Method for determining the compaction state of substrate

Abstract

A method for determining the compaction state of a subgrade to be compacted using a roller compactor comprising at least one compactor drum having an oscillation-inducing arrangement and rotatable about a drum axis of rotation comprising the following steps: during at least one period of oscillating movement of the compactor drum, repeatedly determining the acceleration of the compactor drum in an first direction, representing a first acceleration value; in association with each first acceleration value, determining an acceleration of the compactor drum in a second direction representing a second acceleration value in order to provide acceleration value pairs, each consisting of a first acceleration value and a second associated acceleration value; and for at least one oscillation period, defining a compaction state value representing the compaction state of the subgrade based upon the period of oscillation determined for said acceleration value pairs.

Claims

1. A method for determining the compaction state of a subgrade to be compacted using a roller compactor comprising at least one compactor drum rotatable about a drum axis of rotation, wherein one of the at least one compactor drum of the roller compactor is associated with an oscillation-inducing arrangement for inducing an oscillating rotation in said compactor drum in order to generate an oscillating torque on the drum axis of rotation, wherein the method comprises the following step: a) during at least one period of oscillating movement of the compactor drum, repeatedly determining the acceleration of the compactor drum in a horizontal direction, representing a first acceleration value, b) in association with each first acceleration value, determining an acceleration of the compactor drum in a vertical direction representing a second acceleration value in order to provide acceleration value pairs, each consisting of one of the first acceleration values and the associated second acceleration value, and c) for at least one period of oscillation, defining a compaction state value representing the compaction state of the subgrade based upon the period of oscillation determined for said acceleration value pairs, wherein step c) for determining the compaction state value comprises determining the area of an acceleration value pair curve defined by consecutive plots of acceleration value pairs on a graph of acceleration values during one period of oscillation, wherein the acceleration value graph is defined by a first graph axis associated with the first acceleration values and a second graph axis associated with the second acceleration values.

2. The method according to claim 1, wherein, regarding step c), an acceleration value pair vibration is defined based upon a sequence of acceleration value pairs along the first graph axis.

3. The method according to claim 2, wherein acceleration value pairs from a first group of acceleration value pairs and a second group of acceleration value pairs are assigned in such a way that the acceleration value pairs from the first group of acceleration value pairs generally form the upper end of the acceleration value pair vibration and the acceleration value pairs from the second group of acceleration value pairs generally form the lower end of the acceleration value pair vibration.

4. The method according to claim 3, wherein, regarding step c), an upper envelope is determined based upon the first group of acceleration value pairs, and a lower envelope is determined based upon the second group of acceleration value pairs.

5. The method according to claim 4, wherein, regarding step c), the area value is generally defined as being the area bordered by the upper envelope and the lower envelope.

6. The method according to claim 1, wherein during a rolling motion of the roller compactor, a depression forms beneath said compactor drum, wherein the depression is restricted toward a direction of travel and opposite to the direction of travel through accumulations of material.

7. The method according to claim 6, wherein the said compactor drum oscillates back and forth within the depression and, during each period of oscillation, the compactor drum is moved once up and once down by each of the accumulations of material.

8. The method according to claim 7, wherein a depth of the depression and an amount of the accumulations of materials gradually decreases by the oscillating rotation in said compactor drum causing the acceleration of the compactor drum in a horizontal direction to increase.

9. The method according to claim 8, wherein a frequency of the second acceleration value is double a frequency of the first acceleration value during each period of oscillation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is described hereinafter in reference to the enclosed drawings. Shown are:

(2) FIG. 1 a side view and figurative representation of the surface to be compacted by a compactor drum;

(3) FIG. 2 a graph of the period of oscillation of a compactor drum as shown in FIG. 1 showing a number of acceleration value pairs determined therein, and an acceleration value pair curve spanning the acceleration pair values as determined in chronological order;

(4) FIG. 3 a graph corresponding to that of FIG. 2, in which the acceleration value pairs determined for the period of oscillation are arranged in a different way in order clarify the acceleration value pair vibration;

(5) FIG. 4 a graph, which, based on the arrangement of the acceleration value pairs according to FIG. 3, shows an upper envelope and a lower envelope for the acceleration value pair vibration;

(6) FIG. 5 the progress of a compaction state value determined by the method according to the invention following an increasing number of passes over a subgrade to be compacted.

(7) FIG. 6 plotted with respect to the number of passes, the progress of a compaction state value determined by the method according to the invention, as well as a degree of compaction determined by measurements made at the subgrade.

