compactor and a change, for 
example, of the centrifugal force. Most dynamic soil compacting apparatus 
operate by so-called "jump" progress, that is to say, the exciter force 
raises the working parts from the soil in certain phases; the parts then 
perform a ballistic motion initiated by the exciter force and strike the 
ground at a moment of time which is defined substantially by the laws of 
free fall, at which time the exciter force is not necessarily orientated 
towards the soil. This synchronism between impact pulse and simultaneous 
exciter force, frequently desirable for intensive compacting, can be 
disturbed by even slight changes - including increases - of the unbalance 
or centrifugal force so that the "so-called" jump characteristics of the 
affected working part which defines compaction may experience fundamental 
changes which cannot be quantitatively controlled. 
Finally, there are also certain properties of the bulk itself which is to 
be compacted which may prevent the desired success being achieved even if 
the aforementioned problems are assumed to have been solved. The intrinsic 
dry bulk density of a dumped material fluctuates, rarely less than 3% and 
frequently more than 5% and this also applies to local differences of 
water content. The initial fluctuations are retained almost unchanged 
after final compactions at Proctor values not substantially in excess of 
100% if the dumped material is uniformly worked with a compacting 
apparatus; the final density, assuming a uniform initial bulk density, is 
practically proportional to the local water content since this, in the 
same way as in the Proctor test, has a noticeable effect on the compaction 
achieved with a defined compacting energy. If steps are to be taken to 
ensure that minimum dry bulk weight values are obtained for a given 
compacting problem, these fluctuations must be added to the test value, 
which, although it amounts to only a few percent, nevertheless results in 
a substantial increase of the work input. 
Proposals have been made according to which the adjustment of suitable 
machine parts or the variation of their characteristic values is related 
to measured values which are recorded during the compacting operation. A 
first apparatus of this kind comprises a seismic acceleration pick-up 
disposed on a working part, subjected to superimposed loading, and 
manually operated means for varying the rotational speed of the exciter; 
it is desirable for the said rotational speed to be maintained at or close 
to the value at which the acceleration pick-up delivers its maximum 
signal, that is to say, the system comprising the working part and the 
soil being approximately at resonance under the effect of the periodic 
exciter force. The disadvantages of this solution to the problem are not 
only the basic limitation to the control of superimposed load working 
parts - resonance conditions do not apply to jump operation either in 
terms of appearance or by way of concept - but also the fact that 
co-control of the exciter force through the rotational speed and due to 
the frequently super-critical damping resulting from friction in the soil 
it is not possible for the resonance to become sufficiently clearly 
defined and in these cases there is no adequately significant matching 
criterion for manual regulation. 
It has also been proposed to measure the impact energy of a dynamic soil 
compacting apparatus component which functions in jump operation for the 
purpose of controlling the traveling velocity of the apparatus relative to 
said measurement. A common feature of the proposals is the idea of 
utilizing the operating characteristics of the compacting apparatus as a 
controlled condition in terms of process control technology, the 
compactness produced by the apparatus being the "desired value". Such 
solutions to the problem suffer from the defect that the relationship 
between the "desired value" and the appropriate controlled condition is 
hypothetical because, despite intensive research, it has not been possible 
to establish a generally valid relationship between the dry bulk density 
of a soil on the one hand and the vibration characteristics of a dynamic 
compacting apparatus operated on said soil. Apparatus of this kind 
therefore merely shift the problem of determining suitable operational 
parameters of the compacting apparatus, that is to say, defining the 
relationship between these two magnitudes in a specific, individual case. 
Although progress is achieved, the problem is not yet solved but its 
extent is merely limited and expressed in concrete terms. 
The object of the present invention is to provide means for varying the 
operating parameters of soil compacting apparatus during operation based 
on measurements but in conditions which are free of previous limitations; 
this includes primarily the process-dependent relationship to the 
superimposed loading or "jump" operation of the compacting apparatus or 
its working parts and the condition of validity of the relationships 
between measured value and "desired value" which must be defined, tested 
and allowed for independently of the apparatus in question. 
The invention is based on the idea to arrange the methods for recording 
measured values so that on the one hand they become independent of the 
vibration characteristics of the apparatus or its working parts and on the 
other hand can be related to soil characteristics, relevant to output, 
more directly than this is possible according to the prior art. 
In this sense it is a further object of the invention to differentiate the 
solution of the general problem in accordance with different performance 
features, for example, relative to the compressive strength or shear 
strength in addition to the compactibility. 
According to the basic idea of the invention, the measuring means are 
constructed as measuring transducer for physical soil characteristics of 
the soil which is to be compacted or which is to be partially or solely 
compacted. 
According to the invention, the vibration characteristics of the soil 
compacting apparatus are not utilized as controlled condition as in the 
prior art but the physical soil characteristics themselves are utilized to 
function as controlled condition. 
