Douglas D. Gransberg / Construction Equipment for Engineers, Estimators, and Owners 037X_C004 Final Proof page 84 5.5.2006 11:23pm 84 Construction Equipment for Engineers, Estimators, and Owners 2. How much dirt (bcy) can be moved in one production cycle? The quantity takeoff is in bcy so the lcy load must be converted to bcy. 2:98 lcy=1:23 lcy=bcy ¼ 2:42 bcy=production cycle 3. What is the cycle time for one production cycle? Haul time ¼ 2000=[(3:2 mph)(880=min=mph)] ¼ 0:87 min Backtrack time ¼ 2400=[(3:2 mph)(880=min=mph) ¼ 0:85 min Cycle time ¼ load þ haul þ backtrack þ reposition ¼ 0:08 min þ 0:87 min þ 0:85 min þ 0:06 min ¼ 1:86 min 4. What is the work hour productivity if the operator works 50 min per 60-min hour? Work hour productivity ¼ [(load volume(bcy) )(50 min)]=cycletime ¼ [(2:42 bcy=load)(50 min)]=1:86 min=cycle ¼ 65:05 bcy=work hour 5. How long will it take to move the 1200 bcy? 1200 bcy=65:05 bcy=h ¼ 18:45 h: Use 18:50 work hours 6. How much will it cost? $55=h þ $23=h ¼ $78=h  18:50 h ¼ $1443 7. What is the unit cost to perform the work? $ 1433=1200 bcy ¼ $1:203=bcy to move the dirt with the Case 750K bulldozer 4.4.2 FRONT-END LOADERS Front-end loaders typically are tractor powered and operate on tires. They are typically articulated and very maneuverable, making them ideal for constricted areas. They are used primarily for material moving and re-handling. They are ideal for scooping and hauling materials in storage piles, where it is to be permanently placed, or loading it into dump trucks. Loaders are ideal for dumping soil back into the hole after the necessary below grade work is done. Tracked loaders may be required for extreme surface conditions demanding greater traction or stability. Every concrete or asphalt batch plant has a tire equipped front- end loader to stock the feed to the batch hopper with aggregate and sand. Fixed cycle times for loaders (raise, dump, and lower the bucket) range from about 9 s to about 20 s depending on the size of the loader. General-purpose bucket capacities range from about 0.75 to 18 lcy. Figure 4.10 shows a small loader that is ideal for confined spaces and smaller loads. These small loaders are very maneuverable and are ideal for use in constricted limited working areas. They are used often for moving sand within slab forms or with fork attach- ments to carry brick, mortar, or sand. They are excellent for surface movement of small amounts of material. These machines are generally referred to as ‘‘Bobcats,’’ which was a Douglas D. Gransberg / Construction Equipment for Engineers, Estimators, and Owners 037X_C004 Final Proof page 85 5.5.2006 11:23pm Earthmoving, Excavating, and Lifting Equipment Selection 85 FIGURE 4.10 Skid-steer loader. small skid-steer loader manufactured by Melrose. Readily available attachments include augers, cold planers for light milling, landscape tillers and rakes, trenchers, vibratory com- pactors, and brooms. 4.4.2.1 Loader Production Loaders are used many times with feed hoppers and dump trucks. The loader is sized by the demand of the feed hopper or the size and number of dump trucks that can be filled. Production cycle components are similar whether running on tracks or tires. The work surface stability will influence the cycle time. Small skid-steer loaders are very maneuverable and cycle times might be less. Example 4.4 A Cat 950G wheel loader with a 4.25 lcy heaped bucket is to be used to move fairly loose stockpiled dirt onto a conveyor running under the road. The conveyor is carrying the dirt to another part of the site. The dirt will be used to fill that side of the project site. The Cat Performance Manual suggests a cycle time (load, dump, maneuver) of about 55 s for the way you have the work setup and an O&O cost of about $31/h. Your operator costs about $23/h. The conveyor will haul about 280 lcy/h. Will the production of the loader keep up with the conveyor? 1. How much dirt (lcy) can be moved in one production cycle? V ¼ 4:25 lcy=cycle 2. What is the cycle time for one production cycle? Cycletime ¼ 55 s=cycle=60 s=min ¼ 0:92 min Douglas D. Gransberg / Construction Equipment for Engineers, Estimators, and Owners 037X_C004 Final Proof page 86 5.5.2006 11:23pm 86 Construction Equipment for Engineers, Estimators, and Owners 3. What is the work hour productivity if the operator works 50 min per 60-min hour? Work hour productivity ¼ [(load volume(lcy) )(50 min)]=cycletime ¼ [(4:25 lcy)(50 min)]=0:92 min=cycle ¼ 231 lcy=work hour Based on this calculation, the 950G will be short about 49 lcy/h. Assuming one cannot change the work layout, options to meet the necessary 280 lcy/h production include a larger bucket on the 950 (for this situation, probably not feasible), a larger loader or two smaller loaders. 