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5. STUDY METHODOLOGY AND ANALYSIS OF DATA

The efficiency of the environmentally sound road construction technique using hydraulic excavator as applied in the road projects under review has been investigated with work and time studies analysing the work performance of the operations.

Work and time studies were done in accordance with the forest work study nomenclature (IUFRO, 1995). The study methodology used for all time studies conducted during construction operations and rock disintegration activities was cumulative timing exclusively, with the time for each work element subsequently obtained by subtraction.

The excavator operator and the blasting operator were observed by work and time studies. Additional information on workers assisting, by carrying out supportive construction activities, was collected to support the analysis of time consumption and the interpretation of time distribution of work elements.

5.1. Work and time study on forest road construction

Road construction by excavator comprises a set of activities (see Table 11) undertaken to provide the desired road design. Depending on terrain conditions, type of excavator used and the operators' way of arranging the distinct phases of road construction, these activities vary with respect to their frequency of occurrence.

Nevertheless, at each construction site a sequence of regular work elements can be found for the construction operation that constitutes the work cycle. Work cycle is defined as a sequence of work repeatedly applied to every work object (IUFRO, 1995). A work element is considered a sub-division of a given work task and is limited by break points. Depending on the occurrence in every work cycle, a work element can be considered as a repetitive or an occasional element.

Only workplace time, which is defined as the portion of the total time that a production system or part of a production system is engaged in a specific work task (IUFRO, 1995), has been considered in estimating production rates and costs at the study sites.

Figure 5 shows the structure of work time elements that occurred during time studies.

Figure 5. Structure of Workplace Time (WP) concepts

5.1.1. Work and time study on excavator operations

The classification and the percentage of workplace time consumption observed for each work element in construction operations at the study sites can be found in Appendix 1. General information on construction operations where time studies had been carried out are stated below for all three study sites under review.

On average the workplace time per metre of road constructed by excavator was 10.54 minutes at study site 1, the corresponding figure for study site 2 was 11.46 minutes and 24.75 minutes for study site 3. The time required per metre of road either of workplace time or of work time serves as the basis for estimating production rates, treated in Chapter 5.2.

   

Study site 1

Study site 2

Study site 3

 
 

Subject of

Kobelco

Komatsu

Caterpillar

 
 

observation

Mark IV SK210

PC300LC

320L

 
 

Work time

29 h 00 min

16 h 48 min

16 h 42 min

 
 

Non-work time

2 h 52 min

1 h 43 min

4 h 20 min

 
 

Workplace time

31 h 52 min

18 h 31 min

21 h 02 min

 
           
 

Subgrade width

4.5 m

6.5 m

4.2 m

 
 

Length of section

181.5 m

97.0 m

51.0 m

 

At study site 1, the excavator operator was found to accomplish construction work by following the stated order of the five distinct phases in Chapter 3.2, whereas at study site 2 and 3 the operators chopped and changed between activities of distinct phases. At study site 3, the way single activities had been arranged was mainly determined by the interference of the necessary drilling and blasting operations rather than by a personal preference of the excavator operator.

However, in order to compare construction work at the three study sites, the average productive work time required per metre of road constructed by excavator and time distribution of work elements assigned to the productive work time are stated in Table 11.

Table 11. Distribution of productive work time elements

     

Study site 1

Study site 2

Study site 3

 
 

Work elements (classification)

[min]

[%]

[min]

[%]

[min]

[%]

 
 

Log removal

(MW)

2.09

23.9

2.57

27.0

0.08

0.5

 
 

Topsoil removal

(MW)

2.15

24.6

1.90

20.0

0.73

4.3

 
 

Excavating base

(MW)

0.62

7.1

---

---

0.05

0.3

 
 

Fill slope construction

(MW)

0.96

10.9

1.69

17.8

6.37

37.6

 
 

Subgrade and cut shaping

(MW)

2.79

31.9

3.03

31.8

1.32

7.8

 
 

Use of hammer

(MW)

---

---

0.24

2.5

2.76

16.3

 
 

Loading truck

(MW)

---

---

---

---

3.81

22.5

 
 

Complementary work

(CW)

0.14

1.6

0.09

0.9

1.81

10.7

 
                   
 

Productive work time

(PW)

8.75

100.0

9.52

100.0

16.93

100.0

 

On average the productive work time required per metre of road constructed by excavator was 8.75 minutes at study site 1 and 9.52 minutes at study site 2 where rock disintegration by hydraulic hammer got involved. At study site 3 the corresponding figure amounted even to 16.93 minutes due to the high share of complementary work caused by the interference of blasting operations. The complementary work covers the time for movement from and to the construction area within the road sections under review. At study site 1 and 3 it also includes a negligible time share for checking the road gradient of constructed road sections by the operator.