The invention may be performed by trailing measuring means being provided 
which are constructed as measuring transducers for detecting physical soil 
characteristics after a pass of the soil compacting apparatus. This is not 
genuine regulation since the soil compactor operation characteristics, 
influencing the compaction of the soil which is to be freshly compacted, 
are varied in accordance with the characteristics of the soil which has 
already been compacted, this change of the operating characteristics of 
course having no further effect on the characteristics of the soil which 
is already compacted. Nevertheless, the method may be employed since 
generally it is possible to assume a degree of constancy of the soil 
characteristics. 
The trailing measuring means may be constructed as measuring transducer for 
one or more of the following physical soil characteristics after the 
passage of the compacting apparatus or individual working parts thereof: 
(a) compactibility 
(b) coefficient of soil reaction 
(c) shear strength 
(d) continuous vibration impedance 
(e) pulse or impact impedance 
(f) penetrometric properties of the soil surface 
(g) set of the soil surface. 
One or more command signals may be transmissible to the final control means 
in the manner of command values in process control technology, the signals 
of the measuring transducers and the command signals being connected in 
opposition to each other in an adding stage and, where appropriate, being 
adapted to act through a control amplifier on the final control means. 
Finally the object of the invention is to achieve the desired advance, 
possible, according to the prior art, only by utilizing hypotheses on the 
relationship between the measured value and the desired value by adopting 
a solution to this problem of the unknown part of the controlled 
apparatus. 
In this connection the invention is based on the principle that 
advantageous or optimum adjustment of the operational parameters of 
dynamic soil compacting apparatus cannot be achieved with means and models 
of conventional process control technology owing to the special features 
of the particular art in question. Process control technology is based 
throughout on a knowledge of the relationship between measured value and 
final control value, that is to say, the characteristic of the controlled 
apparatus and only in this way is it possible for the control deviation to 
form the final control value which will sensibly drive the functional 
value in terms of magnitude and direction to the reference value. In the 
present case, the soil to be compacted represents at least part of the 
controlled apparatus and is therefore variable not only from building site 
to building site but also within individual compacting areas and 
furthermore it has a noticeable effect on the operating characteristics of 
the apparatus and moreover defines its reaction to changes of the final 
control element, for example, the throttle of the prime mover for 
controlling the rotational speed. 
A further embodiment of the invention therefore provides that supplementary 
signals of very low frequency may be additively superimposed on the 
command signals and a transfer signal is formed by a multiplier from the 
changed command signal and the measuring transducer signal changed thereby 
through the controller and the controlled part of the apparatus, the said 
transfer signal being adapted to vary the transfer coefficient of the 
controller through another multiplier. 
The following means may be used for measuring the compactibility of the 
soil before, after and during the pass of the compacting apparatus: 
Radio isotope measurements with gamma rays; in this measuring system a 
receiver measures the intensity of the reflected radiation which expresses 
the moist bulk density of the soil by reference to a relationship which 
must be empirically determined and which is practically independent of the 
soil. Since it is not necessary for these means to be manually moved it is 
possible for shieldings to be thicker than those of conventional field 
probes and accordingly it enables sources to be employed which have 
activities higher than 20 mC and thus enable the integration periods for 
the receiver pulses to be reduced. This method may be combined in known 
manner with corresponding measurement of back scattered thermal neutrons 
to enable the dry bulk weight to be displayed. 
Measurement of the electric soil resistance by means of a four-probe 
system. The said four-probes are preferably formed by four substantially 
disc-shaped members with semicircularly radiused edges, electrically 
insulated from each other and guided on a common shaft. They are rolled 
over the measuring position with a corresponding slight pressure. The 
current passing through the outer probes and required to maintain a 
controlled voltage between the inner probes is a clear measure for the dry 
bulk weight if the water content is known. 
A test ram or a test baulk, bearing hydraulically on soil at a defined 
pressure, for example 5 kgf/cm.sup.2, may be used as means for measuring 
the compactibility coefficient of the soil (elastic constant referred to 
the loaded surface) the amount of set being recorded and stored by a 
transducer on the baulk guide from the initial contact to approximately 5 
seconds after full load is reached. To otain a rapid sequence of such 
measured values it is possible for a plurality of test baulks of the kind 
heretofore described to be disposed on the circumference of a 
hydraulically operated measuring cylinder - individually freely rotatable 
over corresponding angular ranges. 
A plate or baulk, placed on the ground at a pressure of approximately 1 
kgf/cm.sup.2 and then retained in its vertical position is suitable as 
transducer for measuring the shear strength of the compacted soil. The 
measuring transducer in the more closely defined sense is a dynamometer 
for defining that force, applied to the said plate by the compacting 
apparatus or by the tractor, at which the said plate begins to move (in 
the direction of the force) relative to the adjacent soil surface. The 
barrel of a roller, rolling with moderate pressure on the soil and driven 
by an unbalance exciter, may be used for measuring the continuous 
vibration impedance. In acceleration pick-up with a vertical operating 
direction defines the accelerations of the measuring roller and therefore 
also of the soil under the effect of the alternating harmonic force 
transmitted under the effect of the exciter; the ratio of these two 
magnitudes is the impedance of the soil. 
