# Influence of Crushed Rock Properties on the Productivity of a Hydraulic Excavator
## 2 Materials and Methods of Field Research  
Measurements were performed under field conditions on seven crushed rock quarries. Two of them are diabase quarries (\"Zervanjska\" and \"Hruskovec\"), four of them are dolomite quarries (\"Zapresicki Ivanec\", \"Gradna\", \"Skrobotnik\" and \"Ocura\"), and limestone was excavated at quarry \"Spica\". The locations of the quarries are shown in Figure 1.  
Figure 1: Locations of quarries where field measurements were conducted.  
Excavators performed either loading of blasted rock material into trucks or mobile crushers or gravitational transport of overburden. Gravitational transport is throwing of overburden and rock material from excavation into haulage benches, and it is common in most quarries of crushed stone in the Republic of Croatia as the most economical method of transport [29].  
The measurement procedure at every location composed of loading the bucket and taking photographs of the top material for measurement of the angle of repose. The next step was taking photographs of the empty ground in the marked area. After unloading the bucket in the same area, the heap was photographed which served as the volume of bucket load determination as well as particle size distribution. Afterwards, a video recording was started and a minimum of 100 excavator cycles were recorded. The procedure was repeated three times and the given results represent average values.  
The volume of the excavator's bucket load was determined by using software for photogrammetric analysis from pairs of photographs, Photomodeler Scanner, in this case. The volume was determined as the difference between the heap surface and base surface. Previously fixed marks were used as common reference points for both surfaces (Figure 2a). The angle of repose was measured using the same software but on the surface generated from the material on top of a strike plane of a bucket (Figure 2b). The angle represents the average slope between the top and bottom points on four sides of the surface.  
Granulometric analysis of each relevant rock material was performed by taking digital images of a heap, simultaneously with the volume measurement (Figure 2a). Two images from opposite angles were selected for the analysis to give representative parameters of a material. Digital images (Figure 3a) were processed by Wipfrag computer software for granulometric analysis, and parameters of rock particle size distribution were obtained (Figure 3b).  
The duration of the excavator loading cycle was measured by analysis of video recordings taken by a digital video camera during the excavator operation. These video recordings, of each observed excavator, were then analyzed in Windows media player, and cycle times were recorded. Table 1 shows the results of field measurements as well as granulometric analyses of the rock material in the bucket.  
For convenience, methodology for calculating the excavator's productivity and forming regression equations is presented in the following chapters, in parallel with the analysis.  
Figure 2: **(a)** Measuring volume of the bucket load and (b) angle of repose of material.