CELE Construction Management & Methods — Construction Methods, Equipment and OperationsRevision Notes

Formulas

Exam Tips

• Memorize: cycles/hr = 3600 ÷ t_c (seconds). Write this on your scratch paper first.
• The 50-min working hour (E = 0.833) is the standard PRC board assumption unless stated otherwise.
• If both fill factor and rated capacity are given, multiply them for effective capacity before plugging into the formula.
• Always label your answer units: m³/hr, LCM/hr, or BCM/hr — examiners notice unit consistency.
• Quick check: For a 1 m³ bucket at 30-s cycle and 50-min hour: Q = 1 × 120 × 0.833 = 100 m³/hr. Use this as a mental benchmark.

Key Points

• The universal productivity equation applies to ALL cyclic construction equipment: excavators, loaders, dozers, scrapers, and cranes.
• Output (m³/hr or tonnes/hr) = Capacity per cycle × Cycles per hour × Efficiency factor.
• Cycles per hour is derived from the cycle time expressed in SECONDS: cycles/hr = 3600 ÷ cycle time (s). NEVER use minutes in this formula directly.
• Efficiency (E) reflects the actual working fraction of the hour. The 50-min working hour is the most common board-exam assumption: E = 50/60 = 0.833.
• For bucket equipment (excavators, loaders, clamshells), multiply by the Bucket Fill Factor (BFF) — a value ≤ 1.0 — to account for the bucket not always being 100% full.
• The fill factor is already included in the rated heaped capacity for some manufacturers; read the problem carefully to avoid double-counting.
• Job efficiency factors also reflect management conditions (excellent = 0.90, average = 0.75, poor = 0.60); the problem will specify which to use.
• Output is expressed in loose cubic metres (LCM) for haulers and bank cubic metres (BCM) for excavators unless stated otherwise — always track your volume units.

Definitions

Section Title

1. Equipment Productivity Fundamentals

Common Mistakes

• Using cycle time in MINUTES in the formula Q = C × (3600/t_c) × E — always convert to seconds first.
• Forgetting to apply the bucket fill factor when it is stated separately from the rated capacity.
• Using 60 min/hr as efficiency when the problem specifies a 50-min or 45-min working hour.
• Reporting output in bank m³ when the question asks for loose m³ (or vice versa) — always note the volume basis.
• Double-applying the fill factor when the problem states 'effective capacity' (which already includes BFF).

Formulas

Exam Tips

• List all cycle components: Load + Haul + Dump + Return. Write them out before computing T_cycle.
• Double-check: T_load must be one component of T_cycle. If N = T_cycle/T_load = 6, it means the loader fills 6 trucks in one truck cycle.
• If the problem gives T_load separately (e.g., '4-minute load time'), use it directly — no need to compute passes.
• If N = 6.2, use 7 trucks (round up). If N = 6.0 exactly, use 6 trucks.
• Bonus insight: With N trucks, loader utilization = 100% only when N equals the exact balance point. With N+1, some trucks queue.

Key Points

• Fleet matching determines the optimum number of haul trucks (dump trucks) required to keep a loader or excavator continuously productive without idle time.
• The fundamental concept: a truck must complete its full cycle (load + haul + dump + return) in the time it takes the loader to fill N trucks.
• N = Truck Total Cycle Time ÷ Truck Load Time (= loader cycle time × number of passes to fill).
• Always ROUND UP N to the next whole number — you cannot have a fractional truck, and rounding down starves the loader.
• If the computed N is exactly a whole number (e.g., 6.0), use 6 trucks — no rounding needed.
• Too few trucks: loader sits idle → lost production. Too many trucks: trucks queue and idle → wasted equipment cost.
• The economically optimal fleet minimizes total cost per unit output; board exams test the formula, not the cost optimization.
• Load time = (truck capacity ÷ loader capacity per cycle) × loader cycle time, when passes-to-fill must be computed from first principles.

Definitions

Section Title

2. Fleet Matching — Trucks and Loaders

Common Mistakes

• Rounding N DOWN instead of UP — always round to the next higher integer unless N is already a whole number.
• Omitting the dump time or maneuver time from the total truck cycle — read the problem for ALL cycle components.
• Using inconsistent time units — mix of seconds and minutes in T_cycle and T_load will give wrong N.
• Forgetting that T_load already appears in T_cycle (it is a component of the truck cycle, not added separately).
• Using gross (heaped) truck capacity without applying swell factor when loading bank material into the truck.

Formulas

Exam Tips

• Draw a simple 3-box diagram: BCM → (×1+S) → LCM and BCM → (×1−Sh) → CCM. This one sketch prevents all formula-confusion errors.
• For truck-loading problems: always convert BCM to LCM first (multiply by 1+S) before dividing by truck capacity.
• For embankment problems: always convert CCM to BCM first [divide by (1−Sh)] before costing the excavation.
• Typical board-exam swell: 20–25% for common earth; typical shrinkage: 10–15%. If the problem omits a value, these are your default assumptions.
• Never round intermediate volume values — carry decimals through and round only the final answer.