The pulse or impact impedance is the reciprocal of the Laplace-transformed 
derivation of the weight function (referred pulse response). The zones of 
minimum frequency, corresponding to those time intervals from the pulse 
time at which the deformation velocity becomes zero, that is to say, when 
the soil begins to swing back, are of significance for a knowledge of the 
soil characteristics. If the soil is hard-elastic, these periods will be 
short. If on the other hand the soil characteristics vary from plastic to 
plastic-flowing, these periods of time will be long to practically 
infinite. The values may be measured by attaching a velocity pick-up on a 
drop weight, the said velocity pick-up being adapted to operate an 
integrating member from the time of impact to the time at which its output 
signal becomes zero; the measured value is the appropriate final value of 
said integrator. 
Penetrometric soil properties can also be measured by a system 
incorporating a cylinder which rolls under a certain thrust on the soil, 
the cylinder barrel having teeth or spikes surmounted upon it which, under 
the applied thrust, penetrate to a greater or lesser depth into the 
surface of the soil. The penetration depth is measured by a distance 
transducer, for example, as the distance between the axis of such a spiked 
cylinder and a smooth cylinder, guided axially parallel thereto and also 
rolling on the soil. 
It is not usually possible to base the operation of soil compacting 
apparatus which is to be suitable for any kind of material to be 
compacted, on a knowledge of the characteristics of the controlled system. 
It is therefore not possible to predict the sense in which the operating 
characteristics of the apparatus, for example, the unbalance, must be 
changed in the event of a deviation of the measured soil characteristics 
from a set value in order to cause such deviation to disappear. Modulation 
of the command variable in conjunction with multipliers for automatically 
changing the control characteristics will be utilized in the above 
described manner for such apparatus. It is also possible for multi-purpose 
apparatus to be provided which can be switched to different pre-programmed 
control characteristics for the purpose of adaptation to different 
materials if the effect of a change of operating characteristics on the 
achieved compaction is known. Finally, it is also possible for 
single-purpose machines to be provided which are intended for use on soils 
with a uniform or rather similar relationship to one operating 
characteristic and in which the regulating direction and slope of 
regulating direction are designed and defined with respect to the purpose 
of the apparatus. Finally, it is also possible for leading measuring means 
to be provided, said means being constructed as a measuring transducer in 
front of the compacting apparatus or the first working member thereof for 
one or more of the following soil-physical characteristics: 
(a) Compactibility 
(b) Water content 
and that the signals of the leading measuring means may be applied to the 
regulating means in the sense of disturbance-variable feed-forward.

DESCRIPTION OF SPECIFIC EMBODIMENTS 
FIG. 1 shows a basic embodiment of the invention. The soil compacting 
apparatus to be controlled in this case is a known double vibratory roller 
1, the rollers thereof forming compacting elements. At its front it guides 
leading measuring means 3 mounted on a frame 2 which may be pivoted 
upwardly. The measuring means shown in FIG. 1 is not detailed. It may, for 
example, be provided for measuring the compactibility of the soil being 
worked. Auxiliary apparatus required for functioning of the measuring 
means 3 are disposed in the enclosed container 4, in particular the 
electronic system required to this end. 
At its rear the compacting apparatus 1 has trailing measuring means 6 
mounted on a frame 5. This measuring means may comprise apparatus for 
mesuring one or more of the seven soil characteristics hereinbefore listed 
in subparagraphs (a) to (g) of the Background And Summary of the 
Invention. The measured values generated thereby either as such or in 
conjunction with the measured values provided by leading measuring means 3 
are processed to yield control signals in apparatus disposed in the 
container 7 which is also provided with setting means or controls 8 and 
indicating means 9 which are in the field of view and within operating 
reach of the driver of the apparatus. Furthermore, the signals supplied to 
the indicating means 9 may also be utilized for generating the control 
signals for automatic control or regulation, for example, of the traveling 
speed of the compacting apparatus 1. 
FIG. 2 is a general signal flow chart according to the basic idea of the 
invention. The numeral 11 refers to a measuring means in accordance with 
leading measuring means 3 of FIG. 1. The output signal of said measuring 
means is supplied to a store 12 which receives and maintains that signal 
until a succeeding measured value is established. Another store 13 is 
associated with the measuring means 14, which is a trailing measuring 
means such as that illustrated at 6 in FIG. 1. A number of specific types 
of measuring means usable for measuring means 14 is subsequently discussed 
in connection with FIGS. 6-7, 8, 9-11, etc. Before use the output signals 
from the sensor thereof are suitably processed by a processing circuit, as 
for example FIG. 13. Store 13 receives and maintains the measured values 
(actual value signal) from measuring means 14 until the succeeding 
measured value is established. The contents of the store 12 are 
transferred to an adding stage 16 through a delay element 15, the delay 
period of which corresponds to the time required for the apparatus to 
travel over the distance between the leading and trailing measuring means. 