4. What is the daily cost for using this loader if the conveyor runs 11 h/day? $31þ $23¼ $54=h  11 h=day ¼ $ 594=day 5. What is the unit cost per day to use the 950G loader? 231 lcy=h(11 h=day) ¼ 2541 lcy=day $ 594=day=2541 lcy=day ¼ $0:233=lcy 4.4.3 MOTOR GRADERS This type of equipment has been around since the start of road building, though originally powered by a team of oxen, mules, or horses. The need for a smooth stable travel surface has always been an important part of a road system. Another name for a motor grade is ‘‘maintainer.’’ This name is appropriate because this equipment is typically used to maintain grade and a smooth surface for rural nonpaved travel roads or haul routes on construction sites. The grader is a long tractor-driven piece of equipment with a blade mounted underneath as shown in Figure 4.11. FIGURE 4.11 Motor grader. Douglas D. Gransberg / Construction Equipment for Engineers, Estimators, and Owners 037X_C004 Final Proof page 87 5.5.2006 11:23pm Earthmoving, Excavating, and Lifting Equipment Selection 87 The blade is used to push dirt straight ahead or to the side at a desired level. The grader can be used for light surface excavation, but is mainly used to move soil to create a level surface. Note the ring to which the blade is attached underneath the frame. This ring can be swiveled vertically and the casting angle of the blade adjusted on it. The blade can be angled to shape road banks. Standard blade widths range from 120 to 140 and speed in midrange gear is approximately 6 mph. Front tires are usually leaning to resist the force created when the blade is cutting and side casting the material. As the dirt is pushed ahead of the blade it fills voids in the surface over which it is moving. Excess dirt is pushed into other surface voids or to the side. When the dirt is cast to the side of the grader, this is called a windrow (row of piled dirt). Usually a front-end loader will follow behind the grader to scoop up excess dirt in the windrow if necessary. For a small amount of excess, a backhoe scoop can be used. Laser level readers can be attached to the motor grader blade so that the operator can establish a desired elevation using the level signal, not having to rely on feel and experience as much. The grader depth of cut is adjusted based on the signal setting. 4.4.3.1 Motor Grader Production On large dirt-moving jobs, the motor grader operator is responsible for the movement, spotting, and leveling of the delivered fill. This operator is like an equipment group foreman. The delivered fill might be from the other side of the project site or brought from a pit miles away. Since soil is leveled and compacted by lift, where and how much soil should be dumped must be managed for efficient spreading as it is delivered. In road base construction, the grader is typically the last major earthmoving equipment used during compaction. Graders are usually set up to run in linear or rectangular patterns. Production is measured in area covered in a certain amount of time (square feet per hour, cubic feet per hour). When grading linearly, the operator usually has the blade dropped (cutting) until the end of the pass, turns, drops the blade, and grades the opposite direction. When grading an area for a parking lot, two methods of the rectangular patterns can be used. Using the ‘‘back and forth’’ method, the operator travels with the blade down to the end of the pass, picks up the blade, backtracks, drops the blade, and starts over. Using the ‘‘looping’’ method, the operator drops the blade for the pass, lifts the blade at the end of the pass, turns the grader in an arc to the other direction, and drops the blade for this pass. The process is repeated until the area is covered with the grader traveling in a forward loop or oval as many times as necessary to cover the surface. To set the ‘‘looping’’ coverage pattern, the turning radius of the motor grader must be considered. The turning radius is typically listed in the performance spec for the model.