Construction Operations and Methods: Safety, Equipment and Productivity

NCEES FE Civil spec: Construction Engineering, B. Construction operations and methods (e.g., safety, equipment, productivity analysis, temporary erosion control). FE Reference Handbook: Civil Engineering chapter, Surveying section (earthwork); Safety chapter.

What the FE Civil Spec Covers

Subtopic B of Construction Engineering is construction operations and methods: safety, equipment, productivity analysis and temporary erosion control. Expect a mix of short calculations (production rates, truck counts, labor productivity, swell) and conceptual questions about safe excavation and site erosion control.

Key Concepts

Equipment production

Production of cyclic equipment (excavators, loaders, scrapers, trucks) is the amount moved per cycle times the number of cycles per hour, reduced by an efficiency factor for delays. Bucket capacity is a loose volume, and a fill factor accounts for how full the bucket actually gets in a given material.

Swell and shrinkage

Soil measured in place is bank volume. Excavated soil is loose and occupies more space; compacted fill occupies less. Always convert to a common state before comparing production with a pay quantity.

Labor productivity

Productivity is output per labor-hour (or its inverse, labor-hours per unit). Crew productivity uses crew-hours.

Safety

Excavations 5 ft or deeper need a protective system (sloping, benching, shoring or a trench box) unless in stable rock.
OSHA soil types: stable rock, Type A, Type B, Type C. Maximum allowable slopes for excavations under 20 ft deep are vertical for stable rock, 3/4H:1V for Type A, 1H:1V for Type B and 1.5H:1V for Type C.
Trenches 4 ft or deeper need a ladder or other egress within 25 ft of lateral travel. Spoil must be kept at least 2 ft back from the edge.
The OSHA incidence rate normalizes injuries to 100 full-time workers (200,000 hours per year).

Temporary erosion and sediment control

Erosion control keeps soil in place (seeding, mulch, erosion control blankets, phasing to limit exposed area). Sediment control captures soil already moving (silt fence, inlet protection, check dams, sediment traps and basins, stabilized construction entrances). Good plans use both.

Core Formulas

Production = (bucket capacity) (fill factor) (\frac{60}{cycle time, min}) (efficiency)

V_{loose} = V_{bank} (1 + swell) V_{compacted} = V_{bank} (1 - shrinkage)

Load factor = \frac{1}{1 + swell} = \frac{V _{bank}}{V _{loose}}

Incidence rate = \frac{N \times 200 , 000}{total hours worked}

Where It Is in the FE Reference Handbook

Earthwork volume formulas (average end area, prismoidal) are in the Surveying section of the Civil Engineering chapter. The Safety chapter covers hazard assessment, confined spaces and incidence rate variables. Equipment production and swell are not spelled out as formulas, so know the relationships above.

Worked Example: Excavator Production and Duration

An excavator with a 3.0 LCY bucket loads trucks. Fill factor is 0.90, cycle time is 30 seconds, and the job runs a 50-minute hour. The soil swells 25%. How long does it take to excavate 5,400 BCY, and how many 12 LCY truck loads per hour does the excavator fill?

Step 1: cycles per hour.

\frac{60 min/hr}{0.5 min/cycle} = 120 cycles/hr

Step 2: loose production.

(3.0) (0.90) (120) (\frac{50}{60}) = 270 LCY/hr

Step 3: convert to bank volume.

\frac{270}{1.25} = 216 BCY/hr

Step 4: duration and truck loads.

\frac{5 , 400 BCY}{216 BCY/hr} = 25 hr \frac{270 LCY/hr}{12 LCY/load} = 22.5 loads/hr

Safety check on the same job: with 3 recordable injuries in 240,000 worker-hours, the incidence rate is $3 (200, 000) /240, 000 = 2.5$ per 100 full-time workers.

Exam Tips

Write the volume state next to every number (BCY, LCY or CCY) as you go. Most wrong answers on production problems come from comparing volumes in different states. If a problem gives a load factor instead of a swell percentage, convert with the load factor formula above: a load factor of 0.80 is the same as 25% swell.

For fleet problems, the slower link controls. If one excavator fills 22.5 truck loads per hour and each truck completes 4 round trips per hour, about 5.6 trucks keep the excavator busy; with 5 trucks the fleet is truck limited, and with 6 the excavator controls.

Common Mistakes

Dividing a bank quantity by a loose production rate (or the reverse) without applying swell.
Using swell to compute compacted fill. Compacted volume uses shrinkage relative to bank volume.
Forgetting the efficiency factor, or applying it twice.
Entering cycle time in seconds in a formula that expects minutes.
Treating silt fence as erosion control. It is a sediment control; it does not stop soil from detaching.

Practice Problems

Try these from the free PolyCalc FE Civil problem bank. Each one has a full worked solution.

Four workers each work 8 hours and together install 64 m². What is their productivity in square meters per labor-hour? See the worked solution or practice the Construction & Scheduling deck
1,000 m³ of bank soil swells by 25% when excavated. Trucks carry 10 m³ loose each. The number of truckloads needed is: See the worked solution or practice the Construction & Scheduling deck
A rectangular trench is 100 m long, 1.5 m wide, and 2 m deep, with vertical sides. What is its in-place excavation volume? See the worked solution or practice the Construction & Scheduling deck
A loader costs $200,000, lasts 20 years and has a $20,000 salvage value. At 7% interest, its equivalent annual cost of ownership is most nearly: See the worked solution or practice the Engineering Economics deck

Related Calculators and Examples

Frequently Asked Questions

What is the difference between bank, loose and compacted cubic yards?

Bank cubic yards are soil in its natural, undisturbed state. Excavation loosens it, so the same soil occupies more loose cubic yards (the swell). Compaction squeezes it into fewer compacted cubic yards than bank (the shrinkage). Trucks and buckets carry loose volume, while pay quantities are usually bank or compacted.

At what depth does OSHA require trench protection?

OSHA requires a protective system such as sloping, benching, shoring or a trench box for excavations 5 feet deep or more, unless the excavation is entirely in stable rock. A competent person must inspect excavations daily, and trenches 4 feet or deeper need a safe means of egress such as a ladder.

What does a 50-minute hour mean?

It is a job efficiency factor. A machine is assumed to work productively only 50 minutes of each hour because of delays, so ideal hourly production is multiplied by 50/60, about 0.83.

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