Chapter 8 — Quiz

B — the boring logs. The recommendations are a generalized summary written for the structural engineer. The logs record what was actually encountered at each depth in each hole, including the SPT blow counts. At Northgate, log B-9 disclosed N-values of 4, 5, and 6 at footing elevation while the recommendations said medium-dense sand at 4,000 psf. Reading only the recommendations cost $59,200 and three calendar days.

C — 40,000 LCY. LCY = BCY × (1 + swell) = 32,000 × 1.25 = 40,000. Option A applies the factor backward, which is the classic direction error; B ignores swell entirely and is the mistake that under-prices a haul by about 25%.

C — 290 LCY/hr. (3,600 ÷ 22) × 2.5 × 0.85 × 0.833 = 163.6 × 2.5 × 0.85 × 0.833 = 290. Note that 232 (option B) is the same machine expressed in bank cubic yards per hour after dividing by the 1.25 swell factor — a correct number for a different question, and exactly the kind of unit confusion that produces wrong durations.

C — 22 trucks. Trucks required = cycle time ÷ load time = 55.0 ÷ 2.5 = 22. Running with only 13 does not save money — the hauling cost per yard-mile is roughly unchanged — but it stretches the duration from 16 work days to 27 and keeps the excavator, operator, foreman, and site on the clock the whole time.

C — 7/8 inch. The eighth-inch rule: the bar number is the diameter in eighths of an inch, so #7 = 7/8 inch, #4 = 1/2 inch, #8 = 1 inch. Above #8 the bars are sized by area and the mnemonic stops working.

B. Hydration needs only a small amount of water; the excess makes the mix flowable but leaves behind an interconnected network of capillary voids as it departs. Voids are where strength isn't, and where chlorides and water get in later. The correct way to gain workability is a superplasticizer, not a hose.

C — the form cycle time. Concrete arrives in a few hours; formwork is designed, set, stripped, flown, and reshored floor after floor. A cycle planned at 5 days and run at 8 adds 3 days per floor, and on a 12-floor building that is 36 work days — roughly 50 calendar days — with every following trade inheriting the slip.

B — the trench box. A shield creates a protected space for people inside it; the soil outside can still move. That distinction matters when someone steps outside the box to make a connection, which is where a large share of trenching fatalities occur.

C — 5 feet. Below 5 feet, a competent person may still require protection based on conditions, and an excavation 20 feet or deeper requires a system designed by a registered professional engineer. The competent-person inspection is required daily, before each shift, and after any event — rain, vibration, a change in loading — that could alter conditions.

C. Precast erects fast at the site precisely because someone spent months making the pieces. Lead time from approved shop drawings to delivery commonly runs 10 to 20 weeks. When the constraint is design and procurement, a system whose advantage is field speed does not solve it.

B — 510 CY. 33,000 × (5 ÷ 12) = 13,750 CF; 13,750 ÷ 27 = 509.3 → 510 CY. This is Northgate's canonical slab quantity. Add a 5% waste factor and you order 536 CY, or 54 whole 10 CY loads.

C — Kestrel. The anchor-bolt and embed submittal sat 11 days in Kestrel's office against a 5-day allowance — 6 days of slip. Caldwell took exactly the 14 days its contract permitted and was not late at all. Those 6 days landed on a fixed mill rolling slot; the next opening was five weeks out, and after Ironbridge compressed fabrication by 12 days the net was +23 calendar days, moving erection start from August 4 to August 27.

False. It is typically furnished as information. Many contracts allow reliance on factual data but not on interpretations and opinions, and many require the contractor to represent that it satisfied itself as to site conditions. What you may rely on is a contract question that varies by form, by owner, and by jurisdiction — read the article.

False. Concrete shrinks as it cures and it will crack. Reinforcement controls crack width and keeps the pieces working together; control joints decide where the cracks go. Anyone who promises an uncracked slab is selling something.

False. A truss is an engineered assembly with a stamped design; every member carries a calculated force. Cutting a chord is a structural failure, not a field fix. The remedy is an engineered repair detail from the truss designer — which is why duct routing belongs in coordination before the trusses are ordered.

True — that is the point of unit pricing. At Cottonwood Creek, extra drilled-shaft footage is simply measured and paid at $412.00/LF. But most such specifications carry a variation threshold, commonly around 25%, beyond which either party may seek an adjusted unit price, because the contractor's fixed costs no longer spread across the assumed quantity.

False. The hazard changes but does not go away. A stressed tendon stores enormous energy, and coring, drilling, or saw cutting into one can release it explosively. Any penetration in a PT slab requires tendon location by as-built drawings and scanning, plus a written procedure — which belongs in your safety plan and subcontractor orientation, not only in a specification.

False — or at least, that is not the one that bites most projects. The dominant construction-phase risk is moisture. Exposed panels that sit in rain cup, check, stain, and can delaminate, and because the panel is often the exposed architectural finish, a water stain is a defect you cannot cover. Real mass timber projects run a written moisture management plan. Fire is real, but it is primarily a code and design question resolved before you break ground.

Lead-time chains do not add — they snap. The six days of slip landed on a discrete, scheduled event: Ironbridge's mill rolling slot, which closed on a fixed date. Missing it did not cost six days; it cost the interval to the next opening, which was five weeks (35 CD). Ironbridge recovered 12 days by running shop overtime and resequencing, leaving a net of 35 − 12 = 23 calendar days — and note the six days are not in that sum, because they are its cause rather than a term in it, or $244,950 of exposure at $10,650 per calendar day. The management lesson is to back-schedule submittal approval dates from the fixed slot, not forward from today.

(1) Subgrade bearing inspection by the geotechnical engineer before any forms or steel go in — two weeks ahead, give the geotech your footing sequence and standing schedule, and flag the footings you identified from the boring logs. (2) Lift-by-lift compaction testing of structural fill — two weeks ahead, book the testing laboratory by the week off your look-ahead, not by the day, and compute how many tests your specification actually requires so you know your real production rate. (3) Rebar and anchor-bolt inspection before each concrete placement, which is both a special inspection and, in most jurisdictions, a building-department footing inspection — two weeks ahead, confirm who the special inspector is, what notice they require, and whether the AHJ inspection can run the same morning. A fourth worth naming: masonry grout inspection and prism tests, or high-strength bolting and welding inspection on the steel.

(a) Cut to fill = 19,000 ÷ (1 − 0.11) = 19,000 ÷ 0.89 = 21,348 BCY. Export = 47,500 − 21,348 = 26,152 BCY.

(b) LCY = 26,152 × 1.24 = 32,428 LCY. Loads = 32,428 ÷ 13 = 2,494.5 → 2,495 loads.

(c) Haul = 9 ÷ 23 = 0.3913 hr = 23.5 min. Return = 9 ÷ 29 = 0.3103 hr = 18.6 min. Cycle = 1.0 + 2.9 + 23.5 + 2.0 + 18.6 = 48.0 min. Trucks = 48.0 ÷ 2.9 = 16.6 → 17 trucks.

(d) 32,428 LCY ÷ 265 LCY/hr = 122.4 hr ÷ 9 = 13.6 → 14 work days.

(e) Twenty trucks is three more than the excavator can serve, so production and duration are unchanged at 14 work days — you would be paying three trucks to queue, and the right move is to release them or add loading capacity so the fleet you are renting is actually used.