Observations - Cement grout method

The shifts at Kristineberg started at 05:30 and at 15:00 with a production meeting above ground.

After the meeting operators drove to their machines to arrive there around one hour later. The operators started the rock bolter and visually check the machine and working face for their conditions. The cement mixing would be started, after this the operator started refilling the carousel with bolts. After this the operator would install rock-bolts until +-30 minutes before lunchtime when the operator would start to clean the machine. The Lunch break took on average 1 hour including driving to the canteen and vice versa. The operator would continue installing bolts until +-90 minutes before the end of the shift, at this time he would start to clean the equipment again. They would leave the rock bolter +-60 minutes before the end of the shift.

During the data collection in the field, the morning shift had been followed to get an understanding of their daily routine.

The morning shift had been followed because this was easier with planning and practical matters. It was explained to the operators that the goal of this study was to get a baseline for the bolting performance and that all the data were anonymous, this was done in order to make sure that the operation would be representative. All reasonable actions have been taken into account to ensure that the data collection process did not influence the daily operation.

The data gathered from field observations and the data that were logged by the described systems was entered into Excel for further processing. All the data gathered were from a machine utilization viewpoint, meaning that if the operator did a task not connected to the productivity of the machine it would be entered as unproductive work time. It was chosen to work from a machine utilization point of view because the machines are being evaluated. For the field observations the data were collected and entered into excel per shift, these data have the highest reliability. A typical shift would consist of over 150 data points. During a shift the start and end times of the following events would be gathered: shift start, arrival at the machine, making cement, drilling, grouting, refilling the carousel and cleaning of the cement. During the shift the number of bolts installed and common stoppages were also recorded.

All these events were divided into a number of categories to make it easier to calculate the productivity of the current method and compare this with the new method.

These categories consist out of the following;

- Cycle time is defined as the time it takes to drill a hole, grout the hole, install a bolt and manoeuvre the boom to the next position.

- Method time is defined as the time all support activities at the face take such as painting the boreholes, filling the bolt carousel, repositioning and start-up/shut down procedures.

- Restocking supplies is defined at the time it takes to travel to the bolt & cement storage and refill the bolter with bolts, cement and other supplies.

- Making cement is defined as the time that is lost when waiting for the grout to be properly mixed.

- Cleaning time is the defined as the time it takes to clean the bolter from cement. This needs to be done before every pause in bolting activity longer than 60 minutes, to prevent

- Unproductive time due to cement is defined as time spent at the face not working because it is not seen as useful to make a new batch of cement and clean the bolter afterwards.

This happens for example when the bolter arrives at a new work face an hour before the break or shift change.

- Operator repair time is defined as the time it takes the operator to replace a hydraulic hose or repair minor breakdowns on the bolter.

- Diesel-time is defined as the time it takes to drive from a working face to another working face or as the time it takes to drive from the bolt-storage to a new work face.

- Lunch & dinner breaks are defined as the time it takes to drive to the canteen, have lunch/dinner and drive back to the bolter.

- Maintenance & service is defined as the time the bolter is in planned maintenance or is reserved for maintenance.

- Logistic delay time is defined as the time spent by the operators to move from above ground to the machines and vice versa, this is also called the ‘logistic delay’.

- Stand-by time is defined as the time spent not working because there was no new work order.

In Figure 29, the typical operations during a day of bolting are shown, the lengths of the blocks do not represent the time spent on the tasks. The bolting operation includes cycle and method time.

All the data were added together to get a better overview of an average shift. In total 94.6 hours were spent observing the cement bolters, while installing 519 bolts. During these shifts two different machines were followed with multiple operators. In Figure 30 an overview of the time spent on activities can be seen. The cement related time has been added together because this is likely to change with the ‘High Performance’ method.

Figure 29. Example of typical cement bolting operations during a day.

Figure 30. Division of time spent on bolting activities.

During a part these observations the drilling, grouting and bolt inserting times have been logged on 5-second scale. This has been done for 55 bolts on multiple shifts to get a clear picture of the length of different steps in the cycle time. These observations are added together to get a total installation time per bolt, this cycle time has been compared with the cycle time we measured on a minute scale. There is a 9% difference in cycle time, this is most likely the result of differences in operator skill and rock conditions.

The categories mentioned above are used to calculate four different bolting productivity rates.

Where the net cycle time consists of the time it takes to manoeuvre the boom, drill a hole, grout the hole and insert a bolt. The method capacity is the productivity that can be reached while working at the face. The operational capacity is the rate that the machine can reach while including all the operations necessary for bolting. The long-term capacity is the rate that the equipment can reach including all the operational steps. See Figure 31 for a detailed division of the operations and capacities.

The operators were asked to record the start and end times of the cement cleaning for the duration of a month. With the start and end times, the duration of each cleaning moment has been calculated. These durations can be used to estimate the productivity gain by not having to clean anymore, 118 data points were collected this way. The durations have been verified with personal observations and are believed to be accurate, there is an 8% deviation. The durations reported by the operators are shorter, they reported an average of 23.6 minutes. During the observations an average of 25.5 minutes was recorded, for the calculations the times reported by the operators will be used this results in a more conservative estimate.

Figure 31. Rock bolting capacity definitions, adapted from (Gustafson, 2016).