UNBOUND GRANULAR MATERIAL

FIELD OF THE INVENTION

The invention relates to a method, manufacture and production of road compaction equipment that adopts the natural geomorphological Angle of Repose of that specific Unbound Granular Material. This invention creates two interlocking layers within the Unbound Granular Material (Sub base and or Base), which as a composite, is supported by the compacted subgrade. The Compaction plant shall be a double drum type where the first drum is ribbed with 45° ridges 10 and troughs; referred to as the Angular Geo-Lock Compactor (AGC), and the second drum an adjustable (upwards), smooth cylindrical type with a central belly-fed hopper. Conversely, a single ribbed drum compactor, Angular Geo-Lock Compactor can be employed to cover a single lane or both lanes that will in the second process (for the top interlocking layer), be finished with a forward belly-fed paver or smooth drum compactor.

BACKGROUND OF THE INVENTION Road failure has been recorded in road construction and it stems from the courses that make up the composite arrangement comprising from the bottom, the Subgrade, Sub base and Base and finally the surface course. The base and sub base, Unbound Granular Material, receive the loads from the road surface and transmits these to the subgrade. The Unbound Granular Material therefore, from its location in the middle is prone to failure. The behavior of the particles from their specific and stable angle of repose impact on the aggregate interlock resulting into failure.

For the Base and Sub base to offer both short term and long term requirement they must be compacted in layers with calculated moisture contents to ensure that the resulting layer is of a compacted stiffness that should serve the purpose of design. It has been confirmed by other researchers through evaluation of resilient modulus of subgrade and base materials that, the stress point for Unbound Granular Material is located mid-layer and that of the subgrade material at the top of the subgrade. This difference, (nonlinear behaviour), requires that the stress levels for subgrade and subbase should be considered separately and yet they make up the whole of the foundation of the road. The invention is that there must be a shift from inter-particle (mid-layer stress arrangement) to an intra-particle geo-lock formation. PURPOSE OF THE INVENTION The purpose of the method and equipment is to localize the stress within the

Unbound Granular Material layer so as to prevent lateral movement referred to as dilatancy or erroneous expansion and also to prevent longitudinal movement that results into rutting. This should result into a geomorphologically stable road foundation that is resilient, stiff and yet able to function in terms of excess moisture flow because the essence of a road foundation is not to create a dense structure but a permeable and stiff resilient base. The invention should bring about road sustainability where ‘unwarranted’ cost of maintenance can be avoided impacting positively on broadening a country’s capacity for economic growth. These ‘savings’ in retrospect can then be channeled to other areas of need. SUMMARY OF THE INVENTION

The invention relates to a method, manufacture and production of equipment that adopts the natural geomorphological Angle of Repose of that specific Unbound Granular Material to create two interlocking layers within the Unbound Granular Material combination of the Sub base and Base. In order to achieve this, a purposely manufactured ribbed angular geo-lock drum compactor, shall be employed to create troughs in the first layer which will be covered by the second layer and compacted by a smooth drum compactor to create an intra-particle geomorphological lock. This should avoid the prevalence of Unbound Granular Material shifting either laterally or longitudinally which results into ‘erroneous expansion’ and rutting due to a localized stress structure within the Unbound Granular Material. This failure is brought about by the different behaviour of material in both the Unbound Granular Material and subgrade. The highest shear stress for the subgrade lies on top of the subgrade whereas that of the Unbound Granular Material lies in the centre or mid-layer. This means that, the interface between subgrade and subbase/base is one that has a stiff bottom surface and a weaker top surface in terms of shear resistance. Loads exerted from the surface layer of the road will therefore be resisted only at mid-layer from inter- particle behaviour; and if this fails, the Unbound Granular Material will have a propensity to move laterally and or longitudinally creating potholes and rutting. The novelty is to create an intra-particle lock that conforms to the natural angle of resistance, which is the angle of repose of that specific material to prevent the Unbound Granular Material from shifting as a ‘unit’. A higher thickness of the Unbound Granular Material will not change the status quo between the top of the subgrade and the bottom of the subbase/base. This re-design of the road foundation will be resilient enough to be sustainable such that road performance and life cycle will be lengthened because of lower maintenance costs. These savings can then be channeled to other areas of need in support of economic growth and development as an investment should. This method can be applied to gravel roads as well, which exhibit erroneous expansion and rutting in the shortterm.