The flat section is designed to interlock with each other to provide strength. They are suitable for construction of cellular structures. The Z section is designed for bending and hence it is more suitable for construction of retaining walls, bulkheads, cofferdams, and for supporting excavation. Table VII.1 gives representative number of sheet piles driven per hour.
Table VII.1 Representative number of sheet piles driven per hour
From Table VII.1, knowing the length of pile and the type of soil, the number of piles that can be driven in an hour can be calculated. From this information, the total time required for the job can be
calculated. Once the total time is determined, the total cost can be calculated by multiplying the respective labor, material and equipment cost with the number of hours.
VII.1.2 Wood piles – Wood piles are classified as load‐bearing and friction piles. If the pile is driven such that it rests on the hard ground and supports the superimposed load, it is called load a bearing pile. If the soil resistance (skin friction – the friction between the pile and the adjoining soil) is adequate to oppose the superimposed load on the pile, the pile need not be driven to the hard stratum. It can be stopped at such depth where the soil resistance developed is more than the load on the pile. Such a pile is called a friction pile. Wood piles are tapered from an end point diameter of 6 to 8 in to a butt
diameter of 12 to 14 in. Lengths vary from 30 to 50 ft. A preservative treatment of creosote or pentachlorophenol is generally applied. A steel boot is placed on the pile end point (tip) to reduce the tendency of breakage during driving of the pile. A reasonable allowance for extra piles should be included in the estimate since the piles may be broken during the driving process. While costing the equipment, use of crane, hammer, leads for hammer, and air compressor must be considered. Table VII.2 gives approximate number of wood piles that can be driven/hour to full penetration for various lengths in two different soil resistances.
Table VII.2 Representative of wood piles driven per hour, full penetration
From the information from Table VII.2, for a given length of the pile and the nature of soil friction, the number of piles that can be driven per hour can be obtained. Then the total time can be calculated by dividing the total number of piles by the piles/hr obtained form Table VII.2. Once the total hours for the job is known, the total cost can be calculated as explained under Section VII.1.1. Example VII.2
illustrates the method of estimating the cost for driving wood piles.
Example VII.2:
Estimate the cost of furnishing and driving 160 wood piles 36 ft long into a soil having normal frictional resistance. The piles will be purchased in 40‐ft lengths and the tops will be cut to the required elevation after driving. The piles will be approximately 14 in. in diameter at the butt, and 7 in. at the tip. The piles will be treated with creosote preservative at a rate of 2.5 lb/cf, and breakage should be considered. The average weight of the pile will be 37 lb/ft. One crane operator, 3 laborers and one foreman will be on the job. The following cost information will apply: piles = $10.85/ft., pile points = $64.78.,
other equipment and supplies = $9.35/hr., foreman = $25.00/hr., crane operator = $21.67/hr., and general laborers = $15.56/hr.
Solution:
Quantity of materials:
Number of piles to be driven = 160 Add 5% for breakage = 8 Total = 168
Number of linear feet of piles to be purchased = 168 x 40 = 6,720 Number of linear feet of piles to be driven = 160 x 36 = 5,760 Number of boots required = 168
Number of piles that must be cut at top = 160 Time to drive piles:
From Table VII.2, for 36‐ft long pile to be driven in normal friction to full penetration, the rate of driving will be 3 piles/hr and time to drive 168 piles = 168/3 = 56 hrs.
Cost of driving:
Material cost:
Treated piles = 6,720 ft x $10.85 = $72,912.00 Pile points = 168 x $64.78 = 10,883.04 Total material cost = $83,795.04 Equipment cost:
Crane = 56 hrs x $82.40 = $4,614.40 Leads for hammer = 56 hrs x $14.63 = 819.28 Hammer = 56 hrs x $10.80 = 604.80 Air compressor = 56 hrs x $14.65 = 820.40 Other equipment and supplies 56 hrs x $9.35 = 523.60 Total equipment cost = $7,382.48 Labor cost: (Add 8 hrs for the crew to setup and take down equipment) Foreman ( 56 + 8)= 64 hrs x $25.00 = $1,600.00 Crane operator = 64 hrs x $21.67 = 1,386.88 General laborers = 64 hrs x 3 x $15.56 = 2,987.52 Total labor cost = $5,974.40
Summary of costs:
Material = $83,795.04 Equipment = 7,382.48 Labor = 5,974.40 Total cost = $97,152.92
Cost/driven pile = $97,151.92/160 = $607.20
Cost/linear foot of driven pile = $97,151.92/5,760 = $16.86
VII.1.3 Cast‐in‐place concrete piles – These piles are suitable for use on projects where the soil
conditions are such that the length of penetration is not known in advance and the depth varies among the piles driven. Tapered steel shells or steel pipes are driven to the required depth and later filled with concrete. The shells are left in place but the pipes are withdrawn as the concrete is deposited. Any length of pile, up to approximately 125 ft, can be obtained by welding extensions to the shell. In
estimating the cost of cast‐in‐place concrete piles, it is necessary to determine the cost of the shells, the cost of equipment and the cost of labor to drive the shells, and the cost of concrete placed in the shells.