The signals from the store 13 are also supplied to the aforementioned 
adding stage. An adjustable fixed-value transmitter 17 generates the 
command signal. A generator 18 produces individual squarewave pulses 
having a duration of, for example, 8 seconds. Generator 18 is triggered 
through its starting input 19. The outputs of the fixed-value transmitter 
17 and of the genertor 18 are also supplied to the adding stage 16 through 
an adding element 20. 
In terms of process control technology, the three inputs of the adding 
stage 16 have the following significance. Data from the store 13 
represents the actual value of the automatic control. Data supplied from 
the delay element 15 represents a form of disturbance-variable 
feed-forward. The signal of the fixed-value transmitter 17 corresponds to 
the command variable of the automatic control and the output signal of the 
generator 18 corresponds to a command variable feed-forward. 
After being subjected to intermediate amplification in an amplifier 21, the 
output signal of the adding stage 16 is supplied to the first input of a 
multiplier 22. The output thereof acts on the soil compacting apparatus 
24, like the one shown in FIG. 1, through a converter 23 which, in terms 
of process control takes the form of a final control drive, the said 
apparatus 24 by virtue of its compacting function varying the soil 25 to 
yield the actual value of the process control function as represented by 
measured signal from the measuring means 14. The basic control circuit 
included in FIG. 2 therefore comprises the units 14, 13, 16, 21, 23, 24 
and 25. In the simplest embodiment of the invention (for single-purpose 
machines with manual control) the multiplier 22 may take the form of an 
indicating instrument for the output signal of the intermediate amplifier 
21 and the converter 23 may take the form of manual adjusting means like 
indicating means 9 and controls 8 in the double vibratory roller 1 as 
shown in FIG. 1. The fixed-value transmitter 17 in this embodiment will 
then also be replaced by a mark on the indicating instrument. In 
single-purpose machines with automatic control the output signal of 
intermediate amplifier 21 is fed to the first input of the multiplier 22, 
the second input of which is provided with a fixed voltage transfer signal 
(from a transfer signal generating means, not shown) so that this 
component transfers data to the converter 23 under fixed transfer 
conditions. In multi-purpose machines the transfer characteristics of the 
multiplier 22 are varied by a variation in the fixed voltage supplied to 
the second input so that a plurality of discrete characteristics are 
obtained. 
In the embodiment for multi-purpose machines the second input value of the 
multiplier 22 is formed in the following manner, utilizing the square-wave 
generator 18. The lower input of the differential amplifier 26 is supplied 
with the instantaneous value of the command variable, formed by the adding 
amplifier 20, the second input being supplied by a value of this quantity 
which is delayed by the store 27. Corresponding conditions apply to the 
differential amplifier 28 and the store 29, but in this case with respect 
to the measured value signal from the measuring means 14 of the trailing 
measuring means 6 instead of with respect to the command variable. The 
output quantities of the differential amplifiers 26 and 28, supplied to 
the further multiplier 30, therefore correspond to the differences between 
the instantaneous value of command variable and the measured (actual) 
value with respect to the values possessed by these quantities at an 
earlier moment of time, defined by further structural components which 
will be described hereinbelow. The multiplier 30 forms an output signal 
which substantially corresponds to the product of these two differences 
and which is supplied to the input of a classifying stage 31. The product 
signal, thus graded, is supplied through a controlled gate 32 to a holding 
element 33 and from there to the second input of the multiplier 22. 
The controlled condition, as yet unevaluated, is tapped off from the 
position designated with the letter a between the amplifier 21 and the 
first multiplier 22 and is supplied to a minimum value limiting stage 34. 
The signal then passes through the succeeding totalizing stage 35 to a 
pulse stage 36. A pulse b will occur at the output of the pulse stage 
whenever the unevaluated controlled condition a is exceeded by a defined 
amount which, in the sense of automatic process control technology, may be 
described as a permissible deviation. At first, this pulse will set the 
output of the holding element 33 to a fixed value which is independent of 
the remaining quantities of the control system; furthermore, the pulse 
will also drive the gate 32 and start a timer 37 which defines the 
duration of the command variable feed-forward. The stores 27 and 29 are 
reset when an output signal appears on the timer 37, the said stores being 
set to receive signals for the measured value and the command variable. 
Disappearance of the output signal of the timer 37 also causes the gate 32 
to be driven to cut off. The pulse also starts the generator 18 via the 
input 19 to form the command variable feed-forward signal. 