Key Points

• Soil exists in three volume states: Bank (in-place, undisturbed), Loose (excavated, loaded in truck), and Compacted (placed and compacted fill).
• Bank volume (BCM) is the reference state — it is the volume measured in the ground before excavation.
• Loose volume > Bank volume because excavation breaks soil apart, increasing air voids. This is quantified by the Swell factor.
• Compacted volume < Bank volume because compaction closes voids. This is quantified by the Shrinkage factor.
• Swell factor (%) — typical values: sand 10–15%, common earth 20–30%, rock 30–50%.
• Shrinkage factor (%) — typical values: sand 5–10%, common earth 10–15%, clay 20–30%.
• For hauling purposes, use LOOSE volume — it determines truck payload and number of loads.
• For fill design, compute required BANK volume from the specified compacted volume — it determines how much earth to cut.

Definitions

Section Title

3. Earthwork Volume Corrections — Swell and Shrinkage

Common Mistakes

• Confusing swell and shrinkage formulas — swell multiplies (1+S), shrinkage divides by (1−Sh).
• Using the shrinkage formula in the wrong direction: V_compacted = V_bank / (1−Sh) is WRONG; it should be V_bank = V_compacted / (1−Sh).
• Applying swell as a subtraction instead of multiplication — 100 m³ + 25% ≠ 125 m³ is correct, but students sometimes compute 100 × 0.25 = 25 and stop.
• Applying both swell AND shrinkage to the same problem when only one conversion is needed — read the question: is it bank-to-loose (use swell) or bank-to-compacted (use shrinkage)?
• Using volume basis inconsistently — mixing BCM and LCM in the same calculation without converting.

Formulas

Exam Tips

• Equipment selection rule: scrapers for 100–500 m haul; trucks for >500 m; dozers for <100 m spreading only.
• Concrete curing: minimum 7 days moist curing for normal Portland cement (Type I) per ACI 308/NSCP 2015.
• The phrase 'lateral movement of concrete with vibrator is NOT allowed' is a direct ACI 318 requirement — expect it as a true/false or multiple-choice item.
• Formwork stripping: soffit forms for beams/slabs are stripped LAST and only after shoring calculations confirm adequate strength.
• RA 544 relevance: A registered Civil Engineer must sign and seal all temporary works calculations (formwork, falsework, cofferdams) for projects above thresholds set by the Board.

Key Points

• EARTHMOVING EQUIPMENT: Excavators (backhoe/clamshell) — digging below ground; Loaders (frontend loader) — loading stockpiles; Dozers (bulldozer) — pushing/spreading; Scrapers — self-loading, hauling, and spreading in one machine; Haulers (dump trucks) — transport over longer distances.
• Equipment selection depends on: haul distance (scrapers for 100–500 m, trucks for >500 m), material type (rock vs. soil), and required output rate.
• CONCRETING OPERATIONS sequence: Batching (proportioning by weight or volume) → Mixing (transit mixer or site mixer) → Transporting (mixer truck or pump) → Placing (chutes, pumps, buckets) → Consolidation (internal vibration, 30-s insertion rule) → Finishing → Curing (minimum 7 days moist curing per ACI 318/NSCP 2015).
• ACI 318-14 Section 26.4: Concrete must be deposited as close as practicable to its final position; lateral movement with a vibrator is prohibited.
• FORMWORK must resist the lateral pressure of fresh concrete. Rate of pour, concrete temperature, and unit weight govern the design pressure.
• ACI 347 (Guide to Formwork): Maximum lateral pressure p = wCh (for slow pours), where w = unit weight (kN/m³), C = chemistry/temperature factor, h = head of concrete.
• Formwork failures are a leading cause of construction fatalities — adequate bracing, re-shoring, and stripping sequence matter.
• DPWH Blue Book and RA 544 (Philippine Civil Engineering Law): Licensed Civil Engineers are responsible for the safety and adequacy of temporary works including formwork and falsework.

Definitions

Section Title

4. Major Construction Operations — Earthmoving, Concreting, and Formwork

Common Mistakes

• Confusing scrapers with dozers — scrapers haul material over longer distances; dozers only push material short distances.
• Neglecting lateral concrete pressure in formwork design — treating formwork as only carrying vertical load.
• Specifying stripping time without checking concrete strength — NSCP 2015 Table 406.3 gives minimum curing periods; stripping before adequate strength gain is a code violation.
• Placing concrete from excessive height (>1.5 m) causing segregation — ACI 318 limits free-fall to prevent aggregate separation.