Impact Rolling / High Energy Impact Compaction

Vibratory and impact rollers achieve deeper lift compaction than static rollers. Ground improvement with impact rollers occurs through rolling dynamic compaction, enabling compaction to significant depths, generally more than 1 m. This provides the opportunity to place thick layers, potentially with a larger maximum particle size than conventional smooth drum rollers, while achieving engineering standards of density and stiffness. The overall consequence of this is that the earth­works exercise becomes a far more sustainable activity. Deeper lift compaction beyond traditional thin compacted layers using conventional heavy vibratory rollers has been achievable for some time, but to lesser depths than is possible with impact rollers. The compaction of deeper lifts at faster operating speeds, albeit, typically with a greater number of passes, requires a fresh look at specifications for infrastruc­ture earthworks. The paper explores the green credentials of deep lift compaction, by comparing earthworks plant, productivity and fuel usage for compaction using conventional circular drum rollers with thin layers, and deeper lift compaction using vibratory and polygonal impact rollers. Quality control to greater depths can be a limiting factor. Testing protocols often require modification to accommodate the changes in layer thicknesses and material specifications.

A finite element model (FEM) of rolling dynamic compaction (RDC) technology of a BH-1300 4-sided 8-tonne impact roller, developed previously by the authors, has shown to have reasonable agreement with that observed in the field. The use of this FEM is likely to provide high fidelity insights into the capability of the BH-1300 4-sided 8-tonne impact roller, namely in predicting the settlement and densification of an underlying granular material. A parametric study utilising this FEM with respect to initial density and shear strength parameters is undertaken to explore the relationship these properties have to the settlement and densification of a soil subject to RDC with a BH-1300 4-sided 8-tonne impact roller. The empirical relationships constructed within this study are validated against field trials from the literature of the roller improving sandy gravel fill at typical operating speeds of 10 km/h.

Rolling dynamic compaction (RDC) is a ground improvement technique, which involves towing heavy (typically 6–15 tonnes) non-circular modules (3-, 4- and 5-sided) behind a towing unit to achieve soil compaction. RDC has gained increased popularity in recent years since it has a greater influence depth and it can be operated at a higher speed. Although RDC has been successfully applied to many construction projects, there is currently very limited understanding of the behaviour of soil beneath the ground during the RDC process. In addition, the relationships between soil response and the effectiveness of RDC are still not well understood. These often results in the use of RDC being based on intuition or experience obtained from previous projects with similar soils and site conditions.

ABSTRACT: The construction and management of haul roads remains a critical element in the efficient operation of all mines. Significant effort has been applied to design practices, extending the use of design charts and computer programs. Attention has been paid to the pavement materials and material properties, based on decades of geotechnical data and experience. Opportunities still exist for improvements to be realised in compaction protocols, particularly in the use of rolling dynamic compaction (RDC). RDC involves the delivery of a dynamic compactive effort using non-circular towed compactors, which are designed to deliver a combination of potential energy of a falling weight and kinetic energy mobilised due to the relatively high towing speed. The objectives include the proof-rolling and preparation of subgrade areas, exposing soft spots and weak zones and often establishing a sufficiently competent raft layer, as well as deep lift compaction offering cost-efficient construction of ramps and haul road pavements with programming benefits. The ability to compact deeper lifts allows fill particles to be larger without inhibiting the compaction process, which increases the sustainability of the process through reducing the constraints on the fill materials by allowing a larger maximum particle size. Case studies are cited where RDC has been trialled on several mine sites and many mines have benefited from the use of the technology. The continued attention to improving haul road construction will result in less road maintenance, less vehicle damage and improved truck tyre life, and RDC offers a method of contributing to these improvements. The compaction energy of RDC offers more leniency in moisture conditioning where adequate compaction densities can be achieved with much lower water addition than conventional laboratory optimum moisture content. When applied to coarse surface layer materials RDC will generate sufficient fines to provide a high-friction tyre-friendly low-maintenance finish on haul road surfaces.

Rolling dynamic compaction (RDC) consists of a non-circular module of 3, 4 or 5 sides, that rotates as it is towed, causing it to fall to the ground and compact it dynamically. There is currently little guidance available for geotechnical practitioners regarding the depths of improvement that are possible in varying soil conditions. Current practice dictates that practitioners rely on personal experiences or available published project case studies that are limited in scope and applicability as they are typically aimed at achieving a project specification. There is a reluctance to adopt RDC as a ground improvement technique as there is uncertainty regarding its limitations and capabilities.

The construction and management of haul roads remains a critical element in the efficient operation of all mines. Significant effort has been applied to design practices, extending the use of design charts and computer programs. Attention has been paid to the pavement materials and material properties, based on decades of geotechnical data and experience. Opportunities still exist for improvements to be realised in compaction protocols, particularly in the use of rolling dynamic compaction (RDC). RDC involves the delivery of a dynamic compactive effort using non-circular towed compactors, which are designed to deliver a combination of potential energy of a falling weight and kinetic energy mobilised due to the relatively high towing speed. The objectives include the proof-rolling and preparation of subgrade areas, exposing soft spots and weak zones and often establishing a sufficiently competent raft layer, as well as deep lift compaction offering cost-efficient construction of ramps and haul road pavements with programming benefits. The ability to compact deeper lifts allows fill particles to be larger without inhibiting the compaction process, which increases the sustainability of the process through reducing the constraints on the fill materials by allowing a larger maximum particle size. Case studies are cited where RDC has been trialled on several mine sites and many mines have benefited from the use of the technology. The continued attention to improving haul road construction will result in less road maintenance, less vehicle damage and improved truck tyre life, and RDC offers a method of contributing to these improvements. The compaction energy of RDC offers more leniency in moisture conditioning where adequate compaction densities can be achieved with much lower water addition than conventional laboratory optimum moisture content. When applied to coarse surface layer materials RDC will generate sufficient fines to provide a high-friction tyre-friendly low maintenance finish on haul road surfaces.

Rolling Dynamic Compaction (RDC) is a generic term associated with densifying the ground using a non-circular roller. The application and use of RDC in the mining industry is increasing because of its ability to compact ground efficiently by means of a faster operating speed (10-12 km/h) and compaction of thicker layers than conventional circular rollers. Whilst conventional rollers are able to compact fill in layers up to 400 mm, thicker layers are able to be adopted using RDC for the construction of tailings dams and mining haul roads. Increased layer thicknesses enable larger particle sizes to be used, therefore greater reuse of mine spoil material can be undertaken with a reduced need to screen out large quantities of oversized materials. As well as demonstrating how RDC has been used effectively for the compaction of bulk earthworks at two different mine sites, this paper also discusses various aspects and factors associated with conducting a compaction trial on mine spoil materials.

Manufactured and further developed in Australia over the last 21 years, the “square” Impact Roller has found a variety of applications in various parts of the world. Employing the well-established principles of rolling dynamic compaction, the Impact Roller densifies the ground to significant depths, without excavation or removal, allowing the retention of materials that may otherwise be considered unsuitable as engineered or controlled fill. It also facilitates the improvement of weak ground, either natural or man-made, breaking concrete and rock, and compressing waste. Broons now manufacture four models of the Impact Roller, all with solid modules, and two designed specifically with the mining sector in mind.