FIG. 3 is a basic system of the multipliers 22 and 30 employed in the 
control system as shown in the flow chart of FIG. 2. The voltages supplied 
to the two inputs 41 and 42 of such a multiplier are supplied to an adding 
stage 43 and a differentiating stage 44 and from there via squaring stages 
45 and 46 to a differentiating stage 47. The function of such a stage is 
determined by the fact that the pure squares of the input values cancel 
each other in the terminating differentiating stage and the mixed products 
are added. FIG. 4 shows a possible embodiment of the squaring stages. In 
this case, the signal to be squared is first superimposed in an adding 
stage 48 on the output signal of a saw tooth generator 49, the frequency 
of said generator being higher by one order of magnitude or more than the 
characteristic frequency of the signal which is to be squared. The output 
signal of the adding stage 48 is supplied to a rectifier stage 50 with 
minimum value suppression, so designed that the suppressed zone 
corresponds to the sweep of the saw tooth generator 49. The proportions of 
generator voltage of higher frequency are filtered out from the square of 
the measuring voltage thus obtained in the succeeding integrating stage 
51. The squaring function of such a stage is obtained by virtue of the 
fact that the saw tooth voltage of the generator 49 cannot pass through 
the rectifier 50 when the measuring voltage disappears, but if a 
non-disappearing measuring voltage is superimposed, those peaks of the 
generator voltage the amplitude of which corresponds to the instantaneous 
value of the measuring voltage will pass through the rectifier 50. The 
timing characteristics of the voltage peaks thus produced on the output of 
the rectifier 50 represent similar triangles the height of which 
corresponds to the measuring voltage. According to a known principle of 
geometry, the areas of these triangles, that is to say the charges 
transmitted by the said pulses and therefore the voltages which appear 
across the integrating capacitor, vary as the squares of the heights of 
the triangles. 
FIG. 5 show a possible embodiment of such a rectifier 50 with minimum value 
suppression. Together with the push-pull amplifier 52 and the two 
rectifiers 53 it initially represents a known full-wave rectifier. The 
half-wave voltages which appear across the working resistors 54 of said 
rectifier are isolated from the stage out-put 56 within the limiting zone 
by means of zener diodes 55 and are generally transferred to the output 56 
only with that voltage proportion by which they exceed the breakdown 
voltage of the zener diodes 55. 
FIG. 6 and 7 show an embodiment of trailing measuring means for determining 
the moist specific gravity of the soil by radio isotope measurment. The 
trailing measuring means are formed by in a single-axle trailer formed by 
the wheels 61, the shaft 62 and the drawbar 63. Two disc cams 64, the 
outer edge 65 of which is circular over a wide angular zone and extends 
more closely to the axis of the apparatus in the remaining angular zone, 
is coupled to the shaft 62. A roller support 68, the supporting rollers 69 
of which are adapted to engage in the inner running surfaces of the disc 
cams 64 is mounted on the surface probe 66 by means of a powerful leaf 
spring 67. The counting apparatus 71 is mounted on a pivoting support 70 
on the shaft 62 adjacent to the aforementioned disc cam 64, the counting 
pulses being supplied to said counting apparatus 71 through a lead 72 from 
the probe 66. The roller support 68 of the supporting rollers 69 is also 
provided with a contact transmitter 72a from which a control signal is 
supplied to the counting apparatus 71 when the disc cams 64 release the 
supporting rollers 69 and the probe 66 is disposed freely on the coil 
surface. In operation the disc cams 64 periodically raise the surface 
probe 66, convey it forward and deposit it for a defined period of time 
(dwell) on the soil surface. During this dwell period of the probe 66 the 
input of the counting apparatus 71 is rendered conductive by the signal of 
the contact transmitter 72a so that the counting apparatus is able to 
transmit the counting rate, corresponding to the moist specific gravity of 
the soil, through the signal conductor 74 to the measuring and control 
system elements according to FIG. 2. 
FIG. 8 is an embodiment of measuring means which may be employed as leading 
as well as trailing measuring means for continuously determining the dry 
specific gravity or the water content of the soil according to an electric 
measuring method. The measuring means is also constructed in the form of a 
single-axle trailer, the four running discs 81 also representing the 
measuring probes. Of these four discs, the two inner running discs 
represent the voltage probes; they are fixedly joined to each other by 
means of a cylindrical support member 82 in which the battery-operated 
electronic circuit 83 design is accommodated. The two coaxially disposed 
outer current probes are guided by torsion-resistant and flexible axle 
coupling elements 84 so that a uniform soil contact of all four running 
discs 81 is obtained in conjunction with the forces of the leaf springs 85 
which act on the outer ends of the axle. The signal, delivered in this 
embodiment through the slip rings 86 and the signal conductor 87 
corresponds to a current flow through the outer probes required for a 
controlled and maintained voltage between the inner probes and, as is 
known, is a direct measure of the dry specific gravity of the soil when 
the water content is known. 
