Development of New Technology

Traditional approaches to compaction specification and control have generally evolved to suit the apabilities of conventional compaction plant, for which relatively thin lift, layered construction and a related stepped density profile is normally specified. The enhanced compaction capabilities of the Landpac Impact Compactors have made traditional methods of specification and control generally inappropriate for use with the new technology.

The traditional approaches to compaction specification and control have the following limitations:
- an unacceptably small ratio between volume of material tested and that compacted (typically up to 1:100,000),
- lack of correlation between laboratory and field compaction,
- poor reproducibility of results,
- long test duration, especially with thick lift compaction, and
- difficulty in testing heterogeneous materials.

In view of the limitations associated with the use of traditional testing methods, new methods of compaction specification and control have been developed, not only to exploit the capabilities of Landpac Impact Compactors but also to overcome the inherent difficulties of employing density as the primary measure of controlling compaction.

The new approaches for testing and certification of ground improvement works using Landpac impact compaction equipment revolve around using conventional testing methods in conjunction with the Landpac CIR and CIS technologies. The preference in this approach is to use testing methods that provide a direct measurement of the soil properties required for design purposes (strength and deformation) rather than the traditional proxy of density.

By using the Landpac CIR and CIS technologies to identify the relative strength and stiffness of the material being treated, it is possible to focus the conventional tests in the relatively weaker areas. By ensuring that the relatively weaker areas conform to specification, it is then possible to use the Landpac CIR and CIS results to extrapolate the conventional test results over the entire site thereby increasing the certainty of the overall future performance of the compaction works . This process can actually allow for a reduced level of conventional testing thereby reducing the cost of testing whilst increasing the level of certainty of the test programme.

Continuous Impact Response (CIR)

In line with the new approach of direct measurement of soil properties, it is possible to use the impact compactor as a proof roller and to measure the soil response to the dynamic loading of the impact compactor.

The Continuous Impact Response (CIR) System, developed and patented by Landpac, is a system capable of measuring the soil response to every impact of the roller, resulting in a direct measurement of soil stiffness, which is a function of the soil density.

The Continuous Impact Response system employs the Landpac Impactometer to measure peak decelerations of the compaction masses with each impact. Each of these points is recorded relative to its position on site as determined by an integrated global positioning system. These accurately measured and recorded decelerations are then correlated back to a direct measurement of engineering properties.

The net result is a deceleration and a predicted soil property mapping of the entire site, at various stages of the compaction process. Improvement is immediately visible and directed emphasis can be placed on areas requiring added improvement.

In summary, the CIR provides a quality control system that quantifies the ground strength and stiffness during the compaction process whilst also monitoring the number of coverages and actual area compacted. Improvement is visible by comparing the first coverage soil property map with the final coverage soil property map.

CIR measurements can be very accurately correlated to all conventional testing methods including density measurements, penetration testing (CPT, DCP, etc) and direct load testing (Plate Load, Zone Load, etc). In doing so, the CIR system can be used in conjunction with conventional testing techniques to provide a quality assurance system capable of certifying the entire site at a reduced cost and an increased level of certainty. The system is currently widely used and has proven to be a very useful tool in contolling the Landpac ground improvement process.

Continuous Induced Settlement (CIS)

Ground improvement utilising the Landpac high energy ground improvement equipment causes the ground surface level to be reduced. Such surface level reduction or “induced settlement” serves as a rudimentary measure of ground improvement. The extent of the induced settlement that is achieved with the Landpac high energy ground improvement equipment varies with material type and condition but it is typically between 5% and 15% of the depth of material being treated.

The actual induced settlement that occurs during the Landpac ground improvement treatment process is measured on a continuous basis using a machine mounted differential GPS system in the case of the HEIC equipment and using a direct measurement sensor in the case of the MDC equipment. The induced settlement data is captured and analysed in conjunction with the CIR data to control the Landpac high energy ground improvement works as it proceeds.
The rate of induced settlement is typically used as a control measure and Landpac high energy ground improvement is performed until the induced settlement between successive treatment coverages reduces to a predefined limit.

The induced settlement data can be presented in colour coded “maps” as with the CIR system data and this provides a useful tool to record and analyse the induced settlement over 100% if the site being treated.