DETAILED DESCRIPTION

(8) FIG. 1 shows a side view and figurative representation of a compactor drum 10 of a roller compactor. Provided within the area of the compactor drum 10 enclosed by the drum mantle 12 is an oscillation-inducing arrangement (not visible in the Figures), which may comprise a plurality of axes parallel to the compactor drum for the rotation of eccentric masses driven around an axis of rotation D. By means of the oscillation-inducing arrangement, an oscillating torque is generated, which induces the compactor drum 10 to perform an oscillating rotation O around the axis of rotation D. During the compaction process, meaning during the forward motion of the roller compactor in the direction of travel F, this oscillating rotation in the rolling motion of the compactor drum 10 is transferred along the rolling direction R.

(9) By way of example, acceleration sensors 16, 18 may be provided in the area of a bearing shell 14 of the compactor drum 10. In doing so, the acceleration sensor 16 for registering the acceleration of the compactor drum 10 in a horizontal direction H may be of such design that it lies along a direction substantially parallel to the plane of the subgrade U to be compacted. The acceleration sensor 18 may be designed or arranged in order to detect a vertical acceleration a.sub.v meaning an acceleration in a vertical direction V, which is substantially orthogonal to the horizontal direction H and thus also orthogonal to the subgrade to be compacted. The output signals provided by the two acceleration sensors 16, 18 can be transmitted to a data acquisition/analysis unit 20.

(10) It should be pointed out here that the acceleration may also take place in other areas of the compactor drum 10 such as the interior of the drum mantle 12, which would then require the respective extrapolation of the horizontal or vertical acceleration through coordinate transformation.

(11) The horizontal acceleration a.sub.h and the vertical acceleration a.sub.v will be recorded repeatedly during a particular period of oscillating movement O. The sampling rate should be at least ten times that of the oscillation frequency of the compactor drum 10, so that, during each period of oscillating movement O, at least ten acceleration value pairs will be recorded or determined, each with a horizontal acceleration a.sub.h representing a first acceleration value and a vertical acceleration value a.sub.v representing a second acceleration value. In the process, both acceleration values in a respective pair of acceleration values are ideally values for vertical acceleration and horizontal acceleration recorded at the same time.

(12) During the rolling motion atop the subgrade U to be compacted, a discernible depression M forms beneath the compactor drum 10 in FIG. 1, which is restricted both toward the direction of travel F and opposite to the direction of travel F through the respective accumulations of material A.sub.1 and A.sub.2. In the course of the oscillating movement of the compactor drum 10, said compactor drum 10 oscillates back and forth within the depression M and, in so doing, experiences not only the acceleration generated by the oscillating torque in a horizontal direction H, but also by the periodic rolling onto and off of the accumulations of material A.sub.1 and A.sub.2, therefore an acceleration in the vertical direction V. During each period of oscillation, the compactor drum 10 is moved by each of the two accumulations of material A.sub.1 and A.sub.2, once up and once down, so that the frequency of the vertical acceleration is double the frequency of the horizontal acceleration.

(13) FIG. 2 shows a graph or coordinate system, in which the first acceleration value, meaning the horizontal acceleration a.sub.h, is assigned to the horizontal axis, and the second acceleration value, meaning the vertical acceleration a.sub.v, is assigned to the vertical axis. FIG. 2 shows a plurality of the respective acceleration value pairs B.sub.P, wherein each acceleration value pair B.sub.P is represented by a horizontal acceleration value a.sub.h and an associated vertical acceleration value a.sub.v recorded at essentially the same time. FIG. 2 shows acceleration value pairs B.sub.P for one period of oscillating movement O of the compactor drum 10. The sequence of the acceleration value pairs B.sub.P over time, which are determined or recorded in chronological order, defines an acceleration value pair curve K, the shape of which generally resembles that of an 8 on its side. This shape is due to the fact that, as was previously set out, two periods of vertical acceleration occur during a period of oscillating movement O, meaning between the two extremes of the horizontal acceleration value a.sub.h, so the sign for the vertical acceleration changes a total of four times.

(14) During the process of compaction, the degree of compaction of the subgrade to be compacted U gradually increases with the number of passes by the roller compactor. Given increasing compaction, the extent to which the compactor drum 10 can press into the subgrade U decreases, which corresponds to a decrease in the depth of the depression M and a decrease in the amount of the accumulations of material A.sub.1 and A.sub.2. Given the decrease in the depth of the depression and the amount of the accumulations of material A.sub.1 and A.sub.2, the firmness of the subgrade U increases. Not only the depth of the depression M and the amount of the accumulations of material A.sub.1 and A.sub.2 but also the firmness of the ground upon which the compactor drum 10 performs its oscillating movement O will affect the values for horizontal acceleration a.sub.h and vertical acceleration a.sub.v occurring during a particular period of oscillating movement O. It was determined that the area defined by the acceleration values pair curve K likewise increases with an increasing degree of firmness, specifically because the horizontal acceleration a.sub.h increases as the firmness of the subgrade increases, thus making the sideways 8 wider. Taking the acceleration value pairs determined during a particular period of oscillating movement O into account, it thus becomes possible to draw conclusions about the subgrade U to be compacted, specifically by determining the size of the area defined by the acceleration value pairs B.sub.P or the acceleration value pair curve K in the acceleration pair graph in FIG. 2.