FIGS. 9 to 11 refer to an embodiment of trailing measuring mean for 
determining the compactibility of a soil. The apparatus is constructed as 
a two-axle trailer, the axle which leads in the traveling direction being 
adapted to support a container 91 which may be filled with water or 
building material in order to provide adequate loading of the said axle. 
The two identically constructed axles of this apparatus have the following 
construction. Separate wheel discs 94 run on the right-hand and left-hand 
sides respectively of shafts 93 which are fixedly disposed at the frame 92 
of the trailer. Thrust members in the form of tiltable rams 95 are 
disposed at equal distances from each other on the circumference of each 
said wheel disc. The wheel discs 94 are positively coupled to each other 
through a hollow shaft 96 and through a chain drive 97. Centrally on each 
shaft 93, the vehicle is provided with a smooth roller 98, having a hollow 
boss 99 on both sides which surrounds the hollow shaft 96 and which is 
coupled thereto through a flange 100, a universal joint 101 and a radius 
rod 102, the hollow shaft 96 being freely rotatable in the bearing 103 of 
the radius rod 102. The radius rod 102 supports a gear rim 104 in the 
shape of a circular sector and adapted to mesh with a gear wheel 105 the 
shaft of which is provided with measuring means, not shown, in the form of 
a distance transmitter. 
This apparatus functions in the following manner. Under the effect of 
material filled into the container 91, the weight of said material acting 
through the frame 92 and the wheel axle 93 causes the front axle rams 95 
located in the respective lowest position on the running discs 94 to 
penetrate into the soil, while the smooth roller 98 is guided by the 
radius rod 102 and rolls on the undisturbed soil surface. The angular 
position of the gear wheel 105 or the output of the measuring means driven 
thereby therefore represents a measure of the depth to which the rams 95 
penetrate into the soil. Positive coupling of the front and rear trailer 
axle simultaneously provides a measured value for the penetration of rams 
95 on the rear wheel discs at a position of the soil on which 
corresponding rams of the leading wheel discs had previously acted. 
FIG. 12 illustrates these relations in a simple thrustset diagram. Staring 
from point 111 of this diagram, the curve 112 shows the penetration of 
rams on the loaded leading wheel discs into the soil to a maximum value 
113 (set value) S1) which corresponds substantially to the traveling phase 
illustrated in FIG. 9. As the measuring apparatus continues to travel, the 
soil loading is reduced at this position and the set is reduced in 
accordance with the curve section 114 to a value S2 which is then measured 
by the rear wheel discs of the measuring trailer. The ratio of maximum set 
S1 to permanent set S2 or the reversible set S1- S2, evaluated by 
reference to the maximum loading, may be used to indicate the degree of 
compaction of the respective soil 25 and to form suitable measured values 
to serve the function of the signals supplied by measuring means 14 of the 
measuring and control system as shown in FIG. 2. 
FIG. 13 shows a processing circuit for forming such measured values. The 
signal derived from the leading vehicle axle, reaches the input 121 of the 
circuit, the corresponding signal from the rear axle reaching the input 
122. 
These measured values are supplied to maximum-value stores 122a and from 
there pass to the junctions 123. This is utilized, in a first processing 
branch, to indicate the ratio through the angular position of the pointer 
127, mounted on the potentiometer spindle of the double-wiper 
potentiometer 126 which is driven by the servomotor 124 through the 
differential amplifier 125. In a second processing branch the voltages are 
transferred from the junctions 123 through coefficient adjusting means 
128, the characteristics of which are set by the loading represented by 
the container 91, to a differential amplifier 129 and from there to an 
indicating instrument 130. The embodiment also incorporates a stepping 
switch 131, of which only two switching positions are shown in FIG. 13 and 
which generally contains as many switching positions as there are 
impressions of the leading trailer axle produced in the soil between said 
axle and the trailing in accordance with the length of the trailer. 
According to FIG. 10, the stepping switch is controlled by pulse 
transmitters 106 which are mounted on the vehicle frame 92 so that cyclic 
indexing of the stepping switch occurs always at the moment at which the 
next rams on the leading trailer axis makes contact with the soil (in FIG. 
10 the said pulse transmitters are disposed on the interior of the frame 
92 near the periphery of the leading wheel disc). The pulse transmitters 
106 may take the form of reed switches which are operated by magnets 
disposed on the exterior of the wheel discs 94 between the rams 95. In an 
additional switching deck 132, according to FIG. 13, these pulses are 
additionaly fed to the cancelling inputs of the maximum-value stores which 
are connected during the preceding pulse interval. 