As already mentioned in Chapter 3.2, road construction by operators who chop and change between activities and/or running metre based payment of contractors might lead to inadequate construction practice.

The figures on time distribution stated in Table 11 clearly indicate that a distinct work element "excavating base for fill foundation" did not occur at study site 2. This does not necessarily mean that a fill failure will take place in the future as the terrain condition of the particular road section under review was quite favourable but if this poor practice had been followed in other parts of the road project there is potential for road failure.

The low time share of the work element "excavating base for fill foundation" at study site 3 was not as a result of poor construction technique but was caused by the difficulty to clearly separate this work element from other activities due to the interference of truck loading and blasting operations.

5.1.2. Work and time study on blasting operations

The classification and the percentage of workplace time consumption observed for each work element in blasting operations at study site 3 can be found in Appendix 2. General information for study site 3 on blasting operations and on supportive construction work carried out by the blasting operator is stated below:

 

Subject of

Study site 3

 
 

observation

Blasting operation

Supportive work

 
         
 

Work time

12 h 57 min

3 h 44 min

 
 

Non-work time

3 h 42 min

20 min

 
 

Workplace time

16 h 39 min

4 h 04 min

 

On average the workplace time used per blasting operation for rock disintegration of an average volume of 76 m³ rock by means of explosives was 166.5 minutes at the study site where six blasting operations had been observed. Due to the excellent planning and timing at study site 3, the non-work time of the blasting operator was dramatically reduced as he operated a small excavator hired only for a few days to carry out supportive construction work. This was to incorporate excess material in the subgrade which had been moved by a dump truck from the construction area to adjacent road sections already established in previous work cycles.

Table 12. Distribution of productive work time elements

     

Study site 3

 

Work elements (classification)

[min]

[%]

 

Rock drilling

(MW)

45.86

39.8

 

Loading of explosives

(MW)

39.87

34.6

 

Connecting loads

(MW)

10.60

9.2

 

Control and preparation

(MW)

7.14

6.2

 

Blasting

(MW)

0.34

0.3

 

Ignition cable removal

(CW)

11.41

9.9

         
 

Productive work time

(PW)

115.22

100.0

On average the productive work time required per blasting operation for rock disintegration of an average volume of 76 m³ rock by explosives amounted to 115.22 minutes (Table 12). For blasting of this rock volume about 11 vertical holes of 3-4 m length were drilled and about 16.5 kg explosives used.

5.2. Estimating production and performance rates

Since productivity is defined as the rate of product output per time unit for a given production system, the production rates of a studied system can easily be estimated if time studies combined with measurements of the output of production have been completed.

5.2.1. Excavator

The estimated production rates for excavator operations stated in Table 13 are based either on the total workplace time or total work time used to perform a certain length of road by the excavator operator at all study sites, regardless of whether a hydraulic hammer has been used or not.

All other construction activities where an excavator will be employed (culvert, retaining structures), might be employed (shaping after surfacing) or might serve as carrier unit (rock drilling) are not included in the estimates of production rates stated in Table 13, neither for workplace time-based nor for work time-based estimates.

Table 13. Estimated production rates in road construction by excavator

   

side slope

subgrade width

Production rate

Production rate

 
 

Study site

[%]

[m]

[m/h WP]

[m/h WT]

 
 

Study site 1

50-55

4.5

5.69

6.26

 
 

Study site 2

40-45

6.5

5.24

5.77

 
 

Study site 3

75-80

4.2

2.42

3.05

 

Note: WP ... workplace time WT ... work time

Based on the hourly productivity found in the studies and on an assumed workplace time of 8 hours per day, the productivity rates range from 16 metres to 48 metres of road per day, where the first figure can be considered indicative for extreme difficult terrain and the latter for favourable conditions in mountainous terrain. It is noteworthy that the actual workplace time observed during the studies often exceeded the regular workplace time for employees of 8 hours per day as the operators tended to make use of favourable weather conditions for construction work.

The figures found in the literature on production rates for hydraulic excavators as in Gorton (1985) and in FAO (1989) are difficult to compare with those stated in Table 13. One main reason is that the activities performed by the excavator are not defined in mentioned papers. If the figures do not cover the first phase of excavator construction, namely, log removal from construction area, this would explain to a high degree the difference between the higher figures found in both papers and the lower rates derived from the data collected in the time studies at the three construction sites. Another reason is the lack of information on the time basis of the production rates stated in the literature mentioned above.