The rate of driving varies with the length of the piles, topography of the site, class of soil into which they are driven, type of driving equipment used, spacing of the piles, and weather conditions.
VII.1.4 Steel piles – These are used where it is necessary to drive piles through considerable depths of poor soil to reach solid rock or another formation having high load‐bearing properties. Standard rolled steel HP sections or wide flange beams are most frequently used. Driving operations are similar to those of other piles. A cap can be installed on the top of piles to reduce the potential for damage during the driving operation. Table VII.3 gives approximate number of steel piles driven to full penetration per hour.
Table VII.3 Approximate number of steel piles driven to full penetration per hour
the number of piles that can be driven per hour can be obtained. Then the total time can be calculated by dividing the total number of piles by the piles/hr obtained form Table VII.3. Once the total hours for the job is known, the total cost can be calculated as explained under Section VII.1.1.
Example VII.3 illustrates the method of estimating the cost for driving steel piles.
Example VII.3:
Estimate the cost of furnishing and driving 180 steel piles, 40 ft long. The piles weigh 73 lbs/ft and are driven to full penetration into soil having high frictional resistance. A foreman with one crane operator and three laborers will be on the job. The following cost information will apply: piles = $0.32/lb., pile caps = $87.00., crane = $82.40/hr., leads for hammer = $14.63/hr., hammer = $10.80/hr., air compressor
= $14.65/hr., other equipment and supplies = $9.35/hr., foreman = $25.00/hr., crane operator =
$21.67/hr., and general laborers = $15.56/hr. Actual working time will be 45 min in one hour.
Solution:
Quantity of materials:
Linear feet of piles = 180 x 40 = 7,200
Total weight of piles = 7,200 x 73 = 525,600 lbs Time to drive piles:
From Table VII.3 for a 75 lb/ft pile and 40 ft long, the driving rate is 2.25piles/hr Total time for driving piles = 180/2.25 = 80 hrs
With only 45 min working in one hour, actual time = 80 x (60/45) = 107 hrs Rounding this to full 8‐hr day, the total time = 112 hrs
Cost to drive piles:
Material cost:
Piles = 525,600 lbs x $0.32 = $168,192.00 Pile caps = 180 x $87.00 = 15,660.00 Total material cost = $183,852.00
Equipment cost:
Crane = 112 hrs x $82.40 = $9,928.80 Leads for hammer hrs = 112 hrs x $14.63 = 1,638.56 Hammer = 112 hrs x $10.80 = 1,209.60 Air compressor = 112 hrs x $14.65 = 1,640.80 Other equipment and supplies 112 hrs x $9.35 = 1,047.20 Total equipment cost = $15,464.96
Labor cost: (Add 8 hrs for the crew to setup and take down equipment) Foreman (112 + 8 )= 120 hrs x $25.00 = $3,000.00 Crane operator = 120 hrs x $21.67 = 2,600.40 General laborers = 120 hrs x 3 x $15.56 = 5,601.60 Total labor cost = $11,202.00 Summary of costs:
Material = $183,852.00 Equipment = 15,464.96 Labor = 11,202.00 Total cost = $210,518.96
Cost/ pile = $210,518.96/180 = $607.20
Cost/linear foot of pile = $210,518.96/7,200 = $29.24
VII.2 Shaft foundation – Shaft foundations are installed by placing reinforced concrete in holes that have been drilled into the soil. Drilling rigs mounted on trucks can drill holes from 12 to 96 in diameter and up to approximately 100 ft depth. The bottom of the drilled hole can be under‐ reamed with a belling tool to provide an increased capacity of the foundation. When drilling into unstable soils or where water may be present, it is usually necessary to install cylindrical steel casing to hold the sides of the shaft until the reinforcing steel and concrete are placed. The casing is pulled from the hole during placement of the concrete. Table VII.4 shows representative rates of drilling various diameters of shafts into soils and Table VII.5 gives approximate rates for drilling into soft rock, such as shales.
Table VII.4 Representative rates of drilling shafts in soils
Vertical reinforcing steel is tied together by horizontal ties or spiral hoops, and lowered into position in the drilled shaft. Lugs attached to the reinforcing cage hold them into position at the center of the hole until concrete is placed. The cost of shaft foundations will include mobilization of equipment, drilling of the shaft, casing (if required), fabrication and placement of the reinforcement steel, and depositing concrete.