Alabama Sitework Contractor

Key Concepts

Direct Cost Estimating Direct costs are the costs that go directly into building the job: labor, equipment, and materials. Estimate each separately, then combine. - Labor: Calculate crew hours × hourly rate (including burden — taxes, insurance, benefits). Never use bare wage rates; always add 30–40% for labor burden. - Equipment: Use ownership cost + operating cost per hour, or rental rates. Track idle time — you pay for equipment whether it's working or not. - Materials: Quantity takeoff × unit price. Include waste factors (typically 5–10% for pipe, aggregate, etc.).

Material Quantity Takeoff Takeoff means measuring plan quantities before pricing. For sitework: - Linear feet of pipe from plan/profile views - Cubic yards of excavation (length × width × depth ÷ 27) - Tons of aggregate or backfill material - Always check both plan view and profile view — plan view gives horizontal distances, profile view gives depth and grade changes.

Overhead: Direct vs. Indirect - Direct job overhead: Costs tied to a specific job — job trailer, temporary utilities, superintendent salary on that job, permits, bonds. - Indirect (general) overhead: Home office costs spread across all jobs — office rent, clerical staff, owner salary, accounting, vehicles not on the job. Typically calculated as a percentage of annual revenue. - Formula: Overhead rate = Total annual overhead ÷ Total annual volume of work

Key Concepts

Backhoe Components & Hydraulic Operation The backhoe uses a hydraulic system to power the boom, dipper (arm), bucket, and swing functions. Hydraulic pressure drives cylinders that control digging depth and reach. The digging cycle consists of four phases: load (dig), swing loaded, dump, swing empty — mastering this cycle is central to production rate calculations.

Backhoe Digging Cycle A standard cycle time for a backhoe is typically 15–20 seconds under ideal conditions. Cycle time increases with swing angle, depth, operator inexperience, and difficult soil. Total production is calculated by multiplying bucket capacity (adjusted for fill factor) by cycles per hour.

Soil States — Critical for Volume Calculations - Bank Cubic Yards (BCY): Undisturbed, in-place soil - Loose Cubic Yards (LCY): Excavated/disturbed soil — always greater than BCY due to swell - Compacted Cubic Yards (CCY): Soil after compaction — less volume than BCY

Common earth swell factor ≈ 1.32 (1,000 BCY = 1,320 LCY). This directly affects hauling and production calculations.

Wheeled vs. Track Excavator Selection - Wheeled backhoe: Faster travel between locations, better on paved/stable surfaces, less ground disturbance — preferred for urban utility work with frequent repositioning - Track excavator: Superior stability and traction in soft, wet, or uneven ground; better for deep or heavy digging; slower to move between sites

Key Concepts

Soil Structure Soil = rock particles + air voids + water. Compaction works by reducing air voids, which increases density and load-bearing capacity. Well-graded soil (wide variety of particle sizes) compacts to greater density than poorly-graded soil. Disturbing soil introduces air voids and reduces stability.

Role of Water in Compaction Water acts as a lubricant, allowing particles to slide together. Too little = insufficient lubrication; too much = particles float and soil "pumps" (becomes unstable). The correct amount is optimum moisture content, expressed as a percentage of maximum dry weight.

Standard Proctor Test – T-99 (AASHTO T 99-70 / ASTM D 698) - Sample crushed to pass a ¾-inch sieve - Filled in 3 layers, each struck 25 times with a 5.5-lb, 2-inch diameter hammer - Total compaction energy: 12,400 foot-pounds - Used for: building slabs, sidewalks, utility trenches under grassy areas

Modified Proctor Test – T-180 (AASHTO T 180-70 / ASTM D 1557) - Same sieve prep as T-99 - Filled in 5 layers, each struck 25 times with a 10-lb hammer - Total compaction energy: 56,250 foot-pounds - Used for: nuclear power plants, federal highways, heavy-duty paved areas, concrete drives, airport runways, any high-design-load application

Key Concepts

OSHA Soil Classification System (29 CFR 1926 Subpart P, Appendix B)

Stable Rock: Natural solid mineral material that can be excavated with vertical sides and remain intact. No sloping or shoring required.