5.2.2. Rock blasting

The estimated performance rate for blasting operations at study site 3 is based on the workplace time used for rock disintegration of a certain volume of rock by means of explosives. Since the vertical drilling holes were placed in a rectangular pattern 1.5 m square in each single blasting operation at the study site, the volume of disintegrated rock has been estimated separately for each blasting operation by multiplying the squared distance between holes by the length of holes and the number of holes.

Time calculations to estimate performance rates of blasting operations based on the total workplace time are considered to be not indicative as the non-work time of the blasting operator can dramatically be decreased by flexible and proper timing of construction and blasting operations as done at the study site.

Therefore, the performance rate stated below is based on the work time only. The efficiency level found at the study site, as the rate of time input per a certain volume of rock to be disintegrated, was about 2.13 min/m³ reflecting an average volume of load of about 76 m³ per blasting operation. The performance rate based on all blasting operations observed amounts to 28.18 m³/h of work time.

5.3. Estimating costs

The estimation of production costs is based on the production and performance rates stated in previous chapters for construction and blasting operations and the hourly costs for construction workforce and equipment involved in both road construction and blasting operations. The hourly costs for workforce and equipment are based upon information obtained from the supervising forest engineer of the Federal Forest Service of Salzburg.

Refinement work stated in Table 14 refers to final shaping and compaction work of the fill slope at study site 1 for part of the road section under review. At study site 3 it refers to incorporating excess material into the road structure after transport by a dump truck. In this particular case incorporation work was carried out by means of a small excavator hired for a few days of anticipated need and which was operated by the blasting operator.

The use of the small excavator provided an effective means of arranging the work in a way that dramatically reduced the non-work time of the blasting operator. It should be noted that in hiring additional equipment, proper timing becomes very important in order to achieve the desired objective of overall cost reduction in road construction.

Table 14 shows the costs for equipment and standby workforce as well as costs for each activity carried out and observed by the work and time studies at the study sites in road construction. As conditions for construction work may considerably vary along the road course, the construction costs stated in Table 14 refer to the particular road section under review of each road project only. This fact has particularly been proven to be true in the road project - Golling where study site 3 was located. For details compare corresponding figures on cost of construction work by excavator stated in Table 14 and Table 15.

Table 14. Estimated costs of road construction work by excavator

     

Study site 1

Study site 2

Study site 3

 
     

cost/unit

cost

cost/unit

cost

cost/unit

cost

 
 

Production costs factor

unit

[US$]

[US$/m]

[US$]

[US$/m]

[US$]

[US$/m]

 
 

Construction work

               
 

hydraulic excavator

    [h]

56.67

9.96

91.67

17.49

57.50

23.76

 
 

hydraulic hammer

    [h]

---

---

39.17

0.15

39.17

1.80

 
 

Refinement work

               
 

hydraulic excavator

    [h]

56.67

0.16

---

---

45.00

3.51

 
 

Rock blasting

               
 

hydraulic drilling unit

    [h]

---

---

---

---

95.83

24.33

 
 

explosives

    [kg]

---

---

---

---

5.42

10.51

 
 

primer

    piece

---

---

---

---

2.50

3.14

 
 

operator (standby)

    [h]

---

---

---

---

37.50

5.48

 
 

Mass transport

               
 

dump truck

    [h]

---

---

---

---

48.33

5.66

 
                   
 

Total construction cost

   

10.12

 

17.64

 

95.83

 

The cost estimates stated in Table 14 refer to the road in the stage of finished subgrade and subsequent establishment of hillside ditch as described in Chapter 3.2 and do not include any further construction activity which will be or might be performed by excavator at a later stage such as to install culverts, to build up retaining structures or to final shape the road after surfacing.

Table 15. Estimated overall construction costs of road projects

     

Study site 1

Study site 2

Study site 3

 
     

cost/unit

cost

cost/unit

cost

cost/unit

cost

 
 

Production costs factor

unit

[US$]

[US$/m]

[US$]

[US$/m]

[US$]

[US$/m]

 
 

Excavator operations*

 

n.a.

11.97

n.a.

17.52

n.a.

70.27

 
 

Culvert (incl. in-/outlet

               
 

protection) culvert pipe

piece

32.92

0.66

32.92

0.66

32.92

0.66

 
 

hydraulic excavator

[h]

56.67

1.13

91.67

1.83

57.50

0.86

 
 

Surfacing material

[rm]

1.04

1.73

1.04

1.04

1.67

0.25

 
 

gravel transport

[rm]

5.83

9.72

5.83

5.83

5.83

0.88

 
 

Grading / shaping

               
 

motor grader

[h]

77.08

0.44

77.08

0.44

---

---

 
 

hydraulic excavator

[h]

---

---

---

---

57.50

1.05

 
 

Rolling

[h]

59.58

0.96

59.58

0.48

59.58

0.48

 
 

Seeding

[m²]

0.15

1.01

0.15

1.13

0.15

1.17

 
                   
 

Overall road cost

   

27.62

 

28.93

 

75.62

 

 

*) corresponding with the total construction cost estimate in Table 14

n.a. not applicable

 

The estimated overall construction costs of the three road projects under review stated in Table 15 are based on the actual costs spent on excavator operations including rock disintegration during the construction season of 1997 in the road projects under review and the assumed costs of construction activities required to finalize the road.

The cost assumptions made for installing culverts including retaining structures, for surfacing, grading and rolling of the road as well as for seeding of slope surfaces are based on the personal experience of the supervising forest engineer. Since these activities had not been observed by work and time studies estimated costs have been used.

5.4. Qualitative assessments of environmental impacts

In mountainous terrain where forest stands not only sustain site productivity by preventing soil developed over centuries to be eroded but often protect human settlements, infrastructure and other land uses from torrents and avalanches, avoidance of site disturbance is imperative. On the other hand, active management of overmature stands on steep slopes which are at risk of loosing their protective function, requires a minimum of forest access provided by forest roads.

Enhancing forest road construction practices, the use of hydraulic excavators and employment of advanced drilling and blasting technology have been proven to be the best solution both environmentally sound and economically feasible, for road construction in difficult terrain.

· the excavator basically operates by digging, swinging and either dumping or controlled placement of excavation depending on the task to be provided;

· all tasks to be accomplished in road construction by excavator can be provided by operating from a fixed position or movement parallel to the road centreline so that no additional road width for manoeuvring is required;

· different types of buckets available and several attachments easily to be changed by quick coupling systems even increase the excavators' versatility to do a wider variety of work e.g. ripping, trenching, loading, compacting, hydraulic hammering or rock drilling;

· less need for blasting due to high ripping and breakout force of the excavator and, alternatively, the use of hydraulic hammer for rock disintegration.

· the type of hydraulic drilling units used, attached to the excavator, facilitates vertical as well as horizontal drilling and therefore to optimise and adjust blasting technique with regard to rock condition;

· "soft" blasting with less disruptive effect on the bedrock avoids loosening of stratified and/or fractured rock as well as other blast-related damage;

· "soft" blasting techniques with less destructive effect enable to control the size of rock material provided;

· "soft" blasting techniques only loosen the rock for being excavated rather than blowing rock fragments away;

In making use of the advantages of construction equipment and techniques mentioned above, the skilled and experienced operator is provided with an effective tool to minimize environmental impacts of road construction activities. This environmentally sound practice of road construction is characterized by:

· additional road width for manoeuvre of construction machinery is not needed; the subgrade width is kept to the absolute minimum determined by safety and anticipated use;

· the length of fill slope can be reduced due to a solid fill foundation established by means of the excavator and the overall construction width is reduced;

· clearing width is reduced as a result of minimized overall construction width and disturbance of canopy and related impacts are reduced;

· cut heights are reduced because of minimized overall construction width;

· roads are designed to balance cuts and fills wherever possible, less rock disintegration is needed and less material is to be excavated;

· the use of hydraulic hammers facilitates accurate rock excavation; over excavation of rock can be avoided;

· rock disintegration by hydraulic hammer and "soft" blasting provides material suitable in size to be incorporated in the road structure, the need for borrow pits is reduced;

· measures are undertaken to stabilize and revegetate cut and fill slopes immediately after completion of road construction work, scars inflicted on the landscape are quickly remedied;

· drainage facilities can already be installed by the excavator during the ongoing road construction process at any time if required;

· most of the excavated material is incorporated in the road structure and properly compacted, it is very likely unavailable for erosion;

· cut and fill slopes are final shaped and compacted by means of the excavator's bucket to prevent erosion;

· branches removed from the construction area are spread on the fill slopes the exposure to erosion of unprotected soil is minimized;

· retaining walls for slope stabilization can be established during road construction at any time if required;

· the excavation is incorporated into the road structure instead of being side cast and excess material from full bench road sections is end-hauled to stable disposal areas;

· the placement of excavated materials can excellently be controlled by the skilled excavator operator and loose material which might escape during construction activities will be trapped by a slash filter windrow established at the base of the fill;

· the use of rock buckets and hydraulic hammers widely replaces the need for blasting where hurled stones or escaping rocks might cause some damage even if advanced blasting techniques are applied;

· "soft" blasting techniques with less destructive and bursting effect are employed if substantial rock blasting is specified;

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