FIGS. 14 to 16 show an embodiment of trailing measuring means for 
determining the shear strength of the compacted soil. The means comprise a 
thrust plate 141, serrated on the underside. It is pulled by the steered 
roller 145 of the leading compacting vehicle from a trail rope 142 and 
through a damped spring 143 and force sensor 144. The thrust plate 141 
supports an axle bearing 146 with an axle 147 on which two rigidly coupled 
running wheels 148 are eccentrically disposed so that when the thrust 
plate 141 is at rest, the torgue produced by the gravitational force of 
the running discs 148 causes these to rotate forwardly in the traveling 
direction of the compacting apparatus so that they bear on the soil 
laterally adjacent of the thrust plate. The force sensor 144 measure the 
force transmitted through the trail rope 142 to the thrust plate 141. This 
force increases while the spring 143 is extended until the shear strength 
of the soil below the thrust plate 141 is exceeded. At this moment the 
signal amplitude of the force sensor 144 will drop spontaneously 
accompanied by the beginning of a rolling motion of the running disc 148 
which raise the thrust plate 141 from the soil and, in accordance with 
their diameter, move the said plate forwardly in the traveling direction 
by at least one plate length and then once again place it on the soil. The 
controlled variable is the peak value of the signal emitted by the force 
sensor 144, said peak value being transferred to a store in accordance 
with store 13 of FIG. 2. 
FIGS. 17 and 18 show an embodiment of trailing measuring means for 
determining the continuous vibration impedance of the compacted soil. The 
said measuring means comprise a single-axle roller drawn by the compacting 
apparatus. In addition to its drawbar 151, said single-axle roller 
incorporates a loading bar 152, journaled on the roller axle and 
supporting on its upper platform 153 a directional force generator 154 the 
principal operative direction of which is vertical. The numeral 155 refers 
to the drive for the aforementioned directional force generator while the 
numeral 156 refers to an angle position transmitter, rigidly coupled to 
the rotor shafts of the generator. Near each of the roller axle ends the 
loading bar 152 is also provided with an acceleration pick-up 157 with a 
vertical operative direction and, centrally below the directional force 
generator, an elongation transducer 158 disposed in a reduced 
cross-sectional zone. 
FIG. 19 shows an embodiment of the associated processing circuit. The 
signals of the acceleration pick-ups 157 are supplied to the inputs 169 
and 170 of the aforementioned circuit, the summated voltage of said 
signals being tapped off by an adjustable potentiometer 171 which connects 
the inputs 169, 170. The summated voltage is integrated by an integrator 
172 and supplied to the inputs of the controlled rectifiers 173. The 
signal of the elongation transducer 158 is supplied to the input 174, said 
signal being supplied to the inputs of the controlled rectifier 176 after 
having superimposed upon it a portion of the summated voltage obtained 
from the tapping of the adjustable potentiometer 175. The control voltages 
of the said rectifiers are derived by means of pulse-forming stages, not 
shown, from the output signals of the phase angle transmitters 156 and are 
supplied to the circuit through the input sockets 177 and 178. These two 
square-wave voltages are phase-displaced relative to each other by one 
quarter of their cycles. The present embodiment dispenses with phase data 
relating to the continuous vibration impedance and merely responds to its 
total amount. To this end, the output voltages of the controlled 
rectifiers 173 and 176 are supplied in pairs to separate co-ordinate 
computers 179, the output voltage of which varies with respect to the 
output voltages of the controlled rectifiers 173 and 176 in the same way 
as the hypotenuse of a right-angle triangle varies with the length of the 
short sides thereof. The voltages thus obtained are supplied through a 
range selector 180, covering both channels, to quotient indicating means 
comprising potentiometer 181 of the kind already described with reference 
to FIG. 13. The position of the pointer 182 thus corresponds to the amount 
of continuous vibration impedance of the compacted soil at the frequency 
of the directional force generator 154 and forms the measured value of the 
measuring means 14 of the control system of FIG. 2 or, respectively, as 
indicated by indicating means 9 of the double vibratory roller 1 in FIG. 
1. 
FIGS. 20 and 21 refer to an embodiment for trailing measuring means adapted 
to obtain a measured value which is characteristic for the pulse or impact 
impedance of the compacted soil. The numeral 191 refers to a greatly 
simplified rearward part of compacting apparatus 24; this supports tamping 
means in which the drop weight 192 is mounted on a bracket 193 at one end 
of a guide rod 194 and may be raised by means of a lever 195. Lever 195 is 
rigidly coupled to a gear wheel 196 adapted to mesh with a gear wheel 197 
the tooth system of which is sub-divided into segments. The guide rod 194 
hinged to the lever 195, is guided in the traveling direction by a spring 
damping element 198. If the segmented gear wheel 197 is driven at a 
moderate and constant angular velocity, it will first raise the drop 
weight 192 on the guide rod 194, by virtue of a rotation of the gear wheel 
196 and the lever 195 coupled thereto, and then allow it to drop 
instantaneously when the gear wheels 197 and 196 are out of mesh. During 
the contact phase the spring damping element 198 absorbs the increasing 
distance resulting from the traveling motion of the compacting apparatus 
24 which will be compensated for during the succeeding lift period of the 
drop weight 192. An acceleration pick-up 199 having a vertical operating 
direction is disposed on the drop weight below the bracket 193. 
