<< Click to Display Table of Contents >> Navigation:  User Manual > Truck & Shovel Simulation > Setting up Haul Roads and Accesses > Virtual Roads and Manifolds

The road design procedures described in previous topics involved the user designing Horizontal and Vertical alignments which define the full three-dimensional path of the truck during simulation. 3d-DigPlus includes a simplified road design system called Virtual Roads. Virtual Roads use the known location of the truck at the start of travel and the location at the destination, together with various user defined parameters to generate a theoretical road model connecting the start and destination points and used for productivity calculation.

Scope of application of Virtual Roads

A typical road system consists of the following components:

•Excavation Manifold. This is the highly variable section of travel connecting the current location of the excavator and the toe of Excavation Access for the current lift.

•Excavation Access. This is the adaptive road that connects the Main Haul Road to toe of Excavation Access for the current excavation lift.

•Main Haul Road. This is the permanent or semipermanent road connecting the Excavation Access to Dump Access.

•Dump Access. This is the adaptive road that connects the Main Haul Road to the crest of Dump Access for the current dump lift.

•Dump Manifold. This is the highly variable section of travel connecting the current  tip point and the crest of Dump Access for the current dump lift.

 

Excavation Manifolds and Dump Manifolds are always modelled as Virtual Roads. The highly variable nature of these paths make them unsuitable for design using other methods. Furthermore their geometry  is generally highly predictable and they are amenable to accurate simulation using Virtual Roads.

Excavation Accesses and Dump Accesses may be modelled as virtual roads. Frequently the geometry of these paths is predictable and they are amenable to simulation which produces acceptable approximate estimates of travel time.

Main All Routes cannot be modelled as Virtual Roads in combination with accesses modelled as Roads on Terrain. However it is possible to model entire road system using Virtual Roads. In this case 3d-DigPlus uses the known starting point of travel (central it of excavation block) and the known destination point (average dump point for block) to create a Virtual Road system to connect excavate and dump. The use of all Virtual Roads provides a very quick means of estimating productivity, however it can be subject to substantial error.

Setting up Virtual Roads and principles of operation

Setting up Virtual Roads is done via the Simulation Settings dialog box, and this interface is described further in the Truck Shovel Simulation section of this manual.

The Virtual Excavation Access dialog shown below:

The the setup for Virtual Excavation Access Virtual Roads is identical to the Virtual Road set up for any other part of the road system.

The first step performed by 3d-DigPlus in creating a Virtual Road is to establish the coordinates (easting, northing and RL) of the start point for travel and the destination point. From the start the minimum straight-line horizontal travel distance is established. Given the elevation difference between the two points and the maximum allowable gradient of trucks the minimum distance required to achieve the change of elevation is also determined. The greater of these two distances is the absolute minimum travel distance to feasibly connect the start and destination points.

Once the minimum feasible distance is established the other user settable parameters are used to determine the actual Virtual Road geometry to be used.

The Virtual Roads parameters are:

•Factor for minimum horizontal distance. The minimum feasible distance as described above is multiplied by this factor and the result is the initial estimate of horizontal distance.

•Constant Extra Horizontal Distance. This is a fixed distance which is added to (1).

•Percent of Maximum Flat Length. There is typically an elevation difference between start and destination points. The Percent of Maximum Flat length is used to determine how the required gradient is applied to the Virtual Road. If the Percent of Maximum Flat Length is set to 100% than the elevation change will occur over a length of the virtual road which has a gradient equal to the maximum gradient, the remainder of the road will be horizontal. If the Percent of Maximum Flat Length is set to 0% the change of elevation will be achieved via a uniform gradient over the entire length of the road.

•Truck Operational Parameters. These are the Truck Operational Parameters described in the previous topics for Roads on Terrain.

Recommended use of Virtual Roads.

When used appropriately Virtual Roads can provide a means of quickly estimating truck and shovel productivity. However Virtual Roads to have their limitations which should be considered before applying them.

Road systems can be complex and travel paths needed to complete a given operation, even a short term plan, can vary greatly. Virtual Roads are not recommended the highly detailed short-term plans.

Full Virtual Roads can produce useful information for conceptual long-term plans. However they are at best approximate and depending on the geometry of the particular pit can produce significant error. As a general rule if the footprint of the excavation and dump zones has a high aspect ratio, that is travel distance from excavation to dump is large relative to the width of excavation with the dump, Full Virtual Roads may produce an acceptable result.  He will often require only a modest amount of extra work to implement Main Haul Roads as Roads on Terrain and use Virtual Roads for accesses and manifolds. This method forces the trucks to move to the appropriate point on the Main Haul Road once loaded and to depart at the base of the dump. This greatly reduces the scope for error in the productivity simulation.

An indication of the likely error incurred by Virtual Roads can be had by setting up a detailed simulation (using Roads on Terrain for all Haul Roads and Accesses) which is representative of the geometry of the proposed extended simulation. Next the simulation is reworked with Virtual Roads for Accesses. Lastly the simulation is reworked again with full Virtual Roads. This approach allows the degradation inaccuracy with the various levels of Virtual Roads to be assessed by comparison with the detailed simulation. This also allows optimising of Virtual Road parameters.