Type A (Strongest Cohesive Soil): - Unconfined compressive strength ≥ 1.5 tons per square foot (tsf) - Examples: clay, silty clay, sandy clay, clay loam - Disqualifiers — soil cannot be Type A if: - Fissured or subject to vibration (traffic, equipment, blasting) - Previously disturbed - Subject to water seepage - Part of a sloped, layered system dipping into the excavation - Subject to spalling or cave-in

Type B (Intermediate Cohesive Soil): - Unconfined compressive strength ≥ 0.5 tsf but < 1.5 tsf - Includes: angular gravel, silt, silt loam, previously disturbed soils that would otherwise be Type A, soils subject to vibration - Granular cohesionless soils where water seepage is not present

Type C (Weakest/Most Hazardous): - Unconfined compressive strength < 0.5 tsf - Includes: granular soils (gravel, sand, loamy sand), submerged/saturated soil, submerged rock, soil from which water is freely seeping - Layered systems sloping into the excavation at ≥ 4H:1V

Layered Soil Systems

When excavations pass through multiple soil layers, classify the entire excavation by the weakest layer encountered. A Type A layer on top does not protect against a Type C layer below.

Manual & Visual Classification Tests

Alabama Sitework Contractor Exam — Study Brief

Key Concepts

Soil Classification (29 CFR 1926 Subpart P, Appendix B)

• Stable Rock: Natural solid mineral; can be cut vertically with no support required
• Type A: Most stable soil (clay, silty clay, sandy clay). Unconfined compressive strength ≥ 1.5 tsf. Cannot be Type A if fissured, subject to vibration, previously disturbed, or has water seepage
• Type B: Medium stability (angular gravel, silt, previously disturbed Type A). Compressive strength 0.5–1.5 tsf
• Type C: Least stable (gravel, sand, loamy sand, submerged soil, soil with water seeping). Compressive strength < 0.5 tsf. Flowing soil is always Type C

Cave-In Protective Systems (§ 1926.652)

Sloping: Excavate sides at angle away from trench - Type A: ¾:1 (H:V) = 53° angle - Type B: 1:1 (H:V) = 45° angle - Type C: 1½:1 (H:V) = 34° angle - Stable Rock: Vertical walls permitted

Benching: Steps cut into trench walls; only allowed in Type A and B soils — never in Type C. Simple bench (Type A): bottom vertical height equals step width. Multiple benches allowed with proper geometry.

Shielding (Trench Boxes/Trench Shields): Protect workers inside the shield from cave-in forces; do NOT prevent cave-in — they protect workers within the structure. Can be premanufactured or job-built per § 1926.652(c)(3) or (c)(4).

29 CFR 1926 Subpart P (Excavations) | 4 Questions, 10% of Exam

Key Concepts

Soil Classification (29 CFR 1926 Subpart P, Appendix B)

• Stable Rock: Natural solid mineral that can be excavated with vertical sides and remains intact.
• Type A: Most stable. Cohesive soils with unconfined compressive strength ≥1.5 tons/sq ft (tsf). Examples: clay, silty clay. Cannot be classified Type A if fissured, subject to vibration, or previously disturbed.
• Type B: Intermediate. Cohesive soils 0.5–1.5 tsf; granular cohesionless soils; angular gravel; previously disturbed Type A soils.
• Type C: Least stable. Cohesive soils <0.5 tsf; granular soils (gravel, sand, loamy sand); submerged soil; soil where water is seeping. Always use most conservative classification when uncertain.

Testing Methods: Pocket penetrometer, shearvane, thumb penetration test, dry strength test, ribbon test, and visual observation of soil behavior.

Cave-In Protection Systems (29 CFR 1926.652)

Required for all excavations 5 feet or deeper (and any depth if a competent person determines a hazard exists).