(15) There are various ways of determining this area. For example, instead of arranging or combining the acceleration value pairs B.sub.P one after the other in chronological order in order to obtain the acceleration pair curve K shown in FIG. 2, one may rather select, for instance, alternating acceleration value pairs beginning with the smallest value for horizontal acceleration a.sub.h, which will form a local minimum or maximum, in order to define a fictional acceleration value pair vibration S, as is illustrated in FIG. 3. In the process, for example, one might proceed by utilizing a corresponding sequence of acceleration pairs B.sub.P alternating with an acceleration value pair B.sub.P for defining a local minimum, being a lower end S.sub.U, and a local maximum, being an upper end S.sub.O. For example, if the chronological sequence of the provided acceleration value pairs B.sub.P should result in a grouping, within which two or more acceleration value pairs, each defining a lower end point, are located between two upper end points S.sub.O, then that acceleration value pair B.sub.P, which in fact defines the local minimum or, as the case may be, the local maximum, can be utilized for the purpose of determining the acceleration value pair vibration S.

(16) As a whole, the acceleration value pairs which define the acceleration value pair vibration S are to be divided into two groups, namely one group G.sub.1, which includes the acceleration value pairs B.sub.p defining the respective upper end S.sub.O, and a second group G.sub.2, which includes the acceleration value pairs B.sub.P defining the lower end S.sub.U. In the process, the two outermost horizontal acceleration values may advantageously be assigned to groups G.sub.1 and G.sub.2, respectively.

(17) On the basis of the respective acceleration value pairs B.sub.P assigned to each of the groups G.sub.1 and G.sub.2, appropriate mathematical methods are used to determine an upper envelope E.sub.O and a lower envelope E.sub.U for the acceleration value pair vibration S.

(18) As determined according to the invention, the size of the area FL, which is an indicator of the compaction state of the subgrade U to be compacted, can now be calculated as the area enclosed between both ends of the envelope E.sub.O and E.sub.U. In doing so, for example, an area calculation can be made through numerical integration using the trapezoidal rule. The area value, the unit for which is m.sup.2/s.sup.4, thus constitutes a compaction control value, meaning a dynamic continuous compaction control value, which may be recorded or determined during the compaction process. As an example, this value may be rescaled along with compaction process parameters or machine parameters such as the compactor drum diameter, the linear load on the vibrating mass itself, or the eccentric moment in order to obtain variables which are easily manageable or more comparable.

(19) FIG. 5, given the length of a subgrade U to be compacted as represented by lengthwise GPS areas, shows the progress of the area size FL as determined in the manner described in the foregoing, which is indicated in FIG. 5 as FDVK [continuous compaction control], the value for which can be clearly seen to shift continuously upwards with an increasing number of passes. Weak points are present in two local regions L.sub.1 and L.sub.2, these being places where, for reasons such as a lack of subgrade preparation, no substantial compression may be achieved.

(20) FIG. 6 shows a comparison between the FDVK [continuous compaction control] area value recorded using the method according to the invention and a value determined using a standardized measurement procedure with a dynamic deformation modulus corresponding to Evd. The progress of these two values proceeds in a nearly comparable manner as the number of crossings increases, thus making it evident that the use of the method according to the invention makes a variable available which allows precise conclusions to be made about the actual degree of compaction existing in the subgrade to be compacted in real time, thus during the compaction process.

(21) Finally, it should be pointed out that, as regards the foregoing reference to the graphs or coordinate systems in FIGS. 2 to 4 and the acceleration value pairs or curves entered therein, the determination of the area value does not, in fact, require entering the respective acceleration values or acceleration value pairs into graphs and evaluating said graphs, but is instead carried out on the basis of mathematical procedures, which, however, are able to be shown via the various graphs and the curves entered therein. Therefore, in terms of the present invention, for example, this does not mean that an acceleration value pair vibration will be plotted on a graphor merely plotted on a graphin the process of defining such an acceleration value pair vibration, but rather that values or coordinate points relevant to said vibration will be determined and utilized in further mathematical procedures.