Louisiana Pile Driving

Topic: Pile and Caisson Drilling and Foundation Preparation

Key Concepts

Pile classification by use and load path. On the basis of use there are two major classifications: sheet piles (earth retention, cofferdams, temporary trench support) and load-bearing piles (CPEM, Ch. 17 — Introduction). If the load is transmitted through skin friction between the pile surface and the soil, it is a friction pile; if through the pile's lower tip, it is an end-bearing pile. A pile driven through a mud deposit to rest on solid rock is an end-bearing pile (CPEM, Ch. 17 — Resistance of Piles to Penetration).

Timber piles. Treated piling lasts 50 years in northern marine waters and 20 years in southern waters, with southern waters defined as south of Cape Hatteras on the East Coast and below San Francisco on the West Coast (CEG, Ch. 17 — Treated Timber Piles). Acceptance requirements are established under ASTM D 25–12, Standard Specification for Round Timber Piles (CEG, Ch. 17 — Timber Pile Quality).

Concrete piles. Precast-prestressed concrete (PPC) piles may be removed from forms in as little as 24 hours, or as soon as the concrete reaches a compressive strength of 3,500 psi, using concrete of 5,000 psi or greater under controlled curing (CEG, Ch. 17 — Precast-Prestressed). Plant-produced piles conform to PCI MNL-116–99.

Hammers and driving. A single-acting steam or air hammer strikes 40 to 60 blows per minute; double-acting hammers strike 95 to 300 (CPEM, Ch. 17 — Single-Acting Hammers). A single-acting hammer should not weigh less than one-third the weight of the pile (CPEM, Example 17.1). Vibratory hammers are especially effective when piles are driven into water-saturated noncohesive soils (CPEM, Ch. 17 — Vibratory Hammers). A new plywood pile cushion is required if it is compressed to less than one-half its original thickness or begins to burn (CPEM, Ch. 17 — Driving Concrete Piles). Where very hard overlying strata exist, spud or preauger before driving (CPEM, Ch. 17 — Spudding and Preaugering).

Key Concepts

Mixture and durability - All concrete exposed to freezing weather in service should be air entrained; it is less susceptible to freezing damage than non-air-entrained concrete (Contractor's Guide, p. 181). To prevent scaling of flatwork exposed to freezing-and-thawing and deicers, use approximately 5 to 8 percent air, slightly more when coarse aggregate is smaller than 3/4 in. (pp. 192, 199). - Exposure requirements, Table 2.5 (p. 24): F3 (freeze-thaw + frequent water + deicing chemicals) = max w/cm 0.40, min 5000 psi; S2 sulfate (1500–10,000 ppm) = max w/cm 0.45, min 4500 psi; W1 (contact with water, low permeability required) = max w/cm 0.50, min 4000 psi. - Jobsite water: adding 1 gal. per cubic yard raises slump about 1 in. and reduces compressive strength about 150 psi, and increases shrinkage (p. 149). Water may be added only prior to discharge and not if concrete has mixed more than 90 minutes (ASTM C94/C94M and ACI 301, p. 147).

Field testing - Field acceptance tests on fresh concrete at delivery: slump, air entrainment, and unit weight (p. 139). Unit weight with batch weights and measured air content gives a good indication of water content (p. 149). - Cylinder storage on site: 60 to 80°F for specified strengths less than 6000 psi; 68 to 78°F applies at 6000 psi or greater (p. 149). - Acceptance: average of any three successive tests must equal or exceed f′c; no test may fall more than 500 psi below f′c for f′c of 5000 psi or less (10 percent for higher strengths) (pp. 149–150). - Alternatives to cylinders: pullout, penetration, and maturity meters (which measure concrete temperature over time to calculate strength) (p. 81).

Key Concepts

Equipment ownership vs. operating cost - Major repairs and overhauls are classified as ownership costs, not operating costs, because they extend a machine's service life and can be considered an investment in a new machine. Fuel, lubricants, and tires are operating costs. (Construction Equipment Guide, Ch. 2, p. 80) - Repairs are normally the largest single component of machine cost over a service life. Manufacturers supply tables of average repair costs by machine type and work application; repair expense increases with machine usage and age. (Ch. 2, pp. 83–84, Table 2.4) - For hydraulic machines, repair cost splits two-thirds materials/parts, one-third labor; for mechanical machines the split is half and half. (Ch. 2 — Repairs) - PCSA guideline: repair and maintenance for crawler cranes = 55% of depreciation, versus 80–95% for crawler-mounted excavators and 80–85% for wheel-mounted excavators, reflecting the intermittent nature of crane use. (Ch. 2 — Repairs) - Average Annual Investment (AAI) is multiplied by the corporate cost-of-capital rate to get the cost-of-money portion of depreciation; straight-line depreciation is then added to arrive at total ownership depreciation. (Ch. 2, pp. 90–91) - Optimum economic life is the ownership duration yielding the minimum total cost per hour (ownership + operating combined). Ownership cost/hr decreases over time while operating cost/hr increases. (Ch. 2, pp. 100–103)

Tax depreciation (MACRS) - Most construction equipment = 5-year property. Cars and light-duty trucks under 13,000 lb unloaded = 3-year property. (Ch. 2, p. 78) - If a machine is disposed of before depreciation is complete, no depreciation can be recovered in the year of disposal; gain measured against adjusted basis is ordinary income. (Ch. 2 — Tax Code Depreciation Schedules)

Rent vs. lease - Rental rates are generally priced daily (8 hr), weekly (40 hr), or monthly (176 hr). (Ch. 2, pp. 104–105) - Leasing is off-balance-sheet financing; an operating lease typically will not hurt bonding capacity. The lessee loses the tax depreciation shield but deducts lease payments as an expense. (Ch. 2, pp. 105–107)

Key Concepts

Competent person and employer duties. A competent person is "one who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them" (§1926.32(f); identical definition in Subpart P, §1926.650(b)). No degree, years of experience, or certificate is required by the definition. The employer must initiate and maintain safety programs and provide for "frequent and regular inspections of the job sites, materials, and equipment ... by competent persons designated by the employers" (§1926.20(b)(1)–(2)). Noncompliant machinery or tools must be tagged, locked out, or physically removed (§1926.20(b)(3)). "The employer shall permit only those employees qualified by training or experience to operate equipment and machinery" (§1926.20(b)(4)). Employees must be instructed in the recognition and avoidance of unsafe conditions (§1926.21(b)(2)).

Fall protection. Fall protection for residential construction begins at 6 ft; scaffolds at 10 ft. Guardrail top rails must be 39–45 inches (§1926.502). Employees working on stored material in silos, hoppers, tanks, and similar storage areas must be equipped with personal fall arrest equipment meeting Subpart M (§1926.250(b)(2)). Under Subpart V, each employee more than 1.2 meters (4 feet) above ground on poles, towers, or similar structures must use a personal fall arrest system, work-positioning equipment, or fall restraint system if other Subpart M fall protection is not provided (§1926.954(b)(3)(iii)(B)).

Cranes and dedicated pile drivers (Subpart CC). §1926.1400(a) applies to power-operated equipment used in construction that can hoist, lower, and horizontally move a suspended load, and expressly includes dedicated pile drivers. It also applies when the equipment is used with attachments, including "augers or drills and pile driving equipment" (§1926.1400(b)). Excluded: equipment converted to non-hoisting use, excavators/backhoes/track loaders (even when rigged to lift suspended loads), and dedicated drilling rigs (§1926.1400(c)).