Alabama Sitework Contractor

Key Concepts

Labor burden. Payroll taxes and insurance (unemployment insurance, FICA, FUTA, worker's compensation, liability insurance) add 20 to 30 cents for every dollar of payroll and must be in every estimate; this burden often exceeds the contractor's profit on the job (Pages 17–18, "Your Labor Burden").

Indirect (office) overhead. Keep overhead low — no more than 10 percent of gross receipts — to stay competitive (Page 23, indirect overhead discussion).

Overhead in the bid — margin vs. markup. To make overhead equal exactly 10 percent of the final price, divide hard costs by (1.0 − desired margin). $90,000 ÷ 0.90 = $100,000. Adding 10 percent markup instead yields $99,000 and recovers only $9,000 (Pages 24–25, "Including Overhead in Your Bid").

Varying markup — the 20-10-10-10 method. Labor and equipment get the higher markup (20 percent); materials and subcontracts get 10 percent, because labor and equipment are riskier and more variable than fixed-price items (Pages 25–26, "Vary the Markup with the Job").

Escalation. The increase in costs of labor, materials and equipment between the time the bid is submitted and the time work is done and paid for. Especially important during high inflation or on jobs lasting several months (Page 27, "Contingency and Escalation").

Source: Pipe and Excavation Contracting

Key Concepts

Backhoe components and hydraulics - A backhoe has four main components: cab and undercarriage (or swing mechanism), boom, dipper (or stick), and bucket. The latter three have hydraulic rams and cylinders. The operator has eight ways to move these components (p. 142). - Ram force = piston area (sq. in.) × oil pressure (psi). A 10 sq. in. piston at 2,000 psi generates 20,000 pounds (p. 143). - Pressures in backhoe hydraulic systems usually range from 2,000 to 3,000 psi (p. 143). - Response time is regulated with the control valves, not by reducing engine speed. Reduced oil flow moves the ram slower but with the same force (p. 144). - Never go beneath the bucket while the machine is operating — a broken hose lets fluid drain and the bucket fall suddenly (p. 144). - The ram is most efficient near the middle of its travel, where leverage disadvantage is least. At either endpoint of stick-cylinder travel (fully extended or retracted), leverage disadvantage is greatest (pp. 144–145). - Dipper leverage disadvantage usually ranges between 1/3 and 1/6, depending on dipper length (p. 144). - A backhoe is most efficient working within 70 percent of maximum digging depth; divide trench depth by 0.70 to pick the right hoe (p. 149).

Key Concepts

Soil structure. Soil consists of rock particles, air voids and water. Spaces between particles are air voids, and more air voids are introduced every time soil is disturbed or excavated. Reducing air voids is the goal of soil compaction (Pipe and Excavation Contracting, p. 182). When a blade or bucket cuts into soil, it loosens up and swells because air cavities are introduced into the mass, making it unstable with poor load-bearing capacity (p. 181).

Moisture. Optimum moisture content is usually expressed as a percentage of maximum dry weight (p. 182). Too much water holds particles apart, causing them to float; water-saturated soil will pump (become unstable) and move away from the compaction equipment (pp. 182–184). If soil is too wet it must be allowed to dry; if too dry, water must be added (p. 184). Wait for wet soil to dry to below optimum moisture levels before making the density measurements required in the specifications (p. 191).

Standard Proctor (T-99) — AASHTO T 99-70 / ASTM D 698. Sample crushed to pass a ¾-inch sieve; mold filled in three layers; each layer struck 25 times with a 5.5-pound, 2-inch-diameter hammer; total compaction effort 12,400 foot-pounds. Specified for fill under building slabs and sidewalks, and in utility trenches under grassy areas (p. 183).

Key Concepts

OSHA soil classification (29 CFR 1926, Subpart P, Appendix A(b)) - Type A: cohesive soil with unconfined compressive strength of 1.5 tsf (144 kPa) or greater. Cemented soils such as caliche and hardpan are considered Type A. - Type B: cohesive soil with unconfined compressive strength greater than 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa). Type B also includes angular gravel, silt, silt loam, sandy loam, and dry rock that is not stable (Type B(v)). Fissured soil with high compressive strength is reclassified as Type B, as is soil subject to vibration (provision (iv)). - Type C: cohesive soil with unconfined compressive strength of 0.5 tsf (48 kPa) or less (Type C(i)); granular soils gravel, sand, and loamy sand (Type C(ii)); submerged soil or soil from which water is freely seeping; submerged rock that is not stable. - Disqualifiers from Type A: fissured, previously disturbed, or subject to vibration from heavy traffic, pile driving, or similar effects. Cementation does not disqualify. - Layered systems (Appendix A(c)(4)): classify by the weakest layer; each layer may be classified individually only where a more stable layer lies under a less stable layer. - Granular soil (definition): gravel, sand, or silt with little or no clay content; has no cohesive strength. - Wet soil (definition): granular material exhibiting cohesive properties when moist loses those properties when wet.

Key Concepts

Soil classification (Subpart P, Appendix A) - Soil classification must be based on at least one visual analysis and at least one manual analysis, conducted by a competent person using tests described in the appendix or other recognized soil classification methods — App. A, §(c)(2). - Type A cohesive soil: unconfined compressive strength of 1.5 tsf or greater, but soil that has been previously disturbed cannot be Type A regardless of strength. Other disqualifiers: fissuring, vibration from heavy traffic or pile driving, and sloped layered systems dipping into the excavation at 4H:1V or steeper — App. A, §(b) Type A(iii). - Type B cohesive soil: unconfined compressive strength greater than 0.5 tsf but less than 1.5 tsf. Soil meeting Type A strength/cementation requirements but that is fissured or subject to vibration is classified Type B — App. A, §(b) Type B(i) and Type B(iv). - Soil at 0.5 tsf or less is Type C — App. A, §(b) Type B(i) explanation. - Layered systems: classify in accordance with the weakest layer; however, each layer may be classified individually where a more stable layer lies under a less stable layer — App. A, §(c)(4). - Stable rock means natural solid mineral material that can be excavated with vertical sides and will remain intact while exposed — §1926.650(b).

Key Concepts

Scope of the excavation rules. Subpart P "applies to all open excavations made in the earth's surface. Excavations are defined to include trenches" (§1926.650(a)). A cave-in is the separation of a mass of soil or rock from the side of an excavation, or loss of soil from under a trench shield or support system, and its sudden movement into the excavation in sufficient quantity to entrap, bury, or otherwise injure and immobilize a person. Benching protects employees from cave-ins by excavating the sides into one or a series of horizontal levels or steps; a protective system includes support systems, sloping and benching systems, shield systems, and other systems providing the necessary protection (§1926.650(b)). Note that the confined-space standard does not apply to construction work regulated by Subpart P (§1926.1201(b)(1)).

Soil classification and reclassification. Type C soil includes "Submerged soil or soil from which water is freely seeping" (Subpart P, Appendix A(b)). If properties, factors, or conditions affecting a deposit's classification change, the deposit shall be reclassified by a competent person to reflect the changed circumstances (Appendix A(c)(5)) — so Type B with water freely seeping from the walls becomes Type C. Behaviorally, water seeping into an excavation "acts as a lubricant, allowing large slabs of dirt to slip out of place, causing dangerous cave-ins," and saturated silt and clay are impossible to compact (Pipe and Excavation Contracting, Dealing with Rock…