The kinematic conditions accompanying operation of the aforementioned 
measuring means are illustrated in FIG. 22. The upper diagram shows the 
output signal of the acceleration pick-up 199 as a function of time, 
corresponding to the difference between effective acceleration and 
gravitational acceleration. The first part of the curve to the moment of 
time 200 therefore corresponds to the dropping motion of the drop weight 
192. At the moment of time at which contact is made with the soil, a 
substantially upwardly directed acceleration occurs but rapidly decreases 
and, after moment of time 201, and in accordance with the soil 
characteristics, returns in a more or less damped oscillation to the 
initial value, the said soil characteristics being of no interest for the 
measured value to be obtained in this context. 
The lower diagram represents a velocity signal as derived from the upper 
diagram. This signal is constant for a first period of time, that is to 
say during the trajectory phase, said constant level corresponding to the 
impact velocity of the drop weight 192. This variable tends towards zero 
in accordance with the substantial positive acceleration after moment of 
time 200, the zero line being reached at the moment of time 202 and then 
being exceeded which is of no interest in the present case. 
FIG. 23 relates to an embodiment of a related processing circuit. The 
signal of the acceleration pick-up 199 is supplied to the input 211. In 
the main branch of this system the signal is supplied to the integrating 
stage 212 which is supplied with its initial value from the dc voltage 
generator 213 through a coefficient adjuster 214. The adjuster 214 is set 
so that the initial value corresponds to the impact velocity as derived 
from the drop height of the drop weight 192. The succeeding stage 215 
performs signal amplification with a high gain and peak limitation and 
therefore functions as a signum. The store 217 is supplied from the 
following differentiating stage 216. After processing by the negating 
circuit 218 the store output signal is supplied to a further integrator 
220 via AND gate 219. The output integrator 220 appears on the indicating 
instrument 221 which corresponds to indicating means 9 at the double 
vibratory roller 1 in FIG. 1. The AND gate 219 on the other hand is 
controlled by the acceleration signal from a limiting amplifier 222 so 
that integration by the integrator 220 will proceed only if the 
acceleration signal is positive. This ensures that in correspondence with 
the lower diagram in FIG. 22 integration will only occur during the period 
of time between moments 200 and 202. After moment of time 202, the pulse 
input 223 of the circuit is supplied, by means not shown, with a 
cancelling pulse for the store 217 and for resetting the integrator 220 to 
the initial value zero. The signal applied to indicating instrument 221 
also may be applied to the measuring and control system shown in FIG. 2 as 
the measured value of the measuring means 14. 
FIGS. 24, 25 and 26 show a further embodiment for trailing measuring means. 
The measuring means comprise a single axle roller, trailing the compacting 
apparatus 24. A frame 230 is journaled on theaxle trunnions and, at both 
sides, supports acceleration pickups 231. The signals of these 
acceleration pick-ups are supplied to the two inputs 232 of the processing 
circuit shown in FIG. 26 and tapped off from an adding potentiometer 233 
in the form of a summated voltage, are then rectified in the stage 234 and 
supplied to an amplifier 235 with multipoint characteristics. The 
following stages in the circuit comprise basically classifying means, 
indicating means 236 for the individual grades driven by timing elements 
(comprising a ramp generator 238, an integrator 239 and a square wave 
generator 237) which suppress the indication of a respective grade value 
if the same is not repeated within a given period of time. The signals at 
indicating means 236 which may serve as indicating means 9 in the double 
vibratory roller 1 as shown in FIG. 1 may be supplied as the measured 
values of the measuring means 14 the measuring and control system as 
represented in FIG. 2. 
FIG. 27 shows an embodiment for of trailing measuring means for determining 
the propagation conditions of surface waves on the compacted sub-grade. 
The numeral 241 refers to single axle roller 241 identical in construction 
with the measuring means as illustrated in FIGS. 17 and 18 except for the 
measuring roller 243. Light-weight measuring roller 243 is provided in 
vertical configuration above the roller axle and on both sides with 
separate acceleration pick-ups 244 of vertical operating direction. The 
roller is drawn by means of a drawbar 242. Reference may also be made to 
FIG. 19 as regards the associated processing circuit, however the 
superimposing element of that circuit is omitted and the input is 
connected directly to the two controlled rectifiers. The indication 
provided by the pointer will then correspond to the amount of the ratio of 
the vertical vibration velocity of the soil occurring at the position of 
measuring roller 243 to the excitation intensity introduced by the roller 
241. 
FIG. 28 shows a simplification of the embodiment in the event that the 
compacting apparatus is a vibration apparatus adapted to operate top load 
mode, for example a duplex roller. The angular position transmitter 196 as 
in FIG. 20 is mounted on the unbalance exciter of the said compacting 
apparatus. The output signals of the transmitters are supplied to control 
inputs 177, 178 of the rectifiers 173, 176; see FIG. 19.