Open pit mining is a complex logistical problem of moving different types of material from multiple points of origin (Load Zones) to multiple destinations (Dump Zones).The distance between the load zones and the dump zones can be anywhere from 100 feet to 12,000 feet; and open pit mining operations usually classify their materials as one or more types of ore and waste. A typical mine may remove waste material to between two and seven dumps and may move ore to a crusher and one or more stock pile dumps. To move all of this material a large mine will have about 10 shovels and 35 to 60 haulage trucks.

PROBLEM

There are two main problems facing an open pit mine. The first problem is with truck and shovel haulage; more specifically the amount of time that the trucks spend queues waiting to be loaded or to dump. The second area of concern is in forecasting production. It is very hard for a mining operation to be able to forecast their production accurately because of the many breakdowns and delays that occur with the trucks and shovels.

SIMULATION

To solve these problems for a mine a simulation model was built that simulated the movement of the trucks and the activity at the load zones and dump zones. The simulation model can be thought of in two parts.

Haulage Trucks

The haulage trucks were represented in the model as Task Executer flowitems and were created at time 0. To help solve the forecasting problem the trucks were given a sorted list of all the breakdowns that they would incur at the time of their creation. This approach was used to make the large number of breakdowns easy to input and manage. The haulage trucks were given differing haul speeds to simulate the reality of having both slow and fast trucks. For this reason the haulage trucks reported their travel times to an average time table every time they finished traveling to give the end user an idea of the expected travel times in the mine. The haulage trucks also kept statistics on all of their state information (Traveling, Waiting in Line, Broken Down, Etc.) to allow the user to see the effects of different dispatching methods, and truck quantities.

Load and Dump Zones

The load zones and dump zones in the model were represented by a breakdown position (Processor), a queue (Queue), and an area to dump or be loaded (Processor). The breakdown position was the designated spot for the trucks to breakdown. This was done as a simplifying assumption to avoid having to complicate the simulation by having the trucks breakdown and block the roadways. Each time a truck entered the breakdown processor in a load zone or dump zone it would check to see if it needed to breakdown and if so for how long. At the end of the repair time the next breakdown time would be calculated and then reinserted into the breakdown list on the haulage truck. The load zones and dump zone breakdowns were done in an almost identical way. However, instead of having to travel to a breakdown area the load zones and dump zones merely sent themselves a message to breakdown the next breakdown time.

The load zones and dump zones kept statistical information on the time the trucks spent in the queue and at the shovel / dump. This information is used in conjunction with the statistical information on the trucks to determine if the trucks are being dispatched correctly and to see the effects different dispatching methods and production ratios. The load zones and dump zones also kept statistical information on the states of the shovels and dumps. This information helped to located shovels and dumps that were being over or under utilized.

SUMMARY

The truck and shovel simulation model proved to be extremely useful to the mine in helping them to locate inefficiencies in their truck fleet and helping them to forecast their future production rates. With better forecasts of their production rates the mine was better able to increase the accuracy of their financial plans and to plan the mandatory down times for their trucks and shovels better.