Achieving soil, asphalt, waste, and other earthen material compaction requirements is critical to earthwork constructions including road beds, pavements, foundations, dams, runways, landfill liners, etc. Compaction is required most often to improve the load bearing capacity of earthen materials, improve their strength and resistance to failure, and/or improve permeability. In most instances, some secondary measurement of compaction quality is necessary in order to proceed to a next stage in construction after a base material has been compacted. In other words, the construction project must be delayed until a compaction quality assurance test is performed and passed.
In the past, many different quality assurance tests have been devised that are often dependent on what the based material is, and the preferences of the controlling authority where the base material is located. For instance, the Iowa Department of Transportation requires a proof rolling test to be performed on a base material using a truck having certain weight and speed requirements to produce ruts less than a prescribed depth when traveling over the supposedly compacted base material. If the prescribed truck at the prescribed speed produces ruts greater than the prescribed depth, then the base material compaction is deemed unsatisfactory and must be further compacted before further construction on the base material can be approved. In another jurisdiction, a nuclear density measure of the base material must be performed, and the test result must come within certain prescribed standards before further construction on the base material can proceed. In relation to soil or waste compaction, some jurisdictions may require a walk out test to confirm that the base material has achieved a prescribed level of compaction. Walk out occurs when a compactor with a tipped roller becomes supported on the base material by the roller tips such that the compactor roller surface is lifted off the base material. In still other instances and/or jurisdictions, a penetrometer test might be performed using a prescribed device in a prescribed manner.
While most of the these quality assurance techniques have proven over time to be valid means by which the compaction quality of a base material can be assured, there are drawbacks to this method of progressing through a construction project. For instance, while in most instances a base material to be compacted has a relatively large area, most, if not all, of the accepted quality assurance techniques only check a compaction status of a very small portion of the compacted area. Since the level of compaction can vary substantially over an area to be compacted, a quality assurance test at one location can be completely inaccurate with regard to another location some distance away from the tested area. Thus, in most cases only a very small fraction of an earthen structure is actually validated to meet compaction requirements. Thus, inadequate compaction in one area can, and sometimes does, go undetected after a quality assurance test at another location on the base material suggests that an entire area has been satisfactorily compacted.
Another drawback in current construction processes involves the costs of waiting for a quality assurance test to be initiated and performed after completion of the compaction process. In other words, the down time involved in waiting to proceed to a next stage of construction after completion of a compaction process can increase inefficiencies and substantially increase the overall costs of a construction project. In addition, if the quality assurance test indicates a failure to meet compaction specifications, further delays can occur in determining what, and how extensive a rework will be required to correct for the failure(s).
In recent years, there have been efforts employed to use a variety of quality control techniques to reduce occurrences of quality assurance test failures in order to reduce costs associated with having to re-compact an area in order to satisfy compaction specifications at a given site. Co-owned U.S. Pat. No. 6,188,942 to Corcoran et al. describes a method and apparatus for determining the performance of a compaction machine based on energy transfer. This patent insightfully recognizes that the dynamic energy interaction of a compactor moving over a base material can provide a basis for generating real time compaction quality control data so that the operator can monitor the compaction status of each location of the base material. While this compaction monitoring technique can improve a operator's confidence that the base material will pass a compaction quality assurance test, the technique does nothing for the costs associated with waiting for the compaction quality assurance test to occur and be completed.
In U.S. Pat. No. 5,942,679 another compaction monitoring strategy is detailed, presumably to avoid the costs associated with failing a quality assurance compaction test. In this patent, a compacting machine continuously moves behind a paver machine. Based upon the pavement material, temperatures of both the material and ambient temperatures and other sensed factors, the reference teaches that the pavement can be satisfactorily compacted with some integer number of passes by the compacting machine. The system continuously monitors the position of the compactor and graphically displays to the operator a grid map showing the number of passes that have been completed for each unit of surface area of the pavement to be compacted. While this system can be affective in monitoring the number of passes that the compactor has made over each location on a pavement surface, it provides only predictions regarding the actual compaction status of any location. Thus, this system must rely heavily on the accuracy of assumptions that go into predicting the number of necessary passes to compact pavement under a set of conditions, which themselves are likely in a state of flux.
In still another technique taught in co-owned U.S. Pat. No. 5,493,494, a three dimensional global positioning system strategy is used to continuously monitor the elevation of the compacting machine at each location on a base material to be compacted. With each pass over a given location, the system compares the current elevation of the compacting machine to the elevation in a prior pass. Based upon these comparisons, the system draws certain conclusions as to the compaction status of the underlying base material. This strategy is taught as being particularly applicable to landfill compaction operations where the base material itself may be changing with each successive pass due to the addition of uncompacted waste material between passes. Nevertheless, this system could have promise, but does suffer from the drawback of reliance upon referencing an off-board elevational reference (GPS Satellite or Elevation Bench Mark) in order to perform as described.
In other known strategies, a density measuring device may be attached to a compactor, but accurate use of the device requires that the compactor remain stationary for some substantial period of time. In still another instance, it is known to sense via accelerometers a dynamic response of the compacting machine to a vibration sent into the underlying base material, and then estimate density based on assumptions and the dynamic response. Such a system is described in U.S. Pat. No. 6,122,601. Unfortunately, this system is also strongly dependent on accurate assumption inputs to its algorithm(s). In addition, a base material exhibiting a certain dynamic vibrational response to a known input does necessarily mean that the base material can statically and rigidly support the weight of construction resting on the base material.
Apart from all of these compaction monitoring devices, there has been long reliance upon the skill and experience of compactor operators to determine when a supporting layer has been adequately compacted based upon qualitative feel and observations. Still, none of these strategies are useful in reducing downtime associated with waiting for a compaction quality assurance test to be performed and completed.
The present invention is directed to overcoming one or more of the disadvantages set forth above.