In highway construction project, a contractor is considering the use of a single-engine scraper to haul material from a

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In Highway Construction Project A Contractor Is Considering The Use Of A Single Engine Scraper To Haul Material From A 1 (75.3 KiB) Viewed 27 times

In highway construction project, a contractor is considering the use of a single-engine scraper to haul material from a pit to a fill area under severe conditions. The material to be hauled is a dry earth. Assume, at an average speed of 5 mph, that 200 ft is required to both accelerate and decelerate. The operating efficiency will be equal to a 50-min hour. the scraper specifications are presented Table 8.1 and on the "performance charts" below. Use a 0.85-min load time which will result in an average load of 91% heaped capacity (from optimum loading time chart). Assume Dump time=0.37 min, turn time fill= 0.21 min and Turn time cut=0.30 min. in push-loaded scraper, the swell factor should be increased by 10%. The travel road is hard, smooth and stabilized roadway with total length of 3,200 ft and has the following individual segments when moving from cut to fill: 600 ft +1% grade 2,200 ft 0% grade 400 ft +4% grade PUSHER TIME= (1.4X Load Time) + 0.25 You are required to analyse the probable pusher/scrapers fleet production and then select the optimum fleet configuration (pusher + scrapers) to minimize the project duration and then calculate the cost of the selected fleet. It should be noted that only one pusher and 6 scrapers are available to contractors. It also given: Scraper operation cost including operator is $250/hr pusher operation cost including operator is $350/hr hourly indirect cost= $450
TABLE 8.1 Specifications for a Caterpillar 631E scraper. Engine: flywheel power 450 Transmission: semiautomatic power shift, eight speeds 21 cy Capacity of scraper: Struck Heaped 31.cy Weight distribution: Empty Drive axle 67% Rear axle 33% Loaded Drive axle 53% Rear axle 47% Operating weight: Empty 96,880 lb* Rated load: 75,000 lb 33 mph Top speed: Loaded "Includes coolant, lubricants, full fuel tank, ROPS canopy, and operator.
RIMPULL lb x 1000 1:50 120 100 70 50 40 30 20 15 10 5 2 ▬▬▬▬▬▬ kg x 1000 65 55 45 35 25 20 15 10 8 6 A 2 30 15 I GROSS WEIGHT 40 50 60 80 100 120 160 200 lb x 1000 ‒‒‒‒‒‒‒‒‒ 20 30 40 50 60 70 90 kg x 1000 30% 25% -20% -15% 12% 10% 8% 5% 4% 3% 2% I Hỳ I ! I 11 5 10 15 20 25 30 35 40 45 50 55 5 10 15 20 25 SPEED km/h 30 35 mph RESISTANCE (Grade plus Rolling Resistance) TOTAL
55 0 75 30 40 5 10 15 Key: 3 3rd gear direct drive 10 100 20 Gross weighs 150 50 25 15 Speed 60 30% 30 175 70 35 40 45 20 25 30 Key: E Empty 43.945 kg (96.880 lb) 50 (x1000) 80 kg (x1000) 22% 165 10% Effective grade (grade minus rolling resistance) Hallo 1% 35 km/h 35 mph
Table 12.2 Typical Rolling Resistance Factors (Caterpillar Tractor Co.) A hard, smooth, stabilized roadway without penetration under load (concrete or blacktop) A firm, smooth-rolling roadway flexing slightly under load (macadam or gravel-topped road) Snow-packed Loose A rutted dirt roadway, flexing considerably under load; little maintenance, no water (hard clay road, 1 in. or more tire penetration) Rutted dirt roadway, no stabilization, somewhat soft under travel (4-6 in. tire penetration) Soft, maddy, nutted roadway, or in sand 40 ]bvton 65 lb/ton 50 lb/ton 90 lb/ton 100 lb/ton 150 lb/ton 200-400 lb/ton
TABLE 4.3 Representative properties of earth and rock. Bank weight Loose weight Percent ko/m³ lb/cykg/m²³ swell kg/m³ Material Ib/cy Clay, dry 2,700 1,600 2,000 1,185 35 Clay, wet 3,000 1,780 2,200 1,305 35 Earth, dry 2,800 1,660 2,240 1,325 25 Earth, wet 3,200 1,895 2,580 1,528 25 Earth and gravel 3,200 1,895 2,600 1,575 20 Gravel, dry 2,800 1,660 2,490 1,475 12 Gravel, wet 3,400 2,020 2,980 1,765 14 Limestone 4,400 2,610 2,750 1,630 60 Rock, well blasted 4,200 2,490 2,640 1,565 60 Sand, dry 2,600 1,542 2,260 1,340 15 Sand, wet 2,700 1,600 2,360 1,400 15 Shale 3,500 2,075 2,480 1,470 40 *The swell factor is equal to the loose weight divided by the bank weight per unit volume. Swell factor 0.74 0.74 0.80 0.80 0.83 0.89 0.88 0.63 0.63 0.87 0